Spatial distribution of microplastics in a coastal upwelling region: Offshore dispersal from urban sources in the Humboldt Current System.

In coastal waters, higher concentrations of microplastics (MPs) are generally related to densely populated and industrialized areas, but intense upwelling and offshore transport in the Eastern Boundary Upwelling Systems (EBUS) may influence this pattern. The Humboldt Current System (HCS) along the coast of northern-central Chile represents a perfect model to test whether the abundance of MP at the sea surface decreases with distance from land-based sources, e.g., river mouths, harbors, and submarine wastewater outfalls. The sea surface was sampled with a manta trawl to examine the abundance, composition, and distribution of floating MPs, and Generalized Additive Mixed Models (GAMMs) were performed to examine the relationship between MP abundance (particles km-2) and the distance to putative sources. MPs were found in all 57 net tows, with an average of ⁓120,000 MP km-2 and maximum values of ⁓1,500,000 MP km-2. The composition of MPs was dominated by fragments (>50% of the total count) and over 80% of all MPs were ≥1 mm. The combined effect of the various sources, spatially concentrated in urban areas, makes it difficult to distinguish their relative contributions, but the MP composition suggested that rivers are more important sources, followed by submarine wastewater outfalls and then harbors. A significant and steep negative relationship with the "distance to source" explained 15.2% of the variance of "MP abundance", suggesting rapid offshore displacement within the HCS. This is the first study to report this pattern along the edges of the South Pacific Subtropical Gyre (SPSG), revealing that continuous offshore transport of microplastic from land-based sources is occurring over large scales and contributing to the accumulation of microplastics in the center of the SPSG. However, the findings additionally suggested that processes at meso- and submeso-spatial scales (driven by geographic and seasonal variables) are disrupting the general pattern.

Fast accumulation of anthropogenic litter on upgraded breakwaters: A persistent and hidden threat to coastal habitats.

Breakwater construction is common on different coasts, and by means of their structural complexity these built infrastructures can trap anthropogenic litter. We investigated the temporal persistence of anthropogenic litter in breakwaters, and how fast litter accumulates on them. We sampled anthropogenic litter in old (>10 years since construction) breakwaters and in a recently upgraded one (5 months) and on rocky shores located in a coastal conurbation, in central Chile (33°S). We found breakwaters had much higher litter densities than rocky habitats, and this pattern was persistent through time (~5 years). Also, a recently upgraded breakwater had similar composition and densities of litter items as older breakwaters. Therefore, litter accumulation on breakwaters is a very fast process related to their topographic structure and to the willingness of people to dispose of anthropogenic litter in the infrastructure. Redesigning the breakwater structure is required to reduce litter accumulation on the coast and their impacts.

Breakwaters as habitats for synanthropes: Spatial associations of vertebrates and vegetation with anthropogenic litter.

Urban infrastructures can provide 'novel' habitats for marine and terrestrial animals and plants, enhancing their ability to adapt to urban environments. In particular, coastal infrastructures characterized by a complex three-dimensional morphology, such as breakwaters, could provide species refuges and food. We investigated the role of breakwaters in providing habitat for vertebrates and plants, and the influence of anthropogenic litter in regulating the value of these structures as habitat. We sampled vertebrate and plant species and quantified the amount of anthropogenic litter on breakwaters and adjacent rocky habitats at several sites in three different countries (Italy, Spain and Chile). We found breakwaters to accumulate more litter items (e.g. especially plastics) than adjacent rocky habitats by means of their large-scale (i.e., 1 m) structural complexity. Birds, which used the artificial infrastructure as transitory habitat, reached similar abundances in breakwaters compared with adjacent rocky platforms. In contrast, synanthropic mammal species, such as Rattus norvegicus and feral cats, were slightly more frequent on breakwaters and appeared to use them as permanent habitat. Plants were frequent in the upper zone of breakwaters and, even though many macrophyte species can trap litter, their cover correlated negatively with anthropogenic litter density. Therefore, breakwaters provide either transitory or permanent habitats for different species, despite functioning as a sink for anthropogenic litter. Thus, new infrastructure should be designed with lower structural complexity in their supralittoral zone limiting the proliferation of synanthropic species. In addition, restricting public access to sensitive areas and enforcing littering fines could enhance the ecological value of these novel habitats by reducing the benefits to pest species.

