Disparate thermal regimes and selective forces across species’ distributions can drive local adaptation within populations creating differences in vulnerability to warming oceans. To predict responses to warming oceans across latitudinal gradients, it is necessary to determine underlying population-level thermal performance differences (i.e., local adaptation) via the integration of physiological experiments with genetic sequencing. Local adaptation arises when selective forces overcome the homogenizing influences of gene flow and is therefore most common in species with low dispersal ability and/or high self-recruitment. The coral reef damselfish (Acanthochromis polyacanthus) lacks a pelagic larval phase and the ability to easily disperse between reefs yet maintains a large latitudinal range stretching from the Indo-Pacific to the southern Great Barrier Reef; across a (summer) thermal range of ~26°C - 32°C, creating favorable conditions for local adaptation. Within this study, three different populations from the southern (i.e., leading-edge; 27°C summer average temperature) and middle (i.e., core; 28.5°C summer average temperature) regions of A. polyacanthus’s range on the Great Barrier Reef were collected and sampled to create population based thermal performance curves. Population based thermal performance curves were created for aerobic physiology (i.e., standard metabolic rate, maximum metabolic rate, net aerobic scope) and cellular enzymatic (i.e., lactate dehydrogenase) metrics, in addition to inter- and intra-regional population comparisons in immunity metrics. Data from these experiments were integrated with genetic sequencing data from each sampled population to provide a comprehensive understanding of local adaptation and the underlying thermal landscape across the species’ distribution.