Total Mercury Levels in Sea Cucumbers Holothuria polii and Holothuria tubulosa and Sediments from Two Sites of Southern Italy

Abstract Holothurians are increasingly recognized as bioindicators and bioremediators in marine ecosystems. This study assessed the relationship between total mercury (THg) levels in Holothuria polii and Holothuria tubulosa from two Southern Italian coastal sites differing for ecological and anthropogenic characteristics, and those in corresponding marine sediments. THg levels in holothurians were consistently low across species and sites (0.0022–0.0146 mg kg − 1 wet mass) and showed no direct correspondence with sediment levels, which were high (1.5080 ± 1.1687 mg kg − 1 dry mass) at the Ionian site (IS), and low (0.0055 ± 0.0028 mg kg − 1 dry mass) at the Adriatic site (AS). Despite lower sediment mercury contamination, the bioconcentration factor, indicator of the efficiency of metal bioaccumulation was higher at the AS site (3.54–4.76) than at the IS site (0.021–0.022), suggesting different mercury bioavailability in the sites. Size-related analyses of THg in holothurians indicated that THg levels in individual holothurians correlated positively with body size ( p < 0.05), except for H. tubulosa from AS. Results demonstrate that site-specific factors, more than species-specific ones, play a key function in controlling mercury bioavailability and uptake in the studied holothurians, supporting their potential role in environmental monitoring and their safe consumption in the studied areas.