The successful growth, propagation and harvest of aquatic animals, whether freshwater or marine, is heavily dependent upon the quality of the surrounding water. The presence of toxic chemicals (i.e. metals, petroleum products, etc.), overloading of nutrients (i.e. untreated, partially treated sewage, point source discharges, non-point source discharges), atmospheric deposition (i.e. lead from internal combustion exhaust, acid rain) artificial or uncontrolled temperature variations (i.e. power plant cooling water) and algal decomposition all degrade water quality. Degradation of water quality eventually results in lower concentrations of dissolved oxygen, contamination of fish, shellfish, and substrates with heavy metals, toxic chemicals, and disease-bearing pathogens.

The die-off of indigenous shellfish populations due to coastal development, shrinking habitats, and pollution through both point- and non-point source discharges, contributes to the descending spiral in water quality. Bivalve filter feeders, such as oysters, clams, quahogs, scallops, and mussels, represent one of the more efficient, natural, available bio-filtration systems. Filter feeders relative to their size, strain enormous quantities of nutrients and algae from the surrounding water. This process helps to maintain and improve water quality. Once die-off or other forms of population depletion begins, so does an associated increase in nutrients and algae and a resulting decrease in water quality.

Coastal Development

The effects of coastal development on shellfish-growing areas is indicated by the increasing acreage degraded by anthropogenic pollution sources from 1985 to 1990. For example, the largest increases are attributed to urban run-off, impacting 23 to 38 percent of harvestable Massachusetts waters. [Division of Marine Fisheries]. The acreage adversely affected by faulty septic systems increased from 22 percent to 37 percent during the same time period. Pollution from septic systems is associated with continuing residential growth, as well as pressure from the increase in tourism and vacation home development. Also indicative of accelerating pressures from coastal recreation is the increase in waters adversely affected by boating, up from 11 to 18 percent (National Shellfish Register, 1991).

Physical alteration of the coastal environment (dredging and filling; erosion and siltation; damming and/or diversion of streams; constriction of estuary mouths by bridges and causeways; construction of malls, shopping centers and housing developments on the waters' edge) has also had a significant negative impact. Increasing demand for building sites in coastal communities has resulted in destruction of tidal wetlands, an important component of the marine ecosystem that provides a habitat and nutrient source for many species.

Since the late 1950s, disease has taken a heavy toll on shellfish populations already weakened and stressed as the result of degraded water. According to the National Shellfish Register, "Preliminary findings suggest that the ability of shellfish to withstand such infection is compromised by environmental pollutant stresses."

In Massachusetts, shellfish populations have historically been regarded as a public resource available to all. Under such conditions, municipal and state agencies must manage shellfish with only limited public funds, relying heavily upon nature to sustain or enhance these natural populations.

Dr. David Belding pointed out "In the early days, when the natural supply was apparently inexhaustible, and practically the entire population resided on or near the seacoast, it was just that all people should have common rights to the shore fisheries. As long as the natural supply was more than sufficient for the demand, no law could have been better adapted for the public good. Now, it is obvious that nature alone cannot be depended upon to sustain these resources."[Profile of the Shellfish Industry in Southeastern Massachusetts, 1930].

Short and Long-Term Impacts

Acute water quality problems are characterized by sudden,easily recognizable changes in the smell, surface appearance, or turbidity of the water. The most common causes include discharges of chemicals, sudden changes in temperature, the kind of emergency that requires an immediate response; i.e. overturned chemical truck discharging into a receiving stream, an oil spill, etc.

Chronic Water Quality Problems, characterized by low levels of dissolved oxygen, high temperatures, advancing eutrophication, fall-off in indigenous species' populations, are typically caused by frequent, small incidents of water pollution, or "non-point source pollution." The leading probable cause of algal growth, low dissolved oxygen concentrations, salinity and temperature fluctuations, high coliform counts, and resultant lower productivity in coastal shellfish populations are non-point source discharges. [U.S. EPA 1992. The Nation's Water; (OSW No. 24-01-W).

