MACROALGAE AS A REFUGE FROM PREDATION FOR RECRUITS OF THE MUSSEL CHOROMYTILUS CHORUS (MOLINA, 1782) IN SOUTHERN CHILE

Settlement of the mytilid, Choromytilus chorus, in the Marine Reserve of Mehuin, Chile, occurs on three different types of filamentous struc tures: (1) the filamentous alga Gymnogongrus furcellatus; (2) the byss us of adult Choromytilus; and (3) the byssus of the small mytilid Semi mytilus algosus. Observations made in permanent plots suggest that onl y the individuals that recruited on the red alga, G. furcellatus, had a high probability of survival. The main agent of post-settlement mort ality was the predatory whelk Nucella crassilabrum. Laboratory feeding trials show that the whelk prefers the small sizes of this mussel (1 to 3 cm in length) and above this size the mussel is largely free from whelk predation. Field observations confirm that mussel recruits rema in attached to this alga for approximately a year and then they become fixed to the rocky substratum. A field experiment was done to test wh ether the alga did indeed provide a refuge from whelk predation. Survi val of mussel recruits that had settled naturally on artificial collec tor was monitored. An artificial collector (Gymnogongrus imitation mad e with plastic nets) that was attached at only a single point to the s ubstratum, restricted access of Nucella, and produced a correspondingl y high level of survival among the mussel recruits. Alternately, an ar tificial collector fixed to the substratum at several point, allowed f ree access to Nucella and mussel survival was significantly lower. The se result indicate that Gymnogongrus provides Choromytilus recruits wi th a short term refuge from predation. By restricting access of the wh elk Nucella, Gymnogongrus allows Choromytilus recruits to reach a size at which Nucella is no longer a threat, ensuring the successful attac hment of Choromytilus to the primary substratum. This algal refuge has important implications for the structure and dynamics of the Choromyt ilus rocky shore community.