Targeting Ecosystem Features for Conservation: Standing Crops in the Florida Everglades

Abstract

The Everglades in southern Florida, U.S.A., is a major focus of conservation activities. The freshwater wetlands of the Everglades do not have high species richness, and no species of threatened aquatic animals or plants live there. We have, however, identified a distinctive ecological feature of the Everglades that is threatened by canal construction, draining, and nutrient enrichment from agricultural runoff. Compared to values reported from other freshwater systems, standing stocks of periphyton in relatively undisturbed areas of the Everglades were unusually high, and standing stocks of invertebrates and fish were unusually low. Averaging data gathered from nine sites and five sampling periods spanning 1 year, we found that periphyton standing crop was 88.2 g/m2 (ash‐free dry mass), invertebrate standing stock was 0.64 g/m2 (dry mass), and fish standing stock was 1.2 g/m2 (dry mass of large and small species combined). We found that fish standing stocks were much higher in phosphorus‐enriched sites than in nearby reference sites but that invertebrate standing stocks were similar in enriched and reference sites. Our results support the notion that oligotrophy is at least partially responsible for the low standing stocks of fish, but they also suggest that species interactions and a paucity of deep‐water refugia are important. Anthropogenic eutrophication in Everglades marshes will lead to the loss of distinctive ecosystem features. A focus on species richness and “hot spots” of threatened species provides no basis for conservation of ecosystems like the Everglades. If oligotrophic ecosystems often have low species richness, they will be underrepresented in preservation networks based on some common criteria for establishing conservation priorities.

Macroinvertebrate and Fish Responses to Experimental P Additions in Everglades Sloughs

“…Urban and Koebel (1992) used litter bags in dense stands of vegetation to conclude that samples at a eutrophic site had greater abundance of Oligochaeta and Chironomidae but depressed abundance of other taxa relative to an oligotrophic site in WCA-2A. Alternatively, Turner et al (1999) found no effect of enrichment on large-invertebrate biomass, although they used throw traps that primarily collected decapods. Aside from differences in collection techniques among these studies, we suspect that differences in vegetation were primarily responsible for their results.…”

“…This is partially supported by the work of Jordan (1996) in WCA-1, where he illustrated the importance of high habitat complexity to most of the small fish assemblage of the Everglades. However, Jordan (1996) as well as Turner et al (1999) found that small fish densities were as much as 5 times greater in nutrient-rich cattail stands than in any habitat in the oligotrophic interior marsh. Turner et al (1999) hypothesized that increases in productivity cascaded up through the food chain and accumulated as high standing crops of small fishes and consequently, as predicted by food web theory (e.g., Oksanen etal.…”

“…Such high biomass accumulation despite low productivity suggests that it receives relatively little grazing pressure from primary consumers due to one or a combination of factors (Murdoch 1966). These may include low nutritional value, unpalatable species composition (e.g., Jones et al 1998), chemical deterrents (Lodge et al 1998), or unavailability due to calcification and structure of the periphyton matrix (e.g., Turner et al 1999). Certainly, more research is needed on the interactions among nutrient additions, periphyton, and grazers in the Everglades.…”

“…To date, only papers resulting from the P-dosing experiment that is presented in this chapter (King 2001, Qian, King, and Richardson 2003 have examined responses of invertebrates or fish to P enrichment using experimental manipulations. Moreover, relatively few observational studies have been conducted on Everglades invertebrates or fish in relation to nutrient enrichment (Terczak 1980, Urban and Koebel 1992, Rader and Richardson 1994, Jordan 1996, Turner et al 1999, King 2001, King and Richardson 2002.…”

Spatiotemporal Variation in Abundance and Social Structure of Bottlenose Dolphins in the Florida Coastal Everglades

“…Within the coastal Everglades, there is an assemblage of multiple, distinct aquatic habitats including sloughs, creeks, rivers, shallow bays with mangrove islands, and coastal oceans. Urbanization of the surrounding land and global climate change have reduced freshwater flow in volume and duration, thus changing patterns of dissolved oxygen, salinity, primary production, and consequently the distribution of many species of consumers (e.g., Turner et al 1999, Chick et al 2004, Rehage and Trexler 2006. Diminished freshwater flow that has resulted from anthropogenic activities has reduced fish populations, and in turn, limited populations of some upper trophic level predators (e.g., wading birds) though decreased food availability Serafy 2006, Trexler andGoss 2009).…”