Coral Resilience Module Project (CReME)

Parrotfishes (uhu in Hawaiian) are amazingly beautiful and complex animals.  As large reef herbivores (seaweed eaters) they provide a variety of important services that stabilize and maintain coral reef communities.  Uhu have special jaws and fused teeth that form a parrot-like beak, which that allows them to scrape dead coral surfaces clean of seaweeds.  This grazing activity provides new space for corals to grow.  As such, parrotfish help to reduce seaweeds so that baby corals (larvae) can settle, grow, and thrive.

The Uhu Conservancy supports the research of Dr. Mark Hixon, his graduate students (including Uhu Conservancy co-founder Eric Dilley), and other colleagues at the University of Hawai‘i.  To determine whether and to what degree resident herbivorous fishes and invertebrates reduce seaweed cover and lead indirectly to increases in coral, Dr. Hixon and his team are conducting an undersea experiment off the south shore of O‘ahu.  The experiment utilizes artificial coral modules (Fig. 1) to examine what type of herbivorous fishes and sea urchins will arise on high and low shelter settings.  High-shelter modules have many holes that provide ample living space for fishes and other herbivores while low-shelter reefs have no holes.  The team hypothesizes that modules with higher relative shelter will produce communities with greater live coral because they will support more herbivores which will remove seaweeds.  They predict that low-shelter modules will have low densities of resident herbivores, and thus more seaweed and less coral (Fig. 2).

​Modules are located at two sites such that 3 high and 3 low shelter reefs will be present at the Hanauma Bay Marine Life Conservation District (unfished treatement) and in the Halekulani Sand Channel off of Waikiki (fished treatement).  Reefs at these two locations test the above hypotheses under different fishing intensities.  This project will serve as a model for use of artificial coral heads in the State of Hawai‘I, and may eventually become a component of the state’s overall strategy to sustainably manage uhu and other coral-reef herbivores.

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Figure 1: Artificial coral module from a field study conducted by Dr. Hixon and colleagues in the Bahamas.

Figure 2: Visual representation of predictions for open and closed hole artificial coral modules. More holes are predicted to provide more shelter for reef herbivores, allowing them to reduce seaweed densities that in turn provides corals with space to settle and grow. In contrast, low shelter modules are predicted to have the opposite effect due to lower resident herbivores and higher densities of seaweeds.