Geoscience Reference
In-Depth Information
Response of the Ecosystem and Living Resources
Although the frequency of observation on various biology and fisheries parameters
was less than that for physical and chemical parameters which reflected the long term
changes in the environmental processes, some responses of the ecosystems to these
environmental changes in the nSCS was still evident.
Comparing the biology and fi sheries data between the two phases discussed above,
the average values of Chla, PP, PA, BB, CC and DTC increased by 6.4, 1.4, 2.4, 0.7,
7.2, and 2.8 times, respectively during the second phase, except for zooplankton abun-
dance which decreased by about 50% (Table 6). The decrease in zooplankton abun-
dance may be related to the increase in its predators, such as fi sh, cephalopods, and
so forth (Figure 11). The R
xt
values of the cephalopod and DTCs were 0.89 and 0.88,
respectively, and highly signifi cant (p ≤ 0.01). Besides, the increase in both the cepha-
lopod and DTCs partially could be attributed to the improvement of demersal trawl
fi shing techniques, and also to the increase in stock and production of low trophic
levels, induced by the alleviation in N limitation in the nSCS.
Table 6.
Comparison of the multi-year mean values of Chl-a, primary production (PP), phytoplankton
abundance (PA), zooplankton biomass (ZB), benthos biomass (BB), cephalopod catch (CC), and
demersal trawl catch (DTC) in the nSCS between two periods, i.e., before and after 1997 (units: mg
m
−
3
, mgC m
−
2
d
−
1
, x 10
3
cell m
−
3
, mgm
−
3
, gm
−
2
, x10
4
t, and x10
4
t, respectively).
Parameter
First phase (data source)
Second phase (data source)
Chi-a
0.29 (Fan 1985)
b
2.16 (Cai et al., 2002a; SOAC 2003)
c
pp
185.7 (Fan, 1985)
b
442.5 (Ning et al., 2004; Jia et al., 2005; Hao et al.,
2007)
PA
161.5 (Lin, 1985)
542.7 (Jia et al., 2005)
b
ZB
44.5 (Zhang, 1984; Chen, 1985; Qian et al., 1990a,
b; Huang et al., 1990; Chen, 1992)
22.05 (Jia et al., 2005)
d
BB
6.6 (Shen, 1985)
11 .3 (Jia et al., 2005)
CC
1.2 (Guo and Chen, 2000)
9.8 (Guo and Chen, 2000)
DTC
89.0 (Guo and Chen, 2000)
334.8 (Guo and Chen, 2000)
a The data listed in the Table are the mean of the water column of the multi-year average for each parameter from differ-
ent sources, except for BB, CC and DTC which are only treated by the multi-year average;
b The data were provided by Chen, X. from The Third Institute of Oceanography, SOA, China;
c The data was from the National Science Foundation of China (NSFC) project under the contract No. 90211021;
d The data from Jia et al. (2005) are the annual mean of the multi-year mean for each season during 1997-2002.
In addition, after 1997, phosphorus depletion in surface waters during summer
coincided with a shift in the dominant species in phytoplankton community from dia-
toms to dinofl agellates and cyanophytes (Ning et al., 2004). Peng et al. (2006) pointed
out that dinofl agellates composed more than 60% of the total PA in the HK Southeast
Anti-Cyclonic Eddy and Hainan Island East Anti-Cyclonic Eddy of the nSCS, where
P concentration was near detection limit in the summer of 2004.
