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
silver trevally Pseudocaranx dentex, prickly toadfish Contusus brevicaudus and several
leatherjackets are common (Plummer et al. 2003).
Depth and sediment affect the distribution of benthic invertebrates along the Victorian coast.
Coleman et al. (2007), and Heislers and Parry (2007) found that species richness was
greater at 40 metres compared to 10 or 20 metres depth. Their coastal survey of benthic
fauna included the benthos of Wilsons Promontory MNP. One transect off Oberon Bay on
the west coast and one off Waterloo Bay on the east sampled the soft sediment with two 0.1
m 2 grab samples in 10, 20 and 40 m of water depth. The grab samples contained between
39 to 734 individuals and 16 to 71 species consisting mainly of crustaceans including
amphipods, cumaceans, isopods and ostracods and polychaetes (Coleman et al. 2007;
Heislers and Parry 2007). The sediment was generally fine sand with some medium sand
(Heislers and Parry 2007).
Reef
Subtidal reefs and the assemblages associated with them are strongly influenced by the
position of the reef, its orientation, slope, depth, exposure and topography (Connell 2007).
These physical parameters influence key physical processes such as light, water flow and
sedimentation, and biological processes such as foraging and recruitment (Connell 2007).
Shallow subtidal reefs are often dominated by canopy forming algae. Deep reefs, where light
penetration is limited, are often dominated by large sessile invertebrates such as massive
sponges, whip corals, soft corals and colonial ascidians. Biotic assemblages can form
habitat and food sources for invertebrates and fish.
Flora
Diversity and species composition varies with location within the Wilson Promontory MNP.
Central Waterloo Bay on the east coast and other areas to the north-east of the MNP are
identified as having high macrophyte species diversity and richness (Edmunds et al. 2000).
The macrophyte population in the southern part of the MNP is of low diversity, predominantly
because a dense canopy is comprised of only one to three species with a sparse
understorey (Edmunds et al. 2000). These three species (Phyllospora comosa, Ecklonia
radiata and Seirococcus axillaris; Figures 7 and 9) form distinct algal assemblages: a
Phyllospora dominated, an Ecklonia-Seirococcus dominated (Figure 9); and mixed brown
algae (Edmunds et al. 2003; Edmunds et al. 2007). The species richness and diversity of the
macroalgal communities is lowest at the exposed western and south-western sites, where
the canopy is predominantly Phyllospora with a reduced cover of understorey species
(Edmunds et al. 2007). Relatively large variations in community structure were observed
between surveys at Oberon Point, Roaring Meg Bight and Fenwick Point (Edmunds et al.
2007).
The Phyllospora dominated assemblage is the most common, present at all MNP sites
(Edmunds et al. 2007). This assemblage consists of a canopy of predominantly Phyllospora
comosa (> 30% cover) and a lesser proportion of Ecklonia radiata. The associated
understorey has a sparse cover of thallose red algae, with much of the underlying rock
covered by encrusting corallines. Common understorey species included Phacelocarpus
peperocarpus, Plocamium angustum, P. dilatatum, Pterocladia lucida, Ballia callitricha,
Haliptilon roseum and Melanthalia obtusata. At sites in the south-west of the MNP, South
Norman Point, Oberon Point and Sea Eagle Bay, Phyllospora cover has increased since the
inception of the monitoring program. Phyllospora has higher abundances, and Ecklonia
proportionately less so, at the most exposed sites, particularly Sea Eagle Bay and West
Landing. At slightly less exposed sites, Ecklonia has a greater proportion of cover in the
canopy, particularly Oberon Point, East Landing and Fenwick Point (Edmunds et al. 2007).
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