Survival and recovery of planktonic organisms in prolonged darkness and their implications on ballast water management

Abstract

Understanding the population dynamics of transported organisms in the ship's ballast tanks during shipping operations and their ability to survive and colonize in the receiving environment (destination) can aid in developing effective ballast water treatment and management strategies. In the present study a natural plankton pool harvested from a tropical coast was used to study their survival in prolonged darkness and their regrowth potential upon re-illumination in laboratory conditions. In darkness, phytoplankton density and chlorophyll-a biomass decreased with increase in nutrient levels attributing to cell lysis. However, when subjected to vital staining using SYTOX® green, about 60% of phytoplankton survived in the dark tanks. Upon re-illumination after 36 days of incubation in darkness, >80% of recovered phytoplankton were pennate diatoms. On the other hand, zooplankton failed to survive/recover during the experiments when incubated in the dark. Less than 30% of the live zooplankton stained using Neutral Red in the dark tanks failed to recover during experiments. The data obtained clearly shows that prolonged dark incubation may promote the growth of opportunistic organisms and may alter their invasive potential through time and cause serious negative impacts to the receiving environment when transported by ballast water.