Juvenile Scallops Research Articles

Effects of high stocking density on growth performance and expression of MyD88, and its temporal expression under the challenge of Vibrio parahaemolyticus in the noble scallop Chlamys nobilis

High stocking density has been regarded as an adverse factor in bivalve aquaculture. However, its subsequent molecular response to pathogenic bacteria has been little studied. In order to study the question, a novel MyD88 was first cloned using adult noble scallops Chlamys nobilis (CnMyD88), and its tissue distribution was investigated. Then, 1860 juvenile scallops were divided into two groups with two initial densities of high density (200 individuals/layer, HD) and normal density (110 individuals/layer, ND) and in-situ cultured for three months, in which their growth, survival, and the differential expression of CnMyD88 were examined, respectively. Finally, scallops were injected with the Vibrio parahaemolyticus to assess the temporal expression of CnMyD88. As the results show, CnMyD88 cDNA has a full length of 2241 bp and contains an 1107 bp ORF that encodes a 368-derived protein. It was widely expressed in examined tissues with a significantly higher level in hemolymph, intestine, mantle, and gonad than others. Besides, the HD group showed lower growth (0.39 ± 0.05 mm/day) and survival (37.00 ± 8.49%) than the ND group (0.55 ± 0.02 mm/day and 76.82 ± 5.78%). More importantly, the HD group exhibited significantly lower expression levels of CnMyD88 in their examined tissues than the ND group. After V. parahaemolyticus challenging, CnMyD88 had significantly lower expression levels in the scallops from the HD group than that of the scallops from the ND group at 6th, 24th, and 36th. The present results indicated that high stocking density not only made adverse impacts on growth and survival but also may induce immunosuppression in the noble scallop. Therefore, appropriate low stocking density may be worth considering to adopt in scallop aquaculture.

Spatiotemporal variations of Chlamys islandica larval shell morphometry between 2000 and 2018 in a depleted coastal scallop fishing area

Bivalves larval shell morphometry can provide valuable information on their planktonic (PI-Prodissoconch I) and early benthic life (PII). We examined spatial (at two scales: fishing sub-areas and exploited beds) and temporal variability (between 2000 and 2018) of PI and PII sizes among 424 Icelandic scallop juveniles (<10 mm total length) from the northern Gulf of St. Lawrence. PI and PII mean sizes were not different from juveniles collected inside or outside of exploited beds. For PI sizes, there were no temporal changes, but there was a difference between the two scallop fishing sub-areas, suggesting a disparity in egg size, origin or in broodstock physiological state. Regarding PII sizes, there was no difference between sub-areas, but PII sizes in 2003 and 2004 were significantly higher, likely related to differential larval growth or delayed metamorphosis associated to synergistic effects of environmental factors. Finally, this study demonstrates the possibility to accurately follow larval morphometry variations from small juvenile bivalve shells to track potential changes of recruitment success in order to sustainably manage stocks of commercial bivalve species.

&lt;i&gt;Francisella halioticida&lt;/i&gt; Infection of Intermediately Cultured Juvenile Scallops &lt;i&gt;Mizuhopecten yessoensis&lt;/i&gt; in Southern Hokkaido

Field surveys of the bacterium Francisella halioticida infection among intermediate-cultured juvenile scallops Mizuhopecten yessoensis in southern Hokkaido revealed that the mortality of juvenile scallops was positively associated with the prevalence of F. halioticida, and that both mortality and prevalence increased in September and January. ​In the intermediate culture experiments, juvenile scallops reared under high density during September and October resulted in high prevalence of F. halioticida and scallop mortality after October, while rearing density from October to March was not associated with infection and mortality, indicating that the high rearing density between September and October determined the infection of F. halioticida and scallop mortality in the following period. ​Furthermore, shell deformity rates, as a proposed index for poor physiological condition of juvenile scallops, were high in the experimental groups with higher density from September to October. ​The high rearing density in this term may have caused a decline in physiological status and, reduced resistance to francisellosis in juvenile scallops, although there is still a possibility that shell deformity was caused by francisellosis.

