Do biogenic sulphur compounds in phytodetritus act as cues for deposit-feeder activity? Field experiments and observations on the echiuran worm Maxmuelleria lankesteri

Abstract

In temperate coastal seas, phytodetritus settling from the spring phytoplankton bloom is a potential food source for benthic deposit-feeders. The ability to exploit this seasonally variable resource could be enhanced by sensitivity to chemical cues signalling its arrival at the seabed. The biogenic sulphur compound dimethylsulphide (DMS), a breakdown product of dimethylsulphonioproprionate (DMSP) produced by some phytoplankton species, is a potential candidate for this role. We investigated the behavioural response of a sedentary surface deposit-feeder, the echiuran worm Maxmuelleria lankesteri, to DMS by observations and manipulative experimentation under natural conditions in a Scottish sea loch. Experimental addition of sediment enriched with DMSP-producing phytoplankton caused no significant increase in either the frequency of feeding by M. lankesteri or the rate of sediment ejection from observed burrows. Naturally occurring (DMSP+DMS) content of surface sediment was low during the winter, then peaked in April before declining in May. There was no consistent relationship between this parameter and rate of sediment ejection from M. lankesteri burrows. The results therefore provide no evidence that M. lankesteri uses DMSP or DMS as a stimulus to increased activity. An observed imbalance between the frequency of surface deposit-feeding and sediment ejection from individual burrows remains unexplained.