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Sea grape, sea peach, sea pork, sea vase, golden startunicate……these are just a few of the sea squirtsor ascidians that inhabit Long Island Sound's

waters. The names sound pleasant enough, but they arefrequently aliens – species that have come to our coastfrom foreign waters. Most of them are unwantedinvaders, known to scientists as invasive species. Theylive in a variety of habitats and can be harmoniousmembers of the bottom-dwelling assemblages of plantsand animals, or can cause serious fouling problems.

Many people are familiar with the devastatingimpacts that the more notorious invasive species such aszebra mussels, gypsy moth, kudzu and snakeheads havehad on terrestrial and freshwater environments. Fewpeople other than resource managers and environmen-talists are as aware of the terrible impacts invasivespecies have on the marine environment. For example,in the Mediterranean and southern California, the sea-weed Caulerpa taxifolia has covered large areas of theseabed resulting in reduced fish and invertebrate popu-lations. The ctenophore or comb jelly, Mnemiopsis leidyi(a jellyfish-like organism) has devoured plankton andfood of fish and caused fisheries to collapse in the Blackand Caspian Seas. Cannonball jellyfish (Stomolophusmeleagris) have devastated larval fish populations in theGulf of Mexico.

Unfortunately, invasions by sea squirts are becominguncomfortably common. For instance, 14 species of seasquirts have invaded California in the last century, eightof these within the last 22 years. Similar rates of inva-sions occur in other areas of the world. Some of thesesea squirts have major ecological or economic impacts

on the areas they invade. In Canada, huge masses ofStyela clava and Ciona intestinalis have overgrowncultured mussels. These sea squirts compete with themussels for food and space and are very costly and diffi-cult to remove during mussel harvesting. Similar prob-lems are being encountered here in Connecticut andelsewhere in New England.

SCIENTISTS CRYING “FOUL” SEA SQUIRTS ARE INVADING LONG ISLAND SOUND!

by Stephan Bullard, Robert B. Whitlatch, Sandra E. Shumway, and Richard W. Osman

"Our waters are being invaded by new species almost faster than we can identify them.Unfortunately we cannot predict which will cause harm, and which will not, so we must do what wecan to prevent all new invaders. You never know when the next invader will cause serious problems,like this new species of Didemnum. Invaders such as Didemnum are not just a problem for conser-vation or protection of native species, but they also cause serious economic harm to industriessuch as shellfish aquaculture. This is one case where industry and conservation should really on thesame side. The collaboration of scientists and aquaculturists in this important study will providemuch needed and useful information. It is best for everyone if we can keep out dangerous invadersfrom our waters." –Dr. Dianna Padilla, SUNY Stony Brook

A fouling community dominated by sea squirts growing on arope. Sea squirts are one of the most common fouling ani-mals in Long Island Sound. They are very common on docks,pilings, and jetties. This rope had been submerged for aboutone year in Groton, Connecticut.

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How can such small and seemingly harmlesscreatures cause so much trouble?

When sea squirts invade a new area, they can quick-ly replace resident plants and animals. They are prolificand spread quickly by overgrowing and smotheringother organisms. In addition some sea squirts containpowerful noxious chemicals or exude acids that helpprotect them from predators by making them unpalat-able to some consumers such as cunners and spidercrabs. Sea squirts can affect economically importantspecies such as clams, mussels, scallops, oysters, andother shellfish by competing for food and space. Theycan also wreak havoc on aquaculture facilities by foulingnets, cages, pipes and other structures. Additionally,they can form dense mats on the underside of boats,which can slow them down and lead to increased fuelcosts.

A few sea squirts are native to New England, butmost have arrived here as the result of biological inva-sions, likely hitching rides on the bottoms of boats com-ing from distant ports in Europe, Asia and the southernhemisphere. Of the species most commonly found inLong Island Sound, only two are currently recognized asnative, and some have been resident for so long thattheir status as native or invasive is debated. The rest arenewcomers. Two of the more recent invaders, thebright orange to red colored colonial Botrylloides vio-laceus, and the green colored colonial Diplosoma listeri-anum arrived in the region about two decades ago. Thewhite to pinkish/orange colored Didemnum sp. is themost recent arrival and reached the region about fiveyears ago from either Asia or Europe. Since their arrival,all of these species have become very abundant in LongIsland Sound.

Common sea squirts from Long Island Sound. An alien head indicates an invasive species. A tri-corner hat indi-cates a native or well-established resident species. A question mark means we're not entirely sure. Top row, leftto right: Sea pork Aplidium constellatum; Ascidiella aspersa; Compound tunicate Botrylloides violaceus. Middlerow, left to right: Golden star tunicate Botryllus schlosseri; Sea vase Ciona intestinalis; Carpet tunicateDidemnum sp.; Bottom row, left to right: Diplosoma listerianum; Sea grape Molgula manhattensis; Asian stalkedtunicate Styela clava.

