Figure 1 - uploaded by Barry C Smith
Content may be subject to copyright.
Red spots typical of Scrippsiella cysts—some turned orangeyellow , calcite crystals and starch grains can be seen embedded within the pellet. Here, one partly intact cyst (lower left) still has a red spot and the other cyst is partly digested (red spot turned yellow, calcite and cyst contents degraded, and cysts rounded shape). Scale bar is 20 mm.
Source publication
Scrippsiella spp. resting cysts, unlike many other dinoflagellate cysts, possess an outer layer of calcite beneath
which is a thin sporopollenin wall. This feature may affect cyst survival through the digestive tract of benthic organisms, when they consume the cysts. The extent of digestibility is related to the degree to which grazing by benthic o...
Citations
... Resting cysts sink and accumulate according to their size, cell-specific density, and morphological features. Thus, cysts assemble somewhat differently depending upon species (Smith et al. 2009;Persson and Smith 2009a) and other factors affecting sinking properties (attachment to marine snow particles or forming clumps). Consumption of sinking cysts by benthic grazers and deposit-feeders is common, and zooplankton fecal pellets can contain many cysts (Persson 2000 and references therein). ...
... This is, however, not at all the case. Many grazing experiments have been performed on both cultured and natural cysts showing that cysts of all types can be ingested and digested by a variety of invertebrates (Persson and Rosenberg 2003;Persson and Smith 2009a) and that digestion of toxic cysts causes toxicity in shellfish (Persson et al. 2006). Direct consumption of resting cysts may thus explain shellfish toxicity in areas without known, recent blooms, but with toxic resting cysts in the sediment (Persson et al. 2006). ...
... Direct consumption of resting cysts may thus explain shellfish toxicity in areas without known, recent blooms, but with toxic resting cysts in the sediment (Persson et al. 2006). In laboratory experiments with feeding mollusks lasting only 24h or less, significant reductions in cyst numbers were seen for both cultured and natural cysts (Persson and Smith 2009a;Persson and Smith 2009b;Persson et al. 2006). Resting cysts in nature are constantly exposed to grazing while in oxygenated conditions. ...
... Grazing reduces the numbers of both living cysts and empty cyst walls and changes the species composition of dinoflagellate cysts [21][22][23]25,32,[39][40][41]. Different grazers affect the species composition differently [21] using different feeding modes and types of digestion. ...
... For accurate measurements of changes in cyst numbers over time, an experimental approach enclosing a certain volume of sediment containing cysts is necessary. In the laboratory, it is possible to feed a certain amount of sediment containing cysts [24] or laboratory-cultured cysts [22,41] to animals in a container of known volume. From a natural sediment sample, not only cysts disappear, but the sediment itself becomes decomposed, which creates problems when quantitative comparisons are desired. ...
This quantitative dinoflagellate cyst study reveals an enormous difference in survival rates in oxygenated versus anoxic sediments. Replicate samples of concentrated natural dinoflagellate cysts with the same initial species composition (1.4 × 104 resting cysts·cm−3 sediment, 61% filled with live-appearing contents) were placed in bags of 20 µm plankton screen. Replicate bags containing 10.0 cm−3 concentrated cyst samples were placed on the seafloor in different environments in Long Island Sound, USA (anoxic and oxygenated), as well as refrigerated in test tubes in the laboratory. Three sets of 15 bags were placed in each environment. Once every year for four consecutive years, three bags were recovered from each set, and the contents were analyzed by cyst counting and germination experiments. An enormous difference in preservation potential between samples in oxygenated versus anoxic environments was revealed. The number of dinoflagellate cysts decreased abruptly within the first year in the oxygen-rich environment; living cysts became very rare (only 5% remained) and also empty walls of cysts disappeared (20% of total cysts remained). In anoxic sediment samples, living cysts also decreased significantly with time, but less quickly. After 1 year, 35% of the living cysts in the anoxic environment and 70% of the living cysts refrigerated in test tubes remained intact. After 4 years, 21% of the cysts with contents in the anoxic environment remained, and 31% in test tubes. The empty cyst walls remained intact for a longer time under anoxic conditions, especially of species known to fossilize well. Germination experiments showed that cysts with live-appearing contents were likely alive, because species with identifiable live-appearing cysts were also identified as vegetative cells in corresponding slurry cultures. The cyst assemblage was dominated by Protoperidinaceae, Dipolopsalidaceae, and Gonyaulacaceae. Of special interest is the ichthyotoxic Margalefodinium polykrikoides, the bloom-forming Peridinium quinquecorne, which has an undescribed resting cyst, and a previously undescribed Krypoperidinium species. The results show greater preservation of dinoflagellate cysts in “dead-zone sea bottoms” and may also provide an answer to the question of the absence of cyst beds in an area despite observed sedimentation of dense blooms.
