Moorea: The Physical Environment

Arriving Hakaui

Located in the remote South Pacific, the island of Moorea is one of the world’s most beautiful landscapes as well as one of the region’s most well studied physical environments. Moorea is part of a chain of islands formed by hot spot volcanism; once an underwater volcano forms the island, it begins to erode and sink back into the ocean, meaning these islands are constantly changing. Moorea is in the beginning stages of transformation from a high island to a coral atoll, a geologic transition that has a profound effect on the island’s physical environment. The island is home to two major research stations: The University of California at Berkley’s Gump Station and the French National Centre for Scientific Research’s Centre de Reherches Insulaires et Observatoire de l’Environnenment (Le CROIBE). Both stations are focused on studying the reef system of the island, which is an ecosystem that has both economic and intrinsic value to the local population.  This stage of transition, extensive academic research, and the reef’s value as a human resource make the island an important site for potential conservation.

Moorea is the second largest island in the Society Archipelago, located in the Southern Equatorial Pacific Ocean. It is roughly twenty km northwest of Tahiti, the largest island, and is a member of the Windward group. Moorea is a high island, making it rugged and mountainous with fertile soils and several watersheds (“Moorea,” Encyclopedia Britannica). Of forty-six watersheds, the two most dominant are the Pao Pao and Opunohi river valleys on the northern edge of the island (Duane 2). The watersheds flow from several small peaks on the island, the highest of which is Mount Tohivea at 1,207 m high (“Moorea,” Encyclopedia Britannica). These small mountains slowly descend to the coastline, ninety percent of which is lined by offshore barrier reefs.  Twelve deep navigable passes separate the reefs and allow access for mariners (Duane 2). The lagoon, an important element of Moorea’s transition from high volcanic island to coral atoll, is an economic resource for both fishing and tourism (

Arriving Hakaui

The process of hot spot volcanism that formed the island defines Moorea’s geology.  Studies on the age of rocks in Moorea have concluded the dormant volcano that is the island was active between 1.2 and 2.6 million years ago (Dymond 236). These dates indicate that Moorea is in the early stages of the process of transformation from a high island to an atoll, a metamorphosis that can be easily visualized by observing Moorea’s significant coral reef, volcanic mountains, and substantial lagoon.

Moorea’s lush vegetation is one of the qualities that gives the island its beautiful tropical appearance. However, the island’s vegetation has changed dramatically as human inhabitants shaped it for their uses. The first Polynesians traveled to Moorea as early as 1200 years ago, bringing with them breadfruit, chestnut, taro, and medicinal species to ensure their survival (Eichenseher). Later, European explorers brought plants from their gardens, including many medicinal and ornamental species. One such species, the ornamental Miconia calvescens--commonly called miconia--has become one of the South Pacific’s most dangerous invasive species. Aggressive invasives like miconia, threaten to overwhelm the islands’ few endemic species as well as introduced species that have value to the islands’ people (Meyer and Florence).

The climate of Moorea, similar to the other islands of French Polynesia, is tropical with a mean annual temperature of 26°C (Male). Moorea experiences a rainy season between December and February, when most of the annual 109 inches of precipitation fall, as well as a dry season between March and November (Male, Duane 3). The rainy season, with an average temperature of 26.5°C, is slightly warmer than the wet season, with an average temperature of 24.5°C, though temperatures are moderate all year (Duane 2).

The prevailing winds in Moorea are the easterly trade winds, which fuel the island’s dominant current—the South Equatorial Current (Segar 242). Easterly trade winds and easterly current are consistent through most of the year. During normal years, the easterly trade winds, which bring warm air to the Western Pacific, make Moorea’s location in the central ocean relatively safe from cyclones. However, this pattern is reversed in El Niño years when westerly winds carry warm air to the central Pacific, making Moorea and other French Polynesian islands vulnerable to cyclones (Meteo France). The extreme variability in storm frequency can make El Niño years dangerous in French Polynesia, whose population may be unprepared for violent and frequent hurricanes.

Arriving Hakaui

An important feature of Moorea’s physical environment is the developing coral reef. Corals, like anemones and jellyfish, are members of the phylum Cnidarians. Corals are tube-like structures with a central cavity and a mouth surrounded by tentacles (CRC Reef Research Centre). Coral reefs are formed when free-swimming larvae attach to hard surfaces along the edge of islands or continents (“What are Corals?”). Moorea’s reef is dominated by four genera: PoritiesPocillopora, Acropora, and Montipora (Gump Station, 5). Once the corals grow vertically to sea level, the colonies then expand horizontally. An indicator of the beginning of high island transformation is the development of a reef. As Moorea ages, the growth of the reef will reflect the progression in transformation.

Currently, the developing reef of Moorea is an offshore barrier reef (Gump Station, 3). This reef system creates a series of shallow and narrow channels ranging from five to seven meters in depth and one to one-and-a-half kilometers in width (Gump Station, 3). On the north shore of the island there is a particularly dense section of reef that contains about fifty percent of the coral around Moorea (Gump Station, 4). Moorea’s reef is relatively pristine and undisturbed and is home to an abundance of reef fish and corals that are high in diversity, indicating the robust condition of the ecosystem (Gump Station, 4).

The impact of human activity on the reef is substantial, and the most prominent threats in Moorea stem from fishing, pollution, and climate disruption. Some fishing methods leave reefs polluted and damaged (“Anthropogenic Threats to Corals”). In addition, overfishing has reduced the number of top predators in Moorea’s reef , which has led to degradation of the trophic cascade (Gump Station, 5). When top predators are removed from the food chain, prey species populations can become large due to a lack of regulation through predation. Increased populations of these prey species changes the demands on the reef environment. Ironically, the lack of predators combined with the relatively low-pressure subsistence fishing by the human population means reef fish populations remain diverse and abundant. Even though the ecosystem appears to be in balance, the lack of top predators represents a regrettable loss of diversity in this unique environment.

