Moorea Porites Size-frequency distributions
Description
These data allows to determine if Porites populations are gueninely stable or are merely surviving as remnant taxon within a depauperate community across lagoonal and bay sites around Moorea Island. To answer this question, we have used the "Size structure" or "Size-frequency distribution" approach that gains valuable insights into demographic dynamics such as : coral post-settlement (by measuring the lowest coral size), growth and mortality patterns. We have also used the "marine substrate" approach to assess the total living coral cover, and the Porites relative abundance (assess the coral community composition). We have compared both approaches, they are complementary. We also used the "marine substrate" approach to quantify some environmental conditions such as macroalgae cover and grain size (proxy of hydrodynamic conditions and sedimentation). By correlations statistics, we have quantified relations between these coral size + coral cover variables and the environmental conditions. The R code and all csv files allow to get all the results and figures mentionned in the study. If you have any questions, please feel free to contact the corresponding author. Thank you, Aitu Raufauore
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Four lagoonal sites and 2 bay sites were chosen in this study. Coral size was measured using a transect-based survey method targeting Porites colonies. At each site, three transects (30m long per 6m wide, covering 180 m2 each) were randomly positioned a few meters apart. All Porites colonies located within the transect area were photographed from the top with an appropriate scale reference. For very large colonies, photographs were taken with a fisheye lens mounted on Olympus TG7, which introduced an image distortion, subsequently corrected using the flattening function in the DxO Photolab 7 software. The planar surface area of each colony was then measured from the calibrated photographs, by manually outlining the total colony area, as a proxy for colony size. Manual delineation was performed in the software ImageJ using the “area” tool (Abramoff et al., 2004). Partial mortality was quantified by delineating and measuring the area of dead tissue (Rich et al., 2022). Partial mortality was calculated for each colony as the proportion of dead tissue relative to its total planar surface area, and expressed as a percentage. For each transect, the mean partial mortality was obtained by averaging individual colony values. The proportion of injured colonies is estimated by counting colonies exhibiting partial mortality at any levels. Colonies at each transect and site were assigned to size classes, following the method of Bak and Meesters (1998). Size-frequency distributions were obtained by counting the number (frequency) of colonies per size class. To check normality and to better visualize distributions, colony sizes were log10‑transformed, following the method of Bak and Meesters (1998). From these log10‑transformed distributions, we calculated key descriptive statistics: colony minimum size (10th percentile), colony mean size (geometric mean), colony maximum size (95th percentile), size variability (coefficient of variation), relative proportion of smaller vs. larger colonies (skewness), and the number of dominant size classes (kurtosis). To characterize benthic cover, the following categories of benthic substrates were recorded along 30m-line transect using the point‑intercept method: macroalgae cover, sand cover, Porites cover, other dominant coral genera cover and dead coral cover (English et al., 1997). Substrate covers were expressed as relative proportions. Coral cover was calculated as the sum of Porites cover and other dominant coral genera cover. The relative abundance of Porites spp. (hereafter referred to as Porites spp. relative contribution) among all alive coral genus was also calculated on coral covers. Sediment grain sizes were analyzed from three sediment samples collected at each site, using an AS 200 mechanic granulometer at Bordeaux University with sieves. The relative proportions of each size fraction were calculated to characterize the sediment size composition. Statistical analysis were used to interpret these data.
Institutions
- Université de BordeauxNouvelle-Aquitaine, Bordeaux