Diversity and abundance of pteropods and heteropods along a latitudinal gradient across the Atlantic Ocean

Shelled pteropods and heteropods are two independent groups of holoplanktonic gastropods that are potentially good indicators of the effects of ocean acidification. Although insight into their ecology and biogeography is important for predicting species-specific sensitivities to ocean change, the species abundances and biogeographical distributions of pteropods and heteropods are still poorly known. Here, we examined abundance and distribution patterns of pteropods (euthecosomes, pseudothecosomes, gymnosomes) and heteropods at 31 stations along a transect from 46 degrees N to 46 degrees S across the open waters of the Atlantic Ocean (Atlantic Meridional Transect cruise AMT24). We collected a total of 7312 pteropod specimens belonging to at least 31 species. Pteropod abundances were low north of 40 degrees N with <15 individuals per 1000 m(3), varied between 100 and 2000 ind./1000 m3 between 30 degrees N and 40 degrees S, and reached >4000 ind./1000 m(3) just south of 40 degrees S. This accounted for an estimated biomass of 3.2 mg m(-3) south of 40 degrees S and an average of 0.49 mg m(-3) along the entire transect. Species richness of pteropods was highest in the stratified (sub)tropical waters between 30 degrees N and 30 degrees S, with a maximum of 15 species per station. The biogeographical distribution of pteropod assemblages inferred by cluster analysis was largely congruent with the distribution of Longhurst's biogeochemical provinces. Some pteropod species distributions were limited to particular oceanographic provinces, for example, subtropical gyres (e.g. Styliola subula) or warm equatorial waters (e.g. Creseis virgula). Other species showed much broader distributions between similar to 35 degrees N and similar to 35 degrees S (e.g. Limacina bulimoides and Heliconoides inflatus). We collected 1812 heteropod specimens belonging to 18 species. Highest heteropod abundances and species richness were found between 30 degrees N and 20 degrees S, with up to similar to 700 ind./1000 m(3) and a maximum of 14 species per station. Heteropods were not restricted to tropical and subtropical waters, however, as some taxa were also relatively abundant in subantarctic waters. Given the variation in distribution patterns among pteropod and heteropod species, it is likely that species will differ in their response to ocean changes. (C) 2016 The Authors. Published by Elsevier Ltd.