Effects of CO\u3csub\u3e2\u3c/sub\u3e on Growth Rate, C:N:P, and Fatty Acid Composition of Seven Marine Phytoplankton Species

Carbon dioxide (CO2) is the primary substrate for photosynthesis by the phytoplankton that form the base of the marine food web and mediate biogeochemical cycling of C and nutrient elements. Specific growth rate and elemental composition (C:N:P) were characterized for 7 cosmopolitan coastal and oceanic phytoplankton species (5 diatoms and 2 chlorophytes) using low density, nutrient-replete, semi-continuous culture experiments in which CO2 was manipulated to 4 levels ranging from post-bloom/glacial maxima (ppm) to geological maxima levels (\u3e2900 ppm). Specific growth rates at high CO2 were from 19 to 60% higher than in low CO2 treatments in 4 species and 44% lower in 1 species; there was no significant change in 2 species. Higher CO2 availability also resulted in elevated C:P and N:P molar ratios in Thalassiosira pseudonana (~60 to 90% higher), lower C:P and N:P molar ratios in 3 species (~20 to 50% lower), and no change in 3 species. Carbonate system-driven changes in growth rate did not necessarily result in changes in elemental composition, or vice versa. In a subset of 4 species for which fatty acid composition was examined, elevated CO2 did not affect the contribution of polyunsaturated fatty acids to total fatty acids significantly. These species show relatively little sensitivity between present day CO2 and predicted ocean acidification scenarios (year 2100). The results, however, demonstrate that CO2 availability at environmentally and geologically relevant scales can result in large changes in phytoplankton physiology, with potentially large feedbacks to ocean biogeochemical cycles and ecosystem structure

A Vulnerability Assessment of Fish and Invertebrates to Climate Change on the Northeast U.S. Continental Shelf

Climate change and decadal variability are impacting marine fish and invertebrate species worldwide and these impacts will continue for the foreseeable future. Quantitative approaches have been developed to examine climate impacts on productivity, abundance, and distribution of various marine fish and invertebrate species. However, it is difficult to apply these approaches to large numbers of species owing to the lack of mechanistic understanding sufficient for quantitative analyses, as well as the lack of scientific infrastructure to support these more detailed studies. Vulnerability assessments provide a framework for evaluating climate impacts over a broad range of species with existing information. These methods combine the exposure of a species to a stressor (climate change and decadal variability) and the sensitivity of species to the stressor. These two components are then combined to estimate an overall vulnerability. Quantitative data are used when available, but qualitative information and expert opinion are used when quantitative data is lacking. Here we conduct a climate vulnerability assessment on 82 fish and invertebrate species in the Northeast U.S. Shelf including exploited, forage, and protected species. We define climate vulnerability as the extent to which abundance or productivity of a species in the region could be impacted by climate change and decadal variability. We find that the overall climate vulnerability is high to very high for approximately half the species assessed; diadromous and benthic invertebrate species exhibit the greatest vulnerability. In addition, the majority of species included in the assessment have a high potential for a change in distribution in response to projected changes in climate. Negative effects of climate change are expected for approximately half of the species assessed, but some species are expected to be positively affected (e.g., increase in productivity or move into the region). These results will inform research and management activities related to understanding and adapting marine fisheries management and conservation to climate change and decadal variability

Changes in enzymatic activity during early development of bay scallops Argopecten irradians and sea scallops Placopecten magellanicus

Poor growth and survival of scallops is often reported during early developmental stages. Stage- and species-specific dietary requirements have been identified, but the mechanisms responsible for these differences remain largely unknown. Dietary success depends on food biochemical properties, digestive and/or assimilative capacity, as well as the animal's specific nutritional demands, which can vary over development and between species. The present study examines developmental changes in the activities of key digestive enzymes in larval and postlarval bay scallops Argopecten irradians and sea scallops Placopecten magellanicus raised on a mixed algal diet until ~4 to 5 mm in shell height (SH) and sampled at intervals encompassing major transitions in feeding organ development. Colorimetric assays measured general protease, lipase (esterase) and carbohydrase (\u3b1-amylase, cellulase and laminarinase) activities. The most pronounced changes in enzymatic activity occurred prior to scallops attaining ~1.2 mm SH in both scallop species. The esterase:protease ratio exhibited similar ontogenetic patterns in both scallop species, decreasing sharply between larval and immediate postlarval stages before increasing to an intermediate level and stabilizing around 1.2 mm SH. In contrast, mean carbohydrase activities measured over the experimental duration differed between species, with bay scallops exhibiting higher specific activities of \u3b1-amylase and cellulase but much lower activities of laminarinase than sea scallops. These findings have implications for understanding scallop utilization of the food supply in nature, as well as developing targeted diets that could enhance their growth and survival in culture.Peer reviewed: YesNRC publication: Ye

