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Modeling an exploited rocky coastal ecosystem: Bahia Tortugas, Mexico
Abstract
A trophic structure model of the rocky coastal ecosystem in Bahia Tortugas, Mexico was constructed using Ecopath software to represent the main biomass flows in the system. Data for the model came from field observations (biomass estimates, stomach contents, and ecological observations for sea snails, abalones, lobster, some demersal finfishes, and macroalgae) carried out through ten field trips from 2006 to 2008. The results provide a snapshot of how the ecosystem operates. The model considers 23 functional groups. The total system throughput was 553t/km2/year, 57% corresponds to internal consumption, 28% to respiration, 14% becomes detritus, and only 1% is removed through commercial fishing. The model suggests that even for exploited populations, predation and competition are heavier stresses than current fishing effort; however, because spiny lobster showed the second highest keystoneness’ index value, increasing fishing pressure on this group could strongly impact the entire ecosystem. We believe that this model has the potential to support management by allowing the exploration of the potential impacts of different fishing decisions at ecosystem level.
... The particular environmental and socio-economic conditions (e.g., high vulnerability to environmental extremes and the presence of strictly controlled voluntary marine reserves), and the unique longterm physical-biological database for this location provided us with an opportunity to construct and calibrate a realistic mass-balanced food web model. To our knowledge, this is the first attempt to build such a model for this area, although there is another Ecopath model for a kelp forest area nearby in Bahia Tortugas (Morales-Zárate et al., 2011). Both of these models are kelp ecosystems food web models and can be compared and contrasted. ...
... This is essential, especially in highly diverse ecosystems such as kelp forests. In models similar to ours, many authors comprise between 20 and 25 FG (Cruz-Escalona et al., 2013;Frausto, 2012;Morales-Zárate et al., 2011). Compared to other models for the Mexican Pacific, ours has 40 FG, almost double that of others. ...
... Secondly, the biomass of the FG is also a key parameter for the development of a mass-balanced trophic network model. For many models, biomass is often obtained from the literature or from monitoring efforts of short periods between 1 and 3 years, as in Cruz-Escalona et al. (2013), Frausto (2012, Morales-Zárate et al. (2011) andOrtiz (2008). Our model, on the other hand, used information from 10 years of detailed ecological monitoring. ...
Coastal ecosystems are influenced by a suite of drivers and interactions, resulting in complex dynamics not captured by single species, single driver approaches. Kelp forest ecosystems of the California Current region are subject to extreme environmental variability as well as a suite of fishing pressures which remove organisms throughout the food web. Here, we present a food-web model to assess ecosystem-wide effects of different fishing strategies which can also be used to estimate the effect of warming, acidification and hypoxia on the structure and function of a highly productive temperate ecosystems. We built a mass-balanced model of a kelp forest ecosystem near the southern limit of distribution in the northern hemisphere (Isla Natividad, Mexico). The model is informed by extensive ecological monitoring of fish, benthic invertebrates, and macroalgae conducted annually from 2006 to 2016 at 5 sites around the island. The model includes 40 functional groups (FG) defined on the basis of commercial interest, ecosystem function and feeding guild, including birds, marine mammals, fish (13 FG), commercial species (7 FG), macroinvertebrates (8 FG), zooplankton, the giant kelp Macrocystis pyrifera, six macroalgae, phytoplankton and detritus. The estimated throughput was 5477.6 t·km⁻²·year⁻¹ (26% consumption, 27% exports, 24% respiration and 23.7% detritus). The sum of all production was 2727.9 t·km²·year⁻¹, and the total primary production/total respiration ratio was 2.4. This model, based on a detailed, multi-year monitoring program in the kelp forests, provides a valuable tool for exploring drivers of change in these vulnerable marine ecosystems and fisheries.
... We looked for articles based on studies performed as close as possible to the study area, and we also used information from other EwE models developed for close ecosystems (Morales-Zárate et al., 2011;Vilalta-Navas et al., 2018). For a more details on the development of the EwE model see Beas-Luna and Ladah (2014) (COBI) through interviews applied to fishers, the details on the construction of the LEK-based model can be found in Zetina-Rejón et al. (2022). ...
There is an urgent need to analyse and understand small-scale fisheries environment under biotic and abiotic stressors. In this work, we use a kelp forest ecosystem in Baja California, Mexico to present a novel approach, comparing two network models based on different information sources. First, we developed a conventional scientific knowledge network model (CSK) parameterized with in-situ observations. Second, we used a local ecological knowledge network model (LEK) based on interviews with local fishers. Our main objectives were: (a) verify if the two knowledge sources generated comparable models, and (b) explore model responses to disturbance scenarios. The CSK model presented greater detail at lower trophic levels, contrary to the LEK model. Additionally, we simulated top-down and bottom-up ecological disturbances. With a top-down disturbance, the groups’ abundance increased following a cascade effect whereas, in the bottom-up disturbance, changes did not transfer uniformly. We also simulated anthropogenic disturbances through fishing pressure on three target species (lobsters, sea urchins, and sea bass). Our findings show similar patterns with the highest degree of change when lobsters are removed. Our findings highlight the potential of model complementarity and support the relevance of ecological network models to navigate future climate and anthropogenic uncertainty.
... However, according to the descriptions of Odum (1969), Christensen (1995), Ulanowicz (1989), Morales-Zárate et al. 2011 andLira et al. (2018), the low values of the attributes Connectivity index, Omnivory index, and unbalanced relationships between total primary production/total respiration and total primary production/total system biomass, indicate that the CB is still an immature ecosystem. Although the CB does not cover the entire GM, it has a well-organized structure with few trophic levels, being a very stable system close to its maximum development capacity. ...
Length (to the nearest 0.01 cm) and weight (to the nearest 0.01 g) relationships (LWR) were estimated for 41 fish species, representing a total of 19 families from the Campeche Bank and the surrounding Yucatan Peninsula, Mexico. All specimens were collected during three oceanographic study surveys (November 2015 –together with April 2016, August to October 2016, and July to August 2018) using a shrimp trawl net (18.3 m in length and 3.4 mesh size), for one mile (2.5 knots) in 18 locations; with one trawl haul per location for the aforementioned survey periods, respectively. North of the Yucatan Peninsula, five lobster traps (1.0 × 0.50 m in dimension, and 2.5 mesh size) were positioned at each of the 20 stations, during two annual periods (October 2016, and July 2018); traps were set for 3–4 h. Depth for the 38 locations ranged between 16 and 200 m. Syacium papillosum and Diplectrum formosum were the most abundant species. New maximum standard length (SL) was obtained for Sargocentron bullisi, Ogcocephalus parvus and Syacium gunteri.
... The samples were taken in fishing camps in Bahia Tortugas, located (27 • 39 ′ 35 ′′ N; 114 • 52 ′ 35 ′′ W) on the western coast of Baja California Peninsula (Fig. 1). The region is scarcely populated, and fishing is considered the most important economic activity (Morales-Zárate et al., 2011). The active upwelling process along the entire west coast of the peninsula largely controls the marine productivity of this region (Zaytsev et al., 2003). ...
