Salinity fluctuations impose physiological challenges on estuarine organisms, but immediate behavioral responses may also depend on available habitat options. We characterized adult male Hemigrapsus crenulatus during the first minutes following transfer from 32 PSU to 6, 16, or 32 PSU. In Experiment 1, crabs had simultaneous access to sand and a submerged rock cavity for 720 s. In Experiment 2, the bottom was covered by either sand or shell hash, without a structural refuge, and crabs were observed for 300 s. Because each condition was represented by a single aquarium, observations, descriptive summaries, and principal coordinates analyses characterized individual patterns rather than independent treatment effects. In Experiment 1, 14 of 18 crabs entered the rock cavity: five of six at 6 PSU, five of six at 16 PSU, and four of six at 32 PSU. Refuge use, substrate occupation, refuge-entry latency, and behavioral transitions varied among individuals. In Experiment 2, completed burrowing occurred only in three of six crabs in shell hash at 16 PSU and was absent from the other salinity × substrate conditions. Median observed burrowing latency among these three crabs was 53.5 s (range 22.0-70.5 s). Wall-associated and wall-climbing events were common across the conditions examined. These findings show that H. crenulatus expressed multiple immediate responses following experimental transfer. Structural shelter was frequently used when available, whereas completed burrowing was uncommon without an alternative refuge. These exploratory patterns highlight the importance of habitat configuration and physiological timescale when examining behavioral responses to salinity variability.

One of the challenges of ecology is to understand how natural and anthropogenic factors determine patterns of species distribution and abundance. The Gulf of Arauco, located in the central part of Chile, is a biologically highly productive area in the eastern South Pacific, with important human settlements and intensive coastal use. There is a submarine pipeline that carries effluent from wood pulp production to the coastal ocean. This study quantified the distribution and abundance of benthic megafauna in the Gulf of Arauco over a 3-year period, and evaluated the spatial dissimilarities from the submarine outfall through 13 seasonal surveys. The main results were as follows: (i) The megafauna in the Gulf of Arauco consisted of 92 taxa. The most abundant were Echinodermata: Ophiuroidea with Ophiactis sp. ; Mollusca-Gastropoda with Nassarius dentifer; and Cnidaria-Anthozoa with Renilla sp.; (ii) Species presence and abundance and community structure were highly heterogeneous at the spatial scale of the site and study Zones within the gulf; (iii) At the spatial scale of the gulf, and based on the gradient of the underwater pipeline, three significantly different areas were identified (Zones 1 and 3, close to the outfall with a signal of terrestrial organic matter, Zone 2 near to the coast, and Zones 4 and 5, far away from it), a pattern that was repeated across years, seasons of the year, and sampling periods; (iv) The areas closest to the submarine outfall were dominated by ophiuroids, probably associated with a greater load of organic matter from terrestrial plants in the sediments; (v) The areas closest to the pulp mill effluent are more influenced by the terrigenous and industrial inputs as indicated by the sediment lignin, tannin and AOXs contents; (vi) The zone closest to the submarine outfall had the highest average species richness, but beta multivariate diversity showed the opposite pattern, with the highest mean values in the zones farthest from the outfall.

La biodiversidad de los ambientes costeros es afectada por actividades antropogénicas locales y junto con el cambio climático, pueden alterar estructuras comunitarias, ciclos biogeoquímicos y su funcionamiento ecosistémico. Se determinó el estatus ecológico del Golfo de Arauco usando la macrofauna bentónica de fondos blandos en tres períodos oceanográficamente contrastantes (primavera 2021, verano e invierno 2022). Se estimaron siete índices bióticos (diversidad de Shannon-Wiener, índice Warwick, AMBI, M-AMBI, Bentix, BOPA y BPA) y su relación con variables fisicoquímicas de los sedimentos. La comunidad estuvo compuesta principalmente por poliquetos (>80%), seguida por crustáceos y moluscos. Estacionalmente los índices bióticos presentaron variaciones significativas a excepción de la diversidad de Shannon-Wiener y M-AMBI. El estatus ecológico fluctuó entre niveles moderadamente perturbado y bueno para todos los índices; salvo para Bentix que clasificó los ambientes como pobres o seriamente perturbados, niveles que también fueron observados en las diversas agrupaciones taxonómicas espaciales existentes en el área de estudio. Se detectó una asociación significativa entre los índices AMBI, Bentix, BOPA y BPA con el potencial redox, carbono orgánico total (TOC) y porcentajes de arena y fango, mientras que, los índices M-AMBI, Warwick y la diversidad de Shannon-Wiener no presentaron asociaciones con las variables del sedimento. Este estudio es el primero en estimar y comparar distintos índices bióticos de la macrofauna bentónica en ambientes costeros submareales del Sistema de Corrientes de Humboldt con un enfoque multivariado. Se sugiere un uso integrado de estos como un aporte al desarrollo de un enfoque ecosistémico a la gestión de ambientes costeros altamente productivos y antropizados.

