Changes in the marine habitat and biota of Pelekane Bay, Hawai’i
over a 20-year period
Brian N. Tissot

Materials and Methods

The study site included the areas previously surveyed by Ball (1977) and Chaney et al. (1977) which includes Pelekane Bay and the areas immediately adjacent to the bay (Figure 1). The one exception is the intertidal zone, which was not surveyed during this study. Surveys were focused on estimating changes in the abundance and distribution of habitat types and the abundance of invertebrates and fishes in the study area relative to those estimated in earlier studies.

The relative abundance of different habitat types within the bay were estimated using both quantitative and qualitative methods. First, the area was examined by freely swimming the entire study site. Using the descriptions in Chaney et al. (1977) we searched for distinct habitat types primarily based on the composition of the substratum (silt, coral rubble, or live coral). Within each habitat type, species lists were compiled and the relative abundance of each species was noted. Infaunal macro-invertebrates were examined by manually taking samples of the sediment to 10 cm depth and visually identifying the species present. In addition, the shape, size and position of animal burrows were also noted.

In order to estimate the relative area of each habitat type, a transect line was extended across the bay in a NW-SE orientation. The distance on the transect where habitat type changed was noted and three-five 0.25 m2 quadrats were placed within each habitat and the percent cover of substratum composition was estimated. In addition, aerial photographs were taken on July 31, 1996 from an altitude of 500-1500 m (Figures 2-3) in order to provide a visual estimate of habitat area and a reference for future studies.

In order to resurvey the areas quantitatively sampled by Chaney et al. (1977) we established three, parallel 50m transects in patch reefs located at the southern mouth of the bay (Figure 1). The transects were oriented in a NW-SE direction and were spaced approximately 20 m apart. The ends of each transect were marked by stainless steel pins cemented into holes drilled into dead coral heads.

Fishes were visually surveyed on these transects at the same time of day on three different days (mid-morning on 21 January, 8 March, and 28 April, 1996) by 2-3 different observers for a total of 24 separate transect-surveys. During each survey each observer surveyed all three transects. Fish abundance was estimated by slowly swimming the transect and counting fish occurring within 2 m of each side of the line. Data from each observer was pooled and averaged for each transect. Thus a total of 200 m2 was surveyed on each transect for a total area of 600 m2 , which was repeatedly sampled nine times. The total area previously surveyed by Chaney et al. (1977) was 1000 m2, which was sampled once.

The abundance of macro-invertebrates, corals, seaweeds and other bottom substrates were estimated by sampling 10 randomly placed 0.5 m2 quadrats along each permanently marked transect line. Macro-invertebrate abundance was estimated by counting the number of individuals seen within the transect. Thus a total of 5 m2 was surveyed on each transect for a total area of 15 m2. Chaney et al. (1977) did not quantitatively survey macro-invertebrates.

The percent cover of corals, seaweeds and other substrates was estimated by recording the substrate type under nine points within each quadrat delineated by intersecting mono-filament lines. Thus, a total of 270 points were sampled. Corals were sampled by Chaney et al. (1977) using two 50 m line transects. Ball (1977) did not quantitatively sample marine plants.


Last update: 1/25/2005