Eos, Transactions American Geophysical Union, 2001
Since 1982, coral reefs worldwide have been subjected to an increased frequency of the phenomenon... more Since 1982, coral reefs worldwide have been subjected to an increased frequency of the phenomenon known as coral bleaching. Bleaching involves the dramatic loss of pigmented, single‐celled endosymbiotic algae that live within the gastrodermal cells of a coral host that depends on this relationship for survival. Prior to the 1980s, and as early as the 1920s when coral reef research intensified, localized bleaching events were reported and attributed to factors such as extremely low tides, hurricane damage, torrential rainstorms, freshwater runoff near reefs, or toxic algal blooms [Glynn, 1993]. However, these early occurrences have recently been overshadowed by geographically larger and more frequent bleaching events whose impact has expanded to regional and global proportions.
This study analyzes data acquired in French Polynesia in the Pacific and The Bahamas (Atlantic), ... more This study analyzes data acquired in French Polynesia in the Pacific and The Bahamas (Atlantic), both oceans affected by recent, well documented and sequential disturbances. For the purposes of this study, a disturbance is defined as a perturbation of environmental, physical or biological conditions that causes a distinct change in the ecosystem. After several decades of coral bleaching events, biological change, and anthropogenic impacts, rapid assessments of the coral community were accomplished by collecting photo-transects across the reefs to extract size structure of the corals, percent live tissue cover and perform a faunal evaluation. Cluster analyses and spatial autocorrelation tests were done to examine the community structure and dynamics at both locations. All multivariate analyses pointed to a disturbed ecosystem and the lack of spatial correlation indicated the impact of a local disturbance over that of a regional event. In assessing the spatial coral community structur...
The spawning sites, embryonic development, and initial larval stages were described for the Chile... more The spawning sites, embryonic development, and initial larval stages were described for the Chilean kelpfish, Myxodes viridis. Six different egg clutches were found attached by an elastic filament to the fronds of the subtidal kelp, Lessonia trabeculata, at shallow depths (0-7 m). All egg clutches were cared by one large (>15 cm TL) male, and egg color varied depending on the developmental stage. Embryonic development until hatching was categorized into 7 stages, which were completed within about 18 days in the laboratory. Recently hatched larvae presented fully pigmented eyes, a well-developed mouth with major shape changes in the head during the first week suggesting their ability to feed on plankton early in their larval development.
Extreme fluctuations in abiotic conditions can induce a biological stress response (e.g. bleachin... more Extreme fluctuations in abiotic conditions can induce a biological stress response (e.g. bleaching) detrimental to an organism's health. In some instances, organisms can recover if conditions are alleviated, such as through cooccurrence with other species that confer protection. Biodiverse, multitrophic communities are increasingly recognised as important promoters of species persistence and resilience under environmental change. On intertidal shores, the role of grazers as top-down determinants of algal community structure is well recognised. Similarly, the harvesting of grazers for human consumption is increasingly prevalent with potential to greatly alter the community dynamics. Here, we assess how differences in harvesting pressure of grazers under three management regimes (no-take; managed access; open-access) alters the trophic interactions between grazers, and algal communities. Grazer density and body size frequencies were different among regimes leading to changes in the photosynthetic performance and recovery of crustose coralline algae (CCA) post-bleaching, as well as their presence altering the strength of interactions between species. The exclusion of grazers from patches using cages led to different emergent communities and reduced negative correlations between taxa. The absence of larger grazers (>9cm) at the managed access site led to macroalgal overgrowth of bleached CCA negatively affecting its recovery, whereas no-take or open-access led to a moderated algal growth and a shift from competitive to facilitative interactions between algal species. Given that CCA play an important role in the population growth and development of other species, the choice of management measure should be carefully considered before implementation, depending on objectives.
ABSTRACTTop-down and bottom-up forces determine ecosystem function and dynamics. Fisheries as a t... more ABSTRACTTop-down and bottom-up forces determine ecosystem function and dynamics. Fisheries as a top-down force can shorten and destabilize food-webs, while climate-change driven effects can alter the bottom-up forces of primary productivity. We assessed the response of a highly-resolved intertidal food-web to these two global-change drivers, using network analysis and bioenergetic modelling. We quantified the relative importance of artisanal fisheries as another predator species, and evaluated the independent and combined effects of fisheries and plankton-productivity changes on food-web dynamics. The food-web was robust to the loss of all harvested species but sensible to plankton-productivity decline. Interestingly, fisheries dampened the negative impacts of decreasing plankton productivity on non-harvested species, while plankton-productivity decline increased the sensitivity of harvested species to fishing. Our results show that strategies for new scenarios caused by climate cha...
