Functional responses of aggregate‐colonizing copepods

Abstract

AbstractZooplankton consumption of aggregates, such as marine snow, is an important factor in determining the efficiency of the biological carbon pump. However, the feeding rates of aggregate‐associated small harpacticoid and poecilostomatoid copepods are largely unknown, as are the factors that influence these rates. We measured the functional responses of pellet production (PP) of aggregate‐feeding copepods on appendicularian houses, algal and detrital aggregates, and on Trichodesmium spp. tufts. The PP rates of all copepods increased with increasing aggregate concentrations, but the response varied depending on the aggregate type. The pelagic harpacticoid copepod Microsetella norvegica had the highest PP rates on algal aggregates, while the poecilostomatoid copepod Oncaea spp. and the benthic harpacticoid copepod Amonardia normanni PP rates were highest on appendicularian houses. The ingestion rates of M. norvegica and Oncaea spp. were typically 0.04–0.13 μg C ind.−1 d−1, with the exception of ca. three times higher rates of Oncaea spp. on appendicularian houses and ca. 10 times higher rates of M. norvegica on algal aggregates. The ingestion rates of the larger species, A. normanni, were generally higher, 0.3–1.3 μg C ind.−1 d−1 on algal aggregates, and even ca. 10‐fold higher on appendicularian houses. Our results suggest that the aggregate degradation rates by copepods can vary many‐fold depending on the quality (origin) of the aggregate and the copepod species. This can have large consequences for the attenuation of vertical carbon flux.