Aquatic Fauna in Peril: The Southeastern Perspective
Edited By George W. Benz And David E. Collins
Managing natural resources specifically to ensure the continued existence of any aquatic insect has yet to become a reality. Weighted down by the pest stigma, insects have garnered relatively little visibility or clout in the realm of species protection. Consequently, past protective measures and management practices have been directed at a few vertebrate and even fewer invertebrate species. Yet on a number of species basis, 95 percent of the world’s fauna is composed of invertebrates, and roughly 70 to 80 percent of this fauna is composed of insects alone (Wilson, 1988). The species richness and enormous population sizes of invertebrates prompted E. O. Wilson to contend that invertebrates drive our planet’s living systems. If we are going to maintain the biological diversity of this world, we must plan for the well-being of invertebrates. Considering that biological diversity is largely a function of insect species richness and that many aquatic insects are imperiled (Morse et al., 1997), work in this area is sadly overdue.
In the southeastern United States (Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, Virginia), there are more than 4,200 species of aquatic insects known to science. At the regional conference where an oral version of this chapter was presented, the grand total of all species addressed was roughly 6,000. Aquatic invertebrates (insects, decapod crustaceans, and molluscs) accounted for at least 5,000 of these, which was more than 80 percent of the total. Of course, this percentage is an underestimate given that not all invertebrate groups were considered (e.g., non-decapod crustaceans, annelids, bryozoans, nematodes, rotifers). Furthermore, there certainly are aquatic invertebrate species awaiting discovery in the Southeast.
Although our knowledge of aquatic insect distributions, population sizes, and habitat requirements is incomplete, it is apparent that some aquatic insect species are imperiled. Morse et al. (1997) considered 153 species in just four orders of aquatic insects as rare and vulnerable to extirpation. This number is 12.6 percent of the 1,212 species contained in these orders known to occur in the Southeast. If this percentage is applicable to the other orders of aquatic insects (beetles, hemipterans, dipterans, etc.), then of the approximately 4,200 species in the Southeast, over 500 may be imperiled. Morse et al. (1997) suspect that at least three species (two stoneflies and one caddisfly) may have been extirpated from the southern Appalachian Mountains. However, many insect species occupy small, unusual habitats that are hard to find, and there are few entomologists searching for certain groups. Therefore, we cannot say whether certain species are extinct, rare, in danger of extinction, or whether they still exist as undiscovered populations.
The degradation of our nation’s streams is clearly associated with human population density and activity. Where humankind has been most active, watersheds and their associated biota have often suffered. Increasing human populations will mean further demand for space, natural resources, and recreation, and will be accompanied by further degradation of our streams and lakes and the drainage and pollution of our wetlands. Morse et al. (1997) pointed out that we do not know if aquatic insect species now considered to be in peril are rare because of natural restrictions or because of human activities. However, we can predict that further disturbance to their habitats probably will hasten population declines. The continued existence of some species over the next few decades appears questionable. Recently, even some once-common stream species have drastically declined in numbers. Clearly something must be done to protect insect species and their habitats if we are going to maintain the biological diversity of the southeastern United States.
One step that has been taken toward protecting aquatic insects is the maintenance of a federal listing of endangered species. In the U.S. Federal Register dated November 15, 1994 (U.S. Fish and Wildlife Service, 1994), 198 species of aquatic insects were proposed for possible addition to the threatened and endangered species list. Of these, 73 species occur in the southeastern United States. The status of most of these candidate species is unsettled, and much time is being spent gathering information necessary to make listing category decisions. Regarding actual listings, 29 insect species are now federally listed as threatened or endangered species. Most of these are terrestrial beetles and butterflies. Only two aquatic species, Ambrysus amargosus, a naucorid bug known only from Nevada, and Somatochlora hineana, a dragonfly which occurs in the Great Lakes region, are on the threatened and endangered (T&E) list.
The U.S. Endangered Species Act as it pertains to insects is administered by the U.S. Fish and Wildlife Service. For each species that becomes listed as threatened or endangered, a species recovery plan aimed at de-listing the species is prepared. A suggestion to amend the Act has been made to allow the listing of many species that share a single ecosystem. This would be a step to shift emphasis from management of single species to management of habitat (Opler, 1993). Although species listing is a positive step that ultimately can afford protection, many species that have not as yet been proposed for listing and which contribute the bulk of biodiversity are declining in numbers due to the widespread disturbance of our running waters.
