Benthic Foraminiferal Indices and Environmental Quality Assessment of Transitional Waters: A Review of Current Challenges and Future Research Perspectives

Abstract

Transitional waters straddle the interface between marine and terrestrial biomes and, among others, include fjords, bays, lagoons, and estuaries. These coastal systems are essential for transport and manufacturing industries and suffer extensive anthropogenic exploitation of their ecosystem services for aquaculture and recreational activities. These activities can have negative effects on the local biota, necessitating investigation and regulation. As a result of this, EcoQS (ecological quality status) assessment has garnered great attention as an essential aspect of governmental bodies’ legislative decision-making process. Assessing EcoQS in transitional water ecosystems is problematic because these systems experience high natural variability and organic enrichment and often lack information about their pre-human impact, baseline, or “pristine” reference conditions, knowledge of which is essential to many commonly used assessment methods. Here, foraminifera can be used as environmental sentinels, providing ecological data such as diversity and sensitivity, which can be used as the basis for EcoQS assessment indices. Fossil shells of foraminifera can also provide a temporal aspect to ecosystem assessment, making it possible to obtain reference conditions from the study site itself. These foraminifera-based indices have been shown to correlate not only with various environmental stressors but also with the most common macrofaunal-based indices currently employed by bodies such as the Water Framework Directive (WFD). In this review, we firstly discuss the development of various foraminifera-based indices and address the challenge of how best to implement these synergistically to understand and regulate human environmental impact, particularly in transitional waters, which have historically suffered disproportionate levels of human impact or are difficult to assess with standard EcoQS methods. Further, we present some case studies to exemplify key issues and discuss potential solutions for those. Such key issues include, for example, the disparate performance of multiple indices applied to the same site and a proper assignment of EcoQS class boundaries (threshold values) for each index. Disparate aptitudes of indices to specific geomorphologic and hydrological regimes can be leveraged via the development of a site characteristics catalogue, which would enable the identification of the most appropriate index to apply, and the integration of multiple indices resulting in more representative EcoQS assessment in heterogenous transitional environments. In addition, the difficulty in assigning threshold values to systems without analogous unimpacted reference sites (a common issue among many transitional waters) can be overcome by recording EcoQS as an ecological quality ratio (EQR). Lastly, we evaluate the current status and future potential of an emerging field, genetic biomonitoring, focusing on how these new techniques can be used to increase the accuracy of EcoQS assessment in transitional systems by supplementing more established morphology-based methods.

Comparison of Four Foraminiferal Biotic Indices Assessing the Environmental Quality of Coastal Mediterranean Soft Bottoms

“…Indices based on diversity and indices based on macrofaunal indicator taxa show discrepancies in Mediterranean transitional waters (lagoons and coastal lakes), whereas diversity indices based on foraminifera and on macrofauna show similar results [27]. Transitional environments (fjords and lagoons) are often highly impacted by multiple stressors, and the organic matter content is naturally higher than in open marine areas [19,22]. It appears that in these naturally organic enriched environments, only the lower part of the total overall environmental quality gradient could be present.…”

Géneros de foraminíferos bentónicos en zonas mesofóticas superior y media del Parque Nacional Natural Corales de Profundidad y su potencial como bioindicadores de hábitats y cambios ambientales

“…En efecto, muchas especies de foraminíferos responden ante cambios ambientales de manera similar a como lo hacen los corales escleractínios. Por ejemplo, las conchillas de muchas especies se componen de carbonato de calcio, y algunas especies se consideran constructoras arrecifales y presentan simbiosis con zooxantelas, por lo que sus requerimientos ambientales también son similares (Hallock et al, 2003;Beccari et al, 2020;O'Brien et al, 2021). De tal forma, estos organismos han sido considerados como indicadores biológicos (ambientales y paleoambientales) ideales ya que su ciclo de vida corto (p.…”

“…Estudios sobre conjuntos de foraminíferos bentónicos en ambientes arrecifales generalmente los clasifican en tres grupos funcionales: (1) portadores de simbiontes, (2) mixótrofos (estrés-tolerantes) y (3) otros foraminíferos pequeños considerados heterótrofos (Hallock et al, 2003;Hallock, 2012;O'Brien et al, 2021). Esta distinción se debe a que las diferencias entre las proporciones de estos tres grupos son una herramienta práctica y eficiente para determinar si un arrecife se encuentra en buen estado de salud o en degradación crónica o si atraviesa eventos agudos de mortalidad específica de corales (Hallock, 2012;Pisapia et al, 2017;Prazeres et al, 2020).…”

“…Para su uso se recomienda identificar los ejemplares a nivel taxonómico de especie, estimar el tamaño de los individuos, cuantificar su abundancia y asignarles grupos funcionales. Con esto se podría calcular el índice FORAM (Hallock et al, 2003) y realizar otras comparaciones a nivel regional para emplearlos como bioindicadores de condiciones del agua (Zarkogiannis et al, 2020;O'Brien et al, 2021;Girard et al, 2022).…”

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

“…Noticeably, tolerant and opportunistic species abundances increase close to the oyster and fish farms while sensitive ones tend to disappear [36,[41][42][43]. To increase their use in environmental monitoring surveys, biotic indices based on benthic foraminifera indices have been developed (see review [44]). 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].…”