Human-derived effects and failure in management drive coastal urban foredune degradation and novel vegetation structure.

Urbanization can drive significant decay in species diversity and abundance; in dune ecosystems the composition changes at a pace with changes in spatial fragmentation. Infrastructure deployment and human activities may provoke synergistically a reduction in dune patch size and/or habitat loss and thus a potential for rapid establishment of exotic species, producing a 'novel' habitat configuration. In this study we examine the effects of coastal urbanization and associated human activities in foredune patch fragmentation and changes in floristic composition and abundance in an urban-rural gradient. Using samples from a recently bulldozed and managed urban foredune area, we assess the legacy of erroneous practices associated with planting of exotic species in urban settings. We found a significant increase in foredune fragmentation, estimated as the occurrence of marks left by vehicles (4WD, 2WD) and people in foredunes close to or within urban settings. A marked change from native to non-native plant species was found from rural to urban environments, with non-native species contributing to increase species richness in urban settings. A positive relationship of non-native species with level of foredunes fragmentation was found. Dominance of non-native species was persistent through time in altered foredune patches. Our findings showed that incorporation of non-native species for aesthetic or engineering purposes in bulldozed foredunes, could limit colonization of native species through rapid establishment and complete dominance of non-native ones. Historical activities associated with coastal infrastructure upgrades seem to configure the present foredune floristic pattern present in urbanized coasts. Management strategies correcting past erroneous actions and promoting foredune rehabilitation could help the conservation of services that these 'novel' habitats provide in coastal urban environments.

Loss of coastal ecosystem spatial connectivity and services by urbanization: Natural-to-urban integration for bay management.

Urbanization has negative consequences for the integrity of ecosystems and services they provide, by reducing their extent and quality in both aquatic and terrestrial environments. Few studies have explored how urban infrastructure expansion affects the spatial connectivity of coastal ecosystems by provoking their fragmentation and loss. Here we explore changes in the spatial connectivity of coastal ecosystems due to urbanization, analyzing ecosystem extent and concatenation with urban infrastructures (shared perimeter) in four bays of the Coquimbo region of northern Chile (from 29°S to 32°S) as model systems. Increase in natural-to-urban concatenation patterns were observed in most urbanized bays; sandy beaches and wetlands were the habitats most connected with urban infrastructures like roads and coastal artificial defenses. Availability of ecosystem services is compromised by progressive loss of natural connectivity and poor governance structure, which seems to confer high vulnerability to urbanized bays with future urban expansion. Complementary actions are proposed to reduce the vulnerability of coastal urban systems, considering 1) investment in nature-based infrastructures for coastal defenses, 2) restoration-rehabilitation of natural (remnant) urban ecosystems and eco-engineering of current artificial infrastructures, focusing on reestablishment of biodiversity patterns and habitat connectivity, and 3) limitation of coastal town and village expansion. Management strategies can improve coastal adaptation to natural hazards, stabilizing changes in the natural-urban concatenation mosaic present in coastal urban systems like bays.

Novel co-occurrence of functionally redundant consumers induced by range expansion alters community structure.