The actual management of aquatic habitats to benefit aquatic insects is only beginning to be considered, and few examples are available for discussion. Field activities aimed at enhancing habitats for other aquatic taxa, such as stream restoration for fish, probably benefit certain insect groups. However, these efforts do not take into account key differences in the life histories and habitat requirements of various aquatic insects (Stewart and Stark, 1988). In general, to enhance stream habitat to maximize insect diversity, a strong emphasis should be placed on providing habitat diversity and bank and substrate stabilization. Specific protection or enhancement efforts will require knowledge of the target species’ life cycle and habitat requirements, both in the immature and adult stages. In providing conditions for a specific insect, care must be taken not to alter the habitat in such a way that would be detrimental to other rare species.
Of course, a species approach to aquatic insect management requires two limited resources — time and money. Research on habitat requirements of individual species is beset with difficulties and uncertainties, and is time-consuming. Unfortunately, time may be something endangered species lack. Furthermore, securing sufficient funds to carry out imperiled species projects can be difficult. In contrast, habitat protection or improvement plans can often be relatively more timely and less costly in achieving results. They often can also be more readily accepted by the parties that are affected by them.
Because of the biological and sociological complexities associated with managing aquatic insects, we will need to skillfully build upon our successes and learn from our mistakes regarding the methods we use to realize improvement. Below I will briefly discuss several habitat management projects to illustrate some of the types of problems that such projects can pose to insects.
Hemiphlebia mirabilis is a small, rare damselfly once thought to be extinct. According to New (1993), it is now listed as a threatened taxon (in accordance with the Victoria Flora and Fauna Guarantee Act of 1988) because of population loss and decline associated with agricultural practices and modifications to river flow and flooding regimes. It is the only species in the family Hemiphlebiidae, and it has several interesting ancestral characteristics important in studies of the evolution of the Zygoptera. With its habitat limited to seasonal swamps that are found on sandy heathland, H. mirabilis is a weak flier that depends on emergent aquatic vegetation for cover and as a substrate in which it lays eggs. At one of its major known population sites, controlled burning in a mosaic pattern was used to prevent successional progression of vegetation and promote earlier seral stages, while also preventing a build-up of dead vegetation on the ground which could fuel more intense, unintentional fires (New, 1993). However, it appears that the burning was intended to create food for vertebrates, and was not necessarily intended to provide continued suitable habitat for the damselfly. In 1987, a "controlled" fire spread to the site of the largest colony of H. mirabilis, destroying the vegetation. No damselflies were seen in the area for two years following the burn. A few individuals were observed during the third year after the burn, and recently, numbers have increased nearly to the level present prior to the fire.
Study of this situation reveals several critical points. First, careful burning of patches of the surrounding habitat can be an important management tool regarding species like H. mirabilis because fires can prevent the maturation of the shrubby trees which can be responsible for the long-term drying of swamps. Secondly, H. mirabilis can withstand even drastic temporary alterations of its habitat if there are nearby locations from which individuals can immigrate when habitat conditions again become favorable. Of course the widescale reduction in the habitat of H. mirabilis makes the last mentioned possibility extremely tenuous, and underlines the vulnerability of this species. Together, the above experiences illustrate the need to carefully monitor habitat alteration projects and to consider the long-term effects they might cause.
In a small area of northeastern Illinois, there is a particular site being managed to restore mid-western prairie habitat. This is accomplished mainly by periodic controlled burning and removal of trees and shrubs. Within this area, a rare dragonfly (Hine’s emerald, Somatochlora hineana) inhabits an unusual microhabitat, namely shallow, spring-fed sheet flow, and narrow streamlets through calcareous (dolomitic) cattail marsh. This dragonfly was once thought to be extinct, but a few isolated colonies have been found recently in northeastern Illinois and eastern Wisconsin (Cashatt, 1991). Somatochlora hineana was recently placed on the T&E list (Beattie, 1995), partly because of its apparent extirpation from previously known localities in Ohio and Indiana.
For two main reasons, the cut-and-burn management practice at the Illinois location creates concern regarding whether the future survival of S. hineana is being considered. First, burning of the wetlands may directly destroy dragonfly individuals if aestivating nymphs occur in dry peat/muck or if the shallow habitat is overheated. Furthermore, this species’ distribution may be limited in part by water chemistry (Vogt and Cashatt, 1994), and an additional problem might be created if burning temporarily changes the water chemistry where eggs are laid and nymphs develop. Secondly, removal of nearby trees and shrubs denies adult dragonflies access to preferred perching sites, as well as to mating and foraging areas. This last issue underscores the importance of the terrestrial environment to an aquatic insect species.