Marine pollution is a threat that can occur through coastal development, agriculture, and land based runoff. All of these factors introduce some type of sediment, nutrient, chemical, insecticide, oil, or debris that is foreign to the reef environment (“Anthropogenic Threats to Corals”). Moorea’s volcanic soils are very productive, and agriculture on Moorea includes the cultivation of products such as vanilla, copra, and even coffee (“Moorea,” Encyclopedia Britannica). Additional development on Moorea could limit reef productivity by introducing extensive runoff to the lagoon or barrier reef (Duane).

Climate disruption is a global problem and its effect on coral reefs is significant. Consequences of climate disruption, such as increased sea surface temperature, ocean acidification, and increased sea level all create change in the coral environment (Gump Station, 5). Ocean acidification and increasing sea surface temperature affect the rate of calcification and therefore the rate of growth for corals (Gump Station, 5). Temperature especially affects the mutualistic relationship between the zooxanthellae and coral, which can cause coral bleaching (Gump Station, 5). The Gump station’s ecological study was unable to detect damage to the reef as a result of climate disruption thus far. However, additional monitoring is important as climate disruption continues on its current path.

Natural threats such as weather, predation, and disease all play a role in the function of Moorea’s reefs. Though uncommon in Moorea, strong cyclones can create large and powerful waves that crush, break, flatten, and scatter coral fragments all over the sea floor (“Natural Threats to Coral Reefs”). When large portions of reef are eliminated, fast growing algae can out-compete coral, which grows at a much slower rate leading to a shift in the ecosystem from coral to algae (“Natural Threats to Coral Reefs”). An extensive study of Moorea’s reef in 2006 by the Gump Research Station, found that cyclones strong enough to spark this shift have not occurred, and reported that algae populations were normal at the time of the study (Gump Station, 4-5). In 2010 the cyclone Ollie passed the island disrupting the reef around Moorea in varying degrees (MCRLTER, 1). A storm of this magnitude may have altered the reef since the aforementioned study.

The coral population on Moorea is extremely vulnerable to predation by fish, crabs, sea stars, and other marine organisms. Crown of Thorn Starfish (Acanthaster planckii), a species with few natural controls, can damage coral reefs extensively. These organisms are large starfish that can grow up to eighty centimeters and are covered in sharp spines measuring between forty to fifty mm (ReefEd). These sea stars live and prey on corals, which ultimately leads to the destruction of the reef (Davis). Moorea’s reefs experienced outbreaks of Crown of Thorn sea stars in the 1970s (Gump Station, 4).  In 2007, a Crown of Thorn Starfish outbreak occurred that significantly reduced the coral cover mostly on the fore edge of the island along with other locations (MCRLTER, 1).

Another naturally occurring threat is Coral diseases. Coral diseases are often the response of the coral to biological stressors such as bacteria and viruses or non-biological stresses such as UV radiation or increased sea surface temperature (“Coral Diseases”). Coral diseases have become more prominent in the last decade, which scientists attribute to the deteriorating water quality associated with human factors (“Coral Diseases”). The diseases lead to widespread coral death. Moorea’s reef has experienced a limited amount of coral disease, but a long-term ecological study focused on this topic failed to mention the time period in which they occurred (Gump Station, 4).

There is an abundance of information pertaining to the reefs of Moorea due to the presence of two research stations, one in each of Moorea’s most prominent bays. The Gump Station is located in Cook’s Bay while Le CROIBE is found on the other side of the island in Oponohu Bay, making Moorea an experimental site for this type of research in French Polynesia. Moorea is far from being an atoll, however this island provides scientists the opportunity to study a young reef as it matures. The research that is being done in Moorea can serve as a template for future research throughout French Polynesia. These stations have extensive relationships with the public of Moorea. They have recently been discussing policies with the government and population to implement some protection, such as the newly designated Marine Protected Areas. Research being done in Moorea today will provide information that will help the Society Islands and other marine communities to better understand their environments. These types of studies, particularly when paired with educational programs, will be able to support conservation initiatives, educate the public, and inform government action to protect such a unique, beautiful, and important environment.

Maintenance and protection of Moorea’s coral reef is important for the island’s human environment. A trip to Moorea will show that the vast majority of the human population now resides along the shoreline. With a majority of the island remaining relatively untouched and overgrown with vegetation, the human-reef interaction is an important element of human life on the island.  The reef provides protection to populated shorelines because corals buffer the shore from waves, erosion, and property damage (NOAA, Importance of Coral). Coral reefs also help to increase the biodiversity of the ecosystem—they are capable of supporting more species per area than any other marine environment (NOAA, Importance of Coral). Preservation of the reef environment could help maintain fishing stocks at a level necessary to sustain the local fishing business. Reefs also have value in the tourism sector.  Recreational diving in coral reefs is a draw for tourists to visit tropical locations like Moorea. The beautiful coastlines associated with coral reefs create an ideal location for hotels, giving Moorea its reputation as a honeymoon destination. The tourism industry provides customers for support businesses that help the local economy.  From subsistence fishing to luxury hotels, there are broad economic interests in Moorea’s reefs that could bolster the initiative to conserve these fragile environments.

Moorea’s physical environment is a landscape in transition. As it moves from high island to coral atoll, the changing dynamics will be monitored and analyzed by two research stations. Moorea’s combination of mountains and reef make it a compelling environment to study over time. The pristine condition of both environments and the human capacity to study them has made Moorea a platform of education and research. This knowledge base about the environment feeds a human interest in conserving this beautiful and exciting landscape for the value it possesses to present and future generations.

Sonya Falcone, Colgate University
Liann Correia, Washington and Jefferson College



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