Estuaries are among the most productive and biologically diverse environments on Earth, yet they are increasingly squeezed by urban expansion, shoreline modification, water extraction, and infrastructure development, particularly in tropical regions where coastal occupation continues to intensify. Conservation strategies have traditionally emphasized protecting habitat patches, but growing evidence indicates that maintaining functional connectivity among freshwater, estuarine, and marine habitats is equally critical for sustaining ecological processes and viable wildlife populations. Unlike structural connectivity, which describes the physical arrangement of habitats, functional connectivity reflects the extent to which landscapes actually facilitate or impede organism movement, making it a more realistic measure of ecological integrity in highly dynamic coastal systems.

Top predators are particularly valuable for evaluating this kind of connectivity because their ecological requirements integrate processes operating across broad spatial and temporal scales. As high-trophic-level species, they respond simultaneously to habitat quality, prey availability, environmental contamination, and landscape permeability, providing an integrative measure of ecosystem integrity. The Neotropical otter is especially suitable for this purpose because its life cycle depends on the continuity of freshwater, estuarine, and marine habitats, and its sensitivity to fragmentation, declining water quality, and changes in prey availability makes it an effective ecological indicator of environmental change in tropical estuaries.

Santa Catarina Island, a 424-square-kilometer granitic island, offers a compressed freshwater-brackish-marine continuum within a single insular landscape. Peri Lagoon, a 5.1-square-kilometer freshwater reservoir in the south, drains to the Atlantic through a narrow 4-kilometer supralittoral corridor. Conceição Lagoon, a 19.71-square-kilometer brackish system in the north, maintains permanent oceanic exchange through the Barra da Lagoa channel with salinity ranging from 6.70 to 18.50. These two lagoons are connected by approximately 80 kilometers of indented rocky coastline punctuated by marine promontories and coastal islands such as Arvoredo, Campeche, Irmã do Meio, and Deserta, which otters regularly use as functional movement corridors. Evidence of scat deposition on 39 percent of surveyed coastal islands highlights their role as ecological stepping stones linking freshwater, estuarine, and marine habitats.

The monitoring protocol was deliberately standardized. Field surveys conducted during daylight hours by two trained observers systematically surveyed shorelines on foot or by canoe and kayak, georeferencing all fresh spraints with GPS receivers accurate to within about 3 meters, photographing them in situ, and refrigerating them within 24 hours to minimize DNA degradation. Because direct counts are difficult for cryptic, wide-ranging carnivores with low detectability, the study adopted intensity of presence, calculated as the number of spraints standardized by the shoreline length surveyed each month. This approach, widely applied in long-term monitoring of the European otter since the 1970s, works because spraint deposition in L. longicaudis is closely associated with territorial marking and movement routes.

Genetic validation strengthened the movement-based inference. Microsatellite analysis of 18 fresh spraints from seven shelters in the Peri Lagoon system generated multilocus genotypes that demonstrated multiple otters used the monitored shelters during the sampling period, confirming that spraint accumulation reflected the activity of several individuals rather than repeated marking by a single resident animal. Identical genotypes occurred at more than one shelter, demonstrating that individual otters moved between different sectors of the lagoon, while individual shelters were visited by different otters over time. The highest similarity was observed between shelters T1 and T7, with a Morisita index of 0.750, providing direct evidence that individual otters regularly traversed substantial portions of the Peri Lagoon shoreline.

Temporal analyses revealed a pronounced decline in movement intensity over the twenty-year study period. Locally weighted polynomial regression identified a gradual reduction in intensity of presence across the monitored landscape, with the strongest declines in the marine coastal sectors while Peri Lagoon maintained comparatively higher and more stable activity. During the same period, Santa Catarina Island experienced substantial urban expansion and infrastructure development, including rapid population growth in neighboring municipalities, highway expansion, and a 52 percent increase in Atlantic Forest deforestation between 2017 and 2018. Importantly, the decline was not accompanied by the disappearance of otter records from any monitoring site, indicating that functional connectivity remained intact despite lower overall movement intensity, though the pattern is consistent with cumulative environmental pressures affecting the island’s coastal ecosystems.

