Direct seeding of mass-cultured coral larvae is not an effective option for reef rehabilitation

Published source details Edwards A., Guest J.R., Heyward A., Villanueva R., Baria M., Bollozos I. & Golbuu Y. (2015) Direct seeding of mass-cultured coral larvae is not an effective option for reef rehabilitation. Marine Ecology Progress Series, 525, 105-116.
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This study is summarised as evidence for the following.

	Action	Category
	Introduce larvae directly onto natural or artificial reefs to encourage settlement Action Link
	Use settlement tiles made from unnatural materials to encourage natural coral settlement Action Link

Introduce larvae directly onto natural or artificial reefs to encourage settlement

A replicated, study in 2007–2008 at Iou Lukes reef, Palau (Edwards et al. 2015), found that using nursery-cultivated stony coral Acropora digitata larvae to directly ‘seed’ artificial reef structures initially led to a higher density of Acropora spp. coral spat (settled larvae) on the structures compared to natural settlement, but there was no difference in density of coral spat over time. Average coral spat density after five weeks was significantly higher on settlement tiles seeded with larvae (205/0.1m²) than unseeded tiles (52). However, after 30 weeks, stony coral density on seeded tiles had declined significantly (60/0.1m²), and there was no longer a statistically significant difference compared to unseeded tiles (33/0.1m²). In January 2007, fourteen concrete/limestone ‘pallet-balls’ (1.2 × 0.9 m) were placed 3–5 m apart, 5–8 m deep on the seafloor adjacent to a natural reef. Fibre cement settlement tiles (10 × 10 × 0.6 cm) were attached to each ball in mid-January 2008 (4 tiles/ball). In April 2008, a tent with an inner 250 × 250 µm mesh was placed over each of seven randomly selected pallet balls, and 40,000–260,000 nursery-cultured stony coral larvae were poured onto each pallet-ball (density 54.6–459.8/0.1m²). Tents remained for 24 hours. Coral density was recorded on tiles retrieved five and 30 weeks after wild-growing coral colonies had spawned.

(Summarised by: Ann Thornton)
Use settlement tiles made from unnatural materials to encourage natural coral settlement

A replicated, paired study in 2008 at Iou Lukes reef, Palau (Edwards et al. 2015), found that settlement tiles allowed to ‘biologically condition’ for three months had a higher density of artificially enhanced or naturally settled stony coral spat (settled larvae) compared to tiles conditioned for one week, and density was higher on tiles with artificially enhanced coral larvae supply. One week or five weeks after nearby wild-growing stony coral spawned or larvae were artificially introduced to the tiles, density of coral spat was higher on tiles conditioned for three months (natural: 50; artificial: 205/0.1m²) compared to tiles conditioned for one week (natural: 4; artificial 29/0.1m²). Density was significantly higher on one-week conditioned and three-month conditioned tiles where larvae supply had been enhanced compared to the natural tiles. In January 2008 and April 2008, four fibre-cement settlement tiles (10 × 10 × 0.6 cm) were attached to each of 28 concrete/limestone ‘pallet-balls’ (1.2 × 0.9 m) placed 3–5 m apart, 5–8 m deep on the seafloor adjacent to a natural reef. Tiles were allowed to ‘condition’ (develop biofilm) for three months (January 2008) or one week (April 2008) before coral spawning. In April 2008, seven randomly selected pallet-balls were ‘seeded’ with nursery-cultivated stony coral Acropora digitata larvae (see paper for methods), and corals on the natural reef spawned. Tiles were retrieved either one or five weeks after wild-growing coral colonies had spawned and the number of coral spat was counted.

(Summarised by: Ann Thornton)