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The most recent invader, Didemnum, doesn’t have acommon name, but has been referred to as “pancakebatter” and “alien vomit” in recent press reports. As thename suggests, the animal resembles soggy scrambledeggs. We prefer the name carpet tunicate. It growsmuch like the creature from the movie “The Blob” andforms slimy mats that blanket just about everything inits path including huge areas of the seafloor. For exam-ple, on Georges Bank, the species covers 50-90% of theavailable space over a 27 square-mile area. At siteswhere Didemnum covers large areas of the seafloor, itsmat-like structure may smother organisms in the sedi-ments. This can reduce the food supply for bottomfeeders and prevent the larvae and juveniles of manyspecies from becoming established. It may also coverthe resting crevices of fishes such as cunner and tautogand expose them to greater predation. Populations ofDidemnum currently exist in the eastern end of LongIsland Sound and the species will likely spread through-out the Sound in the near future. At one site near theLatimer Lighthouse (north of Fishers Island), Didem-num covers more than 50% of the bottom in an exten-sive area.

It’s not just a local issue. Didemnum is generating agreat deal of concern from scientists and coastal zoneresource managers worldwide. Expanding populationshave been reported from Western Canada, NewZealand, Europe, and both coasts of the United States.It currently ranges from Maine to Long Island on theeast coast and from central California to British

Columbia on the west coast of the U.S. The carpettunicate was first seen in the U.S. off the coast ofMaine in 1988 and arrived in Connecticut in 2000.

Now, this species is a global problem Unlike mostother alien sea squirts which are typically restricted toliving in shallow-water, protected harbors and bays andare only found attached to hard substrates (e.g. pilings,rocks, soda cans), the new invader has the ability togrow on gravel and cobble bottoms in much deeperwaters. It commonly overgrows various sea squirts aswell as algae, scallops, mussels and other shellfish whichare particularly vulnerable because most are sessile andhave no way to escape the encroaching Didemnum orother species that foul their shells and aquaculturecages, (see page 8) and under some circumstancescolonies can completely overgrow and smother shellfish.

Very little is known about the general biology ofDidemnum sp. or the specific impacts that it has onshellfish and aquaculture. This summer, scientists fromthe University of Connecticut, the University ofHartford, the Smithsonian Institution and theUniversity of South Florida are in the process of docu-menting its growth rates in different habitats, its effectson shellfish, aquaculture, and its ability to reproduce byfragmentation.

Stephan Bullard returning from a dive with Didemnum inhand. At sites near Groton, Connecticut, huge colonies ofDidemnum cover many submerged rocks.

The carpet tunicate Didemnum sp. blankets the bottom ofLong Island Sound near Latimer Lighthouse. This site isabout 100 feet deep and has a gravel bottom. WhenDidemnum forms thick mats like this it can smother organ-isms in the sediments, prevent larvae from settling, andreduce the number of hiding places for bottom-dwellingfishes and other animals.

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AN ECOLOGICAL AND FINANCIAL MENACE

What can be done about invasive sea squirts? At present, not much. The best means of control is pre-vention of introduction—keep them from invading inthe first place. On average, one new species of seasquirt has invaded the east coast of the U.S. every fiveyears. Most invasive sea squirts reach new areas on thehulls of ships or in ballast water. Commercial and recre-ational boaters can help prevent the spread of sea squirtsby maintaining clean boat hulls. These animals are tinyand clever and often attach to hulls in places where anti-fouling compounds are not applied. Keeping boat hullsclean can greatly reduce the ability of invaders to spread.

With support from National Sea Grant’s AquaticNuisance Species research initiative, a collaborativestudy is underway between UConn scientists BobWhitlatch and Sandy Shumway, Stephan Bullard(University of Hartford), Rick Osman (SmithsonianEnvironmental Research Center), economist ChuckAdams (University of South Florida/Florida SeaGrant), and Connecticut Sea Grant ExtensionEducators Tessa Getchis and Nancy Balcom. Thisteam is studying the ecological and economic impactsthe invaders have on shellfish aquaculture. In addi-tion, they will be assessing how biological controlmethods may be used to reduce the impacts of ascidi-ans in aquaculture operations. Studies are underwayto assess the extent of threat to scallops, mussels,oysters and quahogs. For some animals, it may be amatter of too much fouling on their shells to allowthem to function properly; for others it may be lossof habitat or smothering by the rapidly spreading andencroaching mats of Didemnum.

