Long-term ecological studies are essential for understanding community structure and change. In estuaries, dynamic environmental gradients drive spatiotemporal shifts in populations through complex abiotic and biotic interactions. Biological invasions add novel relationships, including those between hosts and parasites. Estuarine environments often provide low-salinity refugia that reduce parasite pressure, slowing host resistance evolution by maintaining a reservoir of susceptible individuals. When naive hosts emerge from these refugia, they may support host recovery and supply new targets for parasites, diluting resistance in the population. Using a 12-year field survey across a salinity gradient in Chesapeake Bay, MD, USA, we examined how environmental conditions (salinity, temperature) and host demographics (% gravid females, total abundance and size) correlate with infection prevalence of the introduced castrating parasite Loxothylacus panopaei in native, white-fingered mud crabs (Rhithropanopeus harrisii). Infection prevalence varied from 0 to 75.9% (n = 102 632) and peaked with elevated salinity, temperature and host reproduction. Larger crabs (>9 mm carapace width) showed higher infection rates, especially under high salinity and temperature. Salinity was the most consistent predictor of infection, with low salinity (<10 ppt) providing refuge. These findings show how fluctuating environmental conditions structure parasite prevalence across scales, with implications for host population dynamics under climate change. This article is part of the theme issue 'Managing infectious marine diseases in wild populations'.

In coastal ecosystems, the intricate interactions among grazers, microorganisms, and plants play a crucial role in shaping plant health and ecosystem dynamics. Recent work has shown that snail grazing on live seagrass tissue creates wounds that can facilitate fungal infection, suggesting a pathway by which invertebrate grazers may exert top-down control over seagrass growth. However, whether density-dependent snail grazing translates into measurable impacts on fungal infection and seagrass health under field conditions remains untested. To address this gap, we conducted field surveys and experiments to examine how fungal infection in Thalassia testudinum blades and seagrass health varies with different densities of the herbivorous smooth tegula, Tegula fasciata snail in Bocas del Toro on the Caribbean coast of Panama. Field surveys documented snail scarring on seagrass blades and that density of smooth tegula in seagrass beds was positively associated with both scarring prevalence and increased brown tissue (indicative of fungal infection) in seagrass blades. Our six-week experimental manipulation testing densities of tegula snails (0, 1, 2, 4, and 6 snails per 625 cm 2 ) revealed no significant effects of snail density on seagrass metrics including biomass, productivity, shoot density, or degree of fungal colonization, despite visible emergence of radulation scars on blades. The only significant treatment effect was on total shoot number, where treatments with natural snail density (1 snail per 625 cm 2 ) produced more shoots than treatments with the highest snail density (6 snails per 625 cm 2 ). Although snail presence increased scarring on new growth blades relative to snail-free controls, tissue damage did not translate into detectable effects on seagrass biomass, productivity, or fungal colonization. These results suggest that T. testudinum can effectively compensate for snail grazing over short timescales, as it does with other grazers, such as turtles. Fungal biomass did not increase significantly with snail density or scarring presence, indicating that the grazer-pathogen facilitation pathway documented in other marine plant systems may not operate over short experimental timescales in turtlegrass. Together, these findings suggest a degree of ecological co-tolerance between T. testudinum and invertebrate grazers, though whether this resilience holds under sustained grazing pressure or compounding environmental stressors warrants further investigation.

Biogenic structural complexity is a key driver of biodiversity and ecosystem functioning, yet its ecological and environmental determinants remain poorly understood across broad biogeographic scales. Here, we conducted standardized 90-day field experiments at 16 coastal sites, spanning a 41-degree latitudinal gradient, using naturally assembled marine fouling communities on settlement panels. We measured rugosity as our metric of biogenic structural complexity and modeled its relationship with species richness, community composition, community growth rates, and abiotic conditions (salinity and temperature). Species richness increased with temperature and salinity and declined with latitude, with more diverse communities exhibiting greater biogenic complexity due to increased morphological variation. At high-latitude sites, low-diversity communities dominated by arborescent bryozoans also had increased complexity. Structural equation models showed that abiotic conditions influenced growth and composition, which in turn shaped complexity. Warmer, saltier sites promoted richness-driven complexity, while colder conditions favored structurally important dominant taxa. We found that biodiversity is important not only as a beneficiary of complexity but also as a contributor to complexity itself within fouling communities. Our results also demonstrate that both species richness and functional group identity regulate biogenic complexity across environmental gradients, underscoring biodiversity's role in supporting ecosystem structure and resilience in the face of increasing global change. Understanding these relationships is essential for biodiversity conservation and the management of marine ecosystems facing increasing anthropogenic pressures.