Energy metabolism of juvenile scallops Nodipecten subnodosus under acute increased temperature and low oxygen availability

High temperature increases energy demand in ectotherms, limiting their physiological capability to cope with hypoxic events. The present study aimed to assess the metabolic tolerance of juvenile Nodipecten subnodosus scallops to acute hyperthermia combined with moderate hypoxia. A previous study showed that juveniles exhibited a high upper temperature limit (32 °C), but the responses of juveniles to combined hyperthermia and low dissolved oxygen are unknown. Scallops were exposed to control conditions (treatment C: 22 °C, ∼7.1 mg O2 L−1 or PO2 156.9 mmHg), acute hyperthermia under normoxia (treatment T: 30 °C, ∼6.0 mg O2 L−1 or PO2 150.9 mmHg) or acute hyperthermia plus hypoxia (treatment TH: 30 °C, ∼2.5 mg O2 L−1 or PO2 62.5 mmHg) for 18 h. In T, juveniles exhibited an enhanced oxygen consumption, together with a decrease in adenylate energy charge (AEC) and arginine phosphate (ArgP), and with no changes in metabolic enzyme activity in the muscle. In TH, scallops maintained similar AEC and ArgP levels in muscle as those observed in T treatment. This response occurred along with the accumulation of inosine monophosphate and hypoxanthine. Besides, reduced citrate synthase and pyruvate kinase activities, enhanced hexokinase activity, and a higher octopine dehydrogenase/lactate dehydrogenase ratio in the mantle indicated the onset of anaerobiosis in TH. These responses indicate that juvenile scallops showed tissue-specific compensatory responses regarding their energy balance under moderate hypoxia at high temperatures. Our results give an insight into the tolerance limit of this species to combined hyperthermia and hypoxia in its northern limit of distribution.

Experiment on growing of japanese scallop &lt;i&gt;Mizuhopecten yessoensis&lt;/i&gt; in cages in the Aniva Bay

Results of experimental growing of japanese scallop Mizuhopecten yessoensis in the first three years of life in cages mounted in the Aniva Bay (southern Okhotsk Sea) are presented. Mean size and weight of the mollusks are determined and their growth rate and survival are compared with these indices for juvenile scallops from natural settlements in the Aniva Bay and other habitats located in the Far East region. Feasibility of the cage method for commercial cultivation of the scallop in conditions of the Aniva Bay is concluded.

Predation on planted and wild bay scallops (Argopecten irradians irradians) by busyconine whelks: studies of behavior incorporating acoustic telemetry

Quantifying predator–prey interactions and gaining insights into predator behavior are crucial for optimizing restoration strategies. However, such knowledge is often lacking for marine invertebrates. We examined potential impacts of predation by channeled Busycotypus canaliculatus and knobbed whelks Busycon carica on natural and planted populations of bay scallops in the Peconic Bays, New York, through laboratory and field investigations. In lab experiments, mean predation rates exhibited by small channeled whelks were low: 0.06 and 0.005 scallops d−1 for adult and juvenile scallops, respectively. Predation rates of small knobbed whelks on juvenile scallops were 22 × higher. Eighty-six percent (86%) of scallops consumed by channeled whelks had undamaged shells, while 73% eaten by knobbed whelks had notched ventral margins. In field plots where scallop densities were manipulated via removals/plantings, whelks consumed ~ 2% of ~ 19,100 planted juveniles, whereas crabs and presumably finfish consumed > 40% overall. Acoustic telemetry revealed that tagged channeled whelks moved shorter distances and spent more time in plots planted with scallops versus those without scallops. Whelks spent more time in low versus high-density plots, but consumed far more scallops in the latter. In trials without scallops, whelk movement rates were 5 × higher, presumably due to increased exploratory behavior. Overall, whelks were most active during crepuscular hours and during periods of increasing wind speeds. Our results, combined with population abundance data, suggest that whelks (especially B. carica) are drawn to planted bay scallop aggregations, but probably contribute to relatively low overall mortality in the context of restoration efforts.

Semi-automatic recognition of juvenile scallops reared in lantern nets from time-lapse images using a deep learning technique

Semi-automatic recognition of juvenile scallops reared in lantern nets from time-lapse images using a deep learning technique

The Effect of Temperature on Gonadal Sex Differentiation of Yesso Scallop Patinopecten yessoensis.

