Marine Invertebrates of Bermuda Painted Tunicate (Clavelina picta) By Jessica Morris Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links

Photo By: Sara MacSorley

Taxonomy


Phylum: Chordata
      Class: Ascidiacea
        Order: Enterogona
          Family: Clavelinidae

Abstract

    Clavelina picta is a colonial, filter feeding tunicate that can be found in Florida, the Bahamas and the Caribbean. It is abundant in Bermuda as well. C. picta creates a constant water flow pumping into the brachial basket where mucous, secreted by the endostyle, filters out organisms. This species uses asexual reproduction through budding and broods its larvae. Larvae are tadpole-like and mobile containing a notochord and nerve cord. When the larvae settle, they loose these structures and become sessile. Clavepictines have been isolated from C. picta and are used to slow growth in human solid tumor lines and leukemia in rodents.

Habitat

    Clavelina Picta is found in tropical and subtropical areas such as Florida, the Bahamas, and the Caribbean (Rupert and Fox 1988). This sessile species is quite abundant in Bermuda. It can be found growing in colonies of hundreds of individuals often on gorgonians, black corals, and sponges (Fenner online). As seen in Clavelina lepadiformis, C. Picta can also be found in harbors and in mangroves (de Caralt et. al 2002). It is found in relatively shallow waters from below the low tide mark to about 50 meters.

Ecology

Appearance:

    Clavelina picta is a colonial ascidian. They are perfectly clear with purple outlining their siphons and endostyle (Sterrer 1986). C. picta has individual zooids on separate stalks, yet they grow in clumps of hundreds.

Feeding Mechanism:

    Clavelina picta, like all other ascidians has a very specialized feeding system. The main structures that are used for feeding are the endostyle with mucous glands, the peripharyngeal grooves and dorsal grooves lined with cilia, the stigmata, and the esophagus (MacGinitie 1939). C. picta maintains water current through the brachial cavity whether it is feeding or not (MacGinitie 1939).

    These organisms are filter feeders that employ a mucus film to capture prey that has been sucked in with the water. This mucus is secreted by the endostyle continuously which is then moved by cilia into the brachial basket, to the dorsal groove, and finally to the esophagus (MacGinitie 1939). The main capture of C. picta, and other ascidians is plankton or detritus that has been stirred up.

    In case there is something foreign filtered in the water, C. picta has a mechanism to respond. Firstly, there is a ring of tentacles that run along the oral cavity, preventing large objects from getting inside the tunicate (MacGinitie 1939). If smaller foreign material enters the organism, feeding will stop and a contraction of the body wall will force it back out as seen in the study by MacGinitie (1939). Also seen was that the atriopore always has a current pushing out of it. This makes it so that there is no need for tentacles. If the current stops, the atriopore simply closes. Once foreign material has been removed from the tunicate, feeding commences once again.

Chemical Defenses:

    Because of their soft bodied morphology, individuals of Clavelina picta and other ascidians, it would seem, have very little defense against predation. However, both larvae and adult ascidians have been able to ward off predators using sequestered chemical defenses such as inorganic acids or secondary metabolites (Thompson 1988). These chemicals are stored either in the gonads of the individual or in the tunic (Pisut and Pawlik 2002). The chemicals found in the gonads are then passed onto the larvae of the ascidian (Lindquist 1996). C. picta was found to have a higher acidity in its tunic which helps to defend against grazers such as fish and crabs (Pisut and Pawlik 2002). As a colonial species, C. picta zooids have sufficient defensive metabolites, that even if they are localized, they suffice to protect the entire colony (Pisut and Pawlik 2002). In a previous study, it was shown that species that had acid in their tunic were less palatable than species that didn’t have this acid (Stoecker 1978). C. picta is among the species of tunicates that contain this acid.

    C. picta is a monomorphic species, having only one form which means that there is a probability of high levels of inbreeding (Svane and Young 1989). This could be because sexual reproductive stage of C. picta is not the primary form of reproduction. Instead, the primary mode is asexual reproduction. The larvae are brooded in the colony and are released as relatively large and complex larvae (Svane and Young 1989). Larval release is based mainly on light where they are released after a period of light followed by a period of dark adaptation (Svane and Young 1989).

Reproduction and Larval Settlement:

    Ascidians in general are known for their pelagic, mobile larval stage that is followed by a sessile adult stage (McHenry and Patek 2004). The only way that the organisms can disperse is in their larval stage. Therefore, it is very important that they have sufficient locomotion to get them to an appropriate settling site. In colonial ascidians, such as Clavelina picta, the larvae are faster swimmers mainly due to the fact that they are larger (Svane and Young 1989). This is a major advantage in dispersal. The larger larvae, however, is a greater investment, often meaning either lower fecundity or higher reproductive investment of the adult organisms (MacHenry and Patek 2004).