Mercury contamination is a global concern, yet addressing it in developing nations is particularly challenging given the scarcity of data. In 2015, along with many other countries, Panama ratified the Minamata Convention on Mercury– a global effort to tackle mercury contamination and mitigate the risks it poses to humans and the environment. However, there are currently no published data from Panama on mercury contamination in freshwater fishes nor its associated health risks to humans from fish consumption. Here, we quantify for the first time the total mercury (THg) concentrations in two predatory fish species in Panama’s two largest lakes: Lake Gatun and Lake Bayano. Within Lake Gatun, the native predator Hoplias microlepis (“pejeperro”) had significantly higher predicted mercury concentrations (341.77 ng/g wet weight for a fish of 25 cm in standard length) than the introduced Cichla monoculus (“sargento” or “peacock bass”) (196.98 ng/g), and mercury concentrations increased with fish size for both species. H. microlepis from Lake Gatun also had significantly higher predicted THg concentrations than H. microlepis from Lake Bayano (168.37 ng/g). Mercury concentrations at the aquatic food web baseline did not differ between lakes, as shown by the primary consumer snails Pomacea sp. Additionally, using stable isotopes of nitrogen (δ15N), we found that mercury concentrations increased with trophic position in both lakes (resulting in positive and significant Trophic Magnification Slopes), suggesting mercury biomagnification. Based on these findings, we provide fish consumption guidelines for both lakes, using the U.S. EPA current reference dose for mercury exposure. These results provide critical data for Panama as it works towards meeting the objectives set under the Minamata Convention.

DNA metabarcoding is a powerful biodiversity monitoring tool, enabling simultaneous assessments of diverse biological communities. However, its accuracy depends on the reliability of reference databases that assign taxonomic identities to obtained sequences. Here we provide a DNA barcode dataset for aquatic fauna of the Panama Canal, a region that connects the Western Atlantic and Eastern Pacific oceans. This unique setting creates opportunities for trans-oceanic dispersal while acting as a modern physical dispersal barrier for some terrestrial organisms. We sequenced 852 specimens from a diverse array of taxa (e.g., fishes, zooplankton, mollusks, arthropods, reptiles, birds, and mammals) using COI, and in some cases, 12S and 16S barcodes. These data were collected for a variety of studies, many of which have sought to understand recent changes in aquatic communities in the Panama Canal. The DNA barcodes presented here are all from captured specimens, which confirms their presence in Panama and, in many cases, inside the Panama Canal. Both native and introduced taxa are included. This dataset represents a valuable resource for environmental DNA (eDNA) work in the Panama Canal region and across the Neotropics aimed at monitoring ecosystem health, tracking non-native and potentially invasive species, and understanding the ecology and distribution of these freshwater and euryhaline taxa.

Maritime shipping is vital for commercial trade and well recognized as a main pathway for the spread of non-native species.1 For over a century, the Panama Canal in Central America has played a major role in global trade, connecting the Atlantic and Pacific oceans. Historically, the introduction of species through the Panama Canal has been relatively low, largely due to the existence of a soft barrier-the freshwater Lake Gatun-inside the canal.2-4 However, the 2016 expansion of the Panama Canal involved major structural changes to the canal's lock system, which may have increased the likelihood that more marine fish species and greater numbers of them enter the lake and eventually cross the canal. To test this prediction, we used standardized quantitative comparisons of the fish communities of Lake Gatun, a system with a rich record of biological introductions,5,6 before (2013-2016) and after (2019-2023) the canal expansion. We observed a shift from a freshwater-dominated to a marine-dominated fish community in several areas inside the lake after 2016. The increase in marine organisms in this aquatic corridor may represent a potential invasion in progress, with a greater likelihood of some species eventually passing through the canal and colonizing the opposite ocean. The ecological and evolutionary consequences of these changes are difficult to predict. However, as most of these marine fishes are top predators with wide niche breadths, their colonization of Atlantic and Pacific oceans will likely alter ecological interactions and potentially lead to ecosystem-level changes.

