1 Posidonia australis seagrass meadows of the Manning – Hawkesbury ecoregion 2 3 1. Description of the ecological community 4 1.1 Name of the ecological community 5 This advice follows the assessment of a public nomination to list the ‘Posidonia australis 6 seagrass beds’ as a threatened ecological community under the EPBC Act. 7 8 Posidonia australis is a sub-tidal meadow-forming seagrass species. The northernmost limit to 9 the distribution of P. australis on the east coast of Australia is Wallis Lake. Its distribution then 10 extends around the southern half of Australia to Shark Bay on the west coast encompassing 11 significant ecological and biogeographic variation. Given the close links between biodiversity 12 and the underlying abiotic drivers, the definition of the ecological community has been focused 13 on the assemblage of plants, animals and micro-organisms associated with seagrass meadows 14 dominated by Posidonia australis occurring in the temperate Manning Shelf and Hawkesbury 15 Shelf bioregions (IMCRA v4.01). Spalding et al. (2007) consider the Manning Shelf and 16 Hawkesbury Shelf bioregions to be a single ecoregion based on relative homogeneous species 17 composition and clear distinction from adjacent systems. 18 19 It is recommended that the ecological community be named Posidonia australis seagrass 20 meadows of the Manning-Hawkesbury ecoregion (hereafter referred to as the ecological 21 community). The name best describes the dominant component, structure and location 22 characterising the ecological community. 23 24 1.2 Location and physical environment 25 The ecological community occurs mostly within the sheltered environments of permanently 26 open estuaries along the warm temperate New South Wales coastline, from Wallis Lake (32°S) 27 to Port Hacking (34°S). The ecological community occurs wholly within the Manning Shelf 28 and Hawkesbury Shelf bioregions (IMCRA v4.0). Posidonia australis dominated seagrass 29 meadows occurring around islands within the geographic range are also included within the 30 ecological community. 31 32 The ecological community typically occurs in subtidal waters where salinity is close to marine ◦ 33 levels (30-50 /◦◦) (Meehan, 2001), dropping only for short periods following rainfall, at depths 34 ranging less than 1m to 10 m on sand and silty mud substrate (Cambridge and Kuo, 1979; 35 West, 1990). The ecological community is absent from brackish water (i.e. hyposaline) 36 conditions such as in coastal rivers and intermittently open lagoons. The ecological community 37 is known to occur at the following locations: Wallis Lake; Port Stephens; Lake Macquarie; 38 Brisbane Water; Hawkesbury River; Pittwater; Port Jackson (Sydney Harbour); Botany Bay; 39 Port Hacking (Creese et al., 2009); and in the lee of Broughton Island (West et al., 1989). 40 41 1.3 Vegetation 42 The ecological community occurs as almost pure stands of Posidonia australis (monospecific 43 meadows) or multispecies meadows (eg. P. australis, Zostera capricorni, Halophila ovalis) 44 dominated by P. australis. P. australis is a slow growing, long lived seagrass species, with 45 persistent rhizomes and is meadow-forming (Cambridge and Kuo, 1979). Its fronds can grow to 46 over 80 cm long and as much as 90% of the mass of the P. australis plant may be in the roots 47 and rhizomes (Keough and Jenkins, 1995). 48 1 Integrated Marine and Coastal Bioregionalisation of Australia Version 4.0 (Commonwealth of Australia, 2006). 1 The spatial structure of the ecological community is highly variable with meadows ranging 2 from nearly continuous to highly fragmented meadows arranged into a mosaic of discrete 3 patches. Areas of bare sand or other seagrass species that occupy edges, blowouts2 and small 4 areas of meadows (Kirkman and Kuo, 1990) are common in both continuous and patchy3 5 meadows of the ecological community. In some cases, sparse meadows of the ecological 6 community may have an understorey of smaller seagrass species (e.g. Halophila ovalis). The 7 macrophyte, Ruppia, is also found growing within the ecological community (Creese et al., 8 2009). 9 10 The wide, strap-like leaves of Posidonia australis provide substrate for the establishment of a 11 diverse assemblage of benthic flora, in the form of micro and macro epiphytes4 and algae and a 12 complex layer of periphyton5 (Klumpp et al., 1989; Keough and Jenkins, 1995; Carruthers et 13 al., 2007). The epiphytes and some components of the periphyton can photosynthesise and 14 contribute significantly to the overall primary production of the seagrass community. The 15 amount of cover of epiphytes on the seagrass depends largely on the nutrients available in the 16 water – generally, more nutrients means more epiphytes. 