M. Harvey, E.Bourget, N. Gagne-1997
Aquaculture, 148: 277-298
Abstract:
Based on previous studies showing that both passive (flow around filamentous and ramose organisms) and active (selection towards chitin in the perisarc of dead hydroids) processes may be involved in the settlement of scallop larvae on natural substrata, we examine here the possibility of using artificial filamentous material coated with a thin film of chitinous material to maximize spat collection of the giant scallop, Placopecten magellanicus, on artificial collectors. Chitinous material from different sources (hydroid perisarcs and prawn, crab, and lobster exoskeletons) was purified and transformed, and used to coat Netron netting. Two types of collectors were used in three different field experiments. The first type of collector consisted of 13 g of Netron netting (IS 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). This type of collector was used in the first two experiments, respectively designed to test (1) the effect of the type (source) of chitinous film 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 hydroids Tubularia larynx placed into 10 cm cubic Vexar cages. Perisarcs were 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 IIO collectors was placed in the water near Tongue Shoal, Passamaquoddy Bay, New Brunswick, Canada on 8 September 1994 and retrieved on 30 October 1994.
These spat collectors were successful in collecting large numbers of spat of the giant scallop (8179 individuals) and other bivalve species (65 739 individuals). There was a significant positive effect of type of chitinous films on the mean number of spat of each bivalve species collected including the giant scallop P. magellanicus. Over 66% more bivalve and 35% more giant scallop spat were collected in the Netron collectors coated with chitinous films compared with control collectors (Netron without any coating). On the contrary, in collectors other than controls, we observed no significant effect of the types of chitinous films (prawn, hydroids, crab, lobster) and no consistent pattern 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 numbers (N spat/g) on 'Hydroid' compared with 'Netron' collectors. Among the 'Hydroid' collectors there was an occasional lower recruitment with bleached hydroids but no significant differences in the number of spat collected by the hydroids which were either not treated, deproteinized or boiled.
(GIROQ, Departement de Biologie, Universite Laval, Ste-Foy, Quebec, GIK 7P4, Canada)
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