Around Australia, approximately 250 introduced marine species have been reported, some of which have had major ecological impacts.255 For the most part, tropical marine environments seem less susceptible to invasion than temperate ones.256 Asian green mussels are considered the highest risk for invasion and impact in Australia.255 They have been detected in ports along the Great Barrier Reef coastline a number of times over the past decade.257 The most recent report was in September 2013, when they were found in the internal heat exchanger of a work boat in Mackay port.257 Extensive investigations in port areas around Mackay did not detect any further mussel introductions. Introduced species such as rats and dogs affect seabird and turtle nesting on islands and along the mainland coast. Insect invasions have caused serious declines in Pisonia forests258 which are important nesting habitats for several seabird species. In January 2014, an outbreak of fire ants was detected on Curtis Island.259 Originating from South America, fire ants are very aggressive and voracious feeders on small animals including insects, spiders, lizards, frogs, birds and mammals. They can displace or eliminate some of Australia’s unique native species.260 A fire ant restricted area was declared on Curtis Island and the adjacent mainland following the outbreak, restricting the movement of some earth materials which could contain the introduced species.261 Introduced weeds have also affected the native vegetation on a number of islands within the Region.262 There is no regular monitoring of pests on Great Barrier Reef islands.
Introduced species continue to be recorded in and adjacent to the Region.
3.6.4 Other outbreaks
An outbreak of a species refers to a rapid increase in abundance, biomass or population of naturally occurring marine plants and animals. Outbreaks of the naturally occurring crown-of-thorns starfish are examined previously (Section 3.6.2). Outbreaks and blooms of other species can also be harmful or lethal to other marine species as they can compete for resources such as food, sunlight and oxygen. Extensive phytoplankton blooms can result from nutrients in flood discharges.125,263 Trichodesmium is a cyanobacteria found in nutrient-poor tropical waters. Outbreaks of the species appear as slicks on the water’s surface and can be distinctly pungent. It was first described by Captain Cook and, though it occurs naturally, blooms in the central Great Barrier Reef are thought to have increased, possibly due to nutrients in land-based run-off, in particular phosphorus, iron and organic material.264,265 The blooms have been implicated in directly smothering corals and increasing the bioavailability of heavy metals.266 Drupella are marine snails that occur naturally in the Indo-Pacific region, including the Great Barrier Reef, and are known to damage corals when in high densities.267 Outbreaks have been reported in Western Australia, Japan and the northern Red Sea.268 To date, no outbreaks of Drupella have been reported in the Region, although some tourism operators are permitted to implement control measures for this species. Numbers are monitored regularly at some locations in the Region through the Eye on the Reef monitoring program. Periodic blooms of the cyanobacterium Lyngbya majuscula have been recorded on the Great Barrier Reef.269,270 Lyngbya can smother seagrass, corals and other benthic habitats and has been linked with reduced reproductive success in some turtles in Moreton Bay.271 Macroalgal blooms can occur on degraded coral reefs in nutrient-rich waters resulting in a phase shift from a coral-dominated reef to one dominated by macroalgae; this phenomena has been reported from some reefs in the Region.127 There is no regular monitoring of outbreaks for any species other than crown-of-thorns starfish and Drupella.
Outbreaks of some other species are likely to have resulted from declining ecosystem conditions.