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

Abstract

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 μmol l-1); Capitella sp. L (large), sympatric to Capitella sp. S, but living in deeper sediment layers with high sulfide concentrations (up to 350 μmol l-1); Capitella sp. M from the Mediterranean Sea from highly sulfidic sediments (up to 710 μmol l-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 Capitella sp. I are significantly more tolerant to anoxia and 760 μmol l-1 sulfide than Capitella sp. S from the upper North Sea sediments. Respiration rates showed that only Capitella 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 μmol l-1). Conversely, at moderate oxygen levels the anaerobic metabolism of Capitella sp. S is increased at 20 μmol l-1 sulfide. In contrast, even at sulfide concentrations of 130 μmol l-1, the aerobic metabolism of Capitella sp. L is not affected. The anaerobic metabolism of Capitella sp. L is not increased at sulfide concentrations <100 μmol l-1. The anaerobic metabolism of Capitella sp. M from the hydrothermal vents is not affected even at higher sulfide concentrations. This study shows that sibling species of the C. capitata complex from different habitats can be differentiated by their ecophysiological characteristics.