Literature Review and Gaps Analysis
Research Report
Catherine Collier and Michelle Waycott
School of Marine and Tropical Biology, James Cook
University
ISBN 9781921359248
Published February 2009
MTSRF Project 1.1.3 -
Condition, trend and risk in coastal habitats: Seagrass
indicators, distribution and thesholds of potential concern
Introduction
Seagrass meadows are important for a number of reasons:
they act as the foundation of a diverse community with
numerous ecological roles; primary production; habitat and food for
herbivores (including turtles and dugongs); sediment stabilization;
biochemical modification of the local environments; nutrient
cycling and hydrodynamic modifiers. Seagrasses are known to be
under threat from numerous impacts and also play a role as
indicators of coastal ecosystem health (Orth et al. 2006).
Recent analysis of Great Barrier Reef Ecosystem Health (Great
Barrier Reef Marine Monitoring Program Workshop, September 2007)
supports this in the GBR region.
The Great Barrier Reef (GBR) supports a high diversity of
seagrass species across a broad range of habitat types. Seagrasses
are not a taxonomically unified group but are an ecological group,
which through pressures imposed by the marine environment have
converged in general morphology, i.e. they have photosynthetic
leaves and roots and rhizomes to anchor in the sediment and to grow
via rhizome extension (Waycott et al. 2007) . The high
seagrass diversity in the GBR is associated with a broad range of
seagrass forms and functions (Walker et al. 1999) . These
species respond to environmental drivers in different ways and with
different thresholds for tolerance to disturbances. While there are
some generalisations that can be drawn across this broad grouping,
for many aspects being considered in relation to drivers of change,
seagrass species differ. Every effort is made in this review
to consider this diversity where there is enough available
information to do so.
Seagrass monitoring and research has a rich history in the GBR
region and yet there are many key areas of system understanding
that are poorly understood. In this review we summarise the
understanding of drivers in seagrass meadows. In a recent report
(Coles et al. 2007) , the status and trends of seagrass
distribution in the GBR is described. The review here-in describes
drivers of change in seagrass meadows and how these influence
seagrass distributions, natural cycles in distribution and growth
and drivers of disturbances to seagrass meadows. We seek to
identify key processes that explain the distribution, variability
and limitations to growth, enhancing our ability to recognise
ecosystems under stress and when management actions may be
required. The overall aim of this review is to highlight
significant knowledge gaps that, if fulfilled, will improve our
ability to manage seagrasses of the GBR.
To fully describe the processes limiting seagrass growth, an
understanding of the manner in which seagrasses grow and survive
throughout their life is useful. The life of a seagrass plant is
typically dominated by the life-history stage of growth and meadow
expansion following seed recruitment. During this stage of plant
growth, individuals (from germination of a single seed) may persist
for a very long time, forming large, clonal meadows. For all GBR
seagrasses the extent of longevity and scale of individual growth
remains unknown and requires future studies using genetic and
ecological tools. Flowering and seed set provide propagules for
seagrass habitats recovery following disturbance. Germination and
establishment are rate limiting to habitat recovery and potentially
influence the resilience of coastal marine communities. The causes
of habitat loss are multitude and are form the basis of this
review.
