Extreme winter temperatures govern the northern range limit of black mangroves ( Avicennia germinans ) in southeastern North America. There is a pressing need for studies that advance our understanding of how extreme cold temperature events affect mangroves near their range limits. However, such events are infrequent and challenging to study at regional scales. Here, we compared the damage to mangroves from extreme freeze events in 2018 and 2021, using local data from sites in USA (Florida, Louisiana, and Texas) and northeastern Mexico (Tamaulipas). In 2018, mangrove damage was concentrated in Louisiana and the upper Texas coast, where minimum temperatures ranged from -4 °C to -7 °C. In 2021, damage from a more severe freeze event was concentrated along the central to northern coasts of Texas, where minimum temperatures ranged from -4 °C to -10 °C. We used regional temperature and vegetation data from these events to quantify temperature thresholds for A. germinans leaf damage. Our results indicate that A. germinans leaf damage is likely to occur when temperatures are between -4 °C and -6 °C. These findings help refine temperature thresholds for A. germinans leaf damage and advance understanding of the effects of extreme freeze events on mangrove range expansion. This information is valuable for anticipating future range dynamics in a warming world.

Climate change is altering the frequency and intensity of extreme weather events. Quantifying ecosystem responses to extreme events at the landscape scale is critical for understanding and responding to climate-driven change but is constrained by limited data availability. Here, we integrated remote sensing with ground-based observations to quantify landscape-scale vegetation damage from an extreme climatic event. We used ground- and satellite-based black mangrove ( Avicennia germinans ) leaf damage data from the northern Gulf of Mexico (USA and Mexico) to examine the effects of an extreme freeze in a region where black mangroves are expanding their range. The February 2021 event produced coastal temperatures as low as − 10 °C in some areas, exceeding thresholds for A. germinans damage and mortality. We used Sentinel-2 surface reflectance data to assess vegetation greenness before and after the freeze, along with ground-based observations of A. germinans leaf damage. Our results show a negative, nonlinear threshold relationship between A. germinans leaf damage and minimum temperature, with a temperature threshold for leaf damage near − 6 °C. Satellite-based analyses indicate that, at the landscape scale, damage was particularly severe along the central Texas coast, where the freeze event affected > 2000 ha of A. germinans -dominated coastal wetlands. Our analyses highlight the value of pairing remotely sensed data with regional, ground-based observations for quantifying and extrapolating the effects of extreme freeze events on mangroves and other tropical, cold-sensitive plants. The results also demonstrate how extreme freeze events govern the expansion and contraction of mangroves near northern range limits in North America.

Climate change is altering species’ range limits and transforming ecosystems. For example, warming temperatures are leading to the range expansion of tropical, cold-sensitive species at the expense of their cold-tolerant counterparts. In some temperate and subtropical coastal wetlands, warming winters are enabling mangrove forest encroachment into salt marsh, which is a major regime shift that has significant ecological and societal ramifications. Here, we synthesized existing data and expert knowledge to assess the distribution of mangroves near rapidly changing range limits in the southeastern USA. We used expert elicitation to identify data limitations and highlight knowledge gaps for advancing understanding of past, current, and future range dynamics. Mangroves near poleward range limits are often shorter, wider, and more shrublike compared to their tropical counterparts that grow as tall forests in freeze-free, resource-rich environments. The northern range limits of mangroves in the southeastern USA are particularly dynamic and climate sensitive due to abundance of suitable coastal wetland habitat and the exposure of mangroves to winter temperature extremes that are much colder than comparable range limits on other continents. Thus, there is need for methodological refinements and improved spatiotemporal data regarding changes in mangrove structure and abundance near northern range limits in the southeastern USA. Advancing understanding of rapidly changing range limits is critical for foundation plant species such as mangroves, as it provides a basis for anticipating and preparing for the cascading effects of climate-induced species redistribution on ecosystems and the human communities that depend on their ecosystem services.

