Growth variability and feeding of scallop Patinopecten yessoensis on different bottom sediments: Evidence from fatty acid analysis

Abstract

Growth and feeding of the Japanese scallop, Patinopecten (= Mizuhopecten) yessoensis, from two populations inhabiting neighboring sites with similar water temperature, salinity, and hydrodynamic regimes but with different bottom sediment types were investigated. Fatty acid biomarkers were used to investigate the diets of scallops and to evaluate the food availability at the sites with different bottom sediments. Fatty acid composition of digestive gland and soft tissues of scallops from two populations were examined and compared to those of plankton, particular organic matter of near-bottom water and bottom sediments as its potential food sources. The high level of 20:5( n − 3) coupled with the high ratio of 16:1( n − 7) to 16:0 in the digestive gland of scallop indicated an important contribution of diatoms to scallop nutrition. The relatively high proportions of 18:2( n − 6), 20:4( n − 6), and 22:6( n − 3) suggested that heterotrophic flagellates, ciliates, and invertebrate larvae were also an important source of nutrition for the scallop. Trace amounts of branched and odd fatty acids were indicative of an insignificant contribution of detritus to scallop diet. Lipid and fatty acid compositions of scallops from two sites were characterized by pronounced differences pointing to the different food availability in near-bottom water at the muddy and sandy sites. Higher food availability at the muddy site resulted in an increase in the total lipid content in scallop's digestive gland due to increased proportion of triacylglycerols. Increased contents of diatom biomarkers indicated that scallops inhabiting muddy bottom were more reliant on diatom food sources. Scallops from the sandy site showed higher proportions of biomarkers derived from flagellates, ciliates, and invertebrate larvae, compared to scallops from the muddy site. This is consistent with the distribution of the fatty acids in near-bottom water POM at the study sites. In spite of the high microbial biomass in muddy bottom sediments and elevated proportion of bacterial fatty acids in near-bottom water POM, bacterial input in scallop diet increased slightly. Thus, the distribution of marker fatty acids in scallops collected at the two sites indicated spatial variability primarily due to the composition and abundance of near-bottom POM, suggesting that scallop feeding is dependent on food availability. Comparison of linear and weight parameters of scallops showed that, in spite of the best food potential at the muddy site, scallops grew significantly slower at the muddy site than at the sandy site. Thus, food potential was not the only factor regulating growth of scallops inhabiting different bottom sediments. It was found, that oxygen concentration in near-bottom water and bottom sediment resuspension depended on the grain-size composition of the sediments. Most probably, low oxygen concentration in the near-bottom water and high resuspension of inorganic fine-grained particles enriched with inedible dead organic matter are the main reasons of the reduction in growth of scallop inhabiting the muddy site.