Abstract
Using digital holographic cinematography, we quantify and compare the feeding behavior of free-swimming copepods, Acartia tonsa, on nutritional prey (Storeatula major) to that occurring during exposure to toxic and non-toxic strains of Karenia brevis and Karlodinium veneficum. These two harmful algal species produce polyketide toxins with different modes of action and potency. We distinguish between two different beating modes of the copepod’s feeding appendages–a “sampling beating” that has short durations (<100 ms) and involves little fluid entrainment and a longer duration “grazing beating” that persists up to 1200 ms and generates feeding currents. The durations of both beating modes have log-normal distributions. Without prey, A. tonsa only samples the environment at low frequency. Upon introduction of non-toxic food, it increases its sampling time moderately and the grazing period substantially. On mono algal diets for either of the toxic dinoflagellates, sampling time fraction is high but the grazing is very limited. A. tonsa demonstrates aversion to both toxic algal species. In mixtures of S. major and the neurotoxin producing K. brevis, sampling and grazing diminish rapidly, presumably due to neurological effects of consuming brevetoxins while trying to feed on S. major. In contrast, on mixtures of cytotoxin producing K. veneficum, both behavioral modes persist, indicating that intake of karlotoxins does not immediately inhibit the copepod’s grazing behavior. These findings add critical insight into how these algal toxins may influence the copepod’s feeding behavior, and suggest how some harmful algal species may alter top-down control exerted by grazers like copepods.
Highlights
Harmful algal blooms (HABs) are occurring with increasing frequency and magnitude across the globe, and have the potential to alter or disrupt ecosystem functions
We study the behavioral response of A. tonsa to varying diets of toxic and non-toxic isolates of K. brevis and K. veneficum, the same organisms used in [4,20]
Grazing Suppression and Toxicity A question raised from our results is why are grazing and sampling in mixed diets of K. brevis so low? To provide possible explanations, we note that evidence provided in several studies [9,17] and our holographic movies (Video S5 in Supporting Information S8) show that A. tonsa can perform selective feeding
Summary
Harmful algal blooms (HABs) are occurring with increasing frequency and magnitude across the globe, and have the potential to alter or disrupt ecosystem functions. Karenia brevis and Karlodinium veneficum are two common dinoflagellates that form HABs. K. brevis blooms are responsible for the infamous ‘red tides’ prominent in the Gulf of Mexico. K. brevis blooms are responsible for the infamous ‘red tides’ prominent in the Gulf of Mexico It causes neurotoxic shellfish poisoning by producing brevetoxins, which are ladder polyethers that trigger numerous physiological symptoms in exposed organisms. K. veneficum is responsible for major fish kills in estuaries and brackish waters worldwide. It produces karlotoxins, which are pore-forming polyketides that cause cell lysis and death by increasing the membrane permeability. A recent study reported that karlotoxin was used by K. veneficum for capturing its prey, Storeatula major [2]
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