parks victoria technical series marine natural values study vol 2 ...

Parks Victoria Technical Series No. 79
Flinders and Twofold Shelf Bioregions Marine Natural Values Study
Intertidal
Soft sediment
The intertidal soft sediment is in the north-west of Point Hicks MNP as sand beach fronting
an extensive dune system (Ball and Blake 2007). As noted by Plummer et al. (2003) no
specific data on the biota on sandy beaches are available in the MNP or nearby. Intertidal
soft sediment flora is restricted to macroalgae drift and macroalgal epiphytes. Beach-washed
materials in sandy beach habitats are a significant source of food for many shore birds, and
contribute to the detrital cycle that nourishes many of the invertebrates, such as bivalves,
living in the sand (Parks Victoria 2006c).
Reef
Rocky intertidal reefs, also called rocky reefs or intertidal platforms, are generally found in
Victoria on and near headlands with stretches of sandy beaches either side. Along with
beaches, intertidal reefs are one of the most accessible components of the marine
environment as they are the interface between the ocean and the land (Power and Boxshall
2007). As such they are valued as important habitats by people and tend to be visited more
than other sections of the coast (Carey et al. 2007a; Carey et al. 2007b). This means they
are often subjected to human pressures like harvesting, fossicking and trampling as well as
pressures from pollution sources on land and in the sea (Power and Boxshall 2007).
Intertidal reef biota are exposed to large changes in physical conditions such as temperature
and desiccation. There is great spatial and temporal variability in the life histories of the
organisms and the environmental processes in reef habitats (Underwood and Chapman
2004). The recruitment of new biota onto the reef, from the plankton, strongly influences the
ecological patterns for individual species and assemblages. Interactions between biota on
the reef also influence biota distribution. Resources which are often in short supply on
intertidal reefs are space on which to live and the food itself (Underwood and Chapman
2004).
The composition of invertebrate assemblages living on the intertidal reefs at Point Hicks are
more similar to those found at Mallacoota, Merimbula and Bermagui than to assemblages
found further west along the Victorian coast (Hidas et al. 2007). East coast species
contributing to these differences have lower densities at Point Hicks than in NSW (Hidas et
al. 2010).
The MNP has a relatively narrow band rock platform around the base of Point Hicks itself
(Ball and Blake 2007). The remote location of the MNP means that human threats to the
intertidal reef such as biota collection and trampling is low, due to this there is has been no
intertidal reef monitoring program in Point Hicks MNP. As noted by Plummer et al. (2003) no
specific data on the biota on intertidal reefs are available in Point Hicks MNP or nearby.
Subtidal
Soft sediment
Between Whaleback Rock and the isolated reef directly off Point Hicks biogenic gravel,
consisting of whole and broken shells often encrusted in pink algae, covers the ocean floor
(Holmes et al. 2007a). Shell areas tend to have many small orange ball sponges Tethya in
amongst the shells (Holmes et al. 2007a). Sometimes vertical sponges are also present,
attached to larger shells (Holmes et al. 2007a). Areas with rippled sand also contains shells
in the ripple troughs. These shells are usually covered in pink encrusting algae, possibly
indicating the presence of rhodoliths in these areas (Holmes et al. 2007a). Sand areas tend
to be bare, although if vegetation is present, it is usually clumps of Caulerpa. Some areas of
sand are inhabited by sessile invertebrates; however, as the species of invertebrates
observed must attach to a hard substrate, it is assumed that the sand forms a thin veneer
over the reef (Holmes et al. 2007a).
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