Oct 29, 2020

CTSA Project Summary: ‘Opihi Aquaculture Year 5 & 6: Improving Hatchery Technology and Production

‘Opihi (Cellana spp.) aquaculture has been of interest for many years beginning in the 1970’s when research and development began on technology for the ‘opihi makai’auli or blackfoot limpet (Cellana exarata) by Gladys Corpuz (1981). However, research was halted not long after when it was found that the technology established was not transferable to the more desirable species, ‘opihi ‘alinalina or yellowfoot limpet (Cellana sandwicensis) (Kay et al, 1982).  Around the early 2010’s, the idea of ‘opihi aquaculture was brought back to light to help support the increasing market demand, that has great impacts on the wild stocks.

To begin efforts towards closing the life cycle of ‘opihi, which has been the main goal since resurrecting the project, the first phase of the project consisted of engineering a broodstock recirculating system that would maintain the necessary intertidal stimulus (sea spray). Once this system was established, extensive research went into developing formulated feeds that would support good, long-term growth in our closed systems (Hua & Ako, 2014; Mau & Jha, 2018). This formulated feed allowed us to hold and mature wild broodstock in our lab until they were need for spawn trials. Moving forward, major improvements to spawning and larval rearing methodologies have only brought us closer to closing the life cycle of ‘opihi.

This next phase of the project (Years 5 & 6) kicked off with the development of a novel settlement system. To make this system as close to a natural intertidal environment as possible, raceways were constructed using entirely PVC piping. The system is equipped with adjustable water flow and underwater wave fans to help simulate the natural change in currents. Although still in the testing phase, this recirculating system will help to support an increase in production numbers coming out of our settlement experiments.

Maintaining excellent water quality was one of the most important lessons learned during this project. Since we are not equipped with a direct salt-water line here at UH Mānoa, we do not have the ideal flow-through system. Regular water changes on our broodstock systems are crucial in maintaining the health of our animals and when it comes to our larvae, we have taken extra measures to ensure they are healthy. To upgrade our water filtration, we built an additional system that would serve as our inhouse seawater reservoir. This system recirculates water through a 0.35-micron canister filter and a UV sterilizer that removes larges protists and bacteria, giving us clean water to raise our larvae.

Improving settlement was one of the main aspects of these project years. To increase survival beyond settlement key factors had to be identified that would help to formulate the ideal grow-out protocol. Plate orientation, microalgae type, and age of the biofilm were all factors that were tested of the course of various trials. To determine the proper plate orientation, microscope slides seeded with a diatom biofilm were positioned in horizontal (0°), vertical (90°) and slanted (45°) orientations. Overall, the horizontal orientation had the highest settlement and from our qualitative and quantitative observations, it was determined that ‘opihi are passive settlers. Having determined the proper plate orientation, we were able to begin testing the proper diatom for a biofilm. Different combinations of Navicula sp., Nitzchia sp., crustose coralline algae (CCA), and a natural intertidal culture from Makapu’u were tested. After several settlement trials it appeared that CCA and Navicula sp. had the highest settlement, however CCA also had very high mortality rates. It appears that although CCA is one of the main components of a natural intertidal environment, it did not support a healthy settlement surface. The last factor to test was the age of the biofilm and how it effects larval settlement and growth. To do this we introduced larvae to three different ages of Navicula sp. biofilm; a 1-week old biofilm, a three-day old biofilm, and a biofilm introduced the same day as larval stocking. From these trials, we found that the three-day old biofilm had the highest number of metamorphosed larvae compared to the other treatments. This led us to believe that having too dense of a biofilm may be harmful to the survival of the larvae, possibly overloading them with too many settlement cues. It was during these trials that we were able to have a few larvae make it through our bottleneck.

This bottleneck, being unable to go beyond 14 Days of survival, had prohibited us from reaching our goal. Changes had been made during these trials to the overall protocol including the implementation of daily water changes and the removal of larval mortalities to prevent the appearance of pests and an increase in bacterial build-up. These changes to our settlement protocol allowed use to bypass this roadblock by having a few larvae at the end of the 2019 season, enter the juvenile stages and begin the development of their adult shells. These few juvenile ‘opihi gave us the opportunity to monitor early shell growth rates which became a very important metric for understanding life-history and successfully recruitment. These early growth measurements also helped to support interpretations of juvenile daily growth rates of C. sandwicensis using their shell record made during an additional project (Mau et al, unpublished). Although the 2019-2020 season encountered an additional roadblock regarding the maturation of Oahu’s female ‘opihi population, we were still successful in rearing a few larvae onto the juvenile stages and show growth in their adult shells. Having successfully reached this stage again, shows great potential in reaching it in the upcoming seasons.

Each of these accomplishments have helped us to build a story behind the early life stages of ‘opihi, all while giving us valuable information that will aid us in bringing ‘opihi to production for market sale. By consistently producing ‘opihi, we will be able relieve harvesting pressures on wild populations with hopes of reducing the overall decline of their populations, keeping ‘opihi on our coastline for decades to come.

Written by: Angelica Valdez, University of Hawaii at Mānoa; Anthony Mau, Kualoa Ranch; Bridget Murphy, University of Hawaii at Mānoa; and Jon-Paul Bingham, University of Hawaii at Mānoa

Sources Cited:
Corpuz, G. C. (1981). Laboratory culture of Cellana exarata Reeve (Gastropoda: Prosobranchia, Patellidae). Aquaculture, 24, 219-231.
Kay, E. A., Corpuz, G. C., & Magruder, W. H. (1982). Opihi, Their Biology and Culture. Hawaii.
Hua, N. T., & Ako, H. (2014). Reproductive biology and effect of arachidonic acid level in broodstock diet on final maturation of the Hawaiian limpet Cellana sandwicensis. Journal of Aquaculture Research & Development, 5(5), 1.
Mau, A., & Jha, R. (2018). Effects of dietary protein to energy ratios on growth performance of yellowfoot limpet (Cellana sandwicensis Pease, 1861). Aquaculture Reports, 10, 17-22.

Video: Protocols for Spawning Opihi
In Final Production (anticipated completion early 2021)