Spatial Aggregation, Precision, and Power in Surveys of Freshwater Mussel Populations

Abstract

We studied aggregation in 76 populations of freshwater mussels from relatively homogeneous surroundings in a wide range of habitats. Chi-square tests for spatial aggregation found only 53% of mussel populations significantly (p < 0.05) aggregated. The variance of replicate mussel samples (s2) varied with the mean number collected (m) as 1.49m1.17, but conformed to the general variance relation found for other aquatic taxa (m1.5) at m > 1. The number of replicate samples ([Formula: see text]) required to estimate mussel abundance with a given level of precision (D = SE/m) is approximately m−0.5D−2. Sampling mussels with large quadrats requires between 5 and 25 samples for 20% precision. Sampling designs to determine significant impacts (α = (β = 0.05) require 7–50 samples of each population to detect doubling or halving of the population density, or three to nine to detect order-of-magnitude changes. Large sampling units are recommended to ensure acceptable sampling precision and accurate chi-square analyses of spatial aggregation and to permit ecologists to detect significant impacts on freshwater mussel populations.

When and how? Freshwater mussel recolonization in Lake Orta

“…But their presence escaped a subsequent (2003) search targeted specifically to freshwater mussels (Bodon, personal communication). Freshwater mussels are challenging to locate because they are often rare, spatially clustered, and difficult to detect (Downing and Downing, 1992;Strayer and Smith, 2003). The causes of imperfect detection in freshwater mussel surveys are varied (Smith et al, 2010) and only the adoption of appropriate sampling designs can reduce errors and improve survey success and reliability (Strayer and Smith, 2003).…”

Status of Freshwater Mussels in the Lower Ohio River in Relation to the Olmsted Locks and Dam Project: 1999 Studies

“…First, despite a rapid April and May rise in lower Ohio River discharge in both years, there were brief periods of below-average discharge (< 7,000 m 3 s" 1 ) in both early April and early May. Low discharge and associated low water velocity may enhance fertilization success by allowing sperm released into the water by males to be drawn into the mantle cavities of nearby females instead of being carried rapidly downstream (Downing and Downing 1992) Second, the rapid and large rise in lower Ohio River discharge from early May to early June (1990) or mid-June (1981 may have attracted spawning aggregations of A. chrysochloris to the gravelly shoal. In both years, this lower Ohio River rise was accompanied by a similar but earlier ending (mid-May to late May) rise in upper Mississippi River discharge; thus, there was no backwater effect of the upper Mississippi River on the lower Ohio River during this period.…”

Population dynamics of the date mussel,Lithophaga lithophaga (L., 1758) (Bivalvia: Mytilidae), in the Evoikos Gulf (Greece)

“…Depending on the appropriate availability of substratum and predation (Gaucher, 1965, cited in Hughes, 1970, this leads to the random distribution of clumps. Downing & Downing (1992) carried out a study of the spatial aggregation of 76 populations of the freshwater mussel species and found aggregation in 53% of the cases. Downing & Downing (1992) believed that these differences were due to the size and number of sampling units and also to population density.…”

“…Downing & Downing (1992) carried out a study of the spatial aggregation of 76 populations of the freshwater mussel species and found aggregation in 53% of the cases. Downing & Downing (1992) believed that these differences were due to the size and number of sampling units and also to population density. They suggested 5 sampling units as being suitable for an average population density of 100 individuals/m 2.…”