Mixed Algal Diet Research Articles

Larval growth, development, and survival of laboratory-reared Aplysia californica: Effects of diet and veliger density

Over the last three decades, the California sea hare, Aplysia californica, has played an increasingly important role as a model organism in the neurosciences. Since 1995, the National Resource for Aplysia has supported a growing research community by providing a consistent supply of laboratory-reared individuals of known age, reproductive status, and environmental history. The purpose of the present study was to resolve the key biological factors necessary for successful culture of large numbers of high quality larval Aplysia. Data from a sequence of five experiments demonstrated that algal diet, food concentration, and veliger density significantly affected growth, attainment of metamorphic competency, and survival of Aplysia larvae. The highest growth and survival were achieved with a mixed algal diet of 1:1 Isochrysis sp (TISO) and Chaetoceros muelleri (CHGRA) at a total concentration of 250 × 10 3 cells/mL and a larval density of 0.5–1.0 per mL. Rapid growth was always correlated with faster attainment of developmental milestones and increased survival, indicating that the more rapidly growing larvae were healthier. Trials conducted with our improved protocol resulted in larval growth rates of > 14 µm/day, which yielded metamorphically competent animals within 21 days with survival rates in excess of 90%. These data indicate the important effects of biotic factors on the critical larval growth period in the laboratory and show the advantages of developing optimized protocols for culture of such marine invertebrates.

Anti-grazing properties of the toxic dinoflagellate Karlodinium veneficum during predator–prey interactions with the copepod Acartia tonsa

Karlodinium veneficum (syn. Karlodinium micrum, Bergholtz et al. 2006; J Phycol 42: 170-193) is a small athecate dinoflagellate commonly present in low levels in temperate, coastal waters. Occasionally, K. veneficum forms ichthyotoxic blooms due to the presence of cytotoxic, hemolytic compounds, putatively named karlotoxins. To evaluate the anti-grazing properties of these karlotoxins, we conducted food removal experiments using the cosmopolitan copepod grazer Acartia tonsa. Wild-caught, adult female A. tonsa were exposed to 6 monoalgal or mixed algal diets made using bloom concentrations of toxic (CCMP 2064) and non-toxic (CSIC1) strains of K. veneficum. Ingestion and clearance rates were calculated using the equations of Frost (1972). Exposure to the toxic strain of K. veneficum did not contribute to an increased mortality of the copepods and no sig- nificant differences in copepod mortality were found among the experimental diets. However, A. tonsa had significantly greater clearance and ingestion rates when exposed to a monoalgal diet of the non-toxic strain CSIC1 than when exposed to the monoalgal diet of toxic strain CCMP 2064 and mixed diets dominated by this toxic strain. These results support the hypothesis that karlotoxins in certain strains of K. veneficum deter grazing by potential predators and contribute to the formation and continuation of blooms.

Fatty acid composition of larvae of the sand dollar Dendraster excentricus (Echinodermata) might reflect FA composition of the diets

Fatty acid (FA) requirements of echinoderm larvae were examined by a study of the FA composition, growth, and development of Dendraster excentricus larvae fed a microencapsulated diet, and two algal diets. Larvae were assigned to three treatments with three replicates per treatment, a microencapsulated diet, a single algal diet of Dunaliella tertiolecta and a mixed algal diet of Isochrysis galbana and Dunaliella tertiolecta. The percentage of saturated fatty acids (SAFA), short and long chain polyunsaturated fatty acids (PUFA) differed significantly among the algal diets and the microencapsulated diet. Differences in dietary FA composition influenced larval tissue FA composition. Eight day-old sand dollar larvae fed the single and mixed algal diets had a significantly higher percentage of the SAFA myristic acid (14:0), while eight day-old larvae fed the microencapsulated diet had a significantly higher percentage of the SAFA palmitic acid (16:0). Sixteen day-old competent larvae fed all three diets did not differ significantly in the percentage of myristic or palmitic acid. The algal diets had a higher percentage of the short chain PUFAs linolenic (LNA, 18:3n-3) and stearidonic acid (SDA, 18:4n-3) while the microencapsulated diet had the highest percentage of the long chain PUFAs eicosapentanoic acid (EPA, 20:5n-3) docosahexanoic acid (DHA, 22:6n-3) and arachidonic acid (AA, 20:4n-6). The percentage of short chain PUFAs, though high in the algal diets, was low in the larval tissues, while the percentage of long chain PUFAs, though low in the algal diets, was high in the larval tissues. Competent larvae fed the two algal diets had up to ten times the percentage of EPA and AA than those fed the microencapsulated diet. Unexpectedly, despite a high percentage of DHA and EPA in the microencapsulated diet, the percentage of these long chain PUFAs in the tissues of larvae fed this diet was extremely low. Eight day-old larvae fed the three diets did not differ significantly in total larval length. Competent larvae fed algal diets had significantly longer larval arms, bigger stomachs and larger rudiments than those fed the microencapsulated diet. This study indicates that early larval growth and development of Dendraster excentricus were not discernibly affected by differences in dietary FA composition of microencapsulated and algal diets but the competent larval stages were. Similar growth and development of competent echinoderm larvae fed microencapsulated or algal diets might be obtained by enriching the microencapsulated diets with the short chain PUFAs LNA and SDA, and the long chain PUFAs EPA and AA. This is an important research tool as microencapsulated feeds can be used to establish nutritional requirements of fatty acids for echinoderm larval development.

