Local Human Disturbance Research Articles

Exploring local and regional vegetation compositional changes during the Neolithic (5th–3rd millennium BC): A case study on the forager impact on vegetation in north-east Europe

This research explores the vegetation compositional changes between the fifth and third millennium BC on the Karelian Isthmus (north-west Russia). Special emphasis is placed on studying the timing and magnitude of the impact of hunter-fisher-gatherers on the vegetation. First, we reconstruct the local vegetation around Lake Bolshoye Zavetnoye by using the Landscape Reconstruction Algorithm modelling. The application of different scenarios to the relevant source area of pollen is used to assess the local vegetation around Lake Bolshoye Zavetnoye (BZL) at specific distances from 500 to 3000 m. The regional vegetation reconstruction is assessed by using the REVEALS model. Second, we present new pollen and charcoal data from adjacent Lake Ikmenlampi (LI). Third, we calculate indices of vegetation change for BZL, LI and the region. We further explore the potential causes for these differences between the spatial scales and compare all these outcomes with local and regional archaeological data. The results show that foragers actively manipulated their environment. A shift towards more heliophilous conditions is shown by ca 4800 BC. Between 4000 and 3000 BC, an increase in archaeological material suggests intensive resource procurement and landscape management activities, particularly near settlements. Around the BZL site a local decrease in birch is observed from 4100 BC, coinciding with an increase in the rate of vegetation changes. Additionally, a decline in tree species (spruce, hazel, Alder) from 3500 to 3300 BC suggests human activities. The high fire frequency recorded between 4090 and 3150 BC further supports the presence of local human disturbances by the deliberate use of fire to create favourable living conditions. The results from the LI site go in the same direction with fluctuating abundances of spruce and the presence of pollen from Cannabis, Hordeum, Urtica and Plantago lanceolata from ca 4000 to 3600 BC, indicating the use of spruce-dominated forests and an early, incipient cultivation.

Land use outweighs other stressors in declining fish biodiversity in lakes of Eastern China during the 1980s-2010s

Understanding patterns and driving factors of freshwater fish biodiversity in metacommunities is essential for biological conservation but rarely studied in regions experiencing rapid land use changes. We examined changes of both alpha and beta fish diversities in taxonomic, functional, and phylogenetic facets during the 1980 s to 2010 s, and quantified contributions from natural and human drivers in lakes located in China's fastest economic development region. Results showed that almost all indices of alpha and beta diversity decreased through time. For alpha diversity, taxonomic and functional richness declined by 13 to 15%. Rheophilic and piscivorous fish species declined by 50 and 36%, respectively. For beta diversity, the decline of overall functional (-31%) diversity was greater than taxonomic (-17%) and phylogenetic (-19%) diversity. The decline of multiple facets of beta diversity indicated that fish communities in these lakes have homogenized through time. Land use (i.e., increased urban land and aquaculture ponds), hydrology (i.e., increased water level), climate (i.e., increased air temperature), and fishing (i.e., increased lake fishery catch) factors all made significant contributions to both alpha and beta fish diversity decline in multiple facets. The overall contribution from land use to the decline of multidimensional fish diversity was greater than those of other stressors. While attention should be given to both local human disturbance and regional climate factors, in regions experiencing rapid economic development and land use changes, local disturbances should be considered as a priority in biodiversity management plans.

Macroalgae exhibit diverse responses to human disturbances on coral reefs.

Scientists and managers rely on indicator taxa such as coral and macroalgal cover to evaluate the effects of human disturbance on coral reefs, often assuming a universally positive relationship between local human disturbance and macroalgae. Despite evidence that macroalgae respond to local stressors in diverse ways, there have been few efforts to evaluate relationships between specific macroalgae taxa and local human-driven disturbance. Using genus-level monitoring data from 1205 sites in the Indian and Pacific Oceans, we assess whether macroalgae percent cover correlates with local human disturbance while accounting for factors that could obscure or confound relationships. Assessing macroalgae at genus level revealed that no genera were positively correlated with all human disturbance metrics. Instead, we found relationships between the division or genera of algae and specific human disturbances that were not detectable when pooling taxa into a single functional category, which is common to many analyses. The convention to use percent cover of macroalgae as an indication of local human disturbance therefore likely obscures signatures of local anthropogenic threats to reefs. Our limited understanding of relationships between human disturbance, macroalgae taxa, and their responses to human disturbances impedes the ability to diagnose and respond appropriately to these threats.

