Habitat use of inter‐tidal chitons – role of colour polymorphism

This study presents a new approach to examining European chiton habitat use according to morphological characteristics. Time‐search transects were conducted on four Portuguese rocky shores at two shore levels. The chiton species, abundance and individual morphometric features were recorded and related to the substratum dominant epiphytes and surface roughness. The chiton Lepidochitona cinerea (Linnaeus 1767) was the dominant species (77%), followed by Leptochiton algesirensis (Capellini 1859) (15%) and Acanthochitona crinita (Pennant 1777) (8%). Species abundance did not vary significantly with shore level or amongst shores. Six colour morphs were considered for Lepidochitona cinerea, four for A. crinita and one for Lepidochiton algesirensis. Substratum characteristics significantly explained the variation in species and colour morph distribution. There was a high correlation between the presence/absence and type of epiphytic algae and the substratum surface roughness level. We hypothesize that three mechanisms operating either independently or in interaction may explain the non‐random distribution of colour polymorphisms according to their habitat characteristics: (i) presence of algae that are part of their diet; (ii) use of rock as shelter – for instance, crevices and cover resulting from algae fronds and; (iii) morph–rock colour matching as a camouflage mechanism to reduce predation pressure.     

Relationship between somatic growth and otolith growth: a case study of the ornate jobfish Pristipomoides argyrogrammicus from the coast of Réunion (SW Indian Ocean)

The ornate jobfish Pristipomoides argyrogrammicus Valenciennes 1832 occurs in the Indo-West Pacific Ocean, where it is harvested by small-scale coastal fisheries. Management of this species is hindered by lack of adequate biological data. We sampled a total of 113 individuals from the landings of local artisanal fishers on the island of Réunion (southwestern Indian Ocean), from March 2014 to March 2015. The relationships between two types of body length (total and standard length, cm) and total weight (g) were shown to be significant (p < 0.05). The length–weight relationship was described by a power function, with the scaling factor estimated to be 0.008 and the exponent 3.146. Age was determined using whole otoliths. The von Bertalanffy growth equation was estimated to be TL_t = 30.68(1 – e^?0.52(t)). Otolith morphometry variables (length, width and area) were significantly correlated with age estimates (p < 0.05). No significant difference in age estimates was observed between left and right otoliths used as predictors. Readings from observed age and the estimates from modelled age indicated relatively good agreement, suggesting the potential to use whole otoliths for age estimation.