Population Growth and Production of Apocyclops dengizicus (Copepoda: Cyclopoida) Fed on Different Diets

Abstract This study was carried out to investigate the effects of various diets: 4 monoalgal diets: Nannochloropsis oculata (N), Isochrysis galbana (I), Chaetoceros calcitrans (C), and Tetraselmis tetrathele (T); 4 mixed algal diets: N+I+C+T(NICT), N+I+C(NIC), C+T(CT), and I+T(IT); and 2 nonalgal diets: baker’s yeast (BY) and prepared shrimp feed (SF) on population growth and density of Apocyclops dengizicus. The type and density of diet had significant effects on the growth and density of A. dengizicus (P < 0.01). Of tested diets, T and CT were optimum diets due to higher density and growth rate of A. dengizicus compared to other diets. Their high dietary value was related to the higher contents of polyunsaturated fatty acid, particularly docosahexaenoic acid (22:6n‐3), eicosapentaenoic acid (20:5n‐3), and arachidonic acid (20:4n‐6) compared to A. dengizicus cultured on other diets. The results of the present study illustrated that T. tetrathele was the most suitable food for the culture of A. dengizicus.

The effects of a harmful alga on bivalve larval lipid stores

Marine invertebrates often have complex life histories that include a swimming planktivorous larval stage, at which time they are vulnerable to a variety of stressors, including those associated with nutritional stress and harmful algal blooms. Lipid stores have been shown to be especially important for post-metamorphic survivorship and growth in a variety of marine invertebrates. We investigated the effects of the harmful brown tide alga Aureococcus anophagefferens on the lipid stores and growth of larvae of the hard clam (northern quahog, Mercenaria mercenaria), a dominant bivalve in many western Atlantic bays and estuaries . M. mercenaria was the dominant bivalve in Great South Bay, Long Island, until the mid-1970s, but very few larvae are presently found in these waters. Recent brown tide blooms have been hypothesized to pose a barrier to recovery of M. mercenaria populations and hinder recent restoration efforts by negatively affecting clam larvae. To test whether a diet of the brown tide alga affects the accumulation of beneficial lipid stores, we fed larvae one of three diets representing equal biovolumes of Isochrysis galbana, a nutritious control alga; A. anophagefferens, the brown tide alga for which nutritional quality is not presently known; or a mixture of the two. Larvae fed only brown tide had significantly less lipid stores than those in the other dietary treatments. In addition, brown tide negatively affected larval size. We also tested for evidence of tradeoffs between larval growth and lipid stores, predicting that when the diet was less nutritious as in the brown tide treatments, larval size and lipids would be negatively correlated. In contrast, we found that larvae fed a mixed algal diet or only A. anophagefferens showed a significant positive correlation between lipid stores and size, suggesting that some larvae were simply better at obtaining food and associated nutrients. Larval success likely depends on a complex interplay between genetic and environmental factors. Our study suggests that poor nutrition associated with a harmful alga can have negative effects on larval size and lipids stores, which in turn are mediated by the inter-individual variability in the ability to grow and accumulate necessary lipid stores. Phytoplankton quality is likely to be important for the sustainability of bivalve populations even when it primarily impacts the larval phase; and a diet of brown tide algae may have lasting legacies for juveniles and adults.

Tu-P10:481 Relationship of dietary intake of fatty acids to plasma C-reactive protein in Japanese

