The stakes of this work are high. Acropora palmata, listed as critically endangered by the International Union for Conservation of Nature since 2008, once built vast, wave-resistant thickets on Caribbean reef crests. Its branching morphology and rapid growth generate the complex three-dimensional structure that shelters juvenile fish and invertebrates and protects coastlines. Over the past 75 years, disease, pollution, warming waters and hurricanes have reduced populations to near local extinction in some regions. In Cuba, nationwide assessments before the 2023 mass bleaching event already described most A. palmata populations as being in poor or only moderate condition, with low colony densities and high partial mortality. That bleaching event then eliminated most remaining populations across the island, leaving only a handful of refugia, including the Laguna de Maya Wildlife Refuge in Matanzas Province and reefs at Santa Lucía in Camagüey Province.

Restoration programs throughout the Caribbean have responded by outplanting fragments of opportunity, cut from healthy mother colonies, or by raising corals in land-based and in-water nurseries. A. palmata fragments have historically shown high survival, between 63 and 95 percent on metal frames, and growth of around 21 centimeters per year in suspended mid-water line nurseries. Yet most of these projects have lasted only one to two years, and fragment mortality has been attributed to storms, heat, predation and poor water quality. What has remained poorly understood is how ecological processes, particularly competition with neighboring benthic organisms, shape the critical early establishment phase of outplanted fragments. The Cuban team set out to answer exactly that question.

The experiment took place on three shallow reef crests, one to three meters deep, chosen for their contrasting environmental and management contexts. Playa Baracoa and Rincón de Guanabo lie in northwestern Cuba, near Havana, where untreated wastewater discharges, coastal development and nearby industrial activity degrade water quality. Playa Baracoa sits just two kilometers east of the Santa Ana River, which receives untreated wastewater from an institution with roughly ten thousand students. The third site, La Puntica, lies within Jardines de la Reina National Park, a relatively pristine, oligotrophic marine protected area about fifty miles from the mainland, with high fish biomass and one of the largest and healthiest A. palmata populations on Cuban crests at the time of the study.

At each crest, the researchers randomly collected healthy, unbranched apical fragments from local colonies and attached them to cleared substrate with epoxy, following a standardized protocol. Control fragments were placed on substrate cleared of all sessile organisms, while treatment fragments were positioned less than one centimeter from locally abundant competitors: the coral Porites astreoides, the fire coral Millepora complanata, the green alga Cladophora sp., the brown algae Sargassum polyceratium, Dictyota sp. and Stypopodium zonale, and the zoanthid Palythoa caribaeorum. Each treatment and control at each crest comprised seven replicates, yielding 35, 42 and 28 fragments at Playa Baracoa, Rincón de Guanabo and La Puntica respectively. Fragments were monitored over periods ranging from roughly 320 to 423 days, with survival assessed as the retention of any living tissue and growth measured as changes in width, height and live tissue area.

The statistical analysis, based on Kaplan–Meier survival estimates, log-rank tests and Cox proportional hazards regression, produced strikingly uneven results. In Playa Baracoa, fragments paired with Millepora complanata suffered significantly higher mortality than controls, with a hazard ratio of 5.7, and survival fell from 0.5 at 135 days to zero by 275 days. The same pattern emerged at Rincón de Guanabo, where Millepora-paired fragments dropped from 0.6 survival at 125 days to none at 245 days. Field observations showed the fire coral progressively overgrowing the coral fragments between 90 and 180 days, and fragments paired with Millepora consistently exhibited the lowest live tissue area across all three crests. Although the study could not determine the precise mechanism of mortality, Millepora species are known strong spatial competitors that store toxins in their nematocysts, and secondary infections following overgrowth cannot be excluded.

In sharp contrast, Porites astreoides proved to be a remarkably tolerant neighbor. Fragments paired with this weedy coral showed survival similar to controls at Playa Baracoa and significantly higher survival at La Puntica, where 0.9 of the fragments were still alive at 358 days compared with 0.5 for controls. Most remarkably, the A. palmata fragments actually overgrew the living tissue of the Porites colonies, a classic case of asymmetric interference competition. This aligns with earlier work identifying Porites as one of the least aggressive coral species on the reef. The result carries practical weight: in restoration settings where P. astreoides has expanded its cover since the 1960s and 1980s, or in multi-species outplanting designs, this interaction appears unlikely to undermine the transplanted elkhorn coral.

Perhaps the most counterintuitive finding concerned the macroalgae. Despite their reputation as major coral competitors, capable of abrasion, shading, sediment trapping and allelopathy, none of the algal treatments significantly impaired fragment survival or growth. Fragments paired with Cladophora sp. and Sargassum polyceratium at Playa Baracoa increased their live tissue area 2.4-fold and 2.1-fold respectively, and at Rincón de Guanabo the Cladophora treatment produced a 7.8-fold increase. Even more intriguingly, fragments paired with the brown alga Stypopodium zonale at Rincón de Guanabo had significantly higher survival than controls, with a hazard ratio of 0.2. The authors caution that algal contact in the experiment occurred mainly along one side of each fragment, which may have limited competitive intensity, and that coral–algal interactions are known to be density- and context-dependent. Corals themselves can suppress some macroalgae through competitive or allelopathic mechanisms, so the relationship may be reciprocal rather than one-sided.

