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Coastweeks, research paper highlight CRMC aquatic invasive species monitoring efforts
October 26, 2018, WAKEFIELD – Through its specialized monitoring methods, the Rhode Island Coastal Resources Management Council (CRMC) has determined that marine aquatic invasive species are outcompeting native species. Findings collected by the CRMC were recently featured in a research paper, and were the highlight of a Coastweeks session at Point Judith Marina in South Kingstown.
Introduction of non-native species in Rhode Island is not a new phenomenon. European settlers intentionally introduced many non-native plants and animals upon their arrival in the New World. Along with those, settlers also introduced species unintentionally. Rocks used as ships’ ballast discarded in New England’s coastal waters were likely the route for the introduction of some European marine species, including the common periwinkle that covers the rocky shores in Rhode Island today.
An invasive species is defined as a non-native species introduced to an ecosystem within which it demonstrates negative environmental, economic or public health impacts. Regardless of how they land in local waters, they are a threat to marine environments from ecological, economic, and social standpoints, according to a paper recently released by University of Rhode Island graduate student Brandon Fuller, whose research project was based on the CRMC’s Aquatic Invasive Species Monitoring Project..
“Invasive invertebrates occupy nearly every coastal benthic community in New England,” Fuller stated in his paper. “While the locations where introduction takes place are fairly obvious, the transition from introduction to establishment is less understood, since these species often arrive as larvae and their small size makes it difficult to track their dispersion.”
According to Kevin Cute, marine resources specialist for the CRMC, preventing new introductions, monitoring and education are the keys to managing marine invasive species, and preventing the spread of new threats. One of the most proven methods of monitoring is through the use of settlement plates, which have helped in standardizing monitoring efforts and provided valuable information on larval recruitment (the number of settled larvae that survive over a certain period of time), effects of environmental parameters, community structure, and competition.
The CRMC has been conducting larval plate settlement since 2012, and plates are installed at five different sites in Narragansett Bay. The CRMC and its monitoring team check the plates once a month between May and December, and some are replaced periodically and others are left for the entire season.
Fuller’s researches stated that despite having the inherent advantage, native species start out settling in their larval stage at a higher rate but then are quickly outcompeted by invasive species on the settlement plates (this refers to those checked monthly). Monthly and seasonal settlement plate data comparisons also show native species are unable to successfully establish before invasive recruitment rises.
“This suggests that the length of recruitment periods, combined with competition for space and other resources, are likely more important than the timing of recruitment in driving an invasive-dominated community structure,” Fuller said in the paper. (Settlement is defined as the abundance of attached larvae to a material or surface.)
In New England waters, different species of tunicates (sac-like marine invertebrate filter feeders) since the 1980s have posed one of the largest threats to native species and their environment.
“Tunicates tend to settle on hard objects and what we see by examining these plates every month is that the invasives eventually overtake the native species,” Cute said. “What this study is showing us is that clearly natives are being outcompeted.”
Impacts on aquaculture industry
Cute is concerned with the impact to Rhode Island’s aquaculture industry, and hopes to work with members of the industry and CRMC Aquaculture Coordinator David Beutel to research and manage invasives in the coastal ponds and Narragansett Bay. Jeff Gardner, owner of Watch Hill Oysters, said tunicates and crabs are a common observance and nuisance in the coastal ponds.
“We’ve had green crabs for generations, and in the last 10 years, the Asian shore crabs have come into the area,” Gardner said of his lease on Winnapaug Pond. “Asian shore crabs are a pain if they get into the seed bags. They eat the meat inside, so you find a lot of dead shells.”
Gardner confirmed that there are plenty of orange sheath tunicates (Botrylliodes violaceus) and star tunicates (Botryllus schlosseri) in the pond. Vigilance is necessary to keep those from fouling up the gear, though Gardner said he turns his oysters and tends to them often, so the tunicates don’t have much time to colonize on the oysters.
“If you don’t tend your gear, you’re going to have problems,” Gardner said. “You have to brine drip, air dry, redistribute, flip the bags. And if you don’t do those things, you will have an infestation of tunicates.”
