Effect of dissolved domoic acid on the grazing rate of krill Euphasia pacifica

Abstract

Some amino acids released from phytoplankton into the water are known to be feeding stimulants to zooplankton. However, domoic acid (DA), a neuroexcitatory amino acid released by some species of the diatom genus Pseudo-nitzschia, has the potential to be a feeding deterrent due to its neurotoxicity. Euphausiids (krill) are important members of the zooplankton grazer community and key prey items for many high level carnivores in the world's oceans. Although it is known that krill do consume toxic Pseudo-nitzschia spp. during blooms, there is currently no information concerning the effect of dissolved DA on the rate of feeding or the grazing behavior of krill. Therefore, we conducted experiments in which Euphausia pacifica were fed non-toxic P. pungens along with different added levels of either dissolved DA or glutamic acid (GA), an amino acid with a similar structure to DA. Krill grazing rates did not change significantly with added GA, but decreased significantly in the presence of DA. The rapid response of krill to dissolved DA suggests that either direct toxic action on the filtering apparatus or a chemoreceptor-like mechanism may suppress grazing in the krill. We suggest that these dissolved DA concentrations are relevant, given the DA concentrations found in Pseudo-nitzschia spp. populations in Monterey Bay and the feeding biology of krill. In either case, the suppression of feeding by dissolved DA suggests that high dissolved DA concentrations, should they occur in the field, may be a mechanism whereby blooms are perpetuated due to reduced losses to grazers such as krill.

Sex and Life‐history Stage Alter Herbivore Responses to a Chemically Defended Red Alga

“…Similarly, Ginsburg and Paul (2001) showed that A. parvula preferentially feeds on seaweeds that contain secondary metabolites at relatively low concentrations, but is deterred by high concentrations of these same compounds (Ginsburg and Paul 2001). In fact, chemical defenses of marine algae are often concentration dependent, with feeding deterrence occurring above a certain threshold value (Steinberg 1988, Bargu et al 2006). In the multiple-choice feeding assay with the female gametophyte, A. parvula preferred the more nutritious lateral branches to the main axis or the reproductive cystocarps.…”

Halogen radicals contribute to photooxidation in coastal and estuarine waters

“…Consumption of mollusks and fish contaminated with domoic acid has caused deaths and neurological damage in humans (6, 7), seabirds (10), and marine mammals (11). Dissolved domoic acid can affect marine microbial ecology by ligating micronutrients [e.g., iron (12)] and suppressing grazing by krill (13) and copepods (14). Although biological degradation in the water column has not been reported, both direct (15) and indirect (16) photodegradation contribute to domoic acid loss in seawater.…”

Dissolved azaspiracids are absorbed and metabolized by blue mussels (Mytilus edulis)

“…Effectively, when harmful algal blooms degrade, they release toxins into the dissolved phase (surrounding water). Studies have been carried out to evaluate toxin accumulation or effects of dissolved toxins on early stages of development of aquatic organisms (Colman et al, 2005;Korpinen et al, 2006;Lefebvre et al, 2005;Liu et al, 2007) on planktonic species (Babica et al, 2007;Bargu et al, 2006) and on adult fish (Bakke and Horsberg, 2010;Cazenave et al, 2005). However, very little is known about the ability of bivalve molluscs to accumulate dissolved marine biotoxins (Liu et al, 2007;Novaczek et al, 1991;Plakas et al, 2002).…”