A note on the occurrence and feeding habits of Noctiluca and their effects on the plankton community and fisheries

It becomes evident from the above facts that the effects of Noctiluca swarms on fisheries are more adverse than beneficial. Swarming takes place only when the sea is calm and there is an abundant supply of diatoms, the outbursts being usually preceded by diatom blooms. Noctiluca voraciously feed on several species of diatoms and to a very small extent on some of the smaller zooplankters. The presence of a large number of Noctiluca in an area seems to exclude other zooplankters, particularly the copepods. The rapid grazing down of diatoms and the exclusion of other zooplankters result in an almost monospecific population of these abnoxious cystoflagellates. Such a plankton adversely affects the important fisheries for sardines, anchovies, mackerel, etc., as these fishes do not occur in the presence of Noctiluca swarms. The negative indication continues as long as the swarms persist but transient swarms do not seriously affect either the plankton community or fisheries