Seagrass meadows of the Great Barrier Reef: What affects change?

Seagrasses are an important component of the coastal ecosystem for a number of reasons: they are a food source for dugongs and turtles; they provide habitat for numerous plants and animals including key fisheries species; and their high rates of primary production support coastal ecosystems.

Tropical seagrass meadows are highly diverse, extending across broad habitat ranges including estuaries, coasts, reefs and deepwater habitats up to 60m deep. Coastal seagrasses are the most extensive and are at the greatest risk because of their proximity to human activities and land-based runoff. They are highly sensitive to environmental change, which means that they can play a role as indicators of coastal ecosystem health.

Growth, diversity and the reproduction of seagrasses is affected by water turbidity as from dredging and floods which affects light penetration, and from changes in water temperature. Research by Catherine Collier, Michelle Waycott and others funded by the Marine and Tropical Sciences Research Facility, is attempting to determine how changes in light levels and water temperatures affect seagrass meadows.

• How much light is required before different seagrass species become stressed? What are the signs that seagrasses are stressed?

• How do changes in water temperature affect growth, physiology and sexual reproduction? We know that tropical seagrass meadows are already affected by changing water temperature: they show seasonal changes in density; in summer they can experience ‘burn-off’ caused by high temperatures in shallow water.

This information is required for future management and monitoring of these important seagrass meadows. For more information refer to www.seagrasswatch.org.

Contact person: catherine.collier@jcu.edu.au