The most pressing need regarding S. hineana is the immediate protection of the wetlands area, as well as research aimed at developing management strategies that will ensure continued existence of the species’ required habitat. Close communication and cooperation among all concerned parties along with a monitoring program are needed to manage the site properly for the continued existence of the variety of organisms now present.
In an effort to improve levels of dissolved oxygen (DO) and minimum flow in the South Fork Holston River in northeastern Tennessee, the Tennessee Valley Authority (TVA) constructed an aerating labyrinth weir (completed in December, 1991) 2 km (about 1.2 miles) downstream from the South Holston Dam. This was the first project under TVA’s Lake Improvement Plan (Hauser, 1993). DO levels have improved from 1.5-3.0 mg per l upstream of the weir and from 6.0-8.7 mg per l downstream, and a minimum flow of 2.55 cms is usually maintained between electricity generating periods. Rainbow trout have been stocked below the weir, and the monitoring of benthic organisms downstream of the South Holston weir has been conducted.
The impoverished macroinvertebrate fauna in the tailwaters below the South Holston Dam, characterized by low taxonomic diversity and a predominance of stress-tolerant species, is characteristic of hypolimnetic release areas. The minimum flow regime established now provides a more constant habitat for benthic insects. Eleven aquatic insect taxa have been collected immediately downstream of the weir and about twice that number in the 1.6 km (one mile) stretch further downstream (Yeager et al., 1993). However, only two EPT taxa1 were found. Despite a slight increase in biodiversity below the weir compared to the area immediately upstream, there was still a much lower diversity of aquatic insects than would be expected in a river of this size in eastern Tennessee. Moreover, blackfly (Diptera: Simuliidae) production below the weir was extremely high, and was undoubtedly a response to continuous flow combined with the high organic productivity of the upstream lake water.
This example illustrates the need for monitoring the response of aquatic life to supposed habitat improvements. It also raises the question, is altering one or two physical/chemical parameters adequate to improve habitat and enhance biodiversity? Other questions follow. What can be done about nutrient overloading in rivers, especially when conditions are optimum for large populations of pest insects to be produced? What factors other than low DO, low flows, and nutrient loading are responsible for depressing desirable aquatic insects in tailwaters of large dams? Solving these problems would help reinstate well-balanced communities in rivers below reservoirs, of which there are many river-miles in the southeastern United States.
1EPT stands for the three aquatic insect orders Ephemeroptera, Plecoptera, and Trichoptera. EPT counts are generally used as a measure of taxa richness and hence stream quality. An EPT value less than 10 generally indicates a stream in poor biotic condition.
Walker Branch is a tributary of Mud Creek, flowing through an ecotone between an upland area and big river bottomland in Hardin County, Tennessee. The area is a mosaic of aquatic habitat types, including wooded hillside seeps, first-order runs, shaded and partly open second-order streams, larger slow-flowing and pooled streams, and swampy wetlands with bald cypress and Tupelo gum. Disturbance from past farming and logging activities is still evident, although the area has experienced considerable regrowth and habitat recovery. The diversity of Odonata I found while collecting there between 1979 and 1982 prompted me to suggest that the area be looked at by other biologists and perhaps be considered for some type of protection. Besides the great number of Odonata species I found (nearly 40), the combination of rare and unusual species at this site is not easily found elsewhere. In addition to rare insects, several state-listed plants were also found, including Iris brevicaulis, Carex lacustris, and Malanthium virginicum.
The area in which the seeps and cypress wetlands lie is designated to be purchased by the Tennessee Wildlife Resources Agency and registered as a state natural area known as Walker Branch Hills. This positive action is mainly being realized due to efforts by staff at the Tennessee Department of Environment and Conservation. No development or publicity of the area is proposed, in hope of keeping human visitation to a minimum. The seeps I surveyed constitute only a small part of the area, 0.81 ha (roughly two acres). They are vulnerable to trampling and are still recovering from past disturbance. However, prospects are now good for the continued existence of this rich community of dragonflies and other species. This case is a rare example of an important natural area being discovered and eventually protected because of its aquatic insect fauna.
