Production of fishes in a subtropical blackwater ecosystem: The Okefenokee Swamp1

Freeman, Byron J.; Freeman, Mary C.

doi:10.4319/lo.1985.30.3.0686

Cited by 21 publications

(13 citation statements)

References 25 publications

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“…The perception of naturally acidic blackwaters as stressed ecosystems resulting in low diversity and production of consumers (Bayley 1981) is a view that has been questioned (Freeman and Freeman 1985). Microcrustacea within a dystrophic marsh of the Okefenokee Swamp exhibit a much greater diversity than expected from the water chemistry (Fryer 1980).…”

Section: Discussionmentioning

confidence: 99%

“…More thorough studies of long term biomass dynamics are needed to estimate the contribution of microcrustacea to larger consumers. Limited sampling of floodplains and drainage channels near swamps suggests that microcrustacea are an important link in the aquatic food web (Loffler 1979, Mizuno et al 1982 and may contribute to the impressive fish production of these habitats (e.g.. Lemly andDimmick 1982a, Freeman andFreeman 1985).…”

Section: Introductionmentioning

confidence: 99%

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

Schoenberg

1988

Ecography

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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.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Schoenberg

1988

Ecography

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“…These results are consistent with the observation that E. obesus, but not E. gloriosus, is strongly associated with acidic waters in nature (Graham & Hastings 1984). E. obesus was found to be a major tertiary producer in the Okefenokee Swamp (pH 3.7; Freeman & Freeman 1985) while E. g1oriosu.s was absent from this study site. However, E. gloriosus is thought to be found throughout the swamp Table 3.…”

Section: Phmentioning

confidence: 99%

Differences in low pH tolerance among closely related sunfish of the genus Enneacanthus

Gonzalez

Dunson

1989

Environ Biol Fish

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SynopsisThree closely related sunfish in the genus Enneacanthus were examined to determine if differences existed in their tolerance to low pH that could explain their contrasting distributions. Na fluxes of E. obesus, E. gloriosus, and E. chaetodon were measured during 12 h exposure to pH 4.0 and 3.5 (all species), and 3.25 (former 2 species only). All experienced ionic disturbances upon acid exposure resulting from inhibition of active Na influx and stimulation of passive Na efflux, but E. gloriosus and E. chaetodon experienced greater disturbances than E. obesus at all pH's tested. Body and plasma Na concentrations of E. gloriosus were measured after one week of exposure to a range of pH's for comparison with previously published data from E. obesus. Exposure to pH 4.0 and below caused a depression in body and plasma Na concentration of E. gloriosus, and only two of 10 fish survived the one week test period at pH 3.5; none survived at pH 3.25. In contrast, exposure to pH 4.0 for five weeks had no effect on body Na concentration of E. obesus, all 10 fish survived exposure to pH 3.5 for two weeks. Growth of E. gloriosus and E. obesus were measured separately during 12 weeks of exposure to a range of pH's. E. gloriosus exposed to pH 4.25 and 4.0 grew at a lower rate than those at higher PI-I'S (4.5,5.0, and 5.8), and body Na concentrations of fish at pH's 4.25 and 4.0 were significantly less than the others. With declining pH E. obesus did not exhibit reduced growth until pH 3.75 was reached; no depression in body Na concentration occurred at this pH. These results show that there are marked differences in low pH tolerance among closely related species of Enneacanthus which could affect their distributions and competitive interactions.

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“…They were also very high in relation to estimates obtained from small species in subtropical or temperate waters. Freeman & Freeman (1985) found that P/B ratios varied from 1.9-3.3 and from 3.0-3.6 (depending on the method used) in three small (<40 mm) fish species in the subtropical Okefenokee Swamp. O'Hara & Penczak (1987) calculated a P/B ratio of 3.7 for Gasterosteus aculeatus, a small (< 60 mm) temperate species.…”

Section: Discussionmentioning

confidence: 99%

Population dynamics of two small cichlid fish species in a tropical man-made lake (Lake Kariba)

Hustler

Marshall

1990

Hydrobiologia

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The population dynamics of two small cichlid fishes (Pharyngochromis darlingi and Pseudocrenilabrus philander) were studied in Lake Kariba, a very large African man-made lake. They are of no economic importance but make up about 14 % and 7 % respectively of the inshore fish population and are the major components of the diet of fish-eating birds on the lake. P. darlingi is the larger species (Lo = 156.5 mm) and is found on both shelving and steep, eroding shores. Its mortality rate differs in each habitat (Z = 0.44 and 0.72 month-' respectively), only 0.79% survive for 12 months and its P/B ratio is 5.45 (on shelving shores). Ps. philander is smaller (L = 83.9 mm) and is restricted to shelving areas with abundant vegetation. Its monthly mortality rate was high (Z = 7.69), only 0.05% survive to 12 months whilst its P/B ratio was very high (7.69). The estimates of growth obtained for P. darlingi differ considerably from those given in an earlier study in Lake Kariba and some possible reasons for this are discussed. In suitable habitats, the combined production of both species could be 40 kg ha-' yr-1 which indicates their potential importance to the ecology of the lake.

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Production of fishes in a subtropical blackwater ecosystem: The Okefenokee Swamp1

Cited by 21 publications

References 25 publications

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

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

Differences in low pH tolerance among closely related sunfish of the genus Enneacanthus

Population dynamics of two small cichlid fish species in a tropical man-made lake (Lake Kariba)

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