Research Projects 2018-2020

Investigating the origin and impact of sedimentation on the health of Hawaiian mesophotic reefs for sustainable coastal development

PRINCIPAL INVESTIGATOR: Robert Toonen
Graduate Trainee: Evan Barca

A robotic arm holds a label saying HURL7 in front of a dark blue coral reef area
Deep coral reefs in the mesophotic zone are hard to study, necessitating the use of robotic collectors, like HURL, the Hawai’i Undersea Research Laboratory.

Hawaiian coral reefs have been valued at over $33.5 billion per year to the US public, and are a major driver of tourism revenue in the State. Yet, coral reefs are under increasing global threat and need effective, proactive management to maintain the desired ecosystem services. Coral reefs extend from the surface to the mesophotic or “middle light” zone, which extends from 30-180 m (~100 – 600 feet) below the surface of the ocean, and its depth range makes it very difficult to survey with divers or submersibles. This zone is inhabited by a vast array of unique organisms that are specially adapted to thrive in low-light conditions. Because this zone is so light-limited (less than 1% of surface light penetrates to those depths), increased runoff from roads, coastal construction, or agricultural fields may severely impact the light-dependent corals and plants living there by starving them of any light or by physically smothering and killing them.

The first goal of this project is to collect new data to update models and develop predictive maps of corals and algae across the mesophotic zone of Oʻahu and West Maui to understand where these organisms are found. The second goal of our research is to collect sediment samples from each of the upper, mid, and lower mesophotic zones to determine the quantity, type, and origin of sediments coming into these habitats (e.g., land-based runoff or flushing of coral sand from nearshore). We will synthesize our findings in a series of maps which will highlight areas of concern around Oʻahu and Maui where sediments are impacting these habitat-forming species, and our predictive models will allow managers and policy makers to examine the likely outcome of different strategies on the distribution and abundance of these species.