Climate change is a primary driver of tropical mangroves colonizing temperate salt marshes in the Gulf of Mexico. Studies indicate that threshold temperatures of adult and sapling Avicennia germinans survival range from −7 to −10 °C and survival can depend on life history stage during a freeze event. We performed a growth chamber study to explore responses to varying freezing temperature regimes when produced at two different latitudes with varying salinity and nutrient conditions. Propagules were collected from Corpus Christi and South Padre Island, Texas. In Corpus Christi Bay, propagules were harvested from fertilized maternal shrubs (nitrogen, phosphorus, and controls) in an ongoing fertilization experiment (2017 to present). A 2-h hard freeze treatment (−8 °C), resulted in 20

Tropical cyclones drive coastal ecosystem dynamics, and their frequency, intensity, and spatial distribution are predicted to shift with climate change. Patterns of resistance and resilience were synthesized for 4138 ecosystem time series from n = 26 storms occurring between 1985 and 2018 in the Northern Hemisphere to predict how coastal ecosystems will respond to future disturbance regimes. Data were grouped by ecosystems (fresh water, salt water, terrestrial, and wetland) and response categories (biogeochemistry, hydrography, mobile biota, sedentary fauna, and vascular plants). We observed a repeated pattern of trade-offs between resistance and resilience across analyses. These patterns are likely the outcomes of evolutionary adaptation, they conform to disturbance theories, and they indicate that consistent rules may govern ecosystem susceptibility to tropical cyclones.

Abstract Loss of plant biodiversity can result in reduced abundance and diversity of associated species with implications for ecosystem functioning. In ecosystems low in plant species diversity, such as Neotropical mangrove forests, it is thought that genetic diversity within the dominant plant species could play an important role in shaping associated communities. Here, we used a manipulative field experiment to study the effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on the composition and richness of associated soil bacterial communities. Using terminal restriction fragment length polymorphism (T‐RFLP) community fingerprinting, we found that bacterial community composition differed among R. mangle maternal genotypes but not with genetic diversity. Bacterial taxa richness, total soil nitrogen, and total soil carbon were not significantly affected by maternal genotypic identity or genetic diversity of R. mangle. Our findings show that genotype selection in reforestation projects could influence soil bacterial community composition. Further research is needed to determine what impact these bacterial community differences might have on ecosystem processes, such as carbon and nitrogen cycling.

Fine roots are of major importance for belowground processes in mangrove ecosystems. Little is known about individual mangrove root systems, particularly the fine root component. We measured fine root biomass distribution of solitary standing Rhizophora mangle L. individuals with the dual aim of (a) deepening our understanding of the belowground ecology and allometric relations of this species; and (b) gaining further information about its climatic relevance. Twelve trees of variable height (45–240 cm) were measured on three reforested sites in south-east Florida, USA. Soil cores were collected from individual trees at transects by means of auger sampling. Fine roots were extracted, sorted, dried and weighed. Mean fine root biomass varied between 20.56–253.12 g/m2. Two separate mixed-effects models led to statistically sound predictions of spatial fine root biomass distribution. The first model was based on distance function and tree height (Model 1, \(R^2 = 0.77\), p value ≤ 0.001), and the second on prop root density (Model 2, \(R^2 = 0.56\), p value ≤ 0.001). Besides the aforementioned fixed effects, the results of both models indicated random, site-specific variation with regards to fine root biomass distribution. Nevertheless, we were able to explain individual fine root biomass distribution with reference to aboveground characteristics alone. These findings may help to improve the modelling of belowground plant interaction and carbon storage in mangroves, both of which are intrinsically linked to fine roots.

PREMISE OF THE STUDY:The Last Glacial Maximum (LGM) was a period of massive range contraction. Post-LGM, water-dispersed coastal species, including the red mangrove (Rhizophora mangle), expanded poleward as propagules were transported by ocean currents. We assessed postglacial marine expansion pathways for R. mangle within the Caribbean Basin and Florida.METHODS:Six microsatellite loci were used to genotype 237 individuals from nine R. mangle populations in the Caribbean, Florida, and Northwest Africa. We evaluated genetic variation, population structure, gene flow along alternative post-LGM expansion pathways to Florida, and potential long-distance dispersal (LDD) from West Africa to Caribbean islands.KEY RESULTS:These R. mangle populations had substantial genetic structure (FST = 0.37, P < 0.0001) with three discrete population clusters (Caribbean mainland, Caribbean islands, and Florida). Genetic connectivity along the mainland pathway (Caribbean mainland to Florida) vs. limited gene dispersal along the Antilles Island pathway (Caribbean islands to Florida) supported Florida recolonization from Caribbean mainland sources. Genetic similarity of Northwest Africa and two Caribbean islands provided evidence for trans-Atlantic LDD. We did not find a pattern of decreasing genetic diversity with latitude.CONCLUSIONS:We outline a complex expansion history for R. mangle, with discrete pathways of recolonization for Florida and Caribbean islands. Contrary to expectation, connectivity to putative Caribbean mainland refugial populations via ocean currents, and not latitude, appears to dictate genetic diversity within Caribbean island and Florida R. mangle. These findings provide a framework for further investigation of additional water-dispersed neotropical species, and insights for management initiatives.

