Tropical waters

Ocean waters within 23 degrees latitude of the equator. In the western Atlantic, these waters are warm year-round. When a hurricane is moving through these waters, it is considered a tropical cyclone.

A key policy to minimising the effects of climate change on tropical marine organisms (e.g. coral bleaching and loss of seagrass cover) is to improve water quality, thereby reducing the potential for pollution to exacerbate the effects of thermal stress (Reef Plan, 2009). While pesticides are thought to contribute to stress on nearshore habitats, little is known of their chronic effects on tropical species or their persistence in tropical waters.

Pesticides, and particularly herbicides from agricultural sources, have been detected in nearshore sites of the Great Barrier Reef (GBR) all year round. The most commonly detected herbicides inhibit photosynthesis, thereby reducing primary productivity and calcification in key marine species. When plants and corals are stressed from increased sea surface temperatures (SSTs), additional stresses from reduced salinity and at high irradiance the impact of secondary chronic pollution such as herbicides exposure can become additive or synergistic. There is little data to explain to what extent chronic exposure to herbicides might interact with climate change to negatively affect sensitive tropical organisms such as corals and especially seagrass. Furthermore, little is known of the fate and persistence of agricultural herbicides that have been detected in the lagoon of the GBR. Understanding the half lives of these compounds and the toxicity of their breakdown products in the tropical marine environment is also a critical data-gap required to develop realistic ecological risk models for sensitive coastal organisms and communities of the GBR.