Water Quality Impacts on Coastal Resource Areas

Some of the more noticeable effects of degraded water quality are (1) the die-off of eelgrass and other aquatic vegetation, (2) lower levels of dissolved oxygen, (3) contamination of shellfish beds, (4) and the poisoning of fish larvae.

Constant, low-level pollution results in breaking some of the first links in the food chain and killing off organisms upon which small fish feed, thus reducing the quantity of prey available throughout the food chain. Deprived of food and shelter, the populations and species diversity of fish and crustacea decline. Toxic chemicals accumulate, diseases and abnormalities increase. These consequences move up the food chain with more fish, shellfish, birds, and mammals dying or failing to reproduce. These phenomena are not limited to near-shore areas. Many off-shore species spend a portion of their lifetime in the near-shore environment, or depend upon food produced by coastal systems.

Loss of commercial and recreational shellfish catches because of shellfish bed closures due to high coliform counts are directly correlated with human-generated, point source and non- point source discharges. Poorly flushed embayments are particularly susceptible to pollution of shellfish beds. Areas with combined sewer overflows (CSOs) or a high level of recreational boating are also likely to be closed to shellfishing, at least conditionally for portions of the year [Division of Marine Fisheries].

Shellfish Habitat

Quahogs (Mercenaria mercenaria), oysters (Crassostrea virginica), bay scallops (Argopecten irradians), soft shelled clams (Mya arenaria), surf clams (Spisula solidissima), and blue mussels (Mytilus edulis) are culturally and economically the most important species in Massachusetts. The most prolific beds,whether wild or cultured, tend to be established in coves, bays, and similar areas where fresh water flows dilute the seawater, tidal action is regular, there is a constant supply of food, and protection is afforded from storms and surges. These beds are subject to greater risk from bacterial or chemical contamination and consequent degradation due to their proximity to human settlements.

Tidal flats also provide a home to many of the cultivated species in Massachusetts. These are shallow, sloping areas composed of materials ranging from very fine silt and clay to coarse sands. Microscopic algae provide nourishment for tidal flat life, including quahogs, soft-shelled clams, and polycheate worms. It is the combination of salinity, substrate quality, and the character of water movement over the flats that determines the species composition of the plant and animal communities. (Carlozzi, et al. 1975). Contaminants (i.e. TBT anti-fouling bottom paints used on boats) carried to the flats can be taken up by the microscopic algae and worms living in the flat, accumulate in the substrate, accelerate algal growth, lower the dissolved oxygen available, change total salinity, and in turn, impact the shellfish populations by directly killing them or their food sources, or by contaminating them.

Pathogen Contamination

Measurement of fecal coliform is used as an indicator of the possible presence of disease-causing bacteria and viruses. For example, gastroenteritis, hepatitis, and polio are associated with human waste-borne viruses. Shellfishing is prohibited when concentrations reach 14 fecal coliforms per 100 milliliters. Thousands of acres of productive shellfish beds, representing millions of dollars, have been closed to harvesting in recent years because of potential pathogen contamination. Between 1970 and 1990, closed acreage increased by nearly 300% in Massachusetts and Cape Cod Bays. On Cape Cod, over 550 acres are currently closed, a 90% increase from 1980. Closures on the North and South Shores have also been on the rise. Currently, there are over 7400 acres closed to harvesting on the South Shore, and 56,000 on the North Shore. (Buzzards Bay Project, 1990).

Statewide, out of an approximate 1,800,000 acres of waters under state jurisdiction, 67% (1,199,537) are classified as approved (for direct consumption), 5% (88,887) are classified as prohibited (no harvest of any kind), 28% (498,705) are closed because they are unclassified (lack of sanitary survey) and less than 1% (454 or 1416) are classified as Restricted (harvest with depuration). Unclassified areas are not polluted, but rather areas which have not been surveyed mainly due to lack of shellfish habitat. (Division of Marine Fisheries, 1994)

Shellfish that are not directly killed by the discharge of toxics may take them up, either through exposure to contaminated substrates or through feeding. Many shellfish species have the capacity to bioaccumulate toxics to levels that may kill or damage an organism higher up on the food chain.

