Pseudechinus magellanicus is an ecologically important and small sea urchin in coastal and nearshore habitats off southern South America. We provide the first growth assessment for the species using tag (calcein) and recapture procedures in central Patagonia (Argentina). The individual growth rate of P. magellanicus ranged 0.05–1.3 mm year−1. The Brody–Bertalanffy and Richards growth models provided asymptotic maximum diameters of 29.89 and 26.01 mm, respectively. Both models yielded low values for the growth constant (k), with 0.046 (Brody–Bertalanffy) and 0.062 (Richards). Maximum instantaneous growth rate was estimated at 1.36 mm year−1 for the Brody–Bertalanffy model, and 2.69 mm year−1 for the Richards model. Model selection (corrected Akaike information criterion) showed a slight better fit for the Brody–Bertalanffy growth model compared to the Richards model. A significant variability in growth was observed within the studied population, which can be attributed to genetic factors and micro-environmental effects. P. magellanicus displays a combination of slow growth and small body size, with the lowest recorded growth performance index (θ = 3.72) recorded so far in sea urchins. The species has a long lifespan, with the most common adult sizes estimated to range from 15 to 21 years according to the Brody–Bertalanffy model. Due to the broad geographic distribution and occupation of contrasting habitats, further studies are necessary to explore growth of P. magellanicus under different environmental conditions and/or along a bathymetric gradient.

Through rearing known age individuals and maintaining chemically marked adults in captivity, this study explored the rate of increment formation in southern calamary (Sepioteuthis australis) statoliths over seasonal (summer and winter) and ontogenetic (hatchlings and adults) extremes. A ‘one increment–one day’ relationship was verified for captive-reared hatchlings up to 40 days post-hatching which remained stable across the seasonal extremes. This relationship, however, was not evident in the chemically marked adults as inconsistencies of up to 44 days were detected between the number of days elapsed post-stain and the increment count. No seasonal effect was detected in the ratio between increment count and days elapsed, however, the degree of underestimation was consistently greater for winter-caught adults by approximately 2.5 increments relative to summer-caught adults. This less-than-daily increment formation in adults may be due to: (1) the periodicity of increment formation changing throughout the squid's lifespan; (2) deleterious effects associated with rearing squid in captivity; and/or (3) compromised interpretation of the statolith microstructure as a result of the preparation method.

This work focuses on investigating the potential of calcein and manganese as growthmarkers of the common cockle (Cerastoderma edule) in the bay of Somme(France). Recapture of shells, previously marked using a chemical marking and then bred innatural conditions, was performed in order to determine the shell growth patterns. Calceinmarking has shown a fluorescent increment in shells after only 30 min immersion time at150 mg L-1, but also for shells immersed 3 h at 50 mg L-1. Likewise,manganese shell marking was revealed under cathodoluminescence for shells immersed 1 h at120 mg L-1 as well as for shells which spent 4 h at 90 mg L-1. Anumerical analysis performed on each marked cockles has revealed 23 micro-incrementsbetween the mark and the ventral edge of the valves, corresponding to the 23 tides thatoccurred during the 12 days at liberty post marking. The periodicity of incrementformation is thus validated for a tidal frequency. The growth rates of C.edule, ranged from 11.67 to 19.94 μm d-1, decreasedsignificantly with increasing shell length. This preliminary study gives a clue to theunderstanding of cockle growth and could be used in shellfish production for cockle agemonitoring, but also for chemical analysis to learn more about biomineralization processof this species.