SUBLETHAL PREDATION - FIELD-MEASUREMENTS OF ARM TISSUE LOSS FROM THE OPHIUROID MICROPHIOPHOLIS-GRACILLIMA AND IMMUNOCHEMICAL IDENTIFICATIONOF ITS PREDATORS IN NORTH INLET, SOUTH-CAROLINA, USA

A daily rate of sublethal predation of arm tissue of the burrowing amp hiurid brittlestar Microphiopholis gracillima (Stimpson) was determine d by experimental field manipulation. A concurrent field predator surv ey documented the ingestion of arm tissue by invertebrate and vertebra te predators. Fish, shrimps and crabs were collected by seining and tr awling in Debidue Creek, North Inlet, South Carolina, USA. Gut content s of these predators were examined both visually and immunochemically to determine presence or absence of arm tissue. Of white shrimp guts t ested, 88% were positive for M. gracillima arm tissue, while 70 % of b lue crab guts and 39 % of brown shrimp guts tested positive. Several f ish species and hermit crab species were found to prey on the brittles tar arm tissue less frequently or in lesser quantities. To determine t he daily sublethal predation rate, individual brittlestars of known ar m length were emplaced subtidally in Debidue Creek, retrieved after ei ther 24 or 72 h, and then had their arm tissue remeasured. Loss of bri ttlestar arm tissue was statistically measurable over a 24 h period re lative to laboratory controls. Brittlestars held for 32 h in the field lost 3 to 4 times more arm tissue than those exposed to predation for only 24 h. An average daily sublethal loss rate of 20 mm arm tissue b rittlestar(-1) was calculated for the late summer/early fall period. T rophic transfer due to sublethal predation on this individual species of brittlestar in Debidue Creek ranges between 3.3 and 9.7 g AFDW m(-2 ) yr(-1), an amount equivalent to total community macrobenthic seconda ry production in other systems.