AbstractMarine species with planktonic larvae often have high spatial and temporal variation in recruitment that leads to subsequent variation in the ecology of benthic adults. Using a combination of published and unpublished data, we compared the population structure of the salt marsh snail, Littoraria irrorata, between the South Atlantic Bight and the Gulf Coast of the United States to infer geographic differences in recruitment and to test the hypothesis that the Deepwater Horizon oil spill led to widespread recruitment failure of L. irrorata in Louisiana in 2010. Size‐frequency distributions in both ecoregions were bimodal, with troughs in the distributions consistent with a transition from sub‐adults to adults at ~13 mm in shell length as reported in the literature; however, adult snails reached larger sizes in the Gulf Coast. The ratio of sub‐adults to adults was 1.5–2 times greater in the South Atlantic Bight than the Gulf Coast, consistent with higher recruitment rates in the South Atlantic Bight. Higher recruitment rates in the South Atlantic Bight could contribute to higher snail densities and reduced adult growth in this region. The ratio of sub‐adults to adults in Louisiana was lower in 2011 than in previous years, and began to recover in 2012–2014, consistent with widespread recruitment failure in 2010, when large expanses of spilled oil were present in coastal waters. Our results reveal an important difference in the ecology of a key salt marsh invertebrate between the two ecoregions, and also suggest that the Deepwater Horizon oil spill may have caused widespread recruitment failure in this species and perhaps others with similar planktonic larval stages.

AimWe evaluated underlying mechanisms and genetic effects of climate-driven range expansion of Rhizophora mangle L., a coastal foundation species, along both West (WFL) and East (EFL) Florida, USA.LocationEight sites encompassing the entire Florida R. mangle range at a regional scale.MethodsWe characterized R. mangle population genetic structure with a combination of genetic analyses using seven microsatellite loci and model-based propagule transport. We tested hypotheses on the genetic effects of range expansion along both WFL and EFL. Finally, we compared WFL and EFL range edges and assessed potential factors shaping observed differences.ResultsRegional-scale Florida R. mangle genetic structure is shaped in part by the non-independent effects of geographical distance and ocean currents that drive asymmetric propagule transport from WFL to EFL. WFL conformed to theoretical expectations of range expansion, with pronounced divergence at the range edge, whereas EFL deviated from expectations. Significant differences in diversity and differentiation at the WFL and EFL range edges were attributed to differences in migration rates, population size and founder effects.Main conclusionsContrasting genetic landscapes at the WFL and EFL range edges are in part the product of variation in ocean circulation and demographic history. These underlying mechanisms may have potential ecological and evolutionary consequences that need to be addressed with further empirical research.

Mangroves are an ecological assemblage of trees and shrubs adapted to grow in intertidal environments along tropical, subtropical, and warm temperate coasts. Despite repeated demonstrations of their ecologic and economic value, multiple stressors including nutrient over-enrichment threaten these and other coastal wetlands globally. These ecosystems will be further stressed if tropical storm intensity and frequency increase in response to global climate changes. These stressors will likely interact, but the outcome of that interaction is uncertain. Here, we examined potential interaction between nutrient over-enrichment and the September 2004 hurricanes. Hurricanes Frances and Jeanne made landfall along Florida's Indian River Lagoon and caused extensive damage to a long-term fertilization experiment in a mangrove forest, which previously revealed that productivity was nitrogen (N) limited across the forest and, in particular, that N enrichment dramatically increased growth rates and aboveground biomass of stunted Avicennia germinans trees in the interior scrub zone. During the hurricanes, these trees experienced significant defoliation with three to four times greater reduction in leaf area index (LAI) than control trees. Over the long-term, the +N scrub trees took four years to recover compared to two years for controls. In the adjacent fringe and transition zones, LAI was reduced by > 70%, but with no differences based on zone or fertilization treatment. Despite continued delayed mortality for at least five years after the storms, LAI in the fringe and transition returned to pre-hurricane conditions in two years. Thus, nutrient over-enrichment of the coastal zone will increase the productivity of scrub mangroves, which dominate much of the mangrove landscape in Florida and the Caribbean; however, that benefit is offset by a decrease in their resistance and resilience to hurricane damage that has the potential to destabilize the system.

