Strategies, patterns and environmental cues for reproduction in two temperate haliclonid sponges

The reproductive biology of 2 haliclonid sponges was examined over a 2 yr period. Histological samples of Haliclona sp. 1 (green Haliclona) and Haliclona sp. 2 (brown Haliclona) from tagged and haphazardly sampled individuals of both species were examined using light microscopy. Interest in these 2 sympatric species is high, due to the potent and unique bioactive compound (salicylihalamide A) they produce, hence the need to understand the reproductive biology of both species to ensure their proper conservation and management. Green Haliclona is viviparous, with both gonochoric and hermaphroditic individuals in the sponges sampled. Brown Haliclona is also viviparous and is clearly a gonochoric species. Only decreasing wave height showed a significant correlation to gametogenesis, but the onset and progression of reproduction in both species coincided with increases in water temperature and photoperiod. Oogenesis for both species extended from November to April. Spermatogenesis extended over 3 mo for green Haliclona (January to March) and 4 mo for brown Haliclona (January to April). Embryogenesis within brood chambers started in January and extended over 4 mo in green Haliclona and 5 mo in brown Haliclona. The parenchymellae larvae of green Haliclona were observed in tissue samples for 2 mo compared to 4 mo for brown Haliclona. The reproductive output of each species was similar; however, female reproductive output at 2.9 % (green Haliclona) and 2.4 % (brown Haliclona) of the mesohyl was much lower than that of other viviparous species. Male reproductive output (2.3 and 2.4 % for green and brown Haliclona, respectively) compares favourably to that of oviparous species. The high reproductive output of males and the timing of reproduction in both species of sponge appears to help in reducing the risk of unsuccessful fertilisation and lower the probability of larvae being released into unfavourable conditions.