in Queensland waters

CURRENT STATE OF KNOWLEDGE March 2004

Seagrasses are flowering that live in the coastal waters of most of the worlds’ continents. They are the main diet of and green turtles and provide a habitat for many, smaller marine animals, some of which, like prawns and fish, are commercially important. They also absorb nutrients from coastal run-off and stabilise sediment, helping to keep the water clear.

Australia has more species than any other continent. Of some 60 seagrass species found worldwide, 30 species are found in and 15 species are found in Queensland.

Some seagrass meadows are so extensive they can be seen from a space shuttle orbiting earth. It is estimated that there are nearly 6,000km2 of seagrass in Queensland waters shallower than 15 metres, and that up to 40,000km2 of the waters deeper than 15 metres of the are likely to have some seagrass. of species of seagrass are found near the tip of the nutrients that support growth. Grazers Biology of seagrass Cape York with a gradual decline in number of such as dugongs, green turtles and some fish can species down the east coast. There is a transition also change the structure of Queensland Since the time of the dinosaurs, three groups of from subtropical to temperate seagrasses south seagrass communities over space and time. flowering plants (angiosperms) colonised the of Moreton Bay in southern Queensland. oceans. Known as ‘seagrasses’, they are the only Seagrass can reproduce through sexual or flowering plants that can live underwater. The distribution and abundance of tropical asexual methods. In sexual reproduction, the Seagrasses grow like backyard grasses with seagrass meadows can vary with seasons. In plants produce flowers and transfer pollen from roots, leaves and (horizontal most years, Queensland seagrasses are the male flower to the ovary of the female underground stems that form extensive networks abundant in late October through to December flower. Most seagrass species produce flowers of below the surface) but are not true grasses and after months of clear skies, increasing day length a single sex on each individual, so there are are more closely related to water lilies and and rising temperatures provide optimal separate male and female plants. A few seagrass terrestrial plants such as lilies. conditions for growth. species complete their lifecycle within one year and are known as ‘annuals’. These annuals are plants that also colonised the sea and produce seeds that can remain dormant in large are often confused with seagrasses, however, ‘seed banks’ for several months. Seed banks they are more primitive than seagrasses. In ensure that the species can survive until contrast to seagrasses, algae do not have a true conditions return to stimulate the seeds to root system (they have holdfasts) and do not germinate. have veins that carry molecules around the plant. Algae have spores and do not flower or produce Researchers Seagrasses can also grow by asexual (or fruit, while seagrasses have seeds and fruit. are measuring vegetative) reproduction. New ‘plants’ arise changes in the amount of without flowering or setting seed. Seagrasses Seagrasses are commonly found on tidal seagrass. grow vegetatively by extending and branching mudflats in estuaries, on shallow sandy areas their rhizomes in the same way that grass in a close to the coast, in coral reef and lawn grows. This allows significant areas of around sand cays. Seagrasses also grow on the to form from only a few deep sandy areas of the Great Barrier Reef shoots. In this way, seagrasses can recover after lagoon between the mainland and the reefs being ‘cut’ by grazers such as dugongs or where, in clear waters, they can grow as deep as disturbed by storms.

60 metres. Photo by QDPI The growth of seagrass after disturbance is In Australia, seagrasses grow in temperate and There is little known about the longer-term cycles critical to their survival. If all plants of a meadow tropical waters, from the Torres Strait to southern of seagrass abundance and distribution. Summer are lost, a seagrass meadow needs seeds Tasmania. Most tropical seagrasses grow in the rainfall and tropical cyclones and storms can available or vegetative shoots translocated from intertidal and shallow subtidal areas of the Gulf produce flows of sediment-laden freshwater a nearby meadow before it can recover. The of Carpentaria, Torres Strait and the Great Barrier which can temporarily damage seagrass ability of seagrass meadows to recover depends Reef lagoon. In Queensland, the highest number meadows. However, these flows also replenish on the species of seagrass.

