Age determination in echinoderms: first evidence of annual growth rings in holothuroids

Abstract

While age is fundamental in animal biology, forming the basis of critical concepts such as life-history strategies, longevity and population structures, measuring this variable in some taxa remains problematic. Such is the case of holothuroid echinoderms, which play key roles in marine benthic communities from the shore to the abyss, and which are extensively fished in many regions across the globe. Here, we present and validate a promising ageing technique using the cold-water species Psolus fabricii . The method involves the extraction of the oldest dermal plates (largest dorsal ossicles) to preserve their original pigments and structure. While plates initially appear to have a uniform texture, polishing and dying them reveals layered ring patterns. A study of laboratory-reared juveniles, from settlement to 40 months of age, confirmed that one layer is added annually, making plates both larger and thicker, and generating successive light and dark rings, the latter representing the transition (overlap) between two layers. Therefore, each pair of rings represents an annual growth band. Size-at-age data obtained using this method revealed that growth of P. fabricii is slow and that wild individuals collected at diving depths had reached an age of several decades.

Estimating age and growth parameters for three commercial NE-Atlantic sea cucumbers, Holothuria mammata, H. forskali and H. arguinensis, in a marine protected area

“…In the future, validating length-at-age model results with age determined from growth rings (Sun et al, 2019) will lead to more confidence in the models and more robust results. Growth studies provide valuable information that can help implement and improve management measures.…”

“…Individual recognition techniques such as tagging, are usually shed by holothurians (Conand, 1981;Shelley, 1982) and have only been relatively successful in suspension feeders (Gianasi et al, 2015). Determining growth through the identification of annual growth rings in calcified structures has recently been described for sea cucumbers and this method could facilitate the determination of growth rates for holothuroids (Sun et al, 2019).…”

Comparison of Electronic Length Frequency Analysis (ELEFAN) for Estimation of Growth Parameters for Lollyfish, Holothuria (Holothuria) atra and Sand Sea Cucumber, Holothuria (Thymiosycia) arenicola (Holothuroidea: Echinodermata) in the North Arabian Sea, Pakistan

“…Age determination of holothuroid echinoderms is difficult because of their soft-bodied, polymorphic shape, and the small size of hard structures that could exhibit growth rings (Watanabe et al, 2014;Sun et al, 2019). Analyses of length frequency data (LFDA) can be used for estimating age classes and growth parameters (Pauly and David, 1981), and can also be applied to calculate growth of holothuroid echinoderms (Olaya-Restrepo et al, 2018).…”