Harmful algal blooms (HAB) may result from higher growth rates, lower mortality, physical aggregation, or some combination of these factors. We have been focusing on grazing mortality as a mechanism that may be involved in both bloom initiation and demise. In laboratory experiments, we are examining the effects of several estuarine HAB species on common benthic and planktonic grazers, including larval and juvenile bay scallops (Argopecten irradians), the copepod Acartia tonsa, and a variety of ciliate microzooplankton. We are measuring feeding and growth rates and examining sublethal effects using histological methods. To date, most of our efforts have been concentrated on the dinoflagellate Prorocentrum minimum (strain EXUV) and the raphidophyte Heterosigma carterae (strain OL). In temperate estuaries of the US Atlantic coast, these species frequently bloom in summer, and blooms appear to originate in bays and subestuaries, subsequently proliferating into open estuarine waters. Our preliminary results are consistent with the idea that inability of benthic grazers to control these species in shallow nearshore waters results in high populations that are exported to deeper waters of the estuary, where planktonic grazers gradually reduce their numbers. P. minimum, for example, is readily eaten by variety of ciliates, as well as the copepod, but rejected in pseudofeces by the scallop. In addition, this HAB species causes pathological changes in the digestive systems of juvenile scallops when it is ingested.

ALGAL BLOOMS MONITORING WITH A TELEMETRIC TECHNOLOGY : SEAWATCH Indonesia BUOY

Rahmania A. Darmawan

SEAWATCH Indonesia Program, Directorate for Environmental Technology, The Agency for the Assessment and Application of Technology, BPPT New Building 21^st floor, Jl. M. H. Thamrin No. 8 Jakarta 10340, Indonesia.

Field sampling is a usual method for monitoring the algal blooms in Indonesia. As a new alternative for monitoring the algal blooms, SEAWATCH Indonesia project has been assesst the OPTISENS (an optical sensor) for monitoring the algal blooms phenomena in some SEAWATCH buoy sites (Jakarta Bay and Jepara). The coefficient attenuation data produced from the OPTISENS in a near real time manner and transfer via satellite to the read down station at SEAWATCH Indonesia office at BPPT building. Principally the OPTISENS was design to determine particles (phytoplankton or others) at the wave length 650, 555 and 470 nm. By processing the data (until get the ratio of coefficient attenuation relative) and combine with field sampling and others environmental data (oxygen saturation, salinity, brightness, etc.), this SEAWATCH system can be used for monitoring the algal blooms as an early warning system. The result from coefficient attenuation data processing from Jepara buoy shown a high abundance of phytoplankton at that area and the result from field sampling shown that at those time Jepara waters around the buoy site was dominated by Nitzschia, Chaetoceros and Rhizosolenia. But, the result from Pluit buoy coefficient attenuation data processing didn’t show the domination of phytoplankton. The composition of the ratio : c’(B)/c’(R) <1; c’(B)/c’(G) <1 and c’(G)/c’(R) >1 shown others particle dominated Pluit waters at those time.