Copepod feeding selectivity on microplankton, including the toxigenic diatoms Pseudo-nitzschia spp., in the coastal Pacific Northwest

Abstract

As part of the Pacific Northwest ECOHAB project, we measured clearance rates and feeding selectivity of calanoid copepods off the coast of Washington State, USA, during fall of 2003. We tested the hypothesis that copepods discriminate amongst prey, particularly against the toxic diatoms Pseudonitzschia spp. in natural assemblages from this highly productive, upwelling environment. Seven grazing experiments were conducted across and along the shelf using the copepods Calanus pacificus, Metridia pacifica, Acartia longiremis and a small community assemblage dominated by Acartia spp., with minor contributions from Pseudocalanus spp., Paracalanus spp. and Oithona spp. Three general patterns emerged from our experiments. First, all copepods, except A. longiremis in 1 experiment, showed neutral preference or discriminated against Pseudo-nitzschia, but preference did not appear related to cellular domoic acid concentrations. Second, the dominant prey biomass contributors in each experiment were cleared at low rates relative to other prey types. In most cases the dominants were the diatom Thalassiosira spp. or the autotrophic dinoflagellates Ceratium spp. and Prorocentrum spp. The third pattern was high preference for microzooplankton. High clearance on microzooplankton can result in trophic cascades, which were evident in our size-fractionated chlorophyll data. These patterns indicate that copepods could have both direct and indirect effects on the plankton community composition on the Washington coast. However, our estimates of total potential grazing suggest that copepod grazing impact on Pseudo-nitzschia populations is negligible. KEY WORDS: Copepod grazing · Prey selectivity · Pseudo-nitzschia · MicrozooplanktonResale or republication not permitted without written consent of the publisher

Induction of domoic acid production in the toxic diatom Pseudo-nitzschia seriata by calanoid copepods

“…The hypothesis that DA causes physiological incapacitation in copepods does not conflict with findings showing that copepods do not select against toxic Pseudo-nitzschia species, even when nontoxic alternative food is offered (Maneiro et al, 2005;Olson et al, 2006;Leandro et al, 2010). The reason is that the negative effects of DA on grazers are expected to occur only if DA intake by the grazers is high enough, which may not have been the case in the studies by Maneiro et al (2005), Olson et al (2006) and Leandro et al (2010), or that the effects of possible physiological incapacitation by DA are left unnoticed. DA may nevertheless have adverse effects on the fecundity of the grazers, which may lead to subsequent reduced grazing pressure.…”

Seasonal Variability of Mesozooplankton Feeding Rates on Phytoplankton in Subtropical Coastal and Estuarine Waters

“…The grazing impacts of mesozooplankton on total phytoplankton can be counter balanced by trophic cascades, referred by negative clearance rates, especially when trophic cascade effect was greater than direct grazing rate because that the suppression of microzooplankton would in turn cause an increase of phytoplankton (Nejstgaard et al, 2001;Liu FIGURE 9 | Relationship between mesozooplankton clearance rates and phytoplankton Chl a concentrations in the two stations of Hong Kong waters: EO and WE and Dagg, 2003;Olson et al, 2006). The cascading effect was generally neglected for mesozooplankton feeding until when an attempt to calculate the real mesozooplankton grazing rate on phytoplankton by correction factor was published by Nejstgaard et al (2001).…”

Heterotrophic dinoflagellates: a significant component of microzooplankton biomass and major grazers of diatoms in the sea

“…In addition to their role as herbivores in marine systems, ciliates and heterotrophic dinoflagellates in the microzooplankton serve as a quantitatively and qualitatively significant food resource for mesozooplankton (Stoecker & Capuzzo 1990, Kleppel 1993, Suzuki et al 1999, Levinsen et al 2000, Vincent & Hartmann 2001, Leising et al 2005b,c, Liu et al 2005, Olson et al 2006. Due to their cell size and biochemical composition, microzooplanktonic protists are often preferred food for copepods, and feeding on microzooplankton along with phytoplankton can enhance copepod fecundity (Kleppel 1993, Klein Breteler et al 1999, Bonnet & Carlotti 2001, Castellani et al 2005.…”