Marine Aquatic Invasive Species (Marine AIS)

The RI Coastal Resources Management Council (CRMC) first investigated the impact of marine AIS in 2000, by conducting a rapid assessment survey (RAS) in Narragansett Bay, which included thorough documentation of invasive species attached to thirteen floating docks. Floating docks at marinas are hotspots for marine AIS introduction from boats, and introduced species are often prevalent on these artificial structures. Since that time, CRMC has partnered with various agencies to conduct an RAS approximately every three years. The 2013 survey targeted four floating docks in Narragansett Bay and along RI’s Atlantic Coast. The purpose of the RASs is to:

  1. Identify native and introduced marine species,
  2. Expand on data collected in past surveys,
  3. Assess the introduction status and range expansions of documented introduced species, and
  4. Detect new introductions.
Scientists inspecting dock surfaces as part of the Rapid Assessment Survey. Photo courtesy of Mass CZM.

The RAS uses simple manual collection of organisms, such as scraping encrusted organisms from dock surfaces and using nets to sample organisms in the water. Water temperature and salinity are also recorded at the sampling site to determine the ideal or preferred habitat of the marine AIS.

CRMC with the RI Department of Environmental Management (RIDEM), University of Rhode Island, and the RI Natural History Survey developed the RI Aquatic Invasive Species Management Plan that was approved by the federal Aquatic Nuisance Species Task Force in 2007 (RIAIS Plan). CRMC then developed and implemented the Invasive Species Monitoring Project in 2009, which prioritizes the following tasks:

  • Monitoring floating docks for the presence, abundance, and spread of AIS in Rhode Island’s coastal waters.
  • Determining the impact of AIS on native species by investigating larval settlement and competition.
  • Monitoring for the presence of the Chinese Mitten crab by conducting plankton tows in estuarine rivers.
  • Monitoring for the presence of invasive Grass Shrimp at various sampling sites in Rhode Island’s coastal waters.
  • Determining the impact of AIS on eelgrass by sampling eelgrass beds in Rhode Island’s coastal waters.
Measuring an Asian shore crab as part of the NBNERR long-term monitoring program. Photo courtesy of Daisy Durant, NBNERR.

These monitoring tasks will provide the state with a database for marine AIS, and evaluate the impact of marine AIS on native species. CRMC has collaborated with the U.S. Environmental Protection Agency’s Atlantic Ecology Division to investigate the efficacy of remote sensing to monitor eelgrass beds and with RIDEM to address commercial vessel ballast water under the Clean Water Act.  These efforts will provide insight to prevent introductions of marine AIS into the state’s coastal waters. A report summarizing marine AIS monitoring (not including RAS events) from 2009-2016 will be published by CRMC at the beginning of 2018.

The Narragansett Bay National Estuarine Research Reserve (NBNERR) also conducts a long-term monitoring project on Asian shore crabs, aimed at identifying where this species of crab is located throughout cobble beaches in the bay, what physical factors explain patterns in crab abundance, and how this invasive crab impacts beach communities.

Challenges in Invasive Species Management

Managing invasive species in the large, complex ecosystem of Narragansett Bay is a difficult task, which is made even more challenging due to the many unknowns regarding these species and their interactions with the ecosystem. Human travel between Europe and Rhode Island goes back much farther than any comprehensive and detailed biological records of species living in the state. It is unclear whether a few species are native or introduced, which places them in the category of cryptogenic. The 2013 Rapid Assessment Survey identified 13 cryptogenic species in Rhode Island, such as the orange crust bryozoan and the sea vase tunicate.

The Asian Shore Crab, Hemigrapsus sanguineus, has made its way into Narragansett Bay and is aggressively outcompeting native species for food and space. Photo courtesy of CRMC.

The long-term presence of certain introduced species is another challenge to invasive species management. For example, the European green crab, which is not native to Rhode Island, was introduced over 200 years ago. We can observe their current impact on eelgrass beds and soft-shelled clams, but scientific data on the state of eelgrass and clams before the European green crab introduction are sparse.

For other species, the total impact on the ecosystem is unclear. One such species is the Asian shore crab, which, since its introduction in 1988, has significantly impacted some native crab species but not others. Asian shore crabs may pose a threat to lobsters as they eat larval lobsters. On the other hand, adult lobsters and some fish eat the Asian shore crabs. These lobster and fish populations are being impacted by several other factors, including harvesting, climate change, and pollution, so it is difficult to determine what effects can be attributed to the presence of Asian shore crabs.

Overall, it is difficult to predict the long-term relationship between the many different species,—native or not—that live in Narragansett Bay, but the conservative strategy is to prevent introduction of new species with the potential to disrupt the ecological balance, and monitoring is fundamental to prevention.

