In the Xiangshan Bay, the annual mean depth ranged from (7.0±2.1) m (Section D2) to (14.4±8.3) m (Section D12). The average salinity was highest in February (28.3±0.3), and lowest in August (22.8±0.4), and it was globally constant in four different sections (Table 1). August had the highest average temperature of (29.6±0.6)°C, followed by May ((21.5±1.1)°C), November ((18.5±0.6)°C) and February ((12.1±1.9)°C). The increment of temperature (Δt) among stations were different in four seasons, with a peak of 7.83°C in February, 4.86°C in May, 1.99°C in August and 2.71°C in November. The spatial distribution of temperature was uneven. The minimum temperature was at Stations S01, S02 and S09, and the high temperature was at Stations S04 and S08. In generally, decreasing temperatures were found at increasing distances away from the drain outlet of the power plant (Fig. 2).
Month Month average Section D2 D7 D12 D20 February 28.3±0.3 28.4±0.1 28.2±0.2 28.3±0.5 28.3±0.3 May 25.7±1.6 26.5±0.1 25.6±1.8 26.0±0.7 25.0±2.1 August 22.8±0.4 22.9±0.2 22.8±0.2 22.7±0.2 22.8±0.5 November 24.7±0.3 25.1±0.3 24.9±0.2 24.7±0.2 24.6±0.2 Note: D2, D7, D12 and D20 stand for sections at a distance of 0.2, 0.7, 1.2 and 2 km away from the outfall of the power plant, respectively.
Table 1. Mean salinity of sampling months in four sections (mean±SD)
Combined with 120 samples data from three different mesh size nets, we identified 77 zooplankton species belonging to 13 taxa (which included 9 species that were identified to genus level) and 18 pelagic larvae. The annual average abundance from 120 samples was (12 571.8±1 138.7) ind./m3. The total length of zooplankton varied from 93.7 to 40 074.7 μm. Zooplankton total length divided into seven size classes in Table 2. Micro-zooplankton (20−200 μm) were mainly consisted by Tintinnopsis butschlii, Difflugia sp. and Trochophore. Meso-zooplankton (200−2 000 μm) can be subdivided into three classes: small meso-zooplankton (200−500 μm) were mainly made up of copepods nauplius larva, eggs, Oithona brevicornis; medium meso-zooplankton (500−1 000 μm) were mainly consisted like copepods larva, Oithona fallax, Paracalanus aculeatus; large meso-zooplankton (1 000−2 000 μm) were formed with Centropages abdominalis, Centropages tenuiremis, Oikopleura dioica and so on. Macro-zooplankton (2 000−10 000 μm) can be subdivided into two classes: small macro-zooplankton (2 000−5 000 μm) were mainly composed of Eucalanus crassus, Calanus sinicus, Eucalanus subcrassus; large macro-zooplankton (5 000−10 000 μm) contained 5 species, such as Zonosagitta bedoti, Pseudeuphausia sinica and Acanthomysis brevirostris. We only found 4 species Zonosagitta nagae, Abyssisagitta pulchra, Acetes japonicas, Squillidae alima larva belonging to megalo-zooplankton (>10 000 μm).
Size class Main species 20−200 μm Tintinnopsis butschlii, Difflugia sp., Trochophore 200−500 μm copepods nauplius larva, eggs, Oithona brevicornis 500−1 000 μm copepods larva, Oithona fallax, Paracalanus aculeatus 1 000−2 000 μm Centropages abdominalis, Centropages tenuiremis, Oikopleura dioica 2 000−5 000 μm Eucalanus crassus, Calanus sinicus, Eucalanus subcrassus 5 000−10 000 μm Zonosagitta bedoti, Pseudeuphausia sinica, Acanthomysis brevirostris >10 000 μm Zonosagitta nagae, Abyssisagitta pulchra, Acetes japonicus Note: In the same size group, species are listed in descending order according to abundance, and only the top 3 species are listed.
Table 2. Main species of different size-class zooplankton
Combined with the abundance of 120 zooplankton samples from three different mesh size nets, we found the annual average abundance was highest in Section D2, followed by Sections D12 and D20, and lowest in Section D7 (Fig. 3). Higher abundance of micro-zooplankton (20−200 μm) was observed in Sections D12 and D20, averaging 931 and 894 ind./m3, respectively. Meso-zooplankton (200−2 000 μm) were the main component of four sections, while the abundance was highest in Sections D2 and D12 and lowest in D7. Highest abundance of small macro-zooplankton (2 000−5 000 μm) was found in Section D20, up to 2 times greater than other sections. Large macro-zooplankton (5 000−10 000 μm) and megalo-zooplankton (>10 000 μm) were more abundant in Sections D12 and D20, which were disappeared in D2. Table 3 showed increasing individual mean length at increasing distances away from the drain outlet of the power plant. Shannon−Wiener diversity index and evenness index in Sections D7 and D12 were the highest, followed by D20, and lowest in D2. After one-way ANOVA and Tukey’s test, there were no significant differences in diversity indices compared for four sections.
