Comparison of tidepool phytal ostracod abundance and assemblage structure on three spatial scales

Triplicate samples of Corallina officinalis L. were collected from either s ide of 5 large mid-shore pools on 3 shores in north-eastern England (Ravens car, Filey Brigg and Flamborough) in order to examine the patterns of varia tion in abundance of different ostracod species and in assemblage structure over a range of spatial scales. Three-way nested ANOVA showed that there w as no significant difference in total ostracod abundance at any of the spat ial scales examined. However, the 9 most abundant ostracod species showed d ifferent patterns of abundance at the different spatial scales. Only 3 spec ies showed significant variation in abundance between shores; however, most of the variation was recorded at the between-pool, within-shore level. Sev en species showed a significant variation in abundance between pools nested within shores (100 to 200 m scale), but not from within pools (5 to 10 m s cale). Semicytherura nigrescens showed a significant variation in abundance at the km scale and within-pool level but not between pools, whereas Hirsc hmannia viridis showed a significant difference in abundance at 5 to 10 m s cales, but not at the other scales. There was significant variability in sp ecies richness (i.e. number of species per quadrat) at the km scale, but no t at the other scales. However, there was a significant variability in asse mblage diversity (H') at the km scale and the 100 to 200 m scale, but not a t the 5 to 10 m scale. H' and the number of species per quadrat were signif icantly higher at Filey Brigg than on the other 2 shores. An MDS plot gener ated from a Bray-Curtis similarity matrix showed that the Flamborough sampl es formed a discrete cluster, whereas there was some overlap between the Fi ley and Ravenscar samples. Two-way nested ANOSIM showed that there was a si gnificant difference in assemblage similarity both between shores using poo ls as samples and between pools using shores as samples. SIMPER indicated t hat the absence of S, nigrescens and relative abundance of 2 other species accounted for most of the dissimilarity between Flamborough and the other 2 shores. There was a significant negative correlation between the percent s imilarity and the spatial distance between quadrat pairs. The current study showed that there was considerable Variation in individual ostracod specie s abundance and in the assemblage composition at the 3 spatial scales and t hat overall assemblage similarity decreased with spatial distance between s amples.