Changes In Assemblages Research Articles

Multiple drivers and lineage-specific insect extinctions during the Permo–Triassic

The Permo–Triassic interval encompasses three extinction events including the most dramatic biological crisis of the Phanerozoic, the latest Permian mass extinction. However, their drivers and outcomes are poorly quantified and understood for terrestrial invertebrates, which we assess here for insects. We find a pattern with three extinctions: the Roadian/Wordian (≈266.9 Ma; extinction of 64.5% insect genera), the Permian/Triassic (≈252 Ma; extinction of 82.6% insect genera), and the Ladinian/Carnian boundaries (≈237 Ma; extinction of 74.8% insect genera). We also unveil a heterogeneous effect of these extinction events across the major insect clades. Because extinction events have impacted Permo–Triassic ecosystems, we investigate the influence of abiotic and biotic factors on insect diversification dynamics and find that changes in floral assemblages are likely the strongest drivers of insects’ responses throughout the Permo–Triassic. We also assess the effect of diversity dependence between three insect guilds; an effect ubiquitously found in current ecosystems. We find that herbivores held a central position in the Permo–Triassic interaction network. Our study reveals high levels of insect extinction that profoundly shaped the evolutionary history of the most diverse non-microbial lineage.

The Ordovician of the Korean Peninsula: a synthesis

Abstract The Ordovician succession of the Korean Peninsula is part of the Cambro-Ordovician Joseon Supergroup exposed in the Taebaeksan Basin of South Korea and the Pyeongnam Basin of North Korea. This review summarizes the advances made on these successions over the past two decades, focusing on the Taebaeksan Basin. The Ordovician succession in the Taebaeksan Basin comprises the Taebaek, Yeongwol, Yongtan, Pyeongchang and Mungyeong groups, of which the Taebaek and Yeongwol groups have been studied in detail. These strata are mixed carbonate–siliciclastic deposits formed in peritidal to deep-subtidal environments. Sedimentological and palaeontological studies show that the Korean Ordovician succession represents local variations of the Great Ordovician Biodiversification Event, exemplified by reef evolution, changes in sedimentary systems and changes in invertebrate fossil assemblages. Recent studies of the Yongtan, Pyeongchang and Mungyeong groups have demonstrated that these units are important for understanding the tectonic evolution of the Taebaeksan Basin. The Ordovician strata in the Taebaek Group are generally similar to those of the Pyeongnam Basin and North China; however, the Upper Ordovician–Devonian strata between the two Korean basins show palaeontological affinities to those of South China, perhaps recording the Permo-Triassic collision between the Sino-Korean (North China) and South China blocks.

Dissolution does not affect grass phytolith assemblages

Dissolution is one among several taphonomical processes that may bias paleoenvironmental, paleoclimatic or taxonomic interpretation of phytolith assemblages. To improve our understanding of dissolution on grass phytoliths, we studied systematic changes of surface features, morphotype assemblages, and dissolution rates of phytoliths extracted from two grass species Hyparrhenia involucrata (Panicoideae), Nastus borbonicus (Bambusoideae), one soil from La Réunion Island (approximate mean age < 800 yr), and three paleosols from Ethiopia (approximate age of 4.4 million years). We used heavy-liquid to extract phytoliths, and 1% Na2CO3 to perform partial dissolution experiments. Physicochemical surface properties, morphotypes, and assemblages were analyzed using optical and scanning electron microscopy, laser diffraction, and X-ray diffractometry. Our results show that 1) phytoliths from different grass species may have different dissolution rates: phytoliths from the leaves of Hyparrhenia involucrata (Panicoideae) are more prone to dissolution than those from Nastus borbonicus (Bambusoideae). 2) Silicon (Si) released by phytolith assemblages (i.e., phytolith dissolution rate) decreases as follows: plant > soil > paleosol. 3) Dissolution leads to cavity formation on phytolith surfaces and disappearance of fragile silica particles. 4) Partial dissolution does not significantly change percentages of common grass phytolith morphotypes in a given assemblage. These results provide a benchmark for assessing the reliability of paleoenvironmental reconstructions using grass phytolith assemblages from buried soils and sediments.