Understanding the drivers of geographical variation in species distributions, and the resulting c... more Understanding the drivers of geographical variation in species distributions, and the resulting community structure, constitutes one of the grandest challenges in ecology. Geographical patterns of species richness and composition have been relatively well studied. Less is known about how the entire set of trophic and non‐trophic ecological interactions, and the complex networks that they create by gluing species together in complex communities, change across geographical extents. Here, we compiled data of species composition and three types of ecological interactions occurring between species in rocky intertidal communities across a large spatial extent (~970 km of shoreline) of central Chile, and analyzed the geographical variability in these multiplex networks (i.e., comprising several interaction types) of ecological interactions. We calculated nine network summary statistics common across interaction types, and additional network attributes specific to each of the different type...
Sexual reproduction is fundamental to the maintenance and recovery of coraldominated communities ... more Sexual reproduction is fundamental to the maintenance and recovery of coraldominated communities in high-latitude and isolated locations, where replenishment often depends on local reproductive activity rather than recruitment from distant reefs. Rapa Nui (Easter Island) is one of the most remote islands in the Pacific, lying at the southern, subtropical edge of the range of reef-building scleractinians. Here, we describe the sexual reproduction and timing of the 2 dominant corals, Pocillopora verrucosa and Porites lobata. Reproductive activity was inferred from the identification and staging of gametes via histological analyses of monthly samples collected from December 2012 to May 2014 at 12 m depth at Motu Tautara (27°6.6' S, 109°25.5' W) with in situ temperature records. In P. verrucosa, the observed hermaphroditic activity spanned from December to January, resulting in mature oocytes of 117 µm mean diameter. In P. lobata, observed gonochoric activity spanned from December to March, resulting in mature oocytes of 180 µm mean diameter. The observed initiation of gametogenic cycles coincided with the onset of spring warming in both species. Inferred spawning of P. verrucosa followed a relatively calm period of daily variance reduction in local in situ temperature and wind speed prior to the peak in thermal conditions, whereas inferred spawning of P. lobata coincided with peak temperatures in one year but not the other. We suggest temporal restrictions of disruptive coastal activities such as dredging during coral spawning periods and mitigation of land-based sources of pollution and watershed discharge that may reduce water quality.
P rey rarely, if ever, give up their lives willingly to their predators. Predators overcome their... more P rey rarely, if ever, give up their lives willingly to their predators. Predators overcome their prey's resistance by being, on average, larger than their prey, yielding a systematic pattern in communities where the non-cannibalistic average ratio of predator-to-prey body mass (hereafter, body-mass ratio) is higher than unity 1,2. Notable exceptions to this include when animals cooperate to overcome larger prey (for example, pack hunters) and where consumers are parasites or parasitoids. Variation in body-mass ratios within food webs typically spans several orders of magnitude and includes some predators that are smaller than their prey 3 , but is dominated by situations of the larger feeding on the smaller. The varying body-mass ratios limit which trophic interactions are realized in a community 4-6 , and the strength of these interactions 7-9. Predators typically exert the strongest feeding pressure on prey that are 1-2 orders of magnitude smaller 1 , while weaker interaction strengths are realized with prey that are smaller or larger than this size 10,11. Specifically, interactions of predators with small prey are characterized by high body-mass ratios that yield weak interactions with slow dynamics, which play a central role in maintaining foodweb stability 12-16 and ecosystem functioning 10,17,18. Moreover, they
Running head: Species co-occurrence networks Title: Species co-occurrence networks: can they reve... more Running head: Species co-occurrence networks Title: Species co-occurrence networks: can they reveal trophic and non-trophic interactions in ecological communities?
Understanding the processes that drive kelp forest communities is critical for management and con... more Understanding the processes that drive kelp forest communities is critical for management and conservation of these productive ecosystems. As a way to advance in this direction, we explored the effects of fishing pressure and upwelling intensity over kelp forest communities along the central coast of Chile. We sampled kelp communities in different upwelling conditions associated with contrasting management regimes, namely Territorial User Rights for Fisheries (TURFs) and open-access (OA) areas. In TURF areas, we found a 2.6-fold increase in reef fish biomass, higher diversity of all fish trophic groups, mainly dominated by benthic carnivore feeders, and a 1.8-fold reduction in the number of kelp grazers. On the other hand, upwelling regimes evidence a 1.6-fold increase in abundance and recruitment of the dominant kelp (Lessonia trabeculata), and also an increase in biomass of planktivorous reef fishes. We found that grazers were capable of reducing kelp condition (measured as canopy foliage index) in OA areas outside the influence of upwelling. Enclosure experiments in the field revealed the effect of grazers on kelps, reducing kelp growth (i.e., blade elongation) and increasing blade tissue loss. Results provide evidence that TURF areas could be important ancillary conservation instruments in kelp forest ecosystems, if key processes of the subtidal community assemblages (e.g., interactions between grazers and reef fish) are maintained. We conclude that human impact interplays with the influence of upwelling in structuring kelp communities.