A Comment by Rey et al. (2009; Mar Ecol Prog Ser 389:295-300) documents disagreements with Middleton et al. (2008; Mar Ecol Prog Ser 371:117-129), which explored the characteristics of mangrove swamps managed for mosquito control in the Indian River Lagoon, Florida, USA. Rey et al. (2009) provide no data or evidence that invalidate the conclusions in Middleton et al. (2008). Most of the 'factual errors' and 'methodological problems' raised by Rey et at. (2009) are either unfounded or minor points, or reflect differences of opinion regarding appropriate sampling designs and techniques. The disagreement between the two research groups derives mainly from different scientific viewpoints. One is based on a parochial view guided by the immediate needs of local site managers; the other takes a wider view of ecology, which uses a landscape-level approach to develop information with broader application. This Reply Comment clarifies several issues, refocuses attention on the scientific aspects of this discussion, and summarizes information needed to develop a wider perspective for future management of coastal impoundments, especially given anticipated changes in climate, sea level, and other global factors. We discuss the challenges of studying complex ecological systems with the goal of providing useful information to managers, who must often make difficult decisions.

Manipulations of the vegetation and hydrology of wetlands for mosquito control are common worldwide, but these modifications may affect vital ecosystem processes. To control mosquitoes in mangrove swamps in eastern Florida, managers have used rotational impoundment management (RIM) as an alternative to the worldwide practice of mosquito ditching. Levees surround RIM swamps, and water is pumped into the impoundment during the summer, a season when natural swamps have low water levels. In the New World, these mosquito-managed swamps resemble the mixed basin type of mangrove swamp (based on PCA analysis). An assessment was made of RIM, natural (control), and breached-RIM (restored) swamps in eastern Florida to compare their structural complexities, soil development, and resistance to invasion. Regarding structural complexity, dominant species composition differed between these swamps; the red mangrove Rhizophora mangle occurred at a higher relative density in RIM and breached-RIM swamps, and the black mangrove Avicennia germinans had a higher relative density in natural swamps. Tree density and canopy cover were higher and tree height lower in RIM swamps than in natural and breached-RIM swamps. Soil organic matter in RIM swamps was twice that in natural or breached-RIM swamps. RIM swamps had a lower resistance to invasion by the Brazilian pepper tree Schinus terebinthifolius, which is likely attributable to the lower porewater salinity in RIM swamps. These characteristics may reflect differences in important ecosystem processes (primary production, trophic structure, nutrient cycling, decomposition). Comparative assessments of managed wetlands are vital for land managers, so that they can make informed decisions compatible with conservation objectives.

Melampus coffeus, a pulmonate gastropod, forages for mangrove leaf litter at low tide and climbs tree trunks to avoid inundation during high tide. Unlike many grazers, these snails can assimilate mangrove leaf material. At Boca Ceiga Bay, Florida, densities of adult snails were high (>100 snails m -2 ) throughout a 130 m wide intertidal zone. A mark-recapture study indicated that over the course of 1 mo 48.6 ± 6.1% of snails returned to their initial tree during high tides, while those that did relocate moved 6.66 ± 0.60 m and were recorded from 33 new trees at high tide. A field experiment comparing tethered leaves with small and large litter bags showed that snail grazing greatly increased the rate of red (Rhizophora mangle) and black (Avicennia germinans) leaf litter breakdown. Grazing by M. coffeus resulted in 90 % weight loss in 26 wk, R. mangle). Another experiment showed greater leaf litter accumulation on the forest floor in plots where M. coffeus was excluded. The decomposition coefficient (k) was lOx greater when M. coffeus grazing was allowed than k for any studies that enclosed leaves in litterbags. During our experiment, M. coffeus consumed an estimated 40.5% of mangrove leaf fall, and 19.8% of leaf litter was exported as particulate or dissolved material. This M. coffeus population can produce an estimated 3 x 10 6 larvae m -2 y -1 , which suggests that the larval pathway is an important conduit of mangrove leaf resources to the estuarine food web.

