Palmyra Atoll is one of few places in the world that has never been intensively fished. Its marine ecosystems support staggering fish biodiversity. But what do fish do for us? Beyond the aesthetic, how does Palmyra benefit from its pristine fish assemblages? And, by the same token, what benefits are lost on other tropical atolls when fishing spirals out of control?
I run the Palmyra Fish Exclusion Experiment in collaboration with my advisor, Professor Fiorenza Micheli. We designed our experiment with three objectives in mind:
- To assess the ecological benefits and ecosystem services provided by a pristine fish community
- To pinpoint reasons for ecological differences between Palmyra and neighboring islands that permit fishing
- To give us a vision of what Palmyra would look like if it were ever fished
We built our experimental installations on a sheltered sand flat known as “the Nursery”, where we created several “blocks” of three 5-m x 5-m experimental areas. Each experimental area was randomly assigned to one of three treatments (fish exclosure, control, and sham exclosure). In the fish exclosure treatment, we simulate size-selective fishing with a cage that excludes large fishes, such as sharks, jacks, and bonefish. In the control treatment, there is no cage, and the natural fish assemblage is free to pass through the experimental area. The third treatment, called a “sham exclosure”, consists of half an exclosure – which allows us to determine whether differences between the control and fish exclosure are due to the influence of fish or the influence of the cage (for example, shading or reduction of water flow). By measuring the abundance and diversity of bottom-dwelling organisms like crabs, snails, and macroalgae in all three treatments, we are able to assess differences in benthic lagoon flat communities in the presence and absence of large fish. With these data, we can estimate the impacts of fishing on the ecosystem services provided by lagoon flat habitats.
Even at this early stage, the experiment has demonstrated that control of macroalgae may be among the most important services provided by a pristine fish community. In a pilot study, macroalgae remained at constant levels in control and sham exclosure areas, but proliferated in fish exclosures. This is consistent with observations on nearby Kiritimati Island, where macroalgal blooms are common and fishing pressure is intense. As the experiment continues, we will be working to uncover other ecosystem services that accrue to Palmyra as a result of its pristine fish community.
Lagoon sand flats are subject to intensive subsistence fishing pressure throughout the equatorial Pacific, and provide a tremendous amount of protein to the fishermen living on islands near Palmyra, including islands of the Republic of Kiribati - Kiritimati and Tabuaeran. Our intention is to connect the ecological data we collect on Palmyra to quantifiable ecosystem services: what benefit does Palmyra receive from its intact fish assemblage? What benefits do Kiritimati Islanders miss out on due to the intensive fishing of their lagoon flats? In addition to control of macroalgae (which may affect the profitability of recreational bonefishing, the main source of tourism revenue on Kiritimati), we expect that there are other important services arising from an intact fish assemblage, including high filtration and decomposition capacity. This study will be the first experimental assessment of the net ecological impacts of fishing on a tropical lagoon sand flat, and as such will contribute valuably to our understanding of how fishing affects these ecosystems and the services they provide.