Fish hosts, population structure, and landscape control of the distribution of two rare Atlantic slope freshwater mussels in Maine (collaborators: j. rhymer, A. Huyrn, UMaine)
August 2002 - December 2005
- SPP State Partnership Program
The declining condition of the world’s aquatic environments is resulting in a loss of aquatic biodiversity. Freshwater bivalves are experiencing drastic declines in distribution and number due to a variety of disturbances. North America contains the greatest diversity of freshwater bivalves in the world, yet more than half of the remaining species are threatened with extinction. Although in many cases mussel decline can be attributed to manipulations of the local environment, forces at a larger scale may contribute to the occurrence and structure of mussel communities. Cumulative effects of upstream and stream-side land uses and hydrological modifications may affect mussel occurrence in a watershed, potentially deteriorating quality of occupied sites or leading to population isolation due to unsuitable hydrological conditions between occupied sites. These modifications may lead not only to a change in mussel community composition, but also to a change in ecosystem structure and function resulting from modification of the density and composition of the bivalve community. However, mussel distributions may also be somewhat independent of habitat conditions and more tightly regulated by abundance and diversity of host fish. Efforts to conserve North America’s remaining mussel populations must recognize the complexity of relationships among potential determinants of mussel community composition, distribution, and demography and the multiple scales at which those relationships occur (Vaughn 1997). Distributions of Maine’s mussel species have been documented by Maine’s Department of Inland Fisheries and Wildlife (MDIFW). The tidewater mucket (Leptodea ochracea) and the yellow lampmussel (Lampsilis cariosa) are state-listed as threatened species due to their scattered, declining populations. Surveys are currently underway to document age distributions at the occupied sites to determine whether populations are sustainable and to describe the genetic structure of these mussel populations. Two species of host fish (white perch, Morone Americana, and yellow perch, Perca flavenscens) for the yellow lampmussel have been identified in laboratory studies, and their distributions in Maine are documented in a MDIFW database. Studies to identify other host fish species are underway (see State Partner Proposal). The relationships of these mussel and host fish distributions to watershed conditions such as stream connectivity, dam locations, riparian land use, and hydrological condition have not been examined. Identification of landscape- and local-scale conditions of stream reaches, river segments, and ponds and lakes occupied by these mussels and their fish hosts, and an understanding of the spatial relationships of genetic structure and demography of the remaining mussel populations and occurrence of their host fish (which have a history of relocations throughout the state for fisheries management) are critical to conservation of these mussel species. Given that Maine contains some of the last, significant populations of the tidewater mucket and yellow lampmussel in eastern North America, and its watersheds are relatively undeveloped, conservation of these species may hinge on protection of the populations that remain in Maine. The objectives of this study are 1) Increase our understanding of the demography and genetic structure of populations of yellow lampmussels and tidewater muckets in Maine; 2)Continue research to identify host fish species for these mussel species and relate host fish and mussel distributions; 3)Identify landscape-scale factors indicating suitable mussel and host fish habitat; 4)Spatially relate the genetic and demographic composition of existing populations of the tidewater mucket and yellow lampmussel to these factors and distribution of their fish hosts.