Influence of environmental factors on burrow irrigation and oxygen consumption in the mudflat invertebrate Urechis caupo

We examined burrow irrigation activity by the mudflat worm Urechis caupo in response to suspended food, ambient hypoxia (down to 3.3 kPa PO2), hydroge n sulfide exposure (up to 100 mu mol l(-1)), and short-term temperature cha nge (range 10-22 degreesC). In normoxic, nutrient-free water at 14 degreesC , O-2 consumption ((M)over dotO(2)) was 45 nmol min(-1) g(-1) water flow ra te ((V)over dot (W))was 27 ml min (0.66 ml min(-1) g(-1)), frequency of per istaltic waves (F-P) was 2.6 contractions min(-1), stroke volume (SV) was 1 1 ml, and O-2 extraction coefficient (EO2) was 0.27. Adding suspended food to the burrow water occasionally elicited stereotypical feeding behavior bu t had no effect on any measured variables during nonfeeding periods. Hypoxi a greatly decreased (M)over dotO(2)(75% reduction at 3.3 kPa PO2) but did n ot affect (V)overdot(W), F-P, SV, or EO2. Sulfide at 50 mu mol l(-1) or les s had no effect on burrow irrigation activity, whereas 100 mu mol l(-1) sul fide decreased (V)over dot(W) by 58% and F-P by 50% but had no effect on SV . Temperature strongly affected (V)over dot(W) (Q(10) of 1.9 from 10 degree sC to 22 degreesC). We propose that U. caupo's ability to live in the hypox ic, sulfidic mud of productive mudflat environments, combined with its very efficient mucous net, allows it to process much less water for feeding tha n other suspension-feeding invertebrates. This, in turn, necessitates an ef ficient O-2 extraction mechanism, which is provided by the water lung activ ity of U. caupo's unique hindgut.