Predation of Juvenile Japanese Sea Cucumber Apostichopus japonicus by Kelp Crab Pugettia ferox

Nobuharu Inaba,Hiroshi Kawai,Kohei Matsuno,Takuma Matsumoto,Yuji Anaguchi

doi:10.3389/fmars.2021.684989

Abstract

The predation of commercially important Japanese sea cucumber Apostichopus japonicus by the kelp crab Pugettia ferox, widely distributed in coastal northeast Asia, was examined in field sampling and laboratory experiments. The ossicles of A. japonicus were detected from the stomach contents of a natural population of P. ferox at the rate of 32.4% of 68 individuals collected within artificial intermediate sea cucumber reefs for releasing hatchery-produced juveniles in December 2018. In the following laboratory experiments, a high mortality rate (7.7 ± 2.4 individuals day–1) of juvenile A. japonicus (15.35 ± 2.47 mm) was observed despite the different sizes and sex of P. ferox tested. It was also confirmed that a maximum of five sea cucumbers was killed and cut into small pieces within the first 2 h. Smaller and younger P. ferox individuals (adolescent) between carapace widths of 14.2–17.8 mm actively decorated themselves using pieces of chopped sea cucumber after feeding. Attached pieces of sea cucumber were observed to be fully eaten within a week, suggesting a possible strategy by P. ferox of short-term food storage as well as mimicry. This study demonstrates considerable evidence that predation mortality by sufficiently mobile P. ferox on commercially important A. japonicus can be significant, causing high mortality at the early life stage in the natural environment, especially in areas releasing hatchery-produced juveniles. It is also worth noting that the utilization of freshly chopped sea cucumbers as decoration material and food storage is a unique and novel ecological trait of P. ferox.

Highlights

The Japanese sea cucumber Apostichopus japonicus (Selenka, 1867), an Echinoderm of the class Holothuroidea, is widely distributed along the coast of southern far-east Russia, South Korea, northern China, Japan, and United States (Choo, 2008)
The declining wild population of sea cucumber by overfishing, habitat loss, and human-induced pollution have been described by Purcell et al (2013), and A. japonicus was added to the ICUN Red List of threatened species as “Endangered” in the same year (Mercier and Hamel, 2013)
The ossicles of A. japonicus were detected from the stomach contents at a rate of 32.4%, and averages of carapace width (CW), pseudorostral carapace length (PCL), and wet weight of P. ferox containing ossicles were 12.53 ± 3.00 mm varied from 6.80 to 20.33 mm, 18.10 ± 3.17 mm varied from 11.53 to 24.92 mm, and 1.12 ± 0.85 g varied from 0.18 to 4.11 g, respectively

Summary

Introduction

The Japanese sea cucumber Apostichopus japonicus (Selenka, 1867), an Echinoderm of the class Holothuroidea, is widely distributed along the coast of southern far-east Russia, South Korea, northern China, Japan, and United States (Choo, 2008). The declining wild population of sea cucumber by overfishing, habitat loss, and human-induced pollution have been described by Purcell et al (2013), and A. japonicus was added to the ICUN Red List of threatened species as “Endangered” in the same year (Mercier and Hamel, 2013). Japan has taken the initiative in conservation measures such as regulating the total annual catch, harvest size and adopting a closed season to promote reproduction, the wild stocks of A. japonicus have declined at least 30% in the past 30 years (Choo, 2008). To rebuild the wild stocks around the coast of Hokkaido, the vigorous release of juveniles has been carried out (Hokkaido Government, 2020)

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