Species are linked to each other by a myriad of positive and negative interactions. This complex ... more Species are linked to each other by a myriad of positive and negative interactions. This complex spectrum of interactions constitutes a network of links that mediates ecological communities' response to perturbations, such as exploitation and climate change. In the last decades, there have been great advances in the study of intricate ecological networks. We have, nonetheless, lacked both the data and the tools to more rigorously understand the patterning of multiple interaction types between species (i.e., "multiplex networks"), as well as their consequences for community dynamics. Using network statistical modeling applied to a comprehensive ecological network, which includes trophic and diverse non-trophic links, we provide a first glimpse at what the full "entangled bank" of species looks like. The community exhibits clear multidimensional structure, which is taxonomically coherent and broadly predictable from species traits. Moreover, dynamic simulations suggest that this non-random patterning of how diverse non-trophic interactions map onto the food web could allow for higher species persistence and higher total biomass than expected by chance and tends to promote a higher robustness to extinctions.
Advances in our knowledge of eastern tropical Pacific (ETP) coral reef biogeography and ecology d... more Advances in our knowledge of eastern tropical Pacific (ETP) coral reef biogeography and ecology during the past two decades are briefly reviewed. Fifteen ETP subregions are recognized, including mainland and island localities from the Gulf of California (Mexico) to Rapa Nui (Easter Island, Chile). Updated species lists reveal a mean increase of 4.2 new species records per locality or an overall increase of 19.2 % in species richness during the past decade. The largest increases occurred in tropical mainland Mexico, and in equatorial Costa Rica and Colombia, due mainly to continuing surveys of these under-studied areas. Newly discovered coral communities are also now known from the southern Nicaraguan coastline. To date 47 zooxanthellate scleractinian species have been recorded in the ETP, of which 33 also occur in the central/south Pacific, and 8 are presumed to be ETP endemics. Usually no more than 20-25 zooxanthellate coral species are present at any given locality, with the principal reef-building genera being Pocillopora, Porites, Pavona, and Gardineroseris. This compares with 62-163 species at four of the nearest central/south Pacific localities. Hydrocorals in the genus Millepora also occur in the ETP and are reviewed in the context of their global distributions. Coral community associates engaged in corallivory, bioerosion, and competition for space are noted for several localities. Reef framework construction in the ETP typically occurs at shallow depths (2-8 m) in sheltered habitats or at greater depths (10-30 m) in more exposed areas such as oceanic island settings with high water column light penetration. Generally, eastern Pacific reefs do not reach sea level with the development of drying reef flats, and instead experience brief periods of exposure during extreme low tides or drops in sea level during La Niña events. High rates of mortality during El Niño disturbances have occurred in many ETP equatorial areas, especially in Panama and the Galápagos Islands during the 1980s and 1990s. Remarkably, however, no loss of resident, zooxanthellate scleractinian species has occurred at these sites, and many ETP coral reefs have demonstrated significant recovery from these disturbances during the past two decades.
How multiple types of non‐trophic interactions map onto trophic networks in real communities rema... more How multiple types of non‐trophic interactions map onto trophic networks in real communities remains largely unknown. We present the first effort, to our knowledge, describing a comprehensive ecological network that includes all known trophic and diverse non‐trophic links among >100 coexisting species for the marine rocky intertidal community of the central Chilean coast. Our results suggest that non‐trophic interactions exhibit highly nonrandom structures both alone and with respect to food web structure. The occurrence of different types of interactions, relative to all possible links, was well predicted by trophic structure and simple traits of the source and target species. In this community, competition for space and positive interactions related to habitat/refuge provisioning by sessile and/or basal species were by far the most abundant non‐trophic interactions. If these patterns are corroborated in other ecosystems, they may suggest potentially important dynamic constraint...
