The research team surveyed nine sites in the waters off Suhar, dividing them into three depth categories: shallow artificial reefs at 11 to 13 meters, deep artificial reefs between 16 and 22 meters, and natural coral reef areas ranging from 21 to 23.5 meters. Data were collected during two contrasting cruises, one in July 2019 and one in January 2020, allowing a direct comparison between the peak of summer and the depths of winter. At each site, the researchers lowered a Conductivity, Temperature, Depth logger through the water column to record temperature, salinity, and dissolved oxygen continuously from surface to seafloor. Meanwhile, SCUBA divers swam transects with a diver-operated stereo-video rig, a pair of 4K cameras mounted on an 800-millimeter aluminum bar, filming just 30 centimeters above the seabed to capture every fish that crossed their path.

The stereo-video technique is one of the quiet revolutions of modern reef science. Unlike traditional visual censuses, which depend on a diver’s ability to identify and count fish in real time, stereo-video records everything and defers the analysis to the laboratory. The team imported their footage into EventMeasure software, which uses paired image coordinates from the left and right cameras to calculate the three-dimensional position of each fish, its distance from the cameras, and its size. That means abundance estimates are no longer distorted by the fact that some species flee divers while others curiously approach them, at least not in the same way, and body-length measurements come free with every count. The method is fast, relatively cheap, and simultaneously captures fish size, abundance, and habitat complexity, which is precisely why it has become a standard tool for reef monitoring worldwide.

What the footage revealed was a fish community with a stable core and a shifting periphery. Three species, the common snapper Lutjanus lutjanus, the variable-lined fusilier Caesio varilineata, and Ehrenberg’s snapper Lutjanus ehrenbergii, were present at every site in both seasons, forming what ecologists call a persistent assemblage. The Lutjanidae are no ecological footnote in Oman: this family of snappers yielded 7,150 tonnes in 2020, worth 2.7 million Omani Rials, making it one of the country’s most economically important benthic fish groups. Other species were far more seasonal. The grunter Pomadasys aheneus, for instance, showed a strong association with winter, appearing reliably in the cooler months and largely vanishing in summer. In total, the team recorded 15 species in summer and 12 in winter, a difference that sounds modest until you look at how those species were distributed.

That distribution is where the story gets interesting. Although summer hosted more species overall, the winter community was measurably more diverse and more evenly balanced. The Shannon-Wiener diversity index, which combines species richness with how equitably individuals are spread among those species, rose from 0.984 in summer to 1.124 in winter. Pielou’s evenness index climbed even more sharply, from 0.522 to 0.701, while Simpson’s dominance index fell from summer to winter, indicating that no single species monopolized the reef in the cooler season. Species richness, by contrast, was nearly identical across seasons, at 1.042 in summer and 1.047 in winter. In plain terms: summer reefs were dominated by a few abundant players, while winter reefs hosted a more democratic community in which no species towered over the rest. For fisheries managers, evenness matters, because communities with balanced abundances are generally considered more resilient and ecologically healthy.

Depth turned out to be the hidden hand shaping much of this pattern. The interaction plots in the study show that Shannon diversity at shallow artificial sites jumped from 0.84 in summer to 1.18 in winter, while deep sites stayed essentially flat year-round. Species richness told the mirror-image story: deep artificial sites were richer in summer, at 1.24, than in winter, at 0.81, while natural reef sites peaked in diversity and richness during winter. Statistical analysis confirmed that these season-by-depth interactions were significant, with non-parallel lines in the interaction plots and a three-way ANOVA yielding p-values below 0.05. In other words, the effect of season on fish diversity cannot be understood without also knowing the depth, and the effect of depth cannot be understood without knowing the season. Any attempt to design or site an artificial reef without accounting for both variables would be flying blind.

The physical chemistry of the water column explains why. The Sea of Oman is an extreme environment by reef standards, with surface temperatures swinging from roughly 35 degrees Celsius in summer to 23 degrees in winter, and strong seasonal upwelling that reverses the usual latitudinal temperature gradient. The CTD profiles showed that in summer, dissolved oxygen fell steeply with depth, producing a near-perfect negative correlation between depth and oxygen concentration of r = −0.985, statistically significant at p = 0.000. In winter, the relationship flipped: depth correlated positively with dissolved oxygen, at r = 0.828 with p = 0.010, and positively with evenness as well, at r = 0.704 with p = 0.030. The authors attribute this seasonal flip to differences in vertical mixing between the two seasons, with winter storms and cooling breaking down the stratification that traps oxygen near the surface in summer. Salinity, which varies only between about 35 and 37.4 parts per thousand in this sea, correlated strongly with depth in both seasons and with dissolved oxygen, negatively in summer and positively in winter.