Fuller’s research supports this assertion. All tunicates, both native and invasive, are an economic concern for shellfisheries, the gear and product of which is often overgrown with the species, which often kills the oysters and mussels grown in the gear. Most mitigation efforts have focused, Fuller stated, on removing one type of tunicate, Didemnum vexillum, using mechanical and chemical methods – peroxide and anti-fouling paint applied to shellfishing gear; fresh water baths for gear; or letting it air-dry for extended periods of time. D. vexillum directly attached to shellfish can be removed through freshwater rinses, tumbling, and salt brine dips, according to Fuller’s research.
Fuller deducted that as most invasive species are introduced into marine ecosystems via shipping, the locations where introductions take place are fairly obvious.
“What remains more mysterious, however, is the transition from introduction to establishment,” Fuller stated. The use of settlement plates – usually made of a thin slab of substrate material anchored to a weight or frame and suspended in the water column – has been helpful in monitoring a process that is elusive, because of small larval size. The CRMC uses PVC plates and suspends them from floating docks, and observes the abundance of invasive species on a 0-4 scale. At each site, two collectors are left suspended for the season (May through December), and three are replaced monthly during that time.
“You change plates every month, and you leave two in for the entire season, and that way at the end of the season you have two plates at each site that show what the ultimate community structure is by the end of that sampling period,” Cute told the Coastweeks participants. “By bringing fresh plates in throughout the entire sampling period, now we can track who’s still spawning. Who’s got the competitive advantage here? And what we tend to find is that with a lot of the native species, there’s one burst and there will be perhaps a single spawning event when the water gets warmer, but then the invasives, some of them, will continue to spawn so there is a continuous stream of new larvae being introduced.”
Cute said there are plans for the invasive monitoring and aquaculture to intersect, and encouraged members of the aquaculture industry and others to work with the CRMC to monitor invasives growth in the ponds where they work every day. The CRMC’s ongoing efforts to map and monitor eelgrass beds in all of the salt ponds also serves a dual purpose, he added.
“Monitoring eelgrass beds is one more element to the monitoring effort,” Cute said. We’ve hired professional divers to go into salt ponds. We put in three, 100-meter transect lines – nine transects per pond – to study invasives in real habitat, not plates which are proxy habitats. What we’re looking for now is, are there invasive species actually growing on our eelgrass? We know this is occurring in other parts of the country.”
Research has found that tunicates, if growing on eelgrass, can affect an entire bed, resulting in stunted growth as shown by a diminished canopy height when compared to unaffected eelgrass beds, according to Cute. By growing on eelgrass shoots as sheets that can cover significant portions of a shoot’s surface, colonial tunicates interfere with photosynthesis light, which can stress an entire eelgrass bed. They store these naturally occurring sugars because of that stress, instead of using them in the growth process.
“Eelgrass beds are absolutely critical to the health of the marine community here in Rhode Island, and invasive species are among other problems such as poor water quality, that result in cumulative impacts that can damage this resource,” Cute said.
Education of both the general public and users of the salt ponds and Narragansett Bay are major goals of the state’s Aquatic Invasive Species Management Plan, which was written by the CRMC in collaboration with DEM, and URI and adopted by the CRMC Council as part of the state’s Coastal Resources Management Program. Education is also key for the CRMC’s Aquatic Invasive Species Monitoring Project, which relies on well-trained citizen scientists as part of its efforts.
“Prevention, education and monitoring are among the best defenses we have in the fight against invasive species,” Cute said. “Citizen Scientists are often on the front lines, and they are valuable participants in our monitoring program and the CRMC’s statewide efforts to prevent and control the spread of these marine invaders.”
For more information on the CRMC’s marine invasive species efforts and plan, as well as Fuller’s paper, go to http://www.crmc.ri.gov/invasives.html. Those interested in joining the CRMC’s monitoring project efforts should contact firstname.lastname@example.org or call (401)783-3370 for more information.