Contrasting Modes of Reproduction in Two Antarctic Asteroids of the Genus Porania, With a Description of Unusual Feeding and Non-feeding Larval Types

¹ Institute of Marine Sciences and Biology Board of Studies, University of California, Santa Cruz, California 95064 and Department of Larval Ecology, Harbor Branch Institution Inc., Ft. Pierce, Florida 34946

Reproduction and development were markedly different in two morphologically similar asteroids of the genus Porania that occur in shallow waters of McMurdo Sound, Antarctica. Adults of the recognized species, Porania antarctica (Perrier, 1894), are large (R_max = 70 mm) and have genital pores that are situated aborally on the disc; females broadcast spawn large numbers (3-4 x 10⁴) of buoyant eggs that measure 0.55 mm and develop into unusual, yolky planktotrophic larvae. In contrast, adults of the undescribed Porania sp. are considerably smaller (R_max = 30 mm) and their genital pores are located orally on the disc. Female fecundity is low (100-310 eggs); the few eggs produced measure 0.55 mm, are heavier than seawater, and develop into demersal lecithotrophic larvae. These differences conform to general patterns reported for echinoderms with divergent types of reproduction. However, other differences contradict established trends; specifically, P. antarctica with planktotrophic development has a shorter embryonic and larval phase (65 days vs. 78 days) and a larger juvenile size at metamorphosis (0.8 vs. 0.6 mm) than Porania sp., which has lecithotrophic development. The reproduction of P. antarctica incorporates advantages of both planktotrophic and lecithotrophic strategies and may be particularly well-suited for environmental conditions in the Antarctic Ocean.

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