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Salem Sound Water Quality

Overall, Salem Sound is a Healthy Estuarine Environment

Understanding the threats to the waters of Salem Sound and finding solutions that benefit the natural resources of our ocean and coast have always been at the heart of Salem Sound Coastwatch’s work. Salem Sound is well mixed due to tidal action with approximately 70% of its total water volume exchanged with each tidal cycle. But at certain times of the year, people ask Salem Sound Coastwatch about the murky, brown water. Monitoring the water chemistry is important for understanding the condition of our natural resources.  

Establishing Salem Sound’s Baseline Conditions

In its early years as Salem Sound 2000, volunteers and staff assisted Massachusetts Division of Marine (DMF) with a year-long study of Salem Sound, which documented the status of marine resources and water quality, last studied by DMF in 1965 (Jerome et al. 1967). These two documents form the baseline for future comparisons.  

In 2010-2011, Salem Sound Coastwatch worked with Professor Brad Hubeny of the Salem State University Geological Sciences Department to replicate DMF’s 1997 water quality testing. Results showed a measurable improvement in water quality since South Essex Sewer District (SESD) was upgraded to secondary sewage treatment in 1998, which reduced the number of nutrients and organic matter entering the Sound.   

The Marine Resources of Salem Sound, 1997 →

Decline in Water Clarity from 1997 to 2011

Questioning whether the eelgrass decline in Salem Harbor was linked with the decrease in water clarity (I.e. increase in turbidity), the partnership between SSU and Salem Sound Coastwatch continued with the Salem Harbor Turbidity Project (2012-2014). Temperature, conductivity, and turbidity were recorded every 15 minutes in Salem Harbor by four buoy suspended sondes. Sediment and water samples were taken from Salem Harbor, South and Forest Rivers, and stormwater outfalls. The most striking finding was that phytoplankton dominated the suspended particulate matter in the water. 

During this time, SSU also took sediment cores, sampling the mud at the bottom of the Sound to piece together the historic record and the geological sedimentary layers of human impacts through land use changes, sewage disposal practices, and industry from pre-European contact to the present. The sedimentary record showed improvements over the past decades since the Clean Water Act of 1972 with reductions in the amount of organic matter in Salem Sound.   

 

Both projects were published in the peer reviewed journals: 

Case Study from Salem Harbor → 

Anthropogenic Impacts on an Urbanized Mesotidal Estuary → 

Understanding the Role of Phytoplankton in Water Quality

The Turbidity Project led to more research into the nature of the suspended organic matter in the Harbor by SSCW and SSU with Mass Bays Partnership’s Healthy Estuary grant funding (2018). This study confirmed the murky water is correlated with phytoplankton blooms, particularly dinoflagellates (Heterocapsa spp). Blooms occur during the summer when Nitrogen (N) is limited, and Phosphorous (P) is in excess.  The highest turbidity and phytoplankton abundance occurs in the inner harbor near Forest River. High turbidity events occurred 60% of the time when N was limited, while only 10% when P was limited. 

More questions arise from this research: what is causing the N/P imbalance in Salem Harbor, and how can it be remediated? Nutrients are necessary to all ecosystems, but in excess, they can increase algal production to potentially harmful levels.

Chlorophyll-a plume – November 2010 processed satellite image (Applied Analysis Inc.)

What’s Causing the Murky Water in Salem Harbor?

Results were explained by principal investigator, Renee Veresh, at the Underwater in Salem Sound Lecture.

Phosphorus Driving Phytoplankton Blooms

To further understand the conditions of ecosystems in Salem Sound, more data was collected in the summers of 2019 and 2020. This research was funded by EPA (2019) and by NOAA Multipurpose Grant (2020). Salem Sound Coastwatch with Mass Bays Partnership and SSU collected data on water quality and seafloor condition to establish how nutrient loads affect the water quality and habitats of Salem Sound. In 2019, an autonomous vehicle, SeaTrac – a Marblehead company, was equipped with a sonde to collect temperature, salinity, dissolved oxygen, turbidity, pH, and chlorophyll (chl-a) continuously (every 10s) over space (transect) and time (tidal). In addition, grab samples of water were taken during both summers and analyzed. The data clearly show the difference in water chemistry from the freshwater of the Danvers River to Beverly Harbor and then the Sound. Phosphorus was highest in the Danvers River, near shore and at the bottom of Salem Harbor. Once again, data indicate that P is driving phytoplankton blooms (high chl-a) and is the essential nutrient for plankton growth in Salem Sound.  

