Zoological Studies

Vol. 58, 2019

(update: 2019.03.29; 04.30)

Spiny but Subitaneous Eggs: Egg Morphology and Hatching in Acartia Copepods in the Tropics

Ryota Nakajima1,,*, Teruaki Yoshida2,, Sakiko O. Sakaguchi1, Bin Haji Ross Othman3, and Tatsuki Toda4


1Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Natsushima, Yokosuka, Kanagawa 237-0061, Japan. *Correspondence: +81-(0)46-867-9686. E-mail: nakaji.gogogo@gmail.com, nakajimar@jamstec.go.jp. E-mail: oruis@jamstec.go.jp (Sakaguchi)
2Unit for Harmful Algal Bloom Studies, Borneo Marine Research Institute, Universiti Malaysia Sabah, 88400 Kota Kinabalu, Sabah, Malaysia. E-mail: teruaki.yoshida@gmail.com
3School of Marine & Environmental Sciences, Universiti Malaysia Terengganu, Terrengganu, 21030 Kuala Terengganu, Terrenganu, Malaysia. E-mail: othross@gmail.com (Othman)
4Faculty of Science and Engineering, Soka University, Hachioji, Tokyo 192-8577, Japan. E-mail: toda@soka.ac.jp (Toda)

RN and TY contributed equally to this work.

Received 23 October 2018 / Accepted 24 March 2019
Communicated by Ryuji Machida

Egg surface ornamentation, egg production rates, and hatching success of two calanoid copepod species (Acartia pacifica and Acartia cf. erythraea) were examined in a tropical coral reef of Tioman Island, Malaysia, near the the equator (2N). All observed females of A. pacifica and A. cf. erythraea produced eggs with spines on the surface, either short or long, which are common in resting eggs in temperate ecosystems that hatch when environmental conditions are favorable or after a certain refractory period. However, all of these spiny eggs in the present study hatched within 48 hours when exposed to ambient seawater temperature, suggesting that they were subitaneous eggs. Such spine ornamentation has been thought to be an adaptive feature only for resting eggs to survive during egg dormancy, but the presence of spines on subitaneous eggs suggests further possible functions of these spines such as reducing the risks of ingestion by predators.

Key words: Copepods, Subitaneous egg, Spiny, Tropics, Malaysia.

Citation: Nakajima R, Yoshida T, Sakaguchi SO, Othman BHR, Toda T. 2019. Spiny but subitaneous eggs: egg morphology and hatching in Acartia copepods in the tropics. Zool Stud 58:5. doi:10.6620/ZS.2019.58-05.