Ongoing climate change is shifting the geographic distributions of some species, potentially imposing rapid changes in local community structure and ecosystem functioning. Besides changes in population-level interspecific interactions, such range shifts may also cause changes in functional structure within the host assemblages, which can result in losses or gains in ecosystem functions. Because consumer-resource dynamics are central to community regulation, functional reorganization driven by introduction of new consumer species can have large consequences on ecosystem functions. Here we experimentally examine the extent to which the recent poleward range expansion of the intertidal grazer limpet Scurria viridula along the coast of Chile has altered the role of the resident congeneric limpet S. zebrina, and whether the net collective impacts, and functional structure, of the entire herbivore guild have been modified by the introduction of this new member. We examined the functional role of Scurria species in controlling ephemeral algal cover, bare rock availability, and species richness and diversity, and compared the effects in the region of range overlap against their respective "native" abutted ranges. Experiments showed depression of per capita effects of the range-expanded species within the region of overlap, suggesting environmental conditions negatively affect individual performance. In contrast, effects of S. zebrina were commonly invariant at its range edge. When comparing single species versus polycultures, effects on bare rock cover were altered by the presence of the other Scurria species, suggesting competition between Scurria species. Importantly, although the magnitude of S. viridula effects at the range overlap was reduced, its addition to the herbivore guild seems to complement and intensify the role of the guild in reducing green algal cover, species richness and increasing bare space provision. Our study thus highlights that range expansion of an herbivore can modify the functional guild structure in the recipient community. It also highlights the complexity of predicting how functional structure may change in the face of natural or human-induced range expansions. There is a need for more field-based examination of regional functional compensation, complementarity, or inhibition before we can construct a conceptual framework to anticipate the consequences of species range expansions.

Mapping microhabitat thermal patterns in artificial breakwaters: Alteration of intertidal biodiversity by higher rock temperature.

Urbanization is altering community structure and functioning in marine ecosystems, but knowledge about the mechanisms driving loss of species diversity is still limited. Here, we examine rock thermal patterns in artificial breakwaters and test whether they have higher and spatially less variable rock temperature than natural adjacent habitats, which corresponds with lower biodiversity patterns. We estimated rock temperatures at mid-high intertidal using infrared thermography during mid-day in summer, in both artificial (Rip-raps) and natural (boulder fields) habitats. We also conducted diurnal thermal surveys (every 4 hr) in four seasons at one study site. Concurrent sampling of air and seawater temperature, wind velocity, and topographic structure of habitats were considered to explore their influence on rock temperature. Rock temperature was in average 3.7°C higher in the artificial breakwater in two of the three study sites, while air temperature was about 1.5-4°C higher at this habitat at summer. Thermal patterns were more homogeneous across the artificial habitat. Lower species abundance and richness in the artificial breakwaters were associated with higher rock temperature. Mechanism underlying enhanced substrate temperature in the artificial structures seems related to their lower small-scale spatial heterogeneity. Our study thus highlighted that higher rock temperature in artificial breakwaters can contribute to loss of biodiversity and that integrated artificial structures may alter coastal urban microclimates, a matter that should be considered in the spatial planning of urban coastal ecosystems.

Asymmetric competitive effects during species range expansion: An experimental assessment of interaction strength between "equivalent" grazer species in their range overlap.

Biotic interactions are central to the development of theory and concepts in community ecology; experimental evidence has shown their strong effects on patterns of population and community organization and dynamics over local spatial scales. The role of competition in determining range limits and preventing invasions at biogeographic scales is more controversial, partly because of the complexity of processes involved in species colonization of novel habitats and the difficulties in performing appropriate manipulations and controls. We examined experimentally whether competition is likely to affect poleward range expansion hindering or facilitating the establishment of the limpet Scurria viridula along the south-eastern Pacific rocky shore (30°S, Chile) in the region occupied by the congeneric S. zebrina. We also assessed whether competition with the "invader" or range-expanding species could reduce individual performance of the "native" S. zebrina and depress local populations Geographic field surveys were conducted to characterize the abundance and identity of limpets along the south-eastern Pacific coast from 18°S to 41°S, and the micro-scale (few cm) spatial distribution across the range overlap of the two species. Field-based competition experiments were conducted at the southern leading edge of the range of S. viridula (33°S) and at the northern limit of S. zebrina (30°S). Field surveys showed poleward range expansion of S. viridula of ca. 210 km since year 2000, with an expansion rate of 13.1 km/year. No range shift was detected for S. zebrina. The resident S. zebrina had significant negative effects on the growth rate of the invading juvenile S. viridula, while no effect of the latter was found on S. zebrina. Spatial segregation between species was found at the scale of cms. Our results provide novel evidence of an asymmetric competitive effect of a resident species on an invader, which may hamper further range expansion. No negative effect of the invader on the resident species was detected. This study highlights the complexities of evaluating the role of species interactions in setting range limits of species, but showed how interspecific competition might slow the advance of an invader by reducing individual performance and overall population size at the advancing front.

