The combined effects of marine heatwaves and heavy metals on metal accumulation in macroalgae

Heavy metal pollution and marine heatwaves (MHWs) are critical, escalating stressors impacting coastal macroalgae, key organisms in metal accumulation and ecosystem functioning. Using a bibliometric analysis (711 articles, 2005-2024), this review synthesizes research on their combined effects on macroalgal metal accumulation. Analysis reveals burgeoning interest in this interdisciplinary field, highlighting growing global attention to marine climate-pollution interactions. The review demonstrates that MHWs significantly modulate metal accumulation in macroalgae through altered metabolic rates, growth dynamics (leading to dilution or concentration effects), and compromised cellular integrity. Conversely, heavy metal exposure can exacerbate thermal stress responses, inducing oxidative damage and impacting fundamental physiological processes like photosynthesis. These interactions manifest as additive, synergistic, or antagonistic effects, varying across macroalgal types due which exhibit diverse thermal sensitivities. Crucially, while basic metal uptake mechanisms (e.g., adsorption, active transport) are established, a significant knowledge gap persists in understanding how MHWs mechanistically alter these pathways under combined stress. Furthermore, MHWs rarely occur in isolation, often interacting with other environmental factors (e.g., ocean acidification, nutrient regimes), adding layers of complexity to metal accumulation patterns. This comprehensive overview identifies critical research gaps, including the pressing need for more direct mechanistic investigations, realistic multi-stressor eco-physiological studies, detailed assessments of trophic transfer and ecosystem-level impacts, and long-term field observations. By enhancing our understanding of the complex interplay between MHWs, heavy metals, and metal accumulation in macroalgae, this review supports the development of robust adaptive strategies for marine conservation and pollution management in a warming ocean.