Yellow lampmussel (Lampsilis cariosa) COSEWIC assessment and status report: chapter 6

Biology

General

The biology of L. cariosa has been described by Johnson (1947) and summary information has also been provided by Clarke (1981) and Strayer and Jirka (1997). It is typical of most species of the Family Unionidae in terms of its general reproduction and habits; however, more detailed information is needed. There are paired gills or demibranchs, two on each side of the mid-line, which facilitate respiration, filter feeding and early larval development.

Reproduction

The sexes are separate and sexual dimorphism is seen in the shape of the adult shells and form of the mantle margin and other soft tissues. Sperm are released by the male and find their way to the female to fertilize eggs that are located and subsequently develop in modified posterior parts of the two outer demibranchs called the marsupium. The majority of unionids require a fish host for their parasitic larvae. And female L. cariosa like other species of Lamsilinae subfamily have modified their mantles to resemble fishes, possibly to act as lures to attract a piscivorous host fish (Kraemer 1970). When struck by a predatory fish, the lure releases the glochidia which then attach to the would-be predator. After an undetermined period of time on a fish host the glochidia transform into juvenile mussels and drop to the bottom sediment. Here they begin growth to the adult form.

All unionoids are divided into two behavioral groups based upon the duration that glochidia are brooded within female mussel before release onto a fish host. With spring or summer fertilization, bradytictic or long-term breeders hold larvae until the following spring or summer. Tachytictic or short-term breeders will release them later the same year, usually by July or August. Exact timing of fertilization and glochidial release is not known for L. cariosa. However, Wiles (1975) has shown that a related species, Lampsilis radiata radiata release glochidia onto fish hosts at least from spring to early autumn in Nova Scotia. In Lamsilinaespecies, release of glochidia is correlated with display of “mantle lure” and presence of swollen and darkened marsupia (Kraemer 1970). And, it is believed that only gravid females fully display their mantle lure. This characteristic was used as an indicator of gravidity of L. cariosa in the Sydney River.

K. White first observed L. cariosa with swollen marsupia and fully displayed mantle lures in the Sydney River on June 5, 2002 when the water temperature was 11.7 degrees Celsius. Mature glochidia (i.e. presumably ready to parasitize fish hosts) were found within these displaying females.  Maturity was indicated by the observation that glochidia shells snapped shut when exposed to a 1 molar NaCl solution. Females ceased full display of mantle lures by August 15. After this date, only a small portion of the mantle lure could still be seen in females. However, mature glochidia were found within a non-displaying female collected in Blacketts Lake on November 15th, 2002.  No further collections were made after this time. Based on this information, it appears that the L. cariosa in Sydney River are long-term breeders. With a period of gravidity occurring from at least June – November 15.  More information is needed to determine the period of gravidity for the New Brunswick population.

Until recently the host fish for the parasitic glochidia of L. cariosa were unknown and there was no information available on the development of this stage or its duration. However, Wick and Huyrn (2003) investigated the fish hosts of L. cariosa occurring in Maine using laboratory infestations. Pumpkinseed sunfish (Lepomis gibbosus), Yellow Perch (Perca flavescens), and White perch (Morone americana) were used for host fish trials. Juveniles of L. cariosa transformed on P. flavescens and M. americana. Glochidial parasitic periods lasted 43 to almost 80 days for M. americana and an average of 42 days for P. flavescens. P. flavescens does not occur in Cape Breton, M. americana does (Davis and Browne 1996).

Field studies done on the Sydney River confirm that M. americana serves as a host fish for Yellow Lampmussel. In July of 2002, fish within an area of the Sydney River with a high density of female L. cariosa were sampled and examined for glochidial infestations (Table 1). Of the six species represented, only M. americana were found to contain L. cariosa glochidia. Average infestation rate of the twenty-two M. americana sampled was 44 glochidia/fish (±16.7 SD). Average size of M. americana sampled was 128.6 mm (±29.5 SD). No relationship was found between glochidial infestation rate and size of fish. Neither tank nor field studies have been carried out to identify fish host for the New Brunswick population. However, both P. flavescens and M. americana occur in the Saint John River (Gorham 1970), and therefore may serve as fish hosts for L. cariosa in New Brunswick.

