Experimental measurements of the sinking speed of sperm of an acroporid coral, Acropora tenuis, in static seawater
The dispersion of Acropora coral sperm is critical for sexual reproduction via external fertilization. Sperm sinking likely plays an important role in the process of dispersion, but its rate of sinking is still unclear. To estimate the sinking speed of coral sperm without turbulence, two experiments were conducted in a water tank filled with 500 L of static seawater in the 0–60 cm layer. In Exp. 1, suspension of sperm was gently poured from a 2 L plastic beaker onto the surface of the seawater in the tank. In Exp. 2, sperm were released from egg–sperm bundles from coral colonies at the bottom of the tank. Sinking speeds ranged between 0 and 120 cm h−1. In the sperm sinking experiment (Exp. 1), 43% of sperm remained on the surface layer, while the remainder sank 30–180 min after being poured. Sperm that formed clusters might sink faster. Although the effect of turbulence on the sinking speed of sperm in nature has not yet been clarified, the mean residence time of sperm in the 0–10 cm layer (Exp 2; 0.5–0.7 h) implies that sinking speed inherited in sperm is linked to gamete interactions for fertilization.
KeywordsAcropora tenuis Sperm Sinking speed Tank experiment Vertical distribution Coral spawning
This work was supported by ordinary research fund from Tokai University for English proofreading by Editage.
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