Heterogeneity of ecological patterns, processes, and funding of marine manipulative field experiments conducted in Southeastern Pacific coastal ecosystems.

Ecological manipulative experiments conducted in marine coastal ecosystems have substantially improved ecological theory during the last decades and have provided useful knowledge for the management and conservation of coastal ecosystems. Although different studies report global trends in ecological patterns worldwide, Southeastern Pacific coastal ecosystems have been poorly considered. Given that the SE Pacific coast encompasses diverse coastal ecosystems, consideration of studies conducted along this range can shed light on the heterogeneity of processes regulating coastal communities. We reviewed the biotic interactions and habitat type considered, as well as the complexity in terms of spatial and temporal extent of manipulative field experimental studies conducted along the SE Pacific coast from 0°S to 56°S (Ecuador to Chile). We test the effect of funding reported by different studies as a main factor limiting experimental complexity. From field ecological studies published from 1970 to 2016, we found that 81 studies were truly manipulative, in which one or multiple factors were "manipulated." Around 77% of these studies were located between 21°S and 40°S, and conducted in intertidal rocky habitats. An increase in experimental studies was observed between 2010 and 2015, especially focused on herbivore-alga interactions, although we found that both the temporal extent and spatial extent of these studies have shown a decrease in recent decades. Funding grant amount reported had a positive effect on elapsed time of field experiments, but no effect was observed on spatial extent or in the biotic interactions considered. Elapsed time of experiments was different among the main biotic interactions considered, that is, herbivory, predation, and competition. We suggest that to further progress in applied ecological knowledge, it will be necessary to consider pollution and urbanization processes explicitly using a field experimental framework. This information could improve our understanding of how ecosystems present along the SE Pacific coast respond to climate change and increased levels of human interventions.

Context-dependent functional dispersion across similar ranges of trait space covered by intertidal rocky shore communities.

Functional diversity is intimately linked with community assembly processes, but its large-scale patterns of variation are often not well understood. Here, we investigated the spatiotemporal changes in multiple trait dimensions ("trait space") along vertical intertidal environmental stress gradients and across a landscape scale. We predicted that the range of the trait space covered by local assemblages (i.e., functional richness) and the dispersion in trait abundances (i.e., functional dispersion) should increase from high- to low-intertidal elevations, due to the decreasing influence of environmental filtering. The abundance of macrobenthic algae and invertebrates was estimated at four rocky shores spanning ca. 200 km of the coast over a 36-month period. Functional richness and dispersion were contrasted against matrix-swap models to remove any confounding effect of species richness on functional diversity. Random-slope models showed that functional richness and dispersion significantly increased from high- to low-intertidal heights, demonstrating that under harsh environmental conditions, the assemblages comprised similar abundances of functionally similar species (i.e., trait convergence), while that under milder conditions, the assemblages encompassed differing abundances of functionally dissimilar species (i.e., trait divergence). According to the Akaike information criteria, the relationship between local environmental stress and functional richness was persistent across sites and sampling times, while functional dispersion varied significantly. Environmental filtering therefore has persistent effects on the range of trait space covered by these assemblages, but context-dependent effects on the abundances of trait combinations within such range. Our results further suggest that natural and/or anthropogenic factors might have significant effects on the relative abundance of functional traits, despite that no trait addition or extinction is detected.

Artificial breakwaters as garbage bins: Structural complexity enhances anthropogenic litter accumulation in marine intertidal habitats.

