Victorian Subtidal Reef Monitoring Program - Parks Victoria

Parks Victoria Technical Series No. 67PPB Sanctuaries Subtidal Reef Monitoring4 Point Cooke Marine Sanctuary4.1 MONITORING SITESPoint Cooke Marine Sanctuary is close to Werribee on the northwestern shore of the bay.The subtidal reef at Point Cooke consists of low-relief, textured basalt reef interspersed withpatches of sand and mud. The Point Cooke monitoring site (Site 1) was positioned along the3-4 m isobath over the reef and patches of sand (Figure 4.1).A reference monitoring site was located offshore from the RAAF Base at Laverton (RAAFBase; Site 4102), approximately 3 km southwest of Point Cooke Marine Sanctuary. The reefat RAAF Base is similar in structure to Point Cooke but differs substantially in the vegetationpresent (Figures 4.2 and 4.3). The RAAF Base monitoring site is at 3-4 m depth.4.2 MACROALGAEThe reef at Point Cooke (Site 1) was patchy and interspersed with large areas of sediment.This was reflected in the patchy distribution and cover of algae at this site. The dominantspecies was initially common kelp Ecklonia radiata, with approximately 10 % cover for thefirst three surveys at Point Cooke. Ecklonia radiata was absent during the latest survey in2009 (Figure 4.4a). The carpeting green alga Caulerpa remotifolia increased substantially incover between each successive survey, from 2 % cover in 2003 to 48 % cover in 2009(Figure 4.4c). There was a corresponding decline in cover of encrusting coralline algae.Other common species, but with cover generally less than 5 %, included sea lettuce Ulva sp.,brown algae Dilophus marginatus and Dictyota dichotoma and thallose red algae such asGigartina sp.The introduced Japanese Wakame Undaria pinnatifida was formally observed for the firsttime at Point Cooke during the latest survey in April 2009. Most of the individuals observedwere small juveniles 70-400 mm in length (Stages I and II). The coverage was only 1.6 %.Undaria pinnatifida has infested reefs along the northern shore of Geelong Arm and on thepiers and structures of Hobsons Bay for some time and colonisation of reefs in northern PortPhillip Bay was to be expected. This kelp has distinct alteration of generation life phases,with the macroscopic sporophyte stage occurring from late May/June through to early/midsummer, when senescence occurs. Few macroscopic plants are usually present from latesummer to late spring, the population being present as microscopic gametophyte plants. TheSRMP surveys have always been during autumn and therefore were not expected to provideinformation on the colonisation of Undaria. The observed early presence at Point Cookeindicates the establishment of populations of the microscopic gametophyte stage andconsiderable growth and canopy formation may occur in the latter half of 2009.31