... Among marine shellfish, bivalves are recognized as common vectors of toxins to their consumers regarding their intoxication susceptibility through filter-feeding on toxic algae (Basti et al. 2018;Deeds et al. 2008;Lopes et al. 2019;Neves et al. 2019), although, nonbivalve molluscs may also act as toxin vectors (Costa et al. 2005;Mafra Jr et al. 2019;Neves et al. 2015a;Shumway 1995). Deposit-feeders may accumulate toxins by the ingestion of biodeposits (e.g., pseudofeces, feces) containing toxins or directly by microalga consumption (e.g., Dowsett et al. 2011;Neves et al. 2015a;Persson et al. 2006Persson et al. , 2008Persson and Smith 2009). In addition, carnivorous molluscs may accumulate toxins via trophic transfer by predation on contaminated prey (e.g., Bricelj et al. 2012;Carreto et al. 1996;Ito et al. 2004;Wekell et al. 1996). ...
... The highest research effort on bivalves is likely related to the greater importance of this molluscan group as a food item, its higher commercial value, and the amount produced in mariculture systems. In addition, filter-feeder bivalves are traditionally monitored for human safety consumption; while carnivorous, herbivorous, and detritivorous molluscs were lately recognized as phycotoxin sources (e.g., Bricelj et al. 2012;Dowsett et al. 2011;Ito et al. 2004;Neves et al. 2015a;Persson et al. 2008;Persson and Smith 2009). ...
Besides human health risks, phycotoxins may cause physiological injuries on molluscan shellfish and, consequently, damages to marine ecosystems and global fisheries production. In this way, this review aimed to present an overview of HABs impacts on marine shellfish by evaluating the effects of cultivated molluscs exposure to microalgae and cyanobacteria that form blooms and/ or synthesize toxins. More specifically, it was assessed the main molluscan shellfish responses to harmful algae, trophic transfer and dynamics of phycotoxins, and the risks for human health. Of the 2420 results obtained from literature search, 150 scientific publications were selected after thorough inspections for subject adherence. In total, 70 molluscan species and 37 taxa of harmful algae were assessed from retrieved scientific publications. A significant positive correlation was found between the marine production of molluscs and the number of available studies by molluscan category. Molluscan responses to HABs and phycotoxins were categorized and discussed in three subsections: effects on grazing and behavior, metabolic and physiological reactions, and fitness consequences. The main histopathological injuries and toxin concentrations in molluscan tissues were also compiled and discussed. Bivalves often accumulate more toxins than gastropods and cephalopods, occasionally exceeding recommended levels for safe consumption, representing a risk for human health. Harmful algae impact on molluscan shellfish are complex to trace and predict; however, considering the perspective of increase in the occurrence and intensity of HABs, the intensification of efforts to expand the knowledge about HABs impacts on marine molluscs is crucial to mitigate the damages on economy and human health.
... Nitrogen deprivation is considered an important environmental cue leading to changes in metabolism and reproduction specifically leading towards a sexual life cycle and gamete formation. A strain of Scrippsiella lachrymosa isolated by Kalle Olli as a cyst from surface sediments of Casco Bay, Gulf of Maine, was found to have an exceptionally high cyst forming capability (Olli 2001, Olli andAnderson 2002) and has been used in numerous studies on cyst formation and cyst grazing (e.g., Olli 2001, Olli and Anderson 2002, Kremp et al. 2003, Smith and Persson 2004and 2005, Persson et al 2008b, Persson and Smith 2009. Unlike other studied cyst-forming dinoflagellates, discrete life history stages in S. lachrymosa can be produced with high purity which makes it an ideal model organism for comparison of pigmentation between sexual life stages. ...
