Small-scale diversity of Harpacticoida (Crustacea, Copepoda) from an intertidal sandflat in the Jade Bay (German Bight, North Sea)

Abstract

Harpacticoid copepod assemblages from an intertidal sandflat in the Jade Bay (German Bight, North Sea) were investigated during a snapshot study, uncovering a relatively high small-scale organismic diversity: 1952 adult Harpacticoida of 32 species were recorded, belonging to 19 genera and 13 families. With 1232 adult specimens (63.1 %), Ectinosomatidae were the most abundant family, containingPseudobradya minor (T. & A.Scott) as the dominating species (57.4 %). For five species,Dactylopusia vulgaris (Sars),Remanea arenicola Klie,Mesochra pygmaea (Claus),Arenopontia subterranea Kunz, andEnhydrosoma gariene Gurney, the distributional range along the German coast line was extended to the area west of the river Elbe. Two species,Arenosetella tenuissima (Klie) andPseudobradya beduina Monard, were recorded for the first time in the Jade region. Most species recorded in our study are typical inhabitants of interridal sandy and/or muddy environments. Taking into account different aspects of diversity (species richness: species numbers, estimated species numbers by Jack-knife 1 and 2, species richness plots; heterogeneity: Shannon index, rarefaction curves; phylogenetic/taxonomic relationship: taxonomic distinctness) we found only minor diversity differences between four investigated small spatial scales (circles from 18 cm to 20 m diameter). Hypothesis [a] stating increasing diversity with increasing scale had to be rejected. This unexpected result could be caused by the presence of a mosaic of more or less randomly arranged micropatches of species over the sampling domain. Obviously, all citcles were more or less within the range of a single ecological scale. A slight diversity change at the 20 m scale, mainly based on lower species density, may be due to changing tide, or to a beginning overlap of small-scale random micropatches by a larger-scale environmental pattern. Since we found only minor diversity changes from the smallest (centimetres) to the largest investigated scale (tens of metres), biotic and/or abiotic factors and processes acting at spatial scales of centimetres are assumed to be of special relevance for intertidal harpacricoid diversity. Hypothesis [b] of no significant harpacticoid assemblage differences between the investigated scales was tested by ANOSIM for two similarity measures, leading to different results. Cosine similarity revealed no significant difference in assemblage composition between all possible pairwise combinations of circles, whereas [b] had to rejected for Bray-Curtis dissimilarity which produced significant results for two pairs (A/D, C/D). The difference between the test results is suggested to be caused by a lower species density in circle D, since Bray-Curtis dissimilarity is separating similar monitoring units if the difference is only due to multiples in abundance (Pfeifer et al. 1998).