with mangroves are often not suitable habitat for coral reefs, yet in New Guinea there are places where coral reefs grow adjacent to mangroves, and mangroves even grow onto the reef platform (P. Dalzell, per. comm.). Some maps of Papua (e.g., Spalding, Ravilious, and Green 2000) show long stretches of coast containing some of the largest mangrove forests in the world. A long stretch of the north coast is normally depicted as being devoid of coral reefs, but fringing reefs are believed to stretch along much of the coast between Sarmi and the border with Papua New Guinea. Fringing reefs are reported on the northern coast of the Vogelkop Peninsula, as well as east from Jayapura to the Papua New Guinea border, and a fringing reef west of Jayapura for 100 km, possibly for an additional 160 km (Tomascik et al. 1977). The coral reefs of Papua New Guinea are much better studied, and yet about half of its coastline has not been explored for coral reefs (Yamuna and McClanahan 2001). Whitehouse (1973) claimed that on the north coast of Papua New Guinea there are no active coral reefs for 1,250 km, but Kojis, Quinn, and Claereboudt (1985) found fringing reefs with a high coral cover and diversity are common along this coast except near the mouths of rivers. The north coast of Papua probably has similar reefs. The total amount of coral reefs in Papua could be several times that presently known. Reefs in Papua are protected from strong wave action. Reefs at 45 sites in the Raja Ampat Islands off the western end of the Vogelkop Peninsula (described in McKenna, Boli, and Allen 2002) vary from those exposed to the open ocean, to those that are in sheltered bays, to one that was so enclosed it was virtually a saltwater lake (Mayalibit Bay within Waigeo Island). Strong currents were not encountered at most sites. The seas are very calm compared to those at oceanic mid-Pacific reefs or the Great Barrier Reef. The reefs do not feature a reef crest with large crashing waves and high cover of coralline algae, nor extensive reef flats and lagoons. Rather, the bottom usually slopes away directly, starting at the shoreline. This is typical of reefs in the region, as the author has seen in northern Sulawesi (Allen and McKenna 2001), eastern Papua New Guinea (Allen et al. 2003), Malaysia (Harborne et al. 2000), and 11 areas in the Philippines (Fenner, under review c; Werner and Allen 2000). Reefs on the southwest side of Cenderawasih Bay include patch reefs with seaward margins that are sheer drop-offs from the crest to a first ledge at 20–40 m depth. Sub-sea level patch reefs have a variable gradient fore reef. Fringing reefs have a variable gradient in bays and sheltered areas but are steeper elsewhere (UNDP/FAO 1982; UNEP/IUCN 1988).
Coral cover has been used as a measure of coral health. Because damage to reefs reduces coral cover, reefs with higher coral cover have been presumed to be in better condition. Data on coral cover for 13 sites in the Padaido Islands in Cenderawasih Bay are available (Tomascik et al.1997). Most commonly they had cover of 25–50%. In 44 sites in the Raja Ampats, McKenna, Boli, and Allen (2002) found that the average coral cover was 28%. A qualitative scale for coral cover was devised by Gomez et al. (1994), where 75–100% cover was considered excellent, 50–75% good, 25–50% fair, and 0–25% poor. Thus, reefs in these two areas would be considered fair. Indonesia as a whole is reported to have 2.6% of its reefs as excellent, 24.2% good, 31.6% fair, and 41.6% poor condition (Ming et al.1994). Such a scale should be approached with caution, since it implies value judgments that are not based on empirical studies. Coral cover varies substantially depending on habitat and sediment dynamics. No clear generalization can be drawn on the relationship of coral cover to reef health (Maragos 1997). Further, reefs that are among the most pristine known rarely have coral cover in the excellent range, and frequently are in the fair range. Examples include the northwest Hawai’ian Islands (Grigg 1983) and the Great Barrier Reefs (AIMS monitoring, www.aims.gov.au). The scale was originally proposed as a measure of reef health and degradation, yet the natural baseline conditions of reefs are not known. Senior ASEAN scientists assessed eastern Indonesia as having 10% of its reefs degraded 50 years ago and 50% in 1993 (Ming et al. 1994), but figures for Papua were not given. The latest Status of Coral Reefs of the World: 2004 Report (Wilkinson 2004) indicates that the overall reef condition of Indonesia has been improving since 1999, with a shift from reefs with less than 25% cover to reefs with 25–50% cover.
