Morphological Plasticity as a Response to Environmental Heterogeneity: A Comparative Study of Porites lobata in the Spermonde Archipelago and Bone Gulf, Indonesia

Abstract

Phenotypic plasticity enables reef-building corals to respond to environmental variability through modification of morphological characters. This study analyzed the morphological plasticity of Porites lobata from three locations in South Sulawesi, Indonesia: the Spermonde Archipelago (n = 30), Bone Gulf (n = 12), and Taka/Bone Control (n = 6). Morphometric analysis of 21 numerical skeletal characters using Welch's independent-samples t-test revealed 7 characters that differed significantly between Spermonde and Bone (p<0.05), in a bidirectional pattern: four characters were larger in Bone (maximum columella diameter +42.6%; minimum lateral palus diameter +55.5%; lateral septa spacing +18.8%; palus count +12.2%), while three were larger in Spermonde (ventral palus spacing +38.6%; dorsal palus spacing +37.5%; fossa width +17.7%). Taka exhibited the largest corallite dimensions among all sites (29.8% larger than Bone; p<0.001). Of the seven water quality parameters tested, only temperature (p = 0.017) and nitrate (p = 0.026) differed significantly between Spermonde and Bone. Nitrate was negatively correlated with columella diameter (r = −0.999), and dissolved oxygen was positively correlated with palus count (r = 0.983). These findings indicate that P. lobata expresses two functionally distinct plasticity strategies across sites. In Bone Gulf, lower nitrate and higher dissolved oxygen supported more complex corallite architecture, consistent with more efficient skeletal calcification. In Spermonde, a more open architecture reflected in wider palus and fossa spacing appears to facilitate passive sediment clearance and enhance heterotrophic feeding capacity, offsetting reduced autotrophic productivity under multi-stressor conditions.