Paralytic Shellfish Poisoning: Effects on Breeding Terns

-More than 70 Common Terns (Sterna hirundo) and lesser numbers of other terns and gulls were killed on 1 l-l 2 June 1978, by Paralytic Shellfish Poisoning (PSP; toxin of the dinoflagellate Gonyaulax excavata) at a breeding colony in Massachusetts. PSP toxin was detected at lethal levels in sand-launce (Ammodytes americanus), the terns’ principal food. Almost all terns that died were females in pre-laying condition; other birds vomited and survived. Breeding performance of survivors was unaffected. Mortality was greatest in three-year-old birds; lo-25% of three-year-old females were killed. Although PSP toxin was present in local shellfish for about three weeks, tern mortality was limited to a few hours on two days. Much higher levels of toxin were detected in shellfish at other parts of the Massachusetts coast in 1978 and other years, but terns and other susceptible seabirds were unaffected. Paralytic Shellfish Poisoning (PSP) results from ingestion of a toxin produced by marine algae and which accumulates primarily in molluscs. In the North Atlantic, the organism primarily responsible for producing the toxin is a dinoflagellate (Gonyaufax excavata, formerly known as G. tamarensis), whose periodic blooms are known as “red tides” (Loeblich and Loeblich 1975, Sweeney 1976, White 1980a). The toxin acts by blocking propagation of nerve impulses, leading to paralysis of skeletal muscles and, in sufficient doses, to death from respiratory failure (Schantz 1973). It has recently been discovered that the toxin can accumulate in marine zooplankton to levels that are lethal to planktivorous fish (White 1977, 1980b, 198 la, b). However, there are few reports of PSP in piscivorous fish or piscivorous birds. McKernan and Scheffer (1942) reported mortality of Common Murres (Uris adge) and loons (Gavia spp.) in an outbreak off Washington state. Coulson et al. (1968) and Armstrong et al. (1978) reported two incidents in northeastern England, in which large numbers of breeding Shags (Phalacrocorax aristotelis), Great Cormorants (P. carbo) and Northern Fulmars (Fulmarus glacialis) and smaller numbers of Herring Gulls (Larus argentatus) and terns (Sterna spp.) were killed. Effects on the terns in the 1968 incident were described in more detail by Horobin (1970) and Dunn (1972). In this paper I describe a similar incident at a tern colony in Massachusetts, in which I was able to document differential effects upon ageand sex-classes.