Last update: 1/25/2005
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Changes
in the marine habitat and biota of Pelekane Bay, Hawai’i Introduction Pelekane Bay is located along the south Kohala Coast of the island of Hawai’i. The goal of this study was to examine long-term changes in the marine habitat and biota by comparing the present abundance, diversity and distribution of marine organisms to those described 20 years earlier on marine plants (Ball, 1977) and animals (Chaney et al., 1977). As mentioned in these earlier papers, changes in the marine community of Pelekane Bay over this 20-year period are likely due to modifications in the environment of the area surrounding this site. These include large-scale alterations in the Kawaihae watershed over the last 200 years and the construction of the Kawaihae Harbor in the 1950’s and 1960’s. Early historical accounts indicate that the Kawaihae area was dense with hardwood forests which ran from the Kohala mountains (Langlas, 1994) almost to the shore in the late 1700’s and early 1800’s (Greene, 1993). Water also flowed continuously from the two major gulches, Makehua and Makahuna, which drained the majority of the Kawaihae watershed and entered the ocean near Pelekane Bay (Greene, 1993). However, beginning in the early 1800’s, sandalwood was extensively harvested from the upper slopes of the watershed (Kawaihae Uka) and in the Waimea area. By 1845 the harvest had been so extensive that there were "…no trees left larger than mere saplings" (Willis 1845, cited in Kelly, 1974). In addition to the large-scale removal of upland forests, cattle were introduced by Captain George Vancouver in 1793. The cattle, saved from slaughter by a kapu, multiplied rapidly and by 1807 were running wild and grazing the land (Greene, 1993). As a result of deforestation and extensive cattle grazing the Kawaihae area was described as barren with little vegetation by 1830. Moreover, water in the gulches had ceased to flow (Greene, 1993). During the late 1950’s the large fringing reef adjacent to Pelekane Bay was dredged to create Kawaihae Harbor, which was completed in 1959. Coral rubble and sand fill from the dredging was used to build causeways, a dike and a revetment which adjoins the area next to Pelekane (Figures 1,2,3). In 1969, as part of Project Tugboat, the army’s Nuclear Cratering Group used high explosives to excavate the small-boat harbor located 300 m north of Pelekane and to widen the harbor’s entrance and basin (Greene, 1993). The net result of these activities was to scatter coral rubble throughout the northern part of Pelekane Bay and cause a considerable reduction in the degree of ocean circulation. In response to these large-scale changes, increased erosion and the natural funneling of water by three gulches (Makehua, Makahuna and particularly Pohaukole) into Pelekane Bay resulted in chronic instances of high sediment runoff into the ocean. By 1976, turbidity in Pelekane was reported as low compared to offshore waters by Chaney et al. (1977), with visibility ranging from 10m at the mouth of the bay to less than 1m near the shore. Ball (1977) reported a visibility of a few cm in 1976. In addition, the area contains numerous warm freshwater springs, which were used by early Hawaiians for bathing (Kelly, 1974). In 1976 these springs discharged warm fresh water into Pelekane Bay along the shoreline to the south of the bay and up through sediments in several areas, causing a reduction of salinity to 25-32 ppt (Chaney et al., 1977). The goal of this study is to reexamine the study areas surveyed in 1976 by Ball (1977) and Chaney et al. (1977) in order to estimate any changes that may have occurred in the subtidal marine habitat and biota in the intervening 20-year period. Estimates will be made of the area of different habitat types and the abundance and diversity of the plants and animals in the bay. An additional goal of this study is make recommendations on ways to restore the marine environment of Pelekane Bay to the condition that existed prior to the construction of the Kawaihae harbor.
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