Seagrass Meadows in Australia

A typical seagrass meadow

Seagrass meadows are some of the most beautiful ecosystems in the world. The seagrasses grow long and narrow and bunched up, and almost look like a grassland underwater, and contain a great variety of rare species. However, they are also under great threat. Seagrasses have been in decline for the past few decades, largely because of damaging human activities. Of special note is the seagrass meadows of Australia. The seagrass meadows there are some of the largest in the world, and also are one of the most diverse in terms of species. But they are also some of the most negatively impacted by human action.

Historical state of the ecosystem

How seagrasses evolved

Halophila, Zostera, and Posidonia are three of the genera that comprise 55% of the seagrass species. (Duarte, “Seagrass Meadows”). Seagrass meadows tend to be monospecific, however there are some meadows with up to twelve different species together. “Seagrass distribution throughout the region is most likely influenced by shelter, sediment characteristics, water turbidity, and tidal exposure.”(Seagrass-watch). Historically seagrass meadows were very similar to present time meadows with some added diversity both among the grasses and the animals that inhabit the ecosystem. However due to climate change, some species were unable to adapt to the changes and died off. With plant species dying off, the marine life that depended on those plants was also heavily affected, which resulted in a present day loss of diverse of seagrass meadow in Australia.

The image above demonstrates the evolutionary process that took place for the emergence of seagrass meadows. Overtime algae made its way to land and evolved into land plants. These plants further evolved outside of the water and eventually made their way back into the ocean. Consequently seagrass meadows look similar to grasses on land.

Seagrass Meadows in Australia

Current Human Impact

Damage to seagrass meadow in Thomson Bay, Rottnest Island

Similar to dangers that are associated with monoculture in terrestrial regions, seagrass meadows are divided between temperate areas where usually one or a few species dominate, and tropical areas, where regions are much more diverse. The environmental impact on the ecosystem for areas that have a lot of diversity is good, while areas with little diversity have a poor environmental impact. While, Western Australia has seagrass meadows that are rich in species, including endemic ones, they are still impacted by people's dangerous activities. People have impacted this region by purposely collecting seagrass and using them for household purposes. Considering that 1/7th of the world's population lives within 30 miles of a seagrass meadow, it is undeniable that people have an impact on this ecosystem. For instance, some people feed off some of the animals that live in a seagrass and are rich in protein, e.g. fish and shellfish. Some of the most common uses for seagrasses are as a fertilizer for soil, as mattress filling, insulation for houses, and as for furniture padding.

Current impacts on seagrass ecosystems

Legislation to protect the ecosystem

Western Australia has promoted policies for the protection of seagrass meadows in Australia and some policies have alleviated damages to the ecosystem. Human impact from the 1950s and onward took a toll on the seagrasses of Australia. Cockburn Sound on the harbor of West Australia has experienced a 79% loss of seagrass, which is about 3,300 hectares due to waste from factory chemical dumping and sewage runoff. Princess Royal Harbor and Oyster Harbor also fell victim to this human activity and lost and area of 66% (810 Ha) and 46% (720 Ha) respectively. (6)

Loss of seagrass in Australia

After seeing the decline in some species of fish along with the degradation of seagrass meadows, the Western Australian government passed legislation to protect the ecosystem. The legislation that was passed  can be summarised by legislation similar to the Queensland Fishery Act 1994 which provided direct protection of seagrass by preventing cropping of the seagrass or inhabiting the area for human uses.(6) Legislation also focused on secondary protection by protecting the fisheries that benefited the human population such as the Fish Resources Management Act of 1944 which provided protection of commercial and recreational fish as well as their habitat, which happens to include seagrass meadows. The effects of factory dumping and sewage runoffs led to the Environment Protection Act of 1986 which ranked producer systems with high importance and regulated pollution that would affect these systems. Water quality in Western Australia was then managed by Conservation and Land Management after the Fishing and Related Industries Compensation (Marine Reserves) Bill 1997.(6) With further legislation for protection of these lands combined with restoration the loss of seagrass meadows can be dramatically decreased.

Projected future of the ecosystem

Based on their current state and rate of degradation, the future of seagrass meadows is not very promising.  Scientists have had extreme difficulties forming accurate, quantitative predictions, as some data indicate that degradation is slowing and others indicate that it is accelerating (8).  Seagrass loss has evidently increased ten-fold in the last decade, but it is unapparent whether this trend will continue in the future (7).  It is absolutely clear that the ecosystem is currently in danger, mainly due to human activities, and will not recuperate easily.  Humans continue to settle along and develop coastal areas, a trend which will continue in the future (3).

Although smaller areas can recover from impact in a relatively short period of time, these ecosystems generally regenerate extremely slowly; it is estimated that in some areas, it could take 80 to 100 years to recolonize after loss of vegetation has occurred (2, 6).  Even if they do successfully recover, the meadows will probably be dominated by fast-growing, resilient species (this has been at observed at Perth, where mooring scours were recolonized by pioneer species rather than the original dominant species, Posidiana) (7).  It is unknown whether the ecosystem can recover naturally (reinvasion almost never occurs), and even though several restoration projects have been started, they do not have high success rates (7).  Also, these projects can be expensive and time consuming, and are sometimes not considered worth the effort.