Figure 3. Annual average zooplankton abundance of four sampling sections in different size-class (20−200 μm, 200−500 μm, 500−1 000 μm, 1 000 −2 000 μm, 2 000−5 000 μm, 5 000−10 000 μm, >10 000 μm and 20− >10 000 μm). D2, D7, D12 and D20 stand for sections at a distance of 0.2, 0.7, 1.2 and 2 km away from the outfall of the power plant, respectively.
Section D2 D7 D12 D20 Individual mean length/μm 600.7 659.1 672.5 726.2 Shannon−Wiener index 1.27±0.16a 1.56±0.32a 1.57±0.44a 1.43±0.24a Evenness index 0.51±0.09a 0.61±0.12a 0.60±0.14a 0.57±0.08a Note: Diversity indices with same letters (a) among sections in the superscript mean no significant difference at 0.05 levels. D2, D7, D12 and D20 stand for sections at a distance of 0.2, 0.7, 1.2 and 2 km away from the outfall of the power plant, respectively.
Table 3. Individual mean length, Shannon−Wiener index and evenness index in four sections
The 505 μm mesh size community had the lowest annual average abundance of (494.4±104.7) ind./m3. A total of 42 zooplankton species (which included 5 species that were identified to genus level) and 7 pelagic larvae were identified, and mainly belong to large meso-zooplankton (1 000−2 000 μm) (Fig. 4). For the 160 μm mesh size community, annual average abundance was (9 531.1±1 079.5) ind./m3, containing 47 species (which included 3 species that were identified to genus level) and 16 pelagic larvae. The predominant zooplankton component was meso-zooplankton (200−2 000 μm) (Fig. 4). The 77 μm mesh size community had the highest annual average abundance of (27 690.0±1 633.7) ind./m3 and the highest number of zooplankton species (61, which included 6 species that were identified to genus level) and 15 pelagic larvae, which mainly consisted of meso-zooplankton (200−2 000 μm) and micro-zooplankton (20−200 μm) (Fig. 4). Species richness, abundance, evenness index and Shannon−Wiener diversity index of the 505 µm mesh size were significantly lower than those recorded from the 160 µm mesh size (p<0.05) and the 77 µm mesh size (p<0.05). Significant differences between the 160 µm and 77 µm mesh sizes was only found in species richness (p<0.05) and abundance (p<0.05), while evenness and Shannon−Wiener indices were similar (p>0.05) (Table 4).
Mesh size Abundance Species richness Evenness Shannon−Wiener net I 494.4±104.7c 42±0.3c 0.5±0.3b 1.1±0.7b net II 9531.1±1079.5b 47±0.4b 0.7±0.1a 1.9±0.4a net III 27690.0±1633.7a 61±0.4a 0.6±0.1a 2.0±0.5a Note: Mean values with different letters (a, b, c) in the superscript are significantly different at the 0.05 level among mesh, net I = 505 µm mesh size, net II = 160 µm mesh size, and net III = 77 µm mesh size.
Table 4. Differences (mean±SD) among three different mesh size nets in the annual average abundance (ind./m3) and diversity indices (species richness, evenness index and Shannon−Wiener diversity index)
In the zooplankton assemblage sampled by the 505 μm mesh net, C. abdominalis was the dominant species; it had an abundance reduction (AR) of 77.1% with the 160 μm mesh catches, and 39.5% with the 77 μm mesh catches. Paracalanus crassirostris was dominant in both the 160 μm mesh net and 77 μm mesh net, which was underestimated using the 505 μm mesh net, with losses of 100% (AR nII–nI and AR nIII–nI). The other numerically important species were Acartia clausi, C. tenuiremis and Paracalanus parvus, which were the most efficiently sampled with the 160 μm mesh net. The 77 µm mesh net caught great number of smaller zooplankton. Oithona brevicornis, Oithona fallax and Oithona similis were dominant species only in 77 μm mesh net samples. Abundance of Oithona spp. in the plankton samples collected with a 77 μm mesh net was an order of magnitude greater than in samples taken with 160 μm mesh nets. We estimated a loss of 82.5%−97.2% of Oithona copepod individuals through the 160 μm mesh net, and 100% loss through the 505 μm mesh net (Table 5 and Fig. 5).
