Oahu’s marine secured regions don’t sufficiently ensure herbivorous reef fishes

Oahu’s marine secured regions don’t sufficiently ensure herbivorous reef fishes


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  • Source: University of Hawaii at Manoa

  • Date: 28 Feb,2021

Marine protected areas (MPAs) around Oahu do not adequately protect populations of herbivorous reef fishes that eat algae on coral reefs. This is the primary conclusion of a study published in Coral Reefs by researchers from the University of Hawaii at Mānoa School of Ocean and Earth Science and Technology (SOEST).

There are more than 20 species of herbivorous fishes and ten species of herbivorous urchins commonly observed on Hawaiian reefs. These species eat algae which grows on reefs, a procedure called herbivory, that contributes to the resilience of coral reefs by preventing algae dominance that may result in overgrowth of corals.

The group of researchers found that of the four marine protected areas around Oahu they assessed from the study, three failed to provide biologically significant benefits for herbivorous fish populations compared to reefs out the areas.

Marine protected areas are a fishery management tool to limit or prevent fishing to help the recovery and maintenance of fish abundance and biomass inside the MPA. An effective MPA should lead to a considerably higher abundance and biomass of fishes inside the MPA boundaries that would otherwise be caught by fishers but that wasn’t what our study found.”

Erik Franklin, Study Senior Author and Associate Research Professor, School of Ocean and Earth Science and Technology, Hawaii Institute of Marine Biology

Other factors influencing the biomass of herbivorous fishes included habitat complexity and depth, implying that environmental features of coral reefs may have had a greater impact on herbivorous fish populations than MPA protection.

As part of the Sustainable Hawaii Initiative, the State of Hawaii’s Division of Aquatic Resources leads the Marine 30×30 Initiative, which dedicated to effectively manage Hawaii’s nearshore waters with 30 percent established as marine management areas by 2030.

Currently, five percent of waters within state jurisdiction, which is within three nautical miles of shore, have some form of marine management, but no-take MPAs that prohibit fishing only constitute less than half of one percent of the nearshore waters. To achieve the stated goal of this 30×30 Initiative would require an expansion of marine managed areas to add an additional 25 percent of Hawaii state waters.

“Our results suggest that before an expansion of MPAs in Hawaiian waters, more effort should be led to effectively manage the existing MPAs to see if they meet the desired management objectives,” said lead author and UH Mānoa’s Marine Biology Graduate Program graduate student Noam Altman-Kurosaki.

“The addition of MPAs throughout the state that have similar performance to the Oahu MPAs would just result in a series of paper parks that don’t provide biologically significant conservation benefits while diminishing fishing opportunities.”

Franklin said the research resulted in a comparative analysis of herbivorous fish and urchin populations inside and outside of Oahu MPAs that demonstrated biologically insignificant differences in fish biomass between the MPAs and reference regions, except for one site, Hanauma Bay.

The analyses used statistical methods to assess the effects of protecting population within MPAs as well as the impact which differences in benthic habitats contributed to the outcomes.

Journal reference:

Altman-Kurosaki, N. T., et al. (2021) O‘ahu’s marine protected areas have limited success in protecting coral reef herbivores. Coral Reefsdoi.org/10.1007/s00338-021-02054-5.

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