Reproduction

The process of reproduction in Cliona sponges is still a little unclear and not much is known about its oviparous reproduction (Mariani et al. 2000). Cliona sponges are hermaphroditic and are oviparous as opposed to the more common viviparous reproduction usually found in sponges (Mariani et al. 2000).

Cliona is a broadacast spawner (Mariani et al. 2000) with synchronous embryo development, triggered by endogenous or exogenous factors (eg. tides,temp, lunar cycle chemical cues and photoperiod- how much daylight) (Mariani et al. 2000; Piscitelli et al. 2011).Temperature triggers gametogenesis with water temperature being one of the most important factors in sponge settlement, influencing metabolism and growth.

Whether Cliona undergoes external or internal fertilisation is debatable. Internal fertilisation and release of fertilised eggs (zygotes) has been recorded in C.vridis, however external fertilisation with the release of mature eggs excreted via the oscula has also been recorded in C. tenuis.

As Cliona spp. reproduction is highly variable the well documented reproductive cycle of C.virdis has been described (description of C. virdis larva and reproduction adapted from Mariani et al. 2000):

Larvae

• Parenchymella
• Weak swimmers, evenly ciliated
• Crawls during all of free life
• Brownish in colour
• One month old sponge had lots of zooxanthellae
• No ostia or oscula visible
• Cells similar to etching cells were already present in the one moth old sponge

Reproductive cycle

• Oogenesis is a continuous process throughout the year
• However, after egg release oocytes were not produced for a period of 1-4 months. During this time the sponge rebuilds its aquiferous system, as a result of destruction by male gamete development. 
• Spermatogenesis is a fast process which peaks after most oocytes have developed, suggesting asynchrony (Piscitelli et al. 2011). 
• Embryo or larvae was not observed in sponge tissue supporting the fact that Cliona sponges are oviparous with evidence of fertilised egg masses collected from the exterior of C. virdis. Oviparous nature suggests that they do not brood their larvae.
• Annual reproductive cycle
• Single period of zygote release coinciding with temperature increase of water triggered by an abrupt increase in water temp.
• Hermaphroditic. Evidence for this includes the fact that individuals possess both oocytes and spermatic cysts simultaneously (Piscitelli et al. 2011).

Although most Clionaid sponges appear to be hermaphroditic, some gonochoristic Clionaids have been observed, such as the species Cliona tenuis.

More studies into the reproductive cycles of Cliona is needed in order to clearly determine the reproductive process of Clionaid sponges. From this, the reproductive cycle of the particular Cliona sp. found on Heron Island cannot be determined. Multiple contradictions occur in relation to whether spawning and development is synchronous or asynchronous (Mariani et al. 2000; Pisticelli et al. 2011; Gonzalez-Rivero et al. 2013). Therefore, further research is needed to obtain clarity.