At Lough Hyne Marine Reserve in SW Ireland, shallow subtidal, under-rock biodiversity was investigated
to assess (i) any deleterious effects of scientific sampling and (ii) quantitative baseline community
patterns. Comparisons were made between 10 sites with annual rock-turning disturbance and 10 with
multi-decadal (historical) disturbance. At each site, shallow subtidal rocks (N ¼ 1289 total) were lifted,
organisms recorded, and rocks replaced in their original position. Biodiversity indices were calculated to
evaluate how diversity varied with location within the lough, frequency of sampling disturbance, degree
of hypoxia/anoxia, dissolved oxygen (DO) concentration, and number of rocks turned. The richness of
solitary invertebrates surveyed in situ averaged 21 taxa per site with significantly more in the South Basin
(near the lough's connection to the ocean) than in the North Basin. The Shannon-Wiener Index did not
differ significantly with variables investigated. However, evenness was higher at annually disturbed sites
than at historical ones where anemones with algal symbionts often dominated. Several sites were
hypoxic to anoxic under the shallow subtidal rocks. Cup corals were most abundant in the South Basin;
DO was a crucial explanatory variable of these sensitive species. Solitary ascidians were most abundant at
South-Basin annual sites with DO levels being a highly significant explanatory variable.