Am. Wegeberg et Kt. Jensen, Reduced survivorship of Himasthla (Trematoda, Digenea)-infected cockles (Cerastoderma edule) exposed to oxygen depletion, J SEA RES, 42(4), 1999, pp. 325-331
Bivalve populations from inshore waters often accommodate a diverse tremato
de fauna that may have a variety of effects on host specimens. In particula
r, larval trematodes that grow or reproduce within their host are known to
be severe pathogens, whereas trematodes utilising bivalves only for encystm
ent are thought to be relatively benign. Yet this may depend on the environ
mental conditions, and it can be expected that such trematodes in concert w
ith other stress agents can be detrimental to host organisms. To examine th
e impact of such larval trematodes on hosts subjected to stress, we studied
the digenetic trematode Himasthla elongata and one of its second intermedi
ate hosts, the bivalve Cerastoderma edule. Experimentally infected cockles
and non-infected cockles were exposed to oxygen depletion, whereupon we mea
sured their burrowing ability and survivorship. After 30 h of hypoxia, the
survival of infected cockles was significantly reduced compared to non-infe
cted cockles, whereas no effect of parasites on cockles under normoxic cond
itions was found. In addition, parasites tended to reduce the burrowing abi
lity of cockles exposed to hypoxia but the effect was not clear. The effect
of parasites and possible ecological consequences are discussed and it is
suggested that the combined effects of parasites and oxygen deficiency may
explain some hitherto unexplained cases of mass mortalities in bivalve popu
lations. (C) 1999 Elsevier Science B.V. All rights reserved.