Interactions between local disturbance and climate-driven heat stress on central Pacific coral reefs

We investigated how local and global stressors affect coral reefs in situ by taking advantage of a latitudinal gradient in the central equatorial Pacific driven by El Niño-Southern Oscillation, where the past frequency of heat stress decreases away from the equator. We compared benthic communities at 40 sites across 4 atolls in the Gilbert Islands, namely in Kiribati (Tarawa and Abaiang) and the Republic of the Marshall Islands (Majuro and Arno), representing gradients in local chronic human disturbance and past frequency of bleaching-level heat stress. A hierarchical clustering analysis found 3 groupings of benthic communities, corresponding to sites with (1) low human influence and frequency of heat stress, (2) low human influence and high frequency of heat stress, and (3) high human influence, suggesting that the effects of intense, ongoing local disturbance may mask the influence of heat stress on coral reef communities. The frequency of heat stress explained 8.0% of the differences in community compositions across all sites (PERMANOVA), while local anthropogenic stressors explained 16.2%, and the combined effects explained 7.0%. Interactions between stressors were multiplicative and acted synergistically to increase the percent cover of macroalgae and the stress-resistant coral Porites rus. The prevalence of P. rus at locally disturbed sites drives the positive relationship between local stress metrics and live coral cover. At the taxon level, half of the multiplicative interactions were antagonistic, suggesting that actions that reduce local stressors may help some coral taxa respond to climate stress, but possibly at the expense of other taxa.

Size and degree of protection of native forest remnants drive the local occupancy of an endangered neotropical primate.

Although the species-area relationship is well known, it may interact with and be augmented or cancelled out by other factors, such as local human disturbance. We used data on site occupancy of the Endangered blonde capuchin monkey (Sapajus flavius) based primarily on a standardized program of local interviews to model the influence of past human disturbance on the occurrence of this species across remaining forest patches of northeastern Brazil within the Atlantic Forest and Caatinga biomes. To do so, we assessed environmental covariates that best represent the history of human impacts. We then used single-species occupancy models to assess site occupancy, while controlling for detection error during sampling. Surprisingly, we obtained a higher occupancy rate in the more arid Caatinga remnants than in the more mesic Atlantic Forest. Habitat patch size, history of site protection, and annual precipitation were the best predictors of local occupancy. Historical human disturbance, including subsistence hunting, has exerted considerable impact on the modern distribution of the blonde capuchin, whose geographic range largely spans a region historically lacking any wildlife protection. Matrix vegetation structure across the Caatinga, which so far has averted large-scale mechanized agriculture, also creates a benign landscape that likely benefits contemporary capuchin occupancy. Local extinctions of this endangered primate will most likely continue unabated unless a ban on hunting in remaining Atlantic Forest and Caatinga fragments can be enforced.

Historical declines in parrotfish on Belizean coral reefs linked to shifts in reef exploitation following European colonization

Humans have utilized the Mesoamerican Reef (MAR) for millennia but the effects of prehistorical and historical fishing on this ecosystem remain understudied. To assess the long-term coupling of reef ecosystem and human dynamics in this region, we tracked trends in the structure and functioning of lagoonal reefs within the Belizean portion of the MAR using fish teeth fossils and sediment accumulation rates within reef sediment cores. We then paired this with a timeline of demographic and cultural changes in this region’s human populations. The ∼1,300-year timeline encompassed in the core record shows that declines in the relative abundance and accumulation rate of teeth from parrotfish, a key reef herbivore, occurred at all three reef sites and began between ∼1500 and 1800 AD depending on site and metric of abundance. A causality analysis showed that parrotfish relative abundance had a positive causal effect on reef accretion rates, a proxy of coral growth, reconfirming the important role of these fish in reef ecosystem functioning. The timing of initial declines in parrotfish teeth occurred during a time of relatively low human population density in Belize. However, declines were synchronous with cultural and demographic upheaval resulting from European colonization of the New World. The more recent declines at these sites (∼1800 AD) occurred in tandem with increased subsistence fishing on reefs by multiple immigrant groups, a pattern that was likely necessitated by the establishment of an import economy controlled by a small group of land-owning European elites. These long-term trends from the paleoecological record reveal that current parrotfish abundances in central Belize are well below their pre-European contact peaks and that increased fishing pressure on parrotfish post-contact has likely caused a decline in reef accretion rates. The origins of reef degradation in the Belizean portion of the MAR began hundreds of years before the onset of modern declines resulting from the combined effects of local human disturbances and climate change.

