What physical habitat factors determine the distribution of gastropods in neotropical headwater streams?

Freshwater gastropods play a pivotal role in the structure and functioning of freshwater ecosystems,but despite their importance,there are still gaps in their ecology.Our goal was to understand what physical habitat factors are the most important for the distribution of freshwater gastropods in headwater stream ecosystems in the Neotropical Savanna and provide a baseline for conservation and management efforts for freshwater gastropods in this biome.We identified five taxa,each with different environmental prefferences.Littoridina presence related negatively with stream slope,Biomphalaria presence related positively with total dissolved solids and the proportions of cobble,fine sediment and organic matter.Gundlachia presence correlated positively with elevation and the proportion of pools in the site.Physa presence related negatively with total dissolved solids and positively with alkalinity.Melanoides tuberculata presence correlated positively with the proportion of coarse gravel.Our results highlight the challenge for protecting native freshwater gastropod assemblages(and managing non-native invasive species),because environmental preferences vary widely amongst taxa and most are vulnerable to common anthropogenic disturbances.

Assessment of two persistent bioaccumulative toxicants in the UNESCO protected river of Osun-Osogbo, Nigeria

Introduction:Osun River dissecting the Osun-Osogbo Sacred Grove,though inscribed on the World Heritage List,has been rarely assessed for biodiversity values or ecotoxicology.In this study,we investigated the concentrations of Cu and Zn in the benthic sediments and two dominant gastropod species(Melanoides tuberculata and Lanistes varicus)of the Osun River.Benthic sediment and gastropod samples were collected on quarterly basis from June 2015 to March 2016 along the longitudinal stretch of the river.Dry samples were digested and analysed for Cu and Zn using the atomic absorption spectrophotometry.Results:With the exception of September sampling period,the two metals recorded higher values in the animals than in the sediments.Cu(1.23±0.81μg/g)was much lower(p<0.01)than zinc(6.29±2.15μg/g)in the benthic sediments.In the same vein,Cu was significantly lower(p<0.01)than Zn in both species.Both metals recorded much lower values than their average concentrations in the Earth’s crust as well as the recommended limits for freshwater life.Comparatively,L.varicus recorded higher bioaccumulation factor than M.tuberculata.Conclusions:Findings from this study suggest that both metals posed no toxicological risk to the freshwater system of Osun River.Concentrations of both metals in the sediments as well as their accumulation factors in both gastropod species were indicative of an unimpacted freshwater system.