Physiological changes accompanying the presence of black gill syndrome in the high shore amphipod Traskorchestia traskiana

• Black gill disease in talitrids affects osmoregulation not O2 uptake.
• O2 uptake and osmoregulation can occur at extrabranchial exchange surfaces.
• The idea that beachfleas have distinctive gill area distributions is false.
• Black gill disease may physiologically limit the local distribution of talitrids.

This is the first record of black gill syndrome in a natural population of amphipod crustaceans, the supralittoral beachflea, Traskorchestia traskiana and in what follows is the investigation of some of the physiological changes accompanying this condition. Gill area and structure of individuals not displaying the syndrome were very similar in total gill area to other (European) beachflea species, but different in the way that area was distributed among the gills. Affected individuals displayed a marked browning, blackening, or even loss, of some or all of the gills. Rates of O2 uptake in affected (> 70% of gill surface visibly altered) individuals were not significantly different from controls (i.e. individuals with no visible alterations in gill structure or color). Neither did experimental gill excision significantly affect rates of O2 uptake. By contrast individuals with black gill syndrome, and individuals with experimentally excised gills, displayed poorer osmoregulatory ability in reduced salinities. As there was no elevated metabolism in affected individuals, it is suggested that the main physiological consequence of black gill syndrome in this high shore amphipod is compromised osmoregulatory ability. The gills appear to be more important for ion exchange than for O2 uptake (at least when the beachflea is at rest). Black gill syndrome could exclude T. traskiana from some high shore or brackishwater environments, limiting its local distribution in an area.