Abstract
AbstractIn shell-secreting molluscs, age and growth rate of individuals and hence their performance can normally be measured using growth lines that are deposited in the shell throughout their lives. An annual periodicity of growth line formation of the warm-water limpet Patella depressa was established using marked and recaptured individuals from north Wales, UK. Length at age from suitably prepared shell sections was determined in limpets from non-range-edge populations and at two range edges, where different demographic attributes have been recorded. Individuals collected from their poleward range-edge in north Wales were older when compared with individuals at their range-edge in southern England. Shells collected from southern England were characterized by rapid growth with most individuals reaching >30 mm in maximum length by the fourth or fifth year, contrasting with those from north Wales, where most shells only reached this size at 7–10 years of age. Von Bertalanffy growth coefficients (K-values) were negatively related to P. depressa density, showing faster growth in lower total densities of both P. depressa and Patella vulgata combined. Higher intra-specific effects on K-values were found in P. depressa compared with its congener P. vulgata, with stronger effects in north Wales than in southern England. These results confirm differences in population patterns and individual traits between the two leading edges of P. depressa. Understanding annual growth in P. depressa over large scales could help to disentangle the processes determining differences in shell growth and age structure seen at the two range edges of this limpet species.
Highlights
Growth rate can be considered as a metric of performance of an organism (Pörtner et al, 2005), being influenced by both abiotic and biotic factors (Richardson, 2001)
To validate the periodicity of growth lines seen in the shells of P. depressa, 80 specimens between 19–25 mm in maximum length (ML) were selected on rock boulders at mid tide level (MTL) on the exposed rocky shore at Shell Island in north Wales (N Wales) (Figure 1B), between the 22– 29 June 2015
From the seasonal shell samples it was possible to constrain the timing of line formation to the winter period between November 2015 and March 2016 when shell growth ceased
Summary
Growth rate can be considered as a metric of performance of an organism (Pörtner et al, 2005), being influenced by both abiotic and biotic factors (Richardson, 2001). Invertebrate skeletons, of molluscs, frequently provide a continuous record of ontogenetic growth and an archive of environmental variation during the lifespan of an individual (Rhoads & Lutz, 1980) In shelled molluscs, such as limpets, the shell is accreted incrementally as the animal grows (MacClintock, 1967). Seasonal variation in shell deposition in the bivalve Arctica islandica (Butler et al, 2009) and in limpet species such as Patella vulgata (Surge et al, 2013; Ambrose et al, 2016; Gutiérrez-Zugasti et al, 2017) and Patella rustica (Prusina et al, 2015) results in annual growth line formation, but marine benthic molluscs often show increments at daily (Bock & Miller, 1994; Schöne et al, 2005) and tidal scales (Richardson et al, 1979, 1980; Bock & Miller, 1994)
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