The Mediterranean Sea is warming three to four times faster than the global ocean, with a rapid increase in the frequency of extreme temperature events (e.g., marine heatwaves) and evident consequences for coastal ecosystems. Marine heatwaves (MHWs) not only alter the distribution and abundance of species and therefore ecosystem functions but also act synergistically with other local human threats, reshaping coastal habitats, such as Posidonia oceanica (L.) Delile seagrass meadows. Although previous studies have documented the effects of warming and thermal stress on the growth, physiology, and biochemical properties of P. oceanica, the long-term effects of climatic and local anthropogenic pressures remain poorly understood. Here, we used lepidochronological analysis from 9 Mediterranean locations to assess the effects of MHWs and anthropogenic pressures on production, biochemical properties, stability, and spatial synchrony of P. oceanica, accounting for additional production drivers related to water quality, and to evaluate how such metrics change across multiple spatial scales. The results showed three main outcomes: 1) carbon isotopic composition increased with cumulative MHW intensity, 2) leaf production increased under warmer winter conditions and deeper winter mixed layers, and 3) rhizome biomass, as well as leaf production stability, appeared more influenced by local environmental conditions and anthropogenic pressure than by large-scale thermal forcing. Our study highlights the need to integrate physiological responses, growth dynamics, and temporal variability data to monitor the combined effects of climate forcing, local environmental conditions, and anthropogenic pressures on Mediterranean P. oceanica meadows.