Dietary analysis demonstrated that the otters exploited a broad spectrum of aquatic prey throughout the monitored continuum. Fish constituted the dominant prey category, followed by crustaceans, amphibians, insects, birds, reptiles, and small mammals, with secondary prey varying according to habitat type and reflecting opportunistic feeding behavior. The occurrence of both freshwater and marine prey demonstrated that individual otters exploited resources from multiple aquatic environments, and this trophic plasticity constitutes an important ecological mechanism supporting functional connectivity by maintaining ecological links among environments that would otherwise function as isolated habitat patches.

Building on these ecological patterns, the researchers developed the Otter Health Index, a field-based framework that integrates movement integrity, dietary diversity, and shelter availability to support rapid assessments of estuarine condition. Each component is standardized to a common scale from 0 to 10 using linear min-max normalization, with movement activity receiving a weight of 0.50 and dietary composition and shelter availability each receiving 0.25. The resulting index values ranged from 0.91 at Peri Lagoon, classified as excellent, to 0.54 at Pântano do Sul, classified as moderate, and the ranking closely matched independent ecological indicators, suggesting the index successfully captures biologically meaningful variation across the monitored landscape.

The findings carry direct implications for coastal conservation planning. Because otters moved across freshwater, estuarine, and marine environments, strategies should focus not only on protecting individual habitat patches but also on maintaining the ecological processes that sustain connectivity among them, particularly supralittoral rocky habitats, native shoreline vegetation, and coastal islands that function as corridors and stepping stones. The authors argue that conservation planning should shift from a patch-oriented perspective toward a corridor-based approach, integrating functional connectivity into environmental licensing and territorial planning. The combination of long-term monitoring, non-invasive genetic analysis, dietary assessment, and the Otter Health Index offers a practical framework for adaptive conservation that may also be adapted to other semi-aquatic species, reinforcing the role of the Neotropical otter as a practical bioindicator of estuarine ecosystem integrity in the Anthropocene.

Subject of Research: Movement ecology of the Neotropical otter as a bioindicator of estuarine functional connectivity and coastal ecosystem management

Article Title: Estuarine connectivity through the lens of a top predator. Movement ecology of Lontra longicaudis as a management tool for coastal ecosystems

Article References: Carvalho Junior, O. D. O., Bez Birolo, A., Tosatti, M., & Sabbagh, A. (2026). Estuarine connectivity through the lens of a top predator. Movement ecology of Lontra longicaudis as a management tool for coastal ecosystems. Estuarine Management and Technologies, 3, 233-261. https://doi.org/10.3897/emt.3.189805

Image Credits: AI Generated

DOI: 10.3897/emt.3.189805

Keywords: Neotropical otter, Lontra longicaudis, estuarine connectivity, movement ecology, Santa Catarina Island, bioindicator, Otter Health Index, microsatellite DNA, coastal conservation, long-term monitoring, Estuarine, connectivity

The team harnessed more than two decades of satellite observations from NASA’s MODIS instruments, computing three complementary vegetation indices monthly from 2001 to 2025: the Normalized Difference Vegetation Index (NDVI), the Enhanced Vegetation Index (EVI), and the Modified Soil Adjusted Vegetation Index (MSAVI). Each index captures a different facet of canopy condition. NDVI, the workhorse of vegetation remote sensing, responds strongly to chlorophyll content but can saturate in dense canopies. EVI incorporates blue-band reflectance and improved atmospheric correction, making it better suited to the high-biomass tropical forests where NDVI loses sensitivity. MSAVI, designed to suppress the signal of bare soil, proves invaluable in the intertidal zones where tides repeatedly expose mudflats between the trees.

