Title

Interaction between marine calanoid copepods and dimethylsulfoniopropionate

Date of Completion

January 2000

Keywords

Biology, Ecology|Biology, Oceanography|Biogeochemistry|Engineering, Marine and Ocean

Degree

Ph.D.

Abstract

Copepods and other zooplankters represent a previously overlooked pool of particulate dimethylsulfoniopropionate (DMSP). DMSP content of marine copepods varied from pico-moles in Acartia tonsa to nano-moles in Temora longicornis. In eastern Long Island Sound, zooplankton was a negligible pool of DMSP during most of the year, but in spring when the abundance of T. longicornis was large, zooplankton represented up to 72% of the total particulate DMSP in surface water. ^ In laboratory studies, the DMSP content of Temora longicornis was positively related to salinity and food-DMSP concentration, and was reduced by >50% when salinity decreased from 30‰ to 20‰. This reduction in DMSP content was not a result of DMSP cleavage, demethylation, or conversion of DMSP to methionine. Instead, most of the missing DMSP was recovered as dissolved DMSP in the surrounding medium. Thus, this regulatory mechanism shifts the partitioning of DMSP from the particulate phase to the dissolved phase when ambient salinity decreases. ^ The DMSP content of Acartia tonsa was determined mostly by food availability. In an experiment that simulated the migratory behavior of A. tonsa, the copepods' DMSP content increased when feeding in food-abundant surface water, and 88 to 100% of the ingested DMSP was not retained in the bodies. Actively migrating copepods would transport <10% of the ingested DMSP to deep water. Thus, A. tonsa affects DMSP dynamics likely through fecal pellet production. The DMSP content of fecal pellets was correlated with the copepods' body DMSP content, and ambient food concentration. DMSP concentration within pellets was orders of magnitude higher than typical dissolved DMSP concentrations in the ocean. Thus, fecal pellets may represent “hot spots” for DMSP diffusion and microbial consumption in the water column. ^ Field-collected A. tonsa contained DMSP-consuming bacteria (DCB) in their bodies, Recovered DCB increased by over 10-fold after A. tonsa fed on DMSP-containing algae. DCB were also recovered from the copepods' fecal pellets. Enrichment cultures of DCB from copepod bodies converted only a portion of the consumed DMSP to DMS, compared to ∼100% for DCB from fecal pellets. Copepod-bacteria coupling thus represents a novel mechanism for DMSP consumption and DMS production in the ocean. ^