The Gulf of Arauco is the most productive and largest bay in central-south Chile. Soft bottom sublittoral coastal benthic macrofauna was studied in October 2021, January and August 2022, spanning from the Biobio River to Punta Lavapi & eacute;. 118 taxons were identified for the three periods at the 21 sampling sites. The most abundant group was Polychaeta, with its most important species being Mediomastus branchiferus, Prionospio peruana, Aricidea pigmentata, Owenia sp., and Paraprionospio pinnata. Multivariate analysis found significant differences between the three studied periods. 5 spatial assemblages were identified in spring, 3 in summer, and 8 in winter. P. peruana, Goniada uncinigera, and Heterophoxus sp. were the most abundant taxons in spring; P. pinnata, Diopatra chilensis, and Cancer plebejus in summer; and M. branchiferus, A. pigmentata, and P. peruana in winter. Owenia sp. and P. pinnata were present at all sampling sites in the three periods. The northern and southern zones of the Gulf of Arauco showed greater similarities in relation to the central-northern zone, which also exhibited dissimilar taxonomic sub-assemblages for each sampling period. The study sites were associated according to Redox potential, total organic carbon, and sediment grain size variables. Temporal changes in multivariate community structure, the presence of very abundant, rare, and spatially widespread species in the Gulf of Arauco can be explained from an integrated metacommunity approach under the mechanisms of patch dynamics, species sorting, mass effects, and neutral.

Biodiversity in coastal environments is affected by anthropogenic activities and climate change, altering community structures, biogeochemical cycles, and ecosystem functioning. The ecological status of the Gulf ofArauco was determined based on soft bottom benthic macrofauna during three oceanographically contrasting periods (spring 2021, summerand winter2022). Seven biotic indexes were estimated (Shannon- Wiener diversity, Warwick, AMBI, M-AMBI, Bentix, BOPA, and BPA), and their relationships with sediment physicochemical variables were analyzed. The community was mainly composed of polychaetes (>80%), followed by crustaceans and mollusks. Seasonally, the biotic index showed significant variations, except for the Shannon-Wiener diversity index and the M-AMBI. Ecological status fluctuated from "moderately disturbed" and "good" for all indexes, except in the Bentix index, which classified the environment as "poor" or "seriously disturbed", levels which were also observed in various spatial faunal assemblages identified in the study area. A significant association was detected between the AMBI, Bentix, BOPA, and BPA indexes with redox potential, total organic carbon (TOC), and percentages of sand and silt, whereas the M-AMBI, Warwick, and Shannon-Wiener diversity indexes were not associated with environmental variables. This study is the first to estimate and compare different biotic indexes of benthic macrofauna in subtidal coastal environments in the Humboldt Current System using a multivariate approach. We suggest an integrated use, towards contributing to the development of an ecosystem approach to managing highly productive and anthropized coastal environments.

Para identificar patrones en la estructura de las comunidades de playas de arena del Golfo de Arauco y determinar los factores físicos que la explican, entre octubre de 2021 y agosto de 2022 se desarrollaron tres campañas de muestreo donde se evaluó la abundancia, riqueza y estructura comunitaria en 19 sitios. Cada uno de los sitios fue caracterizado con base en seis atributos que incluyeron la dinámica sedimentaria, el tipo de playa, el tamaño de grano, la exposición de la costa, la distancia a centros industriales y la distancia a la desembocadura del río Biobío. Los resultados obtenidos revelaron la presencia de siete especies, entre las que destacaron Emerita analoga y Excirolana hirsuticauda como dominantes. E. analoga mostró dominancia en la campaña de octubre 2021, particularmente entre Coronel y Arauco, mientras que E. hirsuticauda fue dominante en enero 2022 y agosto 2022. En general, las comunidades analizadas mostraron un patrón caracterizado por un cambio en la estructura de las comunidades producido en la zona media del Golfo de Arauco, cerca de Lota, con mayor riqueza y diversidad hacia la sección sur del golfo y predominancia de E. analoga y Orchestoidea tuberculata hacia el norte. Los factores que explicaron esta diferenciación espacial se asociaron con la dinámica sedimentaria, el tipo de playa y la granulometría. La cercanía a centros industriales, a la desembocadura del río Biobío y la exposición de la línea de costa, resultaron significativos, aunque no mostraron estadísticamente la misma importancia de las variables físicas que caracterizan el tipo de playa.

