Chapter 3.3 — Seagrasses of southeastern Australia • 276 3.3 Seagrasses of southeastern Australia Robert J. Williams1, P. R. Scanes2 and James Udy3 1Senior Research Scientist (retired), NSW Department of Primary Industries (Fisheries), Australia 2Senior Team Leader Estuaries and Catchment Science, NSW Office of Environment and Heritage, Australia 3Chief Scientist, Queensland Healthy Waterways, Australia Abstract The southeast portion of Australia has a high energy coastline that generally prohibits growth of seagrasses except in sheltered bays and estuaries. This is also the most densely populated portion of the country, meaning that seagrasses are subject to pressures from agriculture, industry, and urban activities. Yet the maintenance of healthy seagrass meadows is critical to the economy of these regions as it forms a critical link in the food chain of many recreational and commercial fish species as well as providing other functions. In order to generate a better understanding of these pressures and derive appropriate economic and environmental outcomes, an understanding of the biology of seagrasses and their value to the community is critical. This chapter presents an overview of the seagrass habitats of SE Australia as well as the differing management approaches in Queensland, New South Wales and Victoria. It also provides an overview of the role of community monitoring projects in providing important information for management of these critical habitats. Chapter 3.3 — Seagrasses of southeastern Australia • 277 Introduction of the ever growing population pressure to use the locations in which seagrasses live – the shallow The body of knowledge about seagrasses in inshore waters of bays, lagoons and estuaries. Australia, and at the global scale is extensive (see texts in the supplementary reading list). Recent The objectives of this chapter are to provide: output from a National Working Group (see ACEAS • an introduction to seagrass biology and its (Australian Centre for Ecological Analysis and implications for conservation management; Synthesis)) has differentiated three main Australian bio-regions for seagrass: Tropical and Sub-tropical • a simple comparison of the basis for Northern Australia, Temperate SE Australia, management between three principal Temperate SW Australia. This chapter focuses management authorities along the southeast on the seagrasses of the temperate southeast sector of the mainland (southern Queensland, Australian coast, defined somewhat arbitrarily New South Wales, eastern Victoria); and based on the north-south orientation of the coast • a differentiation of the types of community as stretching from the Noosa River (Queensland) monitoring that has been and might be to Corner Inlet in Victoria. The extensive meadows initiated to assist in determining the well being of seagrass in the Great Barrier Reef and those of of beds of seagrass in southeast Australia. Western Port, Port Philip Bay and western Victoria deserve mention at another time. Relative to the There are many species of seagrass, most of which entire Australian coastline this represents less have a specific shape, distribution and behaviour, than 10% of the coastline, but with more than and so it is more apt in scientific and management 80% of Australia’s population. The distribution terms to refer to “seagrasses” rather than seagrass. of seagrasses in the south-east also differs from This is particularly so in the management sense other parts of the continent, being confined with as there is a need to understand better their estuaries and bays rather than forming extensive individual conservation needs. (The same situation offshore meadows as occurs in southern and also prevails with “mangroves”, Chapter 3.4; and western Australia. Each of the states within the “saltmarsh”, Chapter 3.5). southeast sector recognises the value of seagrass At the global scale there is considerable concern (e.g. Queensland: AquaBAMM, Clayton et al. about the present management of seagrasses 2006) and various initiatives are in place to assess and their long term fate (Orth et al. 2006; Global seagrass condition for protection and planning Seagrass Trajectories Working Group 2009). Within purposes (e.g. Queensland: seagrass depth range Australia there is a recent effort to identify and monitoring in Moreton Bay). Further, there are synthesise current knowledge and threats to state-wide reviews based on extensive local seagrasses to support management actions aimed literature (e.g. Victoria: Warry and Hindell 2009). at maintaining healthy meadows. This Seagrass Although the importance of seagrass in protecting Working Group (online), supported by ACEAS, has community values for estuaries and coastal regions initiated two review papers. The