Joint analysis of macrofaunal and meiofaunal assemblages improves the assessment of lagoonal environmental heterogeneity

Matching datasets of macrofaunal and meiofaunal assemblages were jointly analyzed for the first time in a coastal lagoon (Cabras Lagoon, Sardinia) in relation to the lagoonal environmental heterogeneity. Within the common faunal list, indicator species/taxa for different environmental conditions were found evenly for both assemblages, with the two faunal components responding distinctly to the putative environmental gradients according to their autecology. The relationship between the number of individuals and species/taxa richness of both assemblages showed an exponential increase at increasing salinity and DO concentrations in water as expected basing on the confinement theory. Along the trophic gradient, the two metrics of both macrofaunal and meiofaunal assemblages showed a similar belt-shaped curve in agreement with theoretical predictions and quantitative field studies, with a peak at intermediate OM values followed by a sharp decrease at OM above 12% at the most confined site. While not a causality measure, our results indicate that these simple benthic-OM relationships applied to both faunal components represent a valuable screening-level indicator for evaluating the likelihood of reduced sediment quality and associated bioeffects in eutrophic lagoons. The present study demonstrates that macrofaunal and meiofaunal assemblages in coastal lagoons, as commonly shown in marine waters, are coherent and distinct entities and that their joint use represents a more comprehensive and robust tool to assess the environmental heterogeneity and quality of these highly variable systems.