We compared colonization, growth and succession from 1989 to 2000 in a restored mangrove site and in gap and closed canopy sites in a natural mangrove forest. The restored site was created in 1982 and planted with Rhizophora mangle (≈2 m−2) propagules. By 1989, Laguncularia racemosa, with densities up to 12.9 tree m−2, was a dominant in all plots, although densities were greater at edge plots relative to inner plots, and near open water (west plots) relative to further inland (east plots), and in tall mangrove plots relative to scrub plots. Rhizophora mangle (1989 tree densities about 2 m−2) was a codominant in inner and scrub plots, while Avicennia germinans had the lowest densities (<1 tree m−2) in all plots. From 1989 to 2000 L. racemosa experienced reduced recruitment and apparent density-dependent mortality of canopy individuals in plots with high initial densities. Scrub plots experienced high rates of colonization by R. mangle and L. racemosa, rapid growth in height of all species (1989–1996), followed by a dieoff of L. racemosa in later years (1997–2000) as the canopy came to resemble that of tall mangrove plots. Colonization and growth rates were lower in gap and closed canopy regions of the natural forest relative to rates in the restored site. After 11 years, densities of L. racemosa were 10–20× lower and R. mangle slightly less in the gap relative to densities in tall mangrove plots in the restored site at the same age. Although the restored stand had converged with the natural forest by 2000 in terms of some factors such as species richness, vegetation cover, litterfall, and light penetration, trees were still much smaller and stem densities much higher. Full development of mature structure and ecological function will likely require decades more development.

Studies of the effects of oil on coastal species seldom address multiple oilings, even though contamination of systems by more than one spill event is not uncommon. We report the results of two experiments in which first red mangrove (Rhizophora mangle L.) seedling propagules were oiled with No. 6 fuel oil, and 34 mo later the surviving saplings were randomly assigned to new treatments and reoiled with south Louisiana crude oil in a 2 × 2 factorial design (main effects: crude oil and prior history of oiling with No. 6 oil). In Experiment 1 (No. 6 oil), there were no significant effects on seedling growth or survival at 10 mo. At 32 mo, the low-oil group (<50% of propagule surface area covered) produced less lateral stem growth, fewer numbers of lateral stems, and fewer leaves than the control group. There were no significant effects of the high-oil treatment (defined as >50% of surface area covered), although there was a tendency toward reduced survival. In Experiment 2 (crude × No. 6 oil), sapling survival, total stem growth, numbers of lateral stems produced, numbers of live leaves on plants, and leaf production were significantly reduced by application to the soil of 16.0 L/m2 crude oil (the high-crude treatment), but not by the low-crude treatment of 1.6 L/m2. History of prior oiling with No. 6 fuel oil as seedlings had no effects, nor were there significant No. 6 oil × crude oil interactions. Total leaf production, maximum leaf size, numbers of yellow and brown leaves, stem diameter, and extent of main stem lignification in saplings were not significantly affected by the oil treatments. For these life history stages, oil types, and modes of oiling, there was no evidence of cumulative or synergistic effects of two oiling events on R. mangle.

The effects of oil treatments (one-time addition of 120 ml per plant and weekly addition of 15 ml per plant) and environmental conditions at time of oiling (air conditioned laboratory/diffuse light vs hot, direct sunlight) on the survival and growth of Rhizophora mangle and Avicennia germinans seedlings were examined. No oiled A. germinans survived longer than a few weeks. Both one-time and weekly oiling depressed survival, stem growth, leaf production and maximum leaf size in R. mangle. Significant interaction terms between oil treatment and environmental conditions occurred later (50 and 59 weeks) for R. mangle stem growth and earlier (21 and 23 weeks) for leaf production. Relative to other treatment combinations, R. mangle mortality was greatest and growth lowest in the combination of one-time oiling under hot, bright outdoor conditions. Results indicate that synergistic interactions between oil effects and environmental conditions may contribute to the wide range of effects reported in the literature in studies of oil contamination of mangroves.