Differential sensitivity of Saccharina latissima (Phaeophyceae) to emissions from corrosion protection systems informs biomonitoring strategies

Corrosion protection systems used on offshore structures release metals or chlorine-produced oxidants into surrounding waters. Yet, their effects on marine biomonitoring species remain poorly understood. Here, we assess how emissions from induced current cathodic protection systems and zinc- and aluminium-based galvanic anodes affect the early developmental stages of the kelp Saccharina latissima. Zoospores and gametophytes were exposed for three weeks to metals or chlorine-produced oxidants at concentrations ranging from 0.5 to 2500 micrograms per liter under controlled laboratory conditions. Developmental success, survival, and early sporophyte growth were quantified. Our results show that chlorine-produced oxidants from induced current systems caused the strongest inhibition in exposed gametophytes, resulting in reduced growth above 50 micrograms per liter and complete developmental failure at the highest exposure. Zinc and aluminium from galvanic anodes produced comparatively weaker effects in exposed gametophytes, with effects emerging at 500 micrograms per liter, well above concentrations typical of offshore environments. However, sensitivity to zinc and aluminium was greater during the zoospore stage, likely due to the absence of a protective extracellular matrix. Our results provide a basis for determining a safe distance from corrosion protection sources using sensitivity thresholds and suggest the use of transplanted sporophytes for robust biomonitoring strategies. S. latissima is robust against environmentally realistic metal emissions from galvanic anodes but potentially less resistant to oxidants produced by impressed current cathodic protection systems.