Dramatic declines in Euphausia pacifica abundance in the East China Sea: response to global warming? Zhaoli XU, Dong ZHANG East China Sea Fisheries Research Institute, Chinese Academy of Fisheries Sciences

Progress in collaboration  We are still working out for getting a fund to initiate the collaboration.

Progress in the project  Although the collaboration has not been initiated, we have collected some fundamental data related to the proposed project.

Background  Euphausia pacifica is considered one of the key species in the food web of the northwestern Pacific as food for many endemic and migrant fishes, marine mammals and sea birds.  It is a dominant euphausiid species in the East China Sea being the only Euphausia species with temperate distribution in the North Pacific.  It may also be a good indictor of regional warming because several reports have shown significant abundance changes of E. pacifica off the coast of Californiia and Baja, California after the 1976 climate regime.

The questions we attempted to answer  How did the abundance change in the East China Sea in the past years?  How did temporal-spatial distribution change in the Sea?  Whether the changes are related to climate change in the Sea?

Data collection  We compare data collected in 1959 and (no data available between the two periods)

Study area ab Fig. 1 Map of sampling stations. a. sampling stations both in 1959 and , b. sampling stations in 1959

RESULTS Interannual variation of temperature in spring Fig. 2 Surface and bottom temperature in May 1959, and in the East China Sea.

Fig. 3 Isothermal lines in March – June 1959 and 2005

Spatial distribution Fig. 4 Seasonal spatial distribution of Euphausia pacifica in the East China Sea in 1959 and ~15~1010~20>201~5 ind/m 3

Fig.5 Spatial distribution of Euphausia pacifica in the East China Sea in the spring 1959 and in May 2005, no occurrence in March, April, and June ~15~1010~20>201~5 ind/m 3

Effect of temperature on the krill  When temperature is > 18 º C, E. pacifica shrinks between molts (Marinovic and Mangel 1999), and reduces egg production (G ó mez-Guti é rrez et al. 2007), egg hatchability and high larval mortality (Iguchi and Ikeda 1994), resulting in abundance reduction.

Fig. 6 Relationship between temperature and abundance of Euphausia pacifica in May 1959 (a, b) and 2002 (c, d) in the East China Sea Bottom temperature ( ℃ ) Surface temperature ( ℃ ) Abun danc e (ind/ m 3 ) Surface temperature ( ℃ ) Bottom temperature ( ℃ ) a b cd

Table 1. Surface temperature (ST), bottom temperature (BT), surface salinity (SS), bottom salinity (BS), and abundance (A) in May 1959 and 2002 to 2007 (mean±SE, n=27) Year ST BT A O (°C) (°C) (ind/m 3 ) (%) ±0.21 b 17.08±0.32 b 1.91±0.70 a ± ±0.18 a 0.36±0.18 b ±0.23 a 18.15±0.26 a 0.02±0.01 b ±0.21 b 17.72±0.15 b 0.04±0.02 b ±0.30 a 18.29±0.47 a 0.00±0.00 b ±0.35 b 17.25±0.26 b 0.01±0.01 b ±0.23 a 17.25±0.21 b 0.00±0.00 b 0.00 Different letters at each column indicate significant difference (P<0.05) after the multiple comparisons with Duncan method.

Summary  Dramatic reduction in abundance in the East China Sea since 2002 is consistent with temperature anomalies during years  Distribution shift occurred as a response to temperature anomalies  Population in the East China Sea did not recover when temperature became normal

Conclusions  Significant reduction of the abundance of E. pacifica after 2002 (maybe earlier) probably is an associated response to global warming. However, temperature is not only factor to be responsible for the reduction.

Questions remaining to answer  Why did not the krill population recover when temperature became normal? (Temperatures in the spring and fall in recent years (i.e ) were still in the range of temperatures at which E. pacifica used to distribute)  Why does not the population in the Yellow Sea enter the East China Sea?

Questions?