Ecophysiological differentiation of Capitella capitata (Polychaeta). Sibling species from different sulfidic habitats

The ecophysiological differences of 4 sibling species of the Capitella capitata species complex from habitats with different sulfide concentrations were studied: Capitella sp. S (small) from a North Sea intertidal flat, living in the upper sediment layer containing low sulfide concentrations (up to 20 pm01 I"); Capltella sp. L (large), sympatric to Capitella sp. S, but living in deeper sediment layers with high sulfide concentrations (up to 350 pm01 1-'1; Capitella sp. M from the Mediterranean Sea from highly sulfid~c sed~rnents (up to 710 pm01 1.') close to shallow hydrothermal vents, and Capitella sp. I from eutrophicated coastal areas of the North Atlantic. Capitella sp. L, Capitella sp. M and Capjtella sp. I are significantly more tolerant to anoxia and 760 pm01 1.' sulfide than Capitella sp. S from the upper North Sea sedirnents. Respiration rates showed that only CapiteUa sp. S can be characterized as an oxyconformer. The oxygen consumption of Capitella sp. S becomes successively reduced with declining ambient oxygen tensions. The 3 other sibling species are all oxyregulators with different regulation abilities. At moderate oxygen concentrations the aerobic metabolism of Capitella sp. S is inhibited at low sulfide levels (30 pm01 I-'). Conversely, at moderate oxygen levels the anaerobic metabolism of Capitella sp. S is increased at 20 pm01 I-' sulfide. In contrast, even at sulfide concentrations of 130 pm01 l.', the aerobic metabolism of Capjtella sp L is not affected. The anaerobic metabolism of Capitolla sp. L is not increased at sulfide concentrations