Host-parasite associations have historically been considered compelling examples of coevolution and useful in examining cospeciation. However, modern molecular methods have revealed more complex dynamics than previously assumed, with host-switching events appearing commonly across taxa and challenging traditional views of strict coevolution in host-parasite relationships. Monogenean parasites are considered highly host-specific and have long served as models for probing evolution of host-parasite associations, particularly in differentiating geographic and phylogenetic patterns of parasite diversification. We investigated the phylogeographic patterns of monogenean ectoparasites associated with four species of characin fishes across Panama, Nicaragua, and Mexico. We hypothesize that parasite diversity and community structure are more strongly correlated with host species (suggesting cospeciation) than with geographic location (indicative of allopatric speciation). We found high genetic differentiation among parasites and their hosts across different locations. However, while geography explained the genetic structure of both host fishes and parasites, the observed patterns were neither congruent nor parallel. Parasite community structure and genetic similarity were consistently better explained by geographic location than by host species identity, although both factors played a significant role. Contrary to our predictions, we found no evidence of cospeciation. Instead, the diversification of these monogenean parasites appears to be primarily driven by their ability to switch hosts. At this taxonomical scale, host-switching is mediated by the geographical proximity of potential hosts, underscoring the importance of spatial factors in parasite evolution.

Biotic interactions play a critical role in shaping patterns of global biodiversity. While several macroecological studies provide evidence for stronger predation in tropical regions compared with higher latitudes, results are variable even within the tropics, and the drivers of this variability are not well understood. We conducted two complementary standardized experiments on communities of sessile marine invertebrate prey and their associated predators to test for spatial and seasonal differences in predation across the tropical Atlantic and Pacific coastlines of Panama. We further tested the prediction that higher predator diversity contributes to stronger impacts of predation, using both direct observations of predators and data from extensive reef surveys. Our results revealed substantially higher predation rates and stronger effects of predators on prey in the Pacific than in the Atlantic, demonstrating striking variation within tropical regions. While regional predator diversity was high in the Atlantic, functional diversity at local scales was markedly low. Peak predation strength in the Pacific occurred during the wet, non-upwelling season when ocean temperatures were warmer and predator communities were more functionally diverse. Our results highlight the importance of regional biotic and abiotic drivers that shape interaction strength and the maintenance of tropical communities, which are experiencing rapid environmental change.

The rise of the Isthmus of Panama ~3.5 mya separated populations of many marine organisms, which then diverged into new geminate sister species currently living in the Eastern Pacific Ocean and Caribbean Sea. However, we know very little about how such evolutionary divergences of host species have shaped their microbiomes. Here, we compared the microbiomes of whole-body and shell-surface samples of geminate species of marine gastropods in the genera Cerithium and Cerithideopsis to those of congeneric outgroups. Our results show that the effects of the Isthmus on microbiome composition varied among host genera and between sample types within the same hosts. In the whole-body samples, microbiome compositions of geminate species pairs in the focal genera tended to be similar, likely due to host filtering, although the strength of this relationship varied among the two groups and across similarity metrics. Shell-surface communities showed contrasting patterns, with co-divergence between the host taxa and a small number of microbial clades evident in Cerithideopsis, but not Cerithium. These results suggest that (i) the rise of the Isthmus of Panama affected microbiomes of geminate hosts in a complex and clade-specific manner and (ii) host-associated microbial taxa respond differently to vicariance events than the hosts themselves.

