FACTORS INFLUENCING SEAGRASS ECOLOGY IN THE INDIAN RIVER LAGOON
Rice, John D.
Trocine, Robert P.
Wells, Gary N.
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Effects of water depth, water temperature, light intensity, epiphyte coverage, detrital accumulation and sediment resuspension and shifting on seagrass ecology in the Indian River Lagoon system were studied from April 1977 through June 1979. Seagrass beds containing Halophila engelmannii, Halodule wrightii and Syringodium filiforme located between Cocoa and Grant, Florida, were chosen as sampling sites. Increases in vegetative growth for all 3 seagrass&s occurred in spring and to a lesser extent in fall months. Water temperatures ranged between 22 and 30°C. Decreased detrital accumulation, sediment resuspension and shifting, and water depth, increased light transmission and intensities at the seagrass blade level, and reduced epiphytic coverage (less than 300 mg epiphytes/gm blade) were observed during spring. Overall epiphyte levels (expressed as seasonal averages) were 850, 615 and 210 mg epiphytes/gm bladefor Syringodium, Halodule and Halophila, respectively. Net photosynthetic rates were highest during spring and fall, 1185, 1090 and 670 fig C fixed/mg Chl-hr. Periods of decreased vegetative growth (in summer and winter months) were accompanied by increased blade necrosis, rhizome and/or blade detachment, more dense epiphyte coverage (in excess of 100 mg epiphytes/gm blade) and reduced photosynthetic rates. Decreased light intensities at blade level, sub-optimal temperatures (< 20°C in winter and > 30° C in summer), and extensive sediment shifting and detrital accumulation were observed at these times.