Small-scale spatial patterns of meiobenthos in the Arctic deep sea

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A variety of analytical techniques were used to quantify and describe small-scale (centimetre to decimetre) spatial patterns of meiofauna taxa, with emphasis on nematode species, at a bathyal site in the Arctic deep sea. Three cores (10-cm diameter) taken from the same multi- corer were each subsampled as 12 contiguous subcores (1.2-cm diameter) for meiofauna and 16 contiguous subcores (0.9-cm diameter) for bacteria (eight subcores) and phytodetritus (chl a and phaeopigment concentration) (eight subcores). Coefficients of variation and the variance component from PERMANOVAwere estimated to compare variability between cores (20-50 cm) versus within cores (≤10 cm). Both methods showed that spatial variation within cores contributed the main part of total heterogeneity for all parameters, while differences between cores were less important. To further investigate distribution patterns at this small scale (≤10 cm), indices of dispersion were calculated and autocorrelation analyses were performed on the complete data set. Abundances of nematodes, nauplii and 65.5% of the nematode species were significantly aggregated at the scale of subcores (2 cm). Nematode species aggregations were discordant on the small scale, suggesting that processes maintaining diversity in the deep sea can be expected to operate at scales smaller than 10 cm. Autocorrelograms suggested that nematode patch sizes were smaller than 4 cm 2 , while adult harpacticoid copepods and nauplii showed aggregations of ca. 9-25 cm 2 and 64 cm 2 , respectively. Significant spatial autocorrelation at the core scale was also observed for 24 nematode species. These species were grouped in ten different spatial patterns according to their scale of heterogeneity. The spatial patterns observed for the meiobenthos were neither explained by the concentration of chloroplastic pigments nor by bacterial densities. Nevertheless, observations on nematode morphology suggest that morphological charac- ters linked to their locomotion and feeding behaviour may be involved in pattern formation. Finally, our data provide evidence that studies based on few replicates to characterise large-scale or long-term patterns of deep-sea benthic communities may be confounded by inadequate assessment of small-scale variability.