SETTLEMENT OF LARVAE OF THE GIANT SCALLOP, PLACOPECTEN-MAGELLANICUS (GMELIN), ON VARIOUS ARTIFICIAL AND NATURAL SUBSTRATA UNDER HATCHERY-TYPE CONDITIONS

Multi-choice experiments on larval settlement of the giant scallop, Pl acopecten magellanicus (Gmelin), in response to various artificial and natural substrata were conducted in a 1000-1 plastic tank to determin e what conditions optimize larval and spat collection under a normal, hatchery-type environment. The first experiment tested a variety of su bstrata (many of which have been previously used in bivalve spat colle ction studies) including the following: (1) nylon monofilament of diam eters 0.50, 0.75, 1.10, 1.50, and 2.00 mm (N.B. the 0.50-mm diameter m onofilament was tested with and without a marine microbial film at the beginning of the experiment (designated as 'filmed' and 'non-filmed', respectively) whereas all other monofilament treatments and the artif icial substrata to follow lacked a microbial film at the start of the experiment), (2) polyethylene onion bag material, (3) polyethylene Ast roturf, (4) smooth and roughened clear acrylic plastic, (5) polyester aquarium filter-wool, and (6) filmed and non-filmed adult giant scallo p shells. Standardized for surface area, filter-wool collected signifi cantly more larvae and spat than any other non-filmed substratum (Stud ent-Newman-Keuls (SNK) test, P less than or equal to 0.05). There was no significant difference among all other non-filmed substrata in numb ers of larvae or spat collected (SNK test, P greater than or equal to 0.05). Filmed 0.50-mm diameter monofilament and filmed adult shell col lected significantly more spat than their respective non-filmed counte rparts (SNK test, P less than or equal to 0.05). A second experiment e xamined settlement on various types of polyethylene meshes (Vexar) inc luding the following mesh sizes (mm): 3.0, 3.0 x 11.0, 3.8, 7.0, 11.0, and 19.0. All substrata were black except the 3.0-mm mesh which was g reen. Standardized for surface area, the 3.0-mm mesh collected signifi cantly more larvae and spat than any of the other mesh sizes (SNK test , P less than or equal to 0.05). There was only one other significant pairwise comparison of numbers of spat collected, 3.8-mm mesh collecte d significantly more spat per unit surface area than 11.0-mm mesh (SNK test, P less than or equal to 0.05). Polyester filter-wool, which was by far the best substratum for spat collection, is inexpensive and re -usable and could make an excellent settling material for use in hatch eries.