Project Leaders and Host Organisations
Associate Professor Michelle Waycott (James Cook University)
Dr Hugh Sweatman (Australian Institute of Marine Science)
Project Description and Objectives
For detailed descriptions of the outputs for
this project for Year 4 (2009/2010) of the MTSRF Research
Programme, see the Annual Research
Plan.
Project 1.1.1 aims to:
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Identify available indicators of condition and trend in
biodiversity, ecosystem health and thresholds of concern or
triggers for management action for non-reefal coastal systems
(seagrasses) (with reference to the GBR Bioregions, 2003) that are
appropriate for reporting the condition and trend in the health of
the GBR ecosystem;
-
Develop a conceptual approach to testing the further development
of indicators of condition and trend in the health of the GBR
ecosystem as new information becomes available;
-
Assess currently used indicators for the links between reef
water quality and the condition and trend in the health of the GBR
and develop new indicators if appropriate;
-
Develop prospective approach to identifying thresholds of
concern for coastal marine plant community health indicators for
the GBR; and
-
To synthesise broad spatial and the long temporal data collected
by the AIMS LTMP on herbivorous fishes on the GBR.
Herbivorous fishes are considered to have a crucial role in the
resilience of reefs because they consume macroalgae that, under
some circumstances, occupy vacant space caused by disturbance and
impede recolonisation by hard corals. Herbivorous fishes include
parrotfishes, surgeonfishes, rabbitfishes, blennies and reportedly,
batfishes. As well as groupings based on taxonomy,
herbivorous reef fishes can be divided into a number of guilds that
feed in different manners (scrapers, croppers, detritus feeders,
etc). Theories of ecological resilience hold that "functional
redundancy" – the presence of more than one species that
fulfils each ecological function and response diversity –
meaning that populations of the species in a functional group do
not all show the same response to changes in the environment, are
the bases of community resilience. The presence of abundant and
diverse assemblages of herbivorous fishes is often considered an
indicator of a healthy reef.
The feeding guilds of many larger herbivorous reef fishes have
been described, and one component of MTSRF Project 2.5i.3
(Resilience to climate change) has been an assessment of
grazing and grazing capacity of herbivorous fishes on two
cross-shelf transects, one in the northern GBR and another in the
central GBR, plus recent surveys at a range of inshore sites.
To date, it is not known how herbivore abundance varies over the
extent of the GBR, nor is it known how spatial patterns vary over
time. An early output from MTSRF Project 2.5i.3 was a report
reviewing the state of knowledge of herbivory by fishes on the GBR
(Cvitanovic et al. 2007¹) which states:
"It is frequently assumed
that a surfeit of data exists on herbivore distributions and
biomass on the GBR, however Table 2 (containing published baseline
data on the distribution, abundance and biomass of herbivorous
fishes on GBR) reflects the inadequacy of our understanding of
populations of herbivores along the length of the GBR as a whole.
Interesting cross-shelf patterns in herbivore populations and
species composition have been discerned at particular latitudes
… but the scope of our information needs to be extended
across a wider range of latitudes, bioregions and habitats to gain
a more holistic picture of herbivore populations on the GBR."
The AIMS LTMP has surveyed the suite of three major taxonomic
groups of herbivorous fishes: parrotfishes, surgeonfishes,
rabbitfishes, using a standardized survey method in a standard
habitat on reefs in three positions across the continental shelf at
six latitudes over seventeen years. Surveys also record
information on the benthic community and in that time these reefs
have been affected by several kinds of disturbance that removed
coral cover to varying extents.
A preliminary summary of abundances of all herbivorous fishes
counted by the LTMP across the GBR in 2007 (Delean and De'ath
2008²) showed that the total numbers varied across and along
the shelf.
Work conducted under this objective during the final year of the
MTSRF would summarise the LTMP data on herbivores to estimate and
map, (1) the spatial variation in numbers of herbivores across the
GBR, and (2) changes in those herbivore communities over seventeen
years, relating these to habitat changes. The variation in
distribution of assemblages of herbivorous fishes will be
summarised both by taxonomic groups and by feeding guilds. This
will be a significant step towards a holistic picture of herbivore
populations and provide a general context for the interpretation of
localised, short term studies. Phase shifts have occurred on very
few LTMP survey reefs, but the relationship between observed
abundance and composition of herbivore assemblages, the extent of
loss of coral through disturbances such as Acanthaster planci
outbreaks and the subsequent extent of macroalgal increase may help
to identify the critical abundances of herbivore guilds that are
necessary for community resilience and regions of the GBR where
those critical abundances are lacking.
¹Cvitanovic, C., Fox,
R. J. and Bellwood, D. R. (2007)
Herbivory by fishes on the Great Barrier Reef: A review of
knowledge and understanding. Unpublished Report to the
Marine and Tropical Sciences Research Facility. Reef and Rainforest
Research Centre Limited, Cairns (33 pp.).
²Delean, S. and De'ath, G. (2008)
Spatial and temporal patterns of indicators of reef health on
the Great Barrier Reef. Report to the Marine and
Tropical Sciences Research Facility. Reef and Rainforest
Research Centre Limited, Cairns (116pp.).
