Coral Reef Resilience Strategies for Oʻahu, Hawaiʻi

Coral reefs are considered one of the most diverse and valuable ecosystems on Earth, generating an estimated  $2.7 trillion  a year. In addition to providing humanity with seafood, of which 25% of all marine life depend directly on corals, reefs are also responsible for life saving medical treatments, tourism revenue, and coastal property protection.

Unfortunately, coral reefs are in crisis -meaning human life systems are as well. Rising temperatures and related ocean acidification impose stress on corals, resulting in their "bleaching." Currently,  70% of the world's corals are bleached , distressed, and therefore vulnerable to  dying . Along with rising temperatures, stormwater runoff also exacerbates algal blooms, which smother coral.

With the current intensity of carbon dioxide emissions, a 2˚C global average temperature increase will occur in about  twenty five  years, effectively killing all coral reefs. A 1.5˚C increase will occur in about 7 years where the future existence of corals are uncertain. (Schellnhuber, et. al., 2016).

In the United States, about 85% of coral reefs lie within the Hawaiian Archipelago. In 2019 dollars, the economic valuation of the entire reef area was estimated at  $14.8 billion . Immediately quantifiable benefits to the main Hawaiian islands were estimated to be $534 million per year in 2019 dollars, without counting the reef’s role in climate resilience. About 85% of its value came from recreation. Apart from coral reefs’ intrinsic value, there is a strong immediate economic case to be made for the state of Hawaiʻi specifically, which relies on tourism revenue, to be proactive in not allowing the vast majority of U.S. corals to die. Hawaiʻi's coral suffered  mass bleaching in 2018 .

Since the early 2000s the Hawaiʻi Department of Land & Natural Resources (DLNR) have partnered with local communities through the  Makai Watch  program. The program aims for “citizens and NGOs (to) become directly involved with DLNR in the management of marine resources through promoting compliance to its rules, education, and monitoring.” There are two volunteer Makai Watch communities on four of the eight main Hawaiian Islands, though all groups’ relative engagement levels are currently unknown. An active group, Mālama Maunalua, on Oʻahu island, engages in coral reef resilience projects.

Specifically, Mālama Maunalua's Huki Project focuses on removing invasive non-native marine algal blooms that smother coral and kill healthy algae that binds corals to form reefs. Removal is done by hand or by the introduction and monitoring of sea urchins that eat invasive algae. Mālama Maunalua has since removed 3.5 million pounds of algae that is repurposed as fertilizer at local farms. Other projects include green infrastructure implementation on land, seagrass restoration, and habitat monitoring.

The State of Hawaiʻi should encourage and fund other communities to join reef restoration initiatives like that done by Mālama Maunalua. With limited resources, the question remains: where are coral near Oʻahu's shores, and how vulnerable are they to the negative effects of stormwater runoff?

Using ArcMap (Geographic Information System) technology, high risk areas for stormwater runoff can be identified.

Basic Methodology: This analysis is based off of strategies developed by Farrant, et. al. (2018) for Mālama Maunalua. The stormwater runoff vulnerability maps below are composed of four layers: Stormwater Structure, Water permeability, Land Use Land Cover, and Oahu Elevation Contours. Each layer was projected to the same coordinate system (NAD 1983 UTM Zone 4) and adjusted to have identical cell sizes. They were then all converted from vector shapefiles to rasters. Each component of the layer was re-classified from 1-5 with 1 showing low risk to stormwater runoff and 5 showing high risk. The four layers were then compiled into one layer using the raster calculator three times, to produce three differently weighted models.

Although in an ideal world, every shoreline community should have all resources necessary to be a steward of their reefs, this project helps to focus limited resources for an additional Makai Watch project in Kāneʻohe Bay.

Although all models indicate stormwater runoff risk in southern Kāneʻohe Bay, Model 3, which emphasizes storm drains, helps elucidate that risk. Drain density is important because they are direct sources of runoff. Compared with coral cover, the potential importance of establishing stormwater mitigation projects similar to those established by the Maunalua Bay Makai Watch program in Kāneʻohe Bay is highlighted. Since there is no indication of significant coral cover to high stormwater risks on the south shore, also where Mālama Maunalua is located, additional coral resilience programming is not emphasized in this project, but still important.

In May 2019, a unique group of " super corals " or corals resilient to stressful conditions were found in Kāneʻohe Bay. Scientists believe that these local corals hold the key to saving the world's coral reefs: ever the more reason for the state of Hawaiʻi and the citizens of Kāneohe Bay to come together and protect their bay's corals.