Simulating growth and environmental effects in bivalve shellfish

Aquaculture of suspension-feeding bivalve shellfish (i.e. mussels, oysters, cockles, clams, scallops) is among the fastest-growing of all food-producing sectors, with increasing pressure to model sustainable practises. Such modeling is complicated by observations that filter-feeding and metabolism in shellfish are highly responsive to fluctuations in temperature, salinity, food availability and food composition, as frequently occur in near shore environments where most such aquaculture takes place. These physiological adjustments affect growth of the individual. By influencing the relative biogeochemical fluxes of different particles and nutrients, they also affect ecosystem processes.

Only by modeling the complex set of feedbacks, both positive and negative, whereby suspension-feeding shellfish interact with ecosystem processes, such as may include stimulation of primary production by the nitrogen excreted from shellfish, can one realistically hope to assess environmental impacts of and capacities for culture. To account for the complexity of associated processes and their consequences in variable environments, there has been a need for dynamic simulations that use mathematical equations to define functional inter-relationships between the component processes.

Three main challenges in modelling these interactions include to:

  1. identify the environmental variables, and in particular the components of available food, with significant effects on shellfish physiology;
  2. resolve the main interrelations, not only between environmental variables and physiology, but also between separate physiological processes, towards a common model structure that may be calibrated with a different standard set of parameters according to species and/or location; and
  3. integrate these relations within practicable tools that may be used to resolve animal-environment interrelations in real time at scales from individual to community, whether in a farm or natural system.

Typical required applications for such tools are to help quantify:

  1. effects of environmental change on shellfish growth, condition and population dynamics;
  2. optimal culture practices, habitat conservation and/or shellfish restoration plans, whether in terms of species composition, seeding times, seeding densities, spatial distributions etc;
  3. potential environmental carrying capacities for natural and cultured shellfish;
  4. both positive and negative influences of shellfish upon ecological processes and environmental status (i.e. water quality);
  5. nitrogen or carbon credits for nutrient trading; and
  6. financial considerations for profit maximisation and aquaculture insurance.

ShellSIM has been developed to help meet the above requirements by Dr. A. J. S. (Tony) Hawkins of Plymouth Marine Laboratory, as a cost-effective tool for use by farmers, regulators, teachers and scientists.