Abstract
Most studies of coral reproductive biology to date have focused on oocyte numbers and sizes. Only one (ex situ) study has enumerated sperm numbers, even though these data have multiple potential applications. We quantified total coral sperm and eggs per gamete bundle collected from six species in situ during a synchronous spawning event in Singapore. Egg-sperm bundles were captured midwater as they floated towards the surface after being released by the colony. For each sample, a semi-transparent soft plastic bottle was squeezed and released to create a small suction force that was used to ‘catch’ the bundles. This technique provided several advantages over traditional methods, including low cost, ease of use, no diving prior to the night of collection needed, and the ability to target specific areas of the colony. The six species sampled were Echinophyllia aspera, Favites abdita, F. chinensis, Merulina ampliata, M. scabricula and Platygyra pini. The mean number of sperm packaged within one egg-sperm bundle ranged from 2.04 × 106 to 1.93 × 107. The mean number of eggs per egg-sperm bundle ranged from 26.67 (SE ± 3.27) to 85.33 (SE ± 17.79). These data are critical for fertilisation success models, but the collection technique described could also be applied to studies requiring in situ spawning data at the polyp level.
Highlights
86% of scleractinian coral species with documented reproductive traits have been identified as broadcast spawners (Baird, Guest & Willis, 2009)
The majority of broadcast spawning corals release simultaneously both eggs and sperm packaged together in buoyant egg-sperm bundles during a spawning event (Babcock & Heyward, 1986). These egg-sperm bundles aggregate on the surface, concentrating the gametes to ensure that fertilisation can occur in a small space relative to the entire threedimensional seascape (Molacek, Denny & Bush, 2012)
The mean number of sperm packaged within one egg-sperm bundle ranged from 2.04 Â to 1.93 Â
Summary
86% of scleractinian coral species with documented reproductive traits have been identified as broadcast spawners (Baird, Guest & Willis, 2009) This mode of reproduction is prevalent in many aquatic taxa across multiple phyla (Levitan, 1998) and involves the shedding of gametes into the water column where external fertilisation and embryogenesis can occur (Szmant, 1986; Giese & Kanatani, 1987; Wray, 1995). The majority of broadcast spawning corals release simultaneously both eggs and sperm packaged together in buoyant egg-sperm bundles during a spawning event (Babcock & Heyward, 1986) These egg-sperm bundles aggregate on the surface, concentrating the gametes to ensure that fertilisation can occur in a small space relative to the entire threedimensional seascape (Molaˇcek, Denny & Bush, 2012).
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