For a complete description of public health concerns and shellfish contamination, see Chapter Seventeen, Seafood Safety.

Water Quality Standards

The Federal Water Pollution Control Act, 33 U.S.C. Section 1251 et seq. and the Massachusetts Clean Waters Act, Massachusetts General Law Chapter 21 Sections 26 - 53, require the development and update of water quality standards to restore and maintain the chemical, physical, and biological integrity of the Nation's waters. Massachusetts defines "water quality standards" as the criteria necessary to sustain particular uses of various water bodies, as well as to upgrade the water for prospective, designated uses. Water quality standards are developed and evaluated by the Massachusetts Department of Environmental Protection, Division of Water Pollution Control.

314 CMR 4.00: Surface Water Quality Standards, classifies all of the waters of Massachusetts, inland and coastal, into categories based upon the present condition of the water, prescribes minimal water quality criteria to maintain present water quality, and prescribes "antidegradation" requirements to upgrade water quality.

Categories

The regulations divide surface water into Classes in order to maintain or upgrade the uses available when classified; i.e. drinking water, recreation, etc. For coastal and marine waters, the classifications are as follows (314 CMR 4.03):

Class SA - waters designated for the uses of protection and propagation of fish, other aquatic life and wildlife; for primary and secondary contact recreation; and for shellfish harvesting without depuration in approved areas.

Class SB - waters designated for the uses of protection and propagation of fish, other aquatic life and wildlife; for primary and secondary contact recreation; and for shellfish harvesting with depuration (Restricted Shellfish Areas).

Class SC - waters designated for the protection and propagation of fish, other aquatic life and wildlife, and secondary contact recreation.

Parameters and Criteria for Evaluation

The criteria applied to evaluate and classify coastal and marine surface water are (314 CMR 4.03): overall aesthetics, presence and amounts of radioactive substances, presence and amounts of tainting substances, color, turbidity, amount of total suspended solids, presence and amounts of oil and grease, presence and amounts of nutrients, presence and amounts of other constituents, amount of dissolved oxygen, temperature increase, pH level, amount of total coliform bacteria, and amount of fecal coliform bacteria.

Antidegradation

The regulations require that the present quality of surface water be maintained and protected from degradation. To accomplish this, the following requirements are included at 314 CMR 4.04:

(1) Protection of Existing Uses. In all cases, from and after the date these regulations become effective, the quality of the surface waters shall be maintained and protected to sustain existing beneficial uses.

(2) Protection of High Quality Waters. From and after the date these regulations become effective, waters designated by the Division in 314 CMR 4.05(5) whose quality is or becomes consistently higher than that quality necessary to sustain the national goal uses shall be maintained at that higher level of quality unless limited degradation is authorized by the Division.

(3) Protection of Low Flow Waters. Certain waters will be designated...for protection under 314 CMR 4.04 due to their inability to accept pollutant discharges. New or increased discharges of pollutants to waters so designated are prohibited unless a variance is granted by the Division...

(4) National Resource Waters. Waters which constitute an outstanding national resource...shall be preserved. These waters shall be designated for preservation by the Division.... Waters so designated may not be degraded and are not subject to a variance procedure. Existing discharges shall be eliminated unless the discharger is able to demonstrate that:

(a) Alternative means of disposal are not reasonably available or feasible; and

(b) The discharge will not affect the quality of the water as a national resource.

(5) Control of Eutrophication. The discharge of nutrients, primarily phosphorus or nitrogen, to surface waters will be limited or prohibited... as necessary to prevent excessive eutrophication of such waters... . Existing discharges containing nutrients which encourage eutrophication or growth of weeds or algae shall be treated. Activities which may result in non-point source discharges of nutrients shall be conducted in accordance with the best management practices reasonably determined by the Division to be necessary to preclude or minimize such discharges of nutrients.

Click here to go back to the Table of Contents for The Massachusetts Aquaculture White Paper

Published: September 1995