Paralytic shellfish poisoning toxins mediate feeding behavior of sea otters

Abstract

Captive sea otters (Enhydra lutris)fed live Saxidomus giganteus (butter clams) ad libitum either reduced their prey capture and consumption rates or discarded the highly toxic siphons and kidneys when switched from clams containing very low levels of saxitoxin [37±9 µg STX (100 g)−1] to highly toxic clams [226±96 µg STX (100 g)−1]. Feeding rates returned to pretreatment levels when the otters were again switched to low‐toxicity clams, but siphon discard frequency remained high. Paralytic shellfish poisoning symptoms were observed only in an otter calculated to have consumed the most STX (154 µg kg−1 d−1), a dosage within the range of oral LD50s reported for other nonprimate mammals. None of the other otters displayed symptoms, and all subjects were eventually released in good health. These findings suggest that otters are not immune to paralytic shellfish poisoning toxins (PSPT) and that they have the ability to detect and avoid consumption of lethal amounts of toxic prey. This behavioral response is highly adaptive given the importance of butter clams in sea otter diets, and the chronic toxicity of butter clams in areas where toxic dinoflagellate blooms occur. A comparison of the distributions of otters and toxicity levels of butter clams in southeast Alaska suggests that the sequestering of PSPT may protect some clam populations from otter predation and limit the distribution of otters to the exposed outer coast where toxic clams are rare.

Marine chemical ecology: what's known and what's next?

“…The paralytic shellfish toxins acquired by bivalves as they ingest dinoflagellates may have large-scale cascading effects on community structure through their indirect effects on keystone species such as sea otters or other predators, which can play a large part in structuring nearshore temperate ecosystems (Simenstad et al, 1978;Kvitek et al, 1991). As an example, filter feeding butter clams, Suxidomus giganteus, along the west coast of North America, are immune to the effects of paralytic shellfish toxins.…”

“…Marine studies of among-species differences in susceptibility to consumers and presence of secondary metabolites have provided insights into factors (a) driving ecological specialization (Hay, 1992), (b) affecting species' distribution and community organization (Lubchenco and Gaines, 1981;Hay, 1985Hay, , 1991aEstes and Steinberg, 1988;Kvitek et al, 1991), (c) determining feeding patterns and digestive efficiencies (Horn, 1989;Hay, 1991a;Irelan and Horn, 1991;Pennings and Paul, 1992;Targett et al, 1995), and (d) producing parallels and contrasts between marine and terrestrial systems (Hay, 1991b;Hay and Steinberg, 1992). An increased understanding of prey chemical defenses is thus fundamental to a wide range of ecological and evolutionary topics.…”

“…Sea otters, fishes, and birds foraging on butter clams are not immune to the toxins and can become sick, or die, if they ingest the compound-laden portions of clams that have fed on toxic dinoflagellates. Kvitek et al (1991) hypothesized that dinoflagellate toxins affected the regional distribution of sea otters. They noted that otters appear to have been historically absent from areas where dinoflagellate blooms were common, but historically present in areas where dinoflagellate blooms were rare.…”

“…If otters are absent, urchin grazing can destroy kelp beds, create urchin barrens, and dramatically alter ecosystem structure and function. Thus, toxins from planktonic dinoflagellates have the potential to substantially alter the structure and productivity of nearshore ecosystems through their indirect effects on keystone consumers like sea otters (Kvitek et al, 1991).…”

Cephalopods as Vectors of Harmful Algal Bloom Toxins in Marine Food Webs

“…Out of the 5000 species of phytoplankton known today, about only 2% of them are toxin producers [2,3]. Toxins may cause heavy damage to marine animals and even death (e.g., behavior alterations [4], development impairments in early stages of life [5,6], abortion and premature birth of marine mammals [7]). They can also affect human populations, through the consumption of contaminated sea products, mostly shellfish [2].…”