Abstract
Univariate comparison of the benthos community in the fishery-closed OWEZ Wind farm with that in six regularly trawled reference areas did not show any difference in total abundances, total biomass and total annual production in the 2011-survey, five years after the closure. Also multivariate species composition, biomass, and annual production in OWEZ did not differ from those in the reference areas. The same holds for various relevant groups of species like the most common, the most uncommon, all epifauna, all infauna, the separate taxa and all scavengers. The bivalve Spisula solida was the only species among nine other species specified as being sensitive to trawling that had higher abundances in OWEZ than in two of the reference areas. Shell length of the bivalve Tellina fabula and shell width in the bivalve Ensis americanus was larger in OWEZ than in three of the reference areas, but four other mollusc species reached their largest dimensions in one of the reference areas. Both diversity indices, Shannon-Wiener and Simpson index, pointed to OWEZ tending to have a higher diversity, higher number of species and higher eveness than two of the reference areas. In general, Triple-D sampling targeting larger-sized, longer-lived in- and epifauna resulted in more differences between OWEZ and the reference areas than boxcoring.
There is no evidence that the species composition in OWEZ when comparing 2007 (one year after the closure) and 2011 (five years after the closure) has changed relative to that in the reference areas. The distinction observed in all areas between the years 2007 and 2011 was mainly due to relatively small variations in species abundances and not caused by the introduction of new species or species loss. Total numbers of individuals, total biomass, and diversity in OWEZ were not different from the values in the combined reference areas in and between 2003, 2007, and 2011.
Five years after the closure to fisheries of OWEZ only subtle impact on the local benthos community can be measured. The faunal patchiness steered by local factors, the depleted adult stocks in the wider region, and a limited time for recovery (5 years) might have delayed the recovery of OWEZ. It cannot be excluded, however, that the higher species diversity, the higher abundances of Spisula solida, and the larger sizes of Tellina fabula and Ensis americanus found in OWEZ relative to those in (some of) the reference areas is a first step towards the recovery of the local benthos community.