From Genes to Ecosystems: Integrative Approaches in Unionid Ecology III
Presiding: C Vaughn, Oklahoma Biological Survey; D E Spooner, University of Oklahoma
NB43C-01 INVITED 13:30h
Context-Dependent Species Effects in Freshwater Mussel Communities
Riverine unionids typically occur as multi-species assemblages and are considered a `filter-feeding' guild. Through a series of field-enclosure and laboratory stream-mesocosm experiments we are addressing three fundamental questions concerning this guild: (1) What is the overall importance of the mussel guild to stream ecosystem function? (2) Do species perform different ecological roles or are they functionally redundant? and (3) Do species roles vary with environmental context? Results to date demonstrate strong effects of a potentially keystone species, Actinonaias ligamentina, but comparatively weak diversity effects. In summer field experiments, A. ligamentina increased periphyton biomass, and A. ligamentina biomass was correlated with biomass changes in other mussel species. These patterns were not observed in fall field experiments when water temperatures were lower and average discharge higher. Most of the samples from the mesocosm experiments are still being processed, but data we have analyzed also indicate strong effects of A. ligamentina on both whole community respiration rates and biodeposition of organic matter. Our results indicate that some mussel species are performing differently in streams and are thus not redundant, but that performance and potential redundancy are context dependent.
NB43C-02 13:45h
Physiological Ecology of Freshwater Mussel Communities: Effects of Temperature on Community Structure and Ecological Services.
Recent work suggests that freshwater mussel communities significantly influence stream ecosystem function through benthic-pelagic coupling of energy and nutrients. Mussel beds increase sediment organic matter and benthic algal production, facilitating the abundance and diversity of co-occurring benthic invertebrates. The magnitude of these effects appear to be regulated by abiotic factors such as temperature and flow, which influence hydraulic residence time and biological rates of reaction. We are using an integrative approach to examine the role of temperature on measures of physiological condition (metabolic rate, glycogen concentration, RNA: DNA) and measures of ecosystem services (nutrient excretion, biodeposition and clearance rate). Eight different species of unionids were removed from a mussel bed in the Little River, OK and acclimated to four temperatures (5, 15, 25, and 35C) for two weeks prior to the experiment. Measures of condition and ecosystem services were taken for all species at each temperature. Data collected to date suggest that there is significant variation in species-specific thermal performance. These performance curves influence resource acquisition, potentially shaping community structure (species dominance) and subsequent ecological function.
NB43C-03 INVITED 14:00h
Freshwater Mussel Ecological Stoichiometry: C, N, and P Relationships.
One of the goals of ecological stoichiometry is to understand how the relative proportions of chemical elements in organisms influence ecological interactions such as foodweb dynamics and ecosystem processes. Freshwater mussels, with large biomass and long lives, have the potential to be highly influential in foodwebs and ecosystems. The objectives of our study were to investigate the species, spatial, and temporal patterns in mussel stoichiometry. Little Darby Creek mussels were significantly different across seasons and sites for C:N ratios and N:P ratios. Spring C:N were highest (5.22), while lowest in autumn (4.8) and N:P was highest in the spring (5.1) and lowest in the autumn (4.65). Site differences also were observed with C:N of 5.23 and 4.79 and N:P of 5.08 and 4.64, respectively. Meanwhile, Ouachita River mussel C:N was significantly different between species, while N:P was significantly different among seasons and between sites, but not species. Overall, C:N of Ptychobranchus occidentalis (5.52) was higher than Actinonaias ligamentina (4.95). Seasonal N:P was highest in autumn(9.92)and lowest in the spring (6.72) and site N:P differences of 8.53 and 7.39 also were observed. Variability in these ratios suggests variability in mussel stoichiometry could lead to variability in foodwebs and ecosystems.
NB43C-04 14:15h
Evaluation of Freshwater Mussel (Mollusca: Unionoidea) Fitness Pre- and Post- Relocation Efforts
Freshwater mussels are often displaced by human activities. Construction of bridges that offer potential impact to large numbers mussels often results in a relocation strategy to minimize loss. While this may reduce mortality, the metabolic consequences of relocation have not been evaluated. In this study we measured glycogen and lipid concentrations and RNA to DNA ratios to determine fitness impairments on relocated mussels. We hypothesize that organisms subjected to continuous stress should first use stored glycogen, followed by growth cessation measured as a reduction of RNA in relation to the DNA present, and finally a mobilization of tissue lipids, measured as a decrease in tissue lipid concentrations. We collected mantle snips from three surrogate species of mussels from four sites on the White River in eastern Arkansas during late summer, to establish expected glycogen, lipid, and RNA:DNA levels. Mean tissue lipids concentrations (Μg/g) were 63.09, 67.96, and 50.46 for Quadrula quadrula, Q. pustulosa and Obliquaria reflexa, respectively. Mean tissue glycogen concentrations (Μg/g) were 346.66, 592.26, and 336.58 for Q. quadrula, Q. pustulosa, and O. reflexa, respectively. This study can provide response information on relocated individuals as well as provide estimation of sufficient time required for mussel adaptation to novel environments.
NB43C-05 INVITED 14:30h
A Holistic Approach to the Conservation and Propagation of Freshwater, Brackish and Estuarine Bivalves for Ecosystem Services.
Shellfish restoration is increasingly valued in estuaries such as Chesapeake Bay where oyster populations are known to function as living biofilters, performing critical ecosystem services. Less studied are the services rendered by other suspension-feeding bivalves that reside in fringing marshes around these estuaries, in brackish and freshwater tidal portions, and in freshwater tributaries. The potential benefits contributed by other native bivalves will be discussed with two case studies from the Delaware basin. These are the ribbed mussel (Geukensia demissa ), which is abundant in brackish and marine tidal marshes, and the unionid mussel (Elliptio complanata ), which is abundant in many rivers of the system. Ribbed mussels are abundant enough to filter a large portion of the tidal prism flushing marshes, facilitating the role that these systems play as a sink for suspended solids and nutrients. Similarly, data from the lower Brandywine River suggests that a vestigial community of freshwater unionids remains sufficiently abundant to have a measurable beneficial effect on water quality by removing more than 25 metric tons of suspended particulates per year. Hence, the conservation and propagation of freshwater unionids can yield benefits that extend beyond current interest that is focused on protecting their biodiversity. Future efforts to protect or reclaim water quality and ecosystem integrity may benefit by a basin-wide, holistic approach that promotes integrated "biofiltration services" by native bivalves living from the headwaters to the coastal shelf.