Alan P. Covich

Measuring the total economic value of restoring ecosystem services in an impaired river basin: results from a contingent valuation survey

Five ecosystem services that could be restored along a 45-mile section of the Platte river were described to respondents using a building block approach developed by an interdisciplinary team. These ecosystem services were dilution of wastewater, natural purification of water, erosion control, habitat for fish and wildlife, and recreation. Households were asked a dichotomous choice willingness to pay question regarding purchasing the increase in ecosystem services through a higher water bill. Results from nearly 100 in-person interviews indicate that households would pay an average of

Predator-Induced Life-History Shifts in a Freshwater Snail

21 per month or

The Role of Benthic Invertebrate Species in Freshwater Ecosystems: Zoobenthic species influence energy flows and nutrient cycling

252 annually for the additional ecosystem services. Generalizing this to the households living along the river yields a value of

Effects of an Omnivorous Crayfish (Orconectes Rusticus) on a Freshwater Littoral Food Web

19 million to

The function of marine critical transition zones and the importance of sediment biodiversity

70 million depending on whether those refusing to be interviewed have a zero value or not. Even the lower bound benefit estimates exceed the high estimate of water leasing costs (

The Role of Biodiversity in the Functioning of Freshwater and Marine Benthic Ecosystems

1.13 million) and conservation reserve program farmland easements costs (

Non-visual communication in freshwater benthos: an overview

12.3 million) necessary to produce the increase in ecosystem services.

Effects of omnivorous shrimp in a montane tropical stream: sediment removal, disturbance of sessile invertebrates and enhancement of understory algal biomass

The snail Physella virgata virgata, a widely distributed freshwater pulmonate, was observed to change its life-history characteristics in the presence of the crayfish Orconectes virilis in spring-fed Oklahoma streams. These changes were apparently initiated by a water-borne cue released when crayfish fed on conspecific snails. In the presence of the cue, snails exhibited rapid growth rates and little reproduction until they reached a size of about 10 mm after 8 months. In the absence of the cue, snails typically grew to about 4 mm (3.5 months) and then began reproduction. The chemically inducible shift indicates that the life histories of these snails are phenotypically plastic. By increasing the variance associated with size and age of maturity, prey may increase the likelihood of coexisting with seasonal predators.

Geographical and Historical Comparisons of Neotropical Streams: Biotic Diversity and Detrital Processing in Highly Variable Habitats

119 Small invertebrates are functionally important in many terrestrial and aquatic ecosystems (Wilson 1992, Freckman et al. 1997, Palmer et al. 1997, Postel and Carpenter 1997). In freshwater sediments, benthic invertebrates are diverse and abundant, but they are often patchily distributed and relatively difficult to sample, especially when they live in deep subsurface sediments. Thus, the species richness and functional importance of freshwater benthic invertebrates generally go unnoticed until unexpected changes occur in ecosystems. Unanticipated changes in freshwater ecosystems are often due to alterations in the complex connections among sediment-dwelling species and associated food webs (e.g., Goedkoop and Johnson 1996, Lodge et al. 1998b, Stockley et al. 1998) or to disturbances, such as floods or drought (e.g., Covich 1993, Power 1995, Johnson et al. 1998), that alter the species composition of the benthos. In addition, benthic species can themselves constitute a disturbance, such as when they transmit diseases. For example, certain benthic invertebrate species (e.g., Tubifex tubifex) serve as parasite-transmitting vectors; if these invertebrates increase in abundance in stream sediments, they may spread a lethal disease to trout, causing trout populations to decline (Brinkhurst 1997). Fish kills may also occur because of increased accumulation of nutrients, which cause formation of toxic algal blooms, deoxygenation of deeper, density-stratified waters, and high concentrations of ammonia or hydrogen sulfide (Covich 1993). The bottom muds of lakes and streams may at first glance appear to be uniform and, therefore, unlikely habitats for high biodiversity. However, physical, chemical, and biological processes create significant horizontal and vertical heterogeneities in the substrata (Figure 1) that provide a physical template for distinct niches (Hutchinson 1993). These sedimentary processes include changes in direction and rates of flows, differential deposition of sediment grain sizes and dead organisms, growth and death of roots, burrowing and sediment reworking, and fecal production by benthic consumers. Microhabitats are also created by chemical gradients and microzonation in concentrations of dissolved oxygen, hydrogen sulfide, ammonia, phosphorus, and other critical chemicals (Groffman and Bohlen 1999). Colwell (1998) emphasizes that such “biocomplexity” of habitats and biological relationships is an important aspect of biodiversity. Bioturbation and other biotic interactions create extensive biocomplexity in freshwater sediments (Charbonneau and Hare 1998). These biocomplexities must be better understood if clean drinking water and recreational uses of fresh waters are to be maintained. Science-based policies require an ecosystem perspective on the multiple roles of many diverse benthic species. Previous studies have often dealt with the “goods” produced by benthic species, such as the quantity of prey items consumed by fish. These goods are clearly important components of food webs, but how their functional relationships respond to changes in species composition are also important. In this article, we highlight examples of how some species have a disproportionately large impact on food-web dynamics and how particular species provide essential ecosystem services. These ecosystem functions include sediment mixing, nutrient cycling, and energy flow through food webs. The Role of Benthic Invertebrate Species in Freshwater Ecosystems

FRESHWATER SHRIMP EFFECTS ON DETRITAL PROCESSING AND NUTRIENTS IN A TROPICAL HEADWATER STREAM

Cascading trophic interactions are important in many freshwater pelagic food webs, but their importance in more complex, omnivore-rich littoral-zone food webs is less well known. We tested the existence of a trophic cascade involving omnivorous crayfish (Orconectes rusticus), macroinvertebrates, periphyton, and macrophytes using 9-M2 cages in the littoral zone of Plum Lake, Wisconsin, USA. Treatments in the replicated (N = 4) experiment were crayfish enclosures, crayfish exclosures, and cageless references. During June-September, we measured macrophyte shoot numbers, macroinvertebrate numbers, and periphyton (on plastic strips) chlorophyll a, and dry mass (DM). We expected that crayfish foraging would directly reduce abundance and change species composition of macrophytes and macroinvertebrates and would indirectly enhance periphyton abundance by reducing the abundance of grazing snails. In enclosures, macrophyte and snail (but not nonsnail macroinvertebrate) densities declined significantly throughout the experiment, whereas densities of macrophytes, snails, and nonsnail macroinvertebrates increased in exclosures and cageless references. Some of the reduction in macrophytes resulted from nonconsumptive fragmentation of macrophytes by crayfish. Consistent with the cascading trophic interactions model, periphyton chloro- phyll a per unit surface area increased in enclosures, but declined in exclosures. Periphyton quality (as indexed by chlorophyll a/DM) also increased in enclosures relative to exclosures and cageless references. However, because of large reductions in macrophyte surface area (which periphyton colonizes) in enclosures, total amount of periphyton chlorophyll a in enclosures (relative to exclosures) probably declined while periphyton quantity per unit surface area and periphyton quality increased. Thus, the impacts of crayfish omnivory on periphyton, expressed in two conflicting indirect effects, confirm the possibility that om- nivory can complicate cascading trophic predictions. Overall, results support the existence of strong trophic interactions in the littoral zone, in which omnivorous crayfish control abundance of macrophytes, snails, and periphyton.