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Rhodoliths form the substratum for attached fleshy and crustose red, brown, and green seaweeds. Mohawk ROV photos taken on 25 Sept. 2018 in West Flower Garden Bank, FGBNMS. (A) 27°52'7.2732“N, 93°51'34.4088”W, 58.8 m depth (Dive 706_0238_122144). The visible macroscopic seaweed is the green alga Codium isthmocladum Vickers (Codiaceae, Bryopsidales). (B) 27°52' 7.1682“N, 93°51'34.185”W, 58.8 m depth (Dive 706_0268_123120). The visible fleshy macroscopic red algal blades are the red alga Anatheca sp. (Areschougiaceae, Gigartinales). Space between spot lasers = 10 cm.
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Rhodoliths are the main hard substrata for the attachment of benthic macroalgae in the NW Gulf of Mexico rubble habitats that are associated with salt domes, unique deep bank habitats at ~50–90 m depth on the continental shelf offshore Louisiana and Texas. With the advent of additional sequencing technologies, methodologies for biodiversity assessm...
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... Moreover, rhodolith beds provide important ecosystem services worldwide. Among other things, they may act as refugia for other species against acute (Fredericq et al., 2019) or chronic (Voerman et al., 2022) environmental stress, promoting ecosystem resilience, and provide ecological and genetic connectivity with other habitats (Tuya et al., 2023). ...
Abstract Rhodoliths built by crustose coralline algae (CCA) are ecosystem engineers of global importance. In the Arctic photic zone, their three-dimensional growth emulates the habitat complexity of coral reefs but with a far slower growth rate, growing at micrometers per year rather than millimeters. While climate change is known to exert various impacts on the CCA's calcite skeleton, including geochemical and structural alterations, field observations of net growth over decade-long timescales are lacking. Here, we use a temporally explicit model to show that rising ocean temperatures over nearly 100 years were associated with reduced rhodolith growth at different depths in the Arctic. Over the past 90 years, the median growth rate was 85 μm year−1 but each °C increase in summer seawater temperature decreased growth by a mean of 8.9 μm (95% confidence intervals = 1.32–16.60 μm °C−1, p < .05). The decrease was expressed for rhodolith occurrences in 11 and 27 m water depth but not at 46 m, also having the shortest time series (1991–2015). Although increasing temperatures can spur plant growth, we suggest anthropogenic climate change has either exceeded the population thermal optimum for these CCA, or synergistic effects of warming, ocean acidification, and/or increasing turbidity impair rhodolith growth. Rhodoliths built by calcitic CCA are important habitat providers worldwide, so decreased growth would lead to yet another facet of anthropogenic habitat loss.
... Rhodoliths can acquire various complex morphologies, from highly branched to massive round thalli (Bosence 1983). Therefore, they provide a greater array of microhabitats at different scales, from the interstitial spaces between branches (Bernard et al. 2019;Fredericq et al. 2019;Boyé et al. 2019) to the seascape level by increasing habitat heterogeneity (Amado-Filho et al. Responsible Editor: F. Bulleri. ...
... The morphological complexity of the rhodolith is a key driver for the high faunistic and floristic diversity of rhodolith beds (Fredericq et al. 2019;Gabara et al. 2018;Teichert 2014). Our results also support the idea proposed by Jardim et al. (2022) for using the rhodolith interstitial space (or solidity as equivalent indicator) as proxy for habitat complexity. ...