The zoanthid Palythoa caribaeorum, widely regarded as one of the most successful competitors on reefs and a producer of the potent biotoxin palytoxin, also failed to harm the fragments at La Puntica, where paired fragments retained 0.8 survival at 231 days and grew 3.6-fold in live tissue area. Because the organisms were placed adjacent rather than overlapping, direct overgrowth never developed, and the authors note that negative effects might emerge over longer contact periods. Acropora species are known to possess defensive strategies, including sweeper tentacles, mesenteric filaments and nematocyst discharge, which may help explain their resilience.

Underlying all of these species-level patterns was a powerful site effect. Fragments at Rincón de Guanabo had 6.2-fold lower survival than those at Playa Baracoa, and live tissue area was significantly lower at both Rincón de Guanabo and La Puntica compared with Playa Baracoa. Significant interactions between the La Puntica crest and the Porites and Millepora treatments indicate that local ecological conditions modulate the outcome of biotic interactions. The authors suggest that differences in reef community structure, herbivory, nutrient availability, temperature and anthropogenic stress, including untreated wastewater discharges and overfishing in the northwest, likely shaped these contrasting outcomes. Growth rates in the study were slower than those recorded for wild A. palmata, resembling storm-generated fragments, possibly reflecting transplantation shock, and negative growth in some periods may reflect fish bites observed on fragment tips.

For restoration practitioners, the message is clear and actionable. Simply clearing substrate before outplanting, a commonly recommended intervention, may not be enough to maximize fragment performance, because the ecological condition of the crest and its local stressors play a decisive role. The team recommends conducting small-scale pilot outplanting trials and incorporating assessments of benthic competitor abundance into site selection before scaling up, with periodic monitoring and adaptive management where fire coral or other aggressive competitors are abundant. As Caribbean restoration programs confront the functional extinction of Acropora corals across much of the region, this Cuban experiment demonstrates that knowing not just where to plant, but what to plant next to, could determine whether restored elkhorn thickets survive their first year.

Subject of Research: Effects of benthic competition on the survival and growth of outplanted Acropora palmata coral fragments on Cuban reef crests

Article Title: Effect of benthic organisms on Acropora palmata (Lamarck 1816) fragment survival and growth

Article References: Romero, A. R., González-Díaz, P., Pérez, G. A., & Banaszak, A. T. (2026). Effect of benthic organisms on Acropora palmata (Lamarck 1816) fragment survival and growth. Coral Reefs. https://doi.org/10.1007/s00338-026-02957-1

Image Credits: AI Generated

DOI: 10.1007/s00338-026-02957-1

Keywords: Acropora palmata, coral restoration, benthic competition, Millepora complanata, macroalgae, Porites astreoides, Palythoa caribaeorum, reef crests, Cuba, fragment survival, coral growth, marine ecology

The research, published in the journal Discover Ecology, provides the first seasonally explicit quantitative assessment of Cassiopea populations in a natural Caribbean mangrove system. Led by Ramón D. Morejón-Arrojo of the Universidade de São Paulo, together with Marta Mammone of the University of Galway, André C. Morandini, and Leandro Rodríguez-Viera of the University of Cadiz, the team conducted quadrat-based surveys during the dry season in December and the rainy season in July across two consecutive years, from 2023 to 2024. In total, the researchers counted 3,441 individual jellyfish across 190 one-square-meter quadrats positioned in the shallow subtidal zone of the mangrove lagoon.

The contrast between seasons was striking. In December 2023, mean jellyfish density reached 35.64 individuals per square meter, nearly 3.8 times higher than the 9.28 individuals per square meter recorded the previous July. Mean bell diameter told a similar story: jellyfish in December 2023 averaged 8.87 centimeters across the bell, about 29 percent larger than the 6.94-centimeter average measured in July 2023. The authors describe this as a “winter giants, summer dwarfs” pattern, in which both the number and the size of medusae peak during the cooler, clearer dry season.

Yet the pattern proved anything but fixed. In 2024, the seasonal contrast in bell diameter all but vanished, with July and December populations averaging 10.66 and 10.59 centimeters respectively — a difference so small that a Tukey-adjusted statistical comparison returned a p-value of 0.9997, indicating no meaningful seasonal divergence. Overall, jellyfish were larger in 2024 than in 2023 regardless of season. Statistical modeling captured this nuance precisely: negative-binomial and Gamma generalized linear models detected significant effects of both season and year on density and size, along with a highly significant season-by-year interaction, confirming that the strength of seasonal demographic responses shifted between the two years.

To make sense of these fluctuations, the researchers turned to the jellyfish’s unusual life cycle. Like other scyphozoans, Cassiopea alternates between a bottom-dwelling polyp stage and free-swimming medusae produced through strobilation, a process in which polyps sequentially bud off tiny juvenile jellyfish called ephyrae. Laboratory studies have shown that strobilation is typically triggered above 28 degrees Celsius, yet the field temperatures in Bajos de Santa Ana hovered between 28 and 31 degrees Celsius year-round. This suggests that in natural mangroves, the timing of recruitment may depend less on absolute temperature and more on the stabilization of environmental conditions — the return of clear water and steady salinity after the stressful rainy season. The dry-season peak in December 2023, with its broad size range of 2.4 to 19 centimeters, is consistent with a cohort produced by a successful strobilation pulse several months earlier.