Elemental and boron isotopic variations in tourmaline in two-mica granite from the Cuona area, Tibet: Insights into the evolution of leucogranitic melt

Two-mica granite is the most common magmatic rock type in the Himalayan leucogranite belt, which has close relationship with rare metal mineralization. Its genesis is generally attributed to magmatic differentiation. In recent years, the mineral geochemical compositions are increasingly used to study magmatic differentiation, which are significant for deciphering the melt evolution and element migration processes. In this study, in-situ major and trace element and boron isotope compositions for tourmalines from two-mica granites in the Cuona and Cuonadong leucogranites in the Cuona area are conducted to determine microscopic changes in mineral assemblages and geochemical compositions. Analytical results show that the tourmalines in the Cuonadong leucogranite were crystallized earlier relative to the tourmalines in the Cuona leucogranite during magmatic differentiation. The volatile contents have a genetic relationship with incompatible elements in tourmaline, which is possibly responsible for the formation of tourmaline zonation and the enrichment of Sr, Zn, and Pb during magmatic differentiation. The B isotopic composition of tourmaline in the Cuona area suggests that the granitic magma was dominantly derived from the partial melting of the metasedimentary source rocks. Their B isotope variations likely resulted from fluid exsolution during B-rich melt evolution. High rare metal contents in tourmalines indicate that the two-mica granites in the Cuona area may have great mineralization potential.

Diversity and seasonal changes of phyllostomid bats assemblages in montane and pre-montane forests in the Central Peruvian Yungas

Diversity and seasonal changes of phyllostomid bats assemblages in montane and pre-montane forests in the Central Peruvian Yungas

Late Oligocene-Early Miocene Palynological Succession From Marginal Marine Deposits, Nyalau Formation, Bintulu Sarawak: Palynostratigraphy, Paleovegetation And Paleoclimate Significance

Palynological analysis was conducted on one hundred and twenty-four samples collected from ten sedimentary outcrops in Sangan, Tatau, Bintulu and Similajau areas of central Sarawak. These outcrops form part of the Oligocene-Miocene marginal marine successions of the Nyalau Formation. Rich palynomorph assemblages were recovered from the samples and they provide well-preserved palynological record for the Oligocene-Miocene boundary in the onshore of northwest Borneo. Three distinct palynological zones were identified based on changes in pollen assemblages. The three zones are informally named FT-I, FT-II and FT-III. The FT-I zone is characterized by high frequency of Florschuetzia trilobata with common Florschuetzia semilobata including sporadic Meyeripollis naharkotensis. High percentage of F. trilobata and sporadic occurrence of F. semilobata are typical of the FT-II zone. Another important characteristic for this zone is characterized by common to abundant Casuarina type pollen while M. naharkotensis is virtually absent. The FT-III zone is marked by the presence of Florschuetzia levipoli. The zone is also characterized by abundant F. trilobata including regular occurrence of F. semilobata with common montane elements represented by Pinus, Picea, Alnus, Ephedra and Tsuga. All the identified zones record regular occurrence of Gramineae throughout with strong variation in diversity and frequency of peat swamp taxa represented by Blumeodendron type, Calophyllum type, Stemonurus type Calamus type and Dactylocladus type. The mangrove element such as Rhizophora type exhibits gradual increased in number throughout the FT-I and FT-II zone and showing reduced abundance in FT-III zone. These three zones are correlatable to the Late Oligocene to Early Miocene palynostratigraphy of the Cycle I and Cycle II in the Sarawak Basin. The palynological successions from these areas suggest a typical wet climate with intermittent seasonally dry conditions throughout the Late Oligocene - Early Miocene. This is evident from the regular occurrence of grass pollen i.e., Gramineae/Poaceae with common rain forest and peatswamp elements. This is supported by the common to high frequency of mangrove pollen notably Rhizophora type (Zonocostites ramonae). The Early Miocene may have experienced occasional super wet climatic conditions where rain forest pollen assemblages were prevalent including intermittent acme of Casuarina type pollen.

