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Hemolymph, the circulatory fluid of bivalves, transports nutrients, respiratory gases, enzymes, metabolic wastes, and toxicants throughout the body. Hemolymph can provide information pertinent to health assessment of animals or populations, but is not commonly used in freshwater bivalves partly because of the lack of tested, practical techniques for its nonlethal collection. The objective of this study was to evaluate the effect of hemolymph collection on the growth and survival of Elliptio complanata, a freshwater bivalve (Unionidae). We describe a simple technique for the collection of hemolymph from the anterior adductor muscle sinus of E. complanata. To evaluate the effect of hemolymph sampling on mussel survival and growth, 30 mussels sampled using the technique and 30 unsampled controls were followed for 3 mo post collection. Nine animals were sampled 3 times over 7 mo to monitor effects of repeated sampling. No negative impacts on survival or growth were observed in either the singly or repeatedly sampled animals. We also compared the composition of hemolymph collected from the adductor muscle sinus with that collected from the ventricle of the heart. Calcium levels and cell count of hemolymph obtained from the adductor sinus and ventricle were significantly different. There was no significant difference between collection sites for magnesium, phosphorus, ammonia, protein, sodium, potassium, or chloride. We conclude that collection of hemolymph from the adductor sinus is safe for sampled E. complanata and should be explored as a relatively non-invasive, and potentially useful, approach to the evaluation of freshwater mussel health.KEY WORDS: Unionidae · Freshwater mussels · Hemolymph · Nonlethal sampling Resale or republication not permitted without written consent of the publisherDis Aquat Org 65: [159][160][161][162][163][164][165] 2005 water mussels play roles in water filtration, bioturbation, and nutrient cycling and retention (Hauer & Lamberti 1996). They are also food sources for many riparian and aquatic animals (McMahon & Bogan 2001).Health assessment of freshwater bivalves traditionally involves lethal tissue collection from animals for histology (Chittick et al. 2001), contaminant (Muncaster et al. 1990, Cope et al. 1999, enzymatic (Doran et al. 2001, McMahon & Bogan 2001 or energy analysis (Baker & Hornbach 2000, McMahon & Bogan 2001. These techniques have successfully identified unionid populations suffering the impacts of dramatic localized habitat degradation (Foe & Knight 1987) or major infestations of invasive species (Baker & Hornbach 2000). In these situations, because a large proportion of a localized population is affected, only a relatively small number of animals need be sampled to identify the health effect.However, many devastating environmental threats are more insidious, with diffuse impacts. Health effects may be subtle and initially present a picture of low prevalence. Sampling restrictions on endangered or threatened populations limit access to these animals for ...

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Stable isotopes can be used to elucidate ecological relationships in community and trophic studies. Findings are calibrated against baselines, e.g. from a producer or primary consumer, assumed to act as a reference to the isotopic context created by spatiotemporal attributes such as geography, climate, nutrient, and energy sources. The ability of an organism to accurately represent a community base depends on how, and over what time-scale, it assimilates ambient materials. Freshwater mussels have served as references for trophic studies of freshwater communities and as indicators of change in nutrient pollution load or source. Their suitability as reference animals has not yet been fully explored, however. We conducted a series of studies examining the suitability of freshwater mussels as isotopic baselines, using their ability to reXect variation in ambient nutrient loads as a case scenario. (1) 15 N analyses, and that small sample sizes generate means representative of a larger population. Both Wndings can help minimize the impact of sampling on imperiled freshwater mussel populations. (3) In a bivalve transplantation study we showed that hemolymph 15 N compositions responded to a shift in ambient dissolved 15 N-NO 3 , although slowly. The tissue turnover time for bivalve hemolymph was 113 days. We conclude that bivalves serve best as biomonitors of chronic, rather than acute, Xuctuations in stream nutrient loads, and provide initial evidence of their suitability