17 18 1.4 Fauna 19 The ecological community provides habitat, shelter and food for a large diversity and 20 abundance of fauna. Posidonia australis is generally considered to provide the greatest habitat 21 structure of any of the seagrass species found in New South Wales (Middleton et al. 1984; Bell 22 and Pollard, 1989; Creese et al., 2009). The P. australis fronds and rhizome matte provide a 23 stable substratum for the establishment of animals as epifauna and infauna, which in turn 24 support higher food chains (Walker et al., 1991) directly as a food source or via detritus 25 formation. 26 27 The macro-benthic fauna of the ecological community is dominated by polychaetes, 28 crustaceans and molluscs (Collett et al., 1984). These faunal groups process a significant 29 portion of the primary production of the ecological community, and provide an important food 30 resource for larger crustaceans, fish and birds. Common polychaetes include Armandia 31 intermedia, Barantolla lepte, Ceratonereis mirabilis, Eunice australis, Mediomastus 32 californiensis, Neanthes cricognatha, Notomastus torquatus, Onuphis sp., Prionospio 33 aucklandica, Prionospio cirrifera. Common crustaceans include Ampelisciphotis sp., 34 Amphithoe sp., Birubius sp., Cyamodus sp., Macrobrachium intermedium, Tethygeneia sp.. 35 Common molluscs include Anadara trapezia, Mysella sp. and Wallucina assimilis. Other 36 invertebrate taxa associated with the ecological community include sea anemones and 37 nemerteans (Collett et al., 1984). 38 39 The epibenthic fauna of the ecological community includes larger, often predatory, fish and 40 crustaceans. The majority of epibenthic fauna associated with the ecological community only 41 use it for a small part of their life history, as a temporary foraging area or refuge from 42 predation. The ecological community provides nursery habitat to the commercially important 43 Acanthopagrus australis (yellowfin bream), A. butcherii (black bream), Mugil cephalus (sea 44 mullet), Girella tricuspidata (luderick) (Burchmore et al., 1984; McNeill et al., 1992; West and 45 Jones, 2001). The most commonly sampled fish associated with the ecological community are 2 A blowout is an area in a seagrass meadow denuded of seagrass through natural or anthropogenic disturbance. Blowouts are typically areas of instability in sediment movement, shape and size and seagrass species composition (Kirkman, 1985). 3 Patchiness in meadows often reflects processes of recovery from disturbances, natural and human induced, as well as the particular hydrodynamic conditions of the seagrass habitat (Duarte et al., 2006). 4 Epiphytes are larger algae that grow on seagrass fronds (Keough and Jenkins, 1995). 5 Periphyton is a thin layer of microscopic organisms such as bacteria and single-celled plants which colonise exposed areas of the seagrass (Keough and Jenkins, 1995). 2 1 from the families Syngnathidae (including the protected Phyllopteryx taeniolatus (weedy 2 seadragon)), Clupeidae, Latridae, Monacanthidae (leatherjackets), Gobiidae (gobies), 3 Kyphosidae, Hemiramphidae and Mugilidae (Evans et al., pers. comm., 2014). 4 5 The ecological community also provides important foraging habitat for the NSW listed 6 endangered population of Eudyptula minor (little penguin) at Manly (Manly Council, 2009). 7 8 1.5 Key diagnostic characteristics and condition thresholds 9 National listing focuses legal protection on remaining patches of the ecological community that 10 are most functional, relatively natural (as described by the ‘Description’) and in relatively good 11 condition. Key diagnostic characteristics and condition thresholds assist in identifying a patch 12 of the threatened ecological community, determine when the EPBC Act is likely to apply to the 13 ecological community and to distinguish between patches of different quality. The ecological 14 community may exhibit various degrees of disturbance and degradation. This degree of 15 degradation has been taken into account in developing the condition thresholds. 16 1.5.1 Key diagnostic characteristics 17 The key diagnostic characteristics presented here summarise the main features of the ecological 18 community. These are intended to aid the identification of the ecological community, noting 19 that a broader description is given in the other sections. Key diagnostic characteristics for 20 describing the ecological community are: 21 Occurs from Wallis Lake (32◦S) to Port Hacking (34°S) within the Manning Shelf and 22 Hawkesbury Shelf bioregions (IMCRA v4). 23 Occurs in shallow subtidal coastal waters (<10 m) in locations with protection from 24 high wave energy, typically, permanently open estuaries. 25 Consists of seagrass meadows6 >1 ha and dominated7 by Posidonia australis. 26 Occurs on sand or silty-mud substrate.