SEA LEVEL CHANGES
The area of eastern Indonesia and New Guinea is a geologically active area, due to the collision of the Indo-Australian, Eurasian, Caroline, Philippine, and Pacific plates. There are many areas of uplift in eastern Indonesia, and many places that have terraces on slopes above the waterline, including along the northwestern coast of Papua (Tomascik et al.1997). On the Huon Peninsula of northeastern Papua New Guinea, continuous uplift of the landmass along with oscillating changes in sea level have produced a stair step series of fossil coral reefs on land. During ice ages, huge amounts of water are withdrawn from the oceans and locked up in giant ice sheets on land in North America, Europe, and Asia, much like in Antartica today. In addition, lower temperatures in the oceans cause the water to contract. These two processes together cause sea levels to drop substantially during ice ages. The last ice age peaked at about 22,500 years ago, causing a drop in sea level of about 120 m. This is well below the lower limits (usually around 30 m) of all presently living coral reefs. Thus all presently living coral reefs were exposed to air at that time and died. The change in sea level happened sufficiently slowly that larvae of sessile organisms such as corals were able to attach farther down and remain alive in the water, and begin building reefs farther down the slopes of islands and continents.
In an area like the Huon Peninsula where land is rising steadily, coral reefs build up along the shore when the water levels rise at about the same rate as the land rises. Then when the sea level drops, the reef is left out of the water and new corals attach farther down. There have been a whole series of ice ages, and so the hillsides on the coast of the Huon Peninsula have a series of benches made of coral reefs up and down their slopes (Figure 5.2.2). A living fringing coral reef is in the water along the shore, and the series of raised reefs on the hillside begins with the youngest at the bottom and progresses to the oldest at the top. There are nine fossil reefs, spanning a period of 95,000 years. A comparison of the species on the living reef and in the fossil reefs shows that the reefs have the same species composition even though they differ in age by up to nearly a hundred thousand years. Complex reef assemblages have been able to reconstitute themselves in the same form time after time over a very long period of time. Differences were actually greater between points along the coast than at the same reef over 95,000 years (Pandolfi 1996). Similar areas of rising land in Papua are likely to have experienced the same series of events, and have similar fossil reefs. In areas where the land is not rising or is even sinking, reefs produced during lower sea level stands are likely to be found underwater. Such reefs produce terraces or ledges, such as the one reported from Cenderawasih Bay.
ZONATION
Coral reefs have several zones. The term zonation refers to situations where the type of organisms present (i.e., species composition) changes along some environmental gradient. Rocky intertidal zones in temperate climates have zonation, with some organisms living only high in the intertidal, others living in the middle intertidal, and still others in the lower intertidal. On coral reefs there are a series of zones encountered as one moves out from shore (Figure 5.2.3). On a barrier reef, the zone closest to shore is the lagoon, which has a sandy bottom and may have seagrasses and algae on the bottom, along with patches of coral. Farther out, a shallow, hard calcareous (composed of calcium carbonate) bottom is called the reef flat and may have scattered corals. The crest is where waves break on the reef, and is usually dominated by crustose coralline algae. This type of algae forms a smooth hard layer over underlying coral rubble or rock, cementing it together and withstanding the force of breaking waves. From the crest, the reef slopes downward in what is called the forereef slope. On the reef slope there may be a series of ridges and gullies running down the slope called spur and groove, tongue and groove, or ridges and sand channels. On some reefs the slope ends in a vertical drop-off that can be called a wall. Walls commonly have overhangs that alternate with steeply sloping sections. Some reefs have caves on reef slopes or walls, and most reefs have small holes in the reef that may extend in a maze through the reef. At the base of a wall, there is usually a slope of sand and debris, but few or no reef-building corals.
Figure