A principal component analysis added a final layer of insight. Winter samples clustered tightly together across all depths, painting a picture of a well-mixed, homogeneous environment in which fish everywhere experienced similar conditions. Summer samples, by contrast, scattered widely along the second principal component, with shallow sites showing the greatest dispersion, evidence of depth-driven stratification and higher environmental unpredictability during the hot months. This makes ecological sense of the diversity numbers: when the environment is stable, as in winter, fish communities can spread their abundances more evenly because no species gains an overwhelming competitive edge. When the environment stratifies and fluctuates, as in summer, tolerant or dominant species take over, and dominance rises. The study also notes that competition for food and space between seasons, and the tendency of fish to migrate toward preferred conditions, likely contribute to the seasonal shifts in evenness.

The implications reach well beyond Suhar. Oman’s fisheries sector contributed 1.3 percent of national GDP in 2018 and remains a pillar of food security, while coral reefs in the wider region have suffered catastrophic bleaching events, including the 2017 bleaching in the southern Persian/Arabian Gulf. Artificial reefs are increasingly promoted as a tool to buffer these losses by providing alternative habitat and supporting fish populations, but this study shows they are not a one-size-fits-all solution. Their effectiveness depends on depth, season, and the oxygen dynamics of the water column above them. Natural reefs in the study proved more stable and more diverse in winter, reinforcing their value as reference ecosystems, while artificial reefs showed depth-specific seasonal responses that managers must plan around. The authors argue that their correlation and diversity data provide the foundation for future time-series models of fish abundance and water quality, the kind of predictive tooling that could transform reef deployment from an art into a science. For a region on the front line of ocean warming, that is not an academic luxury. It is a blueprint for keeping fish on the reef, and on the plate, for decades to come.

Subject of Research: Seasonal and depth-related effects of temperature, salinity, and dissolved oxygen on fish diversity in artificial reef ecosystems of the Sea of Oman

Article Title: Seasonal variability of physico-chemical parameters and their effects on fish diversity in artificial reefs of the Sea of Oman

Article References: Al Kindi, A., & Dutta, S. (2026). Seasonal variability of physico-chemical parameters and their effects on fish diversity in artificial reefs of the Sea of Oman. Discover Oceans, 3(1), Article 21. https://doi.org/10.1007/s44289-026-00133-5

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00133-5

Keywords: artificial reefs, Sea of Oman, fish diversity, dissolved oxygen, temperature, salinity, Shannon diversity index, stereo-video, depth, seasonality, Oman, fisheries management

The study, published in Discover Oceans, represents the first experimental investigation of bryozoans as biofoulers in the Gulf of Mannar and Palk Bay region. Between June 2020 and June 2021, the team deployed eight static immersion panels, two at each of four locations: Pamban Island, Vedalai, Manouli Island and Ervadi. Each panel carried twelve-inch square plates of four different materials, positioned equidistant from one another to prevent interference. One panel at each site was retrieved after six months, and the experiment was repeated with fresh plates in a second six-month window, while a parallel long-term panel remained submerged for the entire year. This design allowed the researchers to track both seasonal patterns of settlement and the slower dynamics of ecological succession.

The results were strikingly selective. Ten species of encrusting bryozoans were identified over the course of the study, but two dominated almost everywhere: Parasmittina projecta and Celleporaria aperta. These pioneer species appeared on ceramic and terracotta plates at every stage of the experiment, regardless of location or season. Rarer species, including Parasmittina tubula, Parasmittina egyptiaca, Hippopodina feegeensis and Pleurocodonellina signata, showed up only as small colonies or patches. Electra pilosa, a species known for its preference for rough surfaces, colonised the coarse reverse side of a terracotta plate at Pamban Island, while the long-term panels revealed two latecomers, Parasmittina triangularis and Rhynchozoon compactum, that never appeared on the shorter deployments.

