'Opihi age, growth, and longevity influenced by Hawaiian intertidal environment

There are three species of 'opihi commonly observed on Hawaiian rocky shorelines. These species occupy different vertical zones of intertidal habitats and eat crustose coralline algae and microorganisms from rocks. For the study, growth increments were identified from a cross-section of opihi shells with corresponding oxygen isotope measurements used to examine environmental differences.

Erik Franklin, Associate Research Professor at SOEST's Hawaii Institute of Marine Biology, said the study represents a breakthrough for studying the population dynamics of 'opihi in Hawaii that can be used to better develop sustainable fishing approaches for the species.

"'Opihi are a culturally valuable marine resource in Hawaii," Franklin said. "Developing effective strategies to sustainably harvest these populations depends on accurate information about their life history traits such as age, growth, and longevity. Our understanding of 'opihi biology just took a big step forward with the results of this study."

Importance for Hawaii

Historically, 'opihi were highly prized and served as a traditional delicacy within the Native Hawaiian subsistence diet. Today, the fishery operates with fishers collecting 'opihi from rocky intertidal habitats around the main Hawaiian Islands and selling directly to local commercial vendors, but non-commercial fishers also collect for subsistence purposes and important cultural events. Over the past century, harvest amounts of 'opihi have declined dramatically suggesting an opportunity to rebuild this fishery through further research and community-based management actions.

"Our results suggest that 'opihi linalina are fast growers, reaching a size that corresponds to maturity within 8-9 months of settlement and can live to 5 years old," said lead author and UH Manoa's Molecular Biosciences and Bioengineering Department doctoral student Anthony Mau. "That is critical information to better inform fishing practices for 'opihi. We were only able to collect such high-resolution temporal data for aging the 'opihi through a collaboration with the SOEST's Hawaii Institute of Geophysics and Planetology that provided access to cutting edge technology. We're excited about these results which are just one aspect of an ongoing collaboration to learn more about the biology and ecology of 'opihi and identify community-driven options for sustainable harvests."

Study details

The study reconstructed the life-history of the yellowfoot 'opihi limpet Cellana sandwicensis from three shells, two modern and one historical, by investigating oxygen isotope variation in the tropical intertidal environment using near-daily spatial scale secondary-ion mass spectrometry (SIMS) analysis. Further, the team determined seasonal growth and longevity from major, minor, and micro shell growth increments, which reflect the influence of temperature, wave exposure and daily lunar cycles, respectively.

Mau said the research resulted in the first study on a tropical limpet species using the SIMS methodology which demonstrated the utility of the approach for other tropical intertidal molluscan species. The analyses used statistical methods to assess the relationship between oxygen isotopes in the shells and seawater temperatures. The growth, age, and longevity were determined from fitting a growth model to the back-calculated dates from the SIMS analysis and the observed shell increments.