Preliminary Investigations into Adhesion Culture Techniques for Bay Scallops
Richard C. Karney, Shellfish Biologist/Director
Martha's Vineyard Shellfish Group, Inc.
Tasks Completed as of November 7, 2001.
Identify and Order Adhesives
After extensive research on the internet, a number of adhesives were selected for trials: Pacer Thick Gel Super Glue, On-Hand Adhesives Inc. Super Tack/High Profile Glue Dots, 3M Marine Adhesive Sealant Fast Cure 5200, and three epoxy adhesives: Aquastik stone gray Epoxy Putty, Aquatic Eco-Systems Inc. Sweetwater Epoxy Gel, ADTECH Plastic Systems EA-604 Fast Cure Epoxy Adhesive System.
We selected and purchased the plastic netting to which the scallops would be attached. It is an ADPI Durethene Netting (BOP-2L) and has an approximate mesh size of 2 ¼ "x 2 ¼ ".
Lab Test Adhesives
On July 17th 2001 the staff of the MVSG organized a trial to test three of the treatments: Pacer Thick Gel Super Glue, Aquastik stone grey Epoxy Putty, and Aquatic Eco-Systems Inc. Sweetwater Epoxy Gel. For each treatment, empty scallop shells where soaked in seawater and then blotted dry to remove as much moisture as possible. The adhesives were then applied on each shell and the shells attached to the intersections of the strands of a section of netting (14" x 17"). The adhesive was allowed to set in the air for 15 minutes before the net was placed flat into a pan filled with seawater. Observations were recorded after 24 hours.
-The Pacer Thick Gel Super Glue was fairly easy to apply, the observations during the process were that it probably needed longer than 15 minutes to be totally dry. After 24 hours in the water, it was brittle and 85 % of the shells detached from the net leaving the glue attached to the shell.
-The Aquastik stone grey Epoxy Putty was found to be difficult to work with. It stuck better to hands than to the mesh and shells! After 24 hours, 95 % of the shells had come off the netting.
-The Aquatic Eco-Systems Inc. Sweetwater Epoxy Gel stuck very efficiently to the shells but not to the netting at the first application. However when a lot of it was used and the epoxy surrounded the netting intersections, it gave the best results so far (only 25 % of the shell had separated from the netting after 24 hours) but it was fairly easy to pull the shells from the netting.
In late August 2001 another trial was conducted to test two other adhesives : Super Tack/High Profile Glue Dots and the ADTECH EA-604 Fast Cure Epoxy Adhesive System.
-The Super Tack/High Profile Glue Dots were very easy to handle in all sizes but the glue didn’t harden at all and after 24 hours it was as easy to take them off the shells as it was putting them on.
-The ADTECH EA-604 Fast Cure Epoxy Adhesive System is a two part epoxy (resin and hardener). The two compounds needed to be mixed for 5 to 8 minutes before being applied on the shells and netting. The epoxy changed consistency rapidly, which made it challenging to use but still a good candidate for a larger scale experiment. The optimal method was to put the scallops on a hard surface with the netting intersection on top of them and apply the glue on top of both the shell and the netting. After 24 hours the epoxy was observed to have hardened and it held shells and netting strongly together. 100% of the shells remained on the netting after 24 hours.
By mid September 2001, the hatchery’s first culture of scallops had grown to a size where they could be used in an adhesive trial. In this third trial live scallops were used instead of empty shells. The observations of the previous trials led to the conclusion that the epoxy resins Aquatic Eco-Systems Inc. Sweetwater Epoxy Gel and ADTECH EA-604 Fast Cure Epoxy Adhesive System were the most likely to be successful. An order for another adhesive, 3M Marine Adhesive Sealant Fast Cure 5200 had arrived so it was decided that this new sealant would also be tested with the two epoxies without a preliminary test on empty shells. As in the first trials, the scallops were taken out of the water, blotted dry to remove as much dampness from the shell as possible and after a couple of minutes, glued to the netting with three differents adhesives. With a drying time of 5 minutes for the shells and 15 minutes for the glue, the scallops were not out of the water for more than 20 minutes. The net sections with the attached scallops were then attached flat into afloating wooden nursery cage tied to the dock of the Martha’s Vineyard Shellfish Hatchery.
After 24 hours the results were dramaticly different.
-With the Aquatic Eco-Systems Inc. Sweetwater Epoxy Gel, 25% of the scallops had detached and swam to the bottom of the cage. The rest of the animals separated from the netting easily when pulled.
-The 3M Marine Adhesive Sealant Fast Cure 5200 worked better than the previous one but did not meet our expectations. About 15 % of the scallops detached themselves after 24 hours and like the previous adhesive , it was easy to pull the attached scallops off the net.
-The ADTECH EA-604 Fast Cure Epoxy Adhesive System was the most successful. No scallops detached themselves from the net after 24 hours and the epoxy resisted quite well to pulling. Another trial was set up the day after to test the applicability of the ADTECH EA-604 Fast Cure Epoxy Adhesive System on smaller scallops (5mm to 1.5 cm). This second trial gave the same results. The trial nets were left in the floating box until early November when the state of the adhesive was checked again. At that time, 8% of the scallops had detached from the net and the adhesive had become brittle. The animals could be pulled easily from the netting, except for the ones where the netting intersection was covered with a thick coat of epoxy. In the trial with the small live scallops, 50 % of the animals developed deformed shells, possibly from epoxy toxicity.
Hatchery Culture Scallops
The broodstock scallops were spawned on July 2, 2001. The larvae were grown in aerated conicals until eyed and then set in downwellers in a closed, recirculating system. The larvae were initially fed Isochrysis galbana (Tahitian strain) and later a mixed diet of Isochrysis galbana, Tetraselmis chuii and Chaetoceros gracilis. Post-set scallops were moved to flow through systems of ambient seawater. When the scallops reached 2 mm they were moved into 1.5mm mesh spat bags with Netron and suspended from a long line in Lagoon Pond.
The scallop shells and the live scallops used for the experiment were about 2.5 cm length. When the best adhesive was identified, another experiment was set up with smaller live scallops (5 mm to 1.5 cm).
Because an adaquate adhesive was not identified in the initial trials, the large scale experiments have been postponed until the spring of 2002. In the interim, we will try to find a usable adhesive. Seed scallops produced this season will be overwintered to be used in next year’s experiments. We plan to deploy five sections of netting , 5 x 50 feet, in each of five towns. The nets are to be suspended from ropes in long line fashion, supported by floats and anchored at two points. Approximately 27,000 scallops will be needed to load the five nets. Assuming an overwintering mortality of about 50 %, 50 000 scallops are being overwintered in ADPI bags in bottom cages tied off the dock of the Martha’s Vineyard Shellfish Group Hatchery.