Cadmium, selenium, and mercury concentrations were measured in muscle and liver of juvenile blue (Prionace glauca) and smooth hammerhead (Sphyrna zygaena) sharks caught on the west coast of Baja California Sur, Mexico, to evaluate the human health risk associated with its consumption. Cd and Hg were lower than the maximum allowable limit for human consumption established by the Mexican government (Hg = 1.0 μg g-1 and Cd = 0.50 μg g-1). Interspecific differences in trace elements accumulation denoted diet variations and physiological requirements of each shark species. Calculated biomagnification factor (BMF) values confirmed a prey-predator trophic transfer of elements. Not significant results of Selenium health benefit Index value (P. glauca = −0.46; S. zygaena = −0.02) signify no potential risks for human health. However, calculated Hazard Index values displayed possible health hazards to the children who consume blue shark meat regularly. The local population is advised regarding the ingestion rates of shark.
... However, according to the descriptions of Odum (1969), Christensen (1995), Ulanowicz (1989), Morales-Zárate et al. 2011 andLira et al. (2018), the low values of the attributes Connectivity index, Omnivory index, and unbalanced relationships between total primary production/total respiration and total primary production/total system biomass, indicate that the CB is still an immature ecosystem. Although the CB does not cover the entire GM, it has a well-organized structure with few trophic levels, being a very stable system close to its maximum development capacity. ...
Campeche Bank located in the Yucatan Peninsula, Mexico is characterized by particular oceanographic and physiographic conditions that promote great biodiversity, including abundant fishery resources. Systematic sampling through oceanographic campaigns (November 2015, April 2016), produced high-quality data to generate a trophic model balance using Ecopath software. The goal of this study is to know the baseline of the structure and functioning of this important marine area. The predator/prey matrix was drawn up from the stomach content analysis of 186 fish species integrated into 47 families. The schematic representation exemplifies a complex trophic interaction of 22 trophic groups, including 10 fish groups, 8 invertebrate, zooplankton, phytoplankton, benthic producers, and detritus. Production and consumption of biomass and ecotrophic efficiency values were calculated for each of the trophic groups. The Total System Throughput was of 319.514 t/km²/year. The Ascendency, system Overhead, and Development Capacity were of 476.4, 673.1, and 1150.0 flow bits, respectively. Campeche Bank is an oligotrophic system with an intermediate state of resilience to environmental variations, growth potential intermediate, and greatly influenced by loop and Caribbean currents. These properties together with indicators of overfishing in the system and pollution (hydrocarbons), highlight the requirement of controlling fishery pressures and monitor hydrocarbons industry in the area to maintain its function and biodiversity.
... We developed an EwE model for this study due to the practical considerations associated with developing, running, and analyzing a suite of OA simulations as well as the availability of previous OA studies using this framework for comparison [36,45,46], providing a foundation to build upon and compare results with. Only a few ecosystem models have been published for kelp forest ecosystems [46][47][48][49][50][51]. While other quantitatively robust ecosystem modeling software packages are available for this type of ecosystem assessment, such as Atlantis [52], the Atlantis model for the California Current does not include a nearshore kelp community component and developing one would have been a multi-year effort falling outside the scope of this project. ...
Ocean acidification is one the biggest threats to marine ecosystems worldwide, but its ecosystem wide responses are still poorly understood. This study integrates field and experimental data into a mass balance food web model of a temperate coastal ecosystem to determine the impacts of specific OA forcing mechanisms as well as how they interact with one another. Specifically, we forced a food web model of a kelp forest ecosystem near its southern distribution limit in the California large marine ecosystem to a 0.5 pH drop over the course of 50 years. This study utilizes a modeling approach to determine the impacts of specific OA forcing mechanisms as well as how they interact. Isolating OA impacts on growth (Production), mortality (Other Mortality), and predation interactions (Vulnerability) or combining all three mechanisms together leads to a variety of ecosystem responses, with some taxa increasing in abundance and other decreasing. Results suggest that carbonate mineralizing groups such as coralline algae, abalone, snails, and lobsters display the largest decreases in biomass while macroalgae, urchins, and some larger fish species display the largest increases. Low trophic level groups such as giant kelp and brown algae increase in biomass by 16% and 71%, respectively. Due to the diverse way in which OA stress manifests at both individual and population levels, ecosystem-level effects can vary and display nonlinear patterns. Combined OA forcing leads to initial increases in ecosystem and commercial biomasses followed by a decrease in commercial biomass below initial values over time, while ecosystem biomass remains high. Both biodiversity and average trophic level decrease over time. These projections indicate that the kelp forest community would maintain high productivity with a 0.5 drop in pH, but with a substantially different community structure characterized by lower biodiversity and relatively greater dominance by lower trophic level organisms.
... Generally, high EE values are assumed to occur in species that do not die of old age; they are either predated or exploited (Bayle-Sempere et al., 2013). In this context, the model behaved congruently since high EE values were observed in those FG that were known to be highly predated, such as octopuses (0.95) and shrimp (0.95) while other FG, such as marine mammals and sharks showed lower EE values (≤ 0.5) and were consistent with those reported by other authors in similar nearby systems (del Monte-Luna, 2004;Morales-Zárate, 2011;Cruz-Escalona et al., 2013; Table 5). Although some values were considerably different, particularly with those reported by del Monte-Luna, 2004, it is important to note that the systems are not static and may change due to multiple causes, including basic input values, information sources, etc. ...
The oceanographic conditions in the Gulf of Ulloa (GU) region make a distinctive faunal assemblage, allowing the presence of species both ecologically and economically important. Constant interaction of emblematic species with the fishing activity has brought social and conservation problems due to the lack of ecological information and/or management tools. For the loggerhead turtle (Caretta caretta), the GU is an important feeding area, so the interaction with anglers is frequent. In this sense, some events of high loggerhead mortality have resulted in restrictive fishing measures; nevertheless, alternative hypotheses should be explored to explain this fact better. With the purpose of not only knowing the ecosystem ecological attributes but also obtaining specific ecological facts of the loggerhead turtle-as instantaneous total mortality-this study proposes Ecopath with Ecosim (EwE) model by calculating Allen's approximation of production to biomass ratio (P/B). Using the thermoregulation theory of ectotherms and this baseline model, the scenarios were run in Ecosim combining two forcing factors (FF): sea surface temperature (SST) and different fishing effort (F) values. All Ecosim scenarios were run over 30 simulated years taking the (P/B) values of the loggerhead turtle. According to the results in this study, the model allowed us to obtain specific ecological attributes for C. caretta, particularly for the P/B estimates in different simulation scenarios, which showed that colder sea surface temperature increases loggerhead mortality. All the information combined provided a better panorama to understand the role this turtle has within the Biological Action Center of the GU system and its interaction with other activities developed on site, such as fishing.
... Several multispecies trophic models have been developed for the Mexican tropical Pacific Coast (e.g., Arreguín-Sánchez et al., 2002;Morales-Zarate et al., 2004;Diaz-Uribe et al., 2007;Morales-Zárate et al., 2011;Cruz-Escalona et al., 2013); however, this type of study has not been conducted for the coral ecosystems in these three MPAs (IINP, IMNP and SIIBC). Therefore, this work represents the first attempt to quantitatively model and simulate the trophic interactions of these coral ecosystems. ...
... They support the main gastropod grazers of the genera Fissurella, Haliotis, Megastraea, Megathura, and Tegula (Guzmán del Próo et al. 1991, Mazariegos-Villarreal et al. 2012, Mazariegos-Villarreal et al. 2013, León-Cisneros et al. 2017. Of these, the wavy turban snail Megastraea un dosa, the keyhole limpet Megathura crenu lata, and abalone ( Haliotis spp.) are considered keystone species (Morales-Zárate et al. 2011). ...
The wavy turban snail, Megastraea undosa ( W. Wood), is an important fishery resource along the Mexican Pacific coast and a keystone species in subtropical rocky reefs. Its diet was determined from stomach contents of 125 specimens collected in three rocky reefs of the western coast of the Baja California Peninsula in July and November 2006 and March 2007. The snail consumed 20 taxa of seaweeds, 1 seagrass, and 11 taxa of invertebrates. The diet had significant variation depending on site and date. Main food items were Macrocystis
pyrifera, Ecklonia arborea, and Corallina spp. Of secondary importance were red algae of the family Delesseriaceae and the genera Plocamium and Gelidium, the brown alga Stephanocystis osmundacea, the seagrasses Phyllospadix spp., the hydrozoan Dynamena, and the isopod Idotea. Analysis showed that the snail was a grazer with a mixed feeding strategy, feeding abundantly on kelp or coralline algae and
also consuming many other resources, which was reflected in its variable trophic niche width with a Levins index ranging from 0.21 to 0.79.
... We represent biological linkages as possible trophic relationships among target species or species groups, the linkages among species and fisheries operating in the study region based on harvest control rules, and key actors and some relevant socioeconomic components of the system (Fig. 2). The interaction web was assembled based on authors' experience and knowledge of the system and from relationships described in the published literature, including data from sampling and taxonomic identification of the benthic fauna and flora, stomach content analyses of fish and invertebrates, interviews with fishermen and cooperative members, and household surveys (Shester 2008, Martone 2009, Morales-Zárate et al. 2011, Ramírez-Sánchez et al. 2011, Shester and Micheli 2011, McCay et al. 2014, Leslie et al. 2015. ...
Managing for sustainable development and resource extraction requires an understanding of the feedbacks between ecosystems and humans. These feedbacks are part of complex social-ecological systems (SES), in which resources, actors, and governance systems interact to produce outcomes across these component parts. Qualitative modeling approaches offer ways to assess complex SES dynamics. Loop analysis in particular is useful for examining and identifying potential outcomes from external perturbations and management interventions in data poor systems when very little is known about functional relationships and parameter values. Using a case study of multispecies, multifleet coastal small-scale fisheries, we demonstrate the application of loop analysis to provide predictions regarding SES responses to perturbations and management actions. Specifically, we examine the potential ecological and socioeconomic consequences to coastal fisheries of different governance interventions (e.g., territorial user rights, fisheries closures, market-based incentives, ecotourism subsidies) and environmental changes. Our results indicate that complex feedbacks among biophysical and socioeconomic components can result in counterintuitive and unexpected outcomes. For example, creating new jobs through ecotourism or subsidies might have mixed effects on members of fishing cooperatives vs. nonmembers, highlighting equity issues. Market-based interventions, such as ecolabels, are expected to have overall positive economic effects, assuming a direct effect of ecolabels on market-prices, and a lack of negative biological impacts under most model structures. Our results highlight that integrating ecological and social variables in a unique unit of management can reveal important potential trade-offs between desirable ecological and social outcomes, highlight which user groups might be more vulnerable to external shocks, and identify which interventions should be further tested to identify potential win-win outcomes across the triple-bottom line of the sustainable development paradigm.
... The characterization of the SML CWC province in terms of structure and functioning was carried out calibrating a mass-balanced model for the representation of the food web related to the benthopelagic fauna. Each simulation was based on biomass data (B) directly sampled in the SML CWC province and other basic parameters (i.e., P/B, Q/B, Un/Q) that were adopted from other similar studies performed worldwide (e.g., Neira et al. 2004;Sánchez and Olaso 2004;Zuozhi et al. 2011;Morales-Zárate et al. 2011;Bȃnaru et al. 2013) and in the Mediterranean Sea (Coll et al. 2006(Coll et al. , 2007Barausse et al. 2009;Tsagarakis, et al. 2010;Fouzai et al. 2012, Tecchio et al. 2013. In many of these studies, pelagic and demersal domains were generally integrated and simulations were developed at the level of functional group. ...
The benthopelagic fauna distributed in and around the Santa Maria di Leuca (SML) cold-water coral (CWC) province (Northern Ionian Sea–Central Mediterranean Sea) was analyzed through the development of a mass-balanced ecosystem model. A total of nine balanced simulations were provided taking into account the biomass data collected during several experimental bottom trawl surveys carried out from 2005 to 2010 in a depth range between 101 and 541 m. A total of 100 species were included in the analysis corresponding to 15 cephalopods, 25 crustaceans, 7 chondrichthyes and 54 osteichthyes. Simulations were developed maintaining the species-level detail. The total system throughput estimated in the SML CWC province trophic web resulted mainly due to consumption and about 80% of it was maintained by species with trophic level between 2 and 4. Results highlighted important features in terms of the structure and functioning of the system, such as the high level of activity maintained by intermediate trophic levels and the important role of top-down control in the faunal assemblage due to both vertebrate and invertebrate species.
... Gal apagos subtidal rocky reef Ecuador (Okey et al., 2004) Jurien Bay Western Australia (Lozano-Montes et al., 2011) Red Sea coast Eritrean (Tsehaye and Nagelkerke, 2008) Subtidal area in Tongoy Bay Chile (Ortiz and Wolff, 2002) Shallow water in Tongoy Bay (Wolff, 1994) Western Scotland coast (Haggan and Pitcher, 2005) Rocky coastal ecosystem Bahia Tortugas, Mexico (Morales-Z arate et al., 2011) Sublittoral community of the Bay of Calvi, Corsica (Pinnegar, 2000) Median Units 37 13 0 N 0 1 40 0 N 3 0 18 0 S 1 5 61 0 N 3 0 15 0 S 3 0 15 0 S 55.30 0 N 27.67 0 N 4 2 35 0 N (Jin and Tang, 1996;Liu, 2013), leading to a local example of "fishing down marine food webs" . The intense fishing pressure is driven by the lucrative financial incentives due to increasing market demands for sea cucumber (Chen, 2005), abalone (Cheung, 2001) and sea urchin (Ding et al., 2007). ...
This study evaluates the ecosystem structure and function of the nearshore reefs in the Lidao coastal ecosystem of northern China, a region of intensive kelp aquaculture, and fisheries enhancements, including the deployment of artificial reefs and release of cultured marine species. An Ecopath model, with 20 functional groups representing 81 species, was developed for a representative area in the region and Ecosim was used to explore two scenarios for alternative fishing practices and surrounding aquaculture activities. The mean trophic levels (TLs) of the functional groups ranged from 1.0 for the primary producers (phytoplankton, benthic algae and seagrass) and detritus to 4.14 for Type III fishes (fishes found in the water column above the artificial reefs, e.g., Scomberomorus niphonius). The mean transfer efficiency through the whole system was 11.7%, and the ecosystem had a relative low maturity, stability and disturbance resistance, indicating that it was at a developing stage. Nearly half of the total system biomass (48.9% of 620.20 t km⁻² year⁻¹), excluding detritus, was comprised of benthic finfish and invertebrates. The total yield from all fisheries (86.82 t/km²/year) was dominated by low trophic level herbivorous and detritivorous species, such as the sea cucumber Apostichopus japonicus (TL = 2.1, 46.07%), other echinoderms (sea urchins Asterias amurensis and Strongylocentrotus nudus, TL = 2.1, 34.6%) and abalone Haliotis discus hannai (TL = 2.0, 18.4%), and as a consequence, the mean TL of the catch was low (2.1). The results from the Ecosim simulation of closing all fisheries for 20 years predicted an increase of about 100% in the relative biomass of the main exploited species, A. japonicus and H. discus hannai. The simulated removal of all kelp farms over 10 years resulted in a two fold increase in the relative biomass of Type III fishes and a 120% increase in their main prey (i.e. Small pelagic fish), while the relative biomass of A. japonicus and Heterotrophic bacteria decreased by 31.4% and 12.7%, respectively. These predictions indicate that nearshore kelp cultivation favours benthic, rather than water column production, and is likely to be providing energy subsidies for the stock enhancement of benthic species in this region.
