Go with the Flow: Morphological Variation of Pocillopora Corals in the Eastern Tropical Pacific

Katherine Griswold

This thesis is part of a larger joint university effort to examine morphological variation and
adaptability of corals of the genus Pocillopora (family Pocilloporidae) in the Eastern Tropical Pacific.
Under generally low flow water conditions, which are disadvantageous for corals’ metabolic
processes, researchers from the Universidad Autónoma de Baja California Sur documented colonies
of the morphospecies P. damicornis as they changed their skeletal structure to a morphotype
associated with P. inflata over the course of 44 months (Paz-Garcia et al 2015a, 2015b). Using
georeferenced data obtained from those observations, the following thesis investigates water velocity
as a potential driver of morphological plasticity for Pocillopora sp., irrespective of genetic lineage.
Photographic data was collected, georeferenced, and analyzed based on structural metrics (average
thickness of colony branches and distance between branches). Morphological diversity and
distribution across spatial scales was assessed using ArcGIS Pro and PAST software. Results support
and refine conclusions from studies inside and outside of the host research institutions (Paz-Garcia
2015, Salazar 2016, Chindapol et al 2013, Smith et al 2017, Soto et al 2018). It was found that
morphological assemblages are not most similarly grouped based on geography. Instead, closed forms
were associated with low-flow water conditions and more open forms were associated with higher
water velocity. Greater morphological diversity was also apparent in low flow conditions. However,
available data limited conclusions to speculative associations. It is recommended that further studies
on this topic consider more appropriate sampling methods to allow for more complex spatial analysis.