Comparative efficacy of benthic biotic indices in assessing the Ecological Quality Status (EcoQS) of the stressed Ulhas estuary, India

Tracing the impact and recovery trajectory of oil spill affected tropical rocky intertidal macrobenthic communities using the BOPA index

A yearlong study was conducted to assess the impact of an oil spill on macrobenthos of rocky intertidal zone of Uran, India and its recovery processes, by comparing impacted site with a reference. Immediate acute effects observed were elevated sediment hydrocarbons, absence of macroalgae and amphipods, mass mortality of macrofauna and dominance of the opportunistic nereid, Namalycastis senegalensis. As the hydrocarbons reduced at the impacted site by ~50 % within three months, gradual re-appearance of macroalgae and re-colonization of amphipods (51.4 %) and sensitive polychaetes (7 %) indicated that the recovery was well underway. The amphipod, Allomelita pellucida proved to be a potential indicator of oil contamination. BOPA correlated with sediment hydrocarbons and performed effectively as the extant macrobenthic communities had sufficient representation of Polychaeta and Amphipoda. Notwithstanding the distinct initial impacts of the oil spill, comparable macrobenthic assemblages comprised of sensitive species at both sites after a year confirmed complete recovery.

Ecological habitat quality assessment of a tropical estuary using macrobenthic functional characteristics and biotic indices

Seasonal variation in the macrobenthic functional characteristics, such as trophic structure and secondary production, was studied, along with their structural characteristics such as density, biomass, and community distribution in Cochin estuary (CE), a tropical monsoonal estuary along the Southwest coast of India during 2018-2019. The biotic indices, AMBI (AZTI's Marine Biotic Index) and M-AMBI (Multivariate-AMBI) were used to assess the ecological quality of the study area by using the sensitivity of macrobenthic fauna to disturbances. A distinct temporal variation was evident in the macrobenthic structural characteristics, wherein high density, biomass, and species richness were observed during the post-monsoon. Polycheate species were dominant during pre-monsoon (Prionospio cirrifera) and monsoon (Mediomastus sp.), while gastropod species, Stenothyra perpumila, was dominant during post-monsoon. The trophic structure analysis revealed the dominance of deposit-feeding polychaetes during the pre-monsoon in association with the fine sediments laden with high organic carbon. In contrast, during post-monsoon, the polychaete trophic groups were more or less evenly distributed in the sandy substratum. The higher density of suspension feeders and herbivorous-grazers observed during the post-monsoon indicated improved habitat quality compared to the pre-monsoon dominated by the detritivores. The macrobenthic secondary production was also high during the post-monsoon, contributed by a diverse assemblage of molluscs, crustaceans, and polychaetes having size > 0.7 mm. The biotic indices also showed an evident increase in the habitat quality of the estuary from pre-monsoon to post-monsoon (AMBI, moderately disturbed to undisturbed; M-AMBI, poor-moderate-good to good-high conditions), similar to the results of benthic structural and functional characteristics. The study highlights the significance of the utility of benthic functional characteristics while assessing the habitat quality of an ecosystem.

Assessing the benthic quality status of three fine sand tropical beaches from the Andaman Islands through the application of marine biotic indices

The rapid coastal development in the Andaman Islands has resulted in littoral habitat degradation. Understanding the performances of marine biotic indices and the interpretation and translation of those results into coastal health assessment could become an integral tool in future monitoring and management policies. In this line of efforts, the ecological quality status of three sandy beaches, two urban and one nonurban, was evaluated by using three marine biotic indices. The faunal community belonged to moderately well-sorted fine sand biocenosis. The relatively high species richness (15.9 ± 0.80 taxa sample^-1) and moderate abundance (563 ± 38.8 ind.m^-2) were features of the benthic fauna. The urban beaches (Aberdeen Bay and Carbyn's Cove) corresponded to tolerant benthic communities. Malacoceros indicus, Grandidierella megnae and Scolelepis squamata (tolerant species), and Ampelisca diadema (indifferent species) were the major constituents of urban beaches, while Scoloplos capensis, Urothoe grimaldii, and Urothoe platydactyla (sensitive species) were important at the nonurban beach (Wandoor). The high-good quality status prevailed across the spatial and temporal scales except for Carbyn's cove beach, where good-poor status was noticed. The M-AMBI appeared to be the most robust measure in distinguishing the impact between the urban and nonurban beaches. The constrained ordinations revealed a gradient of disturbance across the beaches. The distinct patterns of sample segregation were the result of the ecological response. This attempt should be considered a comprehensive measure of quality assessment of beaches under human pressure and draw a parallel line of evidence to global studies on sandy beaches.

