Sea Level and Its Effects on Reefs in Hawaiÿi
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CHAPTER 5 Reef Fringing i ÿ Reef Corals and the Coral Reefs of South Molokaÿi Paul L. Jokiel1, Eric K. Brown2, Kuÿulei S. Rodgers1, and William R. Smith1 ich and diverse marine benthic habitats exist along much of the conditions and changes over time. Corals are the keystone species that of reef-forming corals on the reefs of south Molokaÿi. They are the “rice south Molokaÿi coral reef, as demonstrated by maps of the area form the reef framework through secretion of limestone skeletons. The corals” Montipora capitata (previously known as Montipora verrucosa), R(see Cochran, this vol., chap. 9 for a complete discussion of benthic abundance and diversity of reef fish are directly related to coral commu- and Montipora patula; the “finger coral” Porites compressa; the massive Character of the South Moloka habitats). Habitats that support corals generally contain a characteristic nity development (see Friedlander and Rodgers, this vol., chap. 7 for a “lobe coral” Porites lobata; and the “cauliflower coral” Pocillopora mean- assemblage of coral species that can be referred to as a “coral community.” complete discussion of reef fish on Molokaÿi). The ecological importance, drina. South Molokaÿi reefs are also inhabited by a number of other species Composition of each coral community is controlled by numerous environ- economic value, and environmental sensitivity of corals make them ideal of reef-forming and soft corals that range in abundance from rare to com- mental factors that influence recruitment, growth, and mortality of each subjects for monitoring and assessment efforts. Brown and others (this vol., mon. These species increase biodiversity, have great aesthetic value, and are component species. Different species show different adaptations to various chap. 6) discuss results from several years of monitoring of coral growth of basic scientific interest, but they account for only a small percentage of environmental conditions, which enable some species to thrive in certain off south Molokaÿi. the total living coral cover. habitats but not others. Corals that develop framework reefs in tropical waters are long-lived Abundant Species of Hard Corals sedentary organisms that have a very narrow range of tolerance to tem- The Corals of South Molokaÿi perature, salinity, water clarity, sedimentation, and nutrients. Therefore, Montipora capitata (figs. 1, 2, 4) is clearly the most widespread spe- corals can serve as excellent indicator species. Data on coral abundance Distinguishing among the hundreds of species of reef corals in the cies off south Molokaÿi. It is highly variable in growth form and occurs in and species composition allow evaluation of prevailing environmental world is based largely on microscopic features of the coral skeleton as all coral habitats, including isolated rocks on the muddy inner reef flat. Its 1 University of Hawaiÿi, Hawaiÿi Institute of Marine Biology, P.O. Box 1346, Kaneohe, HI 96744 well as on skeletal growth form. However, the number of coral species in range extends to a depth of more than 30 m (100 ft) on the deepest por- 2 University of Hawaiÿi, Hawaiÿi Institute of Marine Biology, P.O. Box 1346, Kaneohe, HI 96744; Hawaiÿi is small, and they are relatively easy to distinguish from each other tions of the offshore fore reef, where it takes on a frail and highly branched current address: Kalaupapa National Historical Park, P.O. Box 2222, Kalaupapa, HI 96742 in the field (Maragos, 1977; Fenner, 2005). There are five dominant species growth form reminiscent of a finely branched Anacropora. Vaughan (1907) Figure 1. Encrusting and platelike Figure 2. Platelike and encrusting Figure 3. Purple-polyp form of Monti- Figure 4. The three dominant species Figure 5. Montipora flabellata as- Figure 6. Montipora studeri (= Mon- growth forms of Montipora capitata growth forms of Montipora capitata pora patula (top of photograph) com- of Montipora compete for space on sumes a very unusual branched form tipora incrassata) at depth of 3 m (10 dominate vertical faces and over- (on the right) and encrusting Montipo- pared to brown variety at a depth of 3 shallow reef off Kamalö, Molokaÿi. The on the reef flat of south Molokaÿi ft) at Kamalö, Molokaÿi, with a small hangs on the fore reef. Photograph ra patula (darker colony on the left) at m (10 ft) on the fore reef at Päläÿau, blue species Montipora flabellata (up- though symbiosis with a small shrimp plate of Montipora capitata showing in taken at depth of 5 m (15 ft) at a depth of 3 m (10 ft) on the shallow Molokaÿi. The purple-polyp form of M. per center) struggles to overgrow the known as Gammaropsis sp. (see the upper right. Päläÿau, Molokaÿi. fore reef at Päläÿau, Molokaÿi. patula should not be confused with brown encrusting species Montipora text). Montipora flabellata, which has a patula (lower