Biochemical characterization and nuttritional value of three Pavlova spp. in unialgal and mixed diets with Chaetoceros muelleri for postlarval sea scallops, Placopecten magellanicus

Low growth and survival of sea scallops, Placopecten magellanicus, are often observed during postlarval stages when they undergo a period of protracted morphogenesis and thus may be particularly susceptible to nutritional deficiencies. Diets containing flagellates from the genus Pavlova (especially Pavlova sp. CCMP 459) have proven successful for scallop rearing in previous studies. To further examine their contribution to growth performance, Pavlova sp. (CCMP 459) and Pavlova pinguis, both as unialgal diets and in combination with the diatom Chaetoceros muelleri (CHGRA), were tested as diets for postlarval (~ 350 \ub5m and 1.6 mm) sea scallops in two growth trials each lasting ~ 4 weeks. The Pav 459- and P. pinguis-CHGRA combination diets yielded high and comparable growth of postlarvae whereas previous work found substantial decreases in growth rate (31%) when another algal species of the same genus, Pavlova lutheri, was substituted for Pav 459 in the combination diet. In the present study a unialgal diet of P. pinguis yielded growth rates 32% lower than the combination, and unialgal diets of C. muelleri consistently ranked lowest of all diets tested (54\u201365% lower than the combination). Algal sterol composition may influence scallop growth performance, as CHGRA contains high levels of cholesterol, also present although to a lesser extent, in Pav 459 and P. pinguis. P. pinguis, Pav 459, and C. muelleri are also all characterized by relatively high levels of n-6 polyunsaturated fatty acids (PUFA). Pav 459 and P. pinguis (in contrast to P. lutheri) are characterized by high levels of docosapentaenoic acid (DPA, 22:5n-6), and C. muelleri contains high levels of arachidonic acid (AA, 20:4n-6) which may account for the higher growth obtained on this mixed diet. Enrichment of \u3a3n-6 fatty acids, as well as of the individual n-6 fatty acids AA and DPA, was observed in scallop tissues relative to the diet across dietary treatments. However, no enrichment of \u3a3n-3 fatty acids was observed, which provides evidence of selective uptake, retention and/or metabolism of n-6 fatty acids. This study strongly supports the role of n-6 DPA as an essential nutrient for scallop early life history stages.Peer reviewed: YesNRC publication: Ye

Growth of postlarval sea scallops, Placopecten magellanicus, on microalgal diets, with emphasis on the nutritional role of lipids and fatty acids

Culture of the sea scallop, Placopecten magellanicus, is constrained by a reliable supply of high-quality postlarvae, yet little is known about the diets and essential nutrients required to maximize growth and survival during these vulnerable stages. Therefore, post-settlement sea scallops were exposed to binary microalgal diets consisting of a flagellate: Pavlova lutheri, Pavlova sp. (Pav, CCMP 459) or Tetraselmis striata (Plat-P) and a diatom: Chaetoceros muelleri, Thalassiosira weissflogii or Fragilaria familica for 28\u201330 days. The combination Pav 459/C. muelleri provided a superior diet for sea scallop postlarvae, yielding a growth rate of up to 28 \uc2\ub5m day-1. However, when these algae were offered singly, a 32% (Pav 459) and 64% (C. muelleri) decrease in growth rates was observed, indicating that both species made a significant contribution to the success of the mixed diet. The two species are characterized by unique signatures of n-6 polyunsaturated fatty acids (PUFAs): C. muelleri has high levels of arachidonic acid (AA), and Pav 459 (in contrast to P. lutheri) has high levels of n-6 docosapentaenoic acid (DPA). DPA was selectively incorporated into tissues of scallops fed all binary diets except the one rich in DPA (Pav 459/C. muelleri). These results, coupled with a marked increase in n-6/n-3 ratios between the diet and tissues, provide evidence that n-6 PUFAs may play an important and previously underestimated role in scallop nutrition. The diet of T. striata and C. muelleri, which yielded the lowest growth rate (8.1 \uc2\ub5m day-1) contained dietary docosahexaenoic acid (DHA; 22:6n-3) concentrations 4.5\u20137\uc3\u8212 lower than any other binary treatment. Low DHA levels may thus explain the poor performance of this diet. Tissue protein and triacylglycerol concentrations reflected diet performance, with higher values generally associated with more successful diets. This work suggests that DHA, as well as the n-6 PUFAs AA and DPA, may be essential for optimizing growth of sea scallop postlarvae.Peer reviewed: YesNRC publication: Ye

