The effect of marinas on the infaunal communities in Zostera marina meadows and in unvegetated sediments

Abstract

The aim of this study was to investigate the effects from marinas on infaunal communities in Zostera marina meadows and in adjacent unvegetated sediments. The results from the study showed that Z. marina meadows supported a lower infaunal diversity than unvegetated sediments. However, no direct effects from marinas could be detected. Low infaunal diversity in meadows may be explained by high organic loadings, hypoxic and sulfidic sediments, and the chemical and physical disturbances commonly associated with the activities at marinas.

Sediment samples for fauna, grain size and chemistry from two locations close to marinas and two locations remote from marinas in the Oslofjord, Norway were analysed. A total of 1535 individuals were found, representing 33 taxa and comprising mainly the groups Insecta, Polychaeta, Oligochaeta and Gastropoda. The gastropods represented 53 % of all individuals encountered, followed by insects (22%) and oligochaetes (18%). The polychaetes were the most taxa rich group (10 taxa), followed by crustaceans (6 taxa) and gastropods and bivalves (both, 5 taxa).

There could not be detected a direct negative effect from marinas since locations remote from marinas had higher contaminant loadings than locations close to marinas. The most contaminated stations were dominated by taxa typically for polluted areas. Investigations of the differences in infaunal composition and contamination patterns between Z. marina meadows and unvegetated sediments, indicates that infauna in Z. marina meadows were more affected by contaminants than infauna in unvegetated sediments. Considering their importance, more emphasis should be put on the seagrass ecosystem in coastal management. Relative simple and low cost installments, such as sediment catch basins may be effective in reducing contaminant loads to seagrass meadows.