Limecola petalum

Invasion History

First Non-native North American Tidal Record: 1988
First Non-native West Coast Tidal Record: 1988
First Non-native East/Gulf Coast Tidal Record:

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General Invasion History:

Macoma petalum was formerly treated as a synonym of M. bathica by many authors, and known as the 'Baltic Clam'. It now appears to be part of a complex of at least two sibling species, derived from Pacific ancestors which made multiple invasions of the Atlantic through the Arctic Ocean (Vainola 2003; Nikula et al. 2007). Temperate Northwestern Atlantic populations, based on enzyme allele frequencies, are genetically distinct from East Atlantic and East Pacific populations (Meehan and Carlton 1988; Meehan et al. 1989). Meehan applied the name M. petalum to Northwest Atlantic populations.

In the Northeast Pacific, populations in San Francisco Bay are M. petalum and are distinct from populations in Alsea Bay and Coos Bay, Oregon, which resemble European M. balthica (Meehan and Carlton 1988; Meehan et al. 1989). Further genetic analysis by Vainola (2003) suggested that Pacific populations from British Columbia (M. balthica balthica), were distinct from the European populations (M. balthica rubra), at the subspecies level. However, subsequent sampling indicated that both genotypes are present in European waters, suggesting that multiple Pacific-Arctic-Atlantic invasions have occurred in the Tertiary and Pleistocene (Nikula et al. 2007).

The full biogeographic picture of the M. balthica complex is unresolved. In particular, the northward limit of Macoma petalum in the Northwest Atlantic is unclear. The nature of the boundary between M. petalum and European-Arctic M. balthica is not known (Beukema and Meehan 1985). Populations sampled in the St. Lawrence River estuary, Quebec, were M. balthica, with similarities to Pacific populations (Vainola 2003).

North American Invasion History:

Invasion History on the West Coast:

Molecular studies (amino acid electrophoresis) by Meehan and Carlton (1988) and Meehan et al. (1989) indicate that the San Francisco Bay population is distinct and belongs to the Northwest Atlantic species M. petalum. A second West coast population of M. petalum has been identified in Grays Harbor, Washington (Nikula et al. 2007). The extent and history of West Coast invasions of M. petalum is unclear (Carlton 1979; Meehan et al. 1989; Cohen and Carlton 1995).

The date of introduction of M. petalum to San Francisco Bay is not known. A few shells identified as 'M. balthica' were found in sediments 2000 to 6000 years B. P., but 'M. balthica' shells are absent from Indian shell middens (Meehan et al. 1989), suggesting that M. balthica may have been absent or extinct when M. petalum was introduced. Alternatively, M. petalum may have replaced a native population of M. balthica. Clams of the genus Macoma were found in San Francisco Bay in 1841 by the United States Exploring expedition, by various collectors in the 1860s, and by the 'Albatross' survey in 1912-1913. A transfer with oysters (Crassostrea virginica) from the East Coast seems like the most likely vector (Cohen and Carlton 1995), though a later introduction with ballast water cannot be excluded. Macoma balthica occurs in all regions of the Bay, from Collinsville in the Delta to San Pablo Bay and Central and South Bays, and is especially abundant in shallow water (Nichols and Thompson 1985a; Nichols and Thompson 1985b; Meehan et al. 1989; Cohen and Carlton 1995; Cohen et al. 2005; Brusati and Grosholz 2006).

A second West coast population of M. petalum has been identified in Grays Harbor, Washington (Nikula et al. 2007). Again, transplant of Eastern Oysters (Crassostrea virginica) is a likely vector, but ballast water is also possible.

Macoma balthica, considered to be conspecific with the Arctic-Northeastern Atlantic form, has been found in British Columbia and Oregon, and is presumed to be native to the Northeast Pacific (Meehan et al. 1989; Vainola 2003; Nikula et al. 2007). It was collected in 1837 in the Columbia River, and has been collected in Puget Sound (Meehan et al. 1989).

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Description

Limecola petalum was formerly treated as a synonym of L. bathica by many authors, and known as the 'Baltic Clam', when both wer placed in the genus Macoma. It is now recognized as a member of a circumboreal species complex of estuarine clams (Meehan and Carlton 1988; Vainola 2003; Nikula et al. 2007). Limecola petalum is an oval shaped, laterally compressed clam with small umbones. A strong brown ligament is located behind the umbones, linking the two valves. The hinge lacks lateral teeth. The pallial sinus is larger in one valve than the other. The shell is usually dingy white, with a chalky texture, but sometimes has a rosy flush. Adults range from about 10 to 38 mm (Abbott 1974, as M. balthica; Gosner 1978). Definite identification of L. petalum from Atlantic or North Pacific L. balthica requires molecular methods (Meehan and Carlton 1988; Meehan et al. 1989; Vainola 2003; Nikula et al. 2007). However, some statistical differences have been found in comparing American East coast populations (L. petalum) and European (L. balthica) populations. Limecola petalum shells have a higher frequency of red or yellow in the interior of their shells than European L balthica, and they have fewer white shells, a lower weight-to length ratio, and a higher siphon weight for their size (Beukema and Meehan 1985; Kamermans et al. 1999).