first explores the was poorly understood in the past, the role seagrass different spatial and temporal scales at which plays in supporting coastal fisheries and reducing anthropogenic and natural processes impact on coastal erosion is becoming more understood seagrasses and will provide managers with an and appreciated by the wider community. This understanding of the most appropriate monitoring increased awareness has been assisted by many approaches to assess seagrass condition. The different approaches. One that has assisted greatly second paper will update a previous assessment of is the involvement of community associations, the distribution of seagrass around the Australian such as Coastcare and other local groups that have Coast (Mount and Bricher 2008), provide conceptual become actively involved in the monitoring of understanding of the major processes important for these habitats and the role of seagrasses in coastal maintaining seagrass habitats in the different bio- ecology. Community awareness continues to grow regions of Australia and provide a risk assessment as a result of research efforts to understand better framework for the sustainability of seagrass along the biology of seagrasses and the translation of the Australian coast. those outputs into protective legislation, policy and Taxonomy guidelines. This chapter provides an overview of the management of seagrasses in the southeast “Seagrasses” are a diverse group of aquatic sector of Australia. This sector is instructive because plants that evolved from terrestrial counterparts millions of years ago to inhabit shallow coastal Chapter 3.3 — Seagrasses of southeastern Australia • 278 and estuarine waters across the globe. All species region, from Noosa to the Qld/NSW border of seagrass are flowering plants (angiosperms). is a transition zone that includes both tropical They are not grasses in the true sense of the word and temperate species. However, in NSW and but are distantly related to lilies and gingers. Victoria the seagrass meadows are dominated Seagrasses have leaves and rhizomes – a type of by temperate species. Progressively more robust root that anchors the plants in sand or mud. sophisticated techniques in anatomy, biochemistry Fine roots, with hairs, emerge from the rhizomes and genetics have in recent times distinguished providing structural stability and providing for between similar looking species within these the uptake of nutrients. The leaves contain the families, but studies are underway to reduce chlorophyll necessary for the photosynthetic uncertainty, for example, with regard to the process, which uses light to turn carbon dioxide distribution of species in the genus Zostera and water into the complex molecules of growth. (Sainty et al. 2012, p. 127, p. 129, p. 131). Even though the flowers produce seeds, the main The five families contain at least 12 species with mechanism by which most species of seagrass different distributions (Table 3.3.1). Posidonia sustain and expand themselves is through their australis is the sole species within the family rhizomes. There are many reviews of the complex Posidoniaceae to be found along the southeast anatomical and physiological features of seagrasses coast (Other species within this genus occur along (e.g. Vermaat 2009). the southern and western coasts of Australia.). There are nearly 70 species of seagrass worldwide, Three species are within the family Zosteraceae: with some having restricted distributions but Zostera capricorni, Zostera muelleri and Zostera others occurring globally. Some species are found nigricaulis. The Hydrocharitaceae family includes in nearshore oceanic waters (bays and coastal Halophila australis, Halophila decipiens and lagoons) whereas others grow in estuaries, within Halophila ovalis. Within the Cymodoceaceae are habitats ranging from near marine channels to Halodule tridentata and Halodule univerus. brackish upstream locations. Three species belong to the Family Ruppiaceae: Seagrasses should not be confused with Ruppia maritima, Ruppia megacarpa and Ruppia macroalgae or “seaweeds” which are simple polycarpa. These are usually found in the upper plants with no root system or flowers. (The portions of estuaries where salinity is low. The excellent photos provided by Sainty et al. (2012) plants in this family have a distinctly different life readily distinguish seagrasses from macroalgae; history from other seagrasses – they have emergent other estuarine plants are also identified in this flowers that are pollinated in the air. For other valuable text.) seagrass species this reproductive function takes place under water. All seagrasses fall within the Order Alismatales, a large group of approximately 4,500 species with Some seagrasses, such as Posidonia