center). The branching deep blue coloration throughout the growth form of Montipora capitata sur- colony. rounds the two encrusting species in this photograph. THE CORAL REEF OF SOUTH MOLOKAÿI, HAWAIÿI—PORTRAIT OF A SEDIMENT-THREATENED FRINGING REEF reported that M. capitata (which he called Montipora verrucosa) had the Porites compressa is a conspicuous coral and occurs in abundance at most variable growth form of any coral species. In shaded environments depths of 10–30 m (30–90 ft) on the fore reef (fig. 7) and can be found in Figure 7. The deep fore reef is domi- M. capitata forms large platelike structures; in calm-water environments it most environments at lower abundance. The species is also successful in nated by the “finger coral” Porites com- assumes a branched morphology; and in areas of high wave action it takes many shallow calm-water environments, such as along the rim of “blue pressa along much of the south Molokaÿi on an encrusting growth form. holes” and in the shallows off Kamalö Pier. P. compressa is endemic to the coastline that is not affected by large Montipora patula (figs. 2, 3, 4) is an encrusting and plate-forming Hawaiian Archipelago (Veron, 2000) and is an important framework coral. waves. Photograph at 10-m (30-ft) depth species that does not have a branching growth form. M. patula is somewhat Its highly branched growth form provides cryptic habitats and cover for off Päläÿau, Molokaÿi. more restricted in range than M. capitata, being more common in environ- many species. ments of higher wave energy and less abundant in environments subject to Porites compressa is most abundant in deeper areas on platforms and high sedimentation rates. on the tops of ridges where wave energy is low (Dollar, 1982). This spe- Montipora flabellata (figs. 4, 5) is a blue encrusting species com- cies can outgrow most other corals for space through rapid vertical growth monly found in shallow, high-wave-energy environments (Jokiel and oth- of branches. Several encrusting species of coral are associated with this ers, 2004). This species does not normally have a branching growth form community, but they are generally forced to live in the spaces between the Figure 8. The “finger coral” Porites and, by itself, cannot compete with branched species. However, unique P. compressa branches because of the ability of this branched species to compressa (top) must grow vertically at branched colonies of M. flabellata occur on the outer reef flat at south outgrow the encrusting forms. Occasionally some encrusting species can a rate faster than the encrusting competi- Molokaÿi that have not been reported from other locations in Hawaiÿi. gain the upper hand. For example, Montipora patula can be seen overgrow- tor Montipora capitata in order to survive. The unusual branched morphology is the result of a mutualistic symbio- ing a branch of P. compressa (fig. 8) in some environments. Other encrust- Photograph taken at depth of 10 m (30 ft) sis between the coral and a small shrimp. The shrimp is an unidentified ing species, such as Pavona varians (fig. 9), can be found deeper within at Kamalö, Molokaÿi. species of gammarid amphipod in the genus Gammaropsis. The shrimp the branches of P. compressa as well as in cryptic habitats, such as under forms a tube, and as the tube grows outward, the coral skeleton grows and ledges or in crevices. Pavona maldivensis (fig. 10) also follows this pat- encrusts the tube. Each branch of the coral thus has a hollow tube running tern, but is rare off south Molokaÿi. up the center and an opening at the tip that provides a home for this small The species in the genus Porites with more massive growth habits are crustacean. In this way the coral is able to form a branched colony while ultimately classified by microscopic structures of the skeleton, but they can the amphipod is given the protection of the coral skeleton (fig. 5). To the be distinguished from each other in the field off south Molokaÿi by certain casual observer the opening at the end of the branch resembles a terminal diagnostic features. Porites lobata is the most common species of Porites. Figure 9. Pavona varians is an encrust- polyp, and this growth form could easily be mistaken for a member of the This species is generally yellow in color and forms massive to encrusting ing coral often found in shaded environ- genus Acropora. colonies. P. lobata is a long-lived species able to withstand periodic storm ments. Montipora studeri (fig. 6) is uncommon and generally found in wave- waves that remove the fast-growing and more delicate branching species disturbed habitats, but isolated colonies have been observed as deep as that would otherwise overgrow the colonies (Grigg, 1983). Some shal- 10 m (30 ft) along the south Molokaÿi coastline. Fenner (2005) recently low environments are dominated by colonies of P. lobata measuring 5 to revised this species name to Montipora incrassata Dana, 1846.