Title

Productivity of key seagrass species of importance to dugongs, at selected locations within the Great Barrier Reef

Objectives

1. To determine the productivity of seagrass species of importance to dugongs, at specific locations (coastal and deepwater).
2. To monitor seagrass productivity between seasons and years.

Relevance

Seagrasses are essential food for the dugong and there is relatively little information on the health and distribution of seagrasses within the Great Barrier Reef Marine Park and World Heritage Area. There is no information on productivity for most seagrass species, areas and habitat types. This is a major gap in the knowledge base required for effective management. Dugongs and those fish, turtles and prawns dependent on seagrasses for food rely on both available area of seagrass and the productivity (plant growth rate) as these determine the total available food and nutrient source. Changing conditions such as poorer light penetration could reduce seagrass productivity (leaf and root production and/or nutritional value) and increase the area of seagrass required to support a dugong. Seagrass area may not be affected by some downstream effects but productivity could be. Area alone is not necessarily the best measure of the ability of an area to support the food requirement of dugong and fish/ prawn/ turtle populations.

Feasibility

The methodologies for measuring productivity of near-shore tropical bladed seagrass species are well established and have been successfully conducted at several locations (Green Island, Cairns Harbour, Low Isles). Methodologies for measuring the productivity of deep-water plants are similar to shallow/near-shore plants, however they are currently being modified so as not to compromise safe diving practices.

Approximate cost

Salaries of temporary biologists and technicians estimated at $113 400 per year in 1998–99 (increasing at 5% annually). Operating costs include vessel charter, travelling expenses, data analysis and preparation. Capital costs cover a standard computer workstation.

Time required

This project is to monitor seagrass productivity of key species, in selected areas of the Great Barrier Reef Marine Park, three to four times a year over a period of two to three years.

The project would be initiated in Summer 1998. A summary of results will be available each year in the form of interim reports, so that any finding of importance to management can be identified and appropriate management strategies implemented. The project will conclude late 2001, after which a major report will be produced summarising results of the study and recommendations for further research and management.