Toarcian ammonites of the Polymorphum Zone, Amellago area (eastern central High Atlas), Morocco, with a discussion on ammonite turnover events

In the Amellago area (central High Atlas), the widely distributed Toarcian succession consists of marls and marly limestones of the Tagoudite and Agoudim formations. We here describe, for the first time, the ammonites of the Polymorphum Zone from the Tagoudite Formation, including Canavaria cf. rosenbergi Fucini, C. aff. zancleana (Fucini), Dactylioceras (Eodactylites) mirabile (Fucini), D. (E.) aff. mirabile (Fucini), D. (E.) pseudocommune Fucini, D. (E.) simplex (Fucini), D. (Orthodactylites) aff. crosbeyi (Simpson), Lytoceras gr. villae Meneghini, Neolioceratoides cf. hoffmanni (Gemmellaro) and Praepolyplectus sp. This ammonite assemblage is closely correlated with those reported from the Polymorphum Zone of several basins of the Tethyan margins and the Northwest European Subboreal Realm, indicating marine communications between the different Moroccan Jurassic basins and the central Atlantic trough. The overlying Agoudim Formation yields ammonites of the Levisoni Zone in its base and rare ammonites of the Bifrons Zone in the middle part. Four significant changes in the ammonite assemblages during the early-middle Toarcian and their probable causes are also discussed.

Spatial and temporal changes in moth assemblages along an altitudinal gradient, Jeju-do island

Montane species on islands attract attention due to their small and isolated populations and limited dispersal potential, making them vulnerable to extinction. We investigated the diversity pattern of moth assemblages over the 12-years-period (2009–2020) at 11 study plots on an island mountain (Mount Hallasan, Jeju-do Island, South Korea) to assess the changes in the moth assemblages in terms of species composition, richness, and abundances. We expected to find a decline in the number of species at these sites, given the reported decline in similar taxa in other temperate regions, such as Europe and North America. In contrast, we found that the numbers of species and individuals of moth populations on the island mountain have not significantly changed, except at the high-elevation sites, where the number of species has increased. Our results also show that the numbers of species and individuals are closely related to energy availability, actual evapotranspiration. Moreover, we found that the species composition during the study period has not been greatly changed, except at the lowermost and uppermost elevations. The mechanism driving this high dissimilarity of moth assemblages differed: the low-elevation site experienced high temporal turnover, and the high elevation sites also experienced high temporal turnover and nestedness resulting from active species replacement due to a recent forest fire and vegetation changes and the geographic and ecological constraints of the high elevations. To date, the moth species diversity of the temperate forests of the island mountain is not showing a drastic change. However, we observed that the moth assemblages had changed the number of species and individuals at low and high elevations. Given the biological and ecological limitations of moths (ectothermic organisms with limited habitat range) and considering the results of our study, we infer that climate change has impacted the diversity and species composition of moths on the island mountain.

Restoration of native saltmarshes can reverse arthropod assemblages and trophic interactions changed by a plant invasion.

Plant invasions profoundly impact both natural and managed ecosystems, and removal of the invasive plants addresses only part of the problem of restoring impacted areas. The rehabilitation of diverse communities and their ecosystem functions following removal of invasive plants is an important goal of ecological restoration. Arthropod assemblages and trophic interactions are important indicators of the success of restoration, but they have largely been overlooked in saltmarshes. We determined how arthropod assemblages and trophic interactions changed with the invasion of the exotic plant Spartina alterniflora and with the restoration of the native plant Phragmites australis following Spartina removal in a Chinese saltmarsh. We investigated multiple biotic and abiotic variables to gain insight into the factors underlying the changes in arthropod assemblages and trophic structure. We found that although Spartina invasion had changed arthropod diversity, community structure, feeding-guild composition, and the diets of arthropod natural enemies in the saltmarsh, these changes could be reversed by the restoration of native Phragmites vegetation following removal of the invader. The variation in arthropod assemblages and trophic structure were critically associated with four biotic and abiotic variables (aboveground biomass, plant density,leaf N, and soil salinity). Our findings demonstrate the positive effects of controlling invasive plants on biodiversity and nutrient cycling and provide a foundation for assessing the efficacy of ecological restoration projects in saltmarshes.

