Vital GEO Graphics

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Increasing frequency and area of harmful algal blooms (HABs) in the East China Sea

In the East China Sea, the number of harmful algal blooms increased from 10 in 1993 to 86 in 2003, when they covered an area of 13 000 square kilometres. Fertilizer application in the sea’s catchment area has increased by as much as 250 per cent, notably in the upstream and coastal provinces of Anhui and Jiangsu, contributing a high nutrient load to the sea. The blooms, which mostly occur in the inner shelf of the Yangtze River, have a range of human well-being and ecosystem implications. High mortality rates of fish and benthic organisms have also been observed.

Algal blooms in the East China Sea

100 Frequency of algal blooms/year

Area covered (km 2 )

25 000

20 000

80

15 000

60

40

10 000

20

5 000

0

0

1993

2000

2003

2002

2001

Source: UNEP-GIWA 2006a

Declines in the volumes of global marine and fresh- water fisheries are dramatic examples of large-scale ecosystem degradation related to overfishing, pollu- tion, habitat disturbance and losses. The worldwide fishing fleet grew rapidly in the mid 20th century, with many stocks of fish either being over-exploited or crashing altogether. Many of the more valuable species of fish have been subject to particularly sharp declines and marine ecosystems have been severely damaged. The greatest threat to biodiversity in deep sea areas is bottom-trawling. This type of high seas fishing is most damaging to seamounts and the coldwater cor- als they sustain, which are home for several commer- cial bottom-dwelling fish species.

The seafloor off Northwest Australia showing dense populations of corals and sponges before trawling (left) and after trawling (right). Credit: Keith Sainsbury, CSIRO The seafloor off Nor hwest Australia showing dense populations of corals and sponges before trawling (left) and after trawling (right). Credit: Keith Sainsbury, CSIRO

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Figure 4.13 Exploitation status of marine fish stocks

per cent

100

Crashed Overexploited Fully exploited Developing Underdeveloped

90

80

70

60

50

40

30

20

10

0

Source: SAUP 2006

2003

2002

1998

2000

1988

1992

1994

1996

1980

1984

1986

1990

1970

1972

1974

1976

1978

1982

1954

1956

1958

1960

1962

1964

1966

1968

1952

1950

34 V I TAL GEO GRAPH I CS