Benthic fish guilds in the shallow sublittoral zone of Lough Hyne, Co. Cork, Ireland

The fully marine Lough Hyne in south-west Ireland was designated a marine nature reserve in 1981 because of its high species and habitat diversity as well as intense fishing pressure. Considerable research has described the fish species in the Lough, their behaviour and distributions. Following the population demise of purple urchins in the Lough, the fish communities inhabiting the shallow sublittoral zone, particularly benthic and hyperbenthic fishes, which could be potential predators of sea urchins, were characterised. Three sites were chosen in different parts of Lough Hyne that historically supported dense urchin populations. In August to September 2014, fish density was estimated by snorkel surveying 50m band transects, noting water depth, habitat type and the number of fish by family for each 5m section. The two-way factorial survey design included time of day (morning, midday, late afternoon) and tide (high vs low) as factors with six surveys per transect. Numerically, gobies were the most abundant benthic to hyperbenthic fish in the shallow subtidal habitats; wrasses were the second most abundant. While all factors of site, tide, time and weather had significant effects on fish densities, site was most significant. This pattern indicated that gobies and wrasses were distributed more according to habitat type than small-scale depth and temporal variations, but further work should be done to elucidate nocturnal-diurnal effects and large-scale, seasonal effects. In the absence of direct evidence of predation effects before and after 1981, coupled with observational and/or gut content data, the role of fish predation as the major causal mechanism of urchin demise in the Lough was not supported.