PROJECT DESCRIPTION

Table of contents

 

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Summary

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Statement of Problem

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General Ecology of Zooplankton

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Distribution of Crustacean Zooplankton in the South-Central United States

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Acknowledgements

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References

 

Summary

The current project is designed to improve access to taxonomic records and microphotographs of freshwater zooplankton. The project integrates a large database and set of zooplankton samples with image capture and internet technologies, to provide easy access to images of cladoceran and copepod species common in the south-central United States. This access has numerous benefits, including improved training of graduate and undergraduate students in aquatic biology, documentation of species encountered in research, and internet access to zooplankton data for researchers off campus. Internet access to these images provides a useful tool for the study of freshwater ecology. 

 

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Statement of Problem

Despite the enormous diversity of life on Earth and the well-recognized importance of species conservation (Meffe and Carroll 1994), there are surprisingly large gaps in our understanding of the taxonomy and distribution of major groups (Edmondson 1959, Thorp and Covich 1991). These gaps are particularly acute in single regions, such as the south central United States. A case in point is revealed by a recent study of the spread and impacts of exotic species in the freshwater zooplankton (Havel and Hebert 1993). A search of the literature revealed that lists of native species were unavailable for Missouri, Arkansas, and Oklahoma. Thus, to put invading species and their effects in the proper context, our work required identifying and listing native species. To date, we have detected about 75 species of cladocerans and copepods (Eisenbacher et al. 1996, Havel and Eisenbacher, unpublished). Some of these species are rare or difficult to recognize, and their identification has required specialized training and a large amount of time at the microscope. Similar problems are commonly encountered by biologists working with other aquatic groups, such as algae, aquatic insects, and freshwater mussels (Prescott 1971, Thorp and Covich 1991). However, such taxonomic studies are vitally important, not only as a foundation for understanding of ecology, but also because they allow biologists to recognize nuisance species (Roberts 1990) and community-level effects from pollution (Platfin 1989).

    There are several problems inherent to these methods of identification and information transfer. First, identification of many species requires specialized taxonomic keys. Most specialists use outdated keys in standard guides (e.g. Edmondson 1959), together with more-recent keys published in obscure and hard-to-locate journals (e.g. Reid and Pinto-Coelho 1994). Many biologists need to identify organisms they encounter, yet lack the specialized taxonomic resources. This lack of library resources is particularly acute in smaller colleges and high schools. Second, even though closely-related species can often be discriminated by differences in coloration, publication costs of reference texts usually require that diagrams be published in black and white. Third, many species are highly variable from place to place in their size, shape, and coloration ("morphology", Brooks 1957, Hebert 1995). Keeping a record of samples from a variety of locations is very important, not only for later verification of correct identification, but also to allow researchers to examine the range of variation in natural populations so far discovered.

    A fourth problem entails retrieval of specimens for later reference. For example, an individual of a rare species is very difficult to locate again in a sample containing thousands of individuals. The standard museum technique is to isolate representative species into separate containers for future reference. However, these isolated samples of individual species are expensive and time consuming to maintain, awkward to use, and usually inaccessible to other researchers, particularly if they are unaware of the sample’s existence. Thus archiving samples for later comparisons is very inefficient.

    The recent availability of video capture techniques and internet resources provides a solution to these problems. Here we use these technologies to archive images of zooplankton species recently collected from the south central United States. The images serve the immediate purposes of training, information retrieval, and information transfer.

 

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General ecology of zooplankton

Zooplankton are common in the pelagic and littoral regions of ponds, lakes, large rivers, and oceans. In freshwater, these assemblages are dominated by the rotifers (Wallace and Snell 1991) and two groups of microcrustaceans—the four orders of cladocerans (Dodson and Frey 1991) and the class Copepoda (Williamson 1991). The copepods are also dominant in marine environments. The littoral and benthic regions of freshwater and marine environments characteristically hold large numbers of the diverse and ancient microcrustacean class Ostracoda (Delorme 1991). Most species of these four groups make their living grazing algae from the water column or off of surfaces and are, in turn, a vital link for passing energy up the food chain to fish.

    The majority of freshwater zooplankton have a strong potential for dispersal. Most species so far investigated are capable of forming resting eggs, which are resistant to desiccation, freezing, and digestive enzymes (Dodson and Frey 1991, Delorme 1991, Wallace and Snell 1991, and Williamson 1991). Furthermore, many species are parthenogenetic, which allows single females to reproduce. Nevertheless, the cosmopolitan distribution of many species has been questioned (Frey 1973), and newly-discovered exotics are allowing detailed discovery of the dispersal process (Havel and Hebert 1991, Havel et al. 1995, Havel and Stelzleni in prep).

