Citizen science via social media revealed conditions of symbiosis between a marine gastropod and an epibiotic alga

Environmental factors promote symbiosis, but its mechanism is not yet well understood. The alga Pseudocladophora conchopheria grows only on the shell of an intertidal gastropod Lunella correensis, and these species have a close symbiotic relationship which the alga reduces heat stress of the gastropod. In collaboration with general public, we investigated how environmental conditions alter the symbiotic interaction between the alga and the gastropod. Information about the habitats of each gastropod and images of shells was obtained from the Japanese and Korean coasts via social media. We constructed the hierarchical Bayesian model using the data. The results indicated that the proportion of shell area covered by P. conchopheria increased as the substrate size utilized by the gastropod increased. Meanwhile, temperature did not affect the proportion of P. conchopheria on the shell. These suggested that the alga provides no benefits for the gastropod on small substrates because gastropod can reduce the heat stress by diving into the small sediment. Further, the gastropod’s cost incurred by growing the alga on the shell seems to be low as the algae can grow even in cooler places where no benefits of heat resistance for gastropods. Different environments can yield variable conditions in symbiosis.

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

Morphometric analysis is one of the tools widely used to quantify, analyse and describe the variations in the biological forms of animals. In this study, we examined the linear morphometric variations of the shell of the small intertidal gastropod Echinolittorina lineolata and compared the patterns to identify variations among populations and between sexes. The individuals were collected from latitudes 3°S, 14°S, 21°S and 23°S along the Brazilian coast. Traditional morphometric analysis was performed, and the morphometric variables of the shells, namely, the length and width of the shell and the length and width of the shell opening were obtained. The observed size pattern was influenced by latitude, as well as by local spatial responses to factors such as the substrate changing the morphometric variables of the snail. Of the morphometric variables, the length and the width of the shell were the most representative variables that influenced the gastropods in the different latitudes. These variables were also different in males and females, with females having larger shell lengths and widths across all latitudes.