Influence of dumped munition on the benthic macrofauna: Relation to munition object proximity and explosive compounds...

German waters contain around 1.6 million tons of dumped munition spread in coastal areas of the North and Baltic seas. The current study investigated the effect of sea-dumped munitions on benthic macrofauna at the WWII-era dumpsite, Haffkrug (Lübeck Bay, Baltic Sea). A total of 68 samples were taken using 0.1 m² van-Veen grab along three transects in the southern part of the munition dumpsite, sieved through a 1 mm sieve and fixed in formalin. All taxa were identified, counted and weighted. Additionally, a set of environmental variables was analyzed, including continuous and discrete sediment parameters, obtained with multibeam echosounder (distance to individual munition items, depth and morphological derivatives) and direct sample measurement (grain size and munition compounds content). Random Forests algorithm applied to the dataset revealed that depth and, to a lesser degree, distance to munition items shaped the abundance, biomass and diversity of the benthic community. Specifically, the model predicted elevated abundance and biomass in the proximity of the munition. A possible reason for the distance influence is that munition shells and crates represent hard substrata, which is otherwise rare in the Lübeck Bay region. The modelling revealed five different benthic communities in the study area. Munition compounds in the sediment showed no significant influence on the overall structure of macrofauna. However, the abundance of at least two species - polychaete Spio goniocephala and crustacean Diastylis rathkei - were strongly positively correlated with TNT content in the sediment, although the reasons for this are unknown.