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Aquaculture: More Info


Beggiatoa are infauna (aquatic animals) that live in the substrate of a body of water, especially in a soft sea bottom.

The release of large quantities of nutrient-rich organic matter into the sea is one of the most widespread human impacts on the marine environment. There are several circumstances in which this can occur:

  • Discharge of sewage from coastal outfalls
  • Larger-scale dumping of treated sewage sludge at offshore sites
  • Release of organic effluent from industrial sites (pulp mills)
  • Sedimentation of feces and uneaten food around fish farms

Typically, a moderate input of organic matter can enhance the abundance and diversity of the benthic (sea bottom) fauna by increasing the supply of food. But as the organic load increases, the faunal diversity declines and the sea bottom becomes increasingly dominated by a small number of hardy, opportunistic species, usually polychaetes (marine worms), which may become very abundant.

In grossly polluted situations, even these animals decline and the bottom becomes covered by a whitish blanket of bacteria (Beggiatoa) which obtain energy by oxidizing sulfide diffusing out of anoxic (oxygen-depleted) sediments.

The threshold levels at which these successive stages occur will be determined by temperature, sediment type and local hydrography. Where organic matter is released into the sea from a point source (a salmon cage or sewage outfall), a gradient of faunal and sedimentary change will be produced, with progressively more impacted conditions found closest to the source.

Environmental monitoring of nutrient loading in Maine

Governor's Task Force on the Planning and Development of Marine Aquaculture in Maine
January 30, 2004


Aquaculture has the potential to cause undesirable impacts to surrounding ecological health and biological communities. Although there is limited evidence that marine aquaculture in Maine has caused any significant long-term impacts to the ecological health in the vicinity of farms, there is legitimate concerns that, without proper constraints and the use of prudent husbandry practices, aquaculture can cause significant short and long-term negative impacts on the environment. The most significant risk to the environment and biological communities comes from finfish aquaculture which, since there is active feeding of the animals, is considered to be causing a discharge to the water. To minimize the potential impact of discharges and other features associated with finfish aquaculture operations, the DMR implemented a rigorous monitoring program in partnership with the DEP over 15 years ago. This program, the Finfish Aquaculture Monitoring Program (FAMP) has been funded by a $0.01/lb tax on landed Atlantic salmon and has provided a mechanism for regular assessment of the surrounding water quality and the benthos in the immediate vicinity of salmon pens. Using a combination of water sampling, benthic sampling, and video surveillance, the FAMP has provided baseline information for new installations, and has provided the basis for action by the agency and the farm operator to either improve husbandry practices or to relocate the pen to a more appropriate site. At present, a new waste permit to address discharges from marine finfish aquaculture facilities (Maine Pollutant Discharge Elimination System or MEPDES) is being implemented. This new permit will require more sampling however, at present, it is unclear how this new permit and monitoring protocol will be implemented by the State, how these permit conditions will relate to the FAMP, and what role the industry will have in the process.

How this Topic was Studied

A combination of white papers, expert panels, stakeholder discussions, comments from the public, field trips and laws, regulations and policies were studied and considered. The Task Force was especially interested in identifying problems and concerns specific to Maine and what changes to aquaculture regulations and management should be made to mitigate and/or prevent them.

A. Nutrient Enrichment

Aquaculture operations, by their nature, result in high concentration of animals in relatively close quarters resulting in higher levels of waste byproducts being discharged in an area. Although these nutrients occur naturally and are necessary for plant and microbial life, in excess, they can enrich the water column to a point where oxygen depletion, nuisance and harmful algal blooms, and species shifts cause undesirable impacts to other species and uses. Both finfish and shellfish aquaculture alter the nutrient dynamics of a waterbody, but finfish aquaculture has a greater effect than shellfish due to the fact that finfish culture requires an input of material (feed) not already present in the local system. Coastal nutrient enrichment due to aquaculture emerged as a concern to the state over a decade ago and has been the focus of monitoring efforts.

Limited work has been conducted in Maine to assess the biological carrying capacity of the bays and to determine how much cumulative impact might be occurring when several operations occur in a given waterbody. Evidence from biological oceanographic studies indicates that in some locations such as Cobscook Bay, the greatest contribution of nutrients to our coastal waters comes from offshore in the Gulf of Maine. In other places, nutrient inputs are derived from anthropogenic sources that are delivered to coastal sites from riverine and other land-based sources. Aquaculture is just one of several other contributors of various nutrients to the coastal waters including: atmospheric deposition, non-point source runoff, municipal sewage treatment facilities, industries, watercraft.

Advances in oceanographic modeling may provide tools in the future for assessing the potential impact for aquaculture operations, but these models require the input of area-specific information that is expensive to acquire and not readily available. Therefore DMR relies on monitoring programs rather than models at this time.

Polyculture has the potential to reduce the impact of nutrient enrichment from finfish farming. Raising finfish that release nutrients alongside shellfish and marine algae that remove nutrients, results in less net loading to the environment. Polyculture in New Brunswick shows promise and could be applied here in Maine.


  1. Nutrient enrichment from aquaculture is not currently causing ecological harm. However, there is insufficient data to determine whether nutrient enrichment may be causing effects such as shifts in phytoplankton community composition, increases in benthic algal production, and exacerbating harmful algal blooms (HABs).
  2. Aquaculture is not the only source of nutrients to a waterbody. Private property owners, atmospheric deposition, municipal, recreational, and industrial discharges and even natural sources all contribute to the nutrient budget of a waterbody.
  3. Aquaculture is dependent on clean water and is potentially vulnerable to other types of pollution. Certain areas of the coast are closed to aquaculture due to pollution.
  4. The implementation of the MEPDES discharge permit will address nutrient enrichment from finfish aquaculture.


