Tiny survivor: rare plankton species found thriving in hypersaline Arabian Gulf

Off the coast of Abu Dhabi, in waters so salty that most marine plankton simply cannot survive, scientists have made a discovery that rewrites the map of where one of the ocean’s most important groups of organisms can live. For the first time, modern planktonic foraminifera — microscopic, single-celled organisms that drift through the open ocean and build delicate limestone shells — have been documented in seafloor sediments from the southeastern corner of the Arabian Gulf. The finding, published in the Journal of Micropalaeontology, is remarkable not just because these organisms were found so far from their usual home near the Strait of Hormuz, but because one rare and peculiar species utterly dominates the assemblage: a minute creature called Neogallitellia vivans, which makes up more than 90 percent of the planktonic foraminifera recovered.

Planktonic foraminifera are among the most studied groups of organisms in the entire ocean. Roughly 50 living species inhabit the modern ocean, distributed from tropical to polar waters, and their fossil shells form vast chalk deposits on the seafloor. Because different species prefer different water temperatures, salinities, and nutrient levels, their shells serve as powerful archives of past climate and ocean chemistry. Yet in the Arabian Gulf — a shallow, semi-enclosed basin where evaporation far exceeds freshwater input and salinity routinely exceeds 40 practical salinity units — these organisms were thought to be largely absent, confined to the deeper, better-connected waters near the Gulf’s only oceanic inlet, the Strait of Hormuz.

The new study, led by Sinatrya D. Prayudi of King Fahd University of Petroleum and Minerals together with Thomas Steuber of Khalifa University and Michael A. Kaminski, examined 20 sediment samples collected during two research cruises aboard the R/V Jaywun, a collaboration between the Environment Agency Abu Dhabi and Khalifa University. The first expedition, in September 2024, retrieved sediment cores using a multiple corer; the second, in March 2025, collected 14 grab samples that were stained with rose Bengal to distinguish living from dead specimens. Planktonic foraminifera turned up at only four of the 20 sites, and even there they represented less than 5 percent of the total foraminiferal assemblage — but their presence at all, at water depths of 35 to 40 meters far from the open ocean, was unexpected.

The physical conditions at these sites are extreme by any standard. Conductivity-temperature-depth measurements during the August 2024 survey recorded water temperatures as high as 35.6 degrees Celsius, with values above 35 degrees throughout the upper water column for 200 kilometers offshore. Salinity in the basin south of the Great Pearl Bank ranged from 44 to 45 psu, among the highest values found anywhere in the open marine realm. Only further offshore, where the planktonic foraminifera were recovered, did surface salinity drop to around 39 psu, reflecting the influx of less-salty surface water from the central Gulf, which itself derives from the Indian Ocean inflow of roughly 37 psu entering through the Strait of Hormuz.

The assemblage the team recovered includes at least five taxa: three true planktonic species — Neogallitellia vivans, Globigerinoides tenellus, and Turborotalita cf. clarkei — plus Tretomphalus bulloides, a benthic species that develops a buoyant float chamber and spends part of its life drifting in the water column, and an enigmatic spherical microfossil of uncertain affinity, tentatively assigned to the genus Bachmayerella, a form first described from the Miocene of the Paratethys. Apart from N. vivans, all the planktonic species appeared only as single occurrences, with no more than three specimens of any one species found across the entire sample set. The stained samples confirmed that the planktonic shells in the sediment were dead specimens, not living individuals captured on the seafloor.

What makes the finding truly striking is the overwhelming dominance of N. vivans, a species first described in 1934 from the waters off Little Ki Island in Indonesia. The species is tiny — most specimens measure less than 120 micrometers across, meaning many slip through the standard 125-micrometer sieve that micropaleontologists traditionally use to sort foraminifera — and it is the only triserial planktonic foraminifer alive today, with its globular chambers arranged in three spiraling rows. Previous reports place it mainly in the Indo-Pacific, from the Laccadive Sea and the Banda Sea to the Yellow Sea and the Tsushima Strait. Its abundance in the Arabian Gulf suggests the species may be far more cosmopolitan than previously recognized, particularly in the small size fractions that earlier surveys often overlooked.

