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:


Protected areas have been implemented worldwide to preserve diversity and maintain ecosystem function. Marine Protected Areas (MPAs), which often restrict commercial and recreational fishing and foreshore development, have been shown to increase fish abundance and biomass, compared with unprotected, or partially protected areas.

However, an overarching goal of MPAs is to maintain community stability – so are they actually doing this?

We used a 10-year snorkel survey in Batemans Marine Park in southern NSW to test whether changes in the identity of fish species (turnover) varies between sites that are protected (MPAs), unprotected (OPAs = outside park areas), and partially protected (PPAs – where recreational fishing is still allowed).

Snorkel survey at Batemans Marine Park
Photo credit: Bill Barker

We found that MPAs have a greater capacity to retain species through time, as shown by more shallow zeta diversity decline (i.e., turnover), compared with unprotected (OPAs) and partially-protected (PPAs) areas. This was particularly important for large-bodied harvested species, including red morwong and bream.

Our decadal study provides evidence that MPAs are working – in Batemans Marine Park protection produces stabilising effects on fish diversity. Whether these results hold more generally across other marine parks, and whether MPAs can also confer resilience to fish communities in the face of environmental change still needs to be determined.

This work was funded by the RAAP grant awarded to SIMS and IMOS by the NSW Governmment, and survey work done by Nature Coast Marine Group, and is now published in Conservation Biology. See ‘publications’ or contact me for a PDF copy.