... La mayoria de estos modelos han sido desarrollados en ambientes costeros (90%), más que en ambientes oceánicos o lacustres. Para la costa oeste de la península de Baja California existen sólo dos modelos conocidos: golfo de Ulloa (Del Monte-Luna et al., 2007) y Bahía Tortugas (Morales-Zárate et al., 2011). ...
In the present study we developed a trophic model (ECOPATH with ECOSIM), to describe the structure and functioning of Bahía Magdalena estuarine ecosystem. The model, constituted by 24 functional groups, indicates that one third of the total ecosystem biomass is produced by secondary and tertiary trophic levels. The magnitude of total flows in the system and the transfer efficiency among trophic levels, are similar to those observed in other tropical systems around the world. A large proportion of the total flows are directed to the maintenance of the trophic web structure. The value of the connectance index (CI) was 0.2, meaning that there is only 20% of realized connections within the web. Benthic primary producers contribute with 53% of the total ascendency. We believe that the energy control in this particular ecosystem is top-down type (through the main predators), suggesting that high-trophic level species negatively affect other groups in the system. This trophic model can be used for exploring different hypothesis concerning the biotic and abiotic mechanisms that modify the structure and functioning of the Bahía Magdalena ecosystem, with the ultimate goal of understanding how this attributes determine the resilience of marine communities.
... A continuous reproduction is also reported for the species at other subtropical and temperate localities of the Baja California Peninsula (Fig. 1), including scallops cultivated in Bahía Magdalena (Racotta et al., 2003) and Bahía Juncalito Villalejo-Fuerte et al., 2004), as well as wild scallops from Bahía de Los Angeles (Yee-Duarte, 2009). The three sites, together with Bahía Tortugas, are eutrophic areas reported as Biologically Active Centers or BAC, which offer high primary productivity all year round and optimum conditions for filter feeders to maintain a prolonged breeding (Lluch-Belda et al., 2000;Morales-Zárate et al., 2011). Under these conditions, gameto- genesis appears to be sustained by the energy taken from recently ingested food, following an opportunistic strategy. ...
The reproductive strategy of lion's paw scallop Nodipecten subnodosus was evaluated in a culturing system in Bahia Tortugas, Baja California Sur, Mexico during an annual cycle, comparing its response with data previously reported at other localities. High frequencies of ripe gonads throughout the year indicate that reproduction was continuous, with two main ripening/spawning events: July-September and December-March. A continuous breeding is also reported for the species in Bahia Magdalena, Bahia Juncalito, and Bahia de Los Angeles. These eutrophic areas are Biological Active Centers where gametogenesis appears to be regulated by the energy taken from recently ingested food following an opportunistic strategy. However, the digestive gland index decreased and the muscle indices increased during one of the breeding peaks, suggesting that some stored reserves are also used to sustain gametogenesis (conservative strategy) partially. High incidences of atretic oocytes are likely associated with atypical daily variations in water temperature from May through September (12 to 33 degrees C), or with stressful conditions in the culturing system in summer. Despite this, the culturing system set in Bahia Tortugas appears beneficial for a continuous reproduction of N. subnodosus.
The intricate trophic structure of marine ecosystems defines their ecological properties and network metrics; it has been used extensively to assess the development and maturity of ecosystems. The Eastern Pacific is warming due to climate change, and added human stressors are affecting the trophic architecture of its marine ecosystems. We aimed to explore the maturity of ecosystems in this region under the assumption that the trophic architecture of an ecosystem is a proxy of maturity, and that there is a direct relationship between resistance and maturity and an inverse one with resilience. We applied ecosystem network analysis to model runs of published rebuilt Ecopath models to explore the potential effects of oceanographic variables and human disturbance on the trophic architecture of 13 ecosystem models, 11 models within three different Large Marine Ecosystems (LMEs) and two models describing oceanic islands, that have an array of oceanographic conditions and are subject to different human stressors. We conclude that even when ecosystem attributes cannot conclusively assert maturity stage, they can suggest how close or far the ecosystems are from maturity. We found that the ecosystems in the Gulf of California are resilient because they have a high median trophic level, high Production/Biomass ratio, and median ascendency/capacity ratio, and because they are subject to natural variations of productivity. Upwelling ecosystems are in an intermediate stage of maturity, followed by ecosystems from the Pacific Central American Coastal LME. As expected, oceanic islands, which have a production deficit, must optimize their energy transfer. Our analysis suggests that although trophic architecture cannot serve as a direct indicator of maturity, it can help estimate ecosystem resilience and identify those systems that can withstand future impacts.
In the southern Gulf of California, the Cabo Pulmo reef has been the focus of many studies because it is the northern-most coral reef in the eastern Pacific. It is a paragon of a well-managed marine protected area. Under the assumption that fishing mortality is negligible, we want to identify and quantify major energy flows in an ecosystem without human intervention and describe the ecosystem resources and their interactions among species, to provide a tool for ecosystem-based management. We built a trophodynamic model using Ecopath to perform network analysis. Based on fieldwork (October 2017 – May 2018) and literature review, we identified 57 functional groups comprising 51 consumers (including 15 top predators), five primary producers plus detritus, and cluster analysis of trait profiles. The connectance index (0.17) and the system omnivory index (0.22) are low, suggesting that consumers feed on a few discrete trophic levels. Biomass of primary producers (grazing food chain; 186.8 t km⁻²) provides 9,813 t km⁻² y⁻¹, whereas flow from detritus supply 344.9 t km⁻² y⁻¹. The transfer efficiency decreases as flows go up the food web, from 12% at TL II to 4% at TL X, and throughput cycled (including detritus) = 118.7 t km⁻² y⁻¹. In comparison with other coral reefs, we found that Cabo Pulmo complies with the attributes to resist disturbances, with an estimated total system throughput = 95,789 t km⁻² y⁻¹, a net system production = 38,535 t km⁻² y⁻¹, a large mean path length = 12.11, ascendency = 123,662 (52%) flowbits and overhead = 116,164 (48%) flowbits. The high quality of the ecosystem services provided by Cabo Pulmo and the scenic beauty appeals to developers. Although the system is resilient, unregulated human activities may impact the reef condition and decrease the residents' quality of life and that of all the people who make a living from the low impact activities currently in effect. The trophic web model presented here may help to improve the response capacity of the coalition of residents, authorities, diving companies, and NGO's to preserve the reef and be a key element to conserve the system by contributing to its best management.