Just as telling was what the bryozoans refused to colonise. Metal plates, left unpainted and exposed to seawater, corroded heavily over the study period, rusting and in some cases crumbling apart. Not a single bryozoan colony established itself on metal during the first six-month study, and the researchers attribute this to corrosion-induced surface instability and the release of iron oxides, both known to interfere with larval settlement in sessile invertebrates. Wood fared little better: it degraded rapidly, became infested with serpulid worms and bivalves, and hosted bryozoans only in the crevices of rotten timber during the long-term deployment. Ceramic and terracotta, by contrast, offered the stable, wettable surfaces that bryozoan larvae clearly favour, with post-hoc statistical comparisons confirming significantly greater cover on these two substrates than on wood or metal.

Texture and orientation mattered as much as material. The researchers analysed each retrieved plate using a quadrat method, dividing the surface into a four-by-four grid, and complemented colony counts with photographic point-count analysis in ImageJ to estimate total percentage cover. Across the board, the reverse sides of the plates, which faced away from the prevailing swell and sat in shadow, carried more bryozoan cover than the front-facing surfaces, a difference confirmed by a Mann-Whitney U test. Many encrusting bryozoans are sciaphilic, meaning their larvae preferentially settle in shaded, sheltered microhabitats where algal competition and physical disturbance are reduced. The forty-five-degree inclination of the panels also created a gradient of water movement, with the upper portions experiencing greater flow that delivered larvae and food particles without burying the feeding apparatus, or lophophore, in sediment.

Seasonality left its own fingerprint. The first six-month study, spanning the monsoon months when rainfall was highest and temperatures remained within the optimal range for reef-building organisms, yielded seven bryozoan species. The second window, covering the drier, hotter months when water temperatures in 2020 climbed to between 32 and 35.1 degrees Celsius and salinity rose through evaporation and upwelling, produced only four. The researchers suggest that the favourable calcium concentrations and moderate conditions of the monsoon period supported the calcification that bryozoans, like corals, depend upon, while the hotter, saltier conditions of the second period favoured corrosion over colonisation. Notably, P. delicatula appeared only in the second window, consistent with its known salt tolerance.

Perhaps the most vivid finding came from the year-long panels, which transformed into miniature ecosystems. By the time they were retrieved, they harboured hydroids, serpulid worms, barnacles, thickets of seaweed and even juvenile crabs and other crustaceans sheltering among the growth. Scanning electron micrographs captured Celleporaria aperta overgrowing less competitive species, illustrating the competitive displacement that unfolds as succession progresses. The bryozoans, by secreting an adhesive polysaccharide that rapidly mineralises into a solid crust, had created the foundational substrate on which the entire assemblage depended. In ecological terms, they acted as pioneer species initiating facilitative succession, paving the way for a climax community of the kind long described in port fouling studies but never before documented experimentally in this biosphere reserve.

The study’s authors are careful about its limits. Each site hosted a single short-term and single long-term panel, so the deployments served as parallel observations rather than true statistical replicates, and the analyses were deliberately descriptive and comparative. Several plates and panels were lost to monsoonal currents, corrosion and occasional human disturbance, and environmental parameters such as temperature, salinity and chlorophyll-a were not measured in situ. These constraints, common to open-water colonisation experiments in protected reserves, mean the findings should be read as robust baseline evidence rather than definitive inference. Even so, the consistency of the substrate-driven pattern, reinforced by principal component analysis that cleanly separated high-colonisation ceramic and terracotta samples from wood and metal, gives the conclusions considerable weight.

Why does any of this matter beyond the taxonomy of small colonial animals? Bryozoans have long been cast as villains in the biofouling story, blamed for dragging down ship hulls, clogging cooling pipes and ferrying invasive species across oceans. This study reframes them as ecological engineers whose crusts stabilise reef structures, facilitate the settlement of macro-foulers and sustain biodiversity. Artificial substrates colonised in this way can support fisheries, diving tourism and ecotourism without touching endangered natural reefs, and dense fouling communities may even help engineered structures absorb wave energy during storms and tsunamis. The discovery that Paralicornia obtecta, previously recorded from India’s southwest coast, Sri Lanka and the wider Indian Ocean, now appears in the Gulf of Mannar, adds a biogeographical data point to a region whose fouling fauna had been studied almost exclusively in harbours.