Coastal urban infrastructures are proliferating across the world, but knowledge about their emergent impacts is still limited. Here, we provide evidence that urban artificial reefs have a high potential to accumulate the diverse forms of litter originating from anthropogenic activities around cities. We test the hypothesis that the structural complexity of urban breakwaters, when compared with adjacent natural rocky intertidal habitats, is a driver of anthropogenic litter accumulation. We determined litter abundances at seven sites (cities) and estimated the structural complexity in both urban breakwaters and adjacent natural habitats from northern to central Chile, spanning a latitudinal gradient of ∼15° (18°S to 33°S). Anthropogenic litter density was significantly higher in coastal breakwaters when compared to natural habitats (∼15.1 items m(-2) on artificial reefs versus 7.4 items m(-2) in natural habitats) at all study sites, a pattern that was temporally persistent. Different litter categories were more abundant on the artificial reefs than in natural habitats, with local human population density and breakwater extension contributing to increase the probabilities of litter occurrence by ∼10%. In addition, structural complexity was about two-fold higher on artificial reefs, with anthropogenic litter density being highest at intermediate levels of structural complexity. Therefore, the spatial structure characteristic of artificial reefs seems to enhance anthropogenic litter accumulation, also leading to higher residence time and degradation potential. Our study highlights the interaction between coastal urban habitat modification by establishment of artificial reefs, and pollution. This emergent phenomenon is an important issue to be considered in future management plans and the engineering of coastal ecosystems.

Facilitative Effect of a Generalist Herbivore on the Recovery of a Perennial Alga: Consequences for Persistence at the Edge of Their Geographic Range.

Understanding the impacts of consumers on the abundance, growth rate, recovery and persistence of their resources across their distributional range can shed light on the role of trophic interactions in determining species range shifts. Here, we examined if consumptive effects of the intertidal grazer Scurria viridula positively influences the abundance and recovery from disturbances of the alga Mazzaella laminarioides at the edge of its geographic distributions in northern-central Chilean rocky shores. Through field experiments conducted at a site in the region where M. laminarioides overlaps with the polar range edge of S. viridula, we estimated the effects of grazing on different life stages of M. laminarioides. We also used long-term abundance surveys conducted across ~700 km of the shore to evaluate co-occurrence patterns of the study species across their range overlap. We found that S. viridula had positive net effects on M. laminarioides by increasing its cover and re-growth from perennial basal crusts. Probability of occurrence of M. laminarioides increased significantly with increasing density of S. viridula across the range overlap. The negative effect of S. viridula on the percentage cover of opportunistic green algae-shown to compete for space with corticated algae-suggests that competitive release may be part of the mechanism driving the positive effect of the limpet on the abundance and recovery from disturbance of M. laminarioides. We suggest that grazer populations contribute to enhance the abundance of M. laminarioides, facilitating its recolonization and persistence at its distributional range edge. Our study highlights that indirect facilitation can determine the recovery and persistence of a resource at the limit of its distribution, and may well contribute to the ecological mechanisms governing species distributions and range shifts.

Herbivore-Alga Interaction Strength Influences Spatial Heterogeneity in a Kelp-Dominated Intertidal Community.

There is a general consensus that marine herbivores can affect algal species composition and abundance, but little empirical work exists on the role of herbivores as modifiers of the spatial structure of resource assemblages. Here, we test the consumption/bulldozing effects of the molluscan grazer Enoplochiton niger and its influence on the spatial structure of a low intertidal community dominated by the bull kelp Durvillaea antarctica and the kelp Lessonia spicata. Through field experiments conducted at a rocky intertidal shore in north-central Chile (~30°-32°S), the edge of the grazer and algae geographic distributions, we estimated the strength and variability of consumptive effects of the grazer on different functional group of algae. We also used data from abundance field surveys to evaluate spatial co-occurrence patterns of the study species. Exclusion-enclosure experiments showed that E. niger maintained primary space available by preventing algal colonization, even of large brown algae species. The grazing activity of E. niger also reduced spatial heterogeneity of the ephemeral algal species, increasing bare space availability and variability through time in similar ways to those observed for the collective effect with other grazers. Overall, our result suggests that E. niger can be considered an important modifier of the spatial structure of the large brown algae-dominated community. Effects of E. niger on resource variability seem to be directly related to its foraging patterns, large body size, and population densities, which are all relevant factors for management and conservation of the large brown algae community. Our study thus highlights the importance of considering functional roles and identity of generalist consumers on spatial structure of the entire landscape.

Spatial variability in community composition on a granite breakwater versus natural rocky shores: lack of microhabitats suppresses intertidal biodiversity.

