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Primary production dynamics of epiphytic algae in Mississippi seagrass beds
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Description:Primary production rates of four autotrophic components in Halodule wrightii Aschers. beds off Horn Island in Mississippi Sound were measured over an annual cycle. The epiphytic algal assemblage on Halodule leaves was dominated by the red alga Acrochaetium flexuosum Vickers and 12 taxa of araphid, monoraphid, and biraphid diatoms. The phytoplankton over the beds and microflora associated with the sandy sediments in which Halodule was rooted were dominated by centric and small pennate diatoms, respectively. Hourly production rates varied from as little as 0.9 mg C/m² for Halodule leaves in winter to as high as 1143 mg C/m² for epiphytic algae during summer. Stepwise multiple regression showed that only 15% of the variation in hourly epiphytic algal production could be related to a single environmental variable (i.e. light energy). Variations in hourly production rates for the other three productivity components were best explained by light, water temperature, tidal range, and/or blade density; R² for these regressions ranged from 0.66 to 0.94. A single experiment conducted in August revealed that aIl productivity components exhibited photoinhibition, with the inhibition of the sand microflora and epiphytic algae being the most pronounced. Annual production rates were estimated (g C/m²) as follows epiphytic algae (905), phytoplankton (468), sand microflora (337), and Halodule (256). As far as the benthic components are concerned, system production is dominated by the microalgae with the contribution of Halodule blades being only 17% of the total. The high standing crops and production rates of the epiphytic and benthic microalgae suggest they may be trophically important for consumers feeding in the beds.
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