Pacific Island Variety
The Pacific Islands are difficult to characterize geomorphically (and include atolls, volcanic islands, continental islands, limestone islands, and mixtures of all these geomorphologies. Half of the Caroline Islands and 80% of the Marshall Islands are atolls. These atolls may only be above sea level by a few feet making them extremely susceptible to changes in sea level and storm activity and their impacts on the water table of the atoll. At the other extreme, volcanic islands such as the islands of Hawaii can peak at over 3,962 meters (13,000 feet) above sea level. Island landforms are not solely the product of their geological history. In the Pacific, climatic and oceanographic forces can alter island landforms. Changes in rainfall and water table level are important processes in this respect.
Islands are impacted by the interplay between their geology and climatological and oceanographic processes. Compared to other types of islands found in the Pacific, high volcanic islands like the Hawaiian islands tend to have larger surface areas, more groundwater, better soils for farming, and overall a more diverse resource base. Compared to high volcanic islands, low-lying atolls that are only a few meters above sea level are prone to drought and erosion and have very limited natural resources. High Pacific islands generally can support the growth of tropical forests given their warm temperatures, moisture, and soils whereas atolls generally do not support dense vegetation due to poor soil composition and hydrological constraints.
Pacific island landscapes and biodiversity are varied. Warm temperatures and moisture have supported the growth of tropical rainforest on many islands, particularly the high islands. While even relatively small islands can host a diversity of forest types, atolls generally do not support dense forest vegetation inpart because of the poor soil composition and lack of fresh water. The atolls are basically a coastal zone because the boundary between land and ocean constantly fluctuates throughout the year. Mangrove forests fringe some islands in locations where fresh water from runoff and salt water from the ocean mix. Oceanic islands tend to have lower levels of biodiversity and species found on them are more likely to be endemic, which means the species are native and restricted to that island. Island species are more susceptible to disruption from introduced species.
One example of how island species are susceptible to disruption from the introduction of foreign species is the the Puerto Rican coqui frog's introduction to the Hawaiian Islands -- specifically the Big Island of Hawaii. The coqui frog was accidentally introduced into Hawai'i from Puerto Rico around 1988. Aside from being a major noise nuisance, the frogs pose a threat to Hawai'i’s island ecosystem. Coqui frogs have a voracious appetite that puts Hawai'i’s unique insects and spiders at risk. They can also compete with endemic birds and other native fauna that rely on insects for food. The frogs are quite adaptable to the different ecological zones and elevations in the state and have been found from sea level to 4,000 feet elevation (at sites in Volcano on Hawai'i). Scientists are also concerned that an established coqui frog population may serve as a readily available food source if (or more likely when) brown tree snakes are accidentally introduced in Hawai'i.
Since their introduction to the Big Island within the last 10 years their numbers have ballooned, they have infested Maui and have been sighted on both Oahu and Kauai. Coqui populations have grown in the last 15 years from presumably a single infestation to over 200 on the Big Island alone. They are also present on Maui (40 or more infestations), O`ahu (5 sites) and most recently on Kaua`i (1 site, subject of an eradication effort with citric acid in June 2003). Puerto Rico averages 40 frogs (reproductively mature adults, not including juveniles) per 20 x 20 m plot compared to greater than 200 in Big Island plots, primarily because of the lack of predators (owls, snakes, tarantulas, scorpions) in Hawai'i.
Some effects of the frogs include: 
- Loud annoying calls that disturb sleep (click here to hear the frog's call)
- May prevent the export of infested goods to areas with "No Pest" policies
- Potential vector of nematodes in certified nurseries
- Competition with Hawaiian birds for insect prey
- Predation on Hawaiian insects and spiders
- Could boost mongoose and rat populations by serving as an unlimited food source
- Would provide an abundant food source for more damaging, potential invaders such as the brown treesnake
The lack of biodiversity makes island ecology extremely sensitive to climatological change. The Hawaiian Islands, although they comprise less than 0.002% of the total land area of the United States, are home to nearly 30% of the nation’s endangered species. The ecosystems of the Pacific islands support more rare, endangered and threatened species than anywhere else on earth. The Pacific marine environment comprises an enormous and largely unexplored resource, including the most extensive and diverse reefs in the world, the deepest oceanic trenches and relatively intact populations of many globally threatened species including whales, sea turtles, dugongs and saltwater crocodiles. The high islands support large tracts of intact rainforests that are hosts to unique communities of plants and animals, many species of which are found nowhere else in the world, many more waiting to be discovered and described scientifically. For the small islands, this diversity is the result of thousands of years of physical isolation from continental landmasses; this enabled many island faunal species to evolve independently of relatives in other land masses resulting in a high level of endemism, which according to some reports exceed 80% in many islands.