 

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Distribution of crustacean zooplankton in the South-Central United States Recent studies of exotic species (supported by NSF) and colonization of riparian wetlands (supported by MDC) have provided collections from over 200 sites in Missouri, Arkansas, and Oklahoma, over the period 1994-97. Deep water sites were collected with vertical tows or integrated pump samples. Shallow water sites were collected with sweep nets. Wetlands were also sampled by collecting sediments, followed by hatching and rearing studies in the laboratory. Following identifications and counts, data have been maintained in Excel spreadsheets, and detailed presentation of distributions are currently being organized for publication elsewhere (Havel et al. a, b).

    We have attempted to photograph all species of cladocerans and copepods which we encountered. We photographed both the whole body and taxonomically useful characters. For common species of cladocerans, we photographed multiple populations in order to document the range of variation common among populations in this region. A similar approach was used by Hebert (1995), in his CD monograph on the genus Daphnia. We also photographed the external shell morphology of representative genera of ostracods, a group which is misunderstood by most limnologists.

 

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Acknowledgements

This project would not have been possible without the dedicated assistance of students and staff at Missouri State. Casey Meek participated in most of the collecting trips to reservoirs, logging over 8,000 miles in 1995. Desiree Bethune contributed several species identified from wetland samples and Allison Hickman assisted with sediment hatching experiments. Doug Helmers helped us gain access to sites on the Missouri River floodplain. Matt Eisenbacher took all of the photos and identified many of the specimens. We acknowledge the generous support of the National Science Foundation (grants DEB 93-17869 and DEB 96-41390 to JEH), the Missouri Department of Conservation (to JEH), and a Missouri State Faculty Research grant (to JEH and RGR).

 

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References

Brooks, J.L. 1957. The systematics of North American Daphnia. Yale University Press.

Delorme, L.D. 1991. Ostracoda. Pp. 691-722 in Thorp, J.H., and A.P. Covich (eds.). Ecology and classification of North American freshwater invertebrates. Academic Press.

Dodson, S.I., and D.G. Frey. 1991. Cladocera and other Branchiopoda. Pp. 723-786 in Thorp, J.H., and A.P. Covich (eds.). Ecology and classification of North American freshwater invertebrates. Academic Press.

Edmondson, W.T. (ed.) 1959. Freshwater biology. Wiley.

Eisenbacher, E.M., A.A. Black, and J.E. Havel. 1996. Zooplankton diversity in post-flood scours of the Missouri River floodplain. Annual meeting, American Society of Limnology and Oceanography, Milwaukee, Wisconsin.

Frey, D.G. 1982. Questions concerning cosmopolitanism in Cladocera. Archiv für Hydrobiologie 93: 484-502.

Havel, J.E., and P.D.N. Hebert. 1993. Daphnia lumholtzi in North America: Another exotic zooplankter. Limnology and Oceanography 38: 1823-1827.

Havel, J.E., W.R. Mabee, and J.R. Jones. 1995. Invasion of the exotic cladoceran Daphnia lumholtzi into North American reservoirs. Canadian Journal of Fisheries and Aquatic Sciences 52: 151-160.

Havel, J.E., and J. Stelzleni. Dispersal of zooplankton: Evidence from reservoir and boater surveys. In prep.

Havel, J.E., E. M. Eisenbacher, and J.R. Jones. Site-specific factors governing invasibility of midwestern reservoirs. In prep.

Havel, J.E., E.M. Eisenbacher, and A. Black. Zooplankton diversity in riparian wetlands: The importance of flooding and egg banks. In prep.

Hebert, P.D.N. 1995. The Daphnia of North America: An illustrated fauna. Macromedia CD ROM. University of Guelph.

Meffe, G.K., and C.R. Carroll. 1994. Principles of conservation biology. Sinauer Associates, Inc.

Plafkin, J.L., M.T. Barbour, K.D. Porter, S.K. Gross, and R.M. Hughes. 1989. Rapid bioassessment protocols for use in streams and rivers: Benthic macroinvertebrates and fish. EPA/440/4-89/001.

Prescott, G.W. 1971. How to know the freshwater algae. Wm. C. Brown Publishers.

Reid, J.W., and R.M. Pinto-Coelho. 1994. An afro-asian continental copepod, Mesocyclops ogunnus, found in Brazil; with a new key to the species of Mesocyclops in South America and a review of intercontinental introductions of copepods. Limnologica 24: 359-368.

Roberts, L. 1990. Zebra Mussel invasion threatens U.S. waters. Science 249: 1370-1372.

Thorp, J.H., and A.P. Covich (eds.). 1991. Ecology and classification of North American freshwater invertebrates. Academic Press.

Wallace, R.L., and T.W. Snell. 1991. Rotifera. Pp. 187-248 in Thorp, J.H., and A.P. Covich (eds.). Ecology and classification of North American freshwater invertebrates. Academic Press.

Williamson, C.E. 1991. Copepoda. Pp. 787-822 in Thorp, J.H., and A.P. Covich (eds.). Ecology and classification of North American freshwater invertebrates. Academic Press.

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The Zooplankton Project was conceived by Drs. John Havel and Russell Rhodes in 1998.

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