|The effect of the ecosystem engineer Lanice conchilega reefs on the Baltic Tellin Limecola balthica in the Dutch Wadden Sea|
Verbeek, E. (2017). The effect of the ecosystem engineer Lanice conchilega reefs on the Baltic Tellin Limecola balthica in the Dutch Wadden Sea. NIOZ Royal Institute for Sea Research: Texel. 19 pp.
The Sand Mason worm Lanice conchilega has shown to be an important ecosystem engineer by building polychaete tubes composed of sand and shell fractions. An aggregation of these tubes skims the water flow, which induces descending of small particles and elevates the degree of aggregation. These aggregates are called reefs, and provide refuge from predators, competitive species, physical and chemical stresses and function as nursery or spawning habitats. Lanice conchilega reefs generally relates to a higher biodiversity which making them of pivotal importance to the marine benthic ecosystem. Limecola baltica, also known as the Baltic Tellin, is common in all intertidal areas and is an important food source for many wadingbirds. The number of bathic thellins has severely decreased since 1996. This study examined if Limecola baltica benefits from the Lanice conchilega reefs by analysis of three years (2008, 2009 and 2014) obtained from sampling data from the synoptic intertidal benthic survey (SIBES). The purpose of the study is to find an effect of Lanice conchilega reefs on Limecola balthicaby finding significant differences in numbers, depth, biomass and quality of the bivalve Limecola balthicainside and outside a reef. This study could help showing the importance of the preservation of the Lanice conchilega reefs, and with that the whole benthic ecosystem. Around 4500 benthic samples were divided over a 500 metre grid over the entire Dutch Wadden Sea and the macrobenthos (>1mm) were determined, measured and counted in the laboratory. A number of 200 or more Lanice conchilega individuals per square metre was classified as a reef, and Limecola balthicaindividuals were classified to be in the “top” if they were found in the upper 4 centimetres of the sediment and in the “bottom” in case they were found deeper. Limecola balthicaspat (<8 millimetre) were left out of the data analysis. The results show significant higher numbers of Limecola balthicainside a Lanice conchilega reef in all the three years (p<0.05). Higher biomass rates (ash free dry weight: AFDW) of Limecola balthicaspecies were found inside a reef, two out of three times significant (p=0.039; p=0.055; p=0.018). In addition, the quality (biomass/length ratio: AFDW/shell length) of Limecola balthicaindividuals was significantly higher in all the three years (p<0.035). Furthermore, Limecola balthica numbers were found to be at least two times higher in the top layer compared to the bottom (p<0.043) and appeared to be in higher numbers in the top and bottom layer inside a reef compared to outside a reef. However, only the data of 2014 was significant (p<0.001). As a result, Lanice conchilega reefs showed to have a clear positive effect on average number, biomass and biomass/length ratio (quality) of Limecola balthica. Research shown that these two species do not compete in diet, but the cause of this positive relation stays unclear, so more (experimental) research is needed.