Dimethylsulfoniopropionate (DMSP) in marine copepods and its relation withdiets and salinity

The main goal of this study was to assess the effects of algal diets and wa ter salinity on the bodily content of dimethylsulfoniopropionate (DMSP) in estuarine copepods. In laboratory experiments, Temora longicornis contained more DMSP when fed DMSP-rich Tetraselmis impellucida (prasinophyte) than w hen fed DMSP-poor Dunaliella tertiolecta (chlorophyte). The DMSP content of T. longicornis after gut clearance was curvilinearly related to the ingest ion rate. These observations suggest that the copepods incorporated the die tary source of DMSP into their body tissue. On the same diet, T. longicorni s contained more DMSP at higher salinity, indicating an osmoregulatory func tion of DMSP. However, DMSP appears to be a minor osmolyte compared with fr ee amino acids. The DMSP content of T. longicornis decreased faster in resp onse to a decrease in salinity than it increased with an increase in salini ty, implicating separate mechanisms for accumulation and removal of DMSP in the copepod. We also measured the bodily content of DMSP from field-collec ted animals. Five species of calanoid copepods from Long Island Sound conta ined DMSP, not associated with gut content, which varied interspecifically from 0.02 to 1.03 nmol ind.(-1). Carbon-specific DMSP content of the copepo ds was comparable to that reported for some diatoms, chlorophytes and crypt ophytes. We argue that copepod biomass may, at times, represents a substant ial source of particulate DMSP in the water column.