Ocean acidification is one the biggest threats to marine ecosystems worldwide, but its ecosystem wide responses are still poorly understood. This study integrates field and experimental data into a mass balance food web model of a temperate coastal ecosystem to determine the impacts of specific OA forcing mechanisms as well as how they interact with one another. Specifically, we forced a food web model of a kelp forest ecosystem near its southern distribution limit in the California large marine ecosystem to a 0.5 pH drop over the course of 50 years. This study utilizes a modeling approach to determine the impacts of specific OA forcing mechanisms as well as how they interact. Isolating OA impacts on growth (Production), mortality (Other Mortality), and predation interactions (Vulnerability) or combining all three mechanisms together leads to a variety of ecosystem responses, with some taxa increasing in abundance and other decreasing. Results suggest that carbonate mineralizing groups such as coralline algae, abalone, snails, and lobsters display the largest decreases in biomass while macroalgae, urchins, and some larger fish species display the largest increases. Low trophic level groups such as giant kelp and brown algae increase in biomass by 16% and 71%, respectively. Due to the diverse way in which OA stress manifests at both individual and population levels, ecosystem-level effects can vary and display nonlinear patterns. Combined OA forcing leads to initial increases in ecosystem and commercial biomasses followed by a decrease in commercial biomass below initial values over time, while ecosystem biomass remains high. Both biodiversity and average trophic level decrease over time. These projections indicate that the kelp forest community would maintain high productivity with a 0.5 drop in pH, but with a substantially different community structure characterized by lower biodiversity and relatively greater dominance by lower trophic level organisms.
Ecosystem Based Management (EBM) aims to support the protection of natural ecosystems and to improve economic activities. It requires considering all of the actors interacting in social-ecological systems (e.g., fish and fishers) in the understanding that their interplay determines the dynamic behavior of the single actors as well as that of the system as a whole. Connections are thus central to EBM. Within the ecological dimension of socio-ecological systems, interactions between species define such connections. Understanding how connections affect ecosystem and species dynamics is often impaired by a lack of data. We propose food web network analysis as a tool to help bridge the gap between EBM theory and practice in data-poor contexts, and illustrate this approach through its application to a coastal marine ecosystem in Baja California Sur, Mexico. First, we calculated centrality indices to identify which key (i.e., most central) species must be considered when designing strategies for sustainable resource management. Second, we analyzed the resilience of the system by measuring changes in food web structure due to the local extinction of vulnerable species (i.e., by mimicking the possible effect of excessive fishing pressure). The consequences of species removals were quantified in terms of impacts on global structural indices and species' centrality indices. Overall, we found that this coastal ecosystem shows high resilience to species loss. We identified species (e.g., Octopus sp. and the kelp bass, Paralabrax clathratus) whose protection could further decrease the risk of potential negative impacts of fishing activities on the Baja California Sur food web. This work introduces an approach that can be applied to other ecosystems to aid the implementation of EBM in data-poor contexts.
Spiny lobsters are among the most valuable species in the world's oceans. Because of this they have been a focus of research and several have become among the most studied exploited marine animals. Commercial fisheries exist wherever they occur and because they are generally shallow water species they have been subject to intensive fishing worldwide. The maintenance of the sustainability of the fisheries for spiny lobsters has seen wide-ranging research programs conducted over many years including studies of the biology and ecology of the lobsters and the environments and habitats in which they occur. This chapter concentrates on changes and developments in Panulirus lobster fisheries since 2006, as part of the ongoing quest for sustainable management of existing fisheries as well as increased production through enhancement and aquaculture. Important species including Panulirus cygnus, Panulirus argus, Panulirus interruptus and Panulirus ornatus are given special attention.
The ‘Ecopath’, later expanded to ‘Ecopath with Ecosim’ (‘EwE’), modeling approach has been applied to hundreds of ecosystems around the world, since its first implementation in 1984. The ‘EcoBase’ model repository was developed to gather EwE models published worldwide. For the 433 unique models documented in EcoBase, we compiled, standardized, and analyzed all available metadata describing critical aspects of the models. We proposed a general description of the EwE applications and we analyzed their evolution over the last 30 years, based on the year of publication of the models. Then, we performed a correspondence analysis on the metadata to identify the main types of EwE models. Overall, most models were built to analyze ecosystem functioning and fisheries, principally in the Northern and Central Atlantic Ocean. During the first decade (1984–1993), most EwE applications were Ecopath models representing tropical marine systems and using simple food web representations to analyze trophic functioning only. Over the last two decades (1994–2014), EwE models were applied to study a wider variety of ecosystems, including polar regions and terrestrial systems, and a wider range of research topics , including pollution, aquaculture and Marine Protected Areas. The modeling practices also evolved toward Ecopath (but also Ecosim and Ecospace) models with larger spatial scales, shorter temporal scales, and more complex representations of the food web. In parallel, the numbers of both publications and modelers have steadily increased, while the proportion of journal articles presenting EwE-based studies has been growing. The correspondence analysis confirmed these trends and discriminated three types of models: the basic Ecopath models developed during the first decade, the average models developed over the last two decades using Ecopath and Ecosim routines and an intermediate number of groups, and the most elaborated models including Ecospace simulations and a high number of groups with multi-stanza. We concluded by discussing the challenges and potentials of the compilation and meta-analysis of EwE models, notably by using the EcoBase repository. This global overview showed that the usage of and interest for the EwE modeling approach in the scientific community had evolved and expended over the last three decades to support ecosystem-based fishery management.
El objetivo del presente estudio fue desarrollar un modelo trófico (ECOPATH con ECOSIM) para caracterizar la estructura y función de la trama alimentaria de Bahía Magdalena. El modelo consta de 24 grupos funcionales, siendo dominado por grupos de niveles tróficos secundarios y terciarios, que generan un tercio de los flujos de biomasa total. Los flujos totales del sistema y la eficiencia de transferencia promedio entre niveles tróficos, encajan bien en el rango reportado para otros ecosistemas costeros tropicales del mundo. Una fracción alta de los flujos totales se destina para el mantenimiento de la estructura de la red trófica. El índice de conectancia (IC) fue igual a 0,2, esto significa que sólo hay 20% de las conexiones totales posibles en la trama alimentaria. Una jerarquización de los diversos componentes del sistema en términos de su contribución a la función del sistema reveló que los productores primarios bentónicos y los detritos contribuyen 53% al total de la ascendencia. La idea de un control de la energía de arriba hacia abajo (a través de los principales depredadores) es consistente con otros hallazgos, dicho resultado sugiere que las especies de nivel trófico superior afectan negativamente a otros componentes del ecosistema. Se sugiere emplear el modelo en el corto plazo, para realizar aproximaciones exploratorias que pongan a prueba hipótesis relacionadas con los mecanismos bióticos y abióticos que ocasionen cambios en la estructura y función de la red trófica a través del tiempo, y por tanto contribuyan a entender como la estructura de la trama trófica puede contribuir a la resiliencia de las comunidades biológicas marinas.