Strong differences have been observed between the assemblages on artificial reefs and on natural hard-bottom habitats worldwide, but little is known about the mechanisms that cause contrasting biodiversity patterns. We examined the influence of spatial attributes in relation to both biogenic and topographic microhabitats, in the distribution and composition of intertidal species on both artificial and natural reefs. We found higher small-scale spatial heterogeneity on the natural reef compared with the study breakwater. Species richness and diversity were associated with a higher availability of crevices, rock pools and mussels in natural habitats. Spatial distribution of certain grazers corresponded well with the spatial structure of microhabitats. In contrast, the lack of microhabitats on the breakwater resulted in the absence of several grazers reflected in lower species richness. Biogenic and topographic microhabitats can have interactive effects providing niche opportunities for multiple species, explaining differences in species diversity between artificial versus natural reefs.

Interspecific competition for shelters in territorial and gregarious intertidal grazers: consequences for individual behaviour.

Experiments have shown that interspecific interactions within consumer guilds can alter patterns of distribution, abundance and size of species. Plastic behavioural responses can be modulated by agonistic interactions. In many cases, consumers compete for space and shelters, and these interactions change the manner in which they exploit food. This study investigates the consequences of competition in the spatial and temporal organization of behaviour of intertidal grazers, which share algal resources and the use of rock crevices while resting, but exhibit different body sizes, spatial behaviour and foraging modes. We evaluate interaction strength between small gregarious Siphonaria lessoni and the larger territorial keyhole limpet Fissurella crassa and between S. lessoni and the medium-size gregarious chiton Chiton granosus. Using field manipulations and artificial arenas in the laboratory, we tested whether the use of crevices, micro-spatial distribution and activity are modified by the density of conspecifics and the presence of heterospecifics. Our results show that small-scale spatial segregation observed in the field between S. lessoni and C. granosus result from species-specific differences in habitat use. In turn, we found evidence that spatial segregation between F. crassa and S. lessoni results from highly asymmetric interference competition in the use of shelters. The presence of F. crassa reduced the use of crevices and growth rates of S. lessoni. Effects on growth rates are assumed to result from exposure to harsh environmental conditions rather than food limitation. Thus, neither gregarious behaviour nor differences in activity were sufficient to prevent competition with the larger grazer. Our study illustrates the importance of competition for shelters, which results in behavioural changes of the smaller-sized species, and how these plastic responses can translate into differences in growth rates. Use of shelters can thus be modulated by environmental conditions in a species-specific as well as an interactive manner within consumers' guilds.

Functional identity and functional structure change through succession in a rocky intertidal marine herbivore assemblage.

Despite the great interest in characterizing the functional structure and resilience of functional groups in natural communities, few studies have examined in which way the roles and relationships of coexisting species change during community succession, a fundamental and natural process that follows the release of new resources in terrestrial and aquatic ecosystems. Variation in algal traits that characterize different phases and stages of community succession on rocky shores are likely to influence the magnitude, direction of effects, and the level of redundancy and complementarity in the diverse assemblage of herbivores. Two separate field experiments were conducted to quantify per capita and population effects and the functional relationship (i.e., redundancy or complementarity) of four herbivore species found in central Chile during early and late algal succession. The first experiment examined grazer effects on the colonization and establishment of early-succession algal species. The second experiment examined effects on the late-successional, dominant corticated alga Mazzaella laminarioides. Complementary laboratory experiments with all species and under natural environmental conditions allowed us to further characterize the collective effects of these species. We found that, during early community succession, all herbivore species had similar effects on the ephemeral algae, ulvoids, but only during the phase of colonization. Once these algae were established, only a subset of the species was able to control their abundance. During late succession, only the keyhole limpet Fissurella crassa could control corticated Mazzaella. The functional relationships among these species changed dramatically from redundant effects on ephemeral algae during early colonization, to a more complementary role on established early-successional algae, to a dominant (i.e., keystone) effect on late succession. This study highlights that functional relationship within consumer assemblages can vary at different phases and times of community succession. Differentiation in herbivore roles emphasizes the need to evaluate consumer's impacts through different times of community succession, and through experimental manipulations to make even broad predictions about the resilience or vulnerability of diverse intertidal assemblages to human disturbances.