Biodiveristy_State of Environment report - Mission Beach Cassowaries

Reef at low tideCrown of Thorns Starfish (COTS)Crown of Thorns Starfish (Acanthaster planci) is the majorfactor affecting coral coverage in the Innisfail sector, aswell as elsewhere on the GBR. The Innisfail sector iscurrently classified as recovering from COTS outbreaks bythe Australian Institute of Marine Science (AIMS Website2005).Raised nutrient levels in the ocean from human activitieson land have been postulated as a contributor to COTSoutbreaks. Nutrient availability promotes the growth ofoceanic algae known as phytoplankton. Thesephytoplankton are food for many reef species at the earlystages of development, when they are free-floating oceaniclarvae. Increasing the survival rate of larval COTS becauseof more available food results in greatly increased adultstarfish population. Doubling the levels of phytoplankton isestimated to contribute to a tenfold increase in the survivalof the COTS larvae.Conversely, it has been proposed that fishing and shellcollection have reduced numbers of COTS predators.Among these predators are the giant triton shell, thehumphead Maori wrasse and some emperor fish. In thisscenario increased adult survivorship greatly increases thesuccess of the population over time.Coral DiseasesCoral diseases on the GBR are not as great a problem as oncoral reefs elsewhere in the world. Some reefs, such asthose in the Caribbean, have been greatly affected bydiseases. The AIMS conducts continual monitoring ofdiseases throughout the GBR.Coral diseases have been linked to nutrient availability.Studies on Caribbean corals suggest that the infectiousagents of coral diseases can utilise the nutrients available inthe water (New Scientist Website, 2004a). This increasestheir survival and their potential to affect corals.Another effect seen on the Caribbean is the possible effectof sewage as a cause of infectious coral diseases. A studyinto a coral disease discovered the cause was a bacteriumcommonly found in the human gut. However, a conclusivelink to human pollution has not been established.The potential for human activities to contribute negativelyto reef health through diseases may pass a threshold ifsewage pollutants increase in concentration. Sewagetreatment at Innisfail will undergo upgrades in 2008, butthe majority of rural areas have only septic systems.Climate Change and Coral BleachingCoral bleaching is a world-wide phenomenon. It is thoughtthat climate change and increasingly hot temperatures areraising sea temperatures. Corals are affected when thesetemperatures exceed the level the coral can tolerate. Coralsare a symbiotic lifeform, which depend uponphotosynthetic algae called zooxanthellae to keep themsupplied with nutrients. At higher temperatures thesesymbiotic algae can die, resulting in the characteristicbleached coral, which has expelled its algal symbionts.High intensity light levels, low salinity and pollutants canalso exacerbate coral bleaching.Historically however, over the last 220 million years coralshave continued to exist throughout very varied seatemperatures. There is some evidence to date that coralsmay form relationships with new, more thermotolerantstrains of algal symbionts during elevated sea temperatures(New Scientist Website, 2004b). But, as these symbiontschange, there may be radical changes to the composition ofcoral on the reef.Unusually high water temperatures in 1998 and 2003caused bleaching across the GBR. Inshore reefs were themost badly affected.The bleaching phenomenon is currently under investigationto examine the thermo-tolerance and adaptability of coralsto climate change.PollutantsThere is not a great deal of information on the effects ofchemical and heavy metal pollutants upon corals. However,research in 2003 by Clare Bennett of Melbourne University(New Scientist Website, 2003) showed that even low levelsof copper (below that previously recorded around inshorereefs in the GBR) could seriously affect the success ofcoral spawning. Copper levels of only five parts per billionreduced the recruitment of coral larvae maturing intojuveniles by 30%. Sources of copper can be found inantifouling paints as well as in industrial runoff.The effects of other heavy metals on corals have not beenextensively studied. Recent studies of water quality in theJohnstone estuary (WBM Oceanics 2005 - see Water andAtmosphere chapter, section 4.6 - sewage treatment plant)57