Details on population structure and recruitment for the Sydney River L. cariosa population were gained through quadrat sampling carried out by K. White in 2001 and 2002. An average of 48.7 % of L. cariosa sampled were female with no significant deviation from a 1:1 sex ratio (n = 91, chi-squared 0.06). The minimum and maximum age of live L. cariosa found in the Sydney River was 1 and 17 years respectively with an average of 7.8 (±2.7 SD) years. Both age and length frequency distributions of live L. cariosa were somewhat positively skewed with all age classes represented, suggesting recent recruitment. Age estimates were based on counts of external “annual” shell growth rings and therefore are only approximations. The use of external growth rings for aging has been criticized as underestimating ages of mussels due to inconsistent annulus formation (Downing et al. 1992). Age of sexual maturity is not known for L. cariosa; however, it is estimated to occur ~ age 5 years in a related species of mussel with rate of survival to maturity estimated at 9-18% (Jansen and Hanson 1991).

Animals such as L. cariosa living at low densities and employing direct fertilization are thought to improve reproduction by clumping (e.g. Anscombe 1950). Further clumping of L. cariosa likely occurs due to habitat preferences (see Habitat section for details). Sampling carried out by K. White in 2001 aimed at describing the spatial distribution of the Blacketts Lake L. cariosa suggests that there is significant spatial aggregation exhibited in this population. This was indicated by a high s²/m ratio at 3.71. Chi-square test results indicated that this ratio is significantly different from one and that the spatial distribution is significantly different from a Poisson series (P < 0.05).

Survival

In related unionid species the estimated chances of a glochidium surviving to transform and drop from a host fish range from 0.0001% (Jansen and Hanson 1991) to 0.000001% (Young and Williams 1984). In a study of unionid reproduction and survivorship in an Alberta lake, Jansen and Hanson (1991) found that the mortality rate from the time of excystment (glochidia drops from fish host to the substrate) to the age of sexual maturity (~ age 5) is approximately 82-91%.

No specific details on survival patterns or rates are available for L. cariosa occurring in New Brunswick. Predation mortality patterns and rates for the Sydney River L. cariosa were examined by K. White in 2002. Evidence suggests that muskrats are the main predators of adult L. cariosa in the Sydney River with a total of six muskrat midden sites being actively used on Blacketts Lake (Figure 9). Three of these midden sites were randomly chosen for monitoring. Evidence of muskrat or other predator activity (e.g. trail from woods, tracks, scat, bite marks on shells) was noted at each site. All mussel shells located within middens were removed on June 25th, 2002 and subsequent collections of mussel shells at these sites were made bi-weekly until September 26th, 2002. The estimated predation rate of L. cariosa for this 8 week period was only 10.5 (±8.7 SD) L. cariosa / week. If one assumes that this rate is maintained all year, it is estimated that an average of 546 L. cariosa are eaten by muskrats on Blacketts Lake annually. The length range of L. cariosa shells found at midden sites was 43.1 mm to 86.4 mm, with an average of 57.6 mm (±10.5) suggesting that only adults are preyed upon. The sex ratio of L. cariosa at midden sites was not significantly different from 1:1 ratio (n = 54, chi-square = 0.91) suggesting that females and males are equally likely to be preyed upon by muskrats. Populations in the Saint John River appear to be nearly completely free of muskrat predation, although predation has been noted in the smaller tributary rivers (Sabine pers. comm. 2003)

Figure 9. Sydney River, showing muskrat midden beside the highway causeway, 20 June 1999. The muskrats live between the rocks and feed on mussels from the nearby shallows.

Figure 9. Sydney River, showing muskrat midden beside the highway causeway, 20 June 1999. The muskrats live between the rocks and feed on mussels from the nearby shallows.

There was some concern that the human handling of mussels required for the research being carried out in the Sydney River population of L. cariosa could lead to mortality. This concern was addressed by K. White in 2002 through a field experiment designed to estimate mortality rates of L. cariosa due to human handling. During the course of this experiment Yellow Lampmussel (n = 20) were removed from their natural habitat and handled out of water for 45 minutes. These mussels were then placed in enclosures (1-meter wire mesh “corrals”) and the time it took for resumption of normal positioning in sediments was recorded. All mussels resumed normal filtering position in sediments and gravid females resumed mantle flap display within 1 hour of placement in enclosures and no mortality was observed in these mussels during an 18-week observation period. These results suggest that handling associated with species identification and shell measurement does not result in any significant disturbance or mortality.

