Lanice conchilega structures carbon flows in soft-bottom intertidal areas

Biogenic reefs constructed by the tube-building ecosystem engineer Lanice conchilega (Terrebilidae, Polychaeta) have profound structuring impacts on the benthic environment by altering the biogeochemical and physical properties of the sediment. This study provides new insights in the functioning of L. conchilega reefs in intertidal sediments by quantifying the carbon flows in the food webs in the presence and absence of the tubeworm using linear inverse models (LIMs); yielding insights in the effects of L. conchilega reefs on food webs. The inverse food web models were based on an empirical dataset from two study sites, consisting of biomass and stable isotope data, and general physiological constraints from the literature. The carbon input into reef food webs (191 ± 50 mmol C m-2 d-1) is about 40 times higher compared to bare sand areas (5 ± 2 mmol C m-2 d-1) and is mainly derived from organic matter (OM) in the water column. Most of the OM input towards these reefs is consumed by suspension feeding macrofauna, particularly L. conchilega, however the worm is not an important source of carbon for other macrofaunal organisms. The ratio of OM input to primary production indicates that the OM needs to be produced in an area at least 15 times larger than the reef area, demonstrating significant OM ‘focussing’ within the reef food web. The reef structures created by L. conchilega act as a trap of OM, resulting in overall high macrofaunal biomass in the presence of the tubeworm, and much more diverse food webs