Pacific Science Volume 56, Number 4, 2002

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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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    Polychaetes Associated with a Tropical Ocean Outfall: Synthesis of a Biomonitoring Program off O'ahu, Hawai'i
    (University of Hawai'i Press, 2002-10) Bailey-Brock, J.H. ; Paavo, B. ; Barrett, B.M. ; Dreyer, J.
    A comparison of benthic polychaete communities off the Sand Island Wastewater Outfall was undertaken to recognize organic enrichment indicator species for Hawaiian waters. Primary-treatment sewage is discharged off the south shore of O'ahu at 70 m depth. A historical data set spanning 9 yr for seven sites at 70 m and two recent studies at 20, 50, and 100 m depths were analyzed. Geochemical data did not support the assumption that the outfall is an important source of organic enrichment in nutrient-poor sandy sediments within oligotrophic tropical waters. Five polychaete species, however, appeared particularly sensitive, positively or negatively, to environmental conditions near the outfall. Neanthes arenaceodentata (Nereididae) and Ophryotrocha adherens (Dorvilleidae) have been dominant at sites within the outfall's zone of initial dilution (ZID). Since 1993, N arenaceodentata has virtually disappeared, and 0. adherens concurrently became abundant and continued to flourish at ZID sites. Well known indicators within the Capitella capitata complex (Capitellidae) were present at ZID and control (far field) sites though their ZID abundance was greater. Two sabellids, Euchone sp. Band Augeneriella dubia were inversely distributed, the smaller Euchone sp. B at far field sites and larger A. dubia within ZID stations. The former was most likely restricted to a greater proportion of fine sediment particles at two far field sites. The most abundant and widespread polychaete off O'ahu's south shore was Pionosyllis heterocirrata (Syllidae), which does not seem to represent a sensitive indicator species. Ophryotrocha adherens was the most abundant indicator species within the ZID; P. heterocirrata was the most ubiquitous species at all sites and should always be expected in these sediments. Traditional measurements of numerical abundance, species richness, and diversity (H') have not shown a clear distinction between ZID and far field sites in annual analyses. An examination of composited data over an 11-yr period does support such a distinction. Multidimensional scaling (MDS) analyses clearly delineate different assemblages. We suggest that MDS analyses are sensitive to the community differences present near the outfall. The ZID community is clearly contained within the Environmental Protection Agency-approved ZID boundary. Because each ZID and far field site supports a diverse and coarsely similar polychaete fauna, no pollution level effects seem to be present.
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    Comparison of Managed and Unmanaged Wedge-Tailed Shearwater Colonies on O'ahu: Effects of Predation
    (University of Hawai'i Press, 2002-10) Smith, David G. ; Polhemus, John T. ; VanderWerf, Eric A.
    On O'ahu, Wedge-tailed Shearwaters (Puffinus pacifieus) and other seabirds nest primarily on small offshore islets, but fossil evidence shows that many seabirds formerly bred on O'ahu itself. Predation by introduced mammals is suspected to be the primary factor preventing shearwaters and other seabirds from reestablishing large nesting colonies on O'ahu. We investigated the effects of predation on Wedge-tailed Shearwaters by comparing three small unmanaged colonies at Malaekahana State Recreation Area on O'ahu, where feral cats are fed by the public, with a large managed colony at nearby Moku'auia Island State Seabird Sanctuary, where predators are absent. During three visits on 19 April, 16 June, and 23 October 2000, we located 69 occupied burrows in three colonies at Malaekahana and 85 occupied burrows in four monitoring plots at Moku'auia. Many more nests produced chicks at Moku'auia (62 %) than at Malaekahana (20%). Among plots at Malaekahana, reproductive success was lowest (zero) at the colony closest to the cat feeding site. In addition, 44 adult shearwater carcasses were found at Malaekahana near the cat feeding site. Predation, most likely by cats attracted to supplemental food, had a devastating impact on shearwaters at Malaekahana. At one colony there was complete reproductive failure and almost all adults were killed. Populations of long-lived species like seabirds are sensitive to adult mortality, and Malaekahana may act as a sink, draining birds away from other areas.
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    Rough-Toothed Dolphins (Steno bredanensis) as Predators of Mahimahi (Coryphaena hippurus)
    (University of Hawai'i Press, 2002-10) Pitman, Robert L. ; Stinchcomb, Charles
    We present details of four separate observations of rough-toothed dolphins (Steno bredanensis) apparently preying on adult-sized (>or=1 m) mahimahi (Coryphaena hippurus) in the eastern Pacific. We cite similar sightings from Hawai'i and some additional behavioral observations (synchronized swimming, food sharing, regular association with flotsam), and suggest that rough-toothed dolphins may be specialized predators on large mahimahi.
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    Mass Oviposition and Egg Development of the Ocean-Skater Halobates sobrinus (Heteroptera: Gerridae)
    (University of Hawai'i Press, 2002-10) Cheng, Lanna ; Pitman, Robert L.
    We report the first observation of mass oviposition by the ocean-skater Halobates sobrinus White in the eastern tropical Pacific Ocean. We netted, in one scoop, 833 insects and a single egg mass with an estimated 70,000 eggs on a plastic gallon (3.785-liter) milk jug. Evidently anthropogenic debris could provide potentially important oviposition substrates for Halobates spp. in the open ocean. Freshly laid eggs incubated at 26-32°C hatched within 8-10 days. Eggs kept at temperatures below 22°C did not hatch even after 20 days.
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    Watershed-Scale Comparisons of Algal Biodiversity in High-Quality Proximate Hawaiian Stream Ecosystems
    (University of Hawai'i Press, 2002-10) Sherwood, Alison R. ; Kido, Michael H.
    The stream macroalgal floras of two proximate, high-quality stream valleys (Hanakapi'ai and Limahuli) located on the northern quadrant of the Hawaiian island of Kaua'i were inventoried and compared on a watershed scale, providing interesting insight into Hawai'i's potential taxonomic diversity and the influential role played by physical factors in shaping community characteristics. A total of 26 species of macroalgae (five Cyanophyta, 18 Chlorophyta, one Rhodophyta, and two Chromophyta) was identified, of which only eight were common to both streams. Chlorophyta composed the majority of macroalgal taxa identified (63.2% in Hanakapi'ai Stream and 66.7% in Limahuli Stream). Three macroalgal species are new records for Hawai'i and one (Chamaesiphon curvatus var. elongatum Nordst.) is a Hawaiian endemic. Significant differences in the macroalgal densities between Hanakapi'ai and Limahuli Streams (Chlorophyta versus Chromophyta, respectively) were attributed to measured differences in riparian canopy cover (34.8% versus 70.0% closed, respectively). Significantly lower densities of macroalgal species in rime-run habitats in Hanakapi'ai as compared with Limahuli Stream were potentially explainable by "top-down" control by robust populations of native herbivorous fish species.
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