Sexual Reproduction of Scleractinian Corals in Public Aquariums

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Chapter 2 Sexual Coral Reproduction in Public Aquariums

CHAPTER

2

Sexual Reproduction of Scleractinian Corals in Public Aquariums

Current Status and Future Perspectives

INTRODUCTION

This chapter gives an overview on scleractinian species that have reproduced in public aquariums. It illustrates their reproductive biology and explores tendencies regarding modes of coral reproduction. In addition, methods are suggested that can be easily utilized to optimize ex situ reproduction and potentially broaden the spectrum of species reproduced ex-situ. I further aim at assessing the current status of today’s public aquariums with regard to captive coral reproduction to estimate the potential for achieving self-sustaining ex-situ populations in future. By listing species and institutions, this chapter contributes to the exchange of knowledge and the co-operation within the aquarium community and with other conservation related institutions.

METHODS

Since little literature is available on captive coral reproduction in public aquariums, I designed a questionnaire, which was distributed by the EUAC Coral ASP (Coral Animal Sustainability Program of the European Union of Aquarium Curators) in March and April 2004 via the EUAC Coral ASP list server (49 aquarium professionals who specialize in corals, mainly from Europe) and via the AquaticInfo list server (682 institutional members, mainly aquarium professionals worldwide). The questionnaire was also sent to some institutions that are not members of these lists, but are known for their success in captive coral breeding. This allowed the questionnaire to be distributed to as many public aquariums as possible in order to obtain a maximum number of observations. The questionnaires was developed efficiently such that aquarium professionals required little time to answer the questions, but were able to provide the maximum amount of information possible. The following subjects were covered by multiple-choice questions:

1.  Parental population: origin, population size, timing of first reproduction observed

2.  Reproductive event: description, possible influence by the factors moonlight and temperature

3.  Juveniles: population size

4.  Aquarium system: size, life support system, environmental conditions

All observations were compared with field data based on available literature. In this chapter, sexual coral reproduction is defined as the process that involves either the release of gametes or planulae, or the appearance of juveniles, excluding an origin from asexual reproduction such as polyp bail-out (Sammarco, 1982) or from propagules produced in the field and introduced in the aquarium. The term ‘spawning’ is exclusively used for gamete release in broadcast spawning species. The release of sperm in brooders is difficult to observe and has only been reported from field observations, therefore this process was not considered in the questionnaire.

RESULTS

In total, 29 institutions completed and returned the questionnaire, of which 16 had observed reproduction in scleractinians. Table 1 gives an overview of all observations. Twenty-four species from 9 families, including one temperate coral (Astroides calycularis), were recorded as having reproduced in public aquariums. Among these, 16 species successfully established an F1 generation of a few to more than 100 individuals in at least one of the listed institutions. With regard to reproductive biology, all aquarium observations confirmed former field studies (see Table 2), with the exception of most brooders, which reproduced in captivity independent of the presence of moonlight. Parental colonies were mainly derived from the field or were captive propagated specimens (Fig. 1). The latter were mainly asexually propagated via fragmentation, however, in the case of Favia fragum at Rotterdam Zoo, recruits (F2 generation) were obtained from larvae released by captive bred specimens.

The release of gametes by broadcast spawning species was observed in all cases except for Galaxea fascicularis and Echinopora lamellosa in a 750,000 L exhibit at Burgers’ Zoo, whereas the release of planulae was noticed in one third of all observations (see Fig. 2). In 41.6 % of all observations, spawning occurred regularly. In the remaining cases spawning was observed only once or more than once with a relative frequency of 25% each. Whenever larvae release was observed in brooders, it occurred regularly. Natural moonlight, in some cases with additional artificial moonlight, was present in all spawning observations. However, in the case of larvae release in brooders, the great majority of the systems were not exposed to moonlight at all (Fig. 3). Seasonal temperature fluctuations occurred in all systems where reproduction of broadcast spawners was observed, except for Galaxea fascicularis and Echinopora lamellosa at Burgers’ Zoo (see Table 1), whereas brooders reproduced in systems with and without fluctuating temperature (Fig. 3). In broadcast spawners, almost 60% of all spawning events did not result in recruitment of juveniles (Fig. 4). Recruitment was only achieved by manipulating larval development and the settlement process, except for G. fascicularis and E. lamellosa at Burgers’ Zoo, where less than 10 juveniles of each recruited in a 750,000 l system. In contrast to broadcast spawners all the reproductive activity observed in brooders resulted in recruitment of juveniles. However, the number of recruits was in around two-third of the cases less than 100 if settlement was not manipulated (Table 1 and Fig. 4).