Cymodocea rotuntada Cymodocea serrulata Enhalus acoroides pinifolia Halodule uninervis ■ Flat, strap-like leaves, ■ Linear, strap-like leaves, ■ Very long, ribbon-like leaves, ■ Fine, delicate seagrass with ■ Usually larger than Halodule 2-4mm wide, that can be 5-9mm wide 30-150cm long, 1.25-1.75cm leaves up to 20cm long pinifolia slightly curved ■ The leaf tip appears serrated wide ■ Different plants may have leaves ■ Narrow leaf blades ■ Rounded, smooth leaf tip to the naked eye ■ Thick leaves with many parallel between 0.25-1mm wide 0.25-5mm wide which can look heart-shaped ■ Leaf sheath is broadly triangular veins ■ Black central vein splits into ■ Trident leaf tip with three points ■ Smooth with a narrow base ■ Very thick rhizome (at least two at the rounded leaf tip ■ One central longitudinal vein ■ Well-developed leaf sheath ■ Leaf sheath scars do not form 1cm) with black, fibrous bristles ■ Well-developed leaf sheath which does not usually split and cord-like roots ■ Scars from leaf sheaths form a continuous ring around ■ Thin rhizome with fine thin roots into two at the tip the shoot a continuous ring around ■ preferred food ■ Usually pale ivory rhizome, the shoot with clean black leaf scars along the stem ■ Dugong preferred food .ian.umces.edu) 15 species in Queensland. Species of seagrass are usually identified by the shape of their leaves, the pattern of veins on the leaves, and how the leaves attach to the rhizome. ee download at www From Cape York to Cairns, seagrass communities are dominated by subtidal Halophila species. Species of Zostera, Halodule, Cymodocea and Syringodium can also grow in shallow subtidal onmental Science (fr tesy of the Integration and Application Network, University areas, sheltered from south-east winds. There are nearly 1,000 hectares of seagrass close to Cairns with a mixture of four species of which Zostera capricorni, Halodule uninervis and Halophila yland Center for Envir ovalis are the most common. Almost all the

Symbols for diagrams cour of Mar Cairns seagrasses are protected within a Fish There are four main habitat types for seagrass in Queensland Habitat Area.

Between Cairns and Bowen, a mixture of mostly Seagrass habitats Deepwater seagrass meadows are limited in Halodule and Halophila seagrass grow their growth by the availability of light. Sunlight intertidally and subtidally. In the Townsville area, Scientists recognise four habitats where is filtered by the water column with less light there are many seagrass meadows along Cape seagrasses can grow along the Queensland reaching the bottom in deeper water. As a result, Cleveland, the Strand, Cape Pallarenda and coast. Different factors control the survival of seagrass growth is limited by the clarity of the around Magnetic Island. The main seagrasses in seagrasses in each habitat. seawater above it. Seagrasses can grow 60m shallow waters near Townsville are Halophila deep in the Great Barrier Reef lagoon where ovalis, Halophila spinulosa, Halodule uninervis, River estuaries are dominated by run-off from waters can be very clear. Zostera capricorni and Cymodocea serrulata. the land that carries freshwater, sediment and nutrient into the ocean. In Queensland, run-off is Reef seagrasses are limited by substrate type Between Bowen and Yeppoon, mainly Halodule infrequent and on a massive scale. Run-off can and shelter from waves. Most coral reef waters uninervis and Zostera capricorni grow in produce ‘flood-plumes’ that extend many and sediments also have very limited nutrients intertidal areas. A variety of species grow around kilometres from the coast and affect large areas. available for seagrass growth. the Whitsunday Islands.

Coastal seagrass habitats are dominated by South of Yeppoon, Zostera and Halodule physical disturbance caused by periodic events Types of seagrass communities dominate intertidal areas, with such as cyclones, storms and floods. Major floods Halophila communities dominating subtidal in the Hervey Bay area have caused the temporary While there are about 500 species of algae on areas. There are very large seagrass areas in loss of the extensive seagrass meadows and the the Great Barrier Reef, there are only about 60 Shoalwater Bay, Gladstone Harbour, Hervey Bay subsequent death of hundreds of dugong. species of seagrass around the world, and only and Moreton Bay.

