Seasonal variation in the biochemical composition of the chaetognath Parasagitta elegans from the hyperbenthic zone of Conception Bay, Newfoundland

The biochemical composition of the chaetognath Parasagitta elegans from the hyperbenthic zone of Conception Bay, Newfoundland, was determined from April 1997 to June 1998. Lipid and carbohydrate levels (% dry weight) were relatively high in the spring and summer and low in the fall and winter. Conversely, the relative protein level was low in the spring and summer and high in the fall and winter. Carbon level was generally high in the spring and summer of 1997 but low from fall to the following spring, whereas inorganic ash level showed the opposite seasonal trend. Lipid and carbohydrate levels and the C/N ratio were positively correlated with chaetognath maturity stage, while protein levels were negatively correlated with chaetognath maturity. These results indicate that P. elegans were lipid- and carbohydrate-rich while maturing during spring and summer, and that immature individuals were protein-rich while achieving somatic growth during fall and winter. This increase in the levels of lipid and carbohydrate occurred when mature copepods increased in the spring and summer rather than when total abundance of copepods increased in the fall. Thus, it appears that food quality rather than quantity affects the biochemical levels and reproductive cycle of P. elegans. In addition, the maximum abundance of adult copepods occurred 3 wk after the peak of the spring bloom, and the maximum relative abundance of mature P. elegans occurred 3 wk later. This suggests that there is tight coupling of energy transfer from primary producers to carnivorous hyperbenthic chaetognaths following the spring phytoplankton bloom in Newfoundland coastal waters. Therefore, seasonal variation in the biochemical composition of P. elegans in the hyperbenthic zone of Conception Bay is closely related to its reproductive cycle and to food quality. Furthermore, it is clear that the chaetognath reproductive cycle is synchronized with the massive energy input from the annual spring phytoplankton bloom.