Many marine organisms are generally poikilotherms, making seawater temperature one of the most important environmental factors affecting gonadal sex differentiation. Mollusca is the second-largest animal phylum with diverse reproductive systems, but studies on the impact of temperature on sex differentiation are limited to a few sequential hermaphrodites. By combining morphological and molecular analyses, we investigated the effect of temperature on gonadal sex differentiation of a commercially important gonochoristic scallop Patinopecten yessoensis in the field and under laboratory conditions. Based on the relative expression of FoxL2 and Dmrt1L in the gonads of 6- to 12 month-old scallops, we found the scallops start to differentiate at 7 months old in September when the seawater temperature was 21°C. To eliminate the effect of factors other than temperature on sex differentiation, we compared the gonadal development of juvenile scallops at different temperatures (21, 16 and 11°C) under laboratory conditions. After 50 days of treatment, the 11°C group contain more germ cell types, and have higher sex differentiation rates than the 21°C group. But no obvious sex bias was observed. These results suggest that high temperature (21°C) inhibits sex differentiation, whereas low temperature (11°C) accelerates sex differentiation by 2 months for this cold-water species. It also supports juvenile P. yessoensis is gonochoristic rather than protandrous hermaphroditic. Our study addresses for the first time an environmental influence associated with genetic controls on scallop sex differentiation. It will facilitate a better understanding of how environmental factors affect gonadal development in poikilotherms, especially in the less studied molluscs.

Plasticity in organic composition maintains biomechanical performance in shells of juvenile scallops exposed to altered temperature and pH conditions

The exposure to environmental variations in pH and temperature has proven impacts on benthic ectotherms calcifiers, as evidenced by tradeoffs between physiological processes. However, how these stressors affect structure and functionality of mollusk shells has received less attention. Episodic events of upwelling of deep cold and low pH waters are well documented in eastern boundary systems and may be stressful to mollusks, impairing both physiological and biomechanical performance. These events are projected to become more intense, and extensive in time with ongoing global warming. In this study, we evaluate the independent and interactive effects of temperature and pH on the biomineral and biomechanical properties of Argopecten purpuratus scallop shells. Total organic matter in the shell mineral increased under reduced pH (~ 7.7) and control conditions (pH ~ 8.0). The periostracum layer coating the outer shell surface showed increased protein content under low pH conditions but decreasing sulfate and polysaccharides content. Reduced pH negatively impacts shell density and increases the disorder in the orientation of calcite crystals. At elevated temperatures (18 °C), shell microhardness increased. Other biomechanical properties were not affected by pH/temperature treatments. Thus, under a reduction of 0.3 pH units and low temperature, the response of A. purpuratus was a tradeoff among organic compounds (biopolymer plasticity), density, and crystal organization (mineral plasticity) to maintain shell biomechanical performance, while increased temperature ameliorated the impacts on shell hardness. Biopolymer plasticity was associated with ecophysiological performance, indicating that, under the influence of natural fluctuations in pH and temperature, energetic constraints might be critical in modulating the long-term sustainability of this compensatory mechanism.

Striae in the Antarctic scallop Adamussium colbecki provide environmental insights but not reliable age increments

Subannual growth increments in bivalves provide insight into past seasonal seawater conditions at high temporal resolution. The Antarctic scallop Adamussium colbecki (Smith 1902) accretes putatively fortnightly surficial growth lines (striae) and interstrial growth increments have the potential to archive sea ice variations. Cycles of paired groups of wide and narrow striae are sometimes used to determine ontogenetic age in these scallops, but previous quantitative work describing strial grouping and formation is limited to a few months of juvenile growth. Here, we analyze striae patterns in A. colbecki collected from two sites on western McMurdo Sound, Antarctica that differ by sea ice duration: Explorers Cove with multi-annual sea ice and Bay of Sails with annual sea ice. At both sites, visual analysis of striae groups and cycles (using the methods of previous authors) and wavelet analysis of interstrial increments suggest that striae groups are too variable to age A. colbecki. Only ~ 40% of striae groups and cycles conformed to expectations from annual cycles of fortnightly growth increments (~ 26 striae per cycle). Moreover, only one scallop from each study site displayed consistent periodicity at ~ 26 striae throughout juvenile growth in wavelet analysis. Though striae grouping was inconsistent, analysis of concurrent growth of juvenile scallops from Explorers Cove suggested strong environmental control on interstrial increment size and thus that strial increments are suitable for further analysis as sea ice proxies. Finally, the multi-annual sea ice site had smaller interstrial growth increments and less valve wear than the annual sea ice site, indicating overall slower growth and possibly lower metabolic activity.

