Marine Productivity
Plankton, Derwent River,
magnified 200 times
(Photograph by Gustaff Hallegraeff)
The oceans cover about 70% of the globe, but they produce only about 30% of the total world primary productivity (photosynthetic growth of plants). Areas of high marine productivity tend to occur where cold water upwells from the deep ocean—such as at the western sides of continents and divergence zones. The Antarctic Circumpolar Current—a zone of divergence and upwelling with high marine productivity—flows between Tasmania and Macquarie Island. Plankton (small floating microscopic plants and animals) are the main source of productivity in the marine environment.
The tiny plants (phytoplankton) thrive on the abundant nutrients in the upwelling water. In contrast, much of the open ocean is relatively low in nutrients and may be described as a marine ‘desert’.
Seagrass
Posidonia australis
(Photograph by Chris Rees)
The waters covering the continental shelf are also very productive. Here, productivity is derived from plankton and macrophytes—large fixed marine plants such as seaweed (macroalgae) and seagrasses (marine flowering plants).
Seagrasses colonise, and stabilise, the more sheltered, shallow, sand substrates of the continental shelf and can immobilise large volumes of sediment in the off-shore coastal zone. In contrast, many macroalgae require a firm substrate for successful colonisation. The macrophytes provide refuge for other organisms and a substrate for epiphytic algae (plants that grow upon another organism); in turn, these are a source of food for many other species.
Bull kelp
(Photograph by
Steve Robertson)
The productivity of the State's surrounding seas is harvested by commercial and recreational fishery activities; the different ecosystems—open water, seagrass meadows and macroalgae stands support distinct fisheries.
Several Tasmanian fisheries are based on species that feed (at least at some stage in their life) on open-water plankton, whilst others concentrate on inshore resources (e.g. the kelp harvesting industry). Tasmania’s extensive kelp stands are the key species in an important marine community off the State’s coasts. Along the east coast some of these kelp forests have been in decline in recent years.
See also:
Contact: Coastal and Marine Branch
Coastal and Marine Branch
6th Floor, Lands Building, 134 Macquarie Street
GPO Box 1751
Hobart TAS 7001
Phone: 03 6233 3963
Fax: 03 6233 6800
Email: Coastal.Enquiries@environment.tas.gov.au
