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Chapt 9C10. Ascidians, page 9C10- 1 Chapter 9C10. Focal Taxonomic Collections: Ascidians Gretchen Lambert, Friday Harbor Laboratories, University of Washington Results A total of 12 species of ascidians were collected during this expedition. The highest number of species and of individuals was at Homer, Tatitlek and Cordova, the three locations with the highest salinity. No ascidians were recorded from Seward or Whittier, or the floats at Valdez, where the salinity was only 10-12 parts per thousand, although fouling panels at Valdez, submerged at about 7m, did have some ascidians. Ascidians require at least 25-27 parts per thousand and prefer a salinity of 30 or higher. Three of the 12 species are colonial, the other 9 are solitary forms. Although there were not a large number of species collected, they do represent a good diversity. Both orders and all three suborders of the class Ascidiacea are represented and include a total of 6 families. Seven of the 12 species are known to brood their embryos and release swimming tadpoles; all 7 of these did harbor mature embryos. At the end of this report is a list of the ascidian voucher specimens collected in 1998; there were no additional species to the 1999 collections. The collection includes an undescribed species of Distaplia, a colonial form in the suborder Aplousobranchia. It is surprising that this species is very abundant at both Homer and Cordova marinas, yet has gone unrecognized for nearly a century. It is possible that if Ritter (1901) or Huntsman (1912) collected it, they may have considered it merely a variant of Distaplia occidentalis. On the other hand, this species may have been much rarer during Ritter’s and Huntsman’s time. Its preferred habitat is apparently sheltered surfaces, shallow but never exposed at low tide and away from very much light. It is thus “pre-adapted” for the huge surface area and specialized environment provided by marina floats and the many submerged ropes up to 3m. in length that are often suspended from floats. Before the building of large marinas, this particular type of habitat was not abundant. The marina environment is also somewhat unstable, subject to changing seasonal conditions. Many ascidians are well adapted to take advantage of this instability. Distaplia spp., like most aplousobranchs, are very fast growing, reach sexual maturity in a few weeks, reproduce and then die back to a dedifferentiated basal portion than can survive until environmental conditions are again suitable for rapid growth. This new species is somewhat similar to a cold-water form from the Kamchatka Peninsula of Russia, and an analysis and description of it is being prepared in collaboration with Dr. Karen Sanamyan of the Kamchatka Institute of Science. Two species of the genus Ascidia were collected and present a taxonomic problem. One corresponds to Ascidia adhaerens Ritter, 1901, the other to Ascidiopsis columbiana Huntsman, 1912. (The genus Ascidiopsis is no longer valid; it was synonymized under the genus Ascidia.) Van Name (1945) synonymized these two NE Pacific species under Ascidia callosa, probably incorrectly; A. callosa was described in 1852 by Stimpson from U.S. east coast specimens from Massachusetts. The recent genetic analysis of many Atlantic and Pacific species of various taxa that closely resemble each morphologically and were originally lumped into the same species has resulted in many cases in their separation into different species (R. Strathmann pers. comm.). However, a recent re-examination of Stimpson’s syntypes of Ascidia callosa and Ritter’s paratypes of Ascidia adhaerens, borrowed from the Smithsonian National Museum of Natural
Chapt 9C10. Ascidians, page 9C10- 2 History, has confirmed that these are the same species. Thus, Ascidia adhaerens remains a synonym under A. callosa. The type specimen of Huntsman’s Ascidiopsis columbiana was borrowed from the Royal Ontario Museum in Toronto. I was able to confirm that this species is indeed distinct from Ascidia callosa and thus should be resurrected as a valid species, which will be done in a publication now in preparation. Botrylloides violaceus is not native to Alaska, or to any part of the NE Pacific. It is a Japanese species that appeared on the U.S. Pacific coast about 20 years ago (J. Carlton pers. comm.). Since that time it has spread and become extremely abundant from southern California to British Columbia (Lambert and Lambert, 1998). This is the first report of its presence in any part of Alaska, however. Although large colonies were not observed, the fouling panels at Tatitlek contained numerous newly settled zooids most of which appeared healthy. Thus somewhere close to the panels there had to be mature colonies which were supplying the shortlived tadpoles that settled on the panels. B. violaceus incubates its embryos; the tadpoles that are released are huge, complex, and usually swim for just a very brief period, perhaps only a few minutes, before settling. The unusual tadpole morphology allows for easy recognition of this invasive species (Saito et al., 1981). Molgula retortiformis and Ascidia callosa are apparently the only species collected on this expedition that occur in both the North Pacific and North Atlantic (Van Name, 1945). Chelyosoma productum, Corella inflata and C. willmeriana, Distaplia occidentalis, Pyura haustor and Styela truncata have been recorded only from the NE Pacific. Halocynthia hilgendorfi is known from both the NW and NE Pacific. Sixty-five species of ascidians are known to occur in Alaskan waters. Most of these were obtained by dredging many decades ago and may be restricted to the Bering Sea or the Arctic Ocean. The ascidian fauna of Alaska is still mostly unexplored, and probably there exist a number of undescribed species. Publication of the present work, including a description of the new Distaplia species and redescription of the two Ascidia species, is in preparation with Dr. Karen Sanamyan of the Kamchatka Institute of Ecology. References Huntsman, A.G. 1912. Ascidians from the coasts of Canada. Trans. Canad. Inst. 9: 111-148. Kott, P. 1985. The Australian Ascidiacea. Mem. Qd. Mus. 23: 1-440. Lambert, C.C. & G. Lambert 1998. Non-indigenous ascidians in southern California harbors and marinas. Mar. Biol. 130: 675-688. Lambert, G., C.C. Lambert & D.P. Abbott 1981. Corella species in the American Pacific Northwest: distinction of C. inflata Huntsman, 1912 from C. willmeriana Herdman, 1898 (Ascidiacea, Phlebobranchia). Can. J. Zool. 59: 1493-1504. Nishikawa, T. 1991. The ascidians of the Japan Sea. II. Publ. Seto Mar. Biol. Lab. 35: 25-170.
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page i BIOLOGICAL INVASIONS OF COLD
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page iii • Stephan Benda, Valdez
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