Fatty acid (FA) requirements of echinoderm larvae were examined by a study of the FA composition, growth, and development of Dendraster excentricus larvae fed a microencapsulated diet, and two algal diets. Larvae were assigned to three treatments with three replicates per treatment, a microencapsulated diet, a single algal diet of Dunaliella tertiolecta and a mixed algal diet of Isochrysis galbana and Dunaliella tertiolecta. The percentage of saturated fatty acids (SAFA), short and long chain polyunsaturated fatty acids (PUFA) differed significantly among the algal diets and the microencapsulated diet. Differences in dietary FA composition influenced larval tissue FA composition. Eight day-old sand dollar larvae fed the single and mixed algal diets had a significantly higher percentage of the SAFA myristic acid (14:0), while eight day-old larvae fed the microencapsulated diet had a significantly higher percentage of the SAFA palmitic acid (16:0). Sixteen day-old competent larvae fed all three diets did not differ significantly in the percentage of myristic or palmitic acid. The algal diets had a higher percentage of the short chain PUFAs linolenic (LNA, 18:3n-3) and stearidonic acid (SDA, 18:4n-3) while the microencapsulated diet had the highest percentage of the long chain PUFAs eicosapentanoic acid (EPA, 20:5n-3) docosahexanoic acid (DHA, 22:6n-3) and arachidonic acid (AA, 20:4n-6). The percentage of short chain PUFAs, though high in the algal diets, was low in the larval tissues, while the percentage of long chain PUFAs, though low in the algal diets, was high in the larval tissues. Competent larvae fed the two algal diets had up to ten times the percentage of EPA and AA than those fed the microencapsulated diet. Unexpectedly, despite a high percentage of DHA and EPA in the microencapsulated diet, the percentage of these long chain PUFAs in the tissues of larvae fed this diet was extremely low. Eight day-old larvae fed the three diets did not differ significantly in total larval length. Competent larvae fed algal diets had significantly longer larval arms, bigger stomachs and larger rudiments than those fed the microencapsulated diet. This study indicates that early larval growth and development of Dendraster excentricus were not discernibly affected by differences in dietary FA composition of microencapsulated and algal diets but the competent larval stages were. Similar growth and development of competent echinoderm larvae fed microencapsulated or algal diets might be obtained by enriching the microencapsulated diets with the short chain PUFAs LNA and SDA, and the long chain PUFAs EPA and AA. This is an important research tool as microencapsulated feeds can be used to establish nutritional requirements of fatty acids for echinoderm larval development.

Ingestion rates and dietary lipids affect growth and fatty acid composition of Dendraster excentricus larvae

This study investigated the effect of single and mixed algal diets on growth, fatty acid composition and ingestion rates for Dendraster excentricus larvae. Larvae were assigned to three single algal diet treatments Isochrysis galbana, Dunaliella tertiolecta or Rhodomonas sp. and four mixed algal diet treatments D. tertiolecta and Rhodomonas, I. galbana and D. tertiolecta, I. galbana and Rhodomonas, D. tertiolecta, Isochrysis galbana and Rhodomonas sp. Small amounts (0.36–0.6%) of stearic acid (18:0) were seen in the three algae used but a relatively large percentage (7–25%) of this SAFA was found in Dendraster larvae. The alga D. tertiolecta had the highest percentage (51.7%) of the short chain polyunsaturated fatty acid (PUFA) linolenic acid 18:3(n-3) and trace amounts (0.02–0.14%) of the long chain PUFAs eicosapentanoic (EPA, 20:5(n-3) and docosahexanoic acids (DHA, 22:6(n-3)). However, sand dollar larvae demonstrated the ability to elongate and desaturate shorter chain (18 carbon) polyunsaturated fatty acids (PUFA) to longer chain (20 carbon) n-3 PUFA. Thus high levels of 18:3(n-3) in D. tertiolecta led to high levels of EPA and low levels of 18:3(n-3) in Dendraster larvae fed this diet. Rhodomonas sp. had the highest percentage of stearidonic acid (18:4(n-3), 38.14%) and EPA (10.6%). Despite high levels of 18:4(n-3) in Rhodomonas sp. this acid was absent or found at very low levels in larvae fed this alga, or any combination of this alga. I. galbana had the highest percentage of DHA(14.3%) but was almost devoid of EPA (0.43%). Although Rhodomonas sp. and I. galbana had high levels of EPA and DHA sand dollar larvae did not incorporate higher levels of these long chain PUFAs into their lipids compared to those fed the alga D. tertiolecta. Dendraster larvae synthesized a number of 20 and 22 carbon non-methylene interrupted dienes (NMID), with levels increasing with larval stage. Higher ingestion rates were observed for Dendraster larvae fed single algal diets ( Rhodomonas sp. or D. tertiolecta) and lower ingestion rates for those fed mixed algal diets. The highest ingestion rates were for 8-arm Dendraster larvae fed the large alga Rhodomonas sp. presented as a single algal diet. When fed a combination of three algae, selection of particles varied slightly depending on stage with 8-arm larvae ingesting slightly more of the larger algal cell in the mixture than 6-arm larvae. The present study suggests that regardless of the ratios given larvae might have an optimum ratio of different sized particles at which they can feed. The mixed algal diet of I. galbana and D. tertiolecta was the best algal diet leading to significantly larger larvae with high survival and development to metamorphosis. The single algal diets of Rhodomonas sp. or Dunaliella tertiolecta were the second and third best algal diets based on growth and survival to metamorphosis.