Important, often abrupt, and irreversible shifts associated with the degradation of ecosystem fun... more Important, often abrupt, and irreversible shifts associated with the degradation of ecosystem functioning and services are increasingly commonplace. Thus, a trait-based view of communities may be more insightful than that based solely on species composition, especially when inferring ecological responses to environmental change. This underscores the importance and urgency of establishing benchmarks against which future community changes and functional structure can be evaluated. As a first step toward setting these baselines and their current spatial variability, we here describe geographic and among-habitat patterns in the functional structure of shallow hard bottom communities, including fish assemblages, across the northeast and west coasts of Rapa Nui. We also document temporal patterns of change in dominant benthic functional groups that have taken place over the past 15 years at selected sites on this isolated Pacific island. Generally weak vertical zonation patterns were observed, with most striking differences due to the paucity of branching pocilloporid corals in shallow waters(<7 m), where massive corals of Porites predominate. We identified three main 'groups' of sites in terms of the relative abundance of major functional groups and these did not follow geographic arrangement or strict coastline orientation. The similar spatial change in benthic and fish functional community structure documented here suggests there may be strong coupling with coastal oceanographic conditions that varies on scales of 1s-10s of km. Temporal patterns document relatively rapid recovery of total coral cover, largely via compensatory change in relative coral composition with an increase in Porites upon abrupt decline of Pocillopora, following extensive coral mortality caused by thermal stress (coral bleaching) in 2000. Moreover, coral abundance in shallow habitats increased beyond pre-disturbance levels (i.e., 1999-2000). In contrast to shallow habitats, corals again suffered extensive mortality and reduced cover by 2005 at mid-(10-15 m) and deep (>15 m) habitats, with contrasting recovery. These results suggest depth-dependent disturbance regimes that differ in types and frequency of events, as well as capacity to recover. Overall, our results highlight the apparent resilience of the current system and provide a first-cut benchmark as to where management subsystems might be prescribed so as to spatially match ecosystem characteristics.
Over the past decade, evidence of abrupt latitudinal changes in the dynamics, structure and genet... more Over the past decade, evidence of abrupt latitudinal changes in the dynamics, structure and genetic variability of intertidal and subtidal benthic communities along central-northern Chile has been found consistently at 30-32uS. Changes in the advective and thermal environment in nearshore waters have been inferred from ecological patterns, since analyses of in situ physical data have thus far been missing. Here we analyze a unique set of shoreline temperature data, gathered over 4-10 years at 15 sites between 28-35uS, and combine it with satellite-derived winds and sea surface temperatures to investigate the latitudinal transition in nearshore oceanographic conditions suggested by recent ecological studies. Our results show a marked transition in thermal conditions at 30-31uS, superimposed on a broad latitudinal trend, and smallscale structures associated with cape-and-bay topography. The seasonal cycle dominated temperature variability throughout the region, but its relative importance decreased abruptly south of 30-31uS, as variability at synoptic and intra-seasonal scales became more important. The response of shoreline temperatures to meridional wind stress also changed abruptly at the transition, leading to a sharp drop in the occurrence of low-temperature waters at northern sites, and a concurrent decrease in corticated algal biomass. Together, these results suggest a limitation of nitrate availability in nearshore waters north of the transition. The localized alongshore change results from the interaction of latitudinal trends (e.g., wind stress, surface warming, inertial period) with a major headland-bay system (Punta Lengua de Vaca at 30.25uS), which juxtaposes a southern stretch of coast characterized by upwelling with a northern stretch of coast characterized by warm surface waters and stratification. This transition likely generates a number of latitude-dependent controls on ecological processes in the nearshore that can explain species-specific effects, and add strength to the suggestion of an oceanography-driven, major spatial transition in coastal communities at 30-31uS.
We evaluated interannual variability and the effect of the 1997–1998 El Niño event on recruitment... more We evaluated interannual variability and the effect of the 1997–1998 El Niño event on recruitment of intertidal mussels and barnacles along the coast of central Chile in the southeast Pacific. Monthly monitoring of recruitment at 11 sites spread over 900 km (29–348S) during the 1997–1998 El Niño and over the same months in 1998–1999 and 1999–2000 allowed us to assess geographic patterns in interannual recruitment variation. The geographically most consistent interannual trend was observed for the mussel Perumytilus purpuratus, which showed overall lower recruitment rates during the 1997–1998 El Niño year. However, the magnitude of the effect at any given site was small. Interannual variation in recruitment rates of the other two intertidal mussel species, as well as two chthamaloid barnacles, were not consistent across the region, and overall, few sites exhibited significant differences among years. Differences between two and three orders of magnitude in mean annual recruitment of ...
