The Research Problem

Managers are often faced with needing to make tough but informed decisions about what threats and areas to prioritize to best protect the world’s fragile reefs. With so many different types of human activities now impacting the oceans, it is hard to figure out which are having the most impact where. It is also hard to compare very diverse types of threats, such as pollution and sea level rise – the first smothers reefs and can cause some fish and mammal deaths, and the latter causes loss of shallowest habitat. Which is worse? It depends where you are on the reef and how extensive each is. Our project systematically evaluates the ecological impact of all human impacts to all habitat types in the Northwestern Hawaiian Islands to help answer some of these questions.

Methods

Because scientific studies are not geared toward these sorts of comparisons, we used a novel index of “ecological vulnerability” that accounts for five ways a human activity can adversely impact a coral reef: the area and frequency of impact, the number of species impacted, the biomass lost and the recovery time following the impact.  By surveying 25 experts on marine ecology to get estimates for the index, we found consistent answers that allowed us to rank the threats by their impact. We then gathered all existing data on the location and intensity of these threats and mapped them onto the Northwestern Hawaiian Islands.

We included spatial data over multiple years for alien species occurrences, bottom fishing, lobster trap fishing, ship-based pollution, ship strike risks, marine debris, research diving, research equipment installation, research wildlife sacrifice, and several anthropogenic climate change threats i.e., increase in ultraviolet (UV) radiation, seawater acidification, the number of warm ocean temperature anomalies relevant to disease outbreaks and coral bleaching, and sea level rise. We used another index to measure the cumulative impact of human activities for each pixel in the map.

Findings

The resulting cumulative impact map demonstrated that although the Northwestern Hawaiian Islands are some of the most protected reefs in the world they are sheltered still vulnerable to global threats. Temperature stress was found to be the most serious threat, followed closely by the other climate change effects, marine debris and risks of pollution and grounding from ship traffic.

Importance
The maps can help make informed decisions about granting permits for use based on how sensitive a habitat is, and to select where monitoring program should be implemented. The map can easily be updated every few years with the latest data to determine if cumulative impact is going down or up. Researchers at HIMB have also made use of specific threat data that were gathered for this project for basic science.

Partner Links

• Fragility Of World's Coral Is Revealed Through Study Of Northwestern Hawaiian Islands
• Human Impacts on Coral Reefs of Northwestern Hawaiian Islands Revealed