It is now clear that research addressed at a large scale can allow for new insights on complex phenomena taking place in the global ocean. Ecological studies are more and more based on data-driven methodologies that rely on pre-existing datasets. However, open-access, digital and cross-disciplinary datasets are still uncommon for ecology. In the face of the global overexploitation of marine resources and rapid degradation of ecosystem integrity, new research tools are required to tackle these issues and enable new powerful, interdisciplinary research capabilities. We have, in fisheries research generally, and at the Fisheries Centre in particular, broad experience with fisheries data collection, and analysis of food web aspects of ecosystem dynamics.
With this report titled EcoBase: a repository solution to gather and communicate information from EwE models, Colléter and colleagues have made a big effort at collecting information from all existing ecosystem models worldwide, built using the Ecopath with Ecosim (EwE) approach. EwE is the world’s most widely used ecological modeling approach, and its development is led by Fisheries Centre researchers, including, Villy Christensen, Daniel Pauly and Carl Walters. A new accomplishment is now achieved with the EcoBase project initiated by the Ecopath Research and Development Consortium (ERDC) and carried out by the authors of this report. The ERDC was initiated at the Fisheries Centre in October 2011, and formally established in Edinburgh, Scotland, in May 2012. It contributes to creating synergies and partnerships between scientists in aquatic ecology, and promotes the EwE modeling approach.
The main goals of EcoBase are to (i) gather published EwE models; (ii) communicate on EwE modeling research; (iii) facilitate meta-analyses based on EwE models. EcoBase is meant to be a comprehensive, open-access, digital repository where EwE models are made discoverable, accessible and reusable by the scientific community. The structure, capabilities and current state of the EcoBase models repository are described in further details in this report. This represents new opportunities for research and trans-disciplinary analyses, including, trophic functioning, fisheries impact or economic aspects, for which I commend the authors.
U. R. Sumaila,
Director,
Fisheries Centre, UBC.
The Gulf of Maine (GOM) ecosystem has been observed to experience large changes over the last several decades, switching from a groundfish dominated system to a system dominated by crustacean species such as the American lobster (Homarus americanus) and crabs. The objective of this study is to develop a lobster ecosystem model and to evaluate the changes in the GOM ecosystem for the American lobster between 1980s and 1990s. A mass-balance ecosystem model was developed separately for the two time periods (1980s and 1990s) using Ecopath. The model includes 24 functional groups consisting of lobster, its key predator and prey species, and other ecologically important groups in the ecosystem such as zooplankton, phytoplankton, and detritus. Using the models developed we conducted a comparative analysis of trophic interactions and community structures of the GOM ecosystem for lobster in 1980s and 1990s. The balanced model suggests that the biomasses of shelled mollusk, crab, juvenile lobster, adult lobster, and Atlantic herring (Clupea harengus) were doubled, tripled or even more than tripled, but the groundfish biomass decreased substantially from 1980s to 1990s. The study shows that the trophic structures of the lobster ecosystem in the 1980s are different from those in the 1990s with a decrease in top predator biomass and an increase in the biomass of lower trophic level organisms. The ecosystem in 1990s was found to be more mature than in 1980s. This study suggests a regime switch in the GOM from high trophic groundfish dominated system to low trophic crustacean species dominated system during 1980s–1990s.
A simple model termed ECOPATH is pre- sented which estimates mean annual biomass, produc- tion, and consumption for components of an ecosystem. To use the model, the ecosystem must be partitioned into groups of similar species and provide for these species groups, estimates of production to biomass, diet, and food consumption. The ECOPATH model is applied to an ecosystem at French Frigate Shoals in the Northwest- ern Hawaiian Islands. Extensive field work provides both estimates of the input parameters as well as estimates of mean annual biomass and production. Biomass and pro- duction estimates for some of the species groups mod- eled are used to validate the estimates generated by the model.
The trophic network of the southern Sinaloa benthonic ecosystem was reconstructed for the period 1994–1997, using Ecopath with Ecosim version 5.1. The ecosystem is a resource for finfish and shrimp fisheries. The majority of the 37 functional groups were determined from the makeup of captures taken by commercial trawls similar to those used by the shrimp fishery. Incidental captures represented approximately 91% of the total and consisted mainly of fish from the families Sciaenidae, Haemulidae, and Serranidae, followed by macrocrustaceans (Portunidae) and invertebrates (Echinodermata). The trophic model obtained had a pedigree index of 0.57, which represents an acceptable quality from the data used. The ecosystem is represented by 4 discreet trophic levels; medium-level carnivores, including Pleuronectiformes, birds, Sciaenidae, Serranidae, and Centropomidae, contribute the majority of energy transfer in the third level. The mixed trophic impacts show that detritus positively affects the majority of functional groups, mainly the primary consumers (TL=2). The shrimp fleet also uses the Penaeidae as a resource. Primary producers exert a positive impact on groups taken by the finfish fleet, although to a lesser extent. The ecosystem is in a low state of maturity or development according to system attributes, which indicate an overhead of 2.3 times the ascendance.
Recent work by one of the authors has identified the average mutual information and the conditional entropy as two measures from information theory that are useful in quantifying the system organization and incoherence, respectively. While the scaled average mutual information, or network ascendency, is inherently symmetrical with respect to inputs and outputs, the scaled conditional entropy, or overhead, remains asymmetrical. Employing the joint entropy, instead of the conditional entropy, to characterize the overhead, results in a symmetrical overhead and also permits the decomposition of the system capacity, or complexity, into components useful in following the response of the whole system to perturbations.
A trophic ecosystem model of La Paz Bay, on the southern Baja California Peninsula, was improved from one previously constructed by adding 13 functional groups. In the bay, small-scale fisheries take place, which are aimed at finfish, shark and clams. Also there is a pilot shrimp trawl fishery. At the mouth of the bay, communicating with the Gulf of California, there is the insular complex of Espíritu Santo, which was declared as a protected area by the federal government. The aim for the construction of a model of La Paz Bay is to help run scenarios of the fleets and MPA operating together to support fisheries management within an ecosystem context. We present a full description of the ecosystem structure and basic functions based on Ecopath software. The Ecosim model is used to calibrate time series of relative abundance of several groups, which served as the basis for spatial modeling. Preliminary simulations suggest a limited effect of the MPA around Espiritu Santo Island on marine birds, sharks and red snapper.
Using the Ecopath with Ecosim software, a trophic structure model of the Northern Gulf of California was constructed to represent the main biomass flows in the system. It was based mostly on bibliographic data and provides a snapshot of how the ecosystem operates. The model consisted of 29 functional groups. The total system throughput was 6633 tonnes/km2 per year, from which 51.7% are for internal consumption, 20.0% are for respiration, 16.0% becomes detritus, and 12.2% are removed through commercial fishing. Main results show that most groups were impacted more by predation and competition than by fishing pressure, and that there are some characteristics that indicate that use of the ecosystem is balanced.
Energy fluxes in a mangrove ecosystem were evaluated with Ecopath model through a predator/prey matrix with 19 functional groups including primary producers and three levels of carnivores. Some input data (biomass of the fish groups, zooplankton and benthic communities) were obtained from the field and by stomach content analysis of dominant fish species (32) while others were taken from previous studies. Within fish, nine functional groups were obtained through trophic similarity analysis, being microcrustaceans an important prey in five of them. Results showed that a great proportion of the primary production is exported to adjacent ecosystem while within the system only 4% is grazed and 7% goes to detritus, with a detritivory/herbivory ratio of 2.0. Within the mangrove, detritus plays an important role with 64% of the flows being utilized and transferred to juvenile fish by microcrustaceans. Mixed trophic impacts showed that detritus and low trophic levels had a positive influence on most groups, while a negative one occurred with increasing biomass at high trophic compartments ('other fish' and piscivorous). Small EE for fish groups indicated a low predation rate to these groups, while greater P/B and Q/B suggest that mangrove is a high productive system with characteristic properties of a transition between mature and immature stage. © 2001 Elsevier Science B.V. All rights reserved.