Nutritional Status and Diet Composition Affect the Value of Diatoms as Copepod Prey

The role of diatoms as key food for copepods at the base of pelagic food chains has been questioned recently on the grounds of toxicity. We show, using unialgal versus mixed algal diets of different nutritional status (i.e., nitrogen:carbon ratio) fed to Acartia tonsa, that diatoms per se are not toxic but that single-diatom diets are inadequate. Additionally, the nutritional state of the phytoplankton has a profound effect on copepod growth and growth efficiency. The ecological significance of laboratory demonstrations of diatom toxicity needs to be reconsidered.

THE EFFECT OF PEAT MOSS PARTICLES ON THE PHYSIOLOGY OF THE EASTERN OYSTER, CRASSOSTREA VIRGINICA

This study was designed to evaluate whether the addition of peat moss particles to an algal diet influenced the physiology, biochemical composition, reproductive development, and survival of the Eastern oyster (Crassostrea virginica) under laboratory conditions. In two consecutive 5-wk trials (13°C to 15°C), 70-mm oysters were fed a mixed algal diet (25 μg Chl L−1 or 2.3 mg TPM L−1) supplemented with 3 concentrations of peat particles (2.7, 11.2, or 31.2 mg TPM L−1). The proportion of organic matter (POM:TPM) in the various diets increased from 79% for the algal control to 96% for the highest peat concentration. Following a 5-d acclimation period, oysters in the various treatments exhibited similar clearance rates calculated either on the basis of chlorophyll (2.3 L h−1g−1) or particle removal (2.8 L h−1g−1). Chlorophyll filtration rates were similar among treatments (63 μg Chl h−1g−1), whereas particle filtration rates increased with peat concentration in the diet (9–58 mg TPM h−1 g−1). Although pseudofeces production rates increased with peat concentration (2–30 mg TPM h−1g−1), estimates of particle ingestion rate also increased (7–28 mg TPM h−1g−1). Fecal production rates were similar for the various treatments (2 mg TPM h−1g−1) as were respiration rates (0.32 ml O2 h−1g−1). Oysters sampled after 3-wk and 5-wk exposure to the four diet treatments exhibited no significant differences in biochemical composition, gonad maturation rate or survival. In general, this study suggested that the presence of peat particles in an excess algal diet had no impact on oyster performance. However, the results of these laboratory trials may not be directly applicable to oysters subjected to similar peat concentrations under field conditions.

The effect of the quality of food patches on larval vertical distribution of the sea urchins Lytechinus variegatus (Lamarck) and Strongylocentrotus droebachiensis (Mueller)

Although most invertebrate larvae are weak swimmers and act as passive particles on horizontal scales, they may be able to regulate their vertical position in response to different factors, including increased food concentration. We examined the effect of the quality of food patches on larval vertical distribution for the sea urchins Lytechinus variegatus and Strongylocentrotus droebachiensis, and determined the effect of dietary conditioning on that response in the laboratory. We reared larvae on a mixed algal diet of Dunaliella tertiolecta and Isochrysis galbana under low (500 cells ml −1) and high (5000 cells ml −1) rations. Food patches were maintained in Plexiglas rectangular columns (30×10×10 cm) using a density gradient, where practical salinity in the bottom layer was 33, in the middle layer 30, and in the top layer 27. We examined the magnitude and mechanism of a behavioural response of larvae of L. variegatus in the four-arm stage, and on two developmental stages of S. droebachiensis (four- and six-arm), by manipulating patch quality. In the absence of a patch, larvae of both species and developmental stages swam through to the surface of the experimental columns. In the presence of algae, fewer larvae were present above the patch and more were at the patch than in control columns. More larvae swam through patches of “unflavoured” algal mimics than algal patches, and aggregated at the surface. Larval distribution relative to patches of algal filtrate without algal cells or of “flavoured” algal mimics in algal filtrate was not consistently different from that in either control or algal patches; thus, the magnitude of larval response to filtrate (with or without particles) was intermediate between that to control and algal patches. For L. variegatus, more larvae crossed the patches when reared on low than high rations, indicating that poorly conditioned larvae may be less responsive to environmental cues. Our results suggest that larvae can actively aggregate and maintain a vertical position in response to a food patch that depends on the quality and quantity of food. The response appears to be based mostly on a chemosensory rather than a mechanosensory mechanism.

