Environmental Impact on Razor Clams

Project Description

The razor clam (Ensis directus) has been identified as a potential candidate for commercial aquaculture operations in New England and has been successfully grown on a small scale in Maine. For grow-out operations of razor clams to be successful, razor clams will need to be planted in an estuary, where they will be exposed to the environment. In order for the razor clam industry to continue to develop, studies are needed on their immune system and response to chronic environmental changes. These changes include increasing temperature and highly acidic sediments known as “dead muds.”

Clammers and scientists have discovered that few soft shell clams can be found in these dead muds as the pH is too low; it dissolves their shells. It is unknown whether the conditions in these dead muds impact razor clam health.

To achieve project objectives, researchers are measuring the pH and alkalinity at various depths in the sediments at the collection site in Beals, ME at least once per month for a year and three months. Researchers are establishing the baseline immune capacity of the species by sampling razor clams from the site every month for a year and a month. Researchers will run bacterial challenge trials on clams kept in tanks that replicate the razor clam’s natural environment. Parameters measured to assess immune capacity will include total cell counts and differential cell counts.

After being exposed the marine bacteria Vibrio anguillarum for 3 hours, researchers will measure phagocytosis rates, cell viability, and relative phenoloxidase content. All exposure to bacteria will be done directly to hemolymph (blood) after it has been extracted from the clam. After the seasonality of the species’ immune capacity has been established, researchers will expose adult razors separately to “dead mud” conditions and elevated temperatures for a month-long period before subjecting them to the bacterial stage. The results from the baseline and environmental manipulation trials will be compared to determine if low pH and elevated temperature have an impact on the razor clam’s immune capacity.

Results and Accomplishments

The pH of sediment taken from Beals Island was monitored in 20-gallon lab aquaria containing artificial sea water at cold (6.5°C) and warm (24°C) temperatures over a period of 74 days. Each sediment bed had a depth of about 15cm and porewater samples were taken via syringe at the top, middle and bottom of the sediment column every 2 to 3 days. The effects of razor clam shell hash were tested using a different set of sediment beds for 41 days. The results show that surface sediment porewater pH can be adjusted to a value below field measurements (~6.0) or kept at a value close to field measurements (~7.0) for month-long periods by manipulating the amount of time, temperature, and shell hash the sediment bed is exposed to.

This can be done while keeping the pH of the overlying aquaria water at ~8.0. The method is not reliable for experiments lasting longer than a month at 24⁰C, since the pH started to increase around day 24. Longer acidification experiments could be done at 6.5⁰C, given the pH at the sediment surface in that group did not start increasing until day 65. The accompanying total alkalinity data is currently being analyzed so the aragonite and calcite saturation states for these measurements can be calculated.

Summary of Data Being Collected

Data	Type	Quantity	Location
Animals	Mass, Length	80	Beals, ME
Sediment	pH, temperature, total alkalinity	9	Beals, ME