Tissue-specific trace element accumulation in the coconut crab Birgus latro and its implications for dietary risk assessment and non-lethal biomonitoring

The coconut crab ( Birgus latro ) is the world’s largest terrestrial crustacean and has the potential to accumulate trace elements owing to its longevity and omnivorous diet. Trace element studies in terrestrial crustaceans are scarce, and none has been reported for B. latro . Here, we quantified concentrations of 33 elements, including potentially hazardous metals and metalloids, in B. latro ( n = 9) and evaluated body-size-dependent variation in element concentrations, differences among tissues, and the safety of B. latro as food. We further evaluated the feasibility of a non-lethal monitoring approach for long-term surveillance of this rare species, which has potential as a bioindicator of coastal ecosystem conditions. Cadmium (Cd) and Mercury (Hg) concentrations in cheliped tissue were higher in both the smallest and largest body-size classes than in intermediate-sized individuals. In addition, risk screening indicated that heavy or frequent dietary intake of the hepatopancreas, in which the Cadmium (Cd) concentration reached a maximum of 0.928 µg/g w.w., may raise human health concerns regarding Copper (Cu), Zinc (Zn), Cd, and Lead (Pb), even at the study site, which lacks notable industrialization or intensive agriculture. Non-lethal monitoring using the third pereiopod tissue showed promise, as elemental concentrations in this tissue were positively associated with those in cheliped tissue for multiple elements (e.g., Cu: R² = 0.640, Hg: R² = 0.452). These findings identify the third pereiopod as a promising non-lethal sampling tissue for long-term biomonitoring while also highlighting potential food safety concerns associated with hepatopancreas consumption.