SPAT SETTLEMENT OF THE GIANT SCALLOP, PLACOPECTEN-MAGELLANICUS (GMELIN, 1791), AND OTHER BIVALVE SPECIES ON ARTIFICIAL FILAMENTOUS COLLECTORS COATED WITH CHITINOUS MATERIAL

Based on previous studies showing that both passive (flow around filam entous and ramose organisms) and active (selection towards chitin in t he perisarc of dead hydroids) processes may be involved in the settlem ent of scallop larvae on natural substrata, we examine here the possib ility of using artificial filamentous material coated with a thin film of chitinous material to maximize spat collection of the giant scallo p, Placopecten magellanicus, on artificial collectors. Chitinous mater ial from different sources (hydroid perisarcs and prawn, crab, and lob ster exoskeletons) was purified and transformed, and used to coat Netr on(R) netting. Two types of collectors were used in three different fi eld experiments, The first type of collector consisted of 13 g of Netr on(R) netting (15 mm mesh size), coated with a thin film of chitinous material, placed in 10 mm mesh cubic Vexar cages (10 X 10 X 10 cm), Th is type of collector was used in the first two experiments, respective ly designed to test(1) the effect of the type (source) of chitinous fi lm as well as (2) the combined effects of the type of chitinous film, the number of layers of chitin on the netting, and the surface texture (roughness) of the chitinous film. A third experiment was carried out with collectors made of 150 g (wet weight) of perisarc of dead hydroi ds Tubularia larynx placed into 10 cm cubic Vexar cages. Perisarcs wer e processed using various physical and chemical treatments to examine the stability of the cue(s) responsible for the settlement of scallop larvae and other associated bivalve species. A total of 110 collectors was placed in the water near Tongue Shoal. Passamaquoddy Bay, New Bru nswick, Canada on 8 September 1994 and retrieved on 30 October 1994. T hese spat collectors were successful in collecting large numbers of sp at of the giant scallop (8179 individuals) and other bivalve species ( 65 739 individuals). There was a significant positive effect of type o f chitinous films on the mean number of spat of each bivalve species c ollected including the giant scallop P. magellanicus. Over 66% more bi valve and 35% more giant scallop spat were collected in the Netron(R) collectors coated with chitinous films compared with control collector s (Netron(R) without any coating). On the contrary, in collectors othe r than controls, we observed no significant effect of the types of chi tinous films (prawn, hydroids, crab, lobster) and no consistent patter n of variation in spat recruitment among collectors offering different numbers of layers of chitin and surface textures (roughness). Finally , spat of scallop and other bivalve species were recruited in higher n umbers (N spat.g(-1)) on 'Hydroid' compared with 'Netron(R)' collector s. Among the 'Hydroid' collectors there was an occasional lower recrui tment with bleached hydroids but no significant differences in the num ber of spat collected by the hydroids which were either not treated, d eproteinized or boiled.