The ecological importance of rhodolith beds stems from their role as structurally complex three-dimensional habitat formed by free-living red calcareous algae. Their structural singularity is due to the great variety of complex and branching morphologies exhibited by rhodoliths that create interstitial spaces and increase their surface area. This increases the ecological niches for cryptofauna and provide refuge for a high number of organisms, which is why rhodolith beds are considered biodiversity hotspots. In this work, we studied a rhodolith bed located in the Menorca Channel, formed by several species of red calcareous algae that exhibit a great variety of morphologies and form an extensive and heterogeneous habitat. This study explored the morphological diversity of the rhodolith bed, comparing the ‘Core Habitat’ (within the center of the bed with the highest densities of rhodoliths) with the boundaries or ‘Adjacent Habitat’ where rhodolith density was lower. Our results show that all rhodolith growth forms (branched, pralines and boxwork) in the Core Habitat had higher interstitial space and were larger than the ones from adjacent zones. Moreover, we explored the three-dimensional techniques to study the morphological characteristics that have historically been studied in two dimensions. This study contributes to the knowledge of morphological diversity in well-preserved rhodolith beds from continental shelves in the western Mediterranean Sea and reinforces the use of three-dimensional measurements, specifically the interstitial space of branched rhodoliths, to provide more accurate data on habitat complexity.
... However, DNA barcoding and metabarcoding data capture both presence-absence and relative abundance information, which ensures greater accuracy in monitoring marine benthic diversity [7,20,22]. Consequently, biodiversity assessment methodologies are now rapidly shifting to DNA metabarcoding, driven by advancements in sequencing technologies [30]. For example, Pearman et al. [21] reported that DNA metabarcoding detected differences in the benthic community composition between sites, whereas morphological approaches did not reveal a significant difference in ARMS reef monitoring. ...
Assessing the effectiveness of artificial structures as a monitoring tool for benthic diversity in temperate reefs is crucial to determining their relevance in reef conservation and management. In this study, we utilized Autonomous Reef Monitoring Structures (ARMS) to evaluate sessile benthic communities that colonized ARMS units after 12 and 34 months of immersion within distinct habitats (coral-dominated and macroalgae-dominated habitats) in Jeju Island, Korea. We used two methods: image analysis of the ARMS plates and DNA metabarcoding of the ARMS units. We found significant differences in the sessile benthic community between the plate faces, installation periods, and habitats. DNA metabarcoding also revealed differences in sessile benthic diversity among habitats. Additionally, we identified the Lithophyllum genus within the crustose coralline algae community, whose dominance might trigger a transition to coral-dominated habitats in Jeju Island. We recommend integrating ARMS image analysis with DNA metabarcoding to enhance and complement studies focusing on benthic diversity. By utilizing ARMS, this study provides valuable information for understanding sessile benthic communities and biodiversity, contributing to an enhanced understanding of the responses of ecological communities to climate change.
... Rhodolith beds (RBs) are recognized as structurally complex substrata that host higher associated diversity than the underlying sediments and surrounding habitats (Hall-Spencer, 1998;Steller et al., 2003;Foster et al., 2013;Gabara et al., 2018;Melbourne et al., 2018;Stelzer et al., 2021). Indeed, their three-dimensional structure provides a variety of ecological niches for many species, including epibenthic, epiphytic, cryptic, and infaunal species (De Grave, 1999;Steller et al., 2003;Kamenos, Moore & Hall-Spencer, 2004;Grall et al., 2006;Amado-Filho et al., 2007;Figueiredo et al., 2007;Foster et al., 2007;Peña & Bárbara, 2008a;Peña & Bárbara, 2008b;Riul et al., 2009), and they are therefore classified as 'ecological engineers' (Jones, Lawton & Shachak, 1994;Steller et al., 2003;Nelson et al., 2014;Teichert, 2014;Fredericq et al., 2019). ...
Rhodoliths, formed by free‐living coralline algae, are distributed worldwide, and the rhodolith beds (RBs) that they form are recognized as structurally complex habitats. In the Mediterranean, they are generally distributed in the mesophotic zone, at depths of 30–100 m; so far, only a few shallow RBs (<2 m) have been reported (e.g. Îles Kuriat, Tunisia, and Stagnone Marsala, Italy).
Here a shallow‐water RB located in the Mar Piccolo of Taranto (south‐eastern Italy, Mediterranean Sea) is described. The diversity of associated invertebrates, the rhodolith‐forming algal species, the type of sediments, and the bed extent are characterized.