Processing this volume of data required cloud computing. The researchers used Google Earth Engine to aggregate quality-filtered MODIS scenes into monthly composites, then clipped every raster to the mangrove extent defined by the Global Mangrove Watch Version 3.0 dataset, a product built from L-band radar data from the ALOS PALSAR satellite fused with Landsat optical imagery, achieving an overall classification accuracy of 94 percent. In total, 720 monthly raster layers, covering 240 months across three indices, were processed and then collapsed into national monthly time series by averaging all mangrove-masked pixels across India’s twelve mangrove-bearing states and union territories.

The forecasting engine at the heart of the study is the Seasonal Autoregressive Integrated Moving Average model, or SARIMA. Unlike simpler trend analyses, SARIMA explicitly models both the slowly evolving trend of a time series and its recurring seasonal cycles, making it well matched to ecosystems whose phenology is locked to monsoon rhythms. Before fitting any model, the team tested each vegetation index series for stationarity using the Augmented Dickey-Fuller and KPSS tests. Both tests rejected their respective null hypotheses for all three indices, pointing to seasonal non-stationarity, so the researchers applied one non-seasonal and one seasonal difference to stabilize each series before model selection.

Seasonal decomposition using the STL method revealed just how rhythmically these forests breathe. Seasonal strength coefficients ranged from 0.813 for MSAVI to 0.855 for EVI, far above the 0.3 threshold commonly used to flag strong seasonality. Intriguingly, all three indices peaked during the dry season and bottomed out during the wet season, a counterintuitive pattern the authors attribute to the unique physiology of mangroves, which are adapted to tidal and salinity stress rather than limited by freshwater availability. The trend components told a quieter story: relatively flat through the 2000s, then climbing steadily from around 2010 onward, consistent with the documented 1.2 percent annual growth in India’s mangrove area driven by conservation policies and restoration programs.

Automated model selection using R’s auto.arima function, guided by the Akaike Information Criterion, produced a distinct model for each index. NDVI required a first-order autoregressive structure, EVI relied on a fourth-order moving average with no autoregressive term, and MSAVI demanded a third-order autoregressive specification, likely reflecting the complex interplay of tidal cycles, soil moisture, and vegetation phenology that soil-adjusted indices register. Residual diagnostics were clean across the board: Ljung-Box tests found no remaining autocorrelation in any model, although formal normality tests revealed slight heavy-tailedness, a familiar feature of vegetation index series where post-monsoon greening surges occasionally exceed what a Gaussian distribution would predict.

The critical test came from data the models had never seen. The final five years of observations, from 2021 to 2025, were withheld as an out-of-sample validation set. Against this holdout, the SARIMA models achieved mean absolute percentage errors between 2.5 and 4.9 percent, well inside the 10 percent threshold conventionally considered high-accuracy forecasting. NDVI emerged as the most dependable index, with a MAPE of just 2.50 percent and the only statistically significant improvement over a seasonal-naive benchmark in Diebold-Mariano comparisons. EVI and MSAVI performed respectably in absolute terms but were statistically indistinguishable from simpler benchmarks, and their prediction intervals covered fewer observations than intended, signaling that forecast uncertainty for those indices was underestimated.

With the models validated, the team refit each specification to the full 2001 to 2025 record and generated operational forecasts for 2026 through 2030. All three indices are projected to continue their gentle ascent: NDVI is expected to average about 6.4 percent higher than the 2001 to 2020 training-period mean, while EVI and MSAVI are projected to rise by roughly 9.8 and 10.7 percent respectively. The larger relative gains in MSAVI hint at new vegetation colonizing tidally exposed substrates, where a soil-adjusted index is most responsive, while EVI’s rise is consistent with canopy structural recovery in previously degraded high-biomass zones. NDVI’s more modest climb likely reflects saturation in already dense, mature stands rather than an absence of underlying progress. Crucially, all projections remain within the bounds of historical variability, suggesting stable to improving conditions under current human and climatic pressures.