The clubtail dragonfly, Gomphus sandrius, is unusual in that it has the most restricted distribution known within the entire Gomphus species complex. It occurs in only five tributary streams of the Duck River in a 150 km2 (about 60 square miles) area of the Central Basin south of Nashville, Tennessee. Population sizes are small, estimated to be one to six individuals per 30 m (about 100 feet) depending on the stream and locality (Tennessen, 1994). The streams this clubtail inhabits are shallow and slow-flowing, with bedrock and gravel bottoms. Nymphs of G. sandrius occupy gravel bars consisting of mixed particle sizes that accumulate downstream of rock fissures and small islands of water willows. The surrounding lands are heavily used as pastureland for cattle, with some fields cropped for hay. Cattle have access to the streams and surface runoff contributes organic waste and perhaps agricultural chemicals to the streams. Removal of much of the riparian vegetation undoubtedly has raised water temperatures and increased algal growth and sediment input.
Although G. sandrius is on the federal candidate T&E list and a status survey for this species has been conducted (Tennessen, 1994), a decision to list it has not been made. Populations at several of the streams appear to have declined since discovery of the species, but because aquatic insect population size is difficult to estimate, longer periods of time often are needed to discover trends. It is possible that T&E status would not benefit G. sandrius, because the species might be faced with a range of adversities that place it close to extinction. Furthermore, forcing regulations on private landowners often generates entirely new sets of problems. An alternative and perhaps more timely approach to prevent further damage to these streams is to form cooperative agreements with the local citizenry. By showing landowners the benefits of improved water quality and stream habitat, and involving them in decisions on what can be done to lessen agricultural impacts, their help can be enlisted for the benefit of all forms of aquatic life, including the Tennessee clubtail.
Roberts (1993) pointed out that the mandates of the U.S. Endangered Species Act (ESA) conflict with those of the U.S. Mosquito Abatement Act (MAA). He illustrated this by applying a strict interpretation of these acts to two situations as follows:
Example 1. A wildlife biologist trying to manage a wetland to support an endangered aquatic or semi-aquatic species inevitably might create conditions that produce mosquitoes. This would be in violation of the MAA, which states that aquatic habitats that support mosquito production are public nuisances to be legally abated.
Example 2. A vector biologist trying to control mosquitoes in a wetland could negatively affect an aquatic or semi-aquatic endangered species. This would be in violation of the ESA.
Such dilemmas result from various specialized disciplines considering environmental management independently rather than working together toward a more harmonious approach. Ecosystems are complex, integrated systems, and Roberts (1993) warned that attempts at piecemeal solutions to many environmental problems are bound to fail. Section 7 of the ESA requires federal agencies to consult with the U.S. Fish and Wildlife Service concerning any activity which may adversely affect listed species, and this at least provides a gateway for interagency cooperation. Cooperation between biologists and resource managers during the initial planning stages of projects is especially critical.
Of course, the issue of public health and human rights versus animal protection and animal rights is often at the heart of conflicting legislation, and taking inflexible sides on such matters sets up confrontation scenarios which can thwart lasting achievements. However, through cooperation aimed at trying to resolve or otherwise minimize apparent differences, rewards can often be realized which benefit the greatest number of involved parties. As an example, while no insect species that has been implicated in the transmission of human disease is currently considered endangered or threatened, if such an instance is identified, the insect would not be afforded protection under the ESA.
In contrast to the present gloomy state of affairs regarding the protection of imperiled aquatic insects, the future can bring brightness through education and change. Our industrial, capitalistic society, which put a man on the moon before adopting a national environmental policy, has become conscious of its environment, and a large faction cares for or at least appreciates the other living things around them. The term "biodiversity" is being used outside biological circles by politicians and the general public, and understanding of its importance is being commonly gained. We are in the process of looking at aquatic species and their habitats in hopes of identifying what is in danger of being lost forever. The federal government is concerned with endangered species, including candidate aquatic insects, and is attempting to rectify some of its own past assaults on our rivers. Private citizens are becoming involved in clean-up and restoration activities, and a majority of people express the desire for a "healthy" environment.
On the other hand, the world’s human population continues to increase at an alarming rate. Globally, the human population is increasing at about 10,000 people per hour, or 93 million people per year (source: "People Count," a TBS television production aired August 29, 1994). In the United States, the 1994 census was 261 million, and this number is projected to increase by 25 percent to 326 million by the year 2020 (Campbell, 1994). In the 11 southeastern states considered in this chapter, the population will increase from approximately 60.9 to 78.2 million by the year 2020, a 28 percent jump in just 25 years. The Southeast will remain the most densely populated region in the country. Florida currently has the highest population within the Southeast (about 14 million people) and the greatest projected rate of increase (estimated to be about 36 percent from 1995 to 2020).