Freshwater Aquatic Invasive Species (Freshwater AIS)

Scientist inspects artificial substrates in Warwick Pond to detect the presence of zebra mussels as part of invasive species monitoring efforts. Photo courtesy of RIDEM

Monitoring freshwater AIS is in dire need of stable funding from the state. Currently, limited monitoring activities are accomplished through the collaborative efforts of several organizations and programs, such as the RI Department of Environmental Management (RIDEM) on an ad hoc basis and University of Rhode Island Watershed Watch (URIWW), which carries out regular, seasonal surveys of lakes, ponds, and streams where freshwater AIS may be found. As outlined in the Rhode Island Water Monitoring Strategy (RIDEM 2005), invasive species monitoring can be integrated with these efforts and, through training and information sharing, programs can leverage those eyes in the field to identify invasive species, collate information, and alert the most appropriate agency to respond to discoveries of invasive species. With a greater influx of support for RAS monitoring, the invasive could be “cured” as opposed to “chronic” with ever-escalating costs for the health of the ecosystem.

Since 2007, RIDEM Office of Water Resources has surveyed seasonally for AIS in lakes and ponds. General methods involve visually inspecting pond shorelines from a kayak or canoe. Data are collected recording presence or absence of invasive plants and Asian clams, and the extent of the populations are documented. These data are used to produce statewide distribution maps of lakes in Rhode Island that have had one or more detected invasive species.

Freshwater Aquatic Plants in Rhode Island

Three invasive freshwater plant species are of greatest concern in Rhode Island: variable milfoil, fanwort, and water chestnut; variable milfoil and fanwort are the two most common species in Rhode Island freshwater. While water chestnut is currently only present in five Rhode Island lakes, it is defined as a demonstrated nuisance elsewhere in the northeastern United States. Between 1982 and 2011, federal, state, and non-governmental groups spent $9.6 million to control water chestnut in Lake Champlain alone.

Variable milfoil

Variable milfoil is a plant that lives entirely underwater. It is native to the Southeast and Midwest US, and has spread throughout the Northeast largely due to its ability to reproduce by fragmentation in which a single fragment of the plant can grow roots and become established in a new body of water. Milfoil spreads quickly and creates dense stands that crowd out native vegetation, interfere with recreational activities, and create areas well suited to mosquito breeding. Once established, variable milfoil is very difficult to control and virtually impossible to eradicate, which leads to the need for long-term lake management strategies. Handpulling and herbicides are both somewhat effective control measures, but each has its own downside: handpulling is very labor and time intensive with less than 100% effectiveness, while herbicides are less labor and time intensive but involve sprayed chemicals in the water that may have unintended consequences.


Fanwort is another plant that lives underwater, growing in shallow waters less than 30 feet deep. Like variable milfoil, fanwort is native to other parts of the US, but was introduced to the Northeast as an aquarium plant that was inadvertently dumped into ponds and lakes. Fragments can survive six to eight weeks out of the water, allowing easy transfer and establishment from one lake to another on boats and trailers. Fanwort is made more difficult to control because hand-pulling may be effective for small areas, but may also create more fragments that can drift into new areas, become established, and accelerate the plant’s spread. Herbicides can also be effective, but potential side effects need to be fully understood before implementing on a broad scale.

Water chestnut

Water chestnut was introduced to New York from Europe as an ornamental plant, and is also native to Asia and Africa. It typically spreads by dispersion of seeds on feathers of waterfowl, such as ducks and geese. Water chestnut grows in thick mats on the water’s surface thereby reducing available light for native plants growing under the surface. These mats impede recreation and can decay quickly reducing oxygen in the water, which may lead to fish kills. Water chestnut seeds remain viable for 12 years making control difficult; even if a population is eradicated, over a decade of monitoring is required to ensure that this invasive does not return. In Rhode Island, water chestnut was first documented in 2007, growing in Belleville Pond in North Kingstown. Though currently only established in five lakes in the state, the struggles of other states to control water chestnut demonstrates the importance of constant monitoring to prevent acceleration of this problem in our freshwater lakes and ponds.

Implemented By:

Marine AIS

  • Coastal Resources Management Council: Contact— Kevin Cute (401)783-3370,
  • Rhode Island Department of Environmental Management
  • Rhode Island Natural History Survey
  • University of Rhode Island Watershed Watch
  • Narragansett Bay National Estuarine Research Reserve

Freshwater AIS

  • Rhode Island Department of Environmental Management:
  • Rhode Island Natural History Survey: Contact—David Gregg, (401)874-5800,
  • University of Rhode Island Watershed Watch
  • Save The Lakes
Inflated bladderwort affecting the quality of the Wilson Reservoir in Burrillville, Rhode Island. Photo courtesy of RIDEM.