In conserving marine areas, maps of marine habitats are often used. This is especially the case when there is little or no information on the distribution and diversity of the organisms that the planning is attempting to conserve. But just how good is this assumption? We tested this using seaworms in the Port Stephens-Great Lakes Marine Park and found that their distribution and diversity can be represented by a different, more simple map than the marine habitat map currently used (which is based on the distribution of mud, sand and seagrass beds).

Why use worms? Seaworms are abundant and diverse and studies elsewhere have shown that their distributions also reflect those of other benthic (sea-bed) organisms such as crustaceans and molluscs. They also exhibit a tremendous range of feeding and life styles and are highly dependent on sediment type and organic matter, making them ideal surrogates for benthic communities.

The Port Stephens-Great Lakes Marine Park in NSW has six estuarine habitats identified in the Marine Park’s habitat map (subtidal sand, mud, muddy sand, and seagrass beds comprising Posidonia australis, Zostera capricorni and mixed Posidonia/Zostera). A percentage of each of these habitats is currently conserved within high conservation areas, but the assumption that these six habitats actually represented real variation in benthic biodiversity had not been tested.

By surveying seaworms in the Marine Park, we found that sediment types are important in determining the distribution of sea worms, but that other factors, such as distance to the estuary entrance, depth, sediment grain size were more important. Overall, seaworm distributions reveal that the Marine Park can be divided into three broad areas (1) the entrance to the Bay (2) the inner area in the deeper low energy regions of the bay and (3) where the riverine channels dissect the deeper parts of the estuary.

Studying worms can give a very different picture than if one just uses the types of habitats based on the distribution of sediments, which is traditionally used in marine park zoning around the world, and may provide an important tool in managing our natural estuarine systems. As zoning plans are reviewed every 5 years there is an opportunity to revise the current zoning plan to take on board our findings and more effectively conserve the biodiversity of the areas.

We suggest that this study will assist marine park managers in identifying which areas warrant higher levels of protection. This will help conserve benthic biodiversity and ensure long term ecosystem functioning.

Dr Pat Hutchings
Senior Principal Research Scientist
Australian Museum Research Institute

Prof. Bill Gladstone
Head of School, School of the Environment
University of Technology, Sydney

More information:
Dixon-Bridges, K., Hutchings, P. and Gladstone, W. (2014). Effectiveness of habitat classes as surrogates for biodiversity in marine reserve planning. Aquatic Conserv: Mar. Freshw. Ecosyst. 24: 463–477.