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Taxonomy

Ecology

General:

Limecola petalum is a small clam, typically found in the shallow subtidal to upper intertidal, often in silty brackish waters (Gosner 1978; Coan and Valentich-Scott, in Carlton 2007). The sexes are separate. Females in Chesapeake Bay produced 50,000 -500,000 eggs per female (Long et al. 2008). In San Francisco Bay, with a temperature range of ~10-25°C, spawning occurred in late winter and fall, depending on food supply and additional unknown factors (Thompson and Nichols 1988), but is likely to be much more seasonal in regions with a wider range of temperatures. The larvae are planktotrophic and research from Holland showed that they take a mean of 16-19.5 days to metamorphosis at 15°C, depending on food levels (Bos et al. 2007). In the Chesapeake Bay, larvae settle in spring, at about 10-14°C (Shaw 1965, cited by Chanley and Andrews 1971).

Limecola petalum is tolerant of a wide range of estuarine conditions. Adult M. petalum (from Chesapeake Bay) acclimated at 30°C had 50% mortality when transferred to 33-34°C for 24 hours (Kennedy and Mihursky 1971). When gradually transferred from 16-17 PSU, L. petalum had 97% survival at 2.5 PSU, and 100% survival at 30 PSU (Castagna and Chanley 1973). Limecola petalum is capable of deposit-feeding in sediment, mostly on benthic microalgae, and suspension-feeding in the water column (Thompson and Nichols 1988; Poulton et al. 2004). As a small, often abundant clam, with a fragile shell, it is an important food item for predators ranging from crabs to fishes and birds (Cohen and Carlton 1995).

Food:

Detritus, phytoplankton

Trophic Status:

Deposit Suspension Feeder

DepSusFed

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Habitats

General Habitat	Grass Bed	None
General Habitat	Unstructured Bottom	None
General Habitat	Oyster Reef	None
General Habitat	Salt-brackish marsh	None
Salinity Range	Oligohaline	0.5-5 PSU
Salinity Range	Mesohaline	5-18 PSU
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Tidal Range	Low Intertidal	None
Vertical Habitat	Endobenthic	None

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	0	Based on field occurrences and range in the Northwest Atlantic (Abbott 1974).
Maximum Temperature (ºC)	33	24 hr LC 50, Kennedy and Mihursky 1971
Minimum Salinity (‰)	2.5	Experimental, acclimated at 5-10 ppt (Castagna and Chanley 1973)
Maximum Salinity (‰)	35	Typical marine salinity
Minimum Reproductive Temperature	10	Chespeake Bay, field range for larval set, Chesapeake Bay (Shaw 1965, cited by Chanley and Andrews 1971)
Maximum Reproductive Temperature	14	Chespeake Bay, field range for larval set, Chesapeake Bay (Shaw 1965, cited by Chanley and Andrews 1971)
Minimum Duration	16	Larval duration at 15 C, M. balthica, Netherlands (Bos et al. 2007)
Maximum Duration	19.5	Larval duration at 15 C, M. balthica, Netherlands (Bos et al. 2007)
Minimum Length (mm)	10	Reproduction begins at or near this size (Gosner 1978; Thompson and Nichols 1988)
Maximum Length (mm)	38	(Abbott 1974, as M. balthica; Gosner 1978)
Broad Temperature Range	None	Cold temperate-Warm temperate
Broad Salinity Range	None	Oligohaline-Euhaline

General Impacts

Macoma petalum is historically a very abundant bivalve in San Francisco Bay (Nichols and Thompson 1985a; Nichols and Thompson 1985b). Since 1987, it has been outnumbered and outweighed at many locations by the non-native clam Corbula amurensis, but still plays an important role in the food web of the bay (Poulton et al. 2004). In some habitats, such as Spartina marshes, it is still the dominant bivalve (Brusati and Grosholz 2006).

Ecological Impacts

Herbivory- Macoma petalum is capable of deposit-feeding (mostly on benthic microalgae) in sediment and suspension-feeding in the water column, and is still a significant filter-feeder in parts of San Francisco Bay (Thompson and Nichols 1988; Poulton et al. 2004).

Food/Prey- Macoma petalum, has been an important food resource for crabs, fishes, waterfowl, and shorebirds (Cohen and Carlton 1995; Poulton et al. 2004). Since 1987, it has been outnumbered and outweighed at many locations by the non-native clam Corbula amurensis, but still plays an important role in the food web of the bay (Poulton et al. 2004).

Competition, Habitat Change- Both in its native range, and in San Francisco Bay, M. petalum appears to be inversely correlated with Gemma gemma (Amethyst Gem Clam). This could be the result of feeding competition or alteration of sediment through Macoma's production of pseudofeces (Thompson 1982).

