Degradation and restoration of coral reefs: Experience in Okinawa, Japan

Abstract

Coral reefs in Okinawa, Japan, have declined due mostly to human pressures. There are still possiblities to restore coral reefs locally by amelioration or removal of the local chronic stressors. Political support, scientific information, and the will of local stakeholders are crucial for successful amelioration. Development of techniques for restoration by artificial efforts such as underwater silviculture and transplantation are definitely required. Coral propagules for transplantation may be cultured by either of two approaches: asexual or sexual propagation. The rehabilitation of coral reefs by means of asexual propagation is simple and less labour-intensive compared to sexual techniques. However, most of the transplanted pieces share the donors' limited DNA, giving the reef a smaller gene pool. On the other hand, sexual propagation may result in genetically more diverse corals, but is labour-intensive and more expensive. Both techniques require devices for rearing after transplantation. This will become one of the key areas of research in the near future. Some 4-year-old colonies of Acropora tenuis, cultured from eggs and transplanted to the seabed at Akajima, Okinawa, had grown to 20Á25 cm in diameter and initially spawned in June 2009. This indicated the possibility of using this technique to assist local coral reef restoration. Although the small scale of success so far may not be significant, given the wide range of degradation of coral reefs, certain methods of rehabilitation have proved promising enough to continue our endeavour.

Suppressing antagonistic bioengineering feedbacks doubles restoration success

“…Although these ecosystems were initially considered highly resilient to human disturbance, we now know that most coastal ecosystems do not respond linearly to change, but may often collapse without warning (Silliman et al 2005, van der Heide et al 2007, Hughes et al 2010. It has also emerged that recovery or restoration of coastal ecosystems is extremely difficult (Bakker et al 2002, Orth et al 2006, Halpern et al 2007, Omori 2010.…”

Closing the circle: is it feasible to rehabilitate reefs with sexually propagated corals?

“…A logical extension of this is to have substrates designed specifically for transplantation of sexually propagated corals to the reef (Petersen and Tollrian 2001). Indeed, several such designs have been tested recently (Okamoto et al 2008;Omori and Iwao 2009;Omori 2011;Boch and Morse 2012;Villanueva et al 2012) and in each case, these substrates consist of an area for coral larvae to settle and a device specifically for attachment in a nursery or to the reef.…”

Interspecific Hybridization May Provide Novel Opportunities for Coral Reef Restoration

“…If hybrids are comparatively resilient, interspecific hybridization may be combined with methods being developed for deploying coral larvae or recruits onto reefs requiring restoration (e.g., Nakamura et al, 2011;Omori, 2011;Villanueva et al, 2012;Guest et al, 2014;dela Cruz and Harrison, 2017). Overall, maternal effects were observed in hybrids of the A. tenuis × A. loripes cross and overdominance in hybrids of the A. sarmentosa × A. florida cross, with some variations between traits and treatment conditions.…”

“…Reef restoration is still in its infancy and all of the few successful efforts so far occurred on a small spatial scale (e.g., Nakamura et al, 2011;Omori, 2011;Villanueva et al, 2012;Guest et al, 2014;dela Cruz and Harrison, 2017). Traditionally, locally sourced biological material is used for restoration based on the assumption that these populations are locally adapted and therefore most likely to survive (Breed et al, 2013).…”