One Tree Reef Foraminifera: a relic of the pre-colonial Great Barrier Reef

Abstract Benthic Foraminifera are important elements of coral reef ecosystems and valuable proxies for monitoring reef health in the face of local, regional and global stressors. Here Foraminifera preserved in a sediment core from the One Tree Reef (OTR) lagoon on the southern Great Barrier Reef (GBR) are used to quantify ecological changes associated with European colonization (early 1800s) and the subsequent industrialization of Australia (1950s onward). Core samples are compared to published benthic grab samples from three reefs to compare spatial and temporal variation. Standard measures of richness, diversity and foraminiferal assemblage composition indicate significant differences between the Recent assemblages of OTR lagoon and those from Heron and Wistari reef lagoons. However, there is no discernible change in the OTR lagoon core assemblages from the last four centuries in any of the richness or diversity indices examined. While benthic grabs likely undersample infaunal Foraminifera relative to core samples, these foraminiferal assemblages indicate the OTR lagoon contains a living example of a pre-colonial GBR lagoon ecosystem. Without cores from Heron and Wistari it is unknown if their foraminiferal assemblages have changed due to recent anthropogenic activity or if they have always been distinct.

Impacts of Livestock Grazing on Vegetation and Soil in Lowland Grassland Ecosystem of Nepal

Livestock grazing is one of the largest sectors for land use globally, and contrasting impacts (negative, neutral, and positive) of livestock grazing on vegetation and soil have been observed. In Koshi Tappu Wildlife Reserve (KTWR), livestock grazing is one of the major problems but has been feebly addressed in previous research. This study, therefore, aims to determine the impacts of livestock grazing on vegetation and soil quality in grasslands of core and buffer zones of KTWR. Less grazing intensity was observed at the core zone compared to the buffer zone. Livestock grazing was observed with negative impacts on the richness and diversity of the plant species causing changes in the community assemblages. Invasive plant species richness, however, was found higher in the low grazed areas. Differences in soil pH, phosphorus, and potassium content between high and low grazed areas were not observed. In contrast, soil electrical conductivity, bulk density, and nitrogen content were significantly higher in the high grazed areas. Controlled grazing is recommended at buffer zone grasslands of KTWR to enhance plant diversity and nutrient availability. The core areas of the reserve should be managed for reducing the abundance and distribution of invasive alien plant species.

Responses of avian assemblages to spatiotemporal landscape dynamics in urban ecosystems

ContextUrbanization and its associated impacts on biodiversity are increasing globally. There is a need to enhance our understanding of species responses to inform strategies for sustainable urbanization.ObjectivesThree extensive bird monitoring campaigns took place over the last three decades in the city of Naples, Italy, providing a comprehensive longitudinal dataset to analyse occurrence trends of urban birds. We aimed to assess both species-specific and assemblage-level changes in urban birds according to land cover dynamics.MethodsWe extracted bird data for the periods 1990–95, 2000–05, and 2014–18, and explored the spatial and temporal relationships between bird presence/avian assemblage composition, and land cover variation.ResultsThe species richness of breeding birds remained stable over time, despite a notable species turnover, influenced by changes in the species’ key land cover classes. Species associated with forest and urban land cover tended to colonise the area, while those dependent on abandoned and cultivated areas decreased or went locally extinct. Birds changed their degree of dependence upon their key habitat type over time, as species from marginal and open habitat types needed larger amounts of habitat to persist within the area, while forest species showed an opposite trend.ConclusionsHabitat-driven changes in avian assemblages within the urban landscape led to an increase in forest-associated species, and a decrease in birds associated with declining habitat types. Our findings may inform urban planning to promote more wildlife-friendly cities, which for our study area should prioritise open and marginal habitats.

