Great Barrier Reef Outlook Report 2009 – In Brief

!!!!!!!!!!!!!!3ECOSYSTEM HEALTHThe concept of ecosystem health is associated with one ofnormality: healthy ecosystems are more-or-less unchangedor natural. In the case of marine environments, where thereis usually little historic data, an ecosystem can easily bedescribed as healthy or even pristine, when it may in factbe changing, usually for the worse (that is, the ‘baseline’ ofwhat is considered normal has shifted).Many of the key physical, chemical and ecological processesof the Great Barrier Reef ecosystem are changing and this isnegatively affecting the health of the ecosystem.Physical and chemical processes Increased sedimentationand inputs of nutrients and pesticides to the ecosystemare affecting inshore areas (figure 3.1), causing increasedalgal growth, accumulation of pollutants in sediments andmarine species, reducing light and smothering corals. Seatemperatures are increasing because of climate change,leading to mass bleaching of corals; and increasing oceanacidity is affecting rates of calcification (figure 3.2). Thesephysical and chemical processes combined are essential tothe fundamental ecological processes of primary productionand building coral reef habitats on the Great Barrier Reef.Ecological processes It is considered that the overall foodweb of the Great Barrier Reef is being affected by declinesin herbivory in inshore habitats because the urban coastdugong population is a fraction of its former population;in predation on reef habitats because of potential Reefwidedifferences in coral trout and shark numbers on reefsopen and closed to fishing; and in particle feeding on reefhabitats because of the reduction in at least one species ofsea cucumber. Importantly, populations of herbivorous fishare healthy - they play an important role in maintaining the¬ATotal Suspended Solids(2008)¬BDissolved Inorganic Nitrogen(2008)Very LowLowMediumHighVery HighVery LowLowMediumHighVery HighCooktownCairns !Great Barrier ReefRegionGreat Barrier ReefcatchmentCooktownCairns !Great Barrier ReefRegionGreat Barrier ReefcatchmentTownsville!Townsville!Charters TowersBowenProserpineCharters TowersBowenProserpineQLD!MackayQLD!MackayClermontRockhampton !Gladstone !ClermontRockhampton !Gladstone !Bundaberg !Bundaberg !MaryboroughMaryborough0 300Gympie0 300GympieKilometresKilometresSDC090414 3.7BSDC090414 3.11BFigure 3.1 Modelled exposure to sediments and dissolved inorganic nitrogen, Great Barrier Reef, 2008 6These maps show the modelled exposure of the ecosystem to total suspended solids (A) and dissolved inorganic nitrogen (B) in 2008. Over the past150 years sediment inflow onto the Great Barrier Reef has increased four to five times, and five to 10 fold for some catchments. In addition, dissolvedinorganic nitrogen and phosphorous continue to enter the Great Barrier Reef at greatly enhanced levels, two to five times for nitrogen and four to10 times for phosphorus relative to pre-European settlement. The coastal zone is clearly the part of the Great Barrier Reef most exposed to increasedsedimentation and nutrients, especially areas close to river mouths.5GREAT BARRIER REEF OUTLOOK REPORT 2009 IN BRIEF