The broader lesson is one of hidden complexity in plain sight. A square metre of submerged ceramic, left alone for a year, becomes a stage on which larvae discriminate between textures, pioneers build skeletons, competitors wage slow-motion overgrowth battles and juvenile crustaceans find refuge. Understanding these dynamics matters for anyone designing artificial reefs, managing port infrastructure or predicting how tropical reef communities will respond as seas warm and salinities shift. The Gulf of Mannar’s bryozoans, once dismissed as ecologically insignificant, have now been shown to be among the quiet architects of their underwater world, and the researchers hope their baseline data will guide future studies that pair replicated deployments with continuous environmental sensing to unravel the mechanisms behind the patterns they have revealed.

Subject of Research: Biofouling bryozoan settlement and succession on artificial substrates in the Gulf of Mannar

Article Title: Experimental investigation on biofouling marine bryozoans in reefs

Article References: Sanjay, M. S., Venkatraman, C., Sen, A., & Yogesh Kumar, J. S. (2026). Experimental investigation on biofouling marine bryozoans in reefs. Discover Oceans, 3(1), Article 27. https://doi.org/10.1007/s44289-026-00138-0

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00138-0

Keywords: bryozoa, marine biofouling, Gulf of Mannar, Parasmittina projecta, reef formation, larval settlement, substrate preference, ecological succession, artificial reefs, marine biodiversity, coral reefs, India

That unraveling is now well documented. More than 60 percent of the world’s reefs are already degraded by local pressures such as overfishing, coastal development and watershed pollution, and climate change has become the single greatest threat, compounding every one of those stressors. Approximately half of the planet’s tropical coral reefs have been lost in the past three decades, and the trajectory is expected to continue. According to the Intergovernmental Panel on Climate Change, if global temperatures rise 1.5 degrees Celsius above preindustrial levels, 70 to 90 percent of modern reefs may vanish; beyond 2 degrees, more than 99 percent would be destroyed. Because the pace of decline now overwhelms the natural regenerative capacity of reefs, scientists and practitioners have turned to active restoration, deploying coral transplantation, algae removal, larval propagation, acoustic enrichment and, increasingly, artificial reefs.

Artificial reefs are structures deliberately submerged on the seabed to mimic the characteristics of natural reef habitat, allowing benthic species to colonize and thrive. When correctly implemented, particularly in sediment-affected environments, they have demonstrably enhanced local marine resources. They can serve as recruitment surfaces for coral larvae, as culture substrates for colonies raised in nurseries, and, once established colonies reach sexual maturity, as intermediate platforms that seed surrounding areas with dispersing larvae. But a new mini-review published in Blue Biotechnology by Baptiste Ozanam, Pascal Romans and Raphaël Lami of Sorbonne Université and CNRS argues that the fate of this entire restoration strategy hinges on an unglamorous question: what, exactly, should an artificial reef be made of?

The answer is constrained by economics as much as ecology. The median cost of deploying artificial reefs is 3,341,754 US dollars, and restoration budgets are chronically stretched, so materials must be affordable as well as biocompatible, durable and non-polluting. International guidelines, including the OSPAR convention, require that reefs be built from inert materials capable of withstanding harsh marine conditions without releasing contaminants through biological, physical or chemical alteration. Judged against those criteria, the four workhorse materials of modern artificial reefs, concrete, plastics, metals and wood, each fall short in revealing ways.

Concrete remains the most popular choice because it is strong, moldable into any shape, and resembles natural rock, and its surface can be tuned by adding coarse sand to adjust roughness. Yet freshly immersed cement can exhibit a surface pH of 10 to 11, requiring three to twelve months of seawater aging before it approaches ambient levels. During that window, pH-tolerant organisms such as barnacles colonize the structure and can block coral settlement entirely. There is also a deeper paradox: cement production accounts for roughly six percent of global carbon emissions, meaning the dominant restoration material is manufactured by an industry that directly fuels the climate change threatening the very reefs being restored.

Recycled materials carry their own liabilities. Old tires are cheap and readily colonized, but they are unstable, easily shifted by currents in ways that can damage surrounding reefs, and they leach toxic compounds including zinc, copper, formaldehyde and acetone products that suppress marine life; large-scale tire deployment is no longer considered viable. PVC structures persist in modern projects, most famously in the Coral Tree Nursery developed by the Coral Restoration Foundation, a lightweight system of PVC columns and arms anchored with steel rebar that rears corals in situ before transplantation. It is portable, inexpensive and gentle on the seafloor, but its plastic components degrade in harsh marine conditions and can shed microplastics. Those particles are phagostimulants that corals mistake for prey, consuming energy that should nourish them, clogging digestive systems, killing polyps, and raising disease risk dramatically: one landmark study found that contact with plastic debris increases the likelihood of coral disease from 4 percent to 89.1 percent.

