Fig 1.
Conceptual diagram of processes occurring on emergent reefs, submerged pinnacles and seamounts.
Interactions between abrupt submerged physical structure, incident mean current (Umean), eddies (solid blue arrows), internal waves (Uwi), turbulence (K), oscillating flows and the water column above can lead to doming, upwelling and vertical circulating cells near or above an isolated seamount summit (dashed blue arrows). Adapted from Lavelle and Mohn [43]. Similar processes seem plausible on submerged pinnacles but may not generate larger scale disruptions to current flow like island wakes () or trapped cells above the summit (e.g. Taylor Cones). On emergent reefs, most hydrodynamic energy is focused on the crest, and particularly in nearshore positions, is dominated by tides and surface waves. Solid blue arrows represent currents such as eddies moving either above, around or up the slopes of the different bathymetric features. Depth on the y-axis is not to scale and intended only as an aid to distinguish these submerged morphologies.
Fig 2.
Study site, Kimbe Bay, Papua New Guinea.
Reef type for each site is indicated by the colour of marker circle, nearshore emergent (yellow), offshore emergent (blue) and pinnacle (green). Four dashed boxes represent the 4x4 km grids used to collect average Sea Surface Temperatures (SST) over the same annual period.
Fig 3.
GLMM comparing current speeds between three distinct reef types.
a) Annual daily mean current speed (m s -1) and 95% confidence intervals at each reef type. b) Pairwise contrast estimates based on adjusted Tukey’s tests with 95% confidence intervals. Means are estimated marginal means and contrast estimates represent the difference between each pairwise comparison. 95% confidence intervals for pairwise contrasts are interpreted as significant if the interval does not contain zero.
Fig 4.
Temperature and current speed time series 2018–2019 at three distinct reef types.
a) daily mean temperature (°C) and b) daily mean current speed (m s -1) at nearshore (yellow, n = 4 sites, 1440 observations), offshore (blue, n = 3 sites, 1080 observations) and pinnacle (green, n = 4 sites, 1440 observations) reefs in Kimbe Bay between Sept 2018 –Sept 2019. The dashed line in the temperature panel (a) represents daily mean sea surface temperature (SST) obtained from remote sensing data and averaged over 4x4km grid squares corresponding with the locations of study reefs in Kimbe Bay (200 daily observations).
Fig 5.
Comparison of temperature and current speed variability between three distinct reef types.
Notched boxplots for daily average temperatures a) and current speeds b) during each seasonal period throughout the year 2018–2019. Boxes represent the interquartile range (25th-75th percentiles) and thicker black lines within each box are the median. Notches around the median show 95% confidence intervals where non-overlapping notches suggest evidence of a significant difference between the medians given by m ± 1.58 × IQR/√n. c) Frequency density plots for daily average temperatures throughout the year 2018–2019 (all seasons combined). Dashed lines represent the 25th and 75th percentiles. The median is shown as the solid vertical line at the 50th percentile.
Fig 6.
Current rose plots for individual sites.
The strength (m s-1) and frequency of direction (percentage) of currents is visualised at each site. The bolded degrees in each plot is the average current direction for that reef, calculated by vector analysis. Letters a-k correspond to site locations in Fig 2. Plots were constructed using hourly means from each site for the 1-year study period.
Fig 7.
GLMM comparing in-situ temperature between three distinct reef types and sea surface temperature.
a. Annual daily mean temperature (°C) with 95% confidence intervals at each reef type and for SST. b. Pairwise contrast estimates and 95% confidence intervals from adjusted Tukey tests. Means are estimated marginal means and contrast estimates represent the difference between each pairwise contrast. 95% confidence intervals for pairwise contrasts are interpreted as significant if the interval does not cross zero.
Fig 8.
Polar plots for individual sites.
The direction (degrees from north), strength (m s -1) and sub-surface temperature (°C at 25–30 m) of currents is shown at each reef site. Letters a-k correspond to site locations in Fig 2. Plots were constructed using hourly means from each site for the 1-year study period, represented by each coloured pixel.
Table 1.
Reef type summaries of temperature and current speeds.
Absolute minimum, maximum and range of temperature and current speeds recorded at each reef type during the study period. Site-specific values are listed in S17 Table in S1 File.