The rainy season, by contrast, appears to impose a multi-stressor bottleneck. Satellite-derived environmental data compiled from Landsat 9, the CHIRPS precipitation dataset, and NOAA sea surface temperature products revealed pronounced wet-season spikes in turbidity, with near-infrared turbidity values peaking in June 2024. Elevated turbidity reduces the penetration of photosynthetically active radiation into shallow waters, potentially starving the jellyfish’s symbiotic dinoflagellates of light. Because these Symbiodiniaceae algae can supply up to 70 percent of the host’s basal energy requirements through photosynthesis, shading could force individuals to rely more heavily on capturing plankton and dissolved organic matter. Heavy rainfall events, some exceeding 75 millimeters per day, may also produce transient drops in salinity that are particularly lethal to vulnerable ephyrae and juvenile medusae, even though spot measurements of salinity remained within a tolerable range of roughly 28 to 31 practical salinity units.

The jellyfish’s seasonal swings also track changes in the wider benthic community. Principal component analysis of centered log-ratio transformed cover data separated the sampling periods clearly along environmental gradients, explaining nearly 65 percent of compositional variance in the first two axes. Cassiopea abundance was negatively associated with unvegetated substrate and macroalgal cover, and bell diameter declined significantly as macroalgal cover increased, a correlation the authors suggest might reflect competition for space or the physical impedance of macroalgal mats to the pulsation-driven feeding currents the jellyfish generate. Seagrass cover followed an inverse seasonal pattern relative to jellyfish density, peaking in July 2023 precisely when jellyfish numbers were lowest. Ten fish species, including the ubiquitous yellowfin mojarra and schoolmaster snapper, were recorded in association with the jellyfish aggregations, hinting at the habitat-shaping influence these animals exert on their neighbors.

That influence is far from trivial. Dense Cassiopea beds are known ecosystem engineers: their pulsation can turn over the entire water column every 15 minutes, they pump nutrient-rich porewater out of the sediment, and they can shift lagoon sediments from net oxygen consumption to net oxygen production. Because these effects scale non-linearly with both body size and density, the 3.8-fold dry-season increase in abundance, combined with larger individuals, implies that the winter population exerts a substantially greater biogeochemical footprint than its summer counterpart. The authors caution, however, that they did not directly measure nutrient fluxes at the site, so these functional consequences remain extrapolations grounded in prior experimental literature rather than observations from Bajos de Santa Ana itself.

Perhaps the most provocative comparison emerges when the mangrove populations are set against those in human-modified habitats. In Brazilian shrimp farms, Cassiopea andromeda maintains stable year-round populations and grows to nearly three times the size of mangrove conspecifics. In Cuba’s tourism-heavy Jardines de la Reina National Park, the largest jellyfish occur in the most heavily visited zones. The new findings suggest a gradient from maximally seasonal natural systems to environmentally buffered aquaculture ponds, along which Cassiopea‘s demographic plasticity is progressively expressed — positioning the genus as a potential bioindicator of how much humans have stabilized coastal environments. Because the release of stinging mucus structures called cassiosomes poses documented risks to bathers, the timing of dry-season blooms also carries practical relevance for coastal management.

The authors are careful to frame their results as a baseline rather than a rule. Four sampling events across two years cannot capture the full spectrum of interannual variability, and the researchers call for multi-year monitoring, high-frequency environmental measurements, and direct studies of polyp and ephyra dynamics using tools such as environmental DNA and settlement collectors. Still, the study fills a genuine gap in Caribbean ecology, documenting that Cassiopea populations in natural mangroves are profoundly shaped by seasonal environmental forcing — light, salinity, and resource availability interacting with a life cycle finely tuned to environmental windows. As climate change alters rainfall regimes, turbidity, and hydrology across tropical coastlines, these gelatinous barometers may soon tell scientists a great deal about how quickly those windows are shifting.

Subject of Research: Seasonal population dynamics of Cassiopea upside-down jellyfish in a Caribbean mangrove ecosystem

Article Title: Seasonal dynamics of Cassiopea spp. jellyfish species in a Caribbean mangrove system

Article References: Morejón-Arrojo, R. D., Mammone, M., Morandini, A. C., & Rodríguez-Viera, L. (2026). Seasonal dynamics of Cassiopea spp. jellyfish species in a Caribbean mangrove system. Discover Ecology, 2(1), Article 16. https://doi.org/10.1007/s44396-026-00034-z

Image Credits: AI Generated

DOI: 10.1007/s44396-026-00034-z

Keywords: Cassiopea, upside-down jellyfish, mangrove ecosystem, seasonal dynamics, Caribbean, Cuba, population ecology, benthic communities, symbiosis, strobilation, turbidity, ecosystem engineering