Nodo Estándar: Zona no de Paso (Habitación) 28

The Twofold bioregion is represented by: • Ninety Mile Beach Marine National Park • Point Hicks Marine National Park • Cape Howe Marine National Park • Beware Reef Marine Sanctuary

The western portion of the Twofold bioregion consists largely of a long sandy beach (Ninety Mile Beach) with extensive areas of inshore and offshore sandy beds. This region also has occasional strips of low-relief calcarenite reef immediately behind the surf zone (7–25 m deep), such as within the Ninety Mile Beach Marine National Park at Seaspray. The sandy habitats of the far eastern coastline are punctuated by rocky headlands and localised outcrops of granite and metamorphic rocks, such as at Cape Conran, Point Hicks, Rame Head, Gabo Island and Iron Prince. Sea temperatures are often much warmer in the Twofold region than elsewhere in Victoria because of the warm East Australia current travelling down the eastern coast of the continent. However, the continental slope is quite close to the far eastern Victorian shore and cold-water upwellings are frequent. These upwellings provide nutrients to the inshore ecosystems, contributing to higher productivity. The biota of this region has a high component of eastern temperate species, in addition to many southern temperate and cosmopolitan species.

The Ninety Mile Beach habitats of the Twofold bioregion consist of extensive areas of surf beach as well as shallow and deep sandy seabeds. The animal community living within the sediment beds of the western Ninety Mile Beach region, including burrowing worms and small crustaceans, has an exceptionally high species richness.

A strip of low-profile calcarenite reef is often present behind the surf break, between 5 and 20 m depth. Various portions of the reef are periodically covered by sand transported by wave action and strong currents. Large seaweeds are not present on this reef habitat. The reef has a high cover of sponges and ascidians, with low cover of small red algae, bryozoans and hydroids. These reefs are important foraging ground for snapper Chrysophrys

auratus and juvenile great white shark Carcharadon carcharias, which feed on the snapper. This type of habitat

is represented in the Ninety Mile Beach Marine National Park. This Park also contains the unusual soft coral

Pseudogorgia godeffroyi, which is found only in the

western Ninety Mile Beach region.

The shallow reefs of the eastern Twofold bioregion (Cape Conran to Cape Howe) are inhabited largely by Phyllospora communities. However, the Phyllospora community of the Point Hicks region is quite different to that of the Gabo Island – Cape Howe region. The Point Hicks community has a relatively high abundance and diversity of small thallose red algae (as understorey and on open reef patches). In comparison, the Phyllospora assemblages near Cape Howe are largely depauperate of any understorey algae, with the reef predominantly covered by either encrusting coralline algae or encrusting sponges. These two Phyllospora communities are represented in the Point Hicks and Cape Howe Marine National Parks.

Gorgonia Fan Mopsella klunzingeri at Beware Reef. (Photography John Ariens).

The Point Hicks Phyllospora community includes moderate abundances of blacklip abalone Haliotis rubra and relatively high abundances of the predatory whelk Cabestana

spengleri and the seastar Patiriella calcar. The Cape Howe Phyllospora community has high abundances of Haliotis

and periwinkle Turbo undulatus.

A prominent invertebrate of the eastern Twofold bioregion is the long-spined black sea urchin Centrostephanus

rodgersii. Centrostephanus forms large grazing

aggregations where it denudes the reef of Phyllospora and other erect algal species, forming ‘sea urchin barrens’. These barrens are present on small patches throughout the region between Cape Conran and Cape Howe. The urchin barrens cover extensive areas around Gabo and Tullaberga Islands, near Mallacoota.

The black sea urchin Centrostephanus rodgersii is an important habitat shaper in the Twofold bioregion. The smaller white sea urchin here is Heliocidaris erythrogramma, a common and ecologically important species throughout Victoria. (Photography Matt Edmunds).

The fish assemblages associated with the Twofold

Phyllospora communities are quite different to Phyllospora

communities elsewhere in Victoria. There are higher abundances of banded morwong Cheilodactylus spectabilis,

Neoodax balteatus, maori wrasse Ophthalmolepis lineolata,

one-spot puller Chromis hypsilepis and white-ear damselfish Parma microlepis. The eastern blue grouper

Achoerodus viridis is also a prominent species, but present

in low numbers.

On deeper reefs the abundance of common kelp Ecklonia in the canopy increases substantially, particularly in the Point Hicks region. At Point Hicks Ecklonia is the dominant species at 10 m depth, with Phyllospora still an abundant

component. At 15 m depth, Ecklonia is the principal canopy component. On the deeper, Ecklonia-dominated reefs, the assemblages beneath the canopy vary substantially from reef to reef. At Bemm River the reef is predominantly covered in encrusting coralline algae on the reef tops, with high abundances of filter feeders such as the ascidian

Herdmania momus, feather star Cenolia trichoptera, feather

duster worms Sabellastarte sp and sponges under ledges and on vertical rock faces. At Point Hicks, the reef beneath the canopy has a high cover of encrusting and erect sponges. In contrast, the Ecklonia assemblage at Sensation Reef (also within the Point Hicks Marine National Park) has a diverse and abundant understorey of small fleshy red algae (with many species found only in that area).

Sensation Reef, Pt Hicks, has a canopy of common kelp Ecklonia radiata at 15 m depth, with sponge gardens in deeper waters. The grey colony in the foreground is the soft coral Capnella gaboensis. (Photography Matt Edmunds).

From 15–20 m to approximately 40 m depth, the Ecklonia canopy thins out and is gradually replaced by a ‘garden’ of massive erect sponges, encrusting sponges, gorgonian coral

Mopsella zimmeri, sea-whip coral Primnoella australasiae,

and basket star Conocladus australis (on the corals). These deep reef habitats are present in both the Point Hicks and Cape Howe Marine National Parks.

Both the Point Hicks and Cape Howe Marine National Parks have extensive sandy beach and shallow sandy seabed areas, in addition to very deep sandy mud habitats (50–90 m deep).

Sea whips Primnoella australasiae are common on deeper reefs. (Photography Matt Edmunds).