IntroductionGlobal shipping has accelerated the spread of non-native species. Factors such as environmental filtering and interactions with local biota can affect invasion likelihood, yet their relative contribution to predicting invasion risk remains unresolved. To test how abiotic filters and an experimentally-derived measure of biotic resistance interact with propagule pressure, we developed an integrated model to evaluate their relative effects on invasion risk of marine biofouling organisms to different focal port regions. We predicted that environmental filtering impacts invasion risk when fewer but stronger connections are part of the network. Further, predation is a mechanism of biotic resistance, which can reduce invasion risk, with most pronounced effects predicted in the tropics that decline at higher latitudes.MethodsWe examined shipping traffic and predation impact at three coastal bioregions spanning 47-degrees of latitude al range in the Northeast Pacific (Alaska, California, and Panama). We used vessel traffic databases to characterize propagule pressure and construct a worldwide port network of marine shipping routes and ports. Environmental resistance was estimated using temperature and salinity data from donor and recipient regions. We further used standardized predator exposure experiments to quantify predation impact on fouling community biomass as an estimate of potential for biotic resistance. We then expanded on existing models of relative invasion risk to incorporate the probability that propagules will survive predation by local predators and overcome environmental filtering to generate a predicted invasion risk for each port.ResultsEnvironmental filtering in all regions and predation pressure in the tropics worked to reduce the invasion risk, resulting in markedly different cumulative risk profiles over time among regions.DiscussionIn an increasingly connected world with more vessel traffic, our results highlight that while the number and distribution of shipping routes are important to understand risk, abiotic and biotic filters can modify model predictions.

AimParasites in the genus Perkinsus infect marine molluscs globally, with novel detections expanding and reshaping our knowledge of their biogeographic patterns and the factors influencing those patterns. Here, we aimed to characterize the phylogeography and genetic connectivity of Perkinsus spp. in bivalves across North and Central America, which included infection hot spots (e.g., the Gulf of Mexico, Chesapeake Bay) and areas where these parasites had not been previously reported (e.g., along the California coast).LocationAll coasts of North America and both coasts of Panama.MethodsUtilizing standard PCR and DNA sequencing, we genetically screened 933 bivalves from across North America for parasites in the genus Perkinsus, then combined this with 752 bivalves previously screened from Panama, which included 16 species from three different countries. Phylogenetic methods were used to confirm the identifications of all the bivalves collected and the Perkinsus spp. detected. We combined our data with publicly available sequence data for these parasites to create global haplotype networks to assess regional and continental genetic diversity and phylogeographic patterns.ResultsWe detected three species across North and Central America, including Perkinsus beihaiensis, P. chesapeaki, P. marinus, while P. olseni was only detected in Panama. We report for the first time P. chesapeaki was detected in Isognomon sp. from Mexico and P. beihaiensis detections in Ostrea lurida from California, USA. Additionally, our results indicate extremely low-genetic diversity of P. beihaiensis, P. chesapeaki and P. marinus across continental and global spatial scales.Main conclusionsOur results add further evidence of recent or continuous long-range dispersal and global connectivity for many haplotypes, suggesting that parasite dispersal through anthropogenic activities, such as maritime trade, likely contributes to these phylogeographic patterns.

The loss of genetic diversity due to population bottlenecks during invasion can reduce the fitness of introduced species. Despite this, introduced species often perform better in their introduced range. This conundrum, referred to as the genetic paradox of biological invasions, remains unanswered despite extensive research over the past decades. In this chapter, we propose that parasite release could provide a clue to disentangling the paradox. Along with reducing genetic diversity, population bottlenecks also serve to reduce co-invasion of parasites, resulting in parasite release among introduced populations. Across 27 taxonomically diverse animal species, we found a positive correlation between genetic diversity loss and parasite release. Since these two factors can affect the survival, fecundity and growth in opposing directions, the observed correlation indicates that parasite release could potentially compensate for the negative effects of genetic depletions in the introduced species. We, therefore, posit that parasite release provides an additional explanation for the genetic paradox of biological invasions.

