The respiratory performance and survival of the bivalve Macoma balthica (L.) at the southern limit of its distribution area: a translocation experiment

The hypothesis was tested that animals near their extreme Southern limits, due to high temperatures, have a high respiration rate, whereby they reach an extreme low weight-index and ultimately disappear. At estuarine stations the respiration rate of Macoma balthica (L.) (Baltic clam) did not show in terseasonal changes, indicating seasonal acclimation, but within the season the respiration increased with increasing temperature, indicating the abse nce of short-term acclimation. In clams translocated from the Netherlands t owards the Bidasoa estuary, 200 km South of their Southern distribution lim it, their respiration rate was higher and weight-index lower than in specim ens living in Dutch estuaries, Irrespective of an effect of the temperature , clams exposed in experiments to water from Bidasoa showed a higher respir ation than clams exposed to water from the other stations. Moreover, at non -estuarine stations with a low food content, the clams showed reversed accl imation, i.e., the respiration rates in winter were much lower than summer rates, most probably a strategy to conserve energy by means of a depressed metabolism. A weight index of 5 mg DW/cm(3) and glycogen content of 2% DW a re suggested as the minimal values below which the metabolic energy balance of Baltic clams becomes more negative and the clam population disappears. It was concluded that factors other than temperature influenced the respira tion and weight-index of clams, and hence their presence or absence, e.g., food concentration, innate seasonal cycles, and possible pollutants in the water. (C) 2000 Elsevier Science B.V. All rights reserved.