Yellow lampmussel (Lampsilis cariosa) COSEWIC assessment and status report: chapter 5

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Habitat

Habitat requirements

According to Clarke (1981), Strayer and Jirka (1997) and Nedeau et al. (2000) L. cariosa is predominantly a species of medium to large rivers. Strayer (1993) has made detailed studies of the macrohabitat of common mussel species, including L. cariosa in the middle of its range, in Pennsylvania and New York states. L. cariosa is common in this region and occurs in 26% of the streams examined. His results show that L. cariosa has a preference for hard water, stable low gradient, lowland rivers and streams and that stream size was probably the most important factor. It was generally most common in rivers with a drainage basin of more than 1200 km² and was much less frequent in smaller streams.

The habitats of L. cariosa in Northern Maine and the Maritime Provinces can be examined with respect to the above description. Figure 5 shows a section of Mattawamkeag Stream just south of Island Falls, Maine. Clarke and Meachem Rick (1963) reported the occurrence of L. cariosa in this section of the Penobscott River drainage. There was evidence, from fresh shell fragments, that the species was present in 1999. The habitat appears to be typical as described above, being a large river system with moderate flow, low gradient, riffles and sand/gravel bottom (Davis 1999).

The habitat of L. cariosa in the Sydney River, Nova Scotia is best described as a lake habitat (Figure 8). The river was dammed in 1902 creating a long lake habitat with imperceptible flow rates except at the constriction caused by the road causeway, at the bridge at Blacketts Lake and at the dam. At Blacketts Lake the water is alkaline with conductivity at 35.0 to 130.0 µmhos/cm and Ph at 7.2 to 7.5 (Alexander et al. 1986). No L. cariosa are found below the dam most probably due to the brackish water (2700 µS/cm recorded 200-m below dam). Salinity 100 m above is only (76 µS/cm). The Sydney River habitat above the dam is also suitable for freshwater fish and ten species have been reported (Table 1).

Microhabitat associations of the Sydney River population of L. cariosa were studied by K. White in 2001 and 2002. This consisted of an examination of mussel density in relation to substrate and macrophyte cover within 1-meter quadrats that were randomly placed around the 10 km perimeter of Blacketts Lake at a standardized depth of 0.75 m. Substrate composition was categorized using a modified Wentworth scale (Cummins 1962) with three categories of substrate identified: 1-mostly sandy (n=68), 2-mostly gravel (n=109) and 3-mostly silt (n=104). Macrophyte cover was coarsely categorized in each quadrat as greater than 50% (n=170) or less than 50% (n=111). This cover included emergent rushes (Juncus spp.), Pickerel weed (Pontederia cordata L.) and submerged pondweed (Potamogeton robbinsii Oakes). Mussel density across a depth range of 0.25-6.00 m was also examined by quadrat sampling using SCUBA. Relationships between habitat type and Yellow Lampmussel density were tested using analysis of variance (ANOVA). Tukey’s method was used to make pair-wise comparisons with a Bonferroni correction made for multiple comparisons (Sokal and Rohlf 1995).

Significantly higher densities (68% greater) of L. cariosa occurred in sandy substrate than in silty substrate and quadrats with low macrophyte cover contained a significantly greater number of L. cariosa (77% greater) than quadrats with high macrophyte cover. The microhabitat associations observed here are similar to those reported for other related freshwater mussel species (e.g. Huebner et al. 1990). And the results are consistent with the explanation that heavier shelled species like L. cariosa tend to prefer sandy substrate over silty substrate due to the fact that they encounter difficulties maintaining filtering and reproductive positioning in loose silty substrate. Lighter shelled species like Pyganodon cataracta, (called “Eastern floater” for its ability to ‘float’ on top of silty substrate) do not encounter this problem and were found to thrive equally well in sandy or silty substrates.