Susceptibility of Tidal Pool Fish Assemblages to Climate Change

There is a need for improved understanding of how climate-change driven rises in sea level and increased ocean temperatures will affect fish assemblages in rocky shore tidal pools. Rising sea levels are predicted to alter habitat availability and increasing ocean temperatures will drive tropicalisation, both of which are likely to alter tidal pool fish assemblages. Consequently, we examined changes in fish assemblages in tidal pools at four sites in Coffs Harbour, Australia, using baited video sampling. Data were collected seasonally at each site, in pools at differing tidal elevations. We identified significant differences in tidal pool fish assemblages among elevations and found that assemblages exhibited cyclic seasonal patterns. Modelling identified that ocean temperature was the most powerful factor for explaining variations in assemblages, followed by pool area and pool elevation. Results highlight that distinct fish assemblages occur in tidal pools at different elevations and indicate that assemblages at higher elevations could be squeezed out by rising sea levels and by increased competition from tropical fish species. Future conservation assessments are needed to determine whether latitudinal and vertical range shifts for tidal pool fishes are possible, with facilitation of these range shifts needed to address displacement of tidal pool fishes by rising sea levels and ocean temperatures.

Influence of limestone addition on sodium sulphate activated blast furnace slag cements

The effect of limestone replacement in the reaction and phase assemblage evolution of two sodium sulfate activated slag cements was investigated. The slag composition and its reactivity influenced the reaction kinetics of these materials. Paste with limestone addition exhibited an acceleration in reaction kinetics, particularly for slowly reacting slags. Ettringite and an aluminium substituted calcium silicate hydrate were identified as main reaction products in these cements, independently of the slag type or limestone replacement level. No significant changes in phase assemblages were observed with limestone addition for over 365 days of testing; however, these composite cements exhibited an increased compressive strength, consistent with a refined pore structure. These results indicate that it is possible to partially replace slag by limestone in sulfate activated slag cements without changing the type of reaction products forming in these systems, while also increasing compressive strength and achieving a similar refined pore structure.

Crustose coralline algae and biodiversity enhancement: The role of Lithophyllum stictiforme in structuring Mediterranean coralligenous reefs

Biogenic structures edified by crustose coralline algae (CCA) are known to enhance biodiversity, but the mechanisms involved are only partially defined. This study aims at contributing to the knowledge of the interaction between habitat-builder CCA and epibiont assemblages through a manipulative approach. To achieve this objective, transplantations of the CCA Lithophyllum stictiforme were performed to test the following hypotheses: 1) the structure of L. stictiforme epibiont assemblage changes between depth and biogeographic area; 2) L. stictiforme epibiont assemblage is different and more diversified than the assemblage recruited on bare rock; 3) the early L. stictiforme epibiont assemblage differ from the mature L. stictiforme epibiont assemblage. A total of 63 epibiontic taxa were found on the transplanted L. stictiforme thalli, such as 7 Chlorophyta, 10 Ochrophyta, 40 Rhodophyta, 1 Sarcomastigophora, 1 Porifera, 4 Bryozoa. The sessile assemblage recruited on transplanted L. stictiforme thalli depended on sites and depths, and it had a higher taxa richness compared to that colonizing the bare rock. The early recruited assemblage on L. stictiforme transplanted thalli compared to the mature assemblage on untouched thalli was different mostly in the relative abundance of taxa, rather than in species composition. These manipulative experiments highlighted for the first time the role of a common CCA on the development and biodiversity of coralligenous assemblages, contributing to emphasize the importance of CCA conservation efforts.