A dugong in a seagrass meadow

The difficulty in reestablishing the seagrass population is primarily due to the fact that once seagrass has been removed from an area, the amount of suspended sediment particles in the water increases due to erosion, which prevents sufficient amount of sunlight from reaching the sea floor for seagrass to grow (4).  Also, the increased nutrient levels from eutrophication work more against the sea grasses than with them—the grasses thrive in low-nutrient waters because they internally recycle many nutrients, but an overload simply increases the phytoplankton population and inhibits sunlight penetration (12).  Regions with seagrass meadows are starting to limit fertilizer usage and treating some sewage that is released into the water, but the overall volume of both in the water seems to be increasing at an alarming rate because the ocean is still the most practical place to release waste (12).  Apart from this, increased carbon dioxide levels, and resulting warming and acidification, are changing the sediment chemistry and species composition of the areas, which changes the environment and could adversely affect seagrass growth (12).  However, more evidence shows that this could actually stimulate seagrass ecosystems.  Some natural obstacles in recovery include wave action, which stirs up sediment, and urchin and fish grazing, which manually removes seagrass (12).

Some glimmers of hope do exist, however; in some areas, regulations have led to increased water quality, and the rising sea level could potentially provide new coastal areas for seagrass to grow.  Also, it is interesting to note that regions inhabited by seagrass could shift to higher latitudes, out of tropical areas (13).  However, these are just speculative predictions, and the future of seagrass meadows is difficult to determine.

What can be done to save seagrasses

There are many things people can do to help the maintenance and recovery of this ecosystem, many of them locally oriented:

1. Implement and follow laws to replace destroyed areas (in Queensland, developers must plant an area equal to any area of seagrass they remove) (4)
2. Implement and follows laws regulating effluent release into the ocean (by factories, households, and sewage systems; this includes pesticides, fertilizers, and sewage) (4)
3. Stop development in and near the water that impacts water turbulence and wave energy (this is a major factor in the sediment suspension in the water) (5)
4. Stop swing and cyclone mooring or puts moorings in areas that only contain sand (3)
5. When on private water vehicles, study water charts and stay away from shallow, seagrass-inhabited waters (8)
6. Implement planning and zoning regulations (2)
7. Aid the effort of existing volunteer organizations (10)
8. Monitor and regulate water quality (11)
9. Continue scientific research and data gathering (through aerial surveys, remote sensing, permanent monitoring transects, biomass/density samples (2)

How we can lessen human impact on seagrass ecosystems

In his article “The Future of Seagrass Meadows,” Carlos Duarte summarizes these measures into three main points: “(1) the development of a coherent worldwide monitoring network, (2) the development of quantitative models for predicting the responses of the seagrasses to disturbance, and (3) the education of the public on the functions of seagrass meadows and the impacts of human activity.”

Bibliography

(1) Carruthers, T.J.B. "Seagrasses of South–west Australia: A Conceptual Synthesis of the World's Most Diverse and Extensive Seagrass Meadows." Seagrasses of South–west Australia: A Conceptual Synthesis of the World's Most Diverse and Extensive Seagrass Meadows.

Web. 18 Nov. 2015.

(2) Duarte, Carlos M. "Seagrass Meadows."., 24 Jan. 2010. Web. 19 Nov. 2015.

(3) Duarte, Carlos M. “The future of seagrass meadows.” Environmental Conservation 29 (2): p 192–206. Foundation for Environmental Conservation, 2002.

(4) Edgar, Graham J. “The influence of plant structure on the species richness, biomass and secondary production of macrofaunal assemblages associated with Western Australian seagrass beds.” J. Exp. Mar. Biol. Ecol., Vol. 137, pp. 215-240 Elsevier (Australia), 1990.

(5) "Importance of Seagrass." Importance of Seagrass.  Web. 16 Nov. 2015.

(6) Kirkman, Hugh. “Baseline and Monitoring Methods for Seagrass Meadows.” Journal of Environmental Management 47, p 191–201. CSIRO Division of Fisheries, 1996.

(7) Kirkman, H. "Community Structure in Seagrasses in Southern Western Australia." Aquatic Botany 21.4 (1985): 363-75. Web.

(8) "Help Protect Seagrasses." Help Protect Seagrasses. Florida Fish and Wildlife Conservation Commission, Web. 20 Nov. 2015.

(9) Larkum A.W.D., West, R.J. “Long-term changes of seagrass meadows in Botany Bay, Australia.” Aquatic Botany, 35, p 55-70. Elsevier Science Publishers B.V., (Amsterdam), 1990.

(10) "Roebuck Bay." Western Australia Seagrass. Web. 19 Nov. 2015

(11) SILBERSTEIN, K, CHIFFINGS A.W. and McCOMB, A.J.  “THE LOSS OF SEAGRASS IN COCKBURN SOUND, WESTERN AUSTRALIA. III. THE EFFECT OF EPIPHYTES ON PRODUCTIVITY OF POSIDONIA A USTRALIS HOOK. F.” Aquatic Botany, 24, p 355—371. Elsevier Science Publishers B.V. (Amsterdam), 1986.

(12) Testudinum, Thalassia. "Seagrass: Prairies in the Sea." What Are Seagrasses? Seagrasses and People  Web. 19 Nov. 2015.

(13) WALKER, D.I., LUKATELICH, R.J., BASTYAN, G., and McCOMB, A.J. “Effect of Boat Moorings on Seagrass Beds near Perth, Western Australia.” Aquatic Botany, 36, p 69-77 69. Elsevier Science Publishers B.V. (Amsterdam), 1989.

(14) Walker, D.I., McComb, A.J. “Seagrass Degradation in Australian Coastal Waters.” Marine Pollution Bulletin, Volume 25. 5-8, pp. 191-195. Department of Botany, University of Western Australia (Great Britain) 1992.