First Pacific record of the north Atlantic ascidian Molgula citrina – bioinvasion or circumpolar distribution?

Gretchen Lambert,Noa Shenkar,Billie Swalla

doi:10.3391/ai.2010.5.4.06

Gretchen Lambert, Noa Shenkar + Show 1 more

Open Access

https://doi.org/10.3391/ai.2010.5.4.06

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Abstract

The small brooding ascidian Molgula citrina Alder and Hancock, 1848 has long been known as a common inhabitant of shallow waters on both sides of the north Atlantic on subtidal natural hard substrates and also as a fouler of floating docks. There are published records from the White Sea (NW Russia), but none from the north Pacific. In May and August 2008, a number of adult brooding Molgula sp. specimens were collected from floating docks at the small fishing village of Seldovia on the Kenai Peninsula at Kachemak Bay, Alaska. Morphologically these individuals exactly match Atlantic specimens of Molgula citrina in all characters that were examined. The unique constellation of characters for this species differentiates it from all other Molgula species, as noted by Van Name (1945). In addition, the full-length 18S and 28S rDNA sequences are identical for both the Alaska specimens and New England M. citrina. Is this a new invasion, or is M. citrina a northern circumpolar species that was somehow overlooked? If this new record indicates a natural distribution, why has it not been collected before? If it is a recent introduction, it is unlikely that M. citrina, an inhabitant of cold waters, could survive in sea chests of ships from the N. Atlantic arriving in Alaska via the Panama Canal, but the intriguing idea exists of transport from Atlantic to Pacific through the Northwest or Northeast Passages. As global warming diminishes the ice cover in this region, more and more ships are traversing the Northwest Passage across northern Canada as well as the NE Passage across northern Russia, representing significant new routes for anthropogenic transport of marine species. The tadpoles of this small brooder are retained for some time after hatching, resulting in an extremely short free larval life, but could survive as metamorphosed juveniles attached in sea chests or free-floating in ballast water. They have a wide temperature tolerance and once they metamorphose can live free-floating in sea water for some time. They become very sticky and will ultimately stick to whatever they contact. Thus they could conceivably live for many generations in sea chests and sustain a viable population from which to invade new habitats.

Highlights

In May 2008, a number of Molgula sp. specimens were collected from the floating docks and associated ropes and lines at the Seldovia Marina, Kachemak Bay, Alaska (59.44oN, 151.71oW) (Figure 1)
The morphology proved to match exactly that of Molgula citrina Alder and Hancock, 1848, a widely distributed north Atlantic species long known from the Arctic Ocean, North Sea, Spitsbergen, Scandinavia, White Sea, British Isles and English Channel coast of France, as well as the NE coast of North America from Canada to Woods Hole, Massachusetts (Alder and Hancock 1907; Huntsman 1911; Redikorzev 1916; ÄrnbäckChristie-Linde 1928; Thompson 1930; Van Name 1945; Berrill 1950; Millar 1966, 1970; Monniot 1969)
The north Atlantic has been more thoroughly sampled during the past century than has the north Pacific, a vast region with many thousands of miles of unsampled or undersampled coastline especially in northern British Columbia, Alaska, and NE Russia

Summary

Introduction

In May 2008, a number of Molgula sp. specimens were collected from the floating docks and associated ropes and lines at the Seldovia Marina, Kachemak Bay, Alaska (59.44oN, 151.71oW) (Figure 1). Specimens were collected from the floating docks and associated ropes and lines at the Seldovia Marina, Kachemak Bay, Alaska (59.44oN, 151.71oW) (Figure 1). These were presumed to be a local species and were preserved in seawater formalin for later identification. The morphology proved to match exactly that of Molgula citrina Alder and Hancock, 1848, a widely distributed north Atlantic species long known from the Arctic Ocean, North Sea, Spitsbergen, Scandinavia, White Sea, British Isles and English Channel coast of France, as well as the NE coast of North America from Canada to Woods Hole, Massachusetts (Alder and Hancock 1907; Huntsman 1911; Redikorzev 1916; ÄrnbäckChristie-Linde 1928; Thompson 1930; Van Name 1945; Berrill 1950; Millar 1966, 1970; Monniot 1969). A number of new species and new distribution records have been published in the past 20 years (Lambert 1989, 2003; Lambert and Sanamyan 2001; numerous publications by Sanamyan listed in References)

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