The RB investigated extends over 5 ha at depths of 0.5–1.5 m. The rhodoliths vary in shape and size, from pralines to large spherical structures, and are formed by a single species, Neogoniolithon brassica‐florida , growing around nuclei of both natural and anthropogenic origin. The associated fauna consisted of 158 taxa, 79 (50%) of which were new basin records. The associated diversity was approximately twice that of the underlying and nearby sediments.
The structural complexity of the RBs promotes biodiversity and provides shelter, food, and a breeding ground for numerous species, including seahorses, which are a conservation priority in this basin.
... . Recently, resting stages of phytoplankton and macroalgae have been found within rhodoliths, a nodose form of crustose coralline algae (CCA; Fredericq et al., 2019;Krayesky-Self et al., 2020). Cryptic endolithic diversity in mesophotic rhodoliths has revealed both heterotrophic and autotrophic operational taxonomic units (OTUs), the latter including representatives of seven classes of algae, with the most numerous from the Florideophyceae, Chlorophyceae, Cyanophyceae, and Bacillariophyceae (Fredericq et al., 2019). ...
... . Recently, resting stages of phytoplankton and macroalgae have been found within rhodoliths, a nodose form of crustose coralline algae (CCA; Fredericq et al., 2019;Krayesky-Self et al., 2020). Cryptic endolithic diversity in mesophotic rhodoliths has revealed both heterotrophic and autotrophic operational taxonomic units (OTUs), the latter including representatives of seven classes of algae, with the most numerous from the Florideophyceae, Chlorophyceae, Cyanophyceae, and Bacillariophyceae (Fredericq et al., 2019). Furthermore, Fredericq et al. (2019) noted that "Further exploration worldwide is also essential to … ascertain whether the rhodolith interior functions as seed banks for algal stages, as temporary reservoirs for life history stages of algal bloom-forming species, or as refugia for ecosystem resilience following environmental stress" (Conclusion section). ...
... Cryptic endolithic diversity in mesophotic rhodoliths has revealed both heterotrophic and autotrophic operational taxonomic units (OTUs), the latter including representatives of seven classes of algae, with the most numerous from the Florideophyceae, Chlorophyceae, Cyanophyceae, and Bacillariophyceae (Fredericq et al., 2019). Furthermore, Fredericq et al. (2019) noted that "Further exploration worldwide is also essential to … ascertain whether the rhodolith interior functions as seed banks for algal stages, as temporary reservoirs for life history stages of algal bloom-forming species, or as refugia for ecosystem resilience following environmental stress" (Conclusion section). ...
To examine the potential for the autogenic ecosystem engineers, crustose coralline algae (CCA), to serve as seed banks or refugia for life stages of other species, it is critical to develop sampling protocols that reflect the diversity of life present. In this pilot study on two shallow water species of CCA collected from Raoul Island (Kermadec Islands; Rangitāhua) New Zealand, we investigated two preservation methods (ethanol vs. silica gel), sampled inner and outer regions of the crusts, and used DNA metabarcoding and seven genes/gene regions (16S rRNA, 18S rRNA, 23S rRNA, cox 1, rbc L, and tuf A genes and the ITS rRNA region) to develop a protocol for taxa identification. The results revealed immense diversity, with typically more taxa identified within the inner layers than the outer layers. As highlighted in other metabarcoding studies and in earlier work on rhodoliths (nodose coralline algae), reference databases are incomplete, and to some extent, the use of multiple markers mitigates this issue. Specifically, the 23S rRNA and rbc L genes are currently more suitable for identifying algae, while the cox 1 gene fares better at capturing the diversity present inclusive of algae. Further investigation of these autogenic ecosystem engineers that likely act as marine seed banks is needed.
... Rhodoliths provide shelter for small organisms within its structure, especially the branched forms, and serve as fixation points for epiphytic algae and epibenthos, harbouring a rich microbiome (Carvalho et al., 2020;Cavalcanti et al., 2018;Fredericq et al., 2019). For instance, Boyé et al. (2019) showed that in well-preserved rhodolith beds in the Brittany coast niche diversity and functional redundancy is promoted. ...
