Connecting pH with body size in the marine gastropod Trophon geversianus in a latitudinal gradient along the south-western Atlantic coast

Abstract

There is growing concern about the impact of contemporaneous ocean acidification on marine ecosystems, but strong evidence for predicting the consequences is still scant. We have used the gastropod Trophon geversianus as a study model for exploring the importance of oceanographic variables (sea surface temperature, chlorophyll a, oxygen, calcite and pH) on large-scale latitudinal variation in mean shell length and relative shell weight. Data were collected from a survey carried out in 34 sites along ~1600 km. Neither shell length nor relative shell weight showed any monotonic latitudinal trend, and the patterns of spatial variability were rather complex. After correcting for spatial autocorrelation, only pH showed a significant correlation with mean shell length and relative shell weight, but contrary to expectations, the association was negative in both cases. We hypothesize that this could mirror the negative effect of acidification on growth rate, which may cause larger asymptotic size. Latitudinal trends of body size variation are not easy to generalize using ecogeographic rules, and may be the result of a complex interaction of environmental drivers and life-history responses.

Shell Variability in Trophon geversianus (Gastropoda: Muricidae) at Caleta de los Loros (Northern Patagonia, Argentina) during the Late Holocene: A Strong Local Imprint

“…This context reinforces the idea that local and regional scales are interrelated (Huston, 1999;Resetarits, 2005), and thus studying outlier sites may give us important insights into the local features of an area that can override the large-scale processes that drive regional grouping patterns (Blanchette et al, 2008). Moreover, throughout the geographic range of a species, the distinctiveness and peculiarity of particular sites may disrupt expected general patterns (e.g., ecogeographic rules) when considering multi-ple sites at a regional scale (Malvé et al, 2018a). Embracing a regional approach is therefore of paramount importance since studies that cover the entire geographic range of a species along the south-west Patagonian coast (from Río Negro Province to Tierra del Fuego) are scant, thus limiting our ability to answer basic biogeographic questions (Fenberg & Rivadeneira, 2011).…”

“…In a recent study, Malvé et al (2018b) evaluated biogeographic shell shape variation in the marine snail Trophon geversianus, and recognized two morphotypes matching the biogeographic scheme of the Argentine Sea. In a previous study on the same species, Malvé et al (2018a) also found that neither shell length nor relative shell weight showed any monotonic latitudinal trend, and the patterns of spatial variability were rather complex. These authors recognized a weak, non-significant, tendency of body size increase towards the south, with extremely large individuals at the Magellan Strait and Beagle Channel (southern South America).…”

Morphometric analysis of the shell of the intertidal gastropod Echinolittorina lineolata (d'Orbigny, 1840) at different latitudes along the Brazilian coast

“…The latitudinal increase in body size of co-specific populations has been tested in freshwater, terrestrial and marine animal groups (Blanckenhorn & Demont, 2004; Linse et al ., 2006; Angielczyk et al ., 2015; Malvé et al ., 2018). According to our hypothesis that size of the gastropods would increase according to the latitudinal gradient in our localities, results showed a moderately positive relationship between the size of the individuals and each latitude.…”

“…However, when the whole dataset was considered, the largest sized gastropod was not observed at the highest latitude (23°S in this study). The variability of body size has a complex spatial tendency that cannot be easily framed by ecogeographic rules such as Bergmann's rule (Malvé et al ., 2018).…”

“…This result correlates with the study that body size variation in gastropods (and other molluscs) follows a complex pattern, being related with many variables, not only with latitude (e.g. Bergmann's pattern) (Malvé et al ., 2018). At different spatial scales, factors such as topography, micro-habitat and the slope of the coast can influence the size and shape of the shell as well as animal physiology (Tanaka & Maia, 2006; Lima et al ., 2016).…”