The enemy release hypothesis (ERH) predicts that introduced species leave most enemies behind during the invasion process, resulting in less enemy damage and increased performance in their introduced range. In Hawai‘i, introduced red mangroves ( Rhizophora mangle ) convert open shorelines into dense mangrove forests. While previous studies show introduced mangroves harbor a lower occurrence of damage on various plant structures, it remains unknown if the magnitude of damage to mangrove leaves and metrics of performance differ between introduced and native populations. In this study, we tested some of the predictions of the ERH through leaf damage surveys and a year-long damage experiment replicated in 8–10 sites in the native (Caribbean and Florida) and introduced (Hawai‘i) range of red mangroves. In each site, we (1) compared the percentage of leaf area damaged, (2) measured metrics of performance (leaf loss, leaf, twig, and propagule production), and (3) experimentally tested how rapidly necrosis spreads on artificially-damaged leaves of R. mangle . Our results were largely consistent with the ERH. Native mangroves exhibited orders of magnitude higher leaf damage than introduced mangroves, suffered nearly twice the leaf loss, and produced fewer twigs and propagules than introduced mangroves over one year. Leaf production and the expansion of necrotic area on leaves were similar. Broadly, our study demonstrates that introduced mangroves experience substantially less leaf damage and thus, may be exhibiting evidence of increased growth and fecundity. Our results may help explain why introduced mangroves continue to be so productive and are considered invasive in Hawaiian habitats.

Interoceanic canals can facilitate biological invasions as they connectthe world’s oceans and dissolve dispersal barriers between bioregions.As a consequence, multiple opportunities for biotic exchange arise andthe resulting establishment of migrant species often causes adverseecological and economic impacts. The Panama Canal is a key region forbiotic exchange as it connects the Pacific and Atlantic Oceans inCentral America. In this study, we used two complementary methods(environmental DNA (eDNA) and gillnetting) to survey fish communities inthis unique waterway. Using COI (cytochrome oxidase subunit I)metabarcoding, we detected a total of 142 taxa, including evidence forthe presence of sixteen Atlantic and eight Pacific marine fish insidedifferent sections of the Canal. Of these, ten are potentially newrecords of marine taxa detected in the freshwater segment of the Canal.Molecular data did not capture all species caught with gillnets, butgenerally provided a more complete image of the fish fauna. Diversityindices based on eDNA surveys revealed significant differences acrossdifferent sections of the Canal reflecting in part the prevailingenvironmental conditions. The observed increase in the presence ofmarine fish species in the Canal indicates a growing potential forinteroceanic exchange of fishes across the Isthmus. Monitoring usingeDNA is a rapid and efficient way to assess potential changes in thefishes of this important waterway.

Biological invasions are expected to alter food web structure, but there are limited empirical data directly comparing invaded versus uninvaded food webs, particularly in species-rich, tropical systems. We characterize for the first time the food web of Lake Gatun-a diverse and highly invaded tropical freshwater lake within the Panama Canal. We used stable isotope analysis to reconstruct the trophic structure of the fish community of Lake Gatun and to compare it to that of a minimally invaded reference lake, Lake Bayano. We found significant differences between the trophic structures of these two Neotropical lakes, notably that Lake Gatun's fish community was characterized by a longer food chain, greater isotopic diversity, a broader range of trophic positions and body sizes, and shifts in the isotopic positions of several native taxa relative to Lake Bayano. The degree of isotopic overlap between native and non-native trophic guilds in Lake Gatun was variable, with herbivores exhibiting the lowest (20%-29%) overlap and carnivores the greatest (81%-100%). Overall, our results provide some of the first empirical evidence for the ways in which multiple introduced and native species may partition isotopic space in a species-rich tropical freshwater food web.

Compressed raw sequencing data generated from eDNA collected from the Panama Canal.

