In a recent study, we compiled data on “species” occurrence across six marine assemblages: pelagic bacteria, kelp-associated bacteria, phytoplankton, zooplankton, fish, and benthic groups to test patterns of turnover across ecological traits of body size, habitat, and trophic level.

These ecological traits have been tested in terrestrial systems, however our understanding of how aquatic (and in particular marine) community species composition change across these traits is still poorly understood.

We had some interesting predictions to test! We expected based on theory and previous work on terrestrial systems that 1) turnover should be unimodal with body size, 2) benthic habitats should be patchier and therefore show higher turnover than pelagic habitats, and 3) turnover should increase with trophic position.

Conceptual representation of predicted changes in spatial turnover across the following ecological traits: (a) body size; (b) habitat, and (c) trophic level.

I compiled data from different sources (thanks to my co-authors!) on species incidence along the NSW coastline. The East Australian Current (EAC) has dynamic oceanographic systems and is an ocean warming hotspot and therefore key conservation priority. We used data at 1 degree latitude intervals to compare zeta diversity decline (turnover) across space for the six marine assemblages.

We found that pelagic bacteria showed the highest rate of turnover, while phytoplankton and zooplankton showed a greater proportion of shared species across latitude (and therefore relatively shallower turnover).

We found that our prediction for body size was met, but only for macro-organisms (phytoplankton to fish). Our prediction did not hold for bacteria. It was also unclear whether benthic communities had higher turnover than pelagic communities. However, we did see a clear correlation between turnover and trophic level, particularly within fish. Carnivores showed twice the rate of turnover, compared with herbivores, benthic invertivores and planktivores.

Ultimately, we found that trophic level (and body size for macro-organisms) can provide a useful indicator of the rate of turnover in marine communities. This information can be used to inform sampling protocols and management of marine communities in New South Wales.

Thanks to the co-authors for contributing their data and knowledge to this project. To read more, see the published open access paper here: