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Seagrass

Seagrass are marine flowering plants that form meadows in estuaries and shallow coastal waters with sandy or muddy bottoms.

 

Millennium Ecosystem Assessment Reporting Category

Coastal Ecosystems

 

What ecosystem functions do seagrass perform?

 

Seagrass provide habitat for many marine species.

Seagrass are the only flowering plants that can live underwater. As identified in Table 1, seagrass perform many  ecosystem functions important to the self-regeneration of the system (and other coastal and marine ecosystems) and with potential to contribute to ecosystem service provision.

Water is the main pollinator of seagrass, carrying pollen between male and female flowers. Flowering however, is not common for most tropical seagrass species and propagation is generally by the growth and branching of rhizomes (underground stems). These rhizomes act to trap and combine sediments buffering seagrass and other coastal ecosystems against disturbances such as storms, waves and surges. Seagrass is utilised as a direct food source by herbaceous species such as dugongs, green turtles, urchins and some fish. However, it is the decaying seagrass and the species that live in and on seagrass which usually provide a food source for many other species (from micro-organisms to larger fish, crabs and sea cucumbers just to name a few). 

Seagrass provide supporting habitat and substrate for diverse communities. Juvenile prawns, fish and micro-organisms use seagrass ecosystems as breeding, reproduction, nursery and refugia areas. Seagrasses are “ecological engineers” because they influence their physical, chemical and biological surroundings. They oxygenate the water, regulate nutrients and stabilise sediments helping to maintain a healthy ecosystem. Seagrass defence responses against invading pathogens is the subject of ongoing research as is its ability to control nuisance macroalgae such as Caulerpa taxifolia. Seagrass ecosystems contribute to the landscape opportunity of the SEQ region by providing inspiration, scientific, educational and economic and other opportunities.

 

Table 1:The relative magnitude (to other Ecosystem Reporting Categories) seagrass performs each ecosystem function.

Ecosystem Function Category Ecosystem Function 0
1
2
3
4
5
Regulating Functions
Gas Regulation            
Climate Regulation            
Disturbance Regulation            
Water Regulation            
Soil Retention            
Nutrient Regulation            
Waste Treatment and Assimilation            
Pollination            
Biological Control            
Barrier Effect of Vegetation            
Supporting Functions
Supporting Habitats            
Soil Formation            
Provisioning Functions
Food            
Raw Materials            
Water Supply            
Genetic Resources            
Provision of Shade and Shelter            
Pharmacological Resources            
Cultural Functions
Landscape Opportunity            

 

What types of seagrass are in SEQ?

Seagrass ecosystems in SEQ are located out of the high energy areas (closed waters) in a range of depths but predominantly shallow areas. There are 3 main types of seagrass ecosystems in SEQ:

1/ Estuarine - Predominantly consisting of Zostera capricorni and sometimes Halophila ovalis.
2/ Deep water - Predominantly consisting of Halophila spinulosa and Halophila ovalis.
3/ Coastal - Predominantly consisting of Zostera capricorni, Halophila ovalis, Syringodium isoetifolium, Cymodocea serrulata, Halodule uninervis and Halophila spinulosa.

 

Cymodocea serrulata provides food for dugongs and turtles but is threatened by the epiphytic lyngbya.

Seagrass form dense mats seen at low tide.

Links to other publications and websites

Seagrass Watch- Moreton Bay
Qld Govt - Ag., Fisheries and Forestry
Moreton Bay Marine Park Zoning Plan
The Ramsar Convention
Healthy Waterways

 

What is the area and extent of seagrass in SEQ?

Seagrass ecosystems cover approximately 210 km2 of SEQ. This map shows the extent of seagrass ecosystems in three distinct locations including north coast (e.g. Noosa river), Moreton Bay and Pumicestone Passage, and south coast (e.g. Southport). Some of the largest seagrass ecosystems are found between Moreton Island and North Stradbroke Island.

 

What is the vulnerability of seagrass and threats to this ecosystem in SEQ?

Seagrass is dependent upon light, nutrients, carbon dioxide, a suitable substrate for anchoring, tolerable salinity, temperature and pH. While light availability determines the depth seagrass will grow, nutrients often determine its productivity. Limitations in any of these dependencies will lead to a  decline in the health of the ecosystem. Resilience of the ecosystem will depend upon the type of seagrass community. Structurally smaller and rapidly growing species are generally adapted to higher disturbances; this is in contrast to communities in sheltered bays. Areas like Bramble Bay that once supported large areas of seagrass no longer do indicating tipping points have been reached in some areas in Moreton Bay.

A primary threat to seagrass ecosystems is increased turbidity resulting in reduced light availability. Turbidity due to increased sedimentation arises from poor catchment and land management, vegetation clearing, coastal development and severe flooding. Inefficient sewerage treatment plants and nutrient laden waterways and stormwater result in increased phytoplankton and algal growth in the water column, or epiphytic (but non-parasitic) algae growing on seagrasses likewise reducing light availability. Severe storms and cyclones can structurally damage seagrass communities and resuspend sediment. However, where storm damage has occurred resilient seagrass systems in SEQ have generally recovered.

 

How do we manage seagrass in SEQ?

Seagrass Watch is a global scientific assessment and monitoring program active within Moreton Bay. The aim of Seagrass Watch is to raise awareness on the condition and trend of nearshore seagrass ecosystems and provide an early warning of major coastal environment changes. The program has a strong scientific underpinning with an emphasis on consistent data collection, recording and reporting. Scientific, statistical, data management, data interpretation and logistic support underpins all monitoring efforts.

Seagrass is protected by the Queensland Fisheries Act 1994 because it’s a marine plant and in some instances because it's found within Fish Habitat Areas. The Fisheries Act is managed by the Queensland Government's Department of Agriculture, Fisheries and Forestry. The Queensland Government's Department of Environment Heritage and Protection is responsible for Marine Park Zoning and some areas of seagrass have received protection under this program.

Seagrass within Moreton Bay also receive some indirect protection as they are located within RAMSAR sites. RAMSAR is an international convention on the protection of wetlands and ecosystems found within a RAMSAR site are protected under the Federal Government's Environmental Protection and Biodiversity Conservation Act 1999 (EPBC Act).

Scientific effort undertaken by Healthy Waterways and others has clearly identified hot spots that contribute substantially to sediments loads. While the science is clear the coordination of investment to reduce these loads requires improvement. More importantly a substantial increase in investment is required to address past poor catchment management and reduce growing urban nutrient and sediment loads.