Metal offers light weight and the ability to form complex shapes at low cost. Mars Incorporated deployed hexagonal modular ‘spider’ structures made of rebar, coated in coarse beach sand, on degraded reefs in Indonesia at roughly 15 US dollars apiece, providing substrate suitable for coral recruitment and rapid recovery. But oxidation products released from corroding metal feed algal growth that competes with corals, and comparative studies have recorded lower coral colonization on metal plates than on concrete, partly because thin plates disintegrated within 17 months, too quickly for corals to establish. Repurposed decommissioned ships promise large colonizable areas and dive-tourism value, but they can carry PCBs, petroleum products, lead, mercury, zinc, tributyltin, radioactive control dials and asbestos, and decontaminating them inflates budgets substantially. Wood, meanwhile, is cheap, nontoxic and carbon-neutral, and experiments show it hosts the greatest fouling biomass of any common substrate; tree-reef structures built from felled pear trees became biodiversity hotspots within six months. Yet wood degrades in as little as 18 months, chemical treatments that extend its life leach copper, arsenic and chrome, buoyant timber must be ballasted to stay on the seabed, and no wood reef has yet been used in a dedicated coral restoration project.

The review’s most compelling section catalogs the next generation of substrates now emerging from materials labs. Concrete itself is being reinvented: mixes incorporating crushed recycled oyster shells produce highly porous, texturally complex blocks that attract significantly more larval attachment, while blocks made with fly ash and granitic dust cost 25 to 40 percent less than commercial concrete without significant leaching. Artists such as Jason deCaires Taylor already sculpt with low-carbon, pH-neutral concrete. Miniaturization cuts costs further: concrete tetrapod seeding units designed by Chamberland and colleagues cost just one US dollar each, deployment included. Surface engineering adds another layer of control, since coral larvae settle more frequently on red surfaces, prefer microtopography matching their own body size, and respond to biochemical cues from crustose coralline algae, while non-biocidal fouling-release coatings can suppress algal competitors. Composite inorganic substrates made from lime mortar with quartz-rich sand and strontianite release ions that attract Caribbean coral larvae, and porous ceramics, chemically inert and durable, have achieved high settlement of Pocillopora damicornis larvae with tailored pore sizes.

Two technologies may ultimately redefine the field. Three-dimensional printing can produce complex, biomimetic ceramic structures with heterogeneous features that conventional manufacturing cannot achieve, while reducing costs and environmental impacts; in the Red Sea, 3D-printed terracotta reefs monitored for three years accumulated dozens of coral colonies alongside 15 species of sponges and ascidians, and the company Archireef now prints clay reef tiles commercially. Low-voltage mineral deposition, which grows the material known as Biorock through electrochemical accretion, yields structures stronger than concrete on which corals grow up to 3.17 times faster than controls. Biodegradable biosourced reefs, built from potato-waste-derived Solanyl and coir ropes that mimic mussel byssal threads, have already facilitated bivalve reef formation in the Netherlands and Florida and satisfy OSPAR’s requirement that reefs be removable, dissolving gradually as corals take over. The authors caution, however, that none of these innovations is a silver bullet: their costs must be rigorously evaluated against the accessibility constraints of restoration programs, larger-scale deployments are needed to prove scalability, and artificial reefs can only support recovery on limited scales so long as eutrophication, pollution, overfishing and rising global emissions continue unabated. The substrate, in other words, is necessary but not sufficient, and the future of coral restoration will be decided as much by what humanity stops doing to reefs as by what it sinks beneath them.

Subject of Research: Material selection for artificial reefs used in coral reef restoration

Article Title: Choosing the right substrate to restore coral reefs through artificial reef construction: a mini-review

Article References: Choosing the right substrate to restore coral reefs through artificial reef construction: a mini-review. (n.d.). https://doi.org/10.1186/s44315-025-00047-5

Image Credits: AI Generated

DOI: 10.1186/s44315-025-00047-5

Keywords: coral reefs, artificial reefs, reef restoration, substrate materials, 3D printing, Biorock, microplastics, concrete, biodegradable materials, marine conservation, coral larvae settlement, climate change