Intertidal Seagrass Beds Research Articles

Seasonal changes in environmental variables, biomass, production and nutrient contents in two contrasting tropical intertidal seagrass beds in South Sulawesi, Indonesia.

Seasonal dynamics were studied by monthly monitoring of biological and environmental variables in permanent quadrats in two contrasting intertidal seagrass beds in South Sulawesi, Indonesia, from February 1991 to January 1992. Datasets were analysed with canonical correlation analysis for correlations between environmental and biological variables. Considerable variation in biomass, production and plant tissue nutrient contents in a monospecific seagrass bed of Enhalus acoroides, growing on a coastal terrigenous mudbank (Gusung Tallang), was assumed to be related to riverine influences of the nearby Tallo River. The variation in seagrass variables at this site could, however, not be significantly correlated to seasonal patterns in rainfall, salinity, tides, nutrient availability, water motion or turbidity. A seasonal cycle in biomass, production and nutrient contents in a mixed seagrass bed of Thalassia hemprichii and E. acoroides, growing on carbonate sand on the reef flat of an offshore coral island (Barang Lompo), was found to be largely determined by tidal exposure and water motion. Exposure of the intertidal seagrass bed during hours of low water during spring tides showed a gradual shift from exposure during the night (January-June) to exposure during daylight (July-December). Daylight exposure resulted in a significant loss of above-ground plant biomass through desiccation and 'burning' of leaves. The observed seasonal dynamics of the seagrass bed on reef sediment contrast with reports from the Caribbean, where the effect of tidal exposure on comparable shallow-water seagrass communities is relatively insignificant due to a small tidal amplitude.

Seasonal, diel and tidal variation in beam-trawl catches of juvenile grooved tiger prawns, Penaeus semisulcatus (Decapoda:Penaeidae), in the Embley River, north-eastern Gulf of Carpentaria, Australia

Seasonal, diel and tidal cycles of beam-trawl catches of juvenile tiger prawns, Penaeus semisulcatus, from an intertidal seagrass bed in the Embley River, Gulf of Carpentaria, were studied at three-week intervals between August 1981 and August 1982. Two seasonal peaks in catches of P. semisulcatus were recorded around November and April. Split-plot analysis of variance showed that after seasonal variation was removed, catches were influenced by day-night and tidal cycles. Few P. semisulcatus juveniles were caught during the day, and more were caught around low tide than around high tide. Results from drop-trap sampling at low tide showed that juvenile P. semisulcatus remained in the seagrass bed even when it became exposed and the water temperature exceeded 35°C. These findings, and practical considerations, suggest that to study long-term changes in relative abundance of juvenile P. semisulcatus with beam trawls, sampling should be completed at night and during the early part of the flood tide.

The Effects of Complex Trophic Interactions on a Marine Microbenthic Community

The consequences of complex trophic interactions for the dynamics of a natural microbenthic community from an intertidal Australian seagrass bed were examined during experiments in January, March, April, and June 1989. Effects of meiofauna and protist density manipulations on bacterial numbers and division rates and microalgal biomass were determined over 6 d each months. Results varied among experiments, microbial groups, and vertical positions within the sediment. Meiofaunal effects increased bacterial division rates but not densities in January subsurface and March surface sediments. In June, enhanced meiofaunal densities decreased subsurface but increased surface bacterial densities. A complex, tri—trophic—level interaction among meiofauna, protists, and bacteria probably caused the increased bacterial densities in June surface sediments. Meiofauna had no discernible effect on bacterial densities and division rates in January surface and March subsurface sediments even though relatively small (<50%) differences between treatments could be detected with reasonable statistical power. Changes in microalgal biomass could not be attributed to experimental treatments, and meiofauna likely have a limited effect on microalgae in this intertidal seagrass habitat. Results indicate that the combined effects of meiofauna can alter microbial densities and growth rates and significantly affect microbenthic community structure. Spatial and temporal variability in the nature of trophic interactions will determine the cumulative effects of meiofauna on microbial communities.

Periphyton density and shading in relation to tidal depth and fiddler crab activity in intertidal seagrass beds of the Banc d'Arguin (Mauritania)

Periphyton density and shading in relation to tidal depth and fiddler crab activity in intertidal seagrass beds of the Banc d'Arguin (Mauritania)

Population density and biomass of the bivalves Tellina mariae and Katelysia rhytiphora from a seagrass bed in Western Port, Victoria

Summary Each month from March 1976 to March 1977, samples of the bivalves Tellina mariae and Katelysia rhytiphora were taken from an intertidal seagrass bed in Western Port, Victoria. T. mariae was the more abundant species and had a mean monthly population density of 48 individuals/m2 and a mean monthly population biomass of 5.53 g dry fresh weight/ m2 K. rhytiphora had a mean monthly population density of 17 indi viduals/m2 and a mean monthly biomass of 2.33 g dry flesh weight/m2. The Tellina population was dominated by small individuals. In contrast, the Katelysia population was dominated by large individuals. Possible reasons for this difference in population structure are discussed.