    C. picta is a monomorphic species, having only one form which means that there is a probability of high levels of inbreeding (Svane and Young 1989). This could be because sexual reproductive stage of C. picta is not the primary form of reproduction. Instead, the primary mode is asexual reproduction. The larvae are brooded in the colony and are released as relatively large and complex larvae (Svane and Young 1989). Larval release is based mainly on light where they are released after a period of light followed by a period of dark adaptation (Svane and Young 1989).

    These larvae possess 6 main organ systems including a tunic, epidermis, notochord, tail musculature, adhesive organs and nervous system (Svane and Young 1989). They are capable of movement by whipping their tail back and forth (Berrill 1929). Once an area is selected for settlement, adhesive papillae are used to secure the larvae to whatever substrate it finds suitable (Svane and Young 1989). This is the start of transitioning to sessile organisms and proceeds metamorphosis. C. picta, among other ascidians, metamorphoses by reabsorption of the tail, rotation of the trunk, emigration of blood cells from the hemocoel to the tunic, extension of epidermal ampulae, retraction of the sensory vesicle, and finally destruction of the larval structures.

Recent Research

    There has been ongoing research to try and find natural mosquito repellents that won’t harm other animals or the environment. Clavelina picta has been one of many ascidians collected for their methanol extracts to use in a repellant (Hussein et. al 2002). The extracts taken from the tunicates have been found to show significant repellence, but are found to be lower than DEET and dose dependent (Hussein et. al 2002). However, this is a step in the right direction and with more research ascidian methanol extracts may be seen in the ingredients to commercially used mosquito repellant.

Commercial Importance

    Clavepictines A and B, organic soluble extract have recently been isolated from Clavelina picta (Raub, et. al 1991). These secondary metabolites, which are used as defense in these organisms, have cytotoxicity and antimicrobial activity (Raub, et. al 1991). Both clavepictine A and B inhibit the growth of human solid tumor lines and leukemia in rodents (Raub, et. al 1991).

Bermuda Laws

    There are currently no Bermudian laws involving Clavelina picta.

Personal Interest

    In my travels, I met a woman who did her thesis on tunicates. She was looking at the larval development and metamorphosis. Her enthusiasm inspired me to look a bit further into the subject. She informed me of all the interesting characteristics of tunicates and how though they are tiny, almost insignificant looking organisms; they are capable of far more complex processes than I would have guessed. Also, it is amazing to think that these organisms are more closely related to humans than organisms in any other phyla, including organisms that are mobile and communicate.

    When I came to Bermuda, I noticed the abundance of Clavelina picta in the very first snorkel trip I took. I thought that they were fascinating. It reminded me of what I had learned and I decided it was time to find out more on my own.

References

Berrill, N.J. 1929. Studies in tunicate development. I. General physiology of development of simple
    ascidians. Philos. Trans. R. Soc. Lond. B 218: 37-78.

Fenner, Robert. Online: Google. 11/13/06. http://www.wetwebmedia.com/ascidians.html

Hussein, Z.A.M., I. bin Jantan, A. Awaludin, and N.W. Ahmad. 2002. Mosquito repellant activity of the
    Methanol extracts of some Ascidian species. Pharm. Biol. 40: 358-361.

Lindquist, N. and M.E. Hay. 1996. Palatability and chemical defense of marine invertebrate larvae. Ecol.
    Monogr. 66:93-118.

MacGinitie, G.E., 1939. The method of feeding in tunicates. Biol. Bull. 77:443-447.

MacHenry, M.J. and S.N. Patek. 2004. The evolution of larval morphology and swimming performance in
    ascidians. Evolution. 58: 1209-1224.

Pisut, D.P., 2002. Anti-predatory chemical defenses of ascidians: secondary metabolites or inorganic acids?
    J. Exp. Mar. Biol. Ecol. 270: 203-214.

Raub, M.F., Cardellina, J.H., Choudhary, M.I., Chao-Zhou, N., Clardy, J., and Alley, M.C. 1991.
    Clavepictines A and B: Cytotoxic Quinolizidines from the tunicate Clavelina picta. J. Am. Chem. Soc.
    113:1378-1380.

Rupert, Edward L., R.S. Fox. Seashore Animals of the Southeast: A Guide to Common Shallow-water
    Invertebrates of the Southeastern Atlantic Coast. 1988. University of South Carolina Press.

Sterrer, W., 1986. Marine fauna and flora of Bermuda. A systematic guide to the identification of marine
     organisms. John Wiley & Sons, Inc.

Stoecker, D. 1978. Resistance of a tunicate to fouling. Biol. Bull. 155: 615-626

Svane, I.B. and C.M. Young. 1989. The ecology and behavior of ascidian larvae. Oceanogr. Mar. Biol.
    Annu. Rev. 27:45-90.

Thompson, T.E., 1988. Acidic allomones in marine organisms. J. Mar. Biol. Assoc. U.K. 68: 499-517.

Links

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Tunicata: Macrobenthos of the North Sea