Diet and salinity effects on larval growth and development of the sand dollar Mellita isometra

Summary Larval growth and development of Mellita isometra were investigated by assigning larvae to several single- and mixed-algal diets, three levels of salinity and salinity-diet combinations in the laboratory. Larvae-fed Isochrysis galbana were significantly smaller, developed significantly smaller rudiments and had significantly lower protein content than larvae in all other treatments. Larvae fed Chaetoceros muelleri or the mixed-algal diet of I. galbana and D. tertiolecta developed significantly faster, had significantly bigger rudiments and significantly higher protein content. Eight-arm larvae fed the mixed-algal diet consisting of two small algae, Isochrysis galbana and Chaetoceros muelleri, were significantly wider than those fed mixed-algal diets consisting of a small and a large algal cell (I. galbana and Dunaliella tertiolecta or C. muelleri and D. tertiolecta). No differences were observed in rudiment size and protein content of advanced 8-arm larvae fed these three mixed-algal diets. Larvae maintained at 27%o produced significantly bigger rudiments. Larvae maintained at 32%o and fed C. muelleri were significantly longer, wider and had longer posterodorsal arms than larvae in the other two treatments. In conclusion, a single-algal diet consisting of C. muelleri was just as effective as a mixed-algal diet for optimal larval growth and development of the sand dollar M. isometra. I. galbana was ineffective regardless of salinity. Therefore, the nutritional quality of an alga rather than its size may have a greater effect on larval development of echinoderms.

Evaluation of microalgae and industrial cheese whey as diets for Tapes decussatus (L.) seed: effects on water quality, growth, survival, condition and filtration rate

As reference diets for bivalve molluscs are missing, this study first evaluated the best mixed algal diet (Tetraselmis suecica Butch/Phaeodactylum tricornutum Bohlin) concentration for 4-mm-length Tapes decussatus (L.) clams. It also assessed the performance of an industrial by-product (cheese whey) as a single diet or supplement for the best algal ration previously determined. Growth, survival, condition index and filtration rate were used to compare the different diets. Implications of rations tested on rearing water quality were also investigated, especially ammonium and heterotrophic bacteria levels. With a food concentration as algal dry weight per total seed live weight of 0.7% day−1, seed for grow-out (7 mm) could be obtained within 1 month. A mixture of 25% algal ration and 75% cheese whey gave the best performances. Artificial diets resulted in lower growth rates than live food (20 % to 40% of the best algal ration), but could be considered good maintenance rations in energetic terms. Using cheese whey, and without any algae, hatchery produced seed can be kept economically indoors for at least 30 days without loss in condition.

Effect of temperature on development, growth and reproduction in the marine copepod Pseudocalanus newmani at satiating food condition

Post-embryonic development time, somatic growth, egg production rate, survival and sex ratio for the marine calanoid copepod Pseudocalanus newmani from the Pacific coast off southwestern Hokkaido were determined at five temperatures (3, 6, 10, 15 and 20°C) when a mixed algal diet was provided at satiating food condition (0.36 μg C ml -1 ) in the laboratory. At temperatures between 3 and 15°C, the development time from hatching to adult female increased exponentially with decreasing temperature, being 23.3, 33.1, 46.7 and 74.6 days at 15, 10, 6 and 3°C, respectively. Males developed into adults 2-5 days earlier than did the females. At the highest temperature of 20°C, both embryonic and post-embryonic development and egg production of P newmani were suppressed. This inhibitory effect of high temperature is consistent with the vertical distribution range and seasonal abundance cycle of this copepod in the field; it tends to avoid the warm surface layer (>15°C) and scarcely appears in the water column during summer and autumn. Body size of P newmani was not affected by temperature until C1, but increased with decreasing temperature after C2. The weight-specific growth rate (SGR) increased linearly with temperature (T) until 15°C, which is expressed as SGR = 0. 0095T + 0.0462 (r = 0.996). This growth pattern may also indicate high-temperature stress to this copepod, the general pattern of copepod growth being exponential. The weight-specific egg production rate (SER) also increased with temperature (SER = 0. 02T + 0.014, r = 0.99), below 15°C. The proportion of male offspring of P newmani that grew to adulthood was nearly 50% at 3 and 6°C, but decreased with increasing temperature at 10-15°C. This unequal sex ratio may be due to sex change during juvenile development under temperature control. These results suggest that temperature plays an important role in life history traits of P newmani through not only temperature- dependent growth and reproduction, but also through high-temperature inhibition and temperature- controlled sex ratio under sufficient food supply.

Energy vs. essential fatty acids: what do scallop larvae ( Argopecten purpuratus) need most?