Dominant species net I net II net III AR nII–nI AR nIII–nI AR nIII–nII Centropages abdominalis 0.49 – – –77.1 –39.5 62.2 Acartia clausi – 0.03 – 100 100 –63.9 Centropages tenuiremis – 0.02 – 100 100 –84.5 Paracalanus crassirostris – 0.03 0.04 100 100 70.2 Paracalanus parvus – 0.06 – 100 100 –89.6 Oithona brevicornis – – 0.05 100 100 92 Oithona fallax – – 0.06 100 100 97.2 Oithona similis – – 0.03 100 100 82.5
Table 5. Dominant species, dominance and abundance reductions (AR, %) recorded from each mesh size net (net I=505 μm mesh size, net II=160 μm mesh size, and net III=77 μm mesh size)
Differences related to mesh size were examined by ANOSIM and SIMPER tests (Table 6). The ANOSIM test evaluated significant differences among the three mesh size nets (p=0.001). The SIMPER analysis showed that the average dissimilarity between the 505 µm mesh net and the 160 µm mesh net was 90.7%. Copepod larvae were major contributors to this dissimilarity, followed by O. brevicornis and eggs. The highest average dissimilarity (94.8%) was found between the 505 µm mesh net and the 77 µm mesh net. The contributions to this dissimilarity were almost equally distributed between copepod larvae and copepod nauplius larvae. The lowest average dissimilarity (62.3%) was seen between the 160 µm mesh net and 77 µm mesh net, which was mostly due to copepod nauplius larvae, O. fallax and copepod larvae.
net I, net II net I, net III net II, net III ANOSIM R 0.7 0.8 0.4 p 0.001 0.001 0.001 SIMPER Average dissimilarity/% 90.7 94.8 62.3 Discriminating species 1 copepod larvae copepod larvae copepod nauplius larvae Contribution/% 9.9 8.2 6.5 Discriminating species 2 Oithona brevicornis copepod nauplius larvae Oithona fallax Contribution/% 5.3 8.1 4.1 Discriminating species 3 eggs Oithona brevicornis copepod larvae Contribution/% 5.3 5.2 3.8 Note: Six discriminating species are listed in the table (net I = 505 µm mesh size, net II = 160 µm mesh size, and net III = 77 µm mesh size).
Table 6. ANOSIM and SIMPER showing the differences in zooplankton communities among three different mesh size nets
Zooplankton community size-structure change and mesh size selection under the thermal stress caused by a power plant in a semi-enclosed bay
- Received Date: 2019-12-20
- Accepted Date: 2020-04-17
- Available Online: 2020-12-28
- Publish Date: 2020-08-25
- zooplankton /
- coastal power plant /
- temperature elevation /
- size class /
- community structure /
- mesh size selection
Abstract: Zooplankton samples were collected using 505, 160 and 77 μm mesh nets around a power plant during four seasons in 2011. We measured total length of zooplankton and divided zooplankton into seven size classes in order to explore how zooplankton community size-structure might be altered by thermal discharge from power plant. The total length of zooplankton varied from 93.7 to 40 074.7 μm. The spatial distribution of meso-zooplankton (200 −2 000 μm) populations were rarely affected by thermal discharge, while macro- (2 000 −10 000 μm) and megalo-zooplankton (>10 000 μm) had an obvious tendency to migrate away from the outfall of power plant. Thus, zooplankton community tended to become smaller and biodiversity reduced close to power plant. Moreover, we compared the zooplankton communities in three different mesh size nets. Species richness, abundance, evenness index and Shannon−Wiener diversity index of the 505 µm mesh size were significantly lower than those recorded from the 160 and 77 µm mesh size. Average zooplankton abundance was highest in the 77 µm mesh net ((27 690.0±1 633.7) ind./m3), followed by 160 µm mesh net ((9 531.1±1 079.5) ind./m3), and lowest in 505 µm mesh net ((494.4±104.7) ind./m3). The ANOSIM and SIMPER tests confirmed that these differences were mainly due to small zooplankton and early developmental stages of zooplankton. It is the first time to use the 77 µm mesh net to sample zooplankton in such an environment. The 77 µm mesh net had the overwhelming abundance of the copepod genus Oithona, as an order of magnitude greater than recorded for 160 µm mesh net and 100% loss through the 505 μm mesh net. These results indicate that the use of a small or even multiple sampling net is necessary to accurately quantify entire zooplankton community around coastal power plant.
|Citation:||Qianwen Shao, Yifeng Zhu, Meixia Dai, Xia Lin, Chengxu Zhou, Xiaojun Yan. Zooplankton community size-structure change and mesh size selection under the thermal stress caused by a power plant in a semi-enclosed bay[J]. Acta Oceanologica Sinica, 2020, 39(8): 62-70. doi: 10.1007/s13131-020-1634-9|