El Golfo de Arauco es la bahía de mayor tamaño y más productiva en Chile centro-Sur. Durante octubre 2021, enero y agosto 2022 se estudió la macrofauna bentónica sublitoral costera de fondos blandos, abarcando desde el río Biobío hasta Punta Lavapié. Se identificó 118 taxones para los tres períodos en 21 sitios de muestreo. El grupo más abundante fue Polychaeta, cuyas especies más importantes fueron Mediomastus branchiferus, Prionospio peruana, Aricidea pigmentata, Owenia sp. y Paraprionospio pinnata. El análisis multivariado encontró diferencias significativas entre los tres períodos estudiados. Se identificaron 5 agrupaciones espaciales en primavera, 3 en verano y 8 en invierno. En primavera dominaron P. peruana, Goniada uncinigera y Heterophoxus sp., en verano P. pinnata, Diopatra chilensis y Cancer plebejus y, en invierno M. branchiferus, A. pigmentata y P. peruana. Owenia sp. y P. pinnata estuvieron presentes en todos los sitios de muestreo en los tres períodos. Las zonas Norte y Sur del Golfo de Arauco son más similares entre sí, en tanto que la zona centro-Norte, presentó sub-ensambles taxonómicos disímiles para cada período de muestreo. Los sitios de muestreo se asociaron a las variables potencial Redox, carbono orgánico total y tamaño medio del grano de los sedimentos. Se propone que los cambios temporales en la estructura comunitaria multivariada, la presencia de especies muy abundantes, raras y de mayor presencia espacial en el Golfo de Arauco pueden ser explicadas bajo una aproximación metacomunitaria integrada considerando los mecanismos de dinámica de parches, selección de especies, efecto de masas, y neutral.

Background It is known that aquaculture may produce negative environmental effects on marine ecosystems. Southern Chile is one of the most important salmon and mussel-producing areas in the world. Here we assess the ecological status of benthic communities near farming centers in Caucahue Channel, Chiloe, which has been used intensely for salmon and mussel production for 30 years. Methods The macrofauna, sediments and water column were characterized at distances of 5 to 100 m from three salmon and three mussel-producing centers. Information was also obtained from reference sites 500 to 3000 m from these aquaculture farms. The macrofauna and environmental conditions during winter were analyzed using uni- and multivariate analysis and the AZTI Marine Biotic Index (AMBI) as an indicator of benthic community condition. Results (i) There is a high degree of spatial dissimilarity in macrofauna and environmental variables among sampling sites and types of environments (far from or near farming centers) and between the northern and southern areas of the channel; (ii) sediment structure (mean grain size and percentage of total organic matter) correlated with the observed dissimilarities in macrofauna communities; and (iii) the level of perturbation according to AMBI was heterogeneous, with sites in the undisturbed/normal range to moderately disturbed/polluted. Conclusions We found a high spatial dissimilarity in benthic macrofauna and environmental variables among sampling sites, environmental types and between the northern and southern areas of the channel. AMBI and multivariate community-environment analysis are useful tools to define the level of perturbation of a geographic area at different spatial scales, using all the ecological information from each sample and replicates.