SeaTac Season Average Temperature
SeaTac Average Dissolved Oxygen

The study of the seafloor condition analyzed sediment grain size, which was found to be dependent on its relationship to shore. Stations with coarse material are closest to shore, probably due to wave action that pulls the finer sediments offshore into the Sound. When the benthic invertebrates living in the sediments were examined, we found that shallower areas with waters richer in nutrients and finer sediments had different species from the Salem Sound stations located further offshore with coarser sediment. Abundant important prey for bottom-feeding fishes such as winter flounder, oligochaete worms, and the amphipod – Ampelisca were abundant. These species are subtidal to intertidal species with tolerance to wide temperature and salinity ranges in estuarine waters.  

Our work continues to understand water conditions to protect habitats and marine species. The nature of tidally driven upwellings from the bottom of the Sound to the surface and the source of phosphorus in Salem Harbor are next topics to be studied. 

The water quality, nutrients, and phytoplankton data generated here on trends and conditions in Salem Harbor have filled a critical data gap in the Salem Sound embayment. With this knowledge of phosphorus nutrient loading, associated Heterocapsa activity, and the negative effects of these on the clarity of Salem Harbor’s waters, specific remediation strategies need to be developed for the improvement of Salem Sound’s water. 

What happens on land affects the ocean!

Resources
Clean Beaches and Streams
Eelgrass

Bluefish (Pomatomus saltatrix)

Also known as tailor or snapper elves, blue fish are blue and silver fish with very sharp teeth. Bluefish are schooling fish who feed on the surface of schools of bait fish. Despite their predatorial nature, bluefish are hunted by tuna, sharks, seals, and porpoises. In Massachusetts, bluefish inhabit inshore water from spring to fall before migrating south and offshore in the cooler months. 

Lion's Mane Jellyfish (Cyanea capillata)

Photo by John Tlumacki

Lion’s mane jellyfish are one of the largest varieties of jellyfish, named for its long mane of brown to reddish tentacles that can reach up to 3 m in length. The nematocysts on the lion’s mane jelly are especially powerful and are used to help catch its prey—though its sting can be painful to humans as well! Lion’s mane jellies are also continual swimmers and, when aided by favorable currents, can travel significant distances. 

Atlantic Striped Bass (Morone saxatilis)

Photo by Alex Shure

The Atlantic striped bass is identifiable by its seven to eight horizontal stripes. They can grow up to 5 feet in length, with females generally growing larger than males. Though many Atlantic striped bass live in the ocean, migrating north and south seasonally, they return to freshwater in the spring to spawn. 

Common Moon Jellyfish (Aurelia aurita)

Photo by Sue Scott

Moon jellyfish are almost entirely translucent and feed on medusae, plankton, and mollusks. While they do have short tentacles, their sting has little to no effect on humans as their nematocysts—their stinging cells—are too weak to affect human skin. 

Harbor Seal (Phoca vitulina)

Photo by Amanda Boyd

Also known as the common seal, harbor seals are the most widely distributed pinniped species. When they are not traveling or foraging, harbor seals rest on rocks and beaches to regulate their body temperature, care for their pups, and interact with other seals. They also haul out of the water to avoid predators. In addition to natural predators, harbor seals are threatened by human actions, including habitat degradation, contamination, vessel collisions, and marine entanglement.  

Rockweed (Ascophyllum nodosum)

Photo by Kare Telnes

Rockweed is a species of brown algae that grows on hard surfaces, including dock pilings, rocks, and shells. In addition to providing sheltered habitat and serving as a food source for other species, rockweed also helps to regulate dissolved CO2. This process assists in managing water quality. 

