Effects of Temperature Changes on Infaunal Circalittoral Bivalves, Particularly T. Tenuis and T. Fabula

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Abstract

The limits of thermal tolerance are associated closely with the latitudinal and local variations found within an animals’ range, yet in most situations the absolute limits of tolerance are seldom reached. Under these conditions the survival of a species is related more to its ability for capacity adaptations (e.g. growth rate, reproduction) than to its absolute tolerances (resistance adaptations).

Exceptions to the above can occur in the littoral zone, with the effect being proportional to the height up to the shore: here both elevated temperatures during the summer and lower temperature, during the winter especially those low enough to result in ice, can lead directly to mortality.

The most pronounced sub-lethal effects are those on growth and reproduction. Under conditions of elevated temperatures growth, especially in the initial stages, is faster. Reproduction is earlier in warmer waters and may occur more than once or continuously throughout the summer. This may lead to them being in poorer condition compared to northern populations which spawn once in spring for overwintering and hence to decreased long term survival.