Temporal Variation in Diversity and Community Structure of a Semi-Isolated Neuston Community

Abstract

Temporal variability in neuston diversity and community structure in Lough Hyne Marine Nature Reserve, Co. Cork, was studied over a two-year period. Neuston sampling was carried out at different time scales in order to make between-year, seasonal and monthly comparisons and, in May 2003, at midday and midnight for six consecutive days to make daily and twelve-hourly (diel) comparisons. Three sampling tracks were established in Lough Hyne, each corresponding to a basin subject to different hydrographical environments. Neuston abundance and diversity (Shannon-Wiener index, H′) were estimated for each timescale, and univariate analyses (ANOVA) revealed significant scales of temporal variation. There was significant monthly variation of neuston abundance within seasons, and this was dependent on site and year: summer months showed highest abundances, whereas lows were recorded in January of both years. Generally, higher concentrations of neuston were found at the two sites with reduced water circulation. Diversity maxima occurred during October and September of the consecutive years. The second sampling year showed greater diversity. At smaller temporal scales there was significant variation in neuston numbers and diversity, which was dependent on site, diel period and day. Higher abundances were generally found at night, whereas nocturnal neuston diversity was not always greater than that at midday. Multivariate analysis identified distinct nocturnal and diurnal assemblages, providing indirect evidence for vertical migration of certain taxa. Seasonal succession was evident, as was interannual variation. The community was dominated by 'temporary neuston' typical of neritic, boreal areas and was in a state of flux.