Various life cycle stages of cyst-producing dinoflagellates often appear differently colored under the microscope; gametes appear paler while zygotes are darker in comparison to vegetative cells. To compare physiological and photochemical competency, the pigment composition of discrete life cycle stages was determined for the common resting cyst-producing dinoflagellate Scrippsiella lachrymosa. Vegetative cells had the highest cellular pigment content ( 25.2 +/- 0.5 pg cell-1), whereas gamete pigment content was 22% lower. The pigment content of zygotes was 82% lower than vegetative cells, even though they appeared darker under the microscope. Zygotes of S. lachrymosa contained significantly higher cellular concentrations of beta- carotene ( 0.65 +/- 0.15 pg cell -1) than all other life stages. Photoprotective pigments and the de- epoxidation ratio of xanthophylls- cycle pigments in S. lachrymosa were significantly elevated in zygotes and cysts compared to other stages. This suggests a role for accessory pigments in combating intracellular oxidative stress during sexual reproduction or encystment. Resting cysts contained some pigments even though chloroplasts were not visible, suggesting that the brightly colored accumulation body contained photosynthetic pigments. The differences in pigmentation between life stages have implications for interpretation of pigment data from field samples when sampled during dinoflagellate blooms.
... Therefore, the destruction of the cyst wall or damage to protoplasts caused by repetitive grazing pressure might occur more rapidly than for spiny-type cysts that have protective armor around the cyst body. In addition, the repeated grazing may cause large reductions in cyst numbers (Persson and Smith, 2009b). ...
Mussels Mytilus edulis (35 +/- 2 mm shell length) were fed on cultured Isochrysis galbana in a flow-through system, and measures were undertaken to quantify separate effects of inflow cell concentration, outflow cell concentration, percentage reduction (i.e. recycling), and flow rate and/or feeding history on clearance rate measures (CR; l h(-1)). Findings identify the following features of physiological regulation: (1) a lag phase in the feeding response to changes in food concentration, of around 30 min; (2) a trigger level in algal cell (chlorophyll [chl] a) volume/concentration (4000 cells ml(-1), 0.5 mu g l(-1) chl a) below which filtering in most mussels ceases; (3) saturation reduction, or satiation, resulting in reduced CR and valve closure after feeding for over 2 h at 30 000 or more cells ml-1 (similar to 6 mu g l(-1) chl a); and (4) at food levels between Features 2 & 3, CR increases to maximal rates (ca. 2 to 2.5 l h(-1) ind.(-1) or 6 to 7.5 l(-1) h(-1) g(-1) dry weight). Our findings also help resolve uncertainties associated with the measurement and interpretation of clearance rate variations. These uncertainties are associated with: differences that result from analyses of feeding responses to different components of the available seston; whether variations in seston availability are physiologically relevent; analyses of individual shellfish as compared with average responses computed for >1 ind.; and comparisons between short-term and integrated measures. We think it is important to consider whether measures of feeding are really required per individual in real time, and we stress that population averaging and temporal integration are required for the scaling up of results when simulating ecological interrelations between shellfish populations and their environments.
A natural dinoflagellate- and ciliate-cyst community from anoxic sediment collected from New Haven, Long Island Sound, was concentrated with a particle sorter and fed to oysters Cras- sostrea virginica. The total number of cysts and the species composition of cysts in beakers contain- ing live oysters were measured before and after feeding by the oysters. The oysters significantly reduced the numbers of both dinoflagellate and ciliate cysts. Both empty cyst walls and filled (live) cysts were consumed. The oysters decreased the number of total cysts to less than half compared to control beakers containing empty oyster shells. Results from the experiment show that natural assem- blages of cysts in sediment are degraded by the feeding activities of oysters. If toxic cysts were pre- sent in natural sediments resuspended from the bottom, digestion of resting cysts could lead to toxin accumulation in oysters. There was no major shift in species composition of cysts; cysts known as fossilizable were destroyed, as well as cysts not known to be very resistant or preservable.
