Abstract
Toxic crabs of the family Xanthidae contain saxitoxins (STXs) and/or tetrodotoxin (TTX), but the toxin ratio differs depending on their habitat. In the present study, to clarify within reef variations in the toxin profile of xanthid crabs, we collected specimens of the toxic xanthid crab Zosimus aeneus and their sampling location within a single reef (Yoshihara reef) on Ishigaki Island, Okinawa Prefecture, Japan, in 2018 and 2019. The STXs/TTX content within the appendages and viscera or stomach contents of each specimen was determined by instrumental analyses. Our findings revealed the existence of three zones in Yoshihara reef; one in which many individuals accumulate extremely high concentrations of STXs (northwestern part of the reef; NW zone), another in which individuals generally have small amounts of TTX but little STXs (central part of the reef; CTR zone), and a third in which individuals generally exhibit intermediate characteristics (southeastern part of the reef; SE zone). Furthermore, light microscopic observations of the stomach contents of crab specimens collected from the NW and CTR zones revealed that ascidian spicules of the genus Lissoclinum were dominant in the NW zone, whereas those of the genus Trididemnum were dominant in the CTR zone. Although the toxicity of these ascidians is unknown, Lissoclinum ascidians are considered good candidate source organisms of STXs harbored by toxic xanthid crabs.
Highlights
Toxic crabs of the family Xanthidae accumulate saxitoxins (STXs) and/or tetrodotoxin (TTX) and pose a threat to human health [1] (Figure 1)
The present study revealed small-scale within reef variation in the toxin profile of
We demonstrate that a single reef may contain zones that can be delineated by the toxin profiles of the inhabitants: a zone in which the crabs accumulate extremely high concentrations of STXs (NW; STXs-rich zone) and a zone in which the crabs generally contain small amounts of TTX and little STXs (CTR; STXs-poor zone)
Summary
Toxic crabs of the family Xanthidae accumulate saxitoxins (STXs) and/or tetrodotoxin (TTX) and pose a threat to human health [1] (Figure 1). The molecular weight, toxicity, and intoxication mechanism of the best-known component of STXs, STX, are similar to those of the pufferfish toxin, TTX [3]. Poisoning incidents due to toxic xanthid crabs are reported around the world, including. Australia, Taiwan, and the Philippines, and several epidemiologic investigations, including identification of the causative toxin, have been conducted [4–11]. The toxicity and toxin profile of xanthid crabs vary greatly depending on the species and/or habitat. Atergatis floridus, and Platypodia granulosa, which inhabit coral reefs in the Ryukyu and Amami Islands in Japan, the Philippines, and Australia, are generally highly toxic and contain STXs as their main toxin [4,7,11,12], whereas Z. aeneus from the Tokara Islands in Japan; A. floridus from the Pacific coast of mainland Japan;
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