Eos, Transactions American Geophysical Union, 2001
Since 1982, coral reefs worldwide have been subjected to an increased frequency of the phenomenon... more Since 1982, coral reefs worldwide have been subjected to an increased frequency of the phenomenon known as coral bleaching. Bleaching involves the dramatic loss of pigmented, single‐celled endosymbiotic algae that live within the gastrodermal cells of a coral host that depends on this relationship for survival. Prior to the 1980s, and as early as the 1920s when coral reef research intensified, localized bleaching events were reported and attributed to factors such as extremely low tides, hurricane damage, torrential rainstorms, freshwater runoff near reefs, or toxic algal blooms [Glynn, 1993]. However, these early occurrences have recently been overshadowed by geographically larger and more frequent bleaching events whose impact has expanded to regional and global proportions.
This study analyzes data acquired in French Polynesia in the Pacific and The Bahamas (Atlantic), ... more This study analyzes data acquired in French Polynesia in the Pacific and The Bahamas (Atlantic), both oceans affected by recent, well documented and sequential disturbances. For the purposes of this study, a disturbance is defined as a perturbation of environmental, physical or biological conditions that causes a distinct change in the ecosystem. After several decades of coral bleaching events, biological change, and anthropogenic impacts, rapid assessments of the coral community were accomplished by collecting photo-transects across the reefs to extract size structure of the corals, percent live tissue cover and perform a faunal evaluation. Cluster analyses and spatial autocorrelation tests were done to examine the community structure and dynamics at both locations. All multivariate analyses pointed to a disturbed ecosystem and the lack of spatial correlation indicated the impact of a local disturbance over that of a regional event. In assessing the spatial coral community structur...
The spawning sites, embryonic development, and initial larval stages were described for the Chile... more The spawning sites, embryonic development, and initial larval stages were described for the Chilean kelpfish, Myxodes viridis. Six different egg clutches were found attached by an elastic filament to the fronds of the subtidal kelp, Lessonia trabeculata, at shallow depths (0-7 m). All egg clutches were cared by one large (>15 cm TL) male, and egg color varied depending on the developmental stage. Embryonic development until hatching was categorized into 7 stages, which were completed within about 18 days in the laboratory. Recently hatched larvae presented fully pigmented eyes, a well-developed mouth with major shape changes in the head during the first week suggesting their ability to feed on plankton early in their larval development.
Extreme fluctuations in abiotic conditions can induce a biological stress response (e.g. bleachin... more Extreme fluctuations in abiotic conditions can induce a biological stress response (e.g. bleaching) detrimental to an organism's health. In some instances, organisms can recover if conditions are alleviated, such as through cooccurrence with other species that confer protection. Biodiverse, multitrophic communities are increasingly recognised as important promoters of species persistence and resilience under environmental change. On intertidal shores, the role of grazers as top-down determinants of algal community structure is well recognised. Similarly, the harvesting of grazers for human consumption is increasingly prevalent with potential to greatly alter the community dynamics. Here, we assess how differences in harvesting pressure of grazers under three management regimes (no-take; managed access; open-access) alters the trophic interactions between grazers, and algal communities. Grazer density and body size frequencies were different among regimes leading to changes in the photosynthetic performance and recovery of crustose coralline algae (CCA) post-bleaching, as well as their presence altering the strength of interactions between species. The exclusion of grazers from patches using cages led to different emergent communities and reduced negative correlations between taxa. The absence of larger grazers (>9cm) at the managed access site led to macroalgal overgrowth of bleached CCA negatively affecting its recovery, whereas no-take or open-access led to a moderated algal growth and a shift from competitive to facilitative interactions between algal species. Given that CCA play an important role in the population growth and development of other species, the choice of management measure should be carefully considered before implementation, depending on objectives.
ABSTRACTTop-down and bottom-up forces determine ecosystem function and dynamics. Fisheries as a t... more ABSTRACTTop-down and bottom-up forces determine ecosystem function and dynamics. Fisheries as a top-down force can shorten and destabilize food-webs, while climate-change driven effects can alter the bottom-up forces of primary productivity. We assessed the response of a highly-resolved intertidal food-web to these two global-change drivers, using network analysis and bioenergetic modelling. We quantified the relative importance of artisanal fisheries as another predator species, and evaluated the independent and combined effects of fisheries and plankton-productivity changes on food-web dynamics. The food-web was robust to the loss of all harvested species but sensible to plankton-productivity decline. Interestingly, fisheries dampened the negative impacts of decreasing plankton productivity on non-harvested species, while plankton-productivity decline increased the sensitivity of harvested species to fishing. Our results show that strategies for new scenarios caused by climate cha...