The enemy release hypothesis (ERH) posits that introduced species often leave their enemies behind when introduced to a new range. This release from enemies may allow introduced species to achieve higher growth and reproduction and may explain why some invaders flourish in new locations. Red mangroves (Rhizophora mangle) were introduced to Hawai'i from Florida over a century ago. Because Hawai'i has no native mangroves, the arrival of R. mangle fundamentally changed the structure and function of estuarine shorelines. While numerous enemies affect red mangroves in their native range (tropical America), in Hawai'i, mangroves apparently experience little herbivory, which may explain why introduced mangroves are so productive, fecund, and continue to spread. In this study, we compared the effects of enemies in native and introduced populations of brackish red mangroves (R. mangle) in 8-10 sites in the native range (Florida, Belize, and Panama) and introduced range of mangroves (Hawai'i). At each site, we measured the (1) occurrence of enemies using timed visual surveys, (2) occurrence of damage to different mangrove structures (leaves, apical buds, dead twigs, roots, propagules, and seedlings), and (3) rate of propagule herbivory using tethering experiments. Consistent with the ERH, we found an order of magnitude less damage and fewer enemies in introduced than native mangrove sites. While introduced mangroves harbored few enemies and minimal damage, native mangroves were affected by numerous enemies, including leaf-eating crabs, specialist bud moths, wood-boring insects and isopods, and propagule predators. These patterns were consistent across all plant structures (roots to leaves), among marine and terrestrial enemies, and across functional groups (browsers, borers, pathogens, etc.), which demonstrates enemy escape occurs consistently among different functional groups and via trophic (e.g., herbivores) and non-trophic (e.g., root borers) interactions. Our study is among the first biogeographical enemy release studies to take a comprehensive approach to quantifying the occurrence of damage from a broad suite of marine and terrestrial taxa across an array of wetland plant structures. Understanding how natural enemies alter this key foundation species will become increasingly relevant globally as mangroves continue to invade new regions through intentional plantings or range expansion driven by climate change.

Early naturalists suggested that predation intensity increases toward the tropics, affecting fundamental ecological and evolutionary processes by latitude, but empirical support is still limited. Several studies have measured consumption rates across latitude at large scales, with variable results. Moreover, how predation affects prey community composition at such geographic scales remains unknown. Using standardized experiments that spanned 115° of latitude, at 36 nearshore sites along both coasts of the Americas, we found that marine predators have both higher consumption rates and consistently stronger impacts on biomass and species composition of marine invertebrate communities in warmer tropical waters, likely owing to fish predators. Our results provide robust support for a temperature-dependent gradient in interaction strength and have potential implications for how marine ecosystems will respond to ocean warming.

Understanding the mechanisms of spatial variation of biological invasions, across local-to-global scales, has been a major challenge. The importance of evolutionary history for invasion dynamics was noted by Darwin, and several studies have since considered how biodiversity of source and recipient regions can influence the probability of invasions. For over a century, the Panama Canal has connected water bodies and biotas with different evolutionary histories, and created a global shipping hot spot, providing unique opportunities to test mechanisms that affect invasion patterns. Here, we test for asymmetry in both the extent of invasions and predation effects, a possible mechanism of biotic resistance, between two tropical oceans at similar latitudes. We estimated nonnative species (NNS) richness for sessile marine invertebrates, using standardized field surveys and literature synthesis, to examine whether invasions are asymmetrical, with more NNS present in the less diverse Pacific compared to the Atlantic. We also experimentally tested whether predation differentially limits the abundance and distribution of these invertebrates between oceans. In standardized surveys, observed total NNS richness was higher in the Pacific (18 NNS, 30% of all Pacific species) than the Atlantic (11 NNS, 13% of all Atlantic species). Similarly, literature-based records also display this asymmetry between coasts. When considering only the reciprocal exchange of NNS between Atlantic and Pacific biotas, NNS exchange from Atlantic to Pacific was eightfold higher than the opposite direction, exceeding the asymmetry predicted by random exchange based simply on differences of overall diversity per region. Predation substantially reduced biomass and changed NNS composition in the Pacific, but no such effects were detected on the Atlantic coast. Specifically, some dominant NNS were particularly susceptible to predation in the Pacific, supporting the hypothesis that predation may reduce the abundance of certain NNS here. These results are consistent with predictions that high diversity in source regions, and species interactions in recipient regions, shape marine invasion patterns. Our comparisons and experiments across two tropical ocean basins, suggest that global invasion dynamics are likely driven by both ecological and evolutionary factors that shape susceptibility to and directionality of invasions across biogeographic scales.