Zooplankton feeding behavior and particle selection in natural plankton assemblages containing toxic Alexandrium spp.

Abstract

Laboratory experiments suggest that toxic Alexandrium spp. cells are unpalatable to zooplankton grazers, and that toxic cells should be selectively avoided by zooplankton when feeding in mixtures of different prey species. Such avoidance, if practised in the wild, might contribute to harmful bloom formation by reducing losses of Alexandrium spp. due to grazing. In the spring of 1998 and 1999, during 'red tide' outbreaks in the southwestern Gulf of Maine, weekly experiments were performed using field collected natural water samples with ambient phytoplankton and dominant mesozooplankton grazers. The feeding response of Acartia hudsonica, Semibalanus balanoides nauplii, and Calanus finmarchicus was tested during various weeks in natural water samples with low concentrations of Alexandrium spp. (~1000 cells l -1 , typical natural concentrations for this region). Semibalanus sp. nauplii consistently avoided toxic Alexandrium spp. and other dinoflagellates. C. finmarchicus selectively fed on diatoms when they were abundant, and fed non-selectively on all dinoflagellates (except Ceratium spp.) when the spring bloom declined and dinoflagellates dominated. A. hudsonica non-selectively cleared Alexandrium spp. throughout the study periods. During spring Alexandrium spp. bloom formation, if non-selective grazers such as A. hudsonica dominate the zooplankton, Alexandrium spp. losses from grazing depend on grazer abundance (biomass); if selective feeders such as S. balanoides nauplii dominate, then Alexandrium spp. benefits from reduced grazing losses relative to alternative prey.

Testing for resistance of pelagic marine copepods to a toxic dinoflagellate

“…However, female Acartia hudsonica from Maine ingest toxic A. fundyense at high rates regardless of whether it is provided as a sole or mixed food (Colin and Dam, 2002b). Similarly, Teegarden et al (2001) found that Acartia hudsonica from Casco Bay, ME fed readily on toxic A. fundyense in natural algal assemblages. Thus, their resistance is not through avoidance of A. fundyense.…”

Feeding habits of <i>Calanus sinicus</i> (Crustacea: Copepoda) during spring and autumn in the Bohai Sea studied with the herbivore index

“…(Cataletto et al, 1995). The feeding rate of C. finmarchicus increased rapidly with the cell diameter of the algae in the size range 7 to 17 µm (ESD), and ciliates larger than 30 µm were found to be rejected intensively (Teegarden et al, 2001). Although studies on the upper size limit of its food particles were unavailable, phytoplankton as large as 76 µm might be unsuitable for C. sinicus.…”

Osmotic stress does not trigger brevetoxin production in the dinoflagellateKarenia brevis

“…Because the defensive function of toxic secondary metabolites in organisms is indisputable, it is often accepted that toxin production has largely evolved to defend prey against predators (e.g., 16,[34][35][36]. Within aquatic systems, there is substantial evidence in support of the evolution of chemical defenses (37,38), and this evidence extends to both macro-and microalgae (13,(39)(40)(41). As such, productive lines of inquiry regarding the function of brevetoxins not only should include how production changes with environmental factors but also must consider the role of biological interactions, especially those between phytoplankton and grazing organisms.…”