Understanding the drivers of geographical variation in species distributions, and the resulting c... more Understanding the drivers of geographical variation in species distributions, and the resulting community structure, constitutes one of the grandest challenges in ecology. Geographical patterns of species richness and composition have been relatively well studied. Less is known about how the entire set of trophic and non‐trophic ecological interactions, and the complex networks that they create by gluing species together in complex communities, change across geographical extents. Here, we compiled data of species composition and three types of ecological interactions occurring between species in rocky intertidal communities across a large spatial extent (~970 km of shoreline) of central Chile, and analyzed the geographical variability in these multiplex networks (i.e., comprising several interaction types) of ecological interactions. We calculated nine network summary statistics common across interaction types, and additional network attributes specific to each of the different type...
Sexual reproduction is fundamental to the maintenance and recovery of coraldominated communities ... more Sexual reproduction is fundamental to the maintenance and recovery of coraldominated communities in high-latitude and isolated locations, where replenishment often depends on local reproductive activity rather than recruitment from distant reefs. Rapa Nui (Easter Island) is one of the most remote islands in the Pacific, lying at the southern, subtropical edge of the range of reef-building scleractinians. Here, we describe the sexual reproduction and timing of the 2 dominant corals, Pocillopora verrucosa and Porites lobata. Reproductive activity was inferred from the identification and staging of gametes via histological analyses of monthly samples collected from December 2012 to May 2014 at 12 m depth at Motu Tautara (27°6.6' S, 109°25.5' W) with in situ temperature records. In P. verrucosa, the observed hermaphroditic activity spanned from December to January, resulting in mature oocytes of 117 µm mean diameter. In P. lobata, observed gonochoric activity spanned from December to March, resulting in mature oocytes of 180 µm mean diameter. The observed initiation of gametogenic cycles coincided with the onset of spring warming in both species. Inferred spawning of P. verrucosa followed a relatively calm period of daily variance reduction in local in situ temperature and wind speed prior to the peak in thermal conditions, whereas inferred spawning of P. lobata coincided with peak temperatures in one year but not the other. We suggest temporal restrictions of disruptive coastal activities such as dredging during coral spawning periods and mitigation of land-based sources of pollution and watershed discharge that may reduce water quality.
P rey rarely, if ever, give up their lives willingly to their predators. Predators overcome their... more P rey rarely, if ever, give up their lives willingly to their predators. Predators overcome their prey's resistance by being, on average, larger than their prey, yielding a systematic pattern in communities where the non-cannibalistic average ratio of predator-to-prey body mass (hereafter, body-mass ratio) is higher than unity 1,2. Notable exceptions to this include when animals cooperate to overcome larger prey (for example, pack hunters) and where consumers are parasites or parasitoids. Variation in body-mass ratios within food webs typically spans several orders of magnitude and includes some predators that are smaller than their prey 3 , but is dominated by situations of the larger feeding on the smaller. The varying body-mass ratios limit which trophic interactions are realized in a community 4-6 , and the strength of these interactions 7-9. Predators typically exert the strongest feeding pressure on prey that are 1-2 orders of magnitude smaller 1 , while weaker interaction strengths are realized with prey that are smaller or larger than this size 10,11. Specifically, interactions of predators with small prey are characterized by high body-mass ratios that yield weak interactions with slow dynamics, which play a central role in maintaining foodweb stability 12-16 and ecosystem functioning 10,17,18. Moreover, they
Running head: Species co-occurrence networks Title: Species co-occurrence networks: can they reve... more Running head: Species co-occurrence networks Title: Species co-occurrence networks: can they reveal trophic and non-trophic interactions in ecological communities?
Understanding the processes that drive kelp forest communities is critical for management and con... more Understanding the processes that drive kelp forest communities is critical for management and conservation of these productive ecosystems. As a way to advance in this direction, we explored the effects of fishing pressure and upwelling intensity over kelp forest communities along the central coast of Chile. We sampled kelp communities in different upwelling conditions associated with contrasting management regimes, namely Territorial User Rights for Fisheries (TURFs) and open-access (OA) areas. In TURF areas, we found a 2.6-fold increase in reef fish biomass, higher diversity of all fish trophic groups, mainly dominated by benthic carnivore feeders, and a 1.8-fold reduction in the number of kelp grazers. On the other hand, upwelling regimes evidence a 1.6-fold increase in abundance and recruitment of the dominant kelp (Lessonia trabeculata), and also an increase in biomass of planktivorous reef fishes. We found that grazers were capable of reducing kelp condition (measured as canopy foliage index) in OA areas outside the influence of upwelling. Enclosure experiments in the field revealed the effect of grazers on kelps, reducing kelp growth (i.e., blade elongation) and increasing blade tissue loss. Results provide evidence that TURF areas could be important ancillary conservation instruments in kelp forest ecosystems, if key processes of the subtidal community assemblages (e.g., interactions between grazers and reef fish) are maintained. We conclude that human impact interplays with the influence of upwelling in structuring kelp communities.