Halophila capricorni Halophila minor Halophila spinulosa ■ Small oval leaves that are ■ Small translucent oval leaves ■ Small oval leaves occurring ■ Small oval leaves, 5-20mm long ■ Shoots can be up to 15cm long hairy on one side occurring in pairs in pairs ■ 12 or more cross-veins on leaf ■ 10-20 pairs of leaflets per shoot ■ Central vein on leaf with ■ Leaves are hairy on both sides ■ Central vein on leaf with ■ No hairs on leaf surface ■ Each leaflet arranged in 9-14 cross-veins less than 12 cross-veins ■ Leaves are translucent and ■ Dugong preferred food opposite pairs ■ Usually found deeper than have serrated edges ■ Wedge-shaped leaf sheath ■ Each leaflet is 15-25mm long 10m in coral environments ■ Leaves are usually longer and 3–5mm wide than wide ■ Leaflets have a serrated edge ■ Leaves smaller than Halophila ■ Thin rhizomes capricorni ■ Central vein on leaf with 6-8 cross-veins Seagrass illustrations by Ruth Berry Importance of seagrass due to an El Niño climatic event which increased The recovery of tropical seagrasses depends on water temperature and lowered nutrients so the species and location. Some plants are fairly Seagrasses stabilise coastal sediments, and trap seagrass growth was reduced. resilient in unstable environments. Halodule and recycle nutrients. They also provide food and uninervis and Halophila ovalis grow rapidly shelter for many organisms, and are a nursery Seagrass has been lost in several regions due to and survive well in unstable environments and grounds for commercially important prawn and storms, flooding and cyclones. Thousands of places where sediments are continually being fish species. Twenty prawn species and 134 fish hectares of seagrass also appear to have been deposited. Zostera capricorni can recolonise by species were found in the seagrass meadows lost from northwest Torres Strait possibly due to vegetative growth and so can survive small-scale from Cairns harbour alone. flooding and sedimentation from Papua New disturbances. Halophila tricostata is an annual Guinea. However, changes are difficult to track plant and only appears later in the year being In northern and eastern Australia, dugong and effectively in these remote locations and may be sustained by a substantial seed bank. green turtle feed directly on seagrasses. Both part of a longer-term natural cycle. animals are used by Indigenous Australian Some seagrass meadows in Queensland’s east communities for food and ceremonial use. and Gulf coast have expanded. In coastal waters Dugong Protection Areas have been established where there were large dugong and green turtle along the coast of Queensland. While these areas populations in the past, increases in the size do not specifically protect seagrass, Dugong Dugong and biomass of seagrass meadows may reflect Protection Areas often have large areas of feeding trail decreases in populations of these herbivores. through seagrass. The use of gill and mesh nets is seagrass. In some places (usually away from the coast), restricted in these areas. the area of seagrass may have expanded because the seagrass was previously nutrient Apart from licensed worm and bait collecting limited and now nutrients from land-based

there is little or no collecting activity on seagrass Photo by QDPI activities have increased. in Queensland. Most seagrass losses have been followed by In many areas, it is difficult to estimate changes significant recovery. For example, approximately in seagrass because maps of seagrass Seagrass distribution 1,000km2 of seagrasses in Hervey Bay were lost distribution are imprecise. Researchers from the in 1992 after two major floods and a cyclone Department of Primary Industries and CRC Reef There is little known about long-term natural within a three-week period added to pressure on are involved in extensive mapping of seagrasses cycles in the abundance and distribution of the system. The deepwater seagrasses apparently in Queensland. This work is supported by port seagrasses. Some shorter-term changes in died from lack of light caused by a persistent authorities, local communities and government distribution and abundance of Queensland plume of turbid water from the floods. Heavy agencies. It will help to improve understanding seagrasses have been recorded. In recent years in seas also uprooted seagrass in shallow waters. of the anthropogenic and climatic factors that Deception Bay near Brisbane, seagrasses The subtidal seagrass (below 5m deep) started drive changes in seagrass meadows. Precise declined and then recovered in what may be a to recover within two years. The intertidal mapping of seagrass meadows (at appropriate natural cycle that has been exacerbated by seagrasses only started to recover after four to scales) will enable losses to be more accurately human activities. Recent loss of seagrasses in five years and did not fully recover until measured and tracked. Cairns and the Gulf of Carpentaria region may be December 1998.

