Study of Microphytobenthos Primary Productivity in Pulau Lancang, Kepulauan Seribu

Abstract

Vast and bare substrate area in euphotic zone is not only served as habitat for macroscopic vegetation, but also photosynthetic microorganisms whose abundance is dominating the upper sediment surface. These microorganisms are composed of microalga colonies, called microphytobenthos, living attached to sediment particles. Hence, their existence is sometimes neglected. Microphytobenthos taxonomy is basically the same with pelagic phytoplankton. Another similarity is their photosynthetic characteristic which requires light as the main energy source in photosynthesis (Underwood and Kromkamp, 1999; Urban-Malinga and Wiktor, 2003). Microphytobenthos were easily resuspended to the water column and representing more than 50% of total cholorophyll concentration, then become available as food source for deposit feeder and suspension feeder. The only difference between pelagic phytoplankton and microphytobenthos is their habitat preference. Besides playing an important role in shallow water food chain, microphytobenthos also give contribution to sediment stability, by excreting extracellular polymeric substances (EPS) and influence nutrient flux on sediment – water boundary through their photosynthetic and metabolic activity. However, microphytobenthic community and their primary productivity, particularly in Indonesian waters, were still less studied. Measurement of primary productivity was usually performed only at the surface or water column, neglecting the primary production by sediment-associated microalgae. Research on microphytobenthic community and primary productivity is important since they perform significant role in carbon fixation, particularly in shallow water system, where sunlight intensity still penetrates and reach the sediment surface. The aim of this study is to investigate microphytobenthic primary productivity and estimate the contribution of microphytobenthos contribution towards entire aquatic primary productivity. In this study, primary productivity estimation was based on photosynthetic process by calculating the difference of oxygen concentration before and after photosynthesis. Primary productivity of microphytobenthos in Pulau Lancang was higher compared to that in surface layer. Results from third-day experiment shown an extremely high value from microphytobenthos primary production, reached up to 29 times of surface layer primary productivity. Average of microphytobenthos primary productivity was 42.32 mg C m-3 hour-1, almost two fold higher than phytoplankton primary productivity which was 22.46 mg C m-3 hour-1. Results from pigment analysis using spectrophotometer shown that chlorophyll-a concentration in sediment surface was 4496.08 – 8937.12 mg l-1, much higher than those in surface layer, 0.0003339 – 0.000544 mg l-1. These results were in line with high primary productivity at the sediment surface which strongly caused by the abundant biomass of sediment-associated benthic vii microalgae. According to the measurement of physical and chemical parameters, light intensity was considered as the main factor supporting microphytobenthos primary productivity. Microphytobenthos primary productivity alone cannot describe the entire aquatic productivity since there are a lot of other autotrophic components such as seagrass and mangrove that compose marine ecosystem of Pulau Lancang. However, significant contribution of microphytobenthos indicates that microphytobenthos is feasible to be considered as important component in the study of coastal primary productivity.