Species are linked to each other by a myriad of positive and negative interactions. This complex ... more Species are linked to each other by a myriad of positive and negative interactions. This complex spectrum of interactions constitutes a network of links that mediates ecological communities' response to perturbations, such as exploitation and climate change. In the last decades, there have been great advances in the study of intricate ecological networks. We have, nonetheless, lacked both the data and the tools to more rigorously understand the patterning of multiple interaction types between species (i.e., "multiplex networks"), as well as their consequences for community dynamics. Using network statistical modeling applied to a comprehensive ecological network, which includes trophic and diverse non-trophic links, we provide a first glimpse at what the full "entangled bank" of species looks like. The community exhibits clear multidimensional structure, which is taxonomically coherent and broadly predictable from species traits. Moreover, dynamic simulations suggest that this non-random patterning of how diverse non-trophic interactions map onto the food web could allow for higher species persistence and higher total biomass than expected by chance and tends to promote a higher robustness to extinctions.
Advances in our knowledge of eastern tropical Pacific (ETP) coral reef biogeography and ecology d... more Advances in our knowledge of eastern tropical Pacific (ETP) coral reef biogeography and ecology during the past two decades are briefly reviewed. Fifteen ETP subregions are recognized, including mainland and island localities from the Gulf of California (Mexico) to Rapa Nui (Easter Island, Chile). Updated species lists reveal a mean increase of 4.2 new species records per locality or an overall increase of 19.2 % in species richness during the past decade. The largest increases occurred in tropical mainland Mexico, and in equatorial Costa Rica and Colombia, due mainly to continuing surveys of these under-studied areas. Newly discovered coral communities are also now known from the southern Nicaraguan coastline. To date 47 zooxanthellate scleractinian species have been recorded in the ETP, of which 33 also occur in the central/south Pacific, and 8 are presumed to be ETP endemics. Usually no more than 20-25 zooxanthellate coral species are present at any given locality, with the principal reef-building genera being Pocillopora, Porites, Pavona, and Gardineroseris. This compares with 62-163 species at four of the nearest central/south Pacific localities. Hydrocorals in the genus Millepora also occur in the ETP and are reviewed in the context of their global distributions. Coral community associates engaged in corallivory, bioerosion, and competition for space are noted for several localities. Reef framework construction in the ETP typically occurs at shallow depths (2-8 m) in sheltered habitats or at greater depths (10-30 m) in more exposed areas such as oceanic island settings with high water column light penetration. Generally, eastern Pacific reefs do not reach sea level with the development of drying reef flats, and instead experience brief periods of exposure during extreme low tides or drops in sea level during La Niña events. High rates of mortality during El Niño disturbances have occurred in many ETP equatorial areas, especially in Panama and the Galápagos Islands during the 1980s and 1990s. Remarkably, however, no loss of resident, zooxanthellate scleractinian species has occurred at these sites, and many ETP coral reefs have demonstrated significant recovery from these disturbances during the past two decades.
How multiple types of non‐trophic interactions map onto trophic networks in real communities rema... more How multiple types of non‐trophic interactions map onto trophic networks in real communities remains largely unknown. We present the first effort, to our knowledge, describing a comprehensive ecological network that includes all known trophic and diverse non‐trophic links among >100 coexisting species for the marine rocky intertidal community of the central Chilean coast. Our results suggest that non‐trophic interactions exhibit highly nonrandom structures both alone and with respect to food web structure. The occurrence of different types of interactions, relative to all possible links, was well predicted by trophic structure and simple traits of the source and target species. In this community, competition for space and positive interactions related to habitat/refuge provisioning by sessile and/or basal species were by far the most abundant non‐trophic interactions. If these patterns are corroborated in other ecosystems, they may suggest potentially important dynamic constraint...