Ecological quality status assessment of tropical estuaries with benthic indices using differently derived reference conditions

Setting appropriate reference conditions (RCs) is critical for classifying the Ecological Quality Status (EcoQS) which is extremely challenging, considering the present-day estuaries. The EcoQS of three tropical estuaries was assessed by applying five different RCs to identify the best applicable method for the area. The AZTI's indices (AMBI and M-AMBI) categorised areas with sharper pollution gradient with ease, while classification of moderate-low polluted areas was ambiguous. Indices responded to chemical stressors more clearly in the impacted estuary compared to the less polluted estuaries. Ecological status assigned by the default RC (lowest AMBI and highest diversity and richness values) were more accurate than those obtained on application of other four types of RCs, owing to various estuarine constraints that are discussed herewith. Thus, prior to application, caution should be exercised while setting area-specific RCs. The inclusion of combination of AZTI's indices with professional judgment for successful appraisal of ecosystem is recommended.

Fatty acid signatures of sediment microbial community in the chronically polluted mangrove ecosystem

Phospholipid fatty acid (PLFA) analysis was used to examine variation in the distribution of microbial communities in heavily polluted mangrove sediments of Thane creek, west coast of India. A total of 40 individual PLFAs representing 11 functional groups were identified in the sediment and were mainly dominated by saturated fatty acids (anaerobic prokaryotes) >50%. Significant dominance of PUFA, 16:3 ω6c (34.2%) indicators of micro-eukaryotes, in subsurface depth (p < 0.05) suggests input from the remnants of marine microalgae. Declined mean relative abundance of fungi (<6%) and actinomycetes (<1%) were detected in the sediment indicating their sensitivity to anthropic stressors. Homogenous profile of microbial diversity indicating active bioturbation. Cumulative metabolic stress evident from SAT/MUFA (>1), B/F (>1) and G⁺/G^- (<1) ratio and prolonged hypoxia to be prevalent in the creek during the study. In conclusion, PLFA signatures can thus be used as potential biomarkers of environmental monitoring and proxy for interpreting ecosystem health.

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

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.

Seasonality of macrobenthic assemblages and the biotic environmental quality of the largest monsoonal estuary along the west coast of India

This study deals with the macrobenthic assemblages and the biotic environmental quality of Kochi backwaters (KBW), India. Due to the heavy river discharge, extensive limnetic and turbid conditions prevailed in the KBW during the southwest monsoon (June to September). This exerted a profound adverse effect on the abundance, richness, and diversity of macrobenthic assemblages. Overall, mesohaline conditions with a clayey sand bottom substratum favored the high macrofaunal abundance during the southwest and northeast monsoon seasons. But mesohaline condition and sandy silt bottom were found to support high macrofaunal abundance in the KBW during the pre-monsoon season. Polychaete dominated the macrobenthic community, regardless of seasons. Capitella capitata, Heteromastus similis, Paraheteromastus sp., Prionospio cirrobranchiata, Minuspio cirrifera, Pagurapseudopsis kochindica, P. gymnophobia, Ctenapseudes indiana, C.chilkensis, Tanais sp., Villorita cyprinoides, Grandidierella sp., Ampelisca sp., and Littorina sp. were the dominant ones observed during the study. The sediment organic carbon, in general, showed a positive correlation with polychaete abundance during all three seasons. The ecological status of KBW during all three seasons was assessed as per BO2A index, which ranged from 0.05 to 0.18, suggesting a healthy to a moderately polluted bottom environmental condition.

Assessment of benthic macroinvertebrate response to anthropogenic and natural disturbances in the Kodungallur-Azhikode estuary, southwest coast of India

