VOLCANOES IN THE SEA: THE BIRTH OF ISLANDS AND REEFS IN HAWAI'I

Brian N. Tissot
Kalakaua Marine Education Center
University of Hawai'i at Hilo

Keynote address at the Annual Marine Affairs Symposium, April 1996

Aloha! The focus of my talk is islands. My overall message is that islands are special places and living on islands is a unique experience which promotes wonderful insights into the natural world, especially the ocean. These insights begin when a link is established between people and the sea. Since most of you were born and raised on islands, you probably established this link early in life. For me, it was different. Because my father was a naval aviator we moved every two and a half years. Fortunately, we were mostly near the coast and my link with the ocean started with surfing. Surfing is a wonderful sport because it is an intense and personal interaction with the ocean. Years later when I went on to college, surfing was the link that connected me to marine biology and kept me involved through my undergraduate and graduate degrees. When I was started working at the University of Hawai'i at Hilo I began my first prolonged island experience. Here are my insights into islands.

Islands are metaphors for an oasis. In a cosmic sense galaxies, stars, and planets are islands of the energy and material for life. Mars, for example, is an island of the raw material for life. Mars shares special features with our planet: there are large shield volcanoes -- Olympus Mons is 75,000 feet high! -- and evidence of water in Mars' past, but to our best knowledge there is no life on Mars. When we look at Earth, however, we see a true island of life dominated by a key element: water. Earth is a water planet and an interacting complex between the atmosphere, hydrosphere, lithosphere, and biosphere. Islands on Earth's seas are unique in that they clearly display the dynamic interplay between these global systems.

The Hawaiian islands are a remarkable archipelago located in the middle of the Pacific. On the younger islands, such as Maui and Hawai'i we see the key building blocks of islands, shield volcanoes. Mauna Kea, for example, rises over 35,000 feet from the ocean floor and is the largest volcano on the planet. Next to Mauna Kea are the two most active volcanoes in the world, Mauna Loa and Kilauea, and they are remarkable examples of the cycle of islands. As magma erupts from below the surface it flows into the ocean and eventually builds a shallow coastline. This is the beginning of the process. Soon after coral polyps settle on the cooled rock and begin to form reefs. Reefs in turn begin an another process of building islands. As the islands lose their magma source and sink and erode, the reef they spawned continues to grow. As the island slowly disappears, first fringing then barrier reefs form around its shores. Finally, after millions of years, the island sinks below the ocean's surface but the reef remains as an atoll. This is the cycle of islands: from volcanoes to islands to reefs to islands; a remarkable interplay between the land, the sea, and life.

People that live on islands are a part of this cycle. However, we are integrated on a different time scale. On the island of Hawai'i, for example, frequent lava flows into the ocean provide a unique opportunity to study the reefs birth and growth. In a study I conducted with Michael Childers, we compared reefs on lava flows established at different times, a unique way to "look" at reef growth without waited many decades. We estimated coral cover and diversity on four reefs along the Puna coastline of 4, 21, 38, and 490 years of age. From these studies we learned several important lessons. First, reefs grow slowly: after 30 years coral barely covered 20 percent of the rocky shore at 10 m depths. Moreover, the diversity of corals slowly increased with age, and some species were not established until decades after the reef began. The lesson to be learned is that the reef's cycle is slow and deliberate. Reefs are faced with the pressures of growing under constant erosion by storms and animal grazers, and different species are involved with different phases of reef growth. It is in this part of the cycle of islands that humans are intimately involved.

These human-sea interactions can be illustrated in a study conducted at Pelekane Bay on the island of Hawai'i. Along with Brett Martin, Kent Backman, and Windy Gibson, I am looking at the effects of land use on coral reefs and their community. Pelekane Bay is a unique site: in addition to the historical Hale 'o Kapuni, a heiau for shark feeding, and Pu'ukohola, a heiau built by Kamehameha in his unification of the Big Island, Pelekane was an important breeding ground for numerous fishes, including black-tip reef sharks, and the site of a flourishing coral reef. For the last several hundred years the land mauka (upslope) of Pelekane has experienced dramatic alterations: tropical forests have been eliminated and replaced by cattle which, along with the increased incidence of fires, have reduced plant cover to less than 10% in coastal areas. As a result, during heavy rainfall events, large amounts of soil are washed into Pelekane Bay. Coupled with these changes, in the l960's Kawaihae harbor was built nearby and the resulting landfill blocked natural longshore currents, thereby reducing the natural mechanism for removing land-based sediments. Our study, which compared changes in the marine ecosystem between surveys conducted in 1976 and 1996, found dramatic changes in coral reef communities. Specifically, the cover of coral was reduced by over 80%. Moreover, of the 10 coral species seen in 1976, only 4 remained in 1996. Perhaps in response to these changes, reef fishes were reduced in abundance by 50%, and the species composition has undergone dramatic changes.

The general message of this study is that humans rarely have a positive impact on the sea; most interactions are neutral at best. Monitoring and preventing potential human impacts on the ocean is a challenge we must all address. Our planet currently has 5.6 billion people and is increasing at a rate of 93 million people a year. During the time it takes you to read this paper (10 minutes) the world will have added 2000 new people. The multiple changes wrought by humans are global and are altering the interactions between our atmosphere, hydrosphere, lithosphere, and biosphere. There is no place on the planet immune from these changes. The simple fact is that people have impacts on the world and since most of the world is ocean it ultimately will be our critical resource for survival.

From my perspective you possess unique insights into the natural world as a result of your island upbringings. In addition to being at intimate part of the cycles of islands, you are all fortunate to be associated with some wonderful island cultures. In Hawai'i for example, people lived in a sustainable relationship with the ocean for over a thousand years, despite large populations. There are important lessons to be learned from these cultures. My challenge to you is to take your links to the ocean, take what you have started here in your projects, look at the island cultures around you and learn from them, and address some of the problems are planet is facing. Remember that islands are special places, and living on islands is a unique experience which fosters wonderful insights into the ocean world. You are part of the cycle of islands. Do not let this unique opportunity slip away!

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