To understand why this species succeeds where others fail, the researchers turned to scanning electron microscopy, using both a desktop instrument and a high-resolution field-emission SEM to image broken specimens and reveal the internal structure of the shell. What they found was a wall of extraordinary simplicity: a thin, single calcitic layer only one to two micrometers thick, lacking a visible primary organic sheet, and perforated by micropores smaller than half a micrometer in diameter. These pores are sparsely and irregularly scattered across the surface, often occurring in pairs or triplets arranged in triangles, and are absent near the chamber sutures. The surface is smooth, without the pore mounds or pits that characterize many related genera.

These features may hold the key to the species’ ecological success. In foraminifera, pores function primarily for gas exchange, and pore size and density are known to correlate with ambient oxygen levels. N. vivans is frequently associated with nutrient-rich, low-oxygen environments such as upwelling zones and oxygen-minimum zones, including those of the Arabian Sea. Molecular studies have shown that the species diverged from a benthic ancestor, Stainforthia fusiformis, during the late early Miocene, around 18.2 million years ago — and that ancestor is famous for tolerating oxygen-poor sediments. The researchers suggest that N. vivans carried these adaptive traits with it when it made the evolutionary leap from the seafloor to the open water, equipping it to colonize marginal marine environments that exclude typical planktonic species.

The dominance of N. vivans in the hypersaline southeastern Gulf also echoes a pattern familiar from the deep fossil record. Minute triserial foraminifera related to this lineage famously bloomed in the aftermath of the asteroid impact that wiped out the dinosaurs 66 million years ago, thriving in the devastated oceans when virtually all other planktonic foraminifera perished. Species with this body plan appear to function as ecological opportunists — so-called disaster taxa — capable of occupying niches that more specialized organisms cannot tolerate. In the modern Gulf, a young basin flooded only during the early Holocene sea-level rise, N. vivans may be playing exactly that role, exploiting an environment that is naturally stressed by heat and salinity and increasingly pressured by human activity.

How the planktonic foraminifera arrived in the southeastern Gulf remains an open question. The researchers outline three possibilities: surface currents from the Indian Ocean may carry the organisms into the basin through the Strait of Hormuz; ballast water discharged by the region’s heavy commercial shipping may have introduced them; or a viable population may have established itself in the Gulf’s deepest sectors since the postglacial reflooding of the basin. The evidence currently available cannot settle the matter, and the authors call for future work using plankton nets, sediment traps, and Holocene sediment cores to determine whether N. vivans is an active, living member of the Gulf’s plankton community today or a recent immigrant whose shells are merely accumulating on the seafloor. Either way, the discovery stands as a vivid reminder that even in one of the harshest marine environments on Earth, life finds a way — sometimes in the smallest, most easily overlooked forms.

Subject of Research: First report of modern planktonic foraminifera and the morphology and ecology of Neogallitellia vivans in the hypersaline southeastern Arabian Gulf

Article Title: First report of modern planktonic foraminifera in the southeastern Arabian Gulf, with observations on the morphology and ecology of Neogallitellia vivans (Cushman)

Article References: Prayudi, S. D., Steuber, T., & Kaminski, M. A. (2026). First report of modern planktonic foraminifera in the southeastern Arabian Gulf, with observations on the morphology and ecology of Neogallitellia vivans (Cushman). Journal of Micropalaeontology, 45(1), 415-427. https://doi.org/10.5194/jm-45-415-2026

Image Credits: AI Generated

DOI: 10.5194/jm-45-415-2026

Keywords: planktonic foraminifera, Neogallitellia vivans, Arabian Gulf, Abu Dhabi, hypersaline environment, micropaleontology, foraminiferal ecology, SEM imaging, Strait of Hormuz, disaster taxa, marine biodiversity, Holocene reflooding