Benthic biotic indices are important ecological tools extensively used to understand the ecological quality of coastal wetlands. The present study aimed to assess the ecological status of Kodungallur-Azhikode estuary for the first time by using widely used benthic indices such as species richness (S), Shannon diversity index (H'log₂), BENTIX, benthic opportunistic polychaetes amphipods (BOPA), AZTI's Marine Biotic Index (AMBI) and multivariate AMBI (M-AMBI). In the canonical correspondence analysis, salinity, dissolved oxygen, organic matter, sediment Eh, sediment pH and sand were identified as important variance descriptors. A single species of an opportunist, Americorophium triaeonyx, an amphipod belonging to the ecological group (EG) III, significantly contributed to the total macrofaunal density. Other dominant opportunistic species included Obelia bidentata (EGII), Arcuatula senhousia (EGIII), Cirolana fluviatilis (EGII), Prionospio cirrifera (EGIV) and Capitella sp. (EGV). The overall assessment indicated a 'good to moderate' condition in AMBI, 'good to poor' condition in M-AMBI, 'high to moderate' condition in BENTIX, 'high to poor' condition in BOPA and 'moderate to poor' condition in univariate Shannon diversity index. All the multivariate indices tested in the study were correlated with each other except BOPA and M-AMBI. The group of stations dominated with a sandy substrate and a moderate level of organic content indicated high to good conditions while other stations demonstrated moderate to poor conditions. However, no significant variation in indices tested between seasons was observed. The present study recommends long-term monitoring of benthic macroinvertebrate assemblages with proper taxonomic identification and functional trait analysis for better calibration of indices, which is the key factor for getting better results.

Factors structuring spatio-temporal dynamics of macrobenthic communities of three differently modified tropical estuaries

Tropical estuaries of industrialized northwest coast of India, subject to seasonal and multifarious anthropogenic interventions, are poorly studied. Three estuaries, Ulhas, Amba and Savitri were investigated seasonally to identify the principal factors among natural and anthropic stressors that shaped spatio-temporal macrobenthic patterns. The macrobenthic community structure and chemical parameters differed significantly between estuaries, zones and seasons. Multivariate dispersions were significant between the estuaries whereas for the zones and seasons, significant variability was nonexistent. Multivariate regression analysis indicated that both natural and anthropogenic drivers influenced the spatio-temporal variability of macrobenthos of Ulhas and Amba. In Savitri, no anthropogenic factor was significantly influential. Salinity explained a greater proportion of the variability of macrobenthic structure than other factors in all estuaries. The pollution tolerant species responded largely to salinity changes and were observed to inhabit specific salinity zones. Thus, the spatio-temporal patterns of the estuarine macrobenthos were primarily dictated by the salinity.

Forever young: The successful story of a marine biotic index

In 2000, the AZTI's Marine Biotic Index (AMBI) was published and was one of a number of marine benthic indices development to assess the ecological status of soft-bottom macroinvertebrates. This index, and its derivatives, has been very successful in its application to different geographical areas, across the world, as well as to different environments, from the intertidal to the abyssal, or from tidal freshwater to offshore habitats. In this review, we explain the story behind the AMBI development, and look for an explanation of the index's success. For doing that, we comment on the current practicalities of the index, we present the new AMBI species list, with 9251 taxa, we dismantle six myths around this index, and examine the past and the future of the index. We show that the solid ecological roots of the index make it a robust tool to assess the status of marine benthic communities, at any time and environment. Hence, we think that it will be 'forever young' helping managers in taking informed decisions to improve benthic marine systems.

Ecological quality status evaluation of a monsoonal tropical estuary using benthic indices: comparison via a seasonal approach

The use of biotic indices has garnered attention during the last decade due to its extensive application in evaluating ecological quality status (EcoQS) of marine waters and estuaries. Three seasonal surveys were conducted in the Kundalika estuary, India to evaluate the ecostatus using five benthic indices and comparing their effectiveness considering the estuarine salinity gradient and seasonality. All indices gave divergent results displaying a wide range of classes (good to bad) across salinity zones and seasons. Comparatively, M-AMBI discriminated the EcoQS suitably than other indices. Hence, a seasonally averaged approach for M-AMBI was proposed to obtain a final mean EcoQS which assigned moderate status to the euhaline and poly-mesohaline zones and poor status to the oligohaline zone. Considering the high degree of spatial heterogeneity and seasonality in the estuary, the monsoon data was found to lower the EcoQS due to natural stress in some cases; the exclusion of the monsoon season resulted in a more valid ecostatus. Therefore, this approach which combines information from the non-monsoon seasons stands out in providing a useful basis for ecological management by scrutinizing responses of macrobenthos. Also, we suggest salinity zone-wise evaluation for more effective classification chiefly in tropical monsoonal estuaries. An effort to establish a final EcoQS was performed; however, future in-depth studies are necessary to ascertain the reliability of the successful biotic index (M-AMBI) in estuaries with different stressors.