Identifying factors influencing suspension feeding to optimize culture of the purple-hinge rock scallop, Crassadoma gigantea

Award Period
to
Award Amount
$45,789
Agency Name
UC San Diego
Award Number
A/EA-29
PI First Name
Carolyn
PI Last Name
Culver
CO-PI
Henry Page
Area/s of Research
Ecology and Evolution
Marine Conservation, Policy and Education
Natural Marine Resources
Abstract

Effective and efficient culture of aquatic species requires an understanding of complex abiotic and biotic factors that influence their reproduction and growth. Once key parameters are identified, culturing systems can be designed to maximize production. In particular, determining factors influencing gametogenesis is essential for producing reliable and consistent sources of seed. Also, identifying parameters that affect feeding efficiency is critical for optimizing reproduction and growth.

Traditionally culture of suspension feeders has relied upon methods developed for oysters and/or clams. These species live in low flow environments, such as embayments or protected coastal habitats, often at or near the bottom of the bay or seafloor. Application of culture methods used for these species may not be appropriate for culturing suspension feeders that thrive in different habitats, particularly those that experience high current flow. Diets and feeding behavior vary among suspension feeding species, depending on habitat. Phytoplankton, zooplankton, dissolved organic matter, and particulate organic matter are utilized to varying degrees depending on availability, the nutritional requirements of a species and the particle sizes they can consume, and feeding efficiency is affected by water flow rates.

Current bottlenecks with culture of the purple-hinge rock scallop Crassadoma gigantea, a native west coast species that often is associated with high flow habitats, may be associated with these factors. In particular, commercial production of seed remains a bottleneck due to unreliable spawning, and successful fertilization and larval metamorphosis. Researchers and growers west coast-wide are reporting the same problems. Animals brought into the laboratory directly from the field will readily spawn within the first few weeks. Yet, after several weeks in the laboratory scallops either won't spawn or, if they do, the resulting gametes are less viable with low fertilization and poor embryonic development. Unlike for other bivalves, feeding rock scallops large amounts of microalgae (either alive or as a paste) has not resulted in high gamete production indicating key broodstock conditioning factors are missing. Similarly, larvae that are produced often don't survive metamorphosis despite using well-established bivalve culture methods.

Many factors are known to contribute to gametogenesis and metamorphosis in bivalves, including quality and quantity of food, temperature and photoperiod. Laboratories are exposed to ambient light and water temperatures similar to those in the field, suggesting these factors are less likely to adversely affect scallop gametogenesis and metamorphosis in the laboratory. Instead, we hypothesize that food quantity, food quality and/or water flow may not be optimal to support rock scallop broodstock conditioning and metamorphosis.

We propose to investigate factors associated with feeding and diet to develop effective and efficient methods for maintaining healthy broodstock and achieving successful larval metamorphosis of rock scallops. Our research objectives are to: 1) identify the size and type of particles comprising the diet of scallops in the field; 2) determine key functional groups and species comprising scallop diet required for gametogenesis and metamorphosis; and 3) evaluate the effect of water flow on gonad development and settlement of larvae.

To achieve objectives one and two, we will collect water samples and scallops at offshore platforms and piers where scallops thrive. We will quantify phytoplankton and levels of dissolved and particulate organic matter in the water samples to determine the amount and type of food that is available to the scallops. Phytoplankton composition will also be determined from scallop gut content and this will be compared to what is available to identify key items comprising scallop diet in the wild. The gut content will be visually evaluated using a compound microscope with phytoplankton species enumerated. Because some species of phytoplankton may be difficult to identify, we also will analyze the gut content using DNA metabarcoding techniques to identify key functional groups and species where possible. Trials using adult broodstock and late stage larval scallops will be run, with reproductive condition and settlement recorded respectively.

Results from this study will be used to develop culture protocols for rock scallop. These protocols will be made available to west coast growers and researchers through outreach materials and workshops and conferences as possible. Results also may serve as a model for investigating key requirements for other potential native aquaculture candidates {e.g., gooseneck barnacles) from high flow areas.