Inducing broadcast coral spawning ex situ: Closed system mesocosm design and husbandry protocol

Abstract

For many corals, the timing of broadcast spawning correlates strongly with a number of environmental signals (seasonal temperature, lunar, and diel cycles). Robust experimental studies examining the role of these putative cues in triggering spawning have been lacking until recently because it has not been possible to predictably induce spawning in fully closed artificial mesocosms. Here, we present a closed system mesocosm aquarium design that utilizes microprocessor technology to accurately replicate environmental conditions, including photoperiod, seasonal insolation, lunar cycles, and seasonal temperature from Singapore and the Great Barrier Reef (GBR), Australia. Coupled with appropriate coral husbandry, these mesocosms were successful in inducing, for the first time, broadcast coral spawning in a fully closed artificial ex situ environment. Four Acropora species (A. hyacinthus, A. tenuis, A. millepora, and A. microclados) from two geographical locations, kept for over 1 year, completed full gametogenic cycles ex situ. The percentage of colonies developing oocytes varied from ~29% for A. hyacinthus to 100% for A. millepora and A. microclados. Within the Singapore mesocosm, A. hyacinthus exhibited the closest synchronization to wild spawning, with all four gravid colonies releasing gametes in the same lunar month as wild predicted dates. Spawning within the GBR mesocosm commenced at the predicted wild spawn date but extended over a period of 3 months. Gamete release in relation to the time postsunset for A. hyacinthus, A. millepora, and A. tenuis was consistent with time windows previously described in the wild. Spawn date in relation to full moon, however, was delayed in all species, possibly as a result of external light pollution. The system described here could broaden the number of institutions on a global scale, that can access material for broadcast coral spawning research, providing opportunities for institutions distant from coral reefs to produce large numbers of coral larvae and juveniles for research purposes and reef restoration efforts.

Coral Larvae Every Day: Leptastrea purpurea, a Brooding Species That Could Accelerate Coral Research

“…A controlled induction of spawning in an artificial ex situ culture requires extensive experience and advanced logistics. As mentioned previously, the Horniman Museum London is the only institution worldwide that has repeatedly been able to induce spawning in Acropora species (Craggs et al, 2017). L. purpurea, however, could provide researchers with ready access to larvae without having to simulate lunar cycles and diurnal rhythms.…”

“…Mimicking the natural environment including solar fluctuations throughout the year, the lunar cycle as well as the annual temperature profile and food availability requires advanced technical efforts and extensive experience and can induce spawning in an artificial ex situ environment. This milestone was achieved in 2014 by Jamie Craggs from the London Horniman Museum and has since been replicated many times with several species of the genus Acropora (Craggs et al, 2017). When working with spawning species, there is only a very narrow time frame (1 to 2 events per year and location) in which it is possible to acquire gametes and subsequently larvae, recruits and juveniles.…”

Feeding increases the number of offspring but decreases parental investment of Red Sea coral Stylophora pistillata

“…Experimental studies of carry over effects, which manipulate the parental environment, are few in scleractinian corals (Bellworthy, Menoud, Krueger, Meibom, & Fine, ; Putnam & Gates, ; Putnam, Ritson‐Williams, Cruz, Davidson, & Gates, ). This is likely attributed to corals' relatively long time to sexual maturity, extended gametogenesis period, as well as typically a single annual reproductive cycle, and an inability to reliably induce spawning ex situ (but see Craggs et al, ). Carry over effects have been observed in a single study using brooding reef‐building coral, Pocillopora damicornis , after just 6 weeks of parental exposure to elevated temperature and ocean acidification (Putnam & Gates, ); planulae from exposed parents displayed metabolic acclimation to future ocean conditions, whereas planulae from control parents did not (Putnam & Gates, ).…”

The Life Cycle of the Acropora Coral-Eating Flatworm (AEFW), Prosthiostomum acroporae; The Influence of Temperature and Management Guidelines

“…Acropora spp. are common target species for reef restoration because of their fast growth-rates relative to other scleractinian corals and their contribution to structural complexity (Craggs et al, 2017;Pollock et al, 2017).…”