The authors are careful to frame these results as a statistical baseline rather than a guarantee. Because the analysis aggregated all mangrove pixels nationally, the forecasts cannot resolve state-level or site-specific trajectories, and the study itself notes that localized studies have documented declines, such as falling NDVI in Bhitarkanika and widespread EVI-based browning across much of the Sundarbans. The prediction intervals capture only parameter and stochastic uncertainty, not structural risks like major cyclones or land-use change. Moreover, vegetation indices are optical proxies for canopy greenness, not direct measures of biomass, carbon stocks, or physiological health, and MODIS’s 500-meter pixels can blur the narrow fringing mangrove belts of Gujarat and Kerala with surrounding water and aquaculture ponds.

Even with those caveats, the framework offers conservation managers something they have lacked: a quantitative, forward-looking early warning system. Deviations from forecast trajectories could flag ecosystem stress before it becomes visible on the ground, while the strong, predictable seasonality identified in the data points to optimal windows for restoration planting, roughly November through January, when mangroves show peak physiological resilience. Because the entire pipeline runs on open satellite data, Google Earth Engine, and open-source R and QGIS tools, the approach is readily transferable to mangrove regions across the tropical and subtropical world, offering a scalable template for predictive ecology at a moment when coastlines everywhere face mounting climate pressure.

Subject of Research: SARIMA time-series forecasting of satellite-derived mangrove vegetation indices across India

Article Title: SARIMA-based forecasting of mangrove vegetation indices across India

Article References: Suhail S., M., Sharma, L. K., & Bhaveshkumar, K. I. (2026). SARIMA-based forecasting of mangrove vegetation indices across India. Discover Oceans, 3(1), Article 64. https://doi.org/10.1007/s44289-026-00179-5

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00179-5

Keywords: mangroves, SARIMA, time series forecasting, remote sensing, vegetation indices, NDVI, EVI, MSAVI, MODIS, Google Earth Engine, India, coastal conservation

The research was carried out by Maximiliano Manuel Hernandez and Juan Pablo Seco Pon of the Grupo Ecología y Conservación de Aves Marinas y Costeras at the Instituto de Investigaciones Marinas y Costeras, part of the National University of Mar del Plata and CONICET. Their approach was systematic: every groyne was inspected and each item of fishing debris was classified by origin as either recreational or non-recreational. The team then tested whether debris abundance varied according to three characteristics of the structures themselves, namely the construction material of the groyne, its orientation relative to prevailing winds and waves, and its location along the urban coastline. This design allowed them to separate the influence of physical structure from the influence of human fishing pressure.

The results pointed clearly to recreational anglers as the dominant source of the litter. Recreational debris was more abundant than non-recreational material across the surveyed groynes, and accumulation was greatest on groynes built with orthoquartzite rocks. That geological detail matters more than it might first appear. Orthoquartzite blocks create a rough, crevice-rich surface that snags line, netting and packaging far more effectively than smoother concrete or other materials. Previous work on artificial breakwaters in Chile and elsewhere has shown that structural complexity enhances the trapping of anthropogenic litter, and the Mar del Plata findings extend that pattern to fishing-specific debris on the south-western Atlantic coast.

Among the thousands of items recorded, three categories dominated both in abundance and in how frequently they appeared across sites: monofilament fishing line, bait bags, and ropes. Monofilament nylon is a particularly insidious form of litter because it is nearly invisible underwater, yet it persists for years and poses severe entanglement risks. Studies from northern Patagonia have documented kelp gulls killed and injured by discarded monofilament lines at recreational fisheries, and global reviews identify entanglement and ingestion of fishing gear as major threats to seabirds, turtles and marine mammals. Bait bags and rope fragments, meanwhile, break down into smaller fragments that can enter the food web.

To understand what these plastics are actually made of, the researchers took the analysis a step further than most beach surveys. They used Fourier-transform infrared spectroscopy, or FTIR, to determine the chemical composition of 357 plastic fishing debris items. The technique works by shining infrared light through a sample and reading the characteristic absorption fingerprints of its polymer bonds, allowing precise identification of plastic types that look identical to the naked eye. The dominant polymers turned out to be polyamide, polyethylene and polystyrene, a trio that maps neatly onto fishing practice. Polyamide is the nylon used in monofilament lines and nets, polyethylene is common in bait packaging and bags, and polystyrene appears in floats and rigid gear components.

