Patterns of reproduction in two co-occurring Great Barrier Reef sponges

Reproduction is a key biological process that underpins the persistence and maintenance of populations. However, information on the reproductive biology of Great Barrier Reef (GBR) sponges is depauperate. The present study established the reproductive biology of two co-occurring GBR sponges, namely Ianthella basta (Verongida) and Ircinia sp. (Dictyoceratida). Sponges were haphazardly sampled (monthly) over a period of 1 year. Histological analysis of samples established the sexuality, development, seasonality, gametogenesis and fecundity of the two species, as well as the effects of temperature on reproduction. I. basta is oviparous, whereas Ircinia sp. is viviparous. The mode of sexuality in I. basta could not be determined, because male propagules were not detected, whereas Ircinia sp. is a simultaneous hermaphrodite. Reproduction in I. basta is unique within the verongids and co-occurring oviparous species, with peak reproduction occurring at the minimum annual temperature (23°C) and spawning occurring as the temperature increased above 23.4°C. Reproduction in Ircinia sp. corresponded to patterns reported for other viviparous GBR species, with an increase in reproductive propagules, peak sperm release, fertilisation and spawning occurring at temperatures above 25°C. Fecundity in I. basta and Ircinia sp. is high compared with other sponge species in the region, which may contribute to their apparent abundance on the GBR.