Bay Scallop Growth Rates as Measured by Citizen-Scientist Partners During Restoration Efforts in Florida

Local bay scallop Argopecten irradians populations are threatened or depleted in southwest Florida estuaries (Pinellas through Lee Counties) and in the Panhandle (Bay through Escambia Counties), and community-driven restoration efforts have been ongoing for many years. To obtain juvenile scallops for use in restoration, wild larvae (spat) were allowed to settle on suitable surfaces (settlement traps) at sites known to still have high larval supply. Traps used to harvest spat were constructed with enhanced surface area relative to routine monitoring traps. Enhanced traps resulted in 142 ± 317.1 (mean ± SD) spat per trap and a maximum of 2,321 spat on a single trap, whereas the routine traps resulted in 67 ± 146.7 spat per trap and a maximum of 726. Spat were harvested each winter (2008–2012) from either St. Andrew Bay or Tampa Bay and delivered to restoration sites where citizen-scientists or collaborators measured the growth (shell heights) and mortality (live count) of 25–50 scallops within 3–25 cages each month. Most cages were hung from their own dock or the dock of a partner organization. Scientists from the lead agency also measured growth of caged scallops. Thus, simultaneous sampling occurred across a large geographical range with varied organizations and skill levels. In the shortest trials, survival remained very high, and in most years involving prolonged efforts, some of the planted scallops survived long enough to reach a size where spawning likely occurred. A maximum survival period of 559 days and the greatest mean shell height (65.18 ± 2.48 mm) of caged scallops were observed in Sarasota Bay in 2012. The observed growth in restoration cages fit previously described patterns for Florida Bay scallops, reaching maximum sizes between 60 and 70 mm shell height in 1 y. Mean daily growth rates (mm/day ± SD) increased as latitude decreased: St. Andrew Bay, 0.15 ± 0.096 y; Tampa Bay, 0.21 ± 0.124; Sarasota Bay, 0.22 ± 0.134; Charlotte Harbor, 0.28 ± 0.112; and Pine Island Sound, 0.29 ± 0.086). Temperature, scallop shell height, and the number of days in captivity (a proxy for age) generally had only minor or no effect on growth rates. When combined, the process of collecting wild spat and growing those scallops in cages using volunteer networks offers the advantages of community engagement, relatively low costs, minimal technical skill requirements, and reduced threat of loss of genetic diversity.

Not only greening: The effects of marennine produced by Haslea ostrearia on physiological traits of three bivalve species

The marine diatom Haslea ostrearia is known for its ability to produce marennine, a blue-green water-soluble pigment, which is responsible for the oyster greening phenomenon in the French Atlantic Coast. Marennine can be considered a bioactive extracellular compound (BEC) as it exhibits activities against detrimental pathogens in bivalve aquaculture. However, marennine could also be toxic to animals. The aim of this experimental study was to assess the effect of marennine produced by H. ostrearia upon three commercially important bivalve species, the American oyster Crassostrea virginica, the blue mussel Mytilus edulis and the giant scallop Placopecten magellanicus. Effect of this BEC was also assessed on different ontogenic stages of scallops. The animals were exposed to 3 mg L−1 of marennine and physiological response associated with clearance rates (CR), oxygen consumption and condition index (CI) were measured after 16 h of exposure (day 0), and after one subsequent week of recovery (day 7). In the short term, CR and oxygen consumption on mussels and oysters were significantly altered by marennine but not for scallops. CR recovery was observed in oysters after seven days, but no depuration was observed in mussels. Nevertheless, oxygen consumption in both mussels and oysters recovered on day 7. CI in the marennine-exposed group for both adult oysters and scallops was not significantly different, yet CI of mussels was lowered by 18.2 % compared to control. Scallop adults seemed largely resistant to marennine, but juveniles were more susceptible with a reduced CR and oxygen consumption by 71.9 % and 24.5 %, respectively, and no depuration activity observed until day 7. Additionally, CI in marennine-exposed juvenile scallops was 27 % lower than that of control. This study demonstrates species- and age-specific effect of marennine on bivalves, thus highlighting the importance of further assessment on the utilization of this pigment as a natural product decreasing pathogenicity of bacteria in shellfish aquaculture systems.

