Graphical methods comparing living and dead assemblages, exemplified with benthic foraminifera from the Aveiro Lagoon, Portugal

This work introduces graphical methods documenting density, diversity (species richness combined with heterogeneity) and similarity in combined diagrams for estimating the influence of environmental and taphonomic factors in living (LAs) and dead (DAs) assemblages. In this paper, the diagrams compare: 1) densities per 1 g of sediment expressed in cubic squares; 2) diversities based on rarefaction species richness (x-axis) and Shannon H rarefaction (y-axis), both extended to infinity by the logistic Hull equation, and 3) similarity diagrams based on cosine measures (x-axis) and Spearman correlation coefficients (y-axis). Diagrams were exemplified for LAs and DAs found at 53 stations along channels and intertidal areas of the Aveiro Lagoon (Portugal). Eight 'routes' characterized by different trends in the distribution of the analyzed biotic parameters were recognized in six regions of the Aveiro Lagoon: 'port area', 'central lagoon', 'northeast lagoon', 'northern and southern extremities of the lagoon' and 'city area'. In addition, Detrended Correspondence Analyses (DCA) based on diversity diagrams were performed to show the influence of environmental parameters, especially grain size, salinity, and pH, on the average species composition in each route. The comparative diagrams allow deduction about the impact of parameters that simultaneously affect LAs and DAs, such as hydrodynamics, post-mortem tests dissolution, physicochemical parameters, excessive contribution of organic matter, oxygen depletion, and pollution by metals. Based on these diagrams, the most favorable environments due to the most remarkable development and diversity of LAs and DAs are located in protected coves of the Aveiro Lagoon mouth.

Automated summary

This study introduces graphical methods for estimating the influence of environmental and taphonomic factors on living and dead assemblages using combined diagrams for density, diversity, and similarity. The diagrams were compared for assemblages found in 53 stations along channels and intertidal areas of Aveiro Lagoon in Portugal. Resulting diagrams identified eight "routes" with different trends and Detrended Correspondence Analyses showed the influence of environmental parameters on average species composition in each route. The diagrams also helped deduce the impact of parameters that affect both living and dead assemblages. The most favorable environments for development and diversity were found in protected coves at the mouth of Aveiro Lagoon.