Reproduction of broadcast spawners was exclusively observed in open systems, with two exceptions (G. fascicularis and E. lamellosa at Burgers’ Zoo). The observed reproduction in brooders was almost equal in open and closed systems (Fig. 5). Systems in which broadcast spawners reproduced were mainly maintained under natural light, whereas those, in which brooders reproduced, were mostly equipped with artificial light. Except for skimming (in all closed systems), filtration was generally kept low (Fig. 5). Reproduction occurred in both brooding and broadcast spawning species in systems of all sizes. The smallest tank (all open systems) in which reproduction occurred was recorded at Waikiki Aquarium (56 L; Tubastrea coccinea), followed by 300 L systems at Kushimoto Marine Park (Caulastrea tumida) and at Musée océanographique de Monaco (Astroides calycularis) (Fig. 6).

DISCUSSION

Factors Determining Captive Reproduction

At least 24 species of scleractinian corals have reproduced in public aquariums resulting in highly varied recruitment rates from none to more than 100 recruits. Apart from specific circumstances (e.g. low number of mature specimens; only gametes of one sex released at a time), several factors may determine the reproductive success in captivity: (1) environmental factors like moonlight and temperature, (2) tank size and life support system (LSS), (3) manipulation of reproduction and general experience of aquarium staff, and (4) other factors.

(1) The presence of natural moonlight has been shown in various field observations to trigger the precise spawning date (Babcock et al., 1994; Babcock et al., 1986; Harrison and Wallace, 1990). It can, therefore, be assumed to be essential for reproduction in the broadcast spawning species described in this study. Seasonal temperature fluctuations, which are supposed to determine the month of spawning in field populations (Richmond and Hunter, 1990), seem to be another factor that may stimulate reproduction within a species. Nevertheless all aquarium systems, which recorded reproductive behaviour in broadcast species, except the tank at Burgers’ Zoo, were at the same time open systems, therefore other stimuli, such as hormones released during spawning events (Atkinson and Atkinson, 1992)

