Impact of munition dumpsites on the benthic macrofauna in the western Baltic Sea

Abstract

The German waters of the North and Baltic Sea contain over 1.6 million tons of dumped munition, mostly left after the first and second World Wars. Some of the dumpsites consist of old mines and shells containing TNT, which is known to have toxic effect on marine organisms. The objective of this study was to investigate whether the structure and composition of benthic macrofauna is influenced by the munition.Two munition sites were chosen in the western Baltic Sea – Kolberger Heide (=‘KH’, Kiel Bay) and Haffkrug (=‘H’, Lübeck Bay). Samples were taken with 0.1 m2 van-Veen grab (two replicates per station), sieved through 1 mm sieve and fixed with formalin. Stations were taken at several areas near the munition dumpsites, each time arranged in two short parallel transects with ~100 m step (6-10 station per area). In addition, samples in the background areas away from munition were taken. A total of 19 stations (37 samples) were taken in ‘KH’ and 25 stations (50 samples) were taken in ‘H’. Environmental values used in this study included depth, TNT-content in bottom water layer, distance from the maximum concentration of the munition objects, latitude and longitude.A total of 118 taxa were found in ‘KH’ and 121 taxa in ‘H’. Abundance and biomass values varied among the samples greatly in both areas (from 10 to 1730 ind. 0.1 m-2 and from 0.09 to 155.37 g wet weight 0.1 m-2 respectively), although the dominant taxa were similar in all samples, including polychaetes Scoloplos armiger, Pygospio elegans, Dipolydora quadrilobate and Lagis koreni and gastropods Peringia ulvae.In ‘KH’ notably higher abundance and biomass values were observed in the control sites, while the diversity expressed in different indices (Shannon index, Rarefaction curves, Pielou’s evenness etc.) was relatively higher in the munition sites. According to the canonical correspondence analysis, species and samples were grouped along two axes, roughly corresponding to the larger TNT content and shallower depths. Linear mixed-effect model showed statistically significant values for TNT content vs. Shannon diversity index with negative linear relation.In ‘H’ the results were different with no clear abundance biomass or diversity relations to the environmental factors. However, this can be connected to a different munition distribution within the Lübeck Bay, which is more dispersed through the area, without such clear concentration area as in ‘KH’. Further possible conclusions will be discussed.