Is the ghost crab’s feeding behavior a good early indicator of human pressure in sandy beaches?

Phenotypic plasticity is a trait found among organisms that dwell in dynamic ecosystems such as sandy beaches. One of the main model of ecological studies in this ecosystem are ghost crabs (Crustacea: Ocypodidae), which present trophic plasticity and are considered ecological-disturbance indicator species. Their reactions to these impacts can manifest as sublethal responses, including behavioral aspects. We aimed to evaluate possible effects of urbanization on the feeding behavior of the ghost crab Ocypode quadrata (Fabricius, 1787). The study was conducted in a beach arc categorized into three urbanization levels located in the northern Rio de Janeiro state, Brazil. Each sector was sampled twice during high and low tourist seasons. The crabs’ diet was described by inspecting their digestive tracts with a stereomicroscope. Food preference (the choice of food items by each individual) and behavioral aspects (i.e., time of emergence from burrows, look-out time, number of choices, and handling time of the resource provided) were observed through in situ experiments, where food items were placed around burrows. The behavioral aspects were not affected by urbanization level. The diet mainly consisted of insects and macroalgae, though during experiments the species selected the most caloric items (fish and the bivalve Donax hanleyanus), regardless of the urbanization level. Local human disturbances seemed neither to change the availability of local resources nor to select individuals by feeding behavior. Therefore, there was no evidence that the feeding behavior of ghost crabs can be considered as a potential early indicator of human disturbance.

The Relative Importance of Human Disturbance, Environmental and Spatial Factors on the Community Composition of Wetland Birds

The present study investigates the relative importance of human disturbance, local environmental and spatial factors on variations in bird community composition in natural Ethiopian wetlands with high biodiversity conservation value. We quantified bird abundances, local environmental variables and human disturbances at 63 sites distributed over ten wetlands in two subsequent years. Variation partitioning analyses were used to explore the unique and shared contributions of human disturbance, local environmental variables and spatial factors on variations in community compositions of wetland bird species. Local environmental variables explained the largest amount of compositional variation of wetland bird species. Productivity-related variables were the most important local environmental variables determining bird community composition. Human disturbance was also an important determinant for wetland bird community composition and affected the investigated communities mainly indirectly through its effect on local environmental conditions. Spatial factors only played a minor role in variations in bird community composition. Our study highlights the urgent need for integrated management approaches that consider both nature conservation targets and socio-economic development of the region for the sustainable use and effective conservation of wetland resources.

Level of local human disturbance and feeding state determines escape behaviour in Eurasian Oystercatchers

AbstractHuman disturbances may constitute a significant stressor for wildlife, especially where human recreational activities overlap with fitness‐enhancing activities such as feeding. Disturbances cause an animal to flee from the perceived predation risk, using energy, rather than remaining and gaining energy. Such reactions are, however, context‐dependent, as predicted by optimal escape theory: animals should only flee when the perceived risk of predation of remaining exceeds the risk of starvation of leaving. Animals may also learn that humans do not generally represent a predation risk after repeated false alarms and then learn to only respond when approached deliberately and closely. We tested the Flight Initiation Distance (FID; distance at which an approached animal begins escape) of feeding or roosting Eurasian Oystercatchers Haematopus ostralegus (oystercatchers) to a human (as a simulated predator) in areas with or without humans on beaches in south‐east Scotland. We predicted roosting oystercatchers to respond earlier (greater FID) than feeding birds because the risk of starvation will be lower, and earlier on beaches where there were no humans at the start of the experiment because a human will then represent a more novel predator signal. As predicted, oystercatchers escaped at greater distances away from the perceived threat when feeding and in areas with humans. We found that escape distances decreased (greater tolerance of the perceived threat) as the number of people in an area increased, but people being present or not explained more of the variation in the data. The results show that oystercatchers habituate on a short timescale to non‐lethal human presence and generally respond to perceived predation risk in accordance with the predictions of optimal escape theory.

