Ecology of Indonesian Papua Part Two. Andrew J. Marshall
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and eat the tissue off corals, killing the corals (Dulvy et al. 2004). Humphead Wrasses are known to eat toxic invertebrates like the Crown-of-Thorns starfish, so overfishing them may leave reefs vulnerable to Crown-of-Thorns attacks. Although the reefs of Papua are remote and under relatively little pressure from human populations (but see Birkeland 1982), fishing makes sharks and Humphead Wrasse rare, with just two adult Humphead Wrasse seen in 45 sites (Allen 2002b; McKenna et al. 2002).
Few coral reef researchers or managers have seen what truly pristine coral reef fish populations are like, and the amazing dominance of apex predators. Each generation of scientists remembers what coral reefs were like when they first saw them, and tend to think of that as the standard of undisturbed ecosystems. We have lowered our standards in a process called ‘‘shifting baselines.’’ Coral reefs in the Caribbean have declined in three decades from about 50% coral cover to about 10% coral cover (Gardner et al. 2003). Archeological methods have been used to study the effects of pre-Columbian fishing in the Caribbean, and the studies have found that declines began even before the arrival of Europeans (Wing and Wing 2001). Paleontological methods along with archeological and historical methods have shown declines in 14 coral reef systems worldwide since pre-human times (Pandolfi et al. 2003). The 14 reef systems studied had declined between about 28% and 78% of the way from pristine toward ecologically extinct.
Endemism and Extinction
Endemism is commonly used in terrestrial conservation programs as a measure of the need to conserve areas (Allen 2003). It is especially important to avoid the local extinction of endemic species, because their loss represents the loss of an entire species. Endemic species are more vulnerable to extinction partly because any local disturbance can cause global extinction, and also because endemic species usually have small populations. The rates of endemism on coral reefs are quite different in different groups of organisms. Endemism is uncommon in larger organisms, but may be high in some groups of small organisms, and low in the tiniest microscopic organisms. Most groups of larger coral reef organisms have wide dispersal and very few species are endemic. Many coral reef species are broadcast spawners, releasing tiny eggs into the water that are carried with the currents. Currents can carry the eggs considerable distances during the several days to weeks required for them develop to the stage where they are ready to settle. For example, one species of sea urchin, Echinothrix diadema, has been found to be genetically the same species in Hawai’i and the east Pacific, across the largest expanse of open water in the tropics anywhere in the world (Lessios et al.1998). Some coral species have been observed attached to floating objects and thus are probably able to ‘‘raft’’ over vast distances (Jokiel 1990). This is even true of species that brood their young, releasing larvae that quickly attach close to the parent. Reef fish have also been observed rafting by staying near floating debris (Mora 2001). This wide dispersal means that there are few endemic species on most coral reefs, especially in the western Pacific where there are many reefs close together. For instance, currently no endemic coral species are known in the Philippines or Indonesia, where 535 and 581 coral species are currently known, respectively (Fenner, under review c; Turak 2003; Veron 2002), and only one endemic species 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