Foraminiferal-based biotic indices to assess the ecological quality status of the Gulf of Gabes (Tunisia): Present limitations and future perspectives

Abstract

Biotic indices are tools to assess the ecological status of marine systems, and can be based on different metrics (such as ecological groups, specific diversity). The present study applies five biotic indices based on living (stained) benthic foraminiferal assemblages to assess ecological conditions in a wide area of the Mediterranean Sea in the heavily polluted Gulf of Gabes and along the western and eastern coasts of the Djerba Island, with the eastern coast considered as "pristine". The applied indices are based on epiphytic foraminifera e.g., the "long versus short life span" index (I LS) and the modified FoRAM-Index (FI'), benthic foraminiferal assemblage composition and diversity, e.g., the Tolerant Species index (TS std), the Foram Stress Index (FSI), the diversity Index (exp(H' bc)) and the newly developed Foram-AZTI Marine Biotic Index (Foram-AMBI). This latter index was tested using species of benthic foraminifera presently assigned to ecological groups in the Mediterranean Sea. All indices confirm good ecological conditions eastern of Djerba. The FI' and I LS , % TS std , FSI, indicate a severe anthropogenic impact especially in the central part of the Gulf of Gabes, next to the phosphate industry of Skhira and along the western coast of Djerba Island and confirm direct observations and geochemical data. The indices based on epiphytic foraminifera seem to better reflect actual environmental conditions in the investigated region because of the extended Posidonia oceanica meadow in the area. The exp(H' bc) reflects lower degrees of pollution. The application of the Foram-AMBI index presents limitations that prevent its current use. It strongly underestimates the pollution impact along the Tunisian coast, and additional work is needed to increase the number of species attributed to ecological groups and to possibly modify the coefficients to be used in its equation.

Distribution Patterns of Benthic Foraminifera in Fish Farming Areas (Corsica, France): Implications for the Implementation of Biotic Indices in Biomonitoring Studies

“…These results suggest that TOC under fish farming cages may most likely be composed of labile OM on which benthic foraminifera are feeding rather than refractory OM derived from Posidonia meadows. Furthermore, the positive response of foraminiferal assemblages to a moderate increase in TOC content is in line with previous studies in the Mediterranean Sea [11,31,37,52,69]. Specifically, in the early stages of enrichment, TOC can stimulate the size and specific richness of benthic communities, thanks to an increase in the biotic capacity of the environment [70].…”

“…They are based either on their diversity i.e., the exp(H bc ) [45] or on the species-specific response to total organic carbon content i.e., Foram-AMBI [41,46,47], TSI-Med [48] and Foram Stress Index [49]. These indices were successfully applied to assess the health of benthic habitats in the Mediterranean Sea [31,37,41,[48][49][50][51][52][53][54]. However, benthic foraminifera are not yet acknowledged as a biological quality element for the implementation of the WFD and MSFD.…”

Indicative value of benthic foraminifera for biomonitoring: Assignment to ecological groups of sensitivity to total organic carbon of species from European intertidal areas and transitional waters

“…Recent developments in benthic foraminiferal biotic indices (Alve et al, 2016;Bouchet et al, 2012;Barras et al, 2014;Dimiza et al, 2016;Jorissen et al, 2018) have provided further opportunities for the application of this meiobenthic group as a biological quality element for ecological quality status (EcoQS) assessment in legislations concerning transitional waters (hereafter TWs; see definition in McLusky and Elliott, 2007) and marine environments (see review in Sousa et al, 2020). Foraminiferal indices based either on species diversity (Alve et al, 2009;Bouchet et al, 2012Bouchet et al, , 2013 or on the sensitivity of species to organic pollution (Alve et al, 2016;Barras et al, 2014;Dimiza et al, 2016;Jorissen et al, 2018), have been designed and successfully applied to assess EcoQS of benthic habitats (Alve et al, 2019;Bouchet et al, 2012Bouchet et al, , 2013Bouchet et al, , 2018aBouchet et al, , 2020Damak et al, 2020;Denoyelle et al, 2010;Dijkstra et al, 2017;El Kateb et al, 2020;Francescangeli et al, 2016;Jesus et al, 2020;Mojtahid et al, 2006Mojtahid et al, , 2008Melis et al, 2019).…”

Living (stained) foraminifera in the Lesser Syrtis (Tunisia): influence of pollution and substratum

“…Is the quality of the organic matter playing a role on the abundance of this species? The abundance of this species may be, indeed, linked to the high quality of the organic matter, whose δ 13 C signature corresponds to marine phytoplankton, along the Gabes transect (Supplemental Information S2; El Kateb et al, 2018b;El Kateb et al, 2020). Alternatively, the centimetric bioclasts characterizing Facies G4 may provide a suitable ecological niche for A. mamilla (Fig.…”