... The rhodolith beds are distributed from the Gulf of Alaska (Prince William Sound) to the Gulf of Mexico in North and Central America, [5,7,44,45] at depths of 50-90 m on the continental shelf [46]. These algae are also found along the Pacific coast of the southern hemisphere, from the Gulf of California to the South of Chile [47]. ...
... However, it is still unknown how certain climate change factors, such as ocean acidification, may affect the holobiont community [109]. Additionally, due to the importance of calcium carbonate substrates in the life cycle of many macroalgae, this community (microorganisms and rhodoliths) is crucial for the maintenance of marine ecosystems [46]. ...
Red calcareous algae create bio-aggregations ecosystems constituted by carbonate calcium, with two main morphotypes: geniculate and non-geniculate structures (rhodoliths may form bio-encrustations on hard substrata or unattached nodules). This study presents a bibliographic review of the order Corallinales (specifically, rhodoliths), highlighting on morphology, ecology, diversity, related organisms, major anthropogenic influences on climate change and current conservation initiatives. These habitats are often widespread geographically and bathymetrically, occurring in the photic zone from the intertidal area to depths of 270 m. Due to its diverse morphology, this group offers a special biogenic environment that is favourable to epiphyte algae and a number of marine invertebrates. They also include holobiont microbiota made up of tiny eukaryotes, bacteria and viruses. The morphology of red calcareous algae and outside environmental conditions are thought to be the key forces regulating faunistic communities in algae reefs. The impacts of climate change, particularly those related to acidification, might substantially jeopardise the survival of the Corallinales. Despite the significance of these ecosystems, there are a number of anthropogenic stresses on them. Since there have been few attempts to conserve them, programs aimed at their conservation and management need to closely monitor their habitats, research the communities they are linked with and assess the effects they have on the environment.
... Furthermore, the growing number of new, cryptic and endemic taxa being discovered in rhodolith beds indicates that much of their biodiversity is still unknown (e.g., Santos et al., 2016;Coutinho et al., 2021;Méndez Trejo et al., 2021;Senna et al., 2021;Sissini et al., 2022). Recent studies suggest that rhodolith beds may also act as seedbanks for recovering ecosystems, and as refugia for ecosystem resilience following acute (Fredericq et al., 2019) or chronic (Voerman et al., 2022a) environmental stress. Similarly, the significance of these habitats in sustaining fisheries is greatly underrated , and rhodolith beds may also be far more important in the global carbon budget than currently recognized (Amado-Filho et al., 2012a;Smith and Mackenzie, 2015;van der Heijden and Kamenos, 2015;Mao et al., 2020). ...
... In the Gulf of California, 60% of all examined rhodolith-associated organisms were juveniles (Riosmena-Rodriguez and Medina-López, 2010). Rhodoliths also play a key role as seedbanks and temporary reservoirs of life history stages of ecologically important micro-and macroalgae (Fredericq et al., 2019). The EBSA criterion defines an area with a comparatively higher degree of naturalness, as a result of the lack, or low level of, human-induced disturbance or degradation. ...
Global marine conservation remains fractured by an imbalance in research efforts and policy actions, limiting progression towards sustainability. Rhodolith beds represent a prime example, as they have ecological importance on a global scale, provide a wealth of ecosystem functions and services, including biodiversity provision and potential climate change mitigation, but remain disproportionately understudied, compared to other coastal ecosystems (tropical coral reefs, kelp forests, mangroves, seagrasses). Although rhodolith beds have gained some recognition, as important and sensitive habitats at national/regional levels during the last decade, there is still a notable lack of information and, consequently, specific conservation efforts. We argue that the lack of information about these habitats, and the significant ecosystem services they provide, is hindering the development of effective conservation measures and limiting wider marine conservation success. This is becoming a pressing issue, considering the multiple severe pressures and threats these habitats are exposed to (e.g., pollution, fishing activities, climate change), which may lead to an erosion of their ecological function and ecosystem services. By synthesizing the current knowledge, we provide arguments to highlight the importance and urgency of levelling-up research efforts focused on rhodolith beds, combating rhodolith bed degradation and avoiding the loss of associated biodiversity, thus ensuring the sustainability of future conservation programs.
