Coral nurseries are helping to restore coral reefs in Saipan, Commonwealth of the Northern Mariana Islands

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Coral nurseries are helping to restore coral reefs in Saipan, Commonwealth of the Northern Mariana Islands

By: Steven McKagan, NOAA Fisheries Pacific Islands Regional Office, CNMI Coral Reef Fisheries Liaison

Takeaway

While Saipan, in the Commonwealth of the Northern Mariana Islands, seems remote, the coral reefs are threatened by bleaching and crown-of-thorn starfish outbreaks. To help corals recover from past events, corals are being grown in nurseries in Saipan lagoons and then outplanted on degraded reefs.

A scuba diver swims through clear water where white tree-like structures are anchored to the seafloor. — A scuba diver swims through a newly established coral nursery in Saipan in 2019. Credit: Johnston Applied Marine Sciences.

Background

Saipan experienced coral bleaching events in 2013, 2014, and 2017 that contributed to a loss of over 60% of total coral cover based on surveys of 34 shallow reef sites (5-6m) (Maynard et 2018). Additionally, Acanthaster planci, the crown-of-thorns starfish, feeds on stony corals. While these predators are a natural part of the ecosystem, when coral cover drastically declines over a short period of time, the starfish will concentrate on the few remaining colonies, leading to further coral reef decline. The 2018 Saipan Demonstrated Resilience Study confirmed that many of Saipan's reefs have lost more than 90% of their branching corals since 2014.

To help coral populations recover from bleaching and predation, NOAA funded a pilot project that established an ocean-based coral nursery on Saipan in summer 2019. Initially, the nursery consisted of 10 “tree” structures with a capacity to house 1,000 corals. These donor colonies were survivors of a severe bleaching and mortality event in 2017 and, therefore, had demonstrated resilience to heat stress.

In order to create a coral nursery, PVC “trees” are created and anchored to the bottom of shallow sandy areas. Coral fragments are attached to each arm of the tree with a monofilament line. Divers then collected a total of 40 parent colonies from five different species in 2019. Approximately 400 fragments were transferred to the nursery with an almost 100% survival rate. Growth measurements were taken during initial collection and throughout the growing season to track growth rates.

On left, a yellow ruler is held by a hand and is measuring branching reddish brown coral. On right, several tree-like structures with coral fragments hanging from strings attached to the structures. — Coral fragments at the nursery are measured during the initial collection and periodically thereafter until they are outplanted (left). Coral fragments grow on nursery trees until they are big enough to plant onto reefs (right). Credits: Johnston Applied Marine Sciences.

On the left, a bird's eye view of a coral reef with a yellow grid and a small red square overlaid on it. The red square connects to a smaller photo on the right of a branching tan coral with two white tags attached. — Photomosaic of the outplant site with a 5m x 2m grid digitally overlaid, indicating the locations of the subplots within the site. Inset is a representative photo of a paired set of outplanted fragments secured to the thicket framework with cable ties.

Current Outlook

Over the last nearly five years, the nursery has grown from 10 tree structures to 23 tree structures and four tables, housing thousands of coral colonies representing 11 species, with more plans to expand in the future. Corals in the nursery are tracked and measured to provide information on growth rates and general health in the nursery and eventually on the reef. Johnston Applied Marine Sciences, who NOAA has contracted to implement the nursery project, began outplanting the coral to priority degraded reefs in 2020. JAMS will be greatly upscaling outplanting over the coming years, now that the nursery is well established.

Funding for this work was provided by NOAA's Pacific Islands Regional Office Habitat Conservation Division, Coral Reef Conservation Program, and Restoration Center. For more information, please email Steven McKagan.