Larvae of the Chilean–Peruvian scallop Argopecten purpuratus were fed a Dunaliella tertiolecta diet (Dun-diet) supplemented with lipid emulsions, rich in 20:5n-3 (EmEPA), 22:6n-3 (EmDHA) or in saturated fatty acids (EmCOCO). A mixed algal diet of Isochrysis galbana (T-iso) and Chaetoceros neogracile served as a positive control (St-diet). Lipid supplementation to the Dun-diet improved the larval growth and increased the percentage of eyed larvae significantly, compared to the non-supplemented Dun-diet because of the extra energy supplied and not because of its fatty acid composition. No significant differences were observed between supplementation with EmEPA, EmDHA or EmCOCO. A mixture of 20% EmEPA+20% EmDHA (40% EmHUFA) was more efficient in raising the total lipid content in larvae than 40% EmCOCO. Both emulsions increased the triacylglycerol content in larvae compared to the non-supplemented Dun-diet. The best result, however, was obtained with the St-diet, probably because of a more suitable 18:2n-6/18:3n-3 ratio and a higher level of arachidonic acid. A positive relationship between the 18:2n-6/18:3n-3 ratio and the larval performance was found. No significant difference was observed in post-settlement larval size or percentage of metamorphosed larvae between the St-diet and the St-diet supplemented with 20% EmHUFA or 20% EmCOCO. The metamorphosed larvae had a constant DHA/EPA ratio of 3.7, independent from the diet, which suggested a metabolic control of the two fatty acids and a species-dependency of the ratio.

Impact of the supplementation of a docosahexaenoic acid-rich emulsion on the reproductive output of oyster broodstock, Crassostrea gigas

Pacific oyster [Crassostrea gigas (Thunberg)] broodstock were hatchery-conditioned with either a mixed algal diet of Dunaliella tertiolecta, Tetraselmis suecica and Rhodomonas sp. [1:1:1, on a dry weight (DW) basis] (Control), a single diet of D. tertiolecta (Duna) or a single diet of D. tertiolecta supplemented with an emulsion rich in eicosapentaenoic (20:5n-3) and particularly docosahexaenoic acid (22:6n-3) (Duna+Em). Oysters were spawned after a conditioning period of 7 and 8 weeks and larvae were reared for 1 week on an Isochrysis galbana (clone T-Iso) diet. The percentage recovery of D-larvae from eggs of Control-fed oysters and Duna+Em-fed oysters was not significantly different (80% and 63% after 7 weeks of conditioning; 87% and 74% after 8 weeks of conditioning, respectively] but was much higher than from eggs produced by Duna-fed oysters (24% and 41% after 7 and 8 weeks of conditioning, respectively). A reduction in the percentage recovery of D-larvae as a result of temperature or salinity stress was most severe in eggs from Duna-fed oysters. Neither the broodstock diet nor the conditioning period affected the size of eggs or D-larvae, larval performance, or lipid content and lipid class distribution of the eggs. The fatty acid composition of the eggs was modified by the fatty acid composition of the algal diet and the lipid emulsion. The supplementation of the emulsion resulted in a pronounced increase in the percentage of 22:6n-3 in the polar (PL) and neutral lipids (NL) of the eggs (4.0–13.4% and 8.5–14.7% in NL and PL, respectively). The egg lipids (7–8 ng egg–1) contained about 62% NL and were dominated by triglycerides (TAG), which made up 65% of the NL. The major phospholipids were phosphatidylethanolamine (PE), ceramide aminoethylphosphonate and phosphatidylinositol (CAEP+PI), phosphatidylserine (PS) and phosphatidylcholine (PC). Regardless of the broodstock diet treatment, the PL fraction contained high percentages of non-methylene-interrupted dienes (NMID) and plasmalogens (detected as dimethyl acetals).

Impact of algal diets and emulsions on the fatty acid composition and content of selected tissues of adult broodstock of the Chilean scallop Argopecten pupuratus (Lamarck, 1819)

The impact of dietary fatty acids on the fatty acid composition and content in different organs (digestive gland, adductor muscle and male and female gonad) of Argopecten purpuratus was evaluated during the process of gonad maturation under controlled laboratory conditions. A mixed algal diet of Isochrysis galbana (clone T-Iso), Pavlova lutheri, Chaetoceros gracilis and Tetraselmis suecica was either fed alone (Al) or supplemented with 50% lipids (expressed as % of the algal dry weight (DW)) using an emulsion rich in 22:6 n−3 (Al+EmDHA) or an emulsion rich in 20:5 n−3 (Al+EmEPA). Results showed the algal diet having the greatest impact on the fatty acid composition (mainly an increase of 18:1 n−9, 18:2 n−6; 18:3 n−3 and a decrease of 20:5 n−3) of the digestive gland and female gonad, moderate in the male gonad while the fatty acid composition of the adductor muscle was hardly affected. Our data indicated that 16:1 n−7 and 18:1 n−9 were partially elongated to 18:1 n−7 and 20:1 n−9, respectively. The supplementation of the algal diet with EmDHA or EmEPA (which contained 45% and 19% 22:6 n−3, respectively) increased significantly the concentration of 22:6 n−3 (mg g −1 DW) in the digestive gland, female gonad and male gonad with 78%, 57% and 51%, respectively, for (Al+EmDHA)-fed scallops and 18%, 33% and 19%, respectively, for (Al+EmEPA)-fed scallops, while the 22:6 n−3 concentration in the adductor muscle was not affected. Broodstock conditioning was associated with a significant increase of the lipid content in the female and to a lesser extent in the male gonad. The significant increase (as compared to the initial sample) of the 22:6 n−3 concentration in the digestive gland, female gonad and eggs of A. purpuratus fed 22:6 n−3-rich lipid illustrated that recently ingested fatty acids did significantly contribute to the lipid accumulation process in the maturing female gonad. The similarities between the fatty acid composition of the female gonad and digestive gland suggest that lipids were transferred from the lipid-rich digestive gland to the female gonad.