A simple model termed ECOPATH is presented which estimates mean annual biomass, production, and consumption for components of an ecosystem. To use the model, the ecosystem must be partitioned into groups of similar species and provide for these species groups, estimates of production to biomass, diet, and food consumption. The ECOPATH model is applied to an ecosystem at French Frigate Shoals in the Northwestern Hawaiian Islands. Extensive field work provides both estimates of the input parameters as well as estimates of mean annual biomass and production. Biomass and production estimates for some of the species groups modeled are used to validate the estimates generated by the model.
We constructed a mass-balanced model of a benthic ecosystem exploited by shrimp trawlers in the Gulf of California, Mexico. The model is based on the software ecopath with ecosim Version 4a, which takes into account the contribution of functional groups to bycatch. The model represents the state of the ecosystem in 1978–79, and reflects the exploitation rate of shrimp at that time. We included 27 groups in the model: aquatic birds, marine mammals, shark/rays, 11 groups of teleost fish, five macrocrustaceans, two macromolluscs, polychaetes, meiobenthos, zooplankton, phytoplankton, detritus and dead fish. With respect to the bycatch, it was assumed that fish died on-board the trawlers while macroinvertebrates were returned to the sea alive. The macroinvertebrates would become more vulnerable to predation as a result of this practice but we assumed that this effect would be reflected in diets. The most important families of fish in the bycatch were Haemulidae, Serranidae, Paralichthydae, accounting for 75% of the total fish catch. These families include important shrimp predators, suggesting that fish mortality in the bycatch could have a positive impact on the shrimp stock. Total system throughput was up 4000 t km-2 year-1; total consumption 52%; flows to respiration 40%; and flows to detritus 7%. The total system production was almost equal to its consumption as was net primaty production to respiration. It is suggested that ecosystem efficiency was relatively low. Ecosystem overhead was 2.4 times the Ascendency, indicating that the shrimp-trawl ecosystem was in a develope stage, probably as a result of fishing. Because a decrease in biomass causes a loss of Ascendency, it is hypothesized that the previous state of the ecosystem (unexploited or with low exploitation rate) was more developed, and probably had a higher production.
1. Introduction.- 1.1 The Enigma.- 1.2 The Imprecise Universe.- 1.3 The Dilemma of Modern Biology.- 1.4 Phenomenological Redress.- 1.5 Origins of the Principle.- 2. The Perspective.- 2.1 Thermodynamics: The Phenomenological Science.- 2.2 The First Law and the Nature of Work.- 2.3 The Second Law.- 2.4 Nonequilibrium Thermodynamics and Proto-Communities.- 2.5 Summary.- 3. The Object.- 3.1 The Ubiquity of Flows.- 3.2 Describing Flow Networks.- 3.3 Analyzing Flow Networks.- 3.4 Standing Stocks and Fluxes.- 3.5 Summary.- 4. An Agent.- 4.1 Cycles and Autonomous Behavior.- 4.2 Autonomous Behavior and Holistic Description.- 4.3 The Amount of Cycling in Flow Networks.- 4.4 The Structure of Network Cycles.- 4.5 Summary.- 5. The Calculus.- 5.1 Information Theory and Ecology.- 5.2 The Uncertainty of an Outcome.- 5.3 Information.- 5.4 Summary.- 6 The Description.- 6.1 The Network Perspective.- 6.2 Growth.- 6.3 Development.- 6.4 Simultaneous Growth and Development.- 6.5 Ascendency Arising from a Dynamic Tension.- 6.6 Generic Limits to Growth and Development.- 6.7 Autonomous Growth and Development Ill.- 6.8 The Limits to Autonomous Growth and Development.- 6.9 Phenomenological Basis for Optimal Ascendency.- 6.10 The Principle of Maximal Work.- 6.11 Relationship to Other Variational Principles.- 6.12 Summary.- 7 Extensions.- 7.1 The Incomplete Picture.- 7.2 Spatial Heterogeneity.- 7.3 Temporal Dynamics.- 7.4 Multiple Media.- 7.5 Overall Heterogeneity.- 7.6 Aggregation.- 7.7 Ascertaining Configurations of Optimal Ascendency.- 7.8 Other Applications-Economics and Ontogeny.- 7.9 Summary.- 7.10 Epilogue.- Appendix A: Review of Matrix and Vector Operations.- Appendix B: A Program to Calculate Information Indices.- References.- Author Index.
The impact of some optimized harvesting strategies on ecosystem structure was investigated using a mass-balanced model of the ecosystem in the southwestern Gulf of Mexico, where there are four types of artisanal fisheries and a shrimp fishery that has collapsed. The Ecopath with Ecosim software was used to simulate harvesting strategies aimed at optimizing economic (profit), social (jobs), ecological (conservation of ecosystem structure) and shrimp-recovery criteria. As expected, the ecosystem changes that would ensue vary according to the combination of optimization goals. We found that for some scenarios, the extraction of biomass from a discrete trophic-level changes impacting ecosystem and catch structure. This was clearly observed through the tendency of the mean trophic level of the ecosystem and catch, as well as the fishing-in-balance index (FBI). A particular discussion was made about the collapsed shrimp fishery, where the impact of a specific shrimp-recovery strategy was evaluated. Collapse is strongly associated to physical variables and recovery based on trophic relationships is plausible but with a high ecosystem structure cost.
Ascendency is a system indicator used for describing flow characteristics of ecosystems. Experience shows, however, that ascendency is primarily a function of the flow characteristics at the lowest trophic levels. This is because of the way ascendency is calculated: throughput times information content of the flows. Aggregation of groups with low throughput hardly reduces the information content of the flow system, and therefore hardly influences the ascendency. An emergy-based unit is suggested for calculation of ascendency. The calculation procedure is described and it is demonstrated that emergy-based ascendency has the desired properties, notably sensitivity to the flow characteristics of all trophic levels. The use of ascendency, both energy and emergy based, for aggregation of groups in ecosystems is demonstrated, and it is shown that the higher the information content of the flows the less the difference between energy- and emergy-bound ascendency.
A series of mathematical models of cohorts in animal populations representing various combinations of several different simple growth and mortality functions is examined to investigate the ratio between mean biomass and production over unit time, and to compare this ratio with the mean age and mean life span of the animals in the cohort.For any cohort, the ratio of production per unit time to mean biomass is equal to the ratio of total production by the cohort to its total biomass integral by time. For populations consisting of a number of simultaneous, successive, or overlapping cohorts, the ratio of production per unit time to mean biomass is equal to the mean of the ratios for the individual cohorts weighted by the mean biomasses of the cohorts.If the cohorts are identical, the population ratio is the same as the cohort ratio and problems arising from the presence of more than one cohort may be ignored. Formulations for the total production per cohort, biomass integral, and, where they can be simplified, their ratios, are given.Comparison with mean age and mean life span shows that for constant exponential mortality, mean age and mean life span are both equal to the reciprocal of the production–biomass ratio. For other mortality functions, if growth in weight is linear, the production–biomass ratio equals the reciprocal of the mean age. For other models there is no simple relation. In general, mean age appears a better approximation than mean life span to the reciprocal of the production–biomass ratio.These methods are applied, as an example, to Antarctic krill, using a model having linear growth in length and four periods with different exponential mortality rates. For this model, annual production is 1.8 times the mean biomass so that assumption of equality leads to an underestimate of production. Mean age and mean life span are 0.21 and 0.037 years respectively. Thus, use of either of these as an approximation, and particularly mean life span, leads to severe overestimation of annual production.
