The research team, led by Amanda Martins of the Federal University of Bahia together with Marcos Krull and Francisco Barros, combined two rarely united sources of evidence: a long-term benthic monitoring dataset stretching back to 2004, and controlled laboratory experiments that measured exactly how much organic matter individual worms eat and how much sediment they displace. The monitoring data came from ten sampling stations along the estuary’s salinity gradient, surveyed on six separate occasions between 2004 and 2022. At each station, researchers collected cores of sediment, sieved the samples through a 0.5 millimeter mesh, and identified the invertebrates to the family level. Polychaetes made up more than half of all benthic macroinvertebrates in the system, making them the natural focal group for the study.

To translate counts of worms into estimates of ecosystem-wide function, the team turned to Bayesian generalized linear mixed models, a statistical framework that allows researchers to predict abundance across unsampled areas while quantifying uncertainty. The models incorporated environmental predictors including salinity and sediment grain size fractions—ranging from coarse sand upstream to fine sand and mud downstream—drawn from high-resolution environmental layers covering the modeled estuarine portion of the system. The researchers tested both Poisson and negative binomial distributions, with and without zero-inflation parameters, and compared generalized additive and generalized linear mixed models. Model selection relied on leave-one-out cross-validation using Pareto-smoothed importance sampling, and the winning models were fitted with Markov Chain Monte Carlo methods using a Hamiltonian sampler, with four independent chains and weakly informative priors to regularize the estimates.

The result of this statistical machinery was a population estimate of roughly 2,062.5 million individual polychaetes across the estuarine system, with a 95 percent credible interval spanning about 1.87 to 2.63 billion individuals. Seven families dominated the analysis: Orbiniidae, Spionidae, Eunicidae, Pilargidae, Lumbrineridae, Onuphidae, and Goniadidae. Orbiniidae alone accounted for an estimated 1,045.9 million individuals, followed by Onuphidae with 671.6 million. Densities were highest in the marine-influenced regions of the estuary, particularly for these two dominant families, setting the stage for a strongly spatially patterned delivery of ecological functions.

The functional measurements themselves came from a previous experimental study in which worms collected from the Jaguaripe estuary were kept under controlled laboratory conditions. Organic matter decomposition was quantified as the consumption rate of standardized pieces of shrimp tissue over 96 hours, corrected for natural decomposition using controls. Bioturbation—the reworking of sediment—was measured as the volume of sediment displaced by each species, reconstructed from computed tomography scans of the burrow systems the worms produced. This CT-based approach allowed the researchers to visualize and measure the three-dimensional architecture of worm burrows without disturbing them, providing an unusually precise metric of a notoriously difficult-to-quantify process.

When the per-individual rates were multiplied by the model-predicted abundances across the estuary, the numbers were striking. Polychaetes consumed an estimated 232.56 tons of organic material over 96 hours, with Orbiniidae responsible for 123.16 tons—about 53 percent of the total—and Onuphidae contributing another 89.81 tons, or nearly 39 percent. Bioturbation totaled an estimated 6,098.3 cubic meters of sediment over the same period, again dominated by Orbiniidae at 4,495.1 cubic meters and Onuphidae at 1,070.7 cubic meters, together accounting for more than 91 percent of the total. Smaller families such as Eunicidae, Spionidae, and Lumbrineridae contributed comparatively little to bioturbation, while Eunicidae and Pilargidae were minor players in organic matter consumption as well.

The spatial patterns were equally revealing. Both functions peaked in regions of elevated salinity, in the euhaline and polyhaline zones near the estuary’s mouth. Orbiniidae and Onuphidae delivered their largest contributions at salinities between 25 and 40, whereas Spionidae showed a strikingly different profile, contributing up to 80 percent of decomposition and bioturbation in the lower-salinity upstream reaches, between roughly 5 and 20 on the salinity scale. Sediment grain size also mattered: the dominant families responded to different granulometric fractions, with Orbiniidae and Onuphidae key in coarse sand and mud regions respectively, and Spionidae playing its characteristic upstream role in very fine sand. No single sediment variable was consistently selected across all taxa, underscoring that each family responds to its own combination of environmental conditions.

Correlation analyses of the functional contributions revealed another important pattern: functional redundancy. In the marine lower estuary, the contributions of Orbiniidae, Onuphidae, and Lumbrineridae rose and fell together, with correlation coefficients for bioturbation reaching 0.93 between Orbiniidae and Onuphidae and 0.92 between Lumbrineridae and Onuphidae. This overlap means that if one family were lost, others performing similar roles could partially compensate, buffering the ecosystem against disturbance. In the oligohaline upstream zones, by contrast, fewer families contributed to the functions, and redundancy was correspondingly lower—making those reaches potentially more vulnerable to species loss. Spionidae, with low correlations to all other taxa, stands out as functionally irreplaceable in the upstream areas where it dominates.

The study’s authors are candid about its limitations. Only seven families and two functions were analyzed, other taxa in the estuary may contribute substantially, and variables such as food resources beyond the measured organic matter could not be included. The decomposition measurements represent early-stage, macrofauna-mediated breakdown driven by direct consumption at the sediment surface, not the full complexity of benthic metabolism. Body size, which likely influences per-individual function, could not be incorporated because weight data were unavailable for several taxa. Still, the researchers argue, the demonstration that laboratory experiments can be combined with long-term monitoring and Bayesian modeling to produce ecosystem-level estimates is itself a methodological advance, offering a template for other systems where functional data remain scarce—particularly in the tropics, where most species-specific functional measurements to date have been conducted in temperate terrestrial environments.

The broader implications extend to conservation and climate adaptation. Estuaries are hotspots of organic matter input and nutrient cycling, disproportionately productive relative to their area, yet they face mounting pressures from eutrophication, metal pollution, shrimp farming, and sea-level rise. Because polychaete bioturbation aerates deeper sediment layers, reduces compaction, and accelerates organic matter processing, the loss of these worms could tip sediments toward anoxia, with cascading effects on entire benthic communities. The functional maps generated by the study highlight regions of high activity that could guide conservation priorities, and the identification of low-redundancy upstream zones flags areas where monitoring should be intensified. As climate change reshapes salinity gradients and species distributions, the authors suggest that modeling the distribution and functioning of organisms under future scenarios will be essential for predicting trends—and for protecting the billions of small engineers whose invisible labor keeps coastal ecosystems running.

Subject of Research: Ecosystem-level estimation of polychaete-mediated organic matter decomposition and bioturbation in a tropical estuary

Article Title: Scaling up polychaete contributions to estuarine ecosystem functions

Article References: Martins, A., Krull, M., & Barros, F. (2026). Scaling up polychaete contributions to estuarine ecosystem functions. Discover Ecology, 2(1), Article 6. https://doi.org/10.1007/s44396-026-00023-2

Image Credits: AI Generated

DOI: 10.1007/s44396-026-00023-2

Keywords: polychaetes, estuarine ecology, bioturbation, organic matter decomposition, ecosystem functioning, Bayesian modeling, functional redundancy, salinity gradient, macrofauna, tropical estuary, sediment reworking, conservation