Radiolarian size and silicification across the Paleocene-Eocene boundary and into the early Eocene

The Paleocene-Eocene Thermal Maximum (PETM) was a major environmental perturbation that drove range shifts, adaptation, and faunal turnover in marine and terrestrial clades. Open ocean planktonic responses—including body size trends—have been characterized for calcareous nannoplankton, dinocysts, and planktonic foraminifera. Relatively little, however, is known about the response of radiolarians, which share life modes and phylogenetic history with planktonic foraminifera but make their tests (i.e., ‘shells’) out of silica rather than calcium carbonate. Here, we compare radiolarian assemblage changes in the Southwest Pacific with assemblages from Atlantic and Indian Ocean sites. We also measured radiolarian test size before, during, and after the PETM in a pelagic sedimentary succession at Mead Stream, South Island, New Zealand. Our results show a substantial positive shift in mean radiolarian test size at Mead Stream at the assemblage level concurrent with the onset of the PETM, primarily due to an increase in the size and relative abundance of spumellarian radiolarians. We investigate oligotrophy, elevated seawater silica concentration, and redeposition as potential drivers for this size shift. Mead Stream radiolarians remain large for 1.3 Myr, long past the recovery of the carbon isotope excursion and a return to baseline in terrigenous sedimentation, bioturbation, and benthic foraminifera diversity, leaving the ultimate cause of the observed changes in test size uncertain. We find little evidence for a uniform morphological response to the event or its aftermath across sites, particularly as relates to the relative extent of silicification of different groups of radiolarians.

Birth of the Pearl River at 30 Ma: Evidence from sedimentary records in the northern South China Sea

The Pearl River drains the South China Block and delivers large amounts of sediments to the northern South China Sea, and its development can be closely linked to the regional paleoenvironmental changes. However, the evolutionary history of the Pearl River has been poorly understood, mainly because of the lack of continuous and high-resolution sedimentary records over a long geological time. In this study, we present multiple new analytical results, including clay mineral assemblages and Sr-Nd isotopic compositions of the <2 μm siliciclastic sediments, from the latest deep sea drilling core in the northern South China Sea from International Ocean Discovery Program (IODP) Site U1501. We aim to reconstruct the evolutionary history of the Pearl River by tracing changes in clay mineral assemblages and Sr-Nd isotopic compositions. Provenance analysis indicates that the sediment source experienced a significant change between 32 and 30 Ma. Specifically, sediments prior to 32 Ma were derived from the southeastern Cathaysia coast, whereas sediments post to 30 Ma were mainly supplied by a proto-Pearl River. This provenance transition indicates that the modern-scale Pearl River has fully developed at least ∼30 Ma and began to contribute sediments to the northern South China Sea. We additionally compared the timings of major climatic and tectonic events in this region, and suggest that the topographic uplift of the SE Tibetan Plateau most likely drove the large-scale westward expansion of rivers drainage from the coast located in the Cathaysia Block to the interior of Yangtze Block. As a result of this fluvial drainage evolution followed by the development of Pearl River, geochemical and clay mineralogical characteristics of the deposits in the northern South China Sea correspondingly changed.

Decadal changes in parrotfish assemblages around reefs of Guam, Micronesia

Modern coral reefs face substantial threats that endanger their capacity to function and provide resources for human populations. Chronic human pressure through exploitation and land-based pollution has led to reef degradation and lower productivity. More recently, this pressure is compounded with successive episodes of coral bleaching across the tropical oceans. However, response trajectories of reef resources to exploitation, habitat degradation, and local management may not be straightforward, as these ecosystems are incredibly complex. We employed a comprehensive and standardized survey of parrotfish assemblages within reef systems in Guam to examine trajectories of biomass and function across a decade of change. Parrotfishes represent one of the most commercially and ecologically important coastal resources throughout Micronesia. We found that parrotfish biomass declined by nearly 30% over the course of ten years, with concomitant decreases in grazing and bioerosion rates at a similar magnitude. There was evidence of fishery exploitation playing a role, but overall patterns were not always aligned with the hypothesis of fishery-induced decline. For example, two-thirds of marine-protected area sites declined in biomass and mean body length was stable for several highly targeted species. Further, most biomass decline stemmed from small species with higher resilience to fishery exploitation, whereby three of the most vulnerable fishery target species either maintained or increased total biomass. The ultimate drivers of parrotfish assemblage trajectories in Guam are likely a complex mixture of exploitation, habitat change from multiple stressors, and responses to management measures. However, the potential future decline in fishery production and ecological function is substantial and merits continuous monitoring and proactive management.