Identifying polymer types is not merely an academic exercise. Different polymers carry different hazard profiles, both in their inherent chemistry and in the additives they contain, such as plasticisers and flame retardants that can leach into seawater and be transferred to wildlife that ingests them. Polyamide line, for example, can shed microfibers as it weathers, and beached fishing gear has been shown to release microplastics over time. Because fishing debris is often trapped in intertidal zones where it is repeatedly wetted and dried, abraded by sand and exposed to intense ultraviolet radiation, these structures can act as slow-release sources of microplastics and associated chemicals directly into productive coastal waters.

The study’s most actionable finding concerns where the debris comes from. The trapped recreational debris primarily originates from fishers using the immediate or nearby groyne areas, rather than drifting in from distant waters or from the commercial fleet. That local provenance is, paradoxically, good news for managers. If most of the litter is dropped by the people standing on the groynes themselves, then identifying preferential fishing sectors would allow waste management efforts to be concentrated where they will do the most good. Targeted bins, signage, line-recycling stations and periodic clean-ups at the most heavily used groynes could intercept a large fraction of the debris before it reaches the water.

Mar del Plata offers an ideal setting for this kind of assessment. The city hosts Argentina’s most significant commercial harbour and serves as a key destination for recreational fishing, drawing large numbers of anglers to its coastal defences. It is also a major tourist destination, and the combination of dense human use and engineered shoreline makes its groynes both fishing platforms and potential debris traps. Earlier Argentine studies have documented marine debris on the region’s sandy beaches and in the Mar Chiquita coastal lagoon, and previous work by some of the same researchers has examined anglers’ perceptions and attitudes towards fishing litter, including a conservation programme designed to promote responsible disposal in a coastal reserve. The new groyne survey complements that social science by providing hard numbers on what actually ends up in the environment.

The broader context is sobering. Global estimates suggest that a substantial share of fishing gear enters the ocean each year, and marine debris is now recognised as one of the most pervasive pollution problems facing coastal ecosystems, with documented impacts ranging from ingestion by megafauna to the transfer of hazardous chemicals into food webs and, potentially, human consumers through seafood. Coastal defence structures have emerged in recent years as underappreciated accumulation hotspots, with studies describing artificial breakwaters as functioning like garbage bins for intertidal habitats. What happens on a groyne does not stay on a groyne: storms, tides and wave action eventually liberate trapped items, making these structures reservoirs of pollution that leak into the marine environment over time.

For Argentina, the study establishes a baseline that did not previously exist. No earlier research in the country had combined a city-wide census of fishing debris on groynes with polymer-level chemical identification, and the authors argue that their findings provide a foundation for concentrated, spatially targeted waste management policies. The logic is straightforward: because the debris is overwhelmingly local in origin, the solution is local too. By mapping where recreational fishers cluster and directing infrastructure and outreach to those hotspots, Mar del Plata could reduce the flow of monofilament, bait bags and rope into the South Atlantic. As coastal cities worldwide grapple with the legacy of decades of plastic use, this study shows that sometimes the most effective interventions are also the simplest, aimed squarely at the people and places where the pollution begins.

Subject of Research: Fishing-related debris accumulation and polymer composition on artificial groynes in Mar del Plata, Argentina

Article Title: Assessment of fishing-related debris in artificial groynes along the largest coastal city in Argentina

Article References: Hernandez, M. M., & Seco Pon, J. P. (2026). Assessment of fishing-related debris in artificial groynes along the largest coastal city in Argentina. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38255-0

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38255-0

Keywords: marine debris, fishing gear, artificial groynes, Mar del Plata, recreational fishing, microplastics, FTIR spectroscopy, polyamide, polyethylene, polystyrene, coastal pollution, Argentina