MEPS 312:177-188 (2006)  -  doi:10.3354/meps312177

ABSTRACT: We assessed metabolic balance, RNA content, and egg hatching success (EHS) in Acartia tonsa and A. clausi over a wide salinity range (2 to 33 and 16 to 33, respectively). For A. tonsa, the energy partitioning between ingestion, production and respiration was relatively constant with small differences in gross growth efficiency (GGE) and cost of growth (CG). In contrast, A. clausi exhibited significantly reduced ingestion and GGE, and highly elevated CG at salinities ≤20. In both species, RNA levels mirrored egg production. EHS was generally high in both species, but decreased by 80% for A. clausi at 16. These results contribute to the understanding of distribution patterns of both species along salinity gradients. The observed responses would allow the dominance of A. tonsa at low salinities, although its higher energetic requirement and feeding activity subject it to stronger predation pressure than competing A. clausi.

KEY WORDS: Acartia clausi · Acartia tonsa · Salinity · Metabolic balance · Fitness · RNA content · Distribution