Daily Invader

Chesapeake Bay Tunicates 

Colonial chain tunicate Botrylloides violaceous


Colonial chain tunicate Botrylloides violaceous discovered in the Chesapeake in 2000.




Colonial tunicates are communities of individuals, called zooids, which share a protective nonliving cellulose layer called a tunic. Each zooid is an individual, but they are such an intricate part of the colony that they can’t be separated from it. In fact, the zooids are connected to one another by a network of blood vessels and work together to make the colony act like a single animal. Botrylloides violaceous have zooids that are arranged in parallel chains and are brightly colored (orange, reddish, or purple). Like other tunicates, they are fouling organisms that are often found growing on docks or on the bottom of boats. They are native to Asia but due to shipping, they are widely introduced. They were discovered in the lower Chesapeake Bay in 2000 and 2001 and since then they’ve been seen in several areas in Virginia, including Norfolk, and the Rappahannock and York Rivers. Because they are rare, they do not appear to have any economic impacts. But if their abundance increased they could become a nuisance for boat owners and could displace native fouling organisms. Complete Record


Golden Star Tunicate (Botryllus schlosseri)


Golden Star Tunicate (Botryllus schlosseri) are the stars of the fouling community.





Have you ever seen a bright orange gelatinous mass growing on a rock at the seashore? Golden Star Tunicates are common in fouling communities in the lower Chesapeake Bay. They can grow on a variety of slow-moving submerged objects, even some plants and animals. Golden Star Tunicates are colonial meaning that they are made up of individual zooids sharing a single “skin” or tunic (nonliving cellulose layer) that are all connected by a network of blood vessels. The colony is organized into star-shaped grouping of zooids. Each zooid is small (2-4mm) but the colony is large (7-10cm, 3-4 inches). Like many tunicates, the Golden Star Tunicate’s distribution is widespread, so widespread that its native region is unknown, but some have suspected the Indo-Pacific and the Mediterranean as possible native regions. It was first seen in Chesapeake Bay in 1923 on a ship in Hampton Roads, VA and became abundant during the droughts of the mid-60s, covering bay grasses and oyster trays. However, during a normal year it’s rare and is nearly absent in wet years such as after Hurricane Agnes. Complete Record 


Colonial tunicate Diplosoma listerianum


Colonial tunicate Diplosoma listerianum was discovered in 2001 in Cape Charles and Virginia Beach.  


What are colonial tunicates? Tunicates are marine filter feeders that collect food using a pair of siphons. They are attached to a substrate and are protected by a nonliving cellulose layer called a tunic. Colonial tunicates like Diplosoma listerianum have many individuals, called zooids, sharing a single tunic. While each zooid is an individual, they can’t detach from the colony. In fact colonies not only share a tunic but also an excurrent siphon; each zooid pulls water into its own incurrent siphon but pumps it out a shared excurrent siphon. D. listerianum is widely distributed and was described separately in many different countries, each giving it a different species name. Because of this, its native range is unknown. It was discovered near Cape Charles, VA in 2001 and 2002 and is now abundant there. It was also found in Lynnhaven Bay, Virginia Beach VA in 2002. Chesapeake Record. National Record  


Rough Sea Squirt (Styela canopus)


Rough Sea Squirts (Styela canopus) are so widely distributed their native range is unknown.



Sea squirts are tunicates, marine filter feeders that collect food by pulling water through an incurrent and excurrent siphon. There are many difference types, with different life histories, but most are fouling organisms that can be introduced by boats. Tunicates are distant relatives of vertebrates; their tadpole larvae have a notochord, the precursor of a backbone. They also have muscles arranged along their sides similar to fish. Adult Rough Sea Squirts are 3 cm long and egg-shaped with a smooth reddish-brown outer layer. They are so widely distributed across temperate and tropical coastal waters that their native region is unknown. They were described from the Red Sea in 1816 but are found on both sides of the North Atlantic, the northwest Pacific, the tropical Indo-Pacific, and Australia. They were seen for the first time in the Chesapeake Region in 2000 when two specimens were found at Cape Charles VA; other specimens have since been collected in the lower Bay. Complete Record 


Leathery Sea Squirt (Styela clava)


Leathery Sea Squirt (Styela clava) is a solitary tunicate from Asia that makes a tasty soup.

Tunicate soup anyone? Tunicates, sometimes called sea squirts, are marine filter feeders and are relatives of vertebrates. Their tadpole larvae have a notochord, the precursor of a backbone. Their larvae swim for only a few hours, settling very close to home, losing their tails as soon as they settle. There are many types of tunicates but most are fouling organisms and are often found on docks, pilings, and other hard surfaces. The Leathery Sea Squirt is a type of solitary tunicate that is about 6 inches (15 cm) tall, grows from a stalk, and has a brown or yellow leathery outer layer. They are native to Asia where they are a popular food used in soup. Due to hull fouling, they have been introduced to many parts of the world. To date, only one Leathery Sea Squirt has been collected in the Chesapeake Bay region. It was found in Chincoteague, VA in 1994 but as far as we know, none have been collected inside Chesapeake Bay or adjacent coastal bays. Please contact us if you discover this species in the area. Complete Record


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