L. cariosa density was also found to vary with depth in the Sydney River with lower densities occurring below 0.25 meters when compared to those at 0.75 – 6.0-m. However, no significant differences were found when comparing densities of Yellow Lampmussel at 0.75 m, 2.0 m, 4.0 m, and 6.0 m (n = 10). Mean L. cariosa densities within the study site ranged from 1.7/m² (±1.1) at 0.75-m to 2.3/ m² (±1.2) at 6-m. No individuals were found below the thermocline of Blacketts Lake which is estimated to occur at an approximate depth of 6 meters. Studies conducted on other freshwater mussel species have found similar relationships between depth and density, with lower density being found at depths below 50 cm and above 5.0 m (Ghent et al. 1978; Huebner et al. 1990; Haukiofa and Hakala 1974). No size, age or sex ratio differences were found among substrate type, macrophyte cover, or depth (P > 0.05).

It should be noted that causal interpretations of micro-habitat/density correlation should be made cautiously due to possible confounding factors. K. White found that substrate type and percent macrophyte cover are highly correlated with one another; with predominantly silty areas tending to be areas with greater macrophyte cover. Also, unmeasured factors, which may play a causal role in habitat associations, are likely also correlated with substrate, macrophyte cover and depth.

Figure 6 shows a section of the Saint John River, New Brunswick, about 13 km above Fredericton and 4 km below the Mactaquac Dam. Lampsilis cariosa was collected at this site in 1962, prior to the dam construction, which began in 1965. (Clarke 1981; Clayden et al.1984). The size of the Saint John River fits Strayers (1993) definition of sites most likely to host L. cariosa populations. Lampsilis cariosa has shown a preference for sand substrates elsewhere (Nedeau et al. 2000) and Strayer and Ralley (1993) have described the effect of impoundment in removing fine sediment from the riverbed for some distance below dams. Nonetheless, the low gradient and tidal nature of the lower Saint John River has resulted in the formation of extensive bars of almost pure sand, which Sabine et al. (In press) report appears to offer exceptional conditions for Yellow Lampmussels in the Saint John system. The tidal portion of the river and its lower tributaries are characterized by slow water flow, many large islands, and extensive bars with sparsely vegetated substrates of fine to coarse sand. The upper reaches of the lower tributaries of the Saint John are undammed and of moderate flow, with gravel/cobble substrates and only occasional sand bars. Although Sabine et al. (In press) reported occasionally finding L. cariosa on cobble substrates, they note that greatest numbers occurred on unvegetated bars of fine to coarse sand, and at depths ranging to 5.15 m.

Trends

For the Sydney population the damming of the tidal river has led to increased habitat during the last century (Figure 7). In Nova Scotia suitable habitat may exist in upper parts of some larger streams such as River Inhabitants, St. Mary’s River, Musquodoboit River, Tusket River and the Shubenacadie/Stewiacke rivers. No L. cariosa have been reported from these rivers. However, thorough surveys of these systems have not been done and few mussel specimens from them are present in museum collections. Thus the existence of L. cariosa in these rivers cannot be ruled out. However, the relatively high acidity of all but the Musquodoboit, Shubenacadie, and Stewiake Rivers would likely exclude L. cariosa (Elderkin pers. comm. 2004). Recent surveys within two federal parks in Nova Scotia: Cape Breton Highlands National Park and Louisburg National Historic site which included portions of the St. Mary’s River and River Inhabitants drainage did not find any L. cariosa (Power and Gouthro 2002; Lambert et al. 2003).

In New Brunswickit is possible that damming may have reduced the area of habitat, as L. cariosa was not encountered in surveys of the headpond formed by the Mactaquac dam. However, further survey work effort is required to convincingly eliminate the possibility of extant populations within and upstream of the Mactaquac headpond (Sabine et al. In press). Additional suitable habitat may exist in other large (and unsurveyed) rivers in New Brunswick, such as the Miramichi and Magaguadavic rivers.

Protection/ownership

Most lake and river shorelines in Nova Scotia are privately owned which has led to extensive shoreline modification. In both New Brunswick and Nova Scotia protection of waterways is provided through regulation under Acts administered through provincial environment departments and federal Departments of Environment and Fisheries and Oceans. Protection through these Acts primarily focuses on the prevention of habitat loss for fishes which should provide protection for L. cariosa fish hosts. It is hoped that focusing on fish habitat will also make the regulations sufficient to protect against L. cariosa habitat loss and disturbance of the mussels themselves.