Eelgrass (Zostera marina)

Eelgrass provides a range of ecosystem functions, including improving water quality, storing carbon, preventing erosion, and providing habitat and shelter for other marine life. Degradation to eelgrass beds has primarily occurred due to development, dredging, and pollution, but efforts are currently being undertaken to restore eelgrass populations to Salem Sound. 

Atlantic Horseshoe Crab (Limulus polyphemus)

Photo by Tracy Barbaro

Despite their name, horseshoe crabs are not actually crabs! They are actually arthropods and are more closely related to spiders or scorpions. Horseshoe crabs have a range of suitable habitats depending on what point they are in their life cycle, with mature adults generally residing up to the edge of the continental shelf unless mating. Horseshoe crabs are also known for their use in the biomedical industry, as their blood is used to test equipment and supplies for bacteria. Likewise, the species is regarded to be particularly vulnerable to climate change regarding temperature, acidification, and sea-level rise. 

Atlantic Sea Scallop (Placopecten magellanicus)

Photo by NOAA Fisheries

Atlantic sea scallops are generally found at depths of 18 to 110 m and often aggregate in beds on firm sand, rock, and shells. They are one of the most commercially important fishery species, with Massachusetts being one of the primary harvesters. Scallops feed on phytoplankton and small organisms, helping to improve water quality through filtration. 

American Lobster (Homarus americanus)

Photo by Oceana

The American lobster is the largest species of lobster which lives on the sea floor in habitats that provide shelter such as seagrass beds, reefs, and mud. These lobsters support some of the most valuable fisheries on the Atlantic coast, however their population faces challenges due to environmental changes, particularly regarding temperature. 

Razor Clam (Ensis leei)

Photo by David S. Johnson

The razor clam is easy to identify due to its long thin shell. This shape paired with their strong muscular foot makes the razor clam an especially mobile bivalve species who can burrow very deep into the sand. The motion used to burrow also allows razor clams to swim or jump through the water to escape from predators, or to find more suitable conditions. Despite their mobility, razor clams often inhabit nearshore areas, which makes them susceptible to pollutant contamination. 

Northern Moon Snail (Euspira heros)

Photo by Alex Shure

Moon snails are highly predatory snails who can grow to about 10 cm long and who are identifiable by smooth shells marked with a whorl. They are known to hunt slower mollusks, drilling a round hole into the shell of their prey. When moon snails reproduce, females burrow beneath the surface of the sand, coats her foot in a layer of mucus to bind together the sand and eggs, and leaves behind a “sand collar” which can sometimes be spotted on the beach. 

Northern Quahog (Mercenaria mercenaria)

Photo by Julie Rose

The quahog is a hard-shelled clam found along the coast from Canada to Florida who has a rich historical connection with Indigenous coastal communities. Today, quahogs are harvested both commercially and recreationally for the fishing industry, though they can only support low levels of fishing. Like other bivalves, quahogs are filter-feeders who remove excess nutrients and improve water quality.

American Oystercatchers (Haematopus palliatus)

Photo by Rob Sabatini

The American oystercatcher is a large shorebird who feeds on marine invertebrates. While they are not a common species along Massachusetts’ coasts, their population is increasing as their habitat range expands due to climate change and habitat availability, though is also speculated that these shorebirds are re-occupying habitat lost during European colonization rather than newly expanding their range. Like many other coastal birds, the American oystercatcher is threatened by habitat loss due to climate change and development, and has been designated as a Species of High Conservation Concern.

Piping Plover (Charadrius melodus)

Photo by Lorraine Minns

Massachusetts is a breeding hub for these iconic birds who are threatened both federally and statewide. Nesting on beaches and dunes, they experience threats due to development, human disturbances, predators, and stormtides, all of which decrease suitable habitat or curtail breeding success. Though the piping plover is protected under the Endangered Species Act, rising sea-levels and storm events driven by climate change continue to be a threat to plover populations. 