More people will place greater demands on natural resources, increase demands for living space, and increase encroachment on natural habitats. Many people desire lakefront or streamside property and most seek high standards of living. These demands often result in water quality reductions and habitat degradation. Protecting species requires a constant vigil, because losses are irrecoverable. Increased human habitation of remote areas can result in a greater number of species whose ranges are fragmented or otherwise diminished in size. For many, it is extremely disturbing and ironic that although we have instituted more policies to prevent or regulate the degradation of our waters over the last 20 years than ever before, more damage seemingly has occurred during this period than ever before.
How do we satisfy the needs of our rapidly growing human population and still keep aquatic habitats capable of supporting other life forms? The solution lies in getting appropriate agencies and affected organizations and individuals in watersheds concerned with local projects and to work through cooperative efforts. Where regulation might fail, communication, education, and recruiting stakeholders can often succeed. We need to instill and foster an appreciation of all forms of life at an early age through education, both formal and by example. The belief that other living things were put here for our use must be challenged. Furthermore, we need to educate everyone of the benefits of protecting habitats and maintaining the levels of biodiversity that are still present. By stressing the importance of habitat protection and its benefits to society as well as to the natural world, even skeptical parties might be persuaded to become good stewards of nature. The integrated ecosystem approach to environmental management was recommended by the U. S. National Research Council (1992) in a proposal to embark on a major national aquatic ecosystem restoration program.
I suggest that we might benefit from a more proper term than "resource management" for trying to improve aquatic habitats. To manage means to handle, direct, govern, or control in action or use. This concept is difficult to apply to human tinkering with natural systems. Furthermore, some might question the goodness of human control regarding a workable philosophy in dealing with ecosystems. The term resource management also implies knowledge of how to change things to achieve particular goals. Lastly, the term "resource" carries a connotation that there is something in it for people. A term that is more neutral and also connotes resources for all living things is "habitat."
Terms such as "habitat manipulation" and "habitat alteration" do not imply that we can control the outcome of our actions. After all, a lack of knowledge concerning an organism’s requirements and responses to change reduces our management efforts to trying to manipulate one or two environmental variables and then observing the outcome. The term "restoration" also seems inappropriate, as it means to bring back to a former, original, or normal condition. We have changed many of our larger streams so drastically (by damming, dredging, etc.) that they arguably cannot be restored to their original conditions. Strictly adhered to, habitat restoration of a large system where a reservoir is now in place would dictate that the dam be removed, allowing the river to resume its natural dynamic state. Of course, many problems would result from removal of large dams (e.g., flooding, bank cutting and other forms of erosion) such that this action might lead to new forms of environmental disaster. It might be more prudent to try to improve existing reservoirs and remaining river stretches by re-establishing riparian vegetation and conducting other bank stabilization projects, by reviewing dredging proposals, and by preventing livestock, organic wastes, and toxicants from entering water courses. Monitoring programs should be initiated to document that natural processes are being maintained in our rivers.
The next ten years will probably be critical regarding the overall fate of our aquatic insect fauna in the Southeast. A heightened public awareness of stream biodiversity and its importance will be needed to abate the negative pressures impacting our streams. People from all disciplines will be needed to work together using integrated approaches to maintain watersheds as natural functioning systems. How will we be able to measure our success in these matters? Some will count the numbers of species being removed from the federal T&E list. Some may tally the number of river kilometers improved. I hope to go to a stream, pick up some submerged rocks, and see many various mayflies, stoneflies, caddisflies, and dragonflies crawling on them.
I thank Paul Hartfield (U.S. Fish and Wildlife Service) for discussions on approaches to habitat protection and alteration, and also for reviewing a draft of this chapter. I am indebted to Dr. Joseph C. Cooney, Martin K. Painter, Chris Ungate, and Bruce Yeager (all Tennessee Valley Authority) for criticisms, comments, and information used in this chapter. Dr. Everett D. Cashatt (Illinois State Museum) and Tom E. Vogt (The Nature Conservancy) provided input to the case study on prairie habitat in Illinois. Dr. John C. Morse (Clemson University) provided direction and encouragement. Lastly, I want to publicly recognize the native peoples of this country who were wise stewards of the lands and waters for thousands of years prior to the habitation of North America by Europeans.
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