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... This habitat is also characterized by a strong seasonality, which plays a critical role in temperate maerl beds associated communities (Grall et al. 2006;Peña and Bárbara 2010b;Qui-Minet et al. 2018). This habitat provides a shelter for early-stages of numerous species as well (Fredericq et al. 2019). Coastal habitats are increasingly threatened by human activities (Halpern et al. 2008). ...
Maerl beds are unique marine habitats hosting a great diversity of organisms while macroalgae are a major component of this diversity. The bay of Brest is one of the most studied coastal ecosystems in the world; in addition, it has a significant background concerning historical seaweeds checklists associated to maerl beds. However, no recent work aimed at compiling and completing these data. In this study, a total of 7 subtidal and 3 intertidal maerl beds have been surveyed between 2020 and 2022. These data complete 4 previous inventories, giving the most accurate description of seaweeds colonizing maerl beds in the bay of Brest. The total number of macroalgal species reaches 170 among which 127 are Rhodophyta, 22 Phaeophyceae, and 21 Ulvophyceae, with 51 additions to the French and 19 additions to the European maerl beds checklist. A comparison with other maerl beds of the northeastern Atlantic coasts is compiled. It appears that the maerl beds from the bay of Brest are the most diverse in Atlantic France and among the most diverse in Europe. A description of the stratification of maerl beds and the associated macroalgal communities is proposed. It includes maerl species, encrusting species, maerl-entangling species, erect isolated species, and free-living species. In addition, specimens of the rarely recorded Rytiphlaea tinctoria, reaching its northernmost population in the bay, a possible introduced species/relict population, are described.
... Coralline red algae are calcareous seaweeds belonging to four orders of the phylum Rhodophyta (Corallinales, Corallinapetrales, Hapalidiales, Sporolithales), among which many species play the important role of ecosystem engineers (Ellison 2019;Rindi et al. 2019). These macroalgae exhibit a wide range of ecological functions, including bioconstruction of structurally complex habitats that host a great associated biodiversity (Ballesteros 2006;Peña et al. 2021a, b), stabilization and cementation of coral reef structures (Nelson 2009;Gabrielson et al. 2018), production of carbonate sediments (Canals & Ballesteros 1997), induction of settlement and metamorphosis of invertebrate larvae (Gómez-Lemos et al. 2018;Whitman et al. 2020) and reservoir of microscopic stages of ecologically important microalgae and macroalgae (Fredericq et al. 2019). In recent years, coralline algae have received increasing attention due to their sensitivity to ocean acidification (Kuffner et al. 2008;Peña et al. 2021b), seawater warming (Cornwall et al. 2019) and other environmental changes caused by human activities (McCoy & Kamenos 2015). ...
Non-geniculate coralline algal specimens were collected in 2013 during the XXVIII Italian Expedition to Antarctica in Adélie Cove (Terra Nova Bay; Ross Sea) and deposited in the collections of the Italian National Antarctic Museum (MNAIT, Section of Genoa). Specimens were characterized through a polyphasic approach combining DNA sequence data obtained for four genes (psbA, rbcL, 18S rDNA and cox1) with morpho-anatomical observations. DNA sequences revealed that all specimens belonged to the same species. Phylogenetic reconstructions unambiguously recovered this alga as a member of the order Hapalidiales, but without any close relationship to a genus of this order currently recognized on a molecular phylogenetic basis. Instead, it formed a well-supported lineage with specimens named ‘Hapalidiales sp. ZH-Twist-2019’, collected in New Zealand, for which no formal assignment at genus level has been proposed. Species delimitation methods (ABGD, PTP, GMYC) applied to the psbA dataset indicated that the Adélie Cove coralline alga is a distinct species from all other known hapalidialean species for which such sequences are available. A new genus, Thalassolithon gen. nov., is proposed for T. adeliense sp. nov.