Impact of starvation and of feeding algal and artificial diets on the lipid content and composition of juvenile oysters ( Crassostrea gigas ) and clams ( Tapes philippinarum )

The present study evaluated the effect of starvation and of feeding various algal and lipid-supplemented diets on the lipid content and lipid class distribution in the polar and neutral lipids of early juvenile oysters (Crassostrea gigas) and clams (Tapes philippinarum L.). T. philippinarum was starved, fed a mixed algal diet [Tetraselmis suecica and Isochrysis galbana (clone T-Iso)] or solely T. suecica at three different feeding rations, either supplemented or not supplemented with lipid emulsions. C. gigas was fed T. suecica with and without the supplementation of lipid emulsions or liposomes. When T. philippinarum and C. gigas were fed solely T. suecica, no qualitative and only minor quantitative differences were observed between the lipid class profile of both species. The major neutral lipids were triglycerides (TAG) and free sterols plus diglycerides (FS+DAG), whereas the polar lipids were dominated by phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol plus ceramideaminoethanol phosphonate (PI+CAEP). An increase of the algal feeding ration resulted in an increase of the lipid content of spat which was associated with a significant augmentation of the TAG level (as percentage of the total lipids and as percentage of the neutral lipids). Lipid supplementation evoked a similar though more pronounced effect. Starvation resulted in a significant decline of the lipid content and a complete depletion of the TAG reserve. Contrary to the neutral lipids (NL), the relative proportion (percentage of total polar lipids, PL) of the individual PL classes was hardly affected by the diet. The importance of lipid and TAG reserves in early juveniles is discussed.

The effects of diet mixing on consumer fitness: macroalgae, epiphytes, and animal matter as food for marine amphipods.

Herbivores are thought to achieve adequate nutrition by consuming numerous species of plants or by occasionally consuming animal tissue. Although active selection of diverse foods is common in nature, the relationship between diet mixing and consumer fitness is poorly understood, especially in marine environments. We studied the fitness-based consequences of dietary mixing in the sympatric amphipods Ampithoe marcuzzii, A. valida, Cymadusa compta, and Gammarus mucronatus by measuring survivorship, growth, and fecundity of these amphipods when they were offered single species of algae, a single animal food, a mixture of algal species, or a combination of algae and animal matter. For the more sedentary, tube-building amphipods A. marcuzzii, A. valida, and C. compta, fitness on mixed algal diets was matched by fitness on at least one of the monospecific algal diets, suggesting that they could benefit from preferential feeding on those algae in the field. The more mobile amphipod, G. mucronatus, survived and grew similarly on the mixed diets and on the filamentous brown alga Ectocarpus siliculosus. However, its fecundity was significantly higher when feeding on the algal and animal mixture than on Ectocarpus alone. Additionally, for G. mucronatus, fitness on mixed algae, mixed algae plus animal matter, and animal matter alone was equivalent, although female growth (but not gonad production) was slightly lower on animal matter alone than on the mixed algae combined with animal food. Thus the more mobile amphipod, G. mucronatus, was the only species able to perform well on animal food alone. In contrast, A. valida and C. compta experienced large negative effects when limited to consuming animal matter alone. For these two species, combining algae and animal matter did not enhance fitness over combining only algae. Fitness effects of specific algal diets showed some general similarities, but also considerable variance among the amphipods. For example, E. siliculosus was generally better food than other algae for all four amphipods, whereas Sargassum filipendula was generally poor. However, A. marcuzzii did not suffer negative effects of consuming only Sargassum. The red alga Polysiphonia sp. and the green alga Enteromorpha flexuosa decreased fitness in A. marcuzzii, C. compta, and G. mucronatus, but not A. valida, and the negative effects of Polysiphonia were considerably larger for A. marcuzzii than for the other amphipods. Our data show that nutritional requirements, even among related species (e.g., A. marcuzzii and A. valida), can be dramatically different. Diet mixing may benefit more mobile consumers like Gammarus that are better able to search for different foods, and may be less important for more sedentary herbivores like Ampithoe and Cymadusa that consume, and live in close association with, individual host plants.

