Growth bands are an unreliable indicator of sea urchin age: Evidence from the laboratory and the literature

Abstract

Knowledge of urchin age structure is crucial for understanding their ecosystem impacts and improving their management. In sclerochronology, translucent and opaque growth bands (TGB, OGB) in urchin ossicles are used to estimate age. An essential premise for using this technique is that one TGB and one OGB are formed every year, independent of urchin size or ossicle type. TGB and OGB addition are associated with slow and fast growth, respectively, and assumed to be added seasonally due to changes in water temperature. However, these assumptions are not unanimously supported by experiments, and validation attempts have not generated consensus. We conducted an experiment on Strongylocentrotus droebachiensis to test the validity of these assumptions and reviewed the literature to assess the use and validation of sclerochronology in urchins. The experiment demonstrated that the addition of TGB and OGB was not strictly related to temperature and was not consistent across urchin size-classes or ossicle types. TGB were added in response to temporary stress, and no distinction on the basis of band width or pigmentation could be made between natural TGB and stress-induced TGB. Only 52% of articles that used sclerochronology for aging urchins attempted any validation, and when the methodology was put under scrutiny, it was usually found to be wanting. More detailed studies are needed to address variability in growth bands deposition and endogenous and exogenous factors affecting this process. Sclerochronology in urchins should not be used until standardized procedures are able to provide accurate and precise interpretation of growth band addition.

Morphometry and growth of sea pen species from dense habitats in the Gulf of St. Lawrence, eastern Canada

“…Validation of ageing in non-Ellisellidae octocorals cannot be assumed to apply to sea pens. In absence of validation data from ellisellids and sea pens we concur with Narvaez et al (2016), who caution against interpreting growth rings as annual. This is reinforced by our observations of the presence of lighter rings in some sections that if counted could triple the maximum age recorded.…”

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

“…for using this technique is that a complete cycle (one translucent or dark ring and one opaque or light ring) is added each year (or following any other quantifiable periodicity), independent of individual size. However, these assumptions are not unanimously supported by experiments and their accuracy remains open to discussion [13,14].…”

Sampling Procedure for Establishing Criteria for Sea Urchin (Loxechinus albus) Proportion under the Legal Minimum Length of landings

“…Finally, it is worth noting that other factors could be included in the sampling plan, such as the size-feeding relationship [27]; seasonality, gonadal development and reproductive status [10]; feeding differences and growth [12]; abundance [5]; life history parameters [11]; other environmental factors; and the plan's possible effects on re-population techniques [28]. In addition, the detection of the selective fishing pressure effects allow studying the life history parameters of exploited sea urchins under more natural conditions [12].…”

“…More specifically, almost 50% of the total landings come from the area around Chiloé Island (41 • 47 S-43 • 28 S), which is separated from the mainland on its northern edge by Chacao Channel (∼41 • 47 S) and to the south by Chonos Archipelago (43 • 50 S-45 • 45 S) ( [1,8,9]; see Figure 1). Studies by Balboa et al [7] showed that sea urchin is being harvested under selective fishing pressure (and selective predation on females in Quellón [10]), which suppresses growth rates (see also [4,11]). Individual growth patterns and genetic effects on populations can lead to density-dependent and trophic consequences observed in benthic species and compensatory growth.…”