Coral reefs in the Gilbert Islands of Kiribati: Resistance, resilience, and recovery after more than a decade of multiple stressors.

Coral reefs are increasingly affected by a combination of acute and chronic disturbances from climate change and local stressors. The coral reefs of the Republic of Kiribati's Gilbert Islands are exposed to frequent heat stress caused by central-Pacific type El Niño events, and may provide a glimpse into the future of coral reefs in other parts of the world, where the frequency of heat stress events will likely increase due to climate change. Reefs in the Gilbert Islands experienced a series of acute disturbances over the past fifteen years, including mass coral bleaching in 2004-2005 and 2009-2010, and an outbreak of the corallivorous sea star Acanthaster cf solaris, or Crown-of-Thorns (CoTs), in 2014. The local chronic pressures including nutrient loading, sedimentation and fishing vary within the island chain, with highest pressures on the reefs in urbanized South Tarawa Atoll. In this study, we examine how recovery from acute disturbances differs across a gradient of human influence in neighboring Tarawa and Abaiang Atolls from 2012 through 2018. Benthic cover and size frequency data suggests that local coral communities have adjusted to the heat stress via shifts in the community composition to more temperature-tolerant taxa and individuals. In densely populated South Tarawa, we document a phase shift to the weedy and less bleaching-sensitive coral Porites rus, which accounted for 81% of all coral cover by 2018. By contrast, in less populated Abaiang, coral communities remained comparatively more diverse (with higher percentages of Pocillopora and the octocoral Heliopora) after the disturbances, but reefs had lower overall hard coral cover (18%) and were dominated by turf algae (41%). The CoTs outbreak caused a decline in the cover and mean size of massive Porites, the only taxa that was a 'winner' of the coral bleaching events in Abaiang. Although there are signs of recovery, the long-term trajectory of the benthic communities in Abaiang is not yet clear. We suggest three scenarios: they may remain in their current state (dominated by turf algae), undergo a phase shift to dominance by the macroalgae Halimeda, or recover to dominance by thermally tolerant hard coral genera. These findings provide a rare glimpse at the future of coral reefs around the world and the ways they may be affected by climate change, which may allow scientists to better predict how other reefs will respond to increasing heat stress events across gradients of local human disturbance.

The transformation of Caribbean coral communities since humans.

The mass die‐off of Caribbean corals has transformed many of this region’s reefs to macroalgal‐dominated habitats since systematic monitoring began in the 1970s. Although attributed to a combination of local and global human stressors, the lack of long‐term data on Caribbean reef coral communities has prevented a clear understanding of the causes and consequences of coral declines. We integrated paleoecological, historical, and modern survey data to track the occurrence of major coral species and life‐history groups throughout the Caribbean from the prehuman period to the present. The regional loss of Acropora corals beginning by the 1960s from local human disturbances resulted in increases in the occurrence of formerly subdominant stress‐tolerant and weedy scleractinian corals and the competitive hydrozoan Millepora beginning in the 1970s and 1980s. These transformations have resulted in the homogenization of coral communities within individual countries. However, increases in stress‐tolerant and weedy corals have slowed or reversed since the 1980s and 1990s in tandem with intensified coral bleaching and disease. These patterns reveal the long history of increasingly stressful environmental conditions on Caribbean reefs that began with widespread local human disturbances and have recently culminated in the combined effects of local and global change.

