Masters by Research – University of Wollongong

Meroplankton larval release and supply in temperate saltmarsh and mangrove habitats

I decided while overseas that I wanted to try my hand at research. At this stage I’d hoped to keep my career options open between terrestrial science and marine science – so I chose a happy medium in estuarine ecology. I was also interested in applied science, and wanted involve some of the amazing marine parks I had access to, with some of my field sites back home in Jervis Bay.

Washing the plankton in the flooded mangrove forest

My main supervisors Todd Minchinton and Andy Davis advised me little was known about zooplankton patterns in Australian estuarine habitats. While trying to develop a research question, I learnt that many invertebrates time their reproduction to environmental cues. I’d heard about this early with the well-known example of multispecific coral spawning in the tropics (more on this later) and also with some fish. I immediately took an interest in this research question as the stakes were quite high for my newfound muddy friends. Because the saltmarsh is only flooded for a brief period every two weeks, their larval release would need to be timed perfectly to allow their young to export to the sea and avoid being stranded in evaporating pools. The surge of larvae at certain times could be also be an important source of food to small fish – making an energetic link between the plants and the larger fish. A simple energetic pathway could be i) saltmarsh photosynthesises solar energy to sugars ii) saltmarsh decomposes into detritus, iii) adult crabs forage on detritus and release larvae iii) small fish eat crab larvae, iv) medium-sized fish eat small fish and iv) large fish eats medium sized fish v) humans eat large fish with chips at Huskisson wharf.

Preparing mentally for night-sampling

The flooded mangrove forests of temperate regions are beautiful. In the tropics, they are littered with prop roots of the Red Mangrove in addition to a constant threat of crocs; but in the south the Grey Mangrove dominates, providing a thick canopy and easy passage for a young plankton tower. The main environmental cues I was looking at were sunlight, moonlight, tidal direction and tidal size. Sampling during the tidal cycles was time-dependant but relatively straight forward; however, sampling at night was quite…interesting and in some cases a little spooky. Luckily I had a great intern that kept me company for most of the sampling period.

I never got sick of looking at the weird creatures one sees under the microscope. Most invisible to the eye, animal plankton show intricate structures at 20 times magnification. But finally after 1.5 years of sampling and counting the larvae, I finally finished the data collection part of the project. I decided two years later to write it up into a manuscript and it was published in the journal Marine Biology