Meeting Abstract

18.5  Monday, Jan. 4  Mass aggregation for reproduction by a gymnodoridid nudibranch, Gymnodoris ceylonica (Kelaart, 1858), in Lanyu (Orchid Is.), Taiwan HUANG, H.-D.; National Museum of Natural Science hdhuang@nmns.edu.tw

Widely distributed in Indo-Pacific area, translucent white Gymnodoris ceylonica is moderately common and usually found in seagrass or algae zones preying other invertebrates (Debelius and Kuiter, 2007). Observation by divers pointed out this species swim from 30m up to 10m deep for reproduction. Incidentally encountered in mid-July 2009, a mass aggregation for reproduction by G. ceylonica was observed at Lanyu (Orchid Is.), southeastern Taiwan. Estimated more than 30 individuals occurred in a 20 by 20m reef flat with sandy bottom at 4-8 m deep. Sizes of G. ceylonica individuals ranged from 50 to 80 mm. Over 70% of G. ceylonica at the site were ovigerous, judged by the yellow eggs through their translucent body wall. During the observation of approximately 60 minutes, approximately 60% individuals were mating or laying eggs. Mating pairs copulated with everted bifurcate sex organs at the right side of the body for reciprocal fertilization. Gymnodoris ceylonica deposited light-yellowish messy egg strings instead of the spiral bands like most other dorid nudibranchs do. At the site, no G. ceylonica was foraging; some individuals found weak or dead without eggs inside the body. Few animals ay the site fed on eggs of G. ceylonica, yet some eggs were captured by filter feeders on the sea bottom.