IX.1. Support research to study and assess whether specific relationships exist between finfish aquaculture and phytoplankton community shifts, HABs, and benthic algae (see Section X.B, recommendation 2b). Additional studies should be supported to determine if aquaculture discharges can be managed through polyculture or other means.

IX.2. Explore incentives in the leasing process for aquaculturists to employ methods such as polyculture to reduce nutrient enrichment.

IX.3. The Task Force requests that the Legislature charge DEP to review discharge permits to marine waters to ensure that cumulative impacts from all sources to the receiving water are considered.

IX.4. Maine should continue to support efforts by DMR and DEP to remove all sources of pollution along Maine's coast.

B. Organic Enrichment (Solids)

Both finfish and shellfish aquaculture result in organic material being deposited on the bottom. While shellfish deposition is mostly a result of active metabolism of naturally occurring phytoplankton, solids from finfish can appear considerable. The impact of organic loading has been the subject of many scientific studies which has resulted in the development of several predictive models. Impacts follow the classic Pearson-Rosenberg model of enrichment. First, the number of individuals and number of species increases followed by shift to a few opportunistic species in great numbers. Left unchecked, the system progresses to near azoic[1] conditions. Researchers have found that impacts are generally confined to the area beneath the pens, and are temporary (on the order of months to several years) with recovery beginning immediately after organic loading is reduced. Rarely do the impacts extend more than tens of meters beyond the pen shadow.


  1. Available evidence indicates that organic loading to the bottom from aquaculture is confined to the lease site, reversible and not serious.
  2. Maine has in place policies, standards and permits to monitor for and prevent unreasonable adverse impact from organic enrichment.


IX.5. DMR and DEP should continue to manage aquaculture in a manner that will maintain a diverse benthic species composition and confine impacts to the immediate lease area.

IX.6. Support applied research with the industry to develop effective Best Management Practices[2], standards, and monitoring regimes.

[1] Azoic is a condition in which animal life is absent.
[2] Best Management Practices (BMPs) are husbandry practices designed to maximize efficiency and minimize external impacts. In the case of finfish aquaculture, examples include the use of underwater cameras to monitor feed usage, regular inspections of nets to prevent escapement, etc.

Background Papers Related to Coastal Nutrient and Organic Enrichment in Maine (* specific to Maine aquaculture).

Brooks, D.A., and D.W. Townsend. 1989. Variability of the coastal current and nutrient pathways in the eastern Gulf of Maine. J. Mar. Res., 47, 303-321.

Costa-Pierce, B.A. 2002. (Ed.) Ecological Aquaculture: the evolution of the blue revolution. Blackwell Science, Oxford UK.

*Findlay, R.H. and L. Watling. 1994. Toward a process level model to predict the effects of salmon net-pen aquaculture on the benthos. p. 47-77. In B.T. Hargrave [ed.] Modelling Benthic Impacts of Organic Enrichment from Marine Aquaculture. Canadian Technical Report of Fisheries and Aquatic Sciences 1949: xi +125p.

Garside, C and J. Garside. 2005. Nutrient sources and distribution in Cobscook Bay, Maine. Northeast Naturalist. In press.

Sowles, J. 2001. Nitrogen in the Gulf of Maine; sources, susceptibility and trends. in Worshop Report-2001: Managing nitrogen impacts in the Gulf of Maine. Prepared by the NOAA/UNH Cooperative Institute for Coastal and Estuarine Environmental Technology, the Gulf of Maine Council on the Marine Environment, and NOAA's Ocean Service.

*Sowles, J.W. and L. Churchill. 2005. Predicted nutrient enrichment by salmon aquaculture and potential for effects in Cobscook Bay, Maine. Northeast Naturalist. In press.

*Sowles, J.W. 2005. Assessing Nitrogen Carrying Capacity for Blue Hill Bay, Maine - A Management Case History. In: Hargrave, B.T. (ed.) The Handbook of Environmental Chemistry - Volume 5 Water Pollution: Environmental Effects of Marine Finfish Aquaculture. Springer-Verlag, Heidelberg.

*Sowles, J., L. Churchill, and W. Silvert. 1994. The effect of benthic carbon loading on the degradation of bottom conditions under farm sites, p. 31-46. In B.T. Hargrave [ed.]. Modelling Benthic Impacts of Organic Enrichment from Marine Aquaculture. Can. Tech. Rep. Fish. Aquat. Sci. 1949: xi + 125p.

Townsend, D.W., J.P. Christensen, D.K. Stephenson, J.J. Graham, and S.B. Chenoweth. 1987. The importance of a plume of tidally-mixed water to the biological oceanography of the Gulf of Maine. J. Mar. Res. 45, 699-728.

Townsend, David W. 1991. Influences of oceanographic processes on the biological productivity of the Gulf of Maine. Reviews in Aquatic Sciences 5 (3-4):211-230.

Townsend, D.W., N.R. Pettigrew, and A.C. Thomas. 2001. Offshore blooms of the red tide dinoflagellate, Alexandrium sp., in the Gulf of Maine. Continental Shelf Research. 21: 347-369.

National Science Foundation Maine Department of Inland Fisheries and Wildlife Maine Forest Products Council Irving Woodlands, LLC Desiree Carlson, M.D. More Connected. More Maine.

Major funding is provided by the National Science Foundation.
Additional funding is provided by the Maine Department of Inland Fisheries and Wildlife, Maine Forest Products Council, Irving Woodlands LLC., Desiree Carlson, M.D., and gifts to More Connected. More Maine, The Campaign for Maine Public Broadcasting Network's Programming.

A list of other funders includes:
The Davis Family Foundation, Margaret E. Burnham Charitable Trust, and Lincoln Ladd.

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