Blue Mussel (Mytilus edulis)

Photo by Dr. Keith Hiscock

The blue mussel often grows on docks, buoys, and pilings throughout New England. Blue mussel shells are teardrop shaped, and range in colors from black, dark blue, and brown. Mussels are an important species for maintaining water quality as they remove excess nutrients from the water, however they are also likely to be impacted by ocean acidification due to climate change. 

Plumose Anemone (Metridium senile)

Photo by Paul Newland

Also referred to as “fluffy” or “frilled” anemones, this species is found throughout New England, attached to hard surfaces. M. senile catches small organisms floating past, consuming copepods and various larvae. This type of sea anemone is also a protandric hermaphrodite, meaning it begins its life as a male and changes to female as it matures. 

Green Sea Urchin (Strongylocentrotus droebachiensis)

Photo by Robert Bachand

Green sea urchins are named for their green outer shell and usually do not grow larger than 8 cm. Spines on their exoskeletons help to protect against predators, such as crustaceans, seagulls, and certain fish. Generally, urchins hunt at night for algae, marine worms, and kelp, so you’re unlikely to see them out in the daylight! 

Atlantic Rock Crab (Cancer irroratus)

Photo by Robert Bachand

Atlantic rock crabs are native to New England and can be identified by their reddish-brown to light purple color, as well as the presence of nine smooth spines. Rock crabs are known as opportunistic feeders, eating an assortment of food sources depending on what’s available to them. This can include algae, mussels, and other crustaceans. While at one point, rock crabs were seen as a nuisance to fishers—entering lobster traps and stealing bait—there is now a growing industry for rock crab fishing. 

Periwinkles (Littorina littorea)

Photo by Dr. Keith Hiscock

Though you may see periwinkle snails across the coast, they are actually a non-native invasive species in Salem Sound, originally found in Western Europe. They feed on a range of algae and are able to hold water inside their shells to survive when the tide is out, though they are more active when submerged. 

Carolina Sea Lavender (Limonium carolinianum)

Photo by Y. Laskaris/USFWS

Sea lavender is a saltmarsh plant that grows up to 2 ft high and is characterized by small, purple flowers. It is a slow-growing marsh plant, so populations can be depleted quickly when harvested. Sea lavender is fairly widespread throughout Massachusetts but could face threats due to climate change.

Mummichog Killifish (Fundulus heteroclitus)

Photo by Will Parson

Commonly referred to as “minnows,” mummichog killifish are small, silvery fish that live in marshes, tidal creeks, and a few yards offshore who often form large schools. Mummichog killifish feed on a range of marine plants, as well as small crustaceans, fish, and carrion. They’re also an important species for salt marsh food chains, as many larger marine species feed on them. 

Atlantic Marsh Fiddler Crab (Minuca pugnax)

Photo by Will Parson

Though fiddler crabs have historically lived south of Cape Cod, their range has expanded further north in New England due to warming waters. These crabs build burrows in the marsh and are named for their distinctively large claw found on male crabs. While fiddler crabs have previously been thought to have a positive effect on marshes by encouraging plant growth, north of Cape Cod, this has not been the case. In fact, one study found that fiddler crabs damage plants’ roots as they’ve not yet adapted to burrowing animals, thus resulting in a drop in grass biomass. 

Eastern Oyster (Crassostrea virginica)

Photo by Scott Rikard

Eastern oysters are bivalve mollusks whose populations have declined due to overharvesting, habitat loss, and changing conditions due to climate change. Massachusetts oysters are closely associated with history and coastal economies, especially as a prized food source, but did you know that oysters provide environmental benefits as well? As a filter-feeder, oysters help to improve water quality and mitigate the effects of climate change. 

Saltmarsh Sparrow (Ammodramus caudacutus)

Photo by Liam Wolff

The saltmarsh sparrow is a ground-nesting bird whose population is endemic to the salt marshes of the Atlantic coast. The saltmarsh sparrow only breeds in salt marshes, and as climate change continues to degrade the state of marsh habitats, the population of these sparrows is increasingly vulnerable to climate threats, including sea-level rise and storm events.