¹National Marine Fisheries Service, Southwest Fisheries Science Center Honolulu Laboratory, Honolulu, Hawai'i, USA

Mary.Donohue@noaa.gov

　

²Joint Institute for Marine and Atmospheric Research Honolulu, Hawai'i, USA

　

The endangered Hawaiian monk seal, Monachus schauinslandi, currently numbers 1300-1400 individuals. All six main breeding subpopulations occur within the Northwestern Hawaiian Islands (NWHI). Derelict fishing gear from throughout the North Pacific Ocean accumulates in the region of the NWHI where extensive, shallow coral reefs act as a filter for floating debris. Debris directly impedes monk seal recovery due to entanglement injury and mortality. Our objective was to investigate monk seal entanglements in relation to El Nio events and to propose a mechanism by which entanglement might be influenced by El Nio events. We review historic monk seal entanglement and oceanographic data from 1982 to 2001. Documented monk seal entanglements varied significantly by year, ranging from 2 to 25. Five periods of relatively elevated entanglement occurred in 1982, 1987-89, 1992, 1995-96 and 1998-99, concurrent with or immediately following El Nio events. The Hawaiian Archipelago lies just south of an oceanic zone where wind effects cause surface floating debris to collect or converge. Since 1992, Advanced Microwave Instruments scatterometers onboard European Remote-Sensing Satellites. ERS-1 and ERS-2, have provided ocean surface wind vector measurements from which analyses of spatial and temporal variation of the wind-induced oceanic convergence are derived. The convergence zone is generally found between 30N to 42N Latitude. However, during 1992, 1995, and 1997-98, which are also El Nio years, this convergence intensified and extended as far South as 28N. We hypothesize that in years when this convergence shifts southward reaching the NWHI, a regional increase in marine debris abundance will occur, along with increased monk seal entanglement. This study demonstrates how global climate processes may influence the recovery of an endangered species and highlights the utility of an ecosystem level approach in endangered species management.

　

　

Centre for Research on Ecological Impacts of Coastal Cities - The University of Sydney Sydney, NSW, AUSTRALIA

wwidmer@bio.usyd.edu.au

　

Although the main sources of marine litter are considered to be land-based, water-based activities may also be significant. Therefore, in the first part of this study the hypothesis that recreational boating is a contributing source of benthic marine debris was tested by collecting information about the number of recreational boats anchored at six beaches in Sydney Harbour and the quantity of debris off these beaches.

　

A significant positive correlation was found. The greatest amount of debris was found adjacent to the two beaches most visited by recreational boats, both situated inside a marine protected area. The most frequent types of litter were plastic bags, aluminum cans and glass bottles.

　

In the second part of the study, an experimental approach was used to test hypotheses about fouling assemblages on the three types of litter mentioned above. Several independent replicates of these litter types were deployed in the subtidal zone of two locations in Sydney Harbour and the percentage cover of fouling organisms on them were analysed over a period of six months.

　

The structure of assemblages of fouling organisms on natural substratum (sandstone plates) and on litter items were found to be dependent on location. Of the types of litter examined, only assemblages on plastic bags were consistently different from those on sandstone plates. Large amounts of bare space and silt matrix, and the presence of opportunistic taxa suggest that the biological assemblages had been frequently disturbed. Implications of these results to management and restoration attempts of littered areas are discussed.

　

　

Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus Motobu-cho, Okinawa, Japan

sakaikz@lab.u-ryukyu.ac.jp

　

Coral communities in the Ryukyus Islands were much affected by the mass-bleaching event that occurred in the hot summer of 1998. Mortality of hard and soft corals was especially high around Okinawa Island. In this presentation, I report the changes in coral community structure through the mass-bleaching event and recovery process of the communities after the bleaching around Sesoko Island, which is located at northern Okinawa...

　

Percent cover of hard corals decreased up to 95% through the mass-bleaching event around Sesoko Island. The degree of the decrease was dependent of dominant corals before the event: reefs that were dominated by bleaching susceptible species (Acropora spp.) suffered great reduction in hard coral cover, while reefs dominated by bleaching tolerant species (Porites spp.) suffered a little reduction. At southeastern reef of Sesoko Island, where precise monitoring was conducted, percent cover of hard and soft corals was decreased by 85%, and species richness of hard corals was decreased by 61%, resulting local extinction of some branching species such as Pocillopora damicomis, Stylophora pistillata, and Seriatopora hystrik (Loya et al., 2001).

　

Observations of coral recruits in 2000 suggested that some exposed reefs around Sesoko had recruitment of Acropora in 1999 at similar level before the mass-bleaching events. The absence of sexually mature Acropora colonies around Sesoko in 1999 indicates that the recruits were originated from coral larvae produced elsewhere. Kerama Islands, where coral mortality was low in 1998, might be a source area of the coral larvae. Analysis of gene flow of Acropora digitifera using allozyme electrophoresis supported this. In 2001, density of Acropora recruits declined to half at a reef where the density was the highest in 2000. Recovery of coral communities have not progressed linearly after the mass-bleaching event around Sesoko Island.