A combination of climate, tree diversity and local human disturbance determine the stability of dry Afromontane forests

BackgroundAnthropogenic disturbances are increasingly affecting the vitality of tropical dry forests. The future condition of this important biome will depend on its capability to resist and recover from these disturbances. So far, the temporal stability of dryland forests is rarely studied, even though identifying the important factors associated with the stability of the dryland forests could serve as a basis for forest management and restoration.MethodologyIn a degraded dry Afromontane forest in northern Ethiopia, we explored remote sensing derived indicators of forest stability, using MODIS satellite derived NDVI time series from 2001 to 2018. Resilience and resistance were measured using the anomalies (remainders) after time series decomposition into seasonality, trend and remainder components. Growth stability was calculated using the integral of the undecomposed NDVI data. These NDVI derived stability indicators were then related to environmental factors of climate, topography, soil, tree species diversity, and local human disturbance, obtained from a systematic grid of field inventory plots, using boosted regression trees in R.ResultsResilience and resistance were adequately predicted by these factors with an R2 of 0.67 and 0.48, respectively, but the model for growth stability was weaker. Precipitation of the wettest month, distance from settlements and slope were the most important factors associated with resilience, explaining 51% of the effect. Altitude, temperature seasonality and humus accumulation were the significant factors associated with the resistance of the forest, explaining 61% of the overall effect. A positive effect of tree diversity on resilience was also important, except that the impact of species evenness declined above a threshold value of 0.70, indicating that perfect evenness reduced the resilience of the forest. Precipitation of the wettest month was the most important factor explaining 43.52% of the growth stability variation.ConclusionA combination of climate, topographic factors and local human disturbance controlled the stability of the dry forest. Also tree diversity is an important stability component that should be considered in the management and restoration programs of such degraded forests. If local disturbances are alleviated the recovery time of dryland forests could be shortened, which is vital to maintain the ecosystem services these forests provide to local communities and global climate change.

Direct and Indirect Effects of Climate Change‐Amplified Pulse Heat Stress Events on Coral Reef Fish Communities

Climate change threatens the future of tropical corals, but less is known about how rising ocean temperatures impact reef fishes. We quantified reef fish communities in the equatorial Pacific (Kiritimati Island) before, during, and after an intense marine heatwave. Fish abundance and biomass around the atoll both halved during heat stress, presumably as fish migrated to deeper, cooler waters. One year after the heatwave, however, reef fishes had rebounded to pre-heatwave levels, with some notable exceptions: corallivores plummeted following the heatwave-induced mass coral mortality, herbivores increased as macroalgae proliferated, and reefs highly impacted by local human disturbance showed impaired recovery. These photographs illustrate the article “Direct and indirect effects of climate change-amplified pulse heat stress events on coral reef fish communities” by Jennifer M. T. Magel, Sean A. Dimoff, and Julia K. Baum published in Ecological Applications. https://doi.org/10.1002/eap.2124

Comparison of forest above-ground biomass from dynamic global vegetation models with spatially explicit remotely sensed observation-based estimates.

Gaps in our current understanding and quantification of biomass carbon stocks, particularly in tropics, lead to large uncertainty in future projections of the terrestrial carbon balance. We use the recently published GlobBiomass data set of forest above-ground biomass (AGB) density for the year 2010, obtained from multiple remote sensing and in situ observations at 100m spatial resolution to evaluate AGB estimated by nine dynamic global vegetation models (DGVMs). The global total forest AGB of the nine DGVMs is 365±66Pg C, the spread corresponding to the standard deviation between models, compared to 275Pg C with an uncertainty of ~13.5% from GlobBiomass. Model-data discrepancy in total forest AGB can be attributed to their discrepancies in the AGB density and/or forest area. While DGVMs represent the global spatial gradients of AGB density reasonably well, they only have modest ability to reproduce the regional spatial gradients of AGB density at scales below 1000km. The 95th percentile of AGB density (AGB95 ) in tropics can be considered as the potential maximum of AGB density which can be reached for a given annual precipitation. GlobBiomass data show local deficits of AGB density compared to the AGB95 , particularly in transitional and/or wet regions in tropics. We hypothesize that local human disturbances cause more AGB density deficits from GlobBiomass than from DGVMs, which rarely represent human disturbances. We then analyse empirical relationships between AGB density deficits and forest cover changes, population density, burned areas and livestock density. Regression analysis indicated that more than 40% of the spatial variance of AGB density deficits in South America and Africa can be explained; in Southeast Asia, these factors explain only ~25%. This result suggests TRENDY v6 DGVMs tend to underestimate biomass loss from diverse and widespread anthropogenic disturbances, and as a result overestimate turnover time in AGB.

