Pacific Science Volume 50, Number 2, 1996

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Pacific Science is a quarterly publication devoted to the biological and physical sciences of the Pacific Region.

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    Abstracts of Papers. Twentieth Annual Albert L. Tester Memorial Symposium, 27-28 April 1995
    (University of Hawaii Press, 1996-04)
    The Albert L. Tester Memorial Symposium is held in honor of Professor Albert L. Tester, who, at the time of his death in 1974, was senior professor of zoology at the University of Hawai'i at Manoa. The faculty and students of the Department of Zoology proposed an annual symposium of student research papers as a means of honoring, in a continuing and active way, Dr. Tester's lively encouragement of student research in a broad range of fields in biology. Papers reporting original research in any aspect of biology solicited from graduate students at the university are presented at the spring-semester symposium. Income from contributions to the Albert L. Tester Memorial Fund of the University of Hawai'i Foundation provides two prizes for the best papers. Judges include representatives of the Department of Zoology faculty, winners from the preceding symposium, and a distinguished scholar from another university who also presents a major symposium address. This year Mimi A. R. Koehl, Professor of Integrative Biology, University of California at Berkeley, participated in the symposium.
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    Note of First Records of Isognomon from Easter Island
    (University of Hawaii Press, 1996-04) Ruiz, Cecilia Osorio
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    Fin Whale Sighting North of Kaua'i, Hawai'i
    (University of Hawaii Press, 1996-04) Mobley, J.R. ; Smultea, M. ; Norris, T. ; Weller, D.
    A rare fin whale (Balaenoptera physalus) sighting occurred on 26 February 1994 during an aerial survey of waters north of the Hawaiian island of Kaua'i. The sighting occurred ca. 24 nm north of Makaha Point, at 220 31.5' N, 1590 44.5' W. The fin whale was accompanied by an adult humpback whale (Megaptera novaeangliae) during the entire 25 min of observation. Fin whales are not unknown in Hawaiian waters, but the most recent confirmed sighting on record for Hawaiian waters was 16 February 1979.
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    Macrobenthic Community Structure, Secondary Production, and Rates of Bioturbation and Sedimentation at the Kane'ohe Bay Lagoon Floor
    (University of Hawaii Press, 1996-04) Smith, Craig R. ; Kukert, Helmut
    The Kane'ohe Bay lagoon floor is one of the largest shallowwater, muddy habitats in Hawai'i and is a major repository for sediments and, possibly, pollutants from the Kane'ohe watershed. Nonetheless, macrobenthic community structure, secondary production, and particle-mixing rates at the lagoon floor remain largely unstudied. During 1990-1991, we surveyed macrobenthic community structure at four stations 12 m deep at the lagoon floor and evaluated macrobenthic secondary production, as well as particle mixing and sedimentation, at one representative station. Macrobenthic abundance in the lagoon during our survey was high (44,000-100,000 individuals m-2 ), with very small deposit-feeding polychaetes dominating the community. This lowdiversity assemblage was relatively similar throughout the bay and resembled the communities found in highly depositional environments (e.g., river deltas, and zones of active erosion and redeposition). Macrobenthic secondary production at the representative station was low, with a best estimate of 4.9 g m-2 yr- 1 ash-free dry weight (reasonable range 1.2-20 g m-2 yr- 1); this appeared to be enough production to support <2% of the annual fish yield in Kane'ohe Bay. Tracer-particle experiments at the representative station, sampled after 7 months and 1 yr, indicated low sediment-mixing rates (diffusive mixing coefficient ~0.9 cm2 yr- 1 ), little size dependence in particle mixing, and relatively high short-term rates of sedimentation (6-7 cm yr- 1 ). After corrections for sediment compaction, these short-term sedimentation rates (2.7-3.7 cm yr- 1 ) are about three-fold higher than longer-term (decadal) sedimentation rates (~1.0 cm yr- 1) estimated using Pb-21O geochronology at a nearby site; the discrepancy may be caused by sediment transport from nearby fringing reefs, resuspension of bottom sediments by alpheid shrimp, or interannual variability of sediment flux into the bay. We conclude that the Kane'ohe Bay lagoon harbors a low-diversity, low-productivity macrobenthic assemblage largely structured by high gross sedimentation rates. In addition, we conclude that sandsized particles entering the bay are rapidly (within months) sequestered below the sediment-water interface, where they remain for at least l-yr time scales.
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    Water Quality in a Subtropical Embayment More Than a Decade after Diversion of Sewage Discharges
    (University of Hawaii Press, 1996-04) Laws, Edward A. ; Allen, Colleen B.
    Concentrations of chlorophyll a (chl a), particulate carbon and nitrogen (PC and PN, respectively), inorganic nutrients, and Secchi depths were measured from October 1989 to June 1992 in Kane'ohe Bay, an embayment on the windward coast of O'ahu, Hawaiian Islands. Results were compared with values reported in 1978-1979, the year immediately following diversion of two sewer outfalls from the southeast sector of the bay. Nutrient enrichment experiments indicated that the bay is now distinctly nitrogen limited. In many respects the water column appears more oligotrophic now than in 1978-1979. Inorganic nitrogen and phosphate concentrations now border on the limit of detection by colorimetric methods. Chl a concentrations have declined by 3540% (0.3-0.5 mg m-3 ) and Secchi depths have increased by 15-35% (1.01.5 m) in the southeast sector of the bay since 1978-1979. This has happened despite a population increase of 7,762 persons in the watershed from 1980 to 1990. Characteristics of the water column are now remarkably similar in all sectors of the bay. About 40% of the phytoplankton chl a is accounted for by picoplankton. Pigment analyses indicate that diatoms and cyanobacteria make up ca. 45 and 25%, respectively, of the phytoplankton biomass. It is postulated that the drawdown of inorganic nutrient concentrations and increase in PN/chl a and PC/chl a ratios reflect a shift of the phytoplankton community toward smaller species characteristic of oligotrophic environments. An increase of PN in the central and northwest sectors of the bay is postulated to have been caused by an increase in nitrogen fixation and export from the barrier reef. There is no evidence that human population growth has altered nutrient loading from stream runoff.
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