Physiology

According to Strayer (1993) L. cariosa prefers larger rivers, presumably with good aeration and cooler temperatures as well as adequate calcium supply. As previously mentioned in the Habitat section of this report the water at Blacketts Lake is alkaline with a pH of 7.2 to 7.5 (Alexander et al. 1986), as a result of underlying calcareous bedrock. In normal winters much of the Sydney River is ice covered, with the exception of areas of higher flow at tributary stream outlets. No studies of the physiology of L. cariosa are known.

Movements/dispersal

Adult mussels are able to move locally using their muscular foot. Limited movements may achieve adjustments in orientation for feeding or to accommodate seasonal changes in water level. The main means of dispersal of L. cariosa is through the movement of the fish hosts of its glochidia larvae. As previously discussed in the Reproduction section, White Perch has been found to be a suitable fish host for Sydney River population of L. cariosa. And both Yellow and White Perch are likely fish hosts for Saint John River population. What follows is a description of the movements of White and Yellow Perch, which may also represent the movement and dispersal of attached L. cariosa larvae.

White Perch are found in fresh and brackish water (Scott and Crossman 1973). Sea-run populations are found in some coastal rivers and estuaries. However, sea-run populations are not common in the Maritime provinces. There are virtually no anadromous stocks in the Bay of Fundy. However, in the La Have River, Nova Scotia, provincial fishery survey workers have reported a seaward migration in summer. Spring spawning takes place when water temperatures become 11 to 16 degrees Celsius during late May or June in shallow water over many kinds of bottoms. Fresh and saltwater populations move to surface (or inshore) waters at night, retreating to deeper water during the day.

Yellow Perch are found in freshwater (Scott and Crossman 1973). However, it is occasionally found in brackish water along the Atlantic coast. Spawning occurs from April through July, but usually during May in the Maritime provinces, at water temperatures of 9 to 12 degrees Celsius. At this time, the adults move into shallow areas of lakes or up into tributary streams. Spawning takes place at night or in early morning, most often in areas where there is debris or vegetation on the bottom. Young perch grow quickly and remain near the shore during their first summer. Adults move in schools farther offshore than the young. They also move between deeper and shallow water in response to changing food supplies, seasons, and temperatures.

Nutrition and interspecific interactions

In the Sydney River L. cariosa is associated with, in order of frequency, eastern ellipto (Elliptio complanata both normal and rayed forms), eastern floater (Pyganodon cataracta), tidewater mucket (Leptodea ochracea), and alewife floater (Anodonta implicata).  Margaritifera margaritifera also occurs but not usually in association with L. cariosa (Clarke and Meachem Rick 1963, Davis 1999). The parasitic relationship with fish has been mentioned previously under Reproduction and predation by fish and muskrats under Survival

Freshwater mussels found in association with Yellow Lampmussel in the Saint John system include, in order of frequency, eastern elliptio (Elliptio complanata), alewife floater (Anodonta implicata), eastern lampmussel (Lampsilis radiata), tidewater mucket (Leptodea ochracea), eastern floater (Pyganodon cataracta), triangle floater (Alasmidonta undulata), and eastern pearlshell (Margaritifera margaritifera) (Sabine et al. In press). Sabine et al. (In press) also note that in the Saint John and tributaries they frequently found Leptea ochracea occupying habitat similar to L. cariosa, with the former a useful marker for the possible presence of Yellow Lampmussel. As with all freshwater mussels, L. cariosa is a suspension feeder filtering organic detritus and phytoplankton from the water. Suspended material is pumped into the mantle cavity of the mussel through the lower of two siphons and passes through the gills where food is separated from sediment particles. Food is passed anteriorly to labial palps at the mouth while the unwanted material is passed into the upper exhalent siphon and expelled as pseudofaeces.

Behaviour/adaptability

Apart from aspects previously mentioned under Reproduction and Movement, little is known about the behaviour of L. cariosa. The modification of the mantle edge of the female mussel to attract fish has been described in the Reproductive section along with observations on the timing of mantle lure display. No direct observations of glochidial release behavior have been made for L. cariosa.

Transformation of L. cariosa glochidia from larval to juvenile forms has been successfully carried in tank studies using White and Yellow Perch as host fish (Wick and Huryn 2002). Results of a field experiment carried out by K. White aimed at estimating L. cariosa mortality rates due to human handling, noted above, suggest that this species may respond well to transplanting.

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