Direct and indirect effects of climate change-amplified pulse heat stress events on coral reef fish communities.

Climatechange-amplified temperature anomalies pose an imminent threat to coral reef ecosystems. While much focus has been placed on the effects of heat stress on scleractinian corals-including bleaching, mortality, and loss of reef structural complexity-and many studies have documented changes to reef fish communities arising indirectly from shifts in benthic composition, the direct impacts of heat stress on reef fish are much less well understood. Here, we quantify the direct and indirect effects of heat stress on reef fishes, using underwater visual censuses of coral reef fish communities conducted before, during, and after the 2015-2016 El Niño-induced global coral bleaching event. Surveys took place at the epicenter of this event, at 16 sites on Kiritimati (Republic of Kiribati; central equatorial Pacific) spanning across a gradient of local human disturbance. We expected that heat stress would have both direct and indirect negative effects on the reef fish community, with direct effects resulting from physiological stress during the event and indirect effects manifesting afterward as a consequence of coral mortality, and that the ability of fish communities to recover following the heat stress would depend on levels of local human disturbance. We found that total reef fish biomass and abundance declined by >50% during heat stress, likely as a result of vertical migration of fish to cooler waters. One year after the cessation of heat stress, however, total biomass, abundance, and species richness had recovered to, or even exceeded, pre-heat stress levels. However, the biomass of corallivores declined by over 70% following severe coral loss, and reefs exposed to higher levels of local human disturbance showed impaired recovery following the heat stress. These findings enhance understanding of the projected impacts of climate change-associated marine heatwaves on reef fishes, and highlight the interacting effects of local and global stressors on this vital component of coral reef ecosystems.

HESS Opinions: Beyond the long-term water balance: evolving Budyko's supply–demand framework for the Anthropocene towards a global synthesis of land-surface fluxes under natural and human-altered watersheds

Abstract. Global hydroclimatic conditions have been substantially altered over the past century by anthropogenic influences that arise from the warming global climate and from local/regional anthropogenic disturbances. Traditionally, studies have used coupling of multiple models to understand how land-surface water fluxes vary due to changes in global climatic patterns and local land-use changes. We argue that because the basis of the Budyko framework relies on the supply and demand concept, the framework could be effectively adapted and extended to quantify the role of drivers – both changing climate and local human disturbances – in altering the land-surface response across the globe. We review the Budyko framework, along with these potential extensions, with the intent of furthering the applicability of the framework to emerging hydrologic questions. Challenges in extending the Budyko framework over various spatio-temporal scales and the use of global datasets to evaluate the water balance at these various scales are also discussed.

Climatic and local stressor interactions threaten tropical forests and coral reefs.

Tropical forests and coral reefs host a disproportionately large share of global biodiversity and provide ecosystem functions and services used by millions of people. Yet, ongoing climate change is leading to an increase in frequency and magnitude of extreme climatic events in the tropics, which, in combination with other local human disturbances, is leading to unprecedented negative ecological consequences for tropical forests and coral reefs. Here, we provide an overview of how and where climate extremes are affecting the most biodiverse ecosystems on Earth and summarize how interactions between global, regional and local stressors are affecting tropical forest and coral reef systems through impacts on biodiversity and ecosystem resilience. We also discuss some key challenges and opportunities to promote mitigation and adaptation to a changing climate at local and global scales. This article is part of the theme issue 'Climate change and ecosystems: threats, opportunities and solutions'.

RUNOFF SHRINKAGE IN THE WUYUR RIVER BASIN, NORTH‐EAST CHINA, AND ITS INFLUENCE ON THE SUCCESSION OF SALINE MARSH IN THE LOWER REACHES

