the reef biota at Wilsons promontory marine national - Parks Victoria

Parks Victoria Technical Series #74SRMP Wilsons Promontory MNP1. INTRODUCTION1.1. Subtidal Reef Ecosystems of VictoriaShallow reef habitats cover extensive areas along the Victorian coast. The majority of reefsin this area are exposed to strong winds, currents and large swell. A prominent biologicalcomponent of Victorian shallow reefs is kelp and other seaweeds (Figure 1.1). Largespecies, such as the common kelp Ecklonia radiata and crayweed Phyllospora comosa, areusually present along the open coast in dense stands. The production rates of denseseaweed beds are equivalent to the most productive habitats in the world, includinggrasslands and seagrass beds, with approximately 2 kg of plant material produced persquare metre of seafloor per year. These stands typically have 10 - 30 kg of plant materialper square metre. The biomass of seaweeds is substantially greater where giant speciessuch as string kelp Macrocystis pyrifera and bull kelp Durvillaea potatorum occur.Seaweeds provide important habitat structure for other organisms on the reef. This habitatstructure varies considerably, depending on the type of seaweed species present. Tallvertical structures in the water column are formed by M. pyrifera, which sometimes forms adense layer of fronds floating on the water surface. Other species with large, stalk-like stipes,such as E. radiata, P. comosa and D. potatorum, form a canopy 0.5 - 2 m above the rockysubstratum. Lower layers of structure are formed by: foliose macroalgae typically 10 - 30 cmhigh, such as the green Caulerpa and the red Plocamium species; turfs (to 10 cm high) ofred algae species, such as Pterocladia capillacea; and hard encrusting layers of pinkcoralline algae. The nature and composition of these structural layers varies considerablywithin and between reefs, depending on the biogeographic region, depth, exposure to swelland waves, currents, temperature range, water clarity and the presence or absence ofdeposited sand.Grazing and predatory motile invertebrates are prominent animal inhabitants of the reef(Figure 1.2). Common grazers include blacklip and greenlip abalone Haliotis rubra andHaliotis laevigata, warrener Turbo undulatus and sea urchins Heliocidaris erythrogramma,Holopneustes spp. and Amblypneustes spp.. These species can influence the growth andsurvival of habitat forming organisms. For example, sponges and foliose seaweeds are oftenprevented from growing on encrusting coralline algae surfaces through the grazing actions ofabalone and sea urchins. Predatory invertebrates include dogwhelks Dicathais orbita,southern rock lobster Jasus edwardsii, octopus Octopus maorum and a wide variety of seastar species. Other large reef invertebrates include motile filter feeding animals such asfeather stars Comanthus trichoptera and sessile (attached) species such as sponges, corals,bryozoans, hydroids and ascidians.1