Effects of cold winters and climate on the temporal variability of an epibenthic community in the German Bight

Abstract

Benthic epifauna was sampled in an area of 10 ×10 nautical miles in the German Bight. Samples were collected in January and July/August from 1998 to 2007 with a standard 2 m beam trawl. The epibenthic communities were severely affected by the cold winter in 1995-1996, which also resulted in high abundance and biomass of the opportunistic brittle star Ophiura albida, in connection with low diversity observed at the beginning of our study period. In the following years winter bottom temperature increased simultaneously with the decrease of O. albida and the increase in abundance and biomass of other species. It appears that these changes were caused by trophic interactions as well as mild winters, which resulted in lower mortality, higher reproduction and higher food supply for benthic fauna due to enhanced primary production. Additionally diversity increased and species such as Astropecten irregularis, Corystes cassivelaunus, Crangon crangon and Crangon allmanni revealed distinct seasonal patterns caused by migration, mortality and reproduction cycles. The changes in community structure are discussed in relation to the general warming trend of the North Sea, which is linked to a phase of continuously increasing North Atlantic Oscillation Index (NAOI) since the late 1980s. We found evidence that climatic variability influenced recruitment success, mortality and migration patterns of epifaunal species.

Climate-induced changes in the North Sea Decapoda over the last 60 years

“…Similarly, Rees et al (2007) noted increases in the abundance of mud shrimps in the benthos in parts of the North Sea. An established relationship between temperature and the abundance of benthic invertebrates in the southern North Sea (Neumann et al 2008) also agrees with our findings on larval abundance (Kirby et al 2008). However, the appearance of a similar relationship elsewhere may be influenced by regional hydrographical conditions such as stratification (Neumann et al 2009a), which can also influence the vertical distribution of larvae (Lindley et al 1994) with effects on the results of single depth sampling with the CPR.…”

Common trends in German Bight benthic macrofaunal communities: Assessing temporal variability and the relative importance of environmental variables

“…Surface salinity varied largely during the study period but had no noticeable effect on the long-term dynamics of the benthic macrofauna. This might be partly due to the fact that salinity variations are much lower in the benthic environment of the deeper waters studied here and to the ability of most benthic taxa to cope with variations in salinity (Neumann et al, 2008). However, we should not preclude indirect effects induced by planktonic processes, which are more directly influenced by surface water salinity fluctuations and which are beyond the scope of this study.…”

Loss of persistence of the North Atlantic Oscillation and its biological implication

“…Changes in benthic community structure and functional diversity after 1988 were found for the entire North Sea (Neumann et al, 2008(Neumann et al, , 2009Neumann and Kröncke, 2011;Schückel et al, 2010;Kröncke, 2011;Kröncke et al, 2011). The RS 1988/1989 was detectable in 39 variables in the North Sea (Schlüter et al, 2008) and in 52 biotic and abiotic variables in the Baltic Sea (Möllmann et al, 2009).…”