Institution / Okinawa Churaumi Aquarium, Japan / Okinawa Churaumi Aquarium, Japan / Okinawa Churaumi Aquarium, Japan / Birch Aquarium at Scribbs, USA / Waikiki Aquarium, Hawaii / Waikiki Aquarium, Hawaii / Rotterdam Zoo, The Netherlands / Rotterdam Zoo, The Netherlands / Waikiki Aquarium, Hawaii / National Museum of Marine Biology and Aquarium, Taiwan / Musée océanographique de Monaco, Monaco / Waikiki Aquarium, Hawaii / London Zoo, U.K. / Birch Aquarium at Scribbs, USA / Kushimoto Marine Park, Japan / Burgers’ Zoo, Netherlands / Columbus Zoo and Aquarium, USA / Rotterdam Zoo, The Netherlands / Rotterdam Zoo, The Netherlands / Waikiki Aquarium, Hawaii / Cologne Zoo, Germany / London Zoo, U.K. / National Museum of Marine Biology and Aquarium, Taiwan / New England Aquarium, USA / Oceanopolis, France / Tokyo Sea Life Park, Japan /
Manipulationc / fertilization, settlement / fertilization, settlement / fertilization, settlement / - / - / - / - / settlement / - / settlement / - / - / - / - / fertilization, settlement / - / - / settlement / - / - / - / - / settlement / - / - / - /
Generation / - / - / - / - / - / - / - / - / - / - / - / - / - / - / - / - / - / >100 / >100 (+)g / - / - / - / 0h / - / - / - /
>100 / >100 / >100 / - / - / - / <10 / >100 / - / 10-100 / >100 / 10-100 / <10 / - / <10 / <10 / <10 / >100 / >100 / - / <10 / <10e / >100 / 10-100 / >100e / 10-100 /
Gamete/Larval Release / regularly / regularly / regularly / >1 time / 1 timed / regularly / >1 time / regularly / >1 time / regularly / not observed / not observed / not observed / not observed / not observed / not observed / not observed / regularly / regularly / regularly / not observed / not observed / regularly / not observed / not observed / not observed /
Moonb / N / N / N / N/A / N / N / - / A/- / N / - / - / - / - / N/A / N / N / - / A/- / - / N / - / - / - / - / N/A / A/- /
Temp. / ↑↓ / ↑↓ / ↑↓ / ↑↓ / ↑↓ / ↑↓ / → / ↑↓ / ↑↓ / ↑↓ / → / ↑↓ / → / ↑↓ / ↑↓ / → / ↑↓ / ↑↓ / → / ↑↓ / ↑↓ / → / ↑↓ / → / → / → /
Modea / S / S / S / S / S / S / B / B / S / B / B?f / B / B? / S? / S? / S? / B? / B / B / S / B? / B? / B / B? / B? / B? /
Species / Acropora formosa / A. microphthalma / Acropora nobilis / Acropora valida / Acropora yongei / Montipora capitata / Agaricia humilis / Euphyllia ancora / Euphyllia glabrescens / Astroides calycularis / Tubastrea coccinea / Tubastrea sp. / Turbinaria reniformis / Caulastrea tumida / Echinopora lamellosa / Favia fragum / Sandalolitha robusta / Pocillopora damicornis /
Family / Acroporidae / Agariciidae / Caryophylliidae / Dendrophyllidae / Faviidae / Fungiidae / Pocilloporidae /
Vancouver Aquarium Marine Science Centre, USA / Waikiki Aquarium, Hawaii / Oceanario de Lisoboa, Portugal / National Museum of Marine Biology and Aquarium, Taiwan / Oceanopolis, France / National Museum of Marine Biology and Aquarium, Taiwan / Musée océanographique de Monaco, Monaco / Oceanopolis, France / Waikiki Aquarium, Hawaii / Burgers' Zoo, Netherlands / Skansen-Akvariet, Sweden
- / - / - / settlement / - / settlement / - / - / - / - / -
- / - / - / 0h / - / 0h / - / - / - / - / -
10-100 / 10-100 / - / >100 / <10e / >100 / <10 / <10e / - / <10 / <10e
not observed / not observed / not observed / regularly / not observed / regularly / not observed / not observed / 1 time / not observed / not observed
- / N / N / - / N / - / - / N / N / - / N
→ / ↑↓ / → / ↑↓ / → / ↑↓ / → / → / ↑↓ / → / →
B? / B? / B? / B / B? / B / B? / B? / S / S? / B?
Pocillopora sp. / Seriatopora hystrix / Stylophora pistillata / Goniopora gigas / Galaxea fascicularis / Galaxea sp.
Poritidae / Oculinidae


cannot be completely excluded. However, chemical stimuli can be neglected at least in the case of Waikiki Aquarium, where water is pumped up from deeper water depths to supply open systems (Delbeek, personal communication).

Photoperiod (= day length) suggested by Babcock et al. (1994) as a trigger for seasonal reproduction in high latitude coral reefs was not considered in the questionnaire. Brooding species show more plasticity in their reproductive behaviour. Although species like Pocillopora damicornis, Seriatopora hystrix, or Favia fragum show lunar cycles in the field, moonlight is not an ultimate trigger to induce reproduction in captivity. The aquarium observations listed in this study basically confirm the work of Jokiel et al. (1985), who showed the loss of synchronization, but a continual release of larvae in P. damicornis when night irradiance was kept constant. However, specimens of the F1 generation of F. fragum at Rotterdam Zoo showed lunar periodicity without the presence of moonlight (chapter 6). Seasonal temperature changes are generally not essential for reproduction in those brooding species, which reproduce all year round. Other species such as Seriatopora hystrix will continue to reproduce in aquariums, even when maintained at constant temperatures. Nevertheless, seasonal temperature variation may enhance sexual output of brooders in the field (Van Moorsel, 1983; Jokiel, 1985), therefore it might be beneficial to simulate seasonal temperature regimes in captivity to enhance reproduction. Regarding the enormous intra- and interspecific, regional and geographic variability in coral reproduction (see Fadlallah, 1983; Harrison and Wallace, 1990) the influence of temperature in the reproduction of brooders can currently be only underestimated, hence more investigation is necessary.