Coral Reef Geometry wars: using coral geometry to predict coral competitive outcomes
Corals compete with other sessile organisms for the limited benthic surface. We hypothesized that resources available to fight at a coral’s perimeter depends on the coral’s surface area available for photosynthesis and heterotrophic feeding. To test this hypothesis, the perimeter to surface area ratio of over 50 coral colonies from the Caribbean island of Curaçao were analyzed. A physical and photo chain-link method was used to measure the perimeter length over multiple scales and surface area was calculated using a 3D, overlapping photo method. A visual score of the percentage of coral perimeter losing (%P- losing) the competition to other benthic organisms was also determined. Clade-specific positive relationships between perimeter to surface area ratio (P:SA) and %P-losing were observed in taxa belonging to three separate clades and a negative relationship was found in Montastraea cavernosa. Surface area had a significant negative correlation with %P-losing for all corals. All coral perimeters had a fractal dimension of 1 over a 1 mm – 1 m scale, suggesting that coral perimeters behave more like simple Euclidean shapes than fractal shapes. Together these results show that perimeter to surface area ratios predict competition outcomes for coral at a clade, and possibly guild, level. I propose that the Euclidean shape- like morphology of coral perimeter is a competition strategy to enhance coral success in the war for benthic space.