Pacific Science Volume 52, Number 1, 1998

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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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    Dictyostelid Cellular Slime Molds from Hawai'i
    (University of Hawaii Press, 1998-01) Landolt, John C. ; Wong, George J.
    Soil and litter samples, collected from Hawai'i on the islands of Hawai'i, O'ahu, and Kaua'i, were examined for occurrence and distribution of dictyostelid cellular slime molds. In total, 194 samples, from 20 different sites and representing several plant communities, were collected during June 1995 and processed in the laboratory soon thereafter. A total of 10 species and one variety was recovered, seven of which have not been reported previously from Hawai'i. The greatest species richness (seven) and highest densities (up to 63 clones per gram of fresh soil/litter) were found on the island of Hawai'i, with lower values obtained for sites on O'ahu and Kaua'i. It was rare for dietyostelids to be recovered from more than 30% of the samples collected at any given site. A number of sites were characterized by recovery of a single species, and at least one site on each island sampled was devoid of recoverable dictyostelids. Overall, dictyostelid densities were quite low compared with those at other locations in subtropical and temperate regions of the Northern Hemisphere, and the values for species richness are lower than those reported for most neotropical mainland locations. These observations suggest a rather modest dictyostelid community in Hawai'i, at least during the relatively dry period when sampling was carried out. Lack of a windborne dispersal mechanism may be responsible for the limited distribution of dictyostelids in Hawai'i and possibly other island groups that are remote from continental land masses.
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    Time Variation in Phytoplankton Assemblages in a Subtropical Lagoon System after the 1982-1983 "El Nino" Event (1984 to 1986)
    (University of Hawaii Press, 1998-01) Garate-Lizarraga, Ismael ; Beltrones, David A. Siqueiros
    An analysis of seasonal and geographical distribution and abundance of the total and separate fractions of phytoplankton (nanno- and microphytoplankton) in the Magdalena-Almejas lagoon system was done after the 1982-1983 "El Nino" event. In spite of its being in a subtropical region, the annual variation of phytoplankton abundance in the area was similar to the annual cycle of production of coastal lagoons in temperate regions. There were two peaks of phytoplankton abundance, in spring and in autumn. The upwelling and tidal currents enriching the waters of Bahia Magdalena were responsible for the high concentrations of phytoplankton in the bay. Microphytoplankton was the most important fraction throughout the study period. Nannophytoplankton was somewhat abundant. Using principal component analysis, seasonal variation and frequency were the two factors determining the structure of species assemblages. Lowest values of diversity and dominance were related to circulation patterns and to the phytoplankton blooms that occurred throughout the year in Bahia Magdalena-Almejas. High values of diversity and low dominance were estimated at those areas under the influence of oceanic waters. The 1982-1983 El Nino caused a drastic drop in phytoplankton abundance during 1984. The recuperation process was slow, starting in 1985 and completed by 1986. Recorded increases in phytoplankton abundance surpassed all previous records. "El Nino" caused changes in the structure of the microphytoplankton assemblages. Species richness and specific diversity diminished because of the occurrence of few species.
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    Understory Succession Following a Dieback of Myrica faya in Hawai'i Volcanoes National Park
    (University of Hawaii Press, 1998-01) Adler, Peter B. ; D'Antonio, Carla M. ; Tunison, J Timothy
    Studies of invasion by the introduced nitrogen-fixing tree Myrica faya Aiton in Hawai'i Volcanoes National Park have led to predictions that the nitrogen-rich soil M faya creates will promote invasion by nonindigenous plant species. An insect-caused dieback of M. faya that began in the late 1980s provides an opportunity to test this hypothesis. We compared· percentage cover and density of all plant species under live and dead M. faya, as well as total nitrogen in soil and plant tissue. Mean percentage cover of four common species increased significantly, and no species decreased in cover after dieback. Cover of native shrubs and herbs increased from 4.8 to 15.2%, largely due to the spread of Carex wahuensis C.A. Mey, and introduced grasses increased from 2.3 to 14.1%. Density of native shrubs did not differ beneath live and dead M. faya, but immature introduced grass individuals were significantly more numerous beneath dead M. faya. We found no differences in total nitrogen in soil or plant tissue collected beneath live versus dead M. faya. Beneath dead M. faya, cover of C. wahuensis increased with total soil N, and introduced grass cover decreased. This surprising result may be the legacy of shading effects from the live M. faya canopies, for which total soil N may be an indicator. Success of grass seedlings compared with failure of native shrubs to recruit from seed suggests that dieback promotes nonnative grass species. Replacement of M. faya with introduced grasses may greatly increase fire risk.
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    A Remnant Greensword Population from Pu'u 'Alaea, Maui, with Characteristics of Argyroxiphium virescens (Asteraceae)
    (University of Hawaii Press, 1998-01) Carr, Gerald D. ; Medeiros, Arthur C.
    Two unusual greenswords occurring on Pu'u 'Alaea in 1989 reportedly possessed vegetative features characteristic of the presumed extirpated species Argyroxiphium virescens Hillebr. One of these Pu'u 'Alaea plants flowered in August 1989, allowing detailed comparisons with preserved specimens of A. virescens as well as other species and hybrids of Argyroxiphium native to East Maui. These comparisons suggest that the unusual Pu'u 'Alaea greenswords represent remnants of hybridization between the now presumably extinct A. virescens and the more common Haleaka silversword, A. sandwicense subsp. macrocephalum (A. Gray) Meyrat, that still occurs at and adjacent to this site. The estimated pollen fertility of 62% in the Pu'u 'Alaea plant is consistent with this interpretation. Recovery of a few embryos from fruits of the plant that flowered in 1989 and the possibility of tissue culture of the remaining living plant at Pu'u 'Alaea apparently represent the last opportunities to conserve any vestige of A. virescens.
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    A New Species of Megalomma (Annelida: Polychaeta: Sabellidae) from Phuket, Thailand
    (University of Hawaii Press, 1998-01) Nishi, Eijiroh
    Megalomma miyukiae Nishi, n. sp., occurred among dead coral rubble at Phuket, Thailand. This species has two to ten branchial eyes on the tips of radioles, a collar with developed ventral lappets, and free dorsal margins separated by a wide gap. Scanning electron micrographs show the fine structure of chaetae.
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