Fire Severity Causes Temporal Changes in Ground-Dwelling Arthropod Assemblages of Patagonian Araucaria–Nothofagus Forests

Fire is one of the main drivers of anthropogenic disturbances in temperate forest ecosystems worldwide, with multiple effects spread across ecological networks. Nevertheless, the biodiversity effects of fire are poorly known for species-diverse groups such as arthropods. In this research, we used a burn gradient generated two and three years after a large fire event to assess how different levels of fire severity affect arthropod diversity in the forest with the main forest forming long-living tree species Araucaria araucana, in southern Chile. The species richness and abundance of arthropods among trophic guilds was estimated annually in four fire-severity levels. We found that arthropods responded differently to fire severity levels, depending on their trophic guilds and years after fire (two and three years after fire). During the second year after fire, zoophages, phytophages, and parasitoids were more diverse in areas with high fire severity within the second year after fire, as compared to those in areas with low severity or unburned stands. In the third year after fire, a change in this trend was observed, where the abundance of all groups dropped significantly, with positive changes in the diversity in zoophages, phytophages, polyphages and saprophages, which is more noticeable in sites with high severity. These results indicate that annual variation in environmental conditions triggers bottom-up cascading effects for arthropods. Forests stands severely impacted by fires support highly fluctuating and possibly unstable arthropod assemblages. Hence, restoration efforts should be focused on recovering microhabitat conditions in these stands to allow the persistence of arthropods.

Benthic foraminifera as an environmental proxy for pollutants along the coast of Chennai, India

Benthic foraminifera are increasingly used as an indicator of environmental disturbance. Their sensitivities to pollutants can be reflected by changes in assemblage, which can provide useful information about ecosystem health. This study aimed to investigate the impact of organic and inorganic pollutants on the benthic ecology of the Chennai coast, with a focus on the 2017 oil spill caused by the collision of two ships. Sediment samples collected from five distinct zones along the coast were analysed for pollutants such as polycyclic aromatic hydrocarbons (PAHs), total petroleum hydrocarbons (TPH), heavy metals (Cr, Cd, Pb) and total organic carbon (TOC). The maximum concentrations of Cr (137 μg/g), Cd (6.93 μg/g) and Pb (34.2 μg/g), as well as TPH (84.3 μg/g) and PAHs (227 ng/g), were observed. A total of 47 species of foraminifera were identified in this study, of which 12 were morphologically abnormal. In the low-impact zone, the species diversity index (H′) was higher. TPH and PAH concentrations were positively associated with abnormal species. Pollution-resistant foraminifera species include Ammonia tepida, Elphidium discoidale, and Quinqueloculina lamarckiana, while opportunistic foraminifera include Pararotalia curryi, Nonionella stella, Rosalina globularis, and Spirillina vivipara. PAHs and heavy metals were adversely correlated with foraminiferal abundance, while TPH was positively correlated. To assess the response of the benthic ecosystem to hydrocarbon pollution, indices such as the Foraminiferal Index of Environmental Impact (FIEI), Exponential (H′bc) index and the Foraminiferal Abnormality Index (FAI) were used as environmental health proxies. FIEI, exp(H′bc) and FAI values show the impact of hydrocarbon pollution to an extent along the northern Chennai coast.