Eelgrass Limpet
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Scientific name: Lottia alveus alveus
Taxonomic group: Molluscs
Range: Atlantic Ocean
Status under SARA*: Not applicable
Last COSEWIC**
designation: Extinct (May 2000)
*SARA: The Species at Risk Act
**COSEWIC: The Committee on the Status of Endangered Wildlife in Canada
Quick Links: | Photo | Description | Habitat | Biology | Reasons for extinction | References |
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Description
The Eelgrass Limpet was a marine invertebrate last recorded in 1929. It was a gastropod, which means that it moved by means of a large foot. It possessed a single pair of reduced marginal teeth on the radula, which is a file-like structure used for scraping off and drawing food into the mouth.
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Distribution and Population
The Eelgrass Limpet was first described in 1831 in Massachusetts. It was subsequently found in the western Atlantic Ocean from Labrador to New York. It is the first marine invertebrate known to have become extinct in an ocean basin. The last known specimens were collected right before the dramatic decline of North Atlantic Eelgrass in the early 1930s.
The Eelgrass Limpet originated in the North Pacific from lineage found in Japan. The North Atlantic Eelgrass similarly originated from the western North Pacific. Both species invaded the North Atlantic by way of the Bering Strait and the Arctic Ocean. The Eelgrass Limpet became divided into three subspecies: one located in the Northeast Pacific, another in the Northwest Pacific, a third (Lottia alveus) which occurred in the Northwest Atlantic. Compared with its Pacific counterparts, this third group had less variation in colour and shell pattern. It also possessed an extra first lateral tooth on the left side of the radula. It was known as far south on the Atlantic coast as New York, and occurred as far east as Egg Harbour, Labrador.
Between the 1860s and late 1920s, the species was common enough in northern New England that it could be collected on demand. No Eelgrass Limpets have been collected in the Atlantic Ocean since 1929, though searches have been conducted.
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Habitat
The Northwest Atlantic subspecies of the Eelgrass Limpet occurred solely on the blades of the North Atlantic Eelgrass, Zostera marina. Individual limpets probably became detached from the eelgrass by wave action. Sometimes they were found on other substrates, such as the periwinkle Littorina littoria. All locations in which the species was collected appeared to be fully marine rather than estuarine habitats. Other molluscs that were collected near the species included strictly marine species, as well. No collections indicate that the species lived in low salinity (brackish water) sites. Thus, the Eelgrass Limpet was probably a stenohaline species of open coastal waters.
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Biology
The Eelgrass Limpet fed on epithelial (tissue-forming outer layers) cells of eelgrass rather than on epiphytic diatoms and algae. Its habits were more specialized, and its ranges and tolerances more narrow, than most marine invertebrates.
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Reasons for extinction
It is thought that the subspecies' narrow habitat requirements and seemingly narrow genetic variability led to its extinction. When its sole food source disappeared (from 1930 to 1933) in the eastern and western North Atlantic on a scale far exceeding any previous declines, the species became extinct. The primary cause of the eelgrass decline was probably a wasting disease caused by the slime mould, Labyrinthula. The plant's decline caused other repercussions in the marine ecosystem as well, including large reductions in migratory waterfowl populations, loss of commercial scallop fisheries, and alterations of near-shore soft sediment habitats. Only eelgrass populations in low-salinity areas survived. Presumably due to its extremely narrow salinity tolerance, the Atlantic subspecies of limpet could not coexist with the surviving Atlantic eelgrass. The two remaining limpet subspecies have probably survived because no extensive areas of eelgrass were eliminated in the North Pacific.