Halophila tricostate Syringodium isoetifolium Thalassodendron ciliatum Zostera capricorni ■ Shoots can be 8-18cm long ■ Narrow, spaghetti-like leaves, ■ Ribbon-like, curved leaves ■ Cluster of ribbon-like curved ■ Long strap-shaped leaves ■ 6-18 groups of leaflets 1-2mm diameter 10-40cm long leaves at the end of a which can be wide or narrow per shoot ■ Leaves 7-30cm long, tapering ■ 10-17 longitudinal leaf veins long shoot depending on habitat ■ Leaflets clustered in groups to a pointed tip ■ Short black bars of tannin cells ■ Leaves 10-15cm long and ■ Five longitudinal veins of 2-3 ■ 2-3 leaves arising at each shoot on leaf blade 0.5-1.4cm wide ■ Cross veins which form a ■ Leaflets are 12-20mm long ■ Long leaf sheaths, ■ Leaf sheaths 3-7cm long ■ Tough, woody rhizomes with mesh across the leaf blade scars from successive shoots and 2–4mm wide 15-40mm long ■ Thick rhizome (up to 5mm) ■ Rounded leaf tip ■ Leaflets have a sparsely ■ Thin rhizomes with conspicuous scars ■ Very coiled, branched roots ■ Leaf grows straight from serrated edge between shoots ■ Typically found in rocky areas the rhizome ie no stem ■ Wedge-shaped leaf sheath with strong currents ■ Fibrous root system ■ Thin rhizome ■ Provide nursery grounds for juvenile prawns years (or longer) if the seagrass species does not Threats to seagrass have viable seed banks. Scientists from the Department of Primary Industries are gathering Seagrass meadows worldwide are being lost information about temperature-related seagrass from coastal areas due to human disturbances die-off at Weipa and the Whitsundays to help such as coastal development and water better understand seagrass burning. . Seagrasses can be lost when they are smothered or buried by sediments, or when Reef seagrass habitats are the least threatened these disturbances reduce the amount of seagrass community with minor damage from light underwater. boating and shipping activities. High tourist Photo by Len McKenzie, QDPI Rising sea temperatures could cause burning of visitation rates and associated sewage and poor Estuarine seagrass communities are increasingly seagrass. anchoring practices are a threat at some the most threatened seagrass habitats. As localities. However, these threats are carefully provincial centres develop along the Queensland available for growth and seagrasses could managed in the Great Barrier Reef Marine Park. coast, rivers and inlets need to be carefully increase their photosynthetic rates. Impacts such as ship groundings and associated managed to maintain seagrass habitats and the spills would impact heavily on reef platform fisheries they support. Rising sea temperatures could cause burning or seagrasses. death of seagrasses in some places where they Many seagrass meadows are near busy coastal are close to their thermal limit. In 2002, Deepwater seagrasses could be impacted by the cities and large port facilities where coastal seagrasses were lost and burnt from some areas reduction in light caused by coastal run-off. development, dredging and marina developments in the Whitsundays, Shoalwater Bay, Green These communities may also be affected by can threaten them. However, these developments Island and Weipa. This coincided with coral trawling activities, although the scale of any are usually closely managed through legislative bleaching events on the Great Barrier Reef and impact is largely unknown and difficult to processes and the area of seagrass that is throughout the Indo-Pacific. Although seagrass determine. Recent studies have shown that destroyed is generally small. For example, the meadows are likely to recover faster than coral deepwater seagrasses (down to 30m) are redevelopment of the shoreline in Townsville in reefs, full recovery from severe events may take utilised by dugong. 1999 protected adjacent seagrass meadows from the impacts of building activities using several methods. Special fill materials and linings were used to prevent fine sands being washed into the Seagrass-Watch: ocean. The turbidity of the water and the health of the seagrasses in the area were also monitored. community-based seagrass monitoring program These measures ensured that the seagrass meadows near Townsville were not significantly Seagrass-Watch facilitates links between community networks, government agencies and local industry groups to affected by the construction activities. provide scientific advice on critical seagrass resources. nett, CRC Reef Seagrass-Watch is a community-based monitoring program Threats to seagrasses can originate long yony Bar developed by the Queensland Department of Primary distances from the coast. Coastal agriculture in Industries in conjunction with CRC Reef, Queensland Parks upper catchments may add to sediment and

Photo by Br and Wildlife Service and community groups. herbicide loads in run-off from the land which has the potential to destroy large areas Seagrass-Watch collects data about the condition and trends of nearshore seagrasses throughout of seagrass. Queensland and provides an early warning of major changes in seagrass abundance, distribution and species composition. The program has detected loss and recovery of seagrass ecosystems in relation Global climate change may also threaten to climatic events including flooding. It has also provided valuable information about the health of seagrass communities. Climate change is seagrass ecosystems for local management agencies. predicted to raise sea levels, concentrations of In Queensland, Seagrass-Watch programs involve more than 300 volunteers and have been established carbon dioxide in seawater, and seawater in Hervey Bay, the Great Sandy Strait and the Whitsunday regions, Townsville, Cairns and Cooktown. temperatures. Rising sea levels could increase the distribution of seagrass because more land will be The key community groups involved in the program are the Hervey Bay Dugong & Seagrass covered by seawater. However, rising sea levels Monitoring Program, Great Sandy Strait Fauna & Flora Watch, Whitsunday Volunteers, Order of are likely to destabilise the marine environment Underwater Coral Heroes (OUCH), North Queensland TAFE, Townsville Seagrass & Mangrove and cause seagrass losses. Higher concentrations Volunteers, Wildlife Preservation Society of Queensland Bayside Branch and Cape York Marine of carbon dioxide in seawater could increase the Advisory Group. area of seagrass because more carbon will be For more information contact: Seagrass-Watch, c/- Northern Fisheries Centre, Qld Dept of Primary Industries, PO Box 5396, Cairns, 4870. Email: [email protected] Seagrass protection Seagrasses are habitat for juvenile fish and crustaceans that in many parts of the world form the basis of economically valuable subsistence and/or commercial fisheries. The need to manage fisheries in a sustainable way has also become a motivating factor for protecting seagrass. Ensuring the future of the world’s coral reefs While there is no international legislation that