Las características ecológicas de la macrofauna bentónica, la convierten en un buen indicador para evaluar los efectos de perturbaciones antropogénicas (e.g., acuicultura, emisarios submarinos, etc.) sobre los ecosistemas marinos. La normativa chilena aplicable a monitoreos ambientales establece que su caracterización debe realizarse utilizando tamices de 1.000 µm de abertura. Con el objetivo de evaluar la pérdida de información en composición y abundancia de las especies al utilizar este tamiz respecto de uno de 500 µm, se realizaron muestreos submareales en invierno y verano del 2018 en 5 áreas del Golfo de Arauco, Chile central. El muestreo y análisis consistió en: (i) cernido en tamiz de 1.000 µm, reteniendo los organismos que traspasan este tamiz en uno de 500 µm, (ii) identificación de los organismos retenidos en ambos tamices hasta el nivel taxonómico más bajo posible y, (iii) comparación de la macrofauna entre tamices, períodos y áreas de muestreo, utilizando estadística univariada y multivariada. A partir de los análisis se encontraron diferencias significativas en la estructura comunitaria de la macrofauna entre tamices, áreas y periodos de muestreo. Los índices AMBI y W, utilizados como bio-indicadores comunitarios, también identifican diferencias significativas entre tamices. Los resultados señalan que, si bien el uso de un tamiz de 1.000 µm permite identificar diferencias espaciales y temporales en la macrofauna, con su uso se subestima el nivel de impacto detectado por los bio-indicadores comunitarios. Por tal razón, se recomienda utilizar un tamiz de 500 µm si el objetivo es evaluar impactos antropogénicos en el ambiente marino, especialmente en líneas de base, caracterizaciones preliminares de sitio para la acuicultura y programas de vigilancia ambiental. Toda la información, debiera, además, ser integrada mediante herramientas estadísticas multivariadas, capaces de incorporar en conjunto los antecedentes biológicos y ambientales recopilados en el área de estudio.

The ecological characteristics of the benthic macrofauna make a good indicator to evaluate the effects of anthropic perturbations (e.g., aquaculture, submarine pipelines emissions) on marine ecosystems. Chilean environmental regulation establishes that macrofauna characterization must be performed with sieves with 1,000 mu m opening. To evaluate the loss of information on species composition and abundance by using an opening of 1,000 mu m instead of 500 mu m, subtidal samplings were performed during summer and winter of 2018 in 5 areas of the Gulf of Arauco, central Chile. Sampling and analysis consisted of: (i) samples were sieved through 1,000 mu m mesh and the organisms passing through this sieve were retained in 500 mu m mesh sieves; (ii) identifying the taxa retained in both sieves to the lowest possible level, and (iii) comparison of the macrofauna between sieves, periods and sampling areas, using univariate and multivariate statistics. The analyses showed significant differences in the community structure among sieve sizes, areas and sampling periods. The AMBI and W indexes, used as community bio-indicators, also showed significant differences between sieve sizes. The results revealed that, although a 1,000 mu m sieve can identify spatial and temporal differences in the macrofauna, it underestimates the level of impact shown by community bio-indicators. The use of a 500 mu m sieve is recommended if the objective is to evaluate anthropic impact on the marine environment, especially for baseline studies, preliminary site characterizations for aquaculture, monitoring and/or environmental surveillance programmes. This information should also be complemented with multivariate statistical tools that are capable of incorporating together all the biological and environmental information compiled in the study area.

Non-predatory dead variability in zooplankton remains poorly quantified worldwide. Here, we make the first estimation of the percentage of dead organisms in coastal zooplankton communities in the Humboldt Current System (HCS) under in situ conditions. The study was conducted in four coastal sites of the southern HCS (between 36 and 37°S) over a period of one year. Percentages of dead organisms were based on the classification as live or dead of 158,220 holoplankton and 17,591 meroplankton individuals using neutral red staining technique. The percentage of dead organisms in total-zooplankton was between 4.3% in Coronel Bay (summer) and 76.9% in Llico (autumn). The percentage of dead total-holoplankton varied from 4.2% (Itata River Mouth; autumn) to 77.6% (Llico; autumn), while the percentage of dead total-meroplankton ranged from 1.5% to 56.8% in Coronel Bay and Coliumo Bay, respectively. The most abundant taxa analyzed were the copepods Acartia sp., Paracalanus sp., Calanoides sp., Cladocera, Polychaeta, and the eggs of anchoveta Engraulis ringens. Among these taxa, there was a high degree of interspecific variability in the estimation of the dead organisms. The Pearson correlation shows significant relationships between maximum temperature, and minimum salinity, with the percentage of dead individuals of Acartia sp. and Paracalanus sp. Environmental factors explaining those relationships were: the El Niño 2015-2016 event, and freshwater river runoff. The use of vital staining to estimate non-predatory death for total-zooplankton and selected sentinel species is a promising tool to establish baselines to evaluate natural perturbations (e.g. ENSO), and anthropogenic alterations in coastal pelagic ecosystems.

