Field study of the effects of sedimentation on the tropical seaweeds on intertidal nearshore fringing reefs
Creators: name: Umar, Jafar
Publisher: name: Northern Territory University
Year: 2000

description: There has been considerable concern that nearshore fringing coral reefs in some parts of the world are becoming degradated. This degradation may be caused, in part, by increased sediment and high seaweed abundance is proposed to be one of the first sign of this problem. Most areas of intertidal neashore fringing reefs in the Darwin and Kupang regions are dominated by seaweeds and often subjected to periods of high sedimentation. The present study aims to examine the impact of sedimentation on tropical seaweeds. The study investigates seaweed seasonality and its relation to sediment deposition and surface water quality, and experimentally tests the effects of degree of sediment load on recovery, recruitment, vegetative regeneration, growth, survival and degeneration of dominant or abundant species of the seaweeds. These studies involve several species common on intertidal nearshore fringing reefs in the Darwin and Kupang regions. Three locations were selected as study sites in each region. A 16 month periods of data sampling was carried out in each location to assess seaweed seasonality and its relation to sediment deposition and surface water quality. Experiments on recovery, recruitment and vegetative regeneration of seaweed species were done over a period of 12 months using four sediment levels: experimental removal, experimental removal/readdition, control (ambient conditions or unmanipulated sediment) and experimental addition. Growth, survival and degeneration of seaweeds were evaluated during a 6 month period, also using the four sediment treatments, except for the degeneration experiments in the Darwin region which were only applied three treatments (i.e. experimental removal, control and experimental addition). The percent cover of seaweed populations and of individual selected species, showed peaks in September and troughs in March in Darwin region, and peaks in March and troughs in September in Kupang region. In the Darwin region, the seasonal variations in percent cover, both the seaweed populations and some L IVA individual species, were positively correlated with salinity and conductivity. In the Kupang region, however, there were negative correlations with salinity and conductivity and a positive correlation with temperature. Percent cover of seaweed populations and individual species (with few exceptions) in the Darwin and Kupang regions was not correlated with seasonal sediment deposition. Field experiments revealed that sedimentation significantly affected recovery, recruitment, vegetative regeneration, growth, survival and degeneration of seaweed species studied, both in the Darwin and Kupang regions. It was found that the parameters studied showed higher values in reduced sediment treatment (below the control level) while increased sediment load over the control level resulted in lower values. The results suggest that the seaweed communities were in equilibrium with the present level of sediment load. An increase or decrease in sediment load may result in a change in community structure of the seaweeds.