specifically protects seagrass, there are Photo by Bryony Barnett, CRC Reef international conventions to which Australia is Dead seagrass washed up on the beach plays CRC Reef Research Centre Ltd a signatory that recognise the importance of a role in the bacterial cycle that ultimately is a knowledge-based partnership of supports fisheries. wetlands and coastal areas. These conventions coral reef ecosystem researchers, include Ramsar Convention on Wetlands, and managers and industry. Its mission is to the Convention on Biological Diversity. Australia The future plan, fund and manage world-leading has developed national legislation to address science for the sustainable use of the these conventions. The Queensland Department of Primary Great Barrier Reef World Heritage Area. Industries in conjunction with CRC Reef and Vast areas of seagrass are also protected within Queensland Parks and Wildlife Service CRC Reef Research Centre Ltd the Great Barrier Reef World Heritage Area. This undertakes long-term monitoring programs to is a joint venture between the area is largely protected in legislation by the assess the effect of climatic patterns and Association of Marine Park Tourism Great Barrier Reef Marine Park. Activities in the anthropogenic impacts on seagrass ecosystems Operators, Australian Institute of Marine Park are regulated to protect the Reef throughout the Great Barrier Reef and beyond. Marine Science, Great Barrier Reef while allowing reasonable use of the region. The program is focussed in areas of shipping Marine Park Authority, Great Barrier The Marine Park is unique in that there may be and port activity to assess the effect of dredging Reef Research Foundation, James Cook as much as 40,000km2 of seagrass protected in practices and provide baseline maps of seagrass University, Queensland Department of the area. Many coastal seagrasses, however, areas. In addition, Seagrass-Watch (see box) is a Primary Industries, Queensland Seafood are outside both the Great Barrier Reef World program that provides information on seagrass Industry Association and Sunfish in a seagrass bed. Photo by Len McKenzie, QDPI Design www.boabinteractive.com.au Heritage Area and the Great Barrier Reef Marine habitat condition at more than 100 sites in Queensland Inc. Park. These areas are under the jurisdiction of Queensland and about 35 sites in seven

the Queensland Government. countries in the western Pacific region. Nardoa pauciforis

In Queensland, marine plants are protected To protect the valuable seagrass meadows along Established and

supported under The starfish under the Queensland Fisheries Act 1994 and the coast of Queensland, the community, the Australian cannot be damaged without a permit. Marine government and researchers have to work Government’s Cooperative plants are defined as ‘a plant that usually grows together. Information about the biology and Research Centres on, or adjacent to tidal land whether living, ecology of Australian tropical seagrasses Program dead, standing or fallen.’ This definition including detailed maps of its distribution and recognises the role of even dead plant material, abundance is still limited, however, research by CRC Reef Research Centre such as seagrasses washed up on the beach, in CRC Reef, Queensland Department of Primary PO Box 772 Townsville the bacterial cycle that ultimately supports Industries and James Cook University is Queensland 4810 Australia fisheries productivity. Large fines are applicable continuing to fill the gaps. This knowledge is Email: [email protected] for damaging seagrasses with the possibility of used by environmental managers to assess Website: www.reef.crc.org.au associated restoration orders. stress to seagrass caused by human activity, the potential for natural recovery or options Fish Habitat Areas (FHAs) have also been for mitigation. designated under the Queensland Fisheries Act This brochure was written by Rob Coles, to protect fisheries habitat that is considered Len McKenzie, Stuart Campbell, Jane Mellors especially important or critical to fisheries. These (Qld Dept Primary Industries), Michelle FHAs include some areas of coastal seagrass. Waycott (JCU) and Louise Goggin (CRC Reef). FHAs are usually small (up to several thousand hectares) but provide a high level of protection Published by CRC Reef Research Centre Ltd 2004 against disturbance. Printed on recycled paper