Living in a growing host: growth pattern and dwelling formation of the scallop Pedum spondyloideum in massive Porites spp. corals

Pedum spondyloideum is a byssally attached scallop in the Indo-Pacific that lives in deep fan-shaped dwellings within live scleractinian and hydrozoan corals, with the ventral edges of the scallops’ valves protruding slightly from the dwellings. Juvenile scallops have rounded, oval shells and live in shallow depressions. Complete scallop dwellings are formed by the growth of the host and allometric growth of the scallop, and by chemical and physical interactions between the scallop and its host. Scallops were extracted intact from their dwellings within massive corals in the genus Porites in Thailand (7°36′32″ N, 98°21′55″ E; in May 2019) and Malaysia (2°45′17″ N, 104°13′30″ E; in November 2019) to examine the relationship between shell height (SH) and shell width (SW). The slope of the regression of SH on SW within the first 2 years of settlement was 0.79–0.9, indicating that SW increased slightly faster than SH during this period. As the scallop grew further, the slope of the SH on SW was 1.29–1.54, indicating that SH increased faster than SW. A histological study on scallop pallial tissue, including the tentacles, and SEM observations of the dwelling walls suggested that the scallop has secretions that damage coral tissue and widen the dwelling during growth. Thus, the distinctive fan-shaped dwellings of the adult scallops are caused by a combination of allometric scallop growth and erosion of the host tissue and dwelling walls.

Factors affecting byssus attachment in juvenile scallops, Pecten maximus (L.)

Environmental and husbandry factors play key roles in the control of byssus attachment and detachment in many bivalve species. Identifying and understanding the impact of influential factors is essential for the management of post-settlement hatchery reared juveniles in species, such as the scallop Pecten maximus. We assessed the impact of substrate type and condition, and attachment period on attachment of juvenile scallops between 1.9 and 5.9 mm in shell height. Comparison of a variety of substrates showed that scallop juveniles have a preference for textured hard surfaces, with mean attachment up to 75.6 ± 14.4% after 24 h on riven slate in static conditions. Attachment could be significantly increased by preconditioning substrates in flow-through tanks of unfiltered seawater and by having undisturbed attachment periods longer than 1 h. The effect of substrate type and substrate condition on retention of seed was assessed in a flume. For all substrates, retention decreased with increasing water velocity. However, of the substrates examined (wool, nylon and slate), retention was greatest on the riven slate, with attachment up to 100% at water flow of 12.6 ± 0.2 cm s−1, although this was not statistically greater than on wool or nylon. Across all substrates preconditioning by immersion in seawater for two weeks significantly compromised juvenile retention at higher water velocities. Based on these findings, recommended parameters for maximising juvenile P. maximus attachment and retention in water velocities up to 12.6 ± 0.2 cm s−1 include utilising a riven slate type hard substrate, preconditioned for 1 week, with juveniles allowed to attach for 24 h.

