Peaked abundance of Calanus sinicus earlier shifted in the Changjiang River (Yangtze River) Estuary: a comparable study
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Peaked abundance of Calanus sinicus earlier shifted in the Changjiang River (Yangtze River) Estuary: a comparable study between 1959, 2002 and 2005 XU Zhaoli1∗ , MA Zengling1 , WU Yumei1 1
Key and Open Laboratory of Marine and Estuary Fisheries (Ministry of Agriculture), East China Sea Fisheries Research Institute, Chinese Academy of Fisheries Science, Shanghai 200090, China
Received 2 June 2010; accepted 14 February 2011 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2011
Abstract The sea surface temperature (SST) of the East China Sea (ECS) increased in the past decades, which may have a great impact on the ecosystem of the ECS, including the changes in planktonpopulation structure. In this paper, the changes in peaked abundance of Calanus sinicus in the Changjiang River (Yangtze River) Estuary were compared between 1959 and 2002, based on the data collected from the seasonally oceanographic cruises and those performed in spring of 2005. It was much higher in spring compared with that in other seasons both in 1959 and 2002. Furthermore, in spring 2005, the time for occurrence and decrease of the peaked C. sinicus abundance advanced about one month, accompanying the increase in the sea surface water temperature (SST). It peaked in June and decreased in July in 1959, however, in 2005, it peaked in May and attenuated sharply in early June. The earlier decrease of peaked C. sinicus abundance may further deteriorate the ecosystem in the Changjiang River Estuary and north nearshore of the ECS. Key words: Calanus sinicus, East China Sea (ECS), temperature, Changjiang River (Yangtze River) Estuary, zooplankton
1 Introduction Calanus sinicus (Copepoda: Calanoida) is distributed in the shelf water of the East China Sea (ECS), the Huanghai Sea (Yellow Sea), the Bohai Sea, the Inland Sea of Japan and the adjacent Pacific Ocean (Hwang and Wong, 2005; Uye, 2000). The species is one of the most important mesozooplankton in these areas in terms of biomass (Xu et al., 2003; Huang et al., 1993; Chen, 1964) and supports the production of the commercially important anchovy, sand eels, and sardines (Uye et al., 1999). Therefore, it is regarded as one of the key secondary producer linking phytoplankton and higher trophic level. Its population dynamics was one of the principal foci of the Chinese Global Ocean Ecosystems Dynamics (GLOBEC) of Huanghai Sea and East China Sea Program (Zhang et al., 2005; Pu et al., 2004). Calanus sinicus has been considered as a warmtemperate and coastal species (Hulsemann, 1994;
Chen et al., 1985), with wide temperature and salinity tolerance (Uye, 2000; Huang et al., 1993). Temperature is one of the most important factors that influence its size (Chen, 1964), distribution (Wang et al., 2003) and recruitment (Uye, 1988). Earlier researches indicated that 23 ◦ C and 26–27 ◦ C were the upper limitation for its reproduction and occurrence respectively (Huang et al., 1993). Recent reports suggested its upper sublethal or lethal temperatures were around 23–29 ◦ C (Ozaki et al., 2
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