of Giant Kelp
surveys of M.pyrifera in south-eastern and eastern Tasmania
(eg. Cribb 1954, Olsen 1966, Sanderson 1987), it is clear that
the size and number of beds of M.pyrifera has dramatically
declined over the past 30 years, to perhaps only 5% of the original
area (Edgar 1997).
Beds have declined from approximately 120 km2 in 1954
(Cribb 1954), to 8 km2 in 1986 (Sanderson 1987), to
approximately 0.5 km2 in 1988/89 (SeaCare, pers.comm.).
Possibly the greatest loss occurred on the east coast, with a
greater than 90% decline occurring during 1978-81 (Edgar pers.comm.).
A number of possible causes or factors have been identified by
scale oceanographic changes, specifically the increased penetration
and influence of the warm-water, low-nutrient Eastern Australian
Current southwards along the east coast of Tasmania, which has
resulted in a 1.5oC rise in sea temperature since
1940 (Edgar 1999, Crawford et al.2000) (see
scale ecosystem changes along the east coast (as a result of
the above oceanographic changes) , particularly the increased
abundance, since the 1960s, of the black sea urchin (ie. Centrostephanus
rodgersii), which are known to graze on large kelps (Edgar
effects of marine pollution, particularly in the Derwent estuary
and D’Entrecasteaux Channel (SeaCare,
the introduction of the Japanese Kelp (Undaria pinnatifida)
on the east coast of Tasmania, which has colonised many areas
formerly occupied by M.pyrifera (Sanderson 1987).
Figure 1. Surface Sea Temperatures,
NE Maria Island (20m depth) 1944-1998
(from Crawford et al. 2000)
(Click thumbnail for larger version)
potential causes of kelp loss include, the commercial harvesting
of kelp in the 1970s, coastal runoff, scallop dredging in the
1950s, and ecosystem changes due to fishing.
the only and largest population of M.pyrifera in Australia,
these factors mean that this species is likely threatened with
local extinction (Edgar 1997), with potentially large-scale ecological
and economic consequences. For this reason, the need for protection
of Giant Kelp habitats and the recovery of degraded beds, has
been highlighted as a major policy commitment by the Government
of Tasmania (in it’s Environment Policy), and also, has been highlighted
as a major national and state issue in recent State of the Environment
Reports (Commonwealth of Australia 1996, SDAC 1996).
despite the considerable ecological and economic significance
of Giant Kelp forests in Australia, the basic fundamental knowledge
required for their long-term conservation and management – ie.
distribution, ecology, health, and potential threats or risks
to their survival – is poorly known.
While specific kelp surveys have been conducted on the south-east
and east coasts of Tasmania (eg. Cribb 1954, Olsen 1966, Sanderson
1987), almost nothing is known of the distribution of forests
on the southern, northern and western coasts or the health or
ecology of kelp forests generally. Unfortunately, the large-scale
loss of Giant Kelp forests in Tasmania has also been exacerbated
by the lack of any government policy or integrated research program
to assess the status and management of these marine ecosystems