in many non-reef areas such as parts of the lagoon floor.13 Macroalgae forms an extensive and important habitat covering between 25,000 and 30,000 square kilometres of the Region.116 Algal diversity is greatest off the coast of Gladstone, Rockhampton and Townsville and lowest in areas characterised by high turbidity and muddy sediments.116 Thirty-six species of macroalgae are classified as ‘vulnerable’ or ‘vulnerable within a narrow range’.131
Figure 2.7 Species composition and abundance of seagrass, Cockle Bay, Magnetic Island, 2005–2013
Fast-growing pioneer species are likely to be the first to colonise a disturbed area; however, as meadows grow over time in the absence of disturbances, the longer lived foundation species become more prevalent. Species composition is then likely to remain stable until the next cycle of disturbance and recovery. Source: Adapted from
McKenzie et al. 2014 65
Some fleshy macroalgae are likely to benefit from increased nutrients from land-based run-off but this is likely to be detrimental to natural macroalgal community composition.132,133 Nutrients can cause a shift in the balance between macroalgae and corals (Section 3.4.9).134
In 2011 cyclone Yasi caused a short-term reduction in algal cover on inshore reefs in the central part of the Region with cover re-establishing or exceeding pre-cyclone levels in 2012.83
The diversity of macroalgae is being maintained and abundance has increased in some areas.
The abundance of inshore macroalgae is considered to be generally stable, but some locally significant changes have been recorded in the Fitzroy region (Figure 2.8).83 Between 2005 and 2007 there was an increase in macroalgal cover in the Fitzroy area, partly as a result of the coral bleaching mortality event in 2006135; then in 2010 and 2011, declines in cover followed storm events and associated flooding of the Fitzroy River.83 From 2011, macroalgal cover increased again, probably as the loss of coral cover from the flooding created additional space for growth.83
Figure 2.8 Regional trends in inshore macroalgae cover, 2005–2013
The abundance of macroalgae is stable at a Reef-wide scale, but there have been marked regional changes over the last decade. Solid blue curves represent predicted regional trend bounded by blue dashed lines depicting the 95 per cent confidence intervals of that trend. Data presented in graphs relate to macroalgae cover in inshore areas of mapped regions above. Source:
Thompson et al. 201478
2.4.4 Benthic microalgae
Benthic microalgae are likely to have benefited from elevated nutrients.
Benthic microalgae are microscopic plants which grow on habitats comprising hard bottoms and sandy or muddy sediments. These algae play important roles in primary production and nutrient dynamics in the Region’s ecosystem.136 The biomass of benthic microalgae is typically several orders of magnitude higher than that of plants in the water column (phytoplankton).136,137 These species are little studied and understanding of their condition, distribution and trend has not improved significantly since the Outlook Report 2009. It is assumed they experience similar disturbances to those identified for the lagoon floor (Section 2.3.6). Some are likely to have benefited from elevated nutrient levels.