Biochemical characterization and nuttritional value of three Pavlova spp. in unialgal and mixed diets with Chaetoceros muelleri for postlarval sea scallops, Placopecten magellanicus

Low growth and survival of sea scallops, Placopecten magellanicus, are often observed during postlarval stages when they undergo a period of protracted morphogenesis and thus may be particularly susceptible to nutritional deficiencies. Diets containing flagellates from the genus Pavlova (especially Pavlova sp. CCMP 459) have proven successful for scallop rearing in previous studies. To further examine their contribution to growth performance, Pavlova sp. (CCMP 459) and Pavlova pinguis, both as unialgal diets and in combination with the diatom Chaetoceros muelleri (CHGRA), were tested as diets for postlarval (~ 350 \ub5m and 1.6 mm) sea scallops in two growth trials each lasting ~ 4 weeks. The Pav 459- and P. pinguis-CHGRA combination diets yielded high and comparable growth of postlarvae whereas previous work found substantial decreases in growth rate (31%) when another algal species of the same genus, Pavlova lutheri, was substituted for Pav 459 in the combination diet. In the present study a unialgal diet of P. pinguis yielded growth rates 32% lower than the combination, and unialgal diets of C. muelleri consistently ranked lowest of all diets tested (54\u201365% lower than the combination). Algal sterol composition may influence scallop growth performance, as CHGRA contains high levels of cholesterol, also present although to a lesser extent, in Pav 459 and P. pinguis. P. pinguis, Pav 459, and C. muelleri are also all characterized by relatively high levels of n-6 polyunsaturated fatty acids (PUFA). Pav 459 and P. pinguis (in contrast to P. lutheri) are characterized by high levels of docosapentaenoic acid (DPA, 22:5n-6), and C. muelleri contains high levels of arachidonic acid (AA, 20:4n-6) which may account for the higher growth obtained on this mixed diet. Enrichment of \u3a3n-6 fatty acids, as well as of the individual n-6 fatty acids AA and DPA, was observed in scallop tissues relative to the diet across dietary treatments. However, no enrichment of \u3a3n-3 fatty acids was observed, which provides evidence of selective uptake, retention and/or metabolism of n-6 fatty acids. This study strongly supports the role of n-6 DPA as an essential nutrient for scallop early life history stages.Peer reviewed: YesNRC publication: Ye

And on Top of All That… Coping with Ocean Acidification in the Midst of Many Stressors

Oceanic and coastal waters are acidifying due to processes dominated in the open ocean by increasing atmospheric CO2 and dominated in estuaries and some coastal waters by nutrient-fueled respiration. The patterns and severity of acidification, as well as its effects, are modified by the host of stressors related to human activities that also influence these habitats. Temperature, deoxygenation, and changes in food webs are particularly important co-stressors because they are pervasive, and both their causes and effects are often mechanistically linked to acidification. Development of a theoretical underpinning to multiple stressor research that considers physiological, ecological, and evolutionary perspectives is needed because testing all combinations of stressors and stressor intensities experimentally is impossible. Nevertheless, use of a wide variety of research approaches is a logical and promising strategy for improving understanding of acidification and its effects. Future research that focuses on spatial and temporal patterns of stressor interactions and on identifying mechanisms by which multiple stressors affect individuals, populations, and ecosystems is critical. It is also necessary to incorporate consideration of multiple stressors into management, mitigation, and adaptation to acidification and to increase public and policy recognition of the importance of addressing acidification in the context of the suite of other stressors with which it potentially interacts

Climate exposure factors.

<p>Average climate exposure scores across all species (A) and results of sensitivity analysis for the effect of individual exposure factors on overall climate vulnerability (B).</p

Logic rule for calculating overall species’ climate exposure and biological sensitivity.

<p>The scoring rubric is based on a logic model where a certain number of individual scores above a certain threshold are used to determine the overall climate exposure and overall biological sensitivity.</p

Directional effect of climate change.

<p>Colors represent expected negative (red), neutral (tan), and positive (green) effects. Certainty in score is denoted by text font and text color: very high certainty (>95%, black, bold font), high certainty (90–95%, black, italic font), moderate certainty (66–90%, white or gray, bold font), low certainty (<66%, white or gray, italic font).</p