Sea squirts are eaten in some Asian and SouthAmerican countries (see next page), but the taste for

Didemnum on a rope, overgrowing other sea squirts.

A sea squirt in action. A large Ascidiella aspersa squirtswater from its siphon.

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these animals is highly acquired and few Americansenjoy eating them – one of us likens the pickled varietyto sulphur-flavored sandpaper! In addition, many seasquirts are poisonous and, while this provides them witha built-in defense against predation, they cannot be uti-lized as a food source for humans.

You might not suspect it, but sea squirts are chor-dates which puts them in the same scientific grouping asvertebrates (the group that includes fishes, amphibians,reptiles, birds and mammals), i.e. sea squirts are reallyour marine cousins.

As adults, sea squirts are sessile. Sea squirts obtaintheir food by filtering small particles out of the waterthrough siphons. Large sea squirts often spray waterfrom their siphons when they are picked up, givingthem their common name “sea squirts”.

Most invasions of non-native marine species are theresult of human-related uses of the coastal zone. Forexample, the hulls of early sailing vessels are recognizedas an important vector contributing to the spread ofnon-natives throughout the world. We are also begin-ning to understand better how alterations in coastal landuse patterns and global climate change may actually befacilitating the invasions of some species. While seasquirts are but one group of marine invaders, they arebecoming alarmingly abundant throughout manyregions of the world and often pose a threat to nativebiodiversity and economically important shellfish. It isonly through a better understanding of the biologicaland ecological aspects of the non-natives, that we canbegin developing ways of controlling or reducing theimpacts of them on our coastal waters.

JUST WHAT ARE ASCIDIANS?

Ascidians or “sea squirts” are a group of soft-bodied marine invertebrates that grow onhard surfaces such as rocks, eelgrass blades, shells of bivalve molluscs, docks, pilings,and boat hulls. They can grow either individually or in colonies. Solitary sea squirtstypically look like small cylinders or round balls about the size of grapes. In fact, onecommon species is called “sea grape”. Colonial ascidians, on the other hand, grow inthick, slimy mats that can range from dime-sized to huge colonies as large as sheets ofplywood.

“As an oyster farmer for the past 18 years, Ican attest to the burden that these foulingorganisms pose to those of us who work withcages, lines, buoys and gear in the waters ofNew England. In a matter of weeks a cleanpiece of gear can become totally occluded bysea squirts to the point where water flow isseverely restricted, and growth of our targetorganisms is being stifled. A significant por-tion of my labor budget is devoted to control-ling sea squirt infestation. The aquacultureindustry up and down the East Cost would begrateful if any new control strategies could bedeveloped to minimize or eliminate thesepests.”

–Dr. Robert ‘Skid’ Rheault, MoonstoneOysters.

About the authors: Stephan Bullard is a faculty member atthe University of Hartford. Robert B. Whitlatch and SandyShumway are faculty members in marine sciences at theUniversity of Connecticut. Richard Osman is a researcherwith the Smithsonian Environmental Research Center.

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Squirts for dinner? While few animals eat sea squirts, they are eaten andconsidered a delicacy in many Asian countries. This photograph illustrates a Korean dish known asMideodok-chim (steamedStyela clava). It is a stir fry ofbeef, clams, vegetables, andthe clubbed sea squirt Styelaclava.

Like whiskey,it’s an acquired taste.

Ingredients

Roasted Rice 3 Tbsp.Styela: 4 oz (100g)Beef: 4 oz (100g)Clam meat: 4 oz (100g)Watercress: 4 oz (100g)Bean Sprouts: 4 oz (100g)1 medium onion1 green pepperWater: 1/2 cupRed pepper powder: 1/2 tsp.Paprika: 1 Tbsp.Salt: 1 tsp.2 green onionsGarlic: 1 Tbsp. choppedPeanut oil*: 1 Tbsp.

*Be sure your guests don't have peanut allergy.

Instructions

Prepare 3 Tbsp. roasted ground rice and mix with 1/2 tsp.red pepper powder, 2 tsp. paprika, 1/2 tsp. garlic powder

Stir fry beef and clams lightly

Steam onions, green pepper, bean sprouts, and watercress(1/2 stems, 1/2 leaves), garlic

Steam Styela clava separately.

Once steaming is complete, heat 1 tbsp of peanut oil* and stir fry all other ingredients (vegetables, meats, roasted rice mixture) together. Once heated, add green onions.

Serve over steamed rice. Serves 4 or more, depending on squeamishness of the

guests.

RECIPE

Variation on Mideodock–chim

Warning: this dish may notappeal to everyone!

Stephan Bullard prepared the mealpictured. He said the taste was “ok”but the thick, vinegary odor kept himfrom eating much. Kashmir pepper isa good choice for the red pepperpowder.