Biological strategies in controlling or mitigating marine harmful algal blooms (HABs).

Some biological control or mitigation strategies for harmful algal blooms (HABs), a problem worldwide in coastal waters, are reviewed. Bacteria, viruses and parasites are abundant in marine ecosystems and their abilities for rapid replication and host-specificity make them attractive HAB controlling agents; however, potential ecological impacts need to be taken into account. Species interactions between bloom microalgae and btl.er algae play essential roles in affecting the phytoplankton sequence either by competing for the available nutrient supply or by secreting extfacellular organic substances (allelopathy) into the environmental medium. This control strategy is not well understood due to a lack of experimental data, especially under natural conditions. Grazing of phytoplankton by zooplankton and suspension feeding benthos is also considehKl a promising control agent, but this approach has many logistical problems and is a long way from the application stage. Collectively, some of the biological strategies discussed are decades from possible implementation, but others are further developed and thus worth consideringrin the immediate future.