THE WELL-DEFENDED BRACHIOPOD: YOU DON'T HAVE TO TASTE BAD TO LIVE WELL

While many organisms exhibit greater diversity in the tropics, some taxa, for example modern brachiopods, were once far more widespread (e.g. during the Paleozoic) and are now found primarily in temperate or polar latitudes. It has been argued that intense predation in the tropics restricts brachiopods to refugia such as cryptic habitats, deep water or atropical latitudes; this hypothesis assumes that brachiopods are vulnerable to predation, and that predation on brachiopods is high. However, Thayer (1985) suggested that brachiopods may have evolved a mantle toxin as a defense against predators. To explore brachiopod palatability, we collected three of the most abundant invertebrate predators – seastars (Pycnopodia helianthoidea), crabs (Cancer productus) and gastropods (Fusitriton oregonensis) – as well as brachiopod (Terebratalia transversa) and bivalve (Chlamys hastata, Clinocardium nuttali, Acila castrensis) prey, from depths of 35-70m at Iceberg Point, Puget Sound, WA. These predators and prey co-occur in situ. A series of 26 laboratory feeding trials were conducted, in which brachiopods and bivalves were offered alternately to each predator. At least one individual from each predator species consumed a minimum of two brachiopods without adverse effects. Although brachiopods were clearly consumed by predators, they may not be preferred prey; overall, bivalves were consumed in greater numbers by all three predators (84% of bivalves were consumed versus only 37% of brachiopods). In fact, modern brachiopods may be far better defended than previously thought due to: (1) low profitability (relatively small amount of tissue available for consumption), (2) tight articulation, (3) some internal tissue not easily digested i.e. pedicle and lophophore, and (4) no permanent gape. Therefore, while some terebratulides may not be toxic (or predators may be capable of tolerating the toxin), these brachiopods have other defenses and may be considered by predators to be unattractive prey. These results are inconsistent with the hypothesis that an increase in predation pressure through time resulted in the restriction of brachiopods to regions where predation pressure is low.