Microcrustacean community structure and biomass in marsh and lake habitats of the Okefenokee Swamp: seasonal dynamics and responses to resource manipulations

Abstract

Microcrustacean community and biomass dynamics were studied for two years in a Nymphaea‐Eriocaulon macrophyte marsh and a nearby shallow lake which lacked macrophytes in the Okefenokee Swamp. In this blackwater, acidic wetland, microcrustacean diversity and biomass were similar to other circumneutral lakes and littoral areas, contributing to a productive fish assemblage. In the lake, the annual biomass pattern (15–1627 μg 1−1) was unimodal and was dominated by the crustaceans Diaptomus sinuatus and Eubosmina tubicen. Rotifers were occasionally important, constituting up to 55% of total biomass. Over the long term, mean annual biomass in this post‐drought study are higher than in pre‐drought years. In the marsh, biomass (11–777 μg 1−1) fluctuated biomodally with late winter depressions corresponding to low temperatures and midsummer declines indicative of increasing fish predation. Summer dominance shifted between years from Macrothricidae in 1982 to Sididae in 1983. Variation in biomass correlated most strongly with algal chlorophyll in the marsh and with bacterial density in the lake. In field enclosure experiments in which primary production was reduced by shading, microcrustacean responses varied between lake and marsh habitats and with season. Lake zooplankton were consistently suppressed by reduced algal resources in winter, spring and summer experiments, with greatest responses to shading in the summer. Marsh microcrustacea were most affected in the winter experiment and became less sensitive to manipulated resource levels in spring and summer. Decoupling of these consumers from autotrophic resources in the marsh, but not in the lake, coincides with times of high macrophyte turnover and warming temperatures which promote the conversion of detritus into heterotrophic resources such as bacteria. The conflict between interactions implied by the experimental approach vs statistical criteria emphasizes a need to interpret resource dependence from seasonal dynamics of field populations with caution.

Spatial and temporal patterns of microcrustacean assemblage structure and secondary production in a wetland ecosystem

“…Microcrustacean species richness and composition in the Talladega wetland were similar to those described from other southeastern wetlands (Schoenberg, 1988; Taylor et al. , 1989), floodplain habitats (Anderson, 1995) and lake littoral zones (Lemly & Dimmick, 1982).…”

“…, 1989), floodplain habitats (Anderson, 1995) and lake littoral zones (Lemly & Dimmick, 1982). Species richness in the Talladega wetland (32) corresponded to the higher estimates reported in other studies, ranging from 18 and 19 (Lemly & Dimmick, 1982; Schoenberg, 1988) to 30 and 35 microcrustacean taxa (Taylor et al. , 1989; Anderson, 1995).…”

“…In contrast to lake ecosystems, the roles of microcrustaceans in wetlands have been explored to a much lesser extent (Schoenberg, 1988; Hann, 1999; Rader, 1999). Some studies have been conducted on seasonal dynamics of wetland and floodplain microcrustaceans (Daggett & Davis, 1974; Schoenberg, 1988; Hann & Zrum, 1997) and a few have estimated production (Taylor, Mahoney & Estes, 1989; Anderson, 1995; Leeper & Taylor, 1998; Lewis et al. , 2001).…”

Growth and reproduction of the cladoceran Ceriodaphnia dubia from a forested floodplain swamp

“…populations are common faunal components of wetland ecosystems, but unlike their well-studied counterparts in lake plankton, they have been investigated and quantified on relatively few occasions (e.g. Schoenberg 1988;Taylor et al 1989;Gladden and Smock 1990). A useful indication of the functional role of invertebrates in any aquatic ecosystem is a description of their production dynamics (Benke 1993).…”

Growth and reproduction of three cladoceran species from a small wetland in the south‐eastern U.S.A.

“…Pennak, 1966; Lehtovaara & Sarvala, 1984; Paterson, 1993) and vegetated wetlands (e.g. Schoenberg, 1988; Anderson, 1995; Hann & Zrum, 1997; Lemke, 2000). The functional role of zooplankton in terms of their secondary production and as energetic links between lower and higher trophic levels has been well documented in lakes (e.g.…”