The Chilean scallop Argopecten purpuratus (Lamarck, 1819): II. manipulation of the fatty acid composition and lipid content of the eggs via lipid supplementation of the broodstock diet

Dietary supplementation with lipid emulsions during broodstock conditioning of Argopecten purpuratus was used to manipulate the fatty acid composition of the eggs. The scallops were fed a mixed algal diet either alone (Al) or supplemented with an emulsion rich in ethyl esters of docosahexaenoic acid (DHA; Al+EmDHA) or eicosapentaenoic acid (EPA; Al+EmEPA) at a concentration of 50% lipids per algal dry weight (DW). The longer induction period and the lower fecundity in scallops fed solely on algae indicated a higher food value for the lipid-supplemented diet compared to the non-supplemented diet. Lipid supplementation resulted in a significant increase of the total lipid content (mg/g DW) of the eggs. The fatty acid quality of the diet had no significant effect on the fatty acid profile of the polar lipids. However, the supplementation of the DHA-rich emulsion resulted in a significant increase of the DHA level (% of total fatty acids) in the total and neutral lipids of the eggs compared to eggs from scallops fed solely algae. The absolute DHA content (mg/g DW) increased by 47%. The EPA level in the total and neutral lipids of eggs from broodstock supplemented with EmEPA was significantly higher than in eggs from scallops fed Al+EmDHA but no significant differences were detected with eggs from the non-supplemented diet (Al). The absolute EPA concentration in eggs from scallops fed Al+EmEPA was, respectively, 19 and 17% higher than in eggs from broodstock fed, respectively, solely algae (Al) or Al+EmDHA. The results illustrated that fatty acids, supplied as emulsified ethyl esters, could be ingested and assimilated by adult A. purpuratus and were at least partially allocated to the eggs.

Dietary impact of algal and artificial diets, fed at different feeding rations, on the growth and fatty acid composition of Tapes philippinarum (L.) spat

The effect of lipid supplementation and algal ration on growth and fatty acid composition of juvenile clams, Tapes philippinarum was investigated. A diet of Tetraselmis suecica was supplemented with a lipid emulsion and fed at a daily ration of 0.5, 1.0 and 1.5% WW DW −1 day −1. A mixed algal diet of Isochrysis galbana (clone T-Iso) and T. suecica (1:1 on DW basis) and starvation functioned as positive and negative control treatments, respectively. T. suecica, which contains eicosapentaenoic acid (20:5 n−3) but no docosahexaenoic acid (22:6 n−3), was supplemented with 50% (% of algal dry weight) of a 22:6 n−3-rich emulsion. Higher growth rates of T. philippinarum were associated with higher T. suecica feeding rations. Lipid supplementation resulted in significantly better growth rates of T. philippinarum at a T. suecica ration of 0.5, 1.0 and 1.5% WW DW −1 day −1. The growth promoting effect of lipid supplementation was significantly reduced during 4 consecutive weeks or by increasing the algal feeding ration. Increasing T. suecica rations were associated with a decrease in the % composition of 22:6 n−3 while the 20:5 n−3% composition was hardly affected in the total lipids of T. philippinarum. On the contrary, the absolute concentration of 22:6 n−3 (μg per gram dry weight, μg g DW −1) in the total lipids of T. philippinarum was similar at all T. suecica rations while the 20:5 n−3 concentration significantly increased. The major effect of lipid supplementation on the fatty acid composition of the clams, was a significant increase of the 22:6 n−3% composition in the total lipids, polar lipids and triglycerides. In contrast with 20:5 n−3, the effect of lipid supplementation on the absolute 22:6 n−3 content (μg g DW −1) was more pronounced at a higher T. suecica ration. After a starvation period of 4 weeks, the concentration (μg g DW −1) of all fatty acids was significantly reduced, except the n−7 monoenoic fatty acids (MUFA) and the non-methylene interrupted dienoic fatty acids (NMID). The concentration (μg g DW −1) of the NMID in starved clams and clams fed different diets was similar to the concentration in the initial sample. This indicated that growing spat was actively synthesising NMID and they were selectively retained in unfed animals. The results indicated that either dietary lipid or 22:6 n−3 was a growth-limiting factor when T. suecica was fed at a ration of 0.5, 1 and 1.5% WW DW −1 day −1. A selective retention in starved clams and a preferential accumulation in fed clams was observed for 22:6 n−3 but not for 20:5 n−3 which indicated a greater importance of 22:6 n−3 compared to 20:5 n−3.