Protected coral reproduction

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POP2022-03 Protected coral reproduction study (PDF, 4,228K)

Summary 

This report builds on a previous literature review of the reproductive and larval processes of New Zealand protected deep-sea corals. In that review, the following species were identified as suitable for future reproduction studies: the stony cup coral Desmophyllum dianthus (Order Scleractinia), the stony branching reef-forming corals Goniocorella dumosa and Enallopsammia rostrata (Order Scleractinia), and the Scleralcyonacea gorgonian octocorals Primnoa notialis and Paragorgia arborea.

Within the current project, histological methods were used to understand reproductive strategies for the above species, together with some additional histological samples of black corals (Antipatharia) and Hydrocorals (Stylasteridae), to attempt to obtain reproductive information covering all protected coral groups.

The specific objectives of this project (POP2022-03) are to:

1. Address knowledge gaps in reproductive strategies for protected coral species in the New Zealand region.
2. Use available life history and reproductive data to inform relative productivity/vulnerability parameters for relevant concurrent and future research.
   This study has generated some interesting and important data on the reproductive traits of protected New Zealand deep sea corals. We have confirmed that G. dumosa and E. rostrata collected within the New Zealand region are gonochoric (single sex within a polyp), with both species having either male or female specimens (i.e., all polyps on a specimen were the same sex).

We have also confirmed that G. dumosa is a brooder in wild populations on the Chatham Rise, a reproductive mode whereby gametes are fertilised and develop internally into larvae before being released into the surrounding water. Stage IV oocytes were present throughout the year and the limited number of male specimens examined had mature stage IV spermiaries present in both seasons sampled (April and August). We conclude, from the limited seasonal spread of available data, that there was no evidence of reproductive periodicity in G. dumosa and that G. dumosa may have the ability to reproduce year-round when environmental conditions are favourable. Previous observations of larvae in aquaria from September to November 2020 (Beaumont et al. 2024), and with a consistent food supply, support this theory.

Although there was a limited seasonal spread of data for E. rostrata, there was no evidence of seasonality with mature or maturing oocytes present in all female specimens examined (sampled in April, June and August). There was no evidence of larvae nor brooding and as such, E. rostrata are considered broadcast spawners. Mature (stage IV) spermaries were observed in male specimens from all seasons sampled (April, June and August). We, therefore, suggest that E. rostrata could be a continuous or an aperiodic spawner, rather than a seasonal spawner, though further sampling would be required to confirm this.

Enallopsammia rostrata had a lower estimated fecundity than G. dumosa though they had a similar sized maximum oocyte diameter (although morphologically there are differences as E. rostrata oocytes are long and thin and G. dumosa are more rounded). However, E. rostrata is considered likely to be a broadcast spawner and G. dumosa a brooder. This goes against the general assumption that brooders have fewer but larger oocytes/larvae.

The inclusion of black corals (Antipatharia) and hydrocorals (Stylasteridae) in this study were as a trial only to assess the quality of histological sections that could be prepared from fixed specimen samples in order to enable clear observations of reproductive data. Our trials on the black corals Leiopathes bullosa and Sibopathes sp. showed that it will be possible to assess the reproductive state of future sections of these species. However, hydrocorals proved problematic due to their extensive calcification, with more than 95 % of the animal being comprised of hard carbonate skeletal matrix and therefore difficulty in obtaining adequate tissue for examination.

The histological analyses of the stony cup coral Desmophyllum, and the two gorgonian octocoral species Paragorgia and Primnoa planned for this study are being carried out by a PhD student at the University of Gothenburg but these results have been delayed, and as such they will be added to this report as an addendum when available (expected early 2025).

Specimens used within this study were historic (some dating back to 2000) and many had not been preserved with histological analyses in mind. While we were able to get some data from all specimens used, in some cases the quality of data was compromised by the quality of the histological sections. In addition, the variability observed in reproductive data between polyps and specimens within this study highlights the importance of replicate samples across multiple time points when investigating reproductive mode, seasonality and fecundity. We recommend that, where possible, deep-sea corals specimens are collected and placed into an appropriate preservative to enable further histological analyses to address knowledge gaps.
There remain questions regarding the reproduction of corals that can only be addressed by observations of live animals, such as larval behaviour, pelagic larval duration and settlement preferences.

These data and results have been communicated to relevant concurrent research projects (e.g., INT2022-04, risk assessment for protected corals) where they have been used to help evaluate scores for productivity attributes in Productivity Susceptibility Analyses (PSA). In addition, they will inform future research to support risk assessment and development of appropriate management options.

Publication information

Beaumont, J., Marriott, P.,Connell, A., Moreno Moran, D., Waller, R., Tracey, D. and Clark, M. 2024. Protected coral reproduction. POP2022-03 final report prepared by NIWA for Conservation Services Programme, Department of Conservation. 64 p.