IMIS

Two replicatedly sampled multicorer stations were compared as to their species-level alpha diversity values of all adult Harpacticoida in single cores. This was done by a newly developed procedure: based on a rank-ordered alpha diversity matrix, using each a species richness, evenness, and dominance diversity index, a minimum spanning tree test (MST-test) was performed to test for significant diversity differences between the replicates of stations 325 (depth: 5448 m) and 346 (depth: 5389 m). The Canberra Metric was used as a measure of dissimilarity between multicorer deployments. With this procedure, any choice of combination of diversity indices can be made, according to the desired emphasis on certain aspects of diversity. This freedom of choice, together with the possibilities to test for significant diversity differences and to visualize this test, are desirable features of the presented procedure for diversity comparisons. Testing for diversity differences may be useful in the context of conservational purposes when politicians need clear statements from scientists.

Due to sufficient replicates, for the first time a significant diversity difference between two abyssal (>2000 m depth) multicorer stations was detectable. Station 346 (eight replicates) was significantly more diverse in harpacticoid species than station 325 (seven replicates). Regional-scale differences in food availability are assumed to be of importance for the different patterns of diversity at stations 325 and 346.

The slope of the line of regression in a species/individuals plot on single-core level was not far from (R² = 0.990:y = 0.887x, indicating that most species were represented by singletons and the rest only by very few specimens.

The data supported scale-dependent differences of harpacticoid diversity in the Angola Basin. Local-scale (between replicates) differences in harpacticoid within-core species diversity were lower than regional-scale (between stations) differences.