Geoscience Reference
In-Depth Information
Figure 11.
Variation trends in the catches of cephalopod and fishes of the nSCS. (a) Catches of
cephalopod; (b) Catches of fishes (Data from Guo and Chen, 2000).
In second phase our above observations were consistent with the results obtained
by the multidisciplinary investigations for assessing the environmental health status
and the fi sheries environment quality in the nSCS during 1997-2002 (Jia et al., 2005).
They reported that both PP and PA were relatively high, averaging 409.7 mg C m
−2
d
−1
,
and 837 × 10
3
cell m
−3
, respectively (according to criterion of grade of primary pro-
ductivity and diet organism lever of China, Jia et al., 2003). The benthic biomass (av-
eraging 11.3 g m
−2
) was at normal levels (the same as above row, Jia et al., 2003). The
ZB (averaging 22.1 mg m
−3
) was low (the same as above row, Jia et al., 2003). And
nutrients were also low, that is the mean values of PO
4
-P = 0.28 μmol l
−1
and DIN =
3.63 μmol l
−1
(according to criterion of Nutrition grade of sea water of China, Jia et al.,
2003). The nutrients values (Jia et al., 2005, nutrients) are much lower than those we
observed and the average index of ecological environment quality of fi shing ground is
0.58, indicating it was in good condition (Jia et al., 2005).
The fi rst phase (before 1997) represents the initial status of the biology and fi sher-
ies during the study period, and the second phase (after 1997) represents the response
of the ecosystem to the changed environment, particularly since 1998, when the oc-
currence of N limitation was signifi cantly alleviated. These ecosystem responses dis-
cussed above were clearly the result of environmental changes induced by not only
climate change, but also anthropogenic activities.
RESULTS
Environmental Changes During the 29 Year Time Series
Seawater Temperature and Salinity
The annual means of SST and T
av
(the average temperature in the water column) ex-
hibited highly significant increasing trends (p ≤ 0.01), their annual rates were 0.078
and 0.090°C y
−1
, respectively. However, the temperature at 200 m (T
200
) showed a sig-
nificant decreasing trend with an annual rate of −0.108°Cy
−1
during the 29 years of ob-
servation between 1976 and 2004 (Figure 6, Table 2). During this period, the SST and
T
av
increased by 2.26 and 2.61°C, respectively, while T
200
decreased by 3.10°C (Figure
6, Table 2). The R
xt
of the time series of SST, T
av
, and T
200
were 0.89, 0.85, and −0.71,
respectively, and the variation trends for this time series were significant (p ≤ 0.01).
During the observation period the annual rate of SSS exhibited a decreasing trend
(−0.022 y
−1
), while the annual rates of S
av
and S
200
exhibited increasing trend (0.007 y
−1
