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Marine Invasives

Marine Invasives and Their Impact

Biological invasions have emerged as one of the leading environmental threats to our coastal and marine habitats. Marine invasives are species that have been moved beyond their natural geographic range, either deliberately or unintentionally, by human activities. These introduced species often reproduce in large numbers and outcompete native species for food and space. With no natural controls to keep their numbers in check, these invaders can have damaging effects on our local waters.   

Salem Sound's Marine Invaders

More than 60 marine invaders have been documented in New England waters. Scroll through their “mugshots” to get to know the common marine invasive species in Salem Sound. Click on their photo to access an ID card to learn how to identify them, their origins, and their impact on the marine environment. 

Marine Invaders on the Move - Underwater in Salem Sound 2024
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Marine Invasives Species Monitoring

Invasive species are considered second only to human development in causing declines in the total number of species in the U.S. and worldwide, and millions of dollars are spent in control efforts. Therefore, Salem Sound Coastwatch monitors marine species at docks, in tidepools, and along the rocky shore every summer with the help of community science volunteers. We are a founding member of the Marine Invader Monitoring and Information Collaborative (MIMIC) and share our data with MA Coastal Zone Management, along with other groups in ME, NH, MA, and RI. 

Salem Sound Coastwatch has documented new species moving into Salem Sound with the help of our volunteers. 

Palaemon elegans (European rock shrimp) were first found in 2010 at a dock in Salem and at the same time were collected during salt marsh monitoring at Salem’s Forest River marsh and Gloucester’s Good Harbor marsh. This was the first sighting of this shrimp in North America. They are easily distinguished by their blue claws. 

Several algae have moved into Salem Sound recently. Colpomenia peregrina (Bladder Weed), a bubble-shaped, hollow seaweed that floats on the water’s surface, moved south into our region in 2013. Grateloupia turuturu (Red Algae), a red, slimy seaweed, moved north into Salem Sound in 2018 and has increased in abundance since then. 

Marine Invasives Species Monitoring in New England Story Map
A Citizen’s Guide to Monitoring Marine Invasive Species
Volunteers participate in Marine Invasive Species Monitoring in tidepools on Winter Island.
Participants in Marine Invasive Species Monitoring of tidepools on Winter Island.

We train volunteers to be the eyes on the water. Let us know if you want to participate in our summer dock and intertidal rocky shore monitoring. Help us collect information about the location, abundance, and characteristics of non-native and native species along our shore.   

Sign Up as a Volunteer!

SETL Project

In 2007, we joined the SETL Project, an international effort to detect and quantify fouling marine organisms, by placing settlement plates at the Beverly Harbor Pier. Every three months, the plates are pulled and examined for fouling organisms that have colonized the plates, then scraped and returned to the water. We thank Cell Signaling Technology for providing funds to purchase the materials for the initial deployment. 

What happens on land affects the ocean!

Stormwater Practices
River Initiatives

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.