Toxin-mediated prey capture

Toxins delivered in the bites of aquatic organisms have been discussed in both folklore and modem medicine (Tamiya 1975 Halstead 1978 Russell 1984 Meier White 1995). Despite improved understanding of the chemistry, toxicology, and pharmacology of many of these substances, studies on their ecological roles are rare. 

The mechanisms of envenomation are not always known. For example, early accounts of prey capture by octopi claimed that crabs were killed when the octopi released toxins into the water without the need of biting the prey. Later studies, however, failed to show envenomation by toxins dissolved in the water (see references in Wells 1978). Other studies have shown that crabs trapped by an octopus (Eledone spp.) exhibited signs of paralysis before the octopus had time to drill through the carapace of the crab (see references in Hanlon Messenger 1996), but the site of entry for the toxin remains unknown. 

Cnidarians pose a particularly difficult challenge. The toxins produced by jellyfish and some hydrozoans are among the most powerful known, and have been relatively well characterized (Russell 1984). However, because the toxins are delivered through diverse kinds of nematocysts, experimental manipulations may be difficult. The role of toxins in prey capture has been inferred from the isolation of nematocyst-associated toxins, the behavior of exposed prey, and 

As guidelines, we suggest that researchers interested in the ecology of toxins as means of prey capture consider the following  

If toxins are used to capture food, then the presence of the toxin in the prey tissues should be confirmed once prey have been attacked. No studies have assayed for the presence of metabolites from the attackers inside the prey, even in cases where the toxins are known. 

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It is currently unclear whether toxin-mediated prey capture by mobile invertebrates has a significant impact on prey population size or community composition. In freshwater systems, chemically mediated prey capture by flatworms has been demonstrated to significantly impact prey populations in the laboratory. Neurotoxic chemicals released from the mucus webs of the flatworm Mesostoma can drive entire populations of the cladoceran Daphnia magna to extinction in culture, but the concentration these chemicals normally attain under realistic field conditions is unknown. Nevertheless, because the mucus webs these flatworms build function to trap prey, Dumont and Carels163 likened these flatworms to spiders with toxic webs. Similar impacts may occur in open water marine systems where organisms that employ toxin-mediated prey capture are abundant, or even dominant, predators (e.g., chaetognaths and cnidarians). 

Long-term assays Toxin-mediated prey capture... 

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