is known from Papua New Guinea, where 494 coral species are currently known. Levels of endemism in reef fish are also relatively low (Hughes, Bellwood, and Connolly 2002), and the proportion of reef fish that are endemic is lower in the Coral Triangle than in outlying areas (Randall, 1998). Endemism may be overestimated if recently described species are included, because species are often described from small areas and subsequently found in additional areas (Fenner, under review b). So it is likely that Papua has very few endemic large species on its coral reefs.
RAPID ASSESSMENT TECHNIQUE CONFIRMS PAPUA IS IN THE CENTER OF DIVERSITY
Species diversity comparisons among areas are often based on the total number of species that have been found in each area. However, the number of species found in an area is heavily dependent on the amount of time, effort, and area covered searching for species. Additional searching time, effort or area explored almost always leads to additional species being found. Larger areas contain larger numbers of species, which is called the ‘‘species-area effect.’’ The number of species commonly rises as a power function of the area, as it did in a study of coral reef fishes (Chittaro 2002). Although such curves may appear to approach an asymptote on linear scales, on log scales they can be seen not to approach an asymptote. The search for an asymptote has been reported at times to reach areas the size of continents without reaching an asymptote (Williamson et al. 2001). The total number of coral species known from countries in the western Pacific has approximately doubled in the last three decades (Fenner, in review c).
The author has participated in several rapid assessment programs for coral reef areas, such as those sponsored by Conservation International. The goal of such programs is to rapidly assess diversity in an area. It is an attempt to use limited resources in a targeted fashion, to gain information about diversity of an area without spending the enormous resources necessary to get even a near-complete assessment.
In the present study, one scuba dive of approximately 60 minutes was spent by the author at each site in a roving search for coral species. The search began at the bottom of the reef or at about 30 m depth, whichever was less, and progressed upward during the dive, ending in the shallowest area that was accessible to a scuba diver. Comparisons among areas were based on equal numbers of dives.
A strong latitudinal gradient was found in the central Pacific, with diversity falling off from eastern Papua New Guinea to American Samoa and Hawai’i (Figure 5.2.8). The Raja Ampat Islands are in the area of highest diversity. Across Malaysia to Rodrigues in the southwestern Indian Ocean, there is also a latitudinal diversity gradient (Figure 5.2.8), though Rodrigues may be lower in diversity than Malaysia both due to latitude and longitude.
Diversity gradients are well known in the Pacific for corals and other groups of reef organisms. This rapid technique detects diversity gradients in much the same way as more labor intensive techniques. The lack of a gradient in this reef slope data between central Indonesia and New Guinea is consistent with the report that coral diversity on reef slopes is constant across this area (Karlson et al. 2004).
Figure 5.2.8. Longitudinal diversity gradients from rapid ecological assessments. Raja Ampat Islands, Papua, indicated by the open square, is among the areas of highest diversity. Points, in order from east to west, are for Rodrigues, Andaman Islands, Peninsular Malaysia, Sarawak, Sabah, Sulawesi, Raja Ampat Islands, Milne Bay (Papua New Guinea), Fiji, American Samoa, and Hawai’i.
Most coral reef organisms that have been studied have relatively large individuals. Marine invertebrate species with small individuals frequently brood their off-spring instead of broadcast spawning (Reaka-Kudla, 1995a,b). This may be because their small size restricts them to producing relatively small numbers of offspring, and broadcast spawning is a high-risk strategy in which most offspring die. If a small number of offspring are produced, a high-risk strategy increases the likelihood that all offspring will die. This may select for lower-risk reproductive strategies, where more is invested in each offspring by producing larger offspring, which do not disperse as far. This reduced dispersal ability increases the frequency of endemism (Reaka-Kudla, 1995a,b). A good example may be the amphipods, a large group of small-bodied crustaceans that produce relatively large eggs. Some species of amphipods raft on algae or have pelagic hosts such as jellyfish, and thus have wide ranges. But many amphipod species have very small ranges (Thomas 2000). Most species are small, such as insects on land. The view that most marine species have wide ranges is largely based on larger organisms like corals, fish, and echinoderms. Yet most coral reef species are likely to be small (Reaka-Kudla, 1995a,b), and not yet described, let alone have their reproductive mode or biogeographic range studied. Many or most of these species may turn out to be endemics. In addition, some groups of larger organisms that do not have a larval dispersal stage may have high rates of endemism. For example, many or most reef sponges produce negatively buoyant, sticky eggs that do not go far from their parents. An estimated 43% of the sponges recorded from Indonesia are endemic to the region (van Soest 1997). However, studies of Indonesian sponges and sponge biogeography are in early stages. The total number of sponge species is likely to increase considerably and endemism figures to change. Another example is colonial ascidians (sea squirts), which produce tadpole larvae that go only short distances from their parents. As with corals and fish, the actual ranges of these species may be largely determined by their ability to raft, because rafting can spread widely even species with no larval dispersal phase.
A very different view is presented by Fenchel and Findlay (2004). They report that most microbial marine organisms are cosmopolitan, and that the percentage of species found at one temperate marine location that have large ranges decreases with increasing body size. If this should also prove true of coral reefs, then groups of small organisms that are highly endemic, like amphipods, may be unusual. It may be that only groups like amphipods, sponges, and ascidians have high rates of endemism on coral reefs. Or it may be that that the largest organisms and microbes have low endemism, but intermediate size (small) organisms have high rates of endemism.
If there are large numbers of small, undescribed, and unstudied species on coral reefs that are likely to be endemic, it will not be practical to study each species to determine its range. We will not know the ranges of even a fraction of the small species on coral reefs any time in the near future. Long before we can know which species are endemic, coral reefs may be highly degraded, and endemic species lost before they are even discovered. The primary cause of species extinctions is loss of habitat. The best way to save large numbers of small endemic undescribed coral reef species is to protect the habitat itself, without taking the time to discover all the tiny endemic species. Further, the number of small species present at a site is almost certain to be proportional to the number of large species found there. Bellwood and Hughes (2001) found that there is a high correlation between the diversity of organisms in one size group with those of another size group. Thus, the diversity of large species such as corals and fish is likely to be a good indicator for the diversity of small species. Although we know that low diversity coral reefs have a higher proportion of endemic species among large organisms than high diversity reefs, high diversity reefs are likely to have much higher absolute numbers of small endemic species than low diversity reefs. Thus, the conservation of both low and high diversity coral reefs is important. Further, while large species (‘‘charismatic megafauna’’) may capture public support, small endemic species will not (‘‘save the amphipods’’?). Coral reefs, however, are highly charismatic, and have generated significant public support for conservation.
Threats to Papuan Reefs
Coral reefs face threats from a wide variety of human sources. The ‘‘Reefs at Risk’’ program (Burke et al. 2002) identified six principle threats to coral reefs, and evaluated five of those. The five threats they evaluated were coastal development, marine-based pollution, sedimentation and pollution from inland sources, over-fishing, and destructive fishing. The sixth threat was climate change and coral bleaching. Their method was to identify sources of human pressure that produce stress on coral reefs
