February 1st to 5th 2016
Olhão, Portugal
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Resting egg production of the invasive copepod Acartia japonica in Sagami Bay, Japan

Scientific Exhibition
Biological Invasions
Thursday, February 4, 2016 -
17:30 to 19:30

Takayama, Y. 1 Hirahara, M. 2 Toda, T. 3

1Soka University
2Soka University
3Soka University

The calanoid copepod Acartia japonica Mori, 1940, is one of seven endemic species in the coastal waters of Japan. The occurrence of this species had been limited to the coastal areas of the Sea of Japan and the Ryukyu archipelago. However, A. japonica was recently observed at Manazuru Port in the temperate coastal waters of Sagami Bay, Japan which faces the Pacific Ocean. In order to clarify the invasive qualities, population dynamics and reproductive behaviour of A. japonica at Manazuru Port, the present study investigates the monthly occurrence and abundance of this species from May 2011 to October 2015. The in situ egg production was also examined in 2014 and 2015 to understand its reproduction strategies.A. japonica was not observed in samples collected from 2011 to 2012, but appeared as the dominant species from summer to early autumn from 2013 to 2015. The maximum abundance reached 211 inds. m-3 in October, 2014. The egg production rate ranged from 0.23 ± 0.73 to 5.50 ± 4.27 eggs female-1 day-1, and spawned eggs included resting eggs which do not hatch until the passing of the refractory phase. Subitaneous eggs, which hatch within a few days, comprised 80-100% and 0-55% of total egg production near the beginning and end of the occurrence period, respectively. The ratio of resting to total egg production increased with decreasing temperature where some of the resting eggs did not hatch for more than a year. A. japonica may be utilizing the strategy of producing resting eggs to avoid low temperatures in the invaded area.
keywords: 
Resting eggs, Invasive copepod, Acartia japonica, Sagami Bay, Reproductive strategy,

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