Important, often abrupt, and irreversible shifts associated with the degradation of ecosystem fun... more Important, often abrupt, and irreversible shifts associated with the degradation of ecosystem functioning and services are increasingly commonplace. Thus, a trait-based view of communities may be more insightful than that based solely on species composition, especially when inferring ecological responses to environmental change. This underscores the importance and urgency of establishing benchmarks against which future community changes and functional structure can be evaluated. As a first step toward setting these baselines and their current spatial variability, we here describe geographic and among-habitat patterns in the functional structure of shallow hard bottom communities, including fish assemblages, across the northeast and west coasts of Rapa Nui. We also document temporal patterns of change in dominant benthic functional groups that have taken place over the past 15 years at selected sites on this isolated Pacific island. Generally weak vertical zonation patterns were observed, with most striking differences due to the paucity of branching pocilloporid corals in shallow waters(<7 m), where massive corals of Porites predominate. We identified three main 'groups' of sites in terms of the relative abundance of major functional groups and these did not follow geographic arrangement or strict coastline orientation. The similar spatial change in benthic and fish functional community structure documented here suggests there may be strong coupling with coastal oceanographic conditions that varies on scales of 1s-10s of km. Temporal patterns document relatively rapid recovery of total coral cover, largely via compensatory change in relative coral composition with an increase in Porites upon abrupt decline of Pocillopora, following extensive coral mortality caused by thermal stress (coral bleaching) in 2000. Moreover, coral abundance in shallow habitats increased beyond pre-disturbance levels (i.e., 1999-2000). In contrast to shallow habitats, corals again suffered extensive mortality and reduced cover by 2005 at mid-(10-15 m) and deep (>15 m) habitats, with contrasting recovery. These results suggest depth-dependent disturbance regimes that differ in types and frequency of events, as well as capacity to recover. Overall, our results highlight the apparent resilience of the current system and provide a first-cut benchmark as to where management subsystems might be prescribed so as to spatially match ecosystem characteristics.
Over the past decade, evidence of abrupt latitudinal changes in the dynamics, structure and genet... more Over the past decade, evidence of abrupt latitudinal changes in the dynamics, structure and genetic variability of intertidal and subtidal benthic communities along central-northern Chile has been found consistently at 30-32uS. Changes in the advective and thermal environment in nearshore waters have been inferred from ecological patterns, since analyses of in situ physical data have thus far been missing. Here we analyze a unique set of shoreline temperature data, gathered over 4-10 years at 15 sites between 28-35uS, and combine it with satellite-derived winds and sea surface temperatures to investigate the latitudinal transition in nearshore oceanographic conditions suggested by recent ecological studies. Our results show a marked transition in thermal conditions at 30-31uS, superimposed on a broad latitudinal trend, and smallscale structures associated with cape-and-bay topography. The seasonal cycle dominated temperature variability throughout the region, but its relative importance decreased abruptly south of 30-31uS, as variability at synoptic and intra-seasonal scales became more important. The response of shoreline temperatures to meridional wind stress also changed abruptly at the transition, leading to a sharp drop in the occurrence of low-temperature waters at northern sites, and a concurrent decrease in corticated algal biomass. Together, these results suggest a limitation of nitrate availability in nearshore waters north of the transition. The localized alongshore change results from the interaction of latitudinal trends (e.g., wind stress, surface warming, inertial period) with a major headland-bay system (Punta Lengua de Vaca at 30.25uS), which juxtaposes a southern stretch of coast characterized by upwelling with a northern stretch of coast characterized by warm surface waters and stratification. This transition likely generates a number of latitude-dependent controls on ecological processes in the nearshore that can explain species-specific effects, and add strength to the suggestion of an oceanography-driven, major spatial transition in coastal communities at 30-31uS.
We evaluated interannual variability and the effect of the 1997–1998 El Niño event on recruitment... more We evaluated interannual variability and the effect of the 1997–1998 El Niño event on recruitment of intertidal mussels and barnacles along the coast of central Chile in the southeast Pacific. Monthly monitoring of recruitment at 11 sites spread over 900 km (29–348S) during the 1997–1998 El Niño and over the same months in 1998–1999 and 1999–2000 allowed us to assess geographic patterns in interannual recruitment variation. The geographically most consistent interannual trend was observed for the mussel Perumytilus purpuratus, which showed overall lower recruitment rates during the 1997–1998 El Niño year. However, the magnitude of the effect at any given site was small. Interannual variation in recruitment rates of the other two intertidal mussel species, as well as two chthamaloid barnacles, were not consistent across the region, and overall, few sites exhibited significant differences among years. Differences between two and three orders of magnitude in mean annual recruitment of ...
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Papers by Evie Wieters