The relationships among stability, maturity and complexity of ecosystems have been studied for many years. These ecosystem attributes are important in ecological theory and also for the appropriate management of resources. In a previous work, we proposed the U index, which accounts for complexity and recycling of detritus, and measures maturity in ecosystems according to attributes of E. P. Odum's theory of ecosystem development. Here we compare the behaviour of the U index and its ability to measure stability. Using models of ecosystems, we simulated disturbances and measured stability through resistance, persistence, resilience and recovery time. We found that the index is correlated with these attributes, but in an inverse way to that expected; that is, immature ecosystems were more stable and stability decreased when the systems matured.
Keystones are defined as relatively low biomass species with a structuring role in their food webs. Thus, identifying keystone species in a given ecosystem may be formulated as: (1) estimating the impact on the different elements of an ecosystem resulting from a small change to the biomass of the species to be evaluated for its ‘keystoneness’; and (2) deciding on the keystoneness of a given species as a function of both the impact estimated in (1) and its own biomass. Experimental quantification of interaction strength necessarily focus on few species, and require a priori assumptions on the importance of the interactions, which can bias the identification of keystone species. Moreover, empirical measurements, although very important, are expensive and time consuming and, owing to the spatio-temporal heterogeneity of habitats, physical conditions, and densities of organisms, published results tend to be case-specific and context-dependent.Although models can only represent but a caricature of the complexity of the real world, the modelling approach can be helpful since it allows overcoming some of the difficulties mentioned. Here we present an approach for estimating the keystoneness of the functional groups (species or group of species) of food web models. Network mixed trophic impact analysis, based on Leontief's economic input–output analysis, allows to express the relative change of biomasses in the food web that would result from an infinitesimal increase of the biomass of the observed group, thus identifying its total impact. The analysis of the mixed trophic impacts presented here was applied to a suite of mass-balance models, and the results allow us to rank functional groups by their keystoneness. Overall, we concluded that the straightforward methodology proposed here and the broad use of Ecopath with Ecosim (where mixed trophic impact analysis is implemented) together give a solid empirical basis for identification of keystone functional groups.
This contribution, which serves as introduction to a special issue of Ecological Modelling briefly discusses some of the implication for research of the widely heard calls for a transition toward ecosystem-based management of fisheries. Notably, the case is made that the research required for this transition does not need, in order to be useful at all, to explicitly address the full complexity of ecosystems. Indeed, the EU-funded project, which led to the most of the contributions in this thematic issue all contribute useful insights on the structure and functioning of the marine ecosystem they covered, and in many cases, on their fisheries impact on these ecosystems. This could be done under the constraints of available data sets because of the software used by all, Ecopath with Ecosim (EwE), whose mass-balance assumption lead to food web description, and to temporal and spatial simulations that can be robust even in data-sparse environments. Two additional contributions, on the methodology of EwE point to potential pitfalls, and to issues of uncertainty.
An attempt is made to rank 41 steady-state models of aquatic ecosystems on the basis of their maturity. Maturity is quantified using several of Odum's attributes of ecosystem maturity. It is shown that it is possible to make such a ranking, and that the ranking seems to confirm our intuitive perception of ecosystem maturity. The ranking is compared to rankings based on various ecosystem goal functions. The maturity ranking shows a strong negative correlation with relative ascendency, and thus a strong positive correlation with system overhead, a possible measure of ecosystem stability. The analyses suggest that another goal function, exergy, as calculated here is mainly a function of system biomass, and that it might be appropriate to reconsider the computational aspect of exergy estimation. Most importantly the analyses point to the feasibility of using comparisons of ecosystem models as a tool for enhancing our understanding of ecosystem characteristics, notably sustainability.
The ECOPATH II microcomputer software is presented as an approach for balancing ecosystem models. It includes (i) routines for balancing the flow in a steady-state ecosystem from estimation of a missing parameter for all groups in the system, (ii) routines for estimating network flow indices, and (iii) miscellaneous routines for deriving additional indices such as food selection indices and omnivory indices. The use of ECOPATH II is exemplified through presentation of a model of the Schlei Fjord ecosystem (Western Baltic).
The principles of ecological succession bear importantly on the relationships between man and nature. The framework of successional theory needs to be examined as a basis for resolving man’s present environmental crisis. Most ideas pertaining to the development of ecological systems are based on descriptive data obtained by observing changes in biotic communities over long periods, or on highly theoretical assumptions; very few of the generally accepted hypotheses have been tested experimentally. Some of the confusion, vagueness, and lack of experimental work in this area stems from the tendency of ecologists to regard “succession” as a single straightforward idea; in actual fact, it entails an interacting complex of processes, some of which counteract one another.
Ecopath user's manual and program listings
- J J Polovina
- M D Ow
Polovina, J.J., Ow, M.D., 1983. Ecopath user's manual and program listings.
NMFS/NOAA Honolulu Admin. Rep. H., 83-23 46 p.
Análisis trófico de la ictiofauna de la laguna de San Ignacio
- V H Cruz-Escalona
Cruz-Escalona, V.H., 1998. Análisis trófico de la ictiofauna de la laguna de San Ignacio.
B.C.S. Master Thesis, Centro Interdisciplinario de Ciencias Marinas. La Paz, B.C.S.
México, p. 128.
Caracterización del Centro de Actividad Biológica del Golfo de Ulloa, BCS, bajo un enfoque de modelación ecológica
- P Del Monte Luna
Del Monte Luna, P., 2004. Caracterización del Centro de Actividad Biológica del Golfo
de Ulloa, BCS, bajo un enfoque de modelación ecológica. Ph.D Thesis. Centro
Interdisciplinario de Ciencias Marinas -Instituto Politécnico Nacional, México.
pp. 93.
Ecopath with Ecosim Version 4, Help System
- V Christensen
- C J Walters
- D Pauly
Christensen, V., Walters, C.J., Pauly, D., 2000. Ecopath with Ecosim Version 4, Help System. Univ. of British Columbia, Fisheries Centre/ICLARM, Vancouver, Canada/Penang, Malaysia
FishBase. World Wide Web electronic publication
- R Froese
Froese, R., Pauly, D. (Eds.), 2009. FishBase. World Wide Web electronic publication,
Version (05/2009) www. fishbase. org.
Dinámica de la estructura trófica del ecosistema de Bahía Concepción
- M Gorostieta Monjaraz
Gorostieta Monjaraz, M., 2001. Dinámica de la estructura trófica del ecosistema
de Bahía Concepción, B.C.S., México. Master Thesis. Centro Interdisciplinario de
Ciencias Marinas del Instituto Politécnico Nacional, La Paz, Baja California Sur,
México.