Plenary Presentation Australian Marine Sciences Association 2022

When is plankton not plankton? (#7)

Michael Kingsford 1 2
  1. 2ARC Centre of Excellence for Coral Reef Studie, Townsville, QLD, Australia
  2. College of Science and Engineering, James Cook University, QLD, Australia

Historically we have thought of larval fish and jellyfish as plankton that, by definition, drifts or wanders. Over four decades, my collaborators, students and I have contributed to changing this paradigm with a focus on fishes and jellyfish. Reef fishes hatch from eggs at a few millimetres in length and most spend days to months in the plankton before they settle on reefs. Many settle in the form of well-developed juveniles that can clearly swim well.  Surprisingly, for a supposedly dumb fish life-history stage, we have found they can orientate by responding to cues such as smell and sound, using the sun as a compass, and even utilising the earth’s magnetic field to find a reef.  Intergenerational tags and genetics have demonstrated they can even find home – not bad for a drifter?!  Jellyfish have no brain, but we have found they can stay close to home by having a benthic polyp stage, and as medusae many can swim well with surprising speed. Some can orient to suitable habitat with their 24 eyes while others stick to objects during the day and only swim at night.  These behaviours contribute to small local populations. ‘Plankton’ are not just drifters!