Effects of Pseudoalteromonas espejiana W115 on Enzyme Activity and Disease Resistance of the Yesso Scallop Patinopecten yessoensis

A 49-day rearing trial was conducted to investigate the effects of Pseudoalteromonas espejiana W115 on digestive and immune–related enzyme activities in larval and juvenile Yesso scallop Patinopecten yessoensis. Larvae (day 2 post-fertilization) (day 2 PF) were distributed into three groups and provided with a diet only of microalgae (control group) and supplemented with W115 at final concentrations of 1 × 104 and 1 × 106 cells/mL, respectively. Results showed that umbo larvae (day 13 PF) and/or crawling-pediveliger larvae (day 28 PF) and/or juveniles (day 51 PF) fed with W115 supplementation diet at 104 cells/mL showed a significant increase in pepsin, amylase and cellulase activities compared to those fed the diet of microalgae, however, no significant difference was observed between the 106 cells/mL supplementation and control groups at days 13, 28 and 51 PF. The lysozyme and superoxide dismutase activities of umbo larvae and/or crawling-pediveliger larvae and juveniles treated with 104 and/or 106 cells/mL W115 supplementations were significantly higher than those in the control group, while there were no significant differences in enzyme activities in larvae and juveniles treated with two doses of W115 at days 13, 28 and 51 PF. No significant difference in catalase activity was observed among the three groups at days 13, 28 and 51 PF. In addition, there was increased survival in W115-amended treatments after juveniles were challenged with Vibrio splendidus. The results suggest that a 104 cells/mL supplementation of W115 can be useful in Yesso scallop larviculture.

The First Experience of Cage Farming of Hatchery-Reared Juvenile Scallop, Mizuhopecten yessoensis, off the Eastern Coast of Primorsky Krai

The characteristics of the farming of hatchery-reared juvenile Yesso scallop, Mizuhopecten yessoensis, in suspended net cages off the eastern coast of Primorsky Krai are studied. The work was conducted at a farm located northeast of Moryak-Rybolov Bay during the first 10 days of November 2018. The values of survival and growth rates of scallops on collectors and grow-out cages were determined. The survival rate of the Yesso scallop spat after being transported from Shandong Province, China and seeded in suspended cages was 85%, which is consistent with the regional standard. A high mortality rate of juvenile scallops (56–90%) was recorded in September–November. The mean size (shell height) of hatchery-reared spat in the cages in November did not differ from that of spat on collectors in southern Primorsky Krai. In the waters near Moryak-Rybolov Bay, the growth rate of scallops was somewhat lower than in southern Primorsky Krai but, nevertheless, higher than in Vladimir Bay and Aniva Bay. The mean body weight of scallop spat in November was 1.5 ± 0.1 g. The possible causes of the increased mortality rate of the bivalves and the solutions of the problem are discussed.

Collection of large benthic invertebrates in sediment traps in the Amundsen Sea, Antarctica

Abstract. To study sinking particle sources and dynamics, sediment traps were deployed at three sites in the Amundsen Sea for 1 year from February–March 2012 and at one site from February 2016 to February 2018. Unexpectedly, large benthic invertebrates were found in three sediment traps deployed 130–567 m above the sea floor. The organisms included long and slender worms, a sea urchin, and juvenile scallops of varying sizes. This is the first reported collection of these benthic invertebrates in sediment traps. The collection of these organisms, predominantly during the austral winter, and their intact bodies suggests they were trapped in anchor ice, incorporated into the overlying sea ice, and subsequently transported by ice rafting. The observations imply that anchor ice forms episodically in the Amundsen Sea and has biological impacts on benthic ecosystems. An alternative hypothesis that these organisms spend their juvenile period underneath the sea ice and subsequently sink to the seafloor is also suggested.

FIRST EXPERIENCE OF CAGE CULTIVATION OF HATCHERY-PRODUCED JUVENILE SCALLOP MIZUHOPECTEN YESSOENSIS AT EASTERN COAST OF PRIMORYE