AbstractDrought induced by global climate change and local human disturbance is having a significant impact on the succession of inland saline marshes. This study aims to examine the causes of rapid land degradation in China's Zhalong wetland over the past 65 years (1951–2015) using the Mann–Kendall rank test. Results indicate that local human disturbance (mainly water diversion) is the key detrimental factor in marsh degradation. Water diversion in the upper reaches of the Wuyur river basin has changed the hydrological regime and caused significant water deficit in the Zhalong wetland, thereby leading to rapid shrinkage of the marsh. An increasing runoff trend with an average of 7.44 × 108 m3 was observed in the upper reaches from 1983 to 2015. In contrast, the runoff in the lower reaches had significantly decreased from 8.5 × 108 m3 to 3 × 108 m3 in recent years (P < 0.05), given the water consumed by local anthropogenic activities in the upper reaches. The large water deficit in the lower reaches reduced water storage and caused rapid development of soil sodification, that is, the area of Halaquepts increased from 170 km2 in 1979 to 260 km2 in 2010, in which large areas emerged in the core area of the wetland. Land degradation decreased the habitat of the red‐crowned crane (Grus japonensis). This condition may be an important contributor to the population decline of rare birds and biodiversity loss. © 2019 John Wiley & Sons, Ltd.

Rapid human-driven undermining of atoll island capacity to adjust to ocean climate-related pressures

Most studies addressing the future of atoll islands focused on ocean-climate drivers of risk, especially sea-level rise, and disregarded the role of local human disturbances. However, the future habitability of these countries will critically depend on the response of inhabited and exploited islands to ocean-climate pressures. Here, using the Maldives as a case study and based on a database including 608 islands (representing 56.8% and 86.0% of the country’s land area and population, respectively), we assess the influence of human disturbances on island natural response capacity over the last decade. We show that over the last decade, island change was rapid and primarily controlled by anthropogenic drivers. The great majority of inhabited and exploited islands now exhibit an altered-to-annihilated capacity to respond to ocean-climate pressures, which has major implications for future research and adaptation strategies. First, future studies should consider not only climate, but also anthropogenic tipping points (in contrast to climate tipping points). Second, adaptation strategies must be implemented without delay, despite climate uncertainties, in order to contain any additional detrimental path-dependency effects. This study provides critical information for better addressing the attribution issue under climate change, and a replicable rapid assessment frame.

Extreme spatial heterogeneity in carbonate accretion potential on a Caribbean fringing reef linked to local human disturbance gradients.

The capacity of coral reefs to maintain their structurally complex frameworks and to retain the potential for vertical accretion is vitally important to the persistence of their ecological functioning and the ecosystem services they sustain. However, datasets to support detailed along‐coast assessments of framework production rates and accretion potential do not presently exist. Here, we estimate, based on gross bioaccretion and bioerosion measures, the carbonate budgets and resultant estimated accretion rates (EAR) of the shallow reef zone of leeward Bonaire – between 5 and 12 m depth – at unique fine spatial resolution along this coast (115 sites). Whilst the fringing reef of Bonaire is often reported to be in a better ecological condition than most sites throughout the wider Caribbean region, our data show that the carbonate budgets of the reefs and derived EAR varied considerably across this ~58 km long fringing reef complex. Some areas, in particular the marine reserves, were indeed still dominated by structurally complex coral communities with high net carbonate production (>10 kg CaCO3 m−2 year−1), high live coral cover and complex structural topography. The majority of the studied sites, however, were defined by relatively low budget states (<2 kg CaCO3 m−2 year−1) or were in a state of net erosion. These data highlight the marked spatial heterogeneity that can occur in budget states, and thus in reef accretion potential, even between quite closely spaced areas of individual reef complexes. This heterogeneity is linked strongly to the degree of localized land‐based impacts along the coast, and resultant differences in the abundance of reef framework building coral species. The major impact of this variability is that those sections of reef defined by low‐accretion rates will have limited capacity to maintain their structural integrity and to keep pace with current projections of climate change induced sea‐level rise (SLR), thus posing a threat to reef functioning and biodiversity, potentially leading to trophic cascades. Since many Caribbean reefs are more severely degraded than those found around Bonaire, it is to be expected that the findings presented here are rather the rule than the exception, but the study also highlights the need for similar high spatial resolution (along‐coast) assessments of budget states and accretion rates to meaningfully explore increasing coastal risk at the country level. The findings also more generally underline the significance of reducing local anthropogenic disturbance and restoring framework building coral assemblages. Appropriately focussed local preservation efforts may aid in averting future large‐scale above reef water depth increases on Caribbean coral reefs and will limit the social and economic implications associated with the loss of reef goods and services.