Patterns of association between algae, fishes and grey herons Ardea cinerea in the rocky littoral zone of a Scottish sea loch

The distribution of dominant algae, Fucus vesiculosus and Ascophyllum nodosum, the associated fish community, and the spatial and temporal distributions of the main piscivorous predator, the grey heron Ardea cinerea, were studied on the rocky intertidal zone of Loch Etive, a sea loch on the Scottish west coast. Fucus- and Ascophyllum-dominated shores were not distributed randomly around the shore: the latter was especially common along the more sheltered shores and bays and on the finer substratum types. Coverage and frond length of Ascophyllum were greater than for Fucus. Fourteen fish species were caught in the intertidal zone. Numerically, the catch was dominated by four species caught in Fucus- and Ascophyllum-dominated habitats in both winter and summer: Spinachia spinachia, Pholis gunnellus, Taurulus bubalis and Zoarces viviparus. A higher species richness and fish abundance were recorded on Ascophyllum shores than on Fucus ones in both seasons. On Loch Etive, grey herons foraged exclusively in the intertidal zone usually as solitary, well-spaced individuals. The models suggest the number of foraging birds tended to increase with increasing total algal area (i.e. the two dominant species plus Fucus serratus) and with area of Ascophyllum and decreased with increasing area of Fucus and distance from the breeding colony. Adult grey herons showed a preference for foraging in Ascophyllum habitat and first-years showed no preference, suggesting that Ascophyllum-dominated areas are optimal foraging habitats for coastal-living grey herons. One section of shore was particularly important in establishing these habitat relationships: an Ascophyllum-dominated section with the largest intertidal area and where the highest number of foraging adults but no first-years were recorded. Future conservation and management considerations for the rocky intertidal zone should include associated fish communities and their predators, for which this habitat, and Ascophyllum-dominated areas especially, are of particular importance