Yesso scallop Mizuhopecten yessoensis is the main object of aquaculture in Primorye with annual yield measured in hundreds ton. However, further development of its farming could be restricted by lack of the spat. Availability of the spat imported from China using for the scallop cultivation at the coast of Primorye is explored. The spat from Chinese hatchery located in Shandong province was supplied for one aquaculture company in Primorye in the volume of 660 . 106 ind. in 2018 and settled to hanging collectors (1000 ind. per bag), then to cages in the marine farm located north-eastward from the Moryak-Rybolov Bay. Survival and growth rate of the scallop juveniles were examined in early November 2018, when the water temperature was from 10.3–10.4 оС at the sea surface to 9.7–9.9 оС at the bottom, salinity was about 33.60 psu in the whole water column, chlorophyll a concentration varied in the range 0.4–0.8 mg/L with the maximum in the layer 8–24 m. The spat mortality during transportation was estimated as 15 %, but it increased to 56–90 % during its growing up in cages. This level of mortality is much higher than mortality of the spat collected from the coastal waters at southern Primorye. The highest mortality of artificial spat was observed for large-sized mollusks, whereas it was satisfactory for the small-sized ones. Possible reason of high mortality is too high density of juveniles and damaging of their soft tissues by other shells. The spat shells height did not exceed 5–10 mm in the collectors but increased during their growing in cages to 20–25 mm. This size is similar to the size of scallop growing from natural spat in southern Primorye. However, growth rate of the scallop growing at the Moryak-Rybolov Bay (2.0–2.7 mm/month) is lower than in Peter the Great Bay (3.0–3.5 mm/month) though higher than in the Vladimir Bay and Aniva Bay. Mean body weight of the cultivated scallop in November was 1.5 ± 0.1 g.

Assessing effects of genetic, environmental, and biotic gradients in species distribution modelling

AbstractTo develop more reliable marine species distribution models (SDMs), we examine how genetic, climatic, and biotic interaction gradients give rise to prediction error in marine SDM. Genetic lineages with distinct ecological requirements spanning genetic gradients have yet to be treated separately in marine SDM, which are often constrained to modeling the potential distribution of one biological unit (e.g. lineage or species) at a time. By comparing SDM performance for the whole species or where observation and predictions were partitioned among geographically discontinuous genetic lineages, we first identified the appropriate biological unit for modeling sea scallop. Prediction errors, in particular contiguous omissions at the northern range margins were effectively halved in genetic lineage SDM (Total error=15%) verses whole species SDM. Remaining SDM prediction error was strongly associated with: i) Sharp climatic gradients (abrupt and persistent spatial shifts in limiting temperatures) found within continental shelf breaks and bottom channels. ii) A biotic gradient in the predation of sea scallop juveniles by the sand star within the Hudson Shelf USA. Our findings highlight how the accuracy of marine SDM is dependent on capturing the appropriate biological unit for modeling (e.g. lineages rather than species) and adequately resolving limiting abiotic and biotic interaction gradients.

Incorporation of Feed and Fecal Waste From Salmon Aquaculture in Great Scallops (Pecten maximus) Co-fed by Different Algal Concentrations

Juvenile scallops of Pecten maxiumus were studied to see the capability to clear out and incorporate salmon feed and feces (30 µg L-1). Algae were also given, in a low and high concentration in addition to feed and faeces, to mimic a winter and summer situation in Norwegian waters. Rhodomonas baltica and Chaetoseris muelleri were provided in a concentration of 50 µg L-1 and 300 µg L-1. The feeding trial lasted for 27 days. Clearance rate was measured to study filtration characteristics, while fatty acid profiling and stable isotopes of nitrogen and carbon were used to trace the uptake of salmon feed and feces in the digestive gland and muscle of juvenile scallops (30–35 mm shell height). The results show that the scallops could clear out and retain both salmon feed and feces particles, although at a statistically lower clearance rate than the algae. Fatty acid profiling revealed that the scallops assimilated and incorporated the consumed salmon feed and feces, given with either high or low algae concentrations, in their tissues, where the fatty acid C18:1n9 was used as a tracer fatty acid. The digestive gland of the scallops that were fed salmon feed and feces contained a higher share of C18:1n9 than those that were only fed algae. The digestive gland reflected the fatty acid composition of the diet, while the fatty acid composition of the muscle, which also changed, reflected a more complex relation between diet and metabolic processes in the tissue. The use of stable isotopes of carbon and nitrogen to trace food sources was inconclusive in this study due to low differences between samples fed different feeds. Fatty acid profiling was a more sensitive method for tracing low concentrations of salmon feed and feces in the algae diet of scallops. Our results suggest that P. maximus could be a candidate for integrated multi trophic aquaculture (IMTA) and that scallops have the potential to utilize small particles of wasted salmon feed and feces during a winter situation with low phytoplankton concentration and during an algal bloom in Norwegian waters.