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Regional Impacts

NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Herbivory
Limecola petalum, historically a very abundant bivalve in San Francisco Bay (Nichols and Thompson 1985a; Nichols and Thompson 1985b), is capable both of deposit-feeding in sediment and suspension-feeding in the water column. Since 1987, it has been outnumbered and outweighed at many locations by the non-native clam Corbula amurensis, but still plays an important role in the food web of the bay (Poulton et al. 2004).
NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Food/Prey
Limecola petalum, historically a very abundant bivalve in San Francisco Bay (Nichols and Thompson 1985a; Nichols and Thompson 1985b), has been an important food item for crabs, fishes, and waterfowl (Cohen and Carlton 1995; Poulton et al. 2004). Since 1987, it has been outnumbered and outweighed at many locations by the non-native clam Corbula amurensis, but still plays an important role in the food web of the bay (Poulton et al. 2004).
P090	San Francisco Bay		Ecological Impact	Herbivory
Limecola petalum, historically a very abundant bivalve in San Francisco Bay (Nichols and Thompson 1985a; Nichols and Thompson 1985b), is capable both of deposit-feeding in sediment and suspension-feeding in the water column. Since 1987, it has been outnumbered and outweighed at many locations by the non-native clam Corbula amurensis, but still plays an important role in the food web of the bay (Poulton et al. 2004).
P090	San Francisco Bay		Ecological Impact	Food/Prey
Limecola petalum, historically a very abundant bivalve in San Francisco Bay (Nichols and Thompson 1985a; Nichols and Thompson 1985b), has been an important food item for crabs, fishes, and waterfowl (Cohen and Carlton 1995; Poulton et al. 2004). Since 1987, it has been outnumbered and outweighed at many locations by the non-native clam Corbula amurensis, but still plays an important role in the food web of the bay (Poulton et al. 2004).
NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Habitat Change
Gemma gemma (Amethyst Gem Clam) appears to be negatively correlated with Limecola petalum. Pseudofeces of L. petalum may make the sediment unfavorable for G. gemma (Thompson 1982).
P090	San Francisco Bay		Ecological Impact	Habitat Change
Gemma gemma (Amethyst Gem Clam) appears to be negatively correlated with Limecola petalum. Pseudofeces of L. petalum< may make the sediment unfavorable for G. gemma (Thompson 1982).
NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Competition
Gemma gemma (Amethyst Gem Clam) appears to be negatively correlated with Limecola petalum. This could be due, in part, to feeding competition (Thompson 1982).
CA	California		Ecological Impact	Competition
Gemma gemma (Amethyst Gem Clam) appears to be negatively correlated with Limecola petalum. This could be due, in part, to feeding competition (Thompson 1982).
CA	California		Ecological Impact	Food/Prey
Limecola petalum, historically a very abundant bivalve in San Francisco Bay (Nichols and Thompson 1985a; Nichols and Thompson 1985b), has been an important food item for crabs, fishes, and waterfowl (Cohen and Carlton 1995; Poulton et al. 2004). Since 1987, it has been outnumbered and outweighed at many locations by the non-native clam Corbula amurensis, but still plays an important role in the food web of the bay (Poulton et al. 2004)., Limecola petalum, historically a very abundant bivalve in San Francisco Bay (Nichols and Thompson 1985a; Nichols and Thompson 1985b), has been an important food item for crabs, fishes, and waterfowl (Cohen and Carlton 1995; Poulton et al. 2004). Since 1987, it has been outnumbered and outweighed at many locations by the non-native clam Corbula amurensis, but still plays an important role in the food web of the bay (Poulton et al. 2004).
CA	California		Ecological Impact	Habitat Change
Gemma gemma (Amethyst Gem Clam) appears to be negatively correlated with Limecola petalum. Pseudofeces of L. petalum may make the sediment unfavorable for G. gemma (Thompson 1982)., Gemma gemma (Amethyst Gem Clam) appears to be negatively correlated with Limecola petalum. Pseudofeces of L. petalum< may make the sediment unfavorable for G. gemma (Thompson 1982).
CA	California		Ecological Impact	Herbivory
Limecola petalum, historically a very abundant bivalve in San Francisco Bay (Nichols and Thompson 1985a; Nichols and Thompson 1985b), is capable both of deposit-feeding in sediment and suspension-feeding in the water column. Since 1987, it has been outnumbered and outweighed at many locations by the non-native clam Corbula amurensis, but still plays an important role in the food web of the bay (Poulton et al. 2004)., Limecola petalum, historically a very abundant bivalve in San Francisco Bay (Nichols and Thompson 1985a; Nichols and Thompson 1985b), is capable both of deposit-feeding in sediment and suspension-feeding in the water column. Since 1987, it has been outnumbered and outweighed at many locations by the non-native clam Corbula amurensis, but still plays an important role in the food web of the bay (Poulton et al. 2004).

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