Faunal assemblages of subtidal sedimentary environments are key components of coastal ecosystems. Benthic communities inhabiting the coastal zone near urban centers in Concepción Bay (Chile) have been described as highly disturbed (i.e. impoverished in diversity and species richness). This is due to the frequent presence of hypoxic conditions at the bottom due to the intrusion of low oxygen Equatorial Subsurface Water, high natural productivity and the high load of organic matter generated by several anthropogenic activities. A mega-earthquake (8.8 Mw) and subsequent tsunami occurred on the coast of south-central Chile on February 27, 2010 (27F), heavily impacting Concepción Bay, which is located 30 km south of the epicenter. The objectives of the present study are: (i) to evaluate the effect produced by the mega-earthquake and tsunami on the benthic community, and (ii) to assess dissimilarity in macrofauna composition and abundance in Concepción Bay at an inter-decadal time scale based on a comparison between our sampling conducted between 2010 and 2013 and information published since 1969. Our results show that the benthic macrofauna of Concepción Bay was disturbed by the 27F (i.e. high community dissimilarity in 2010). Changes in community structure were observed at an inter-annual scale (i.e. diminished community dissimilarity in 2013), suggesting a recovery post-27F. At an inter-decadal scale, community structure post-27F was dissimilar to the structure described for the 1980's and 1990's but more similar to that reported for 1969. The reducing conditions of the sediments due to the high input of organic matter that took place in the 1980's and 1990's may explain this dissimilarity.

In January 2008 there was an intensive and extensive upwelling event in the southern Humboldt Current System. This event produced an intrusion of water with low dissolved oxygen into Coliumo Bay, which caused massive mortality and the beaching of pelagic and benthic organisms, including zooplankton. During this event, which lasted 3 to 5 days, we studied and evaluated the effect of the hypoxic water in the bay on the abundance of macrozooplankton, nanoplankton and microphytoplankton, the concentration of several nutrients and hydrographic conditions. At the beginning of the hypoxia event the water column had very low dissolved oxygen concentrations (<0.5 mL O2 L-1), low temperatures and high salinity which are characteristics of the oxygen minimum zone from the Humboldt Current System. Redox, pH, nitrate, phosphate, silicate and chlorophyll-a values were the lowest, while nitrate and the phaeopigment values were the highest. The N:P ratio was below 16, and the abundance of nano- and microphytoplankton were at their lowest, the latter also with the lowest proportion of live organisms. Macrozooplankton had the greatest abundance during hypoxia, dominated mainly by crustacean, fish eggs and amphipods. The hypoxia event generated a strong short-term alteration of all biotic and abiotic components of the pelagic system in Coliumo Bay and the neighboring coastal zone. These negative effects associated with strong natural hypoxia events could have important consequences for the productivity and ecosystem functioning of the coastal zone of the Humboldt Current System if, as suggested by several models, winds favorable to upwelling should increase due to climate change. The effects of natural hypoxia in this coastal zone can be dramatic especially for pelagic and benthic species not adapted to endure conditions of low dissolved oxygen.

Sandy beaches are characterised by high temporal and spatial variability, resulting in environmental gradients between beaches based on morphodynamic differences. This variability is less well known when beaches are affected by abrupt and highly energetic perturbations such as earthquakes and tsunamis. Here, we analysed the changes in the morphodynamic characteristics of six beaches in south-central Chile. Morphodynamic variables were analysed seasonally, and as a function of changes caused by a mega-earthquake and subsequent tsunami on 27 February 2010 (Mw=8.8). The results indicate that Dichato and Lenga have reflective morphodynamic states, while Cobquecura, Mela, Perales and Puda have intermediate states. The canonical analysis of principal coordinates (CAP) biplot of the first two components showed that the second component (CAP2) related Dichato and Mela significantly to mean grain size, frequency of effluent line crossing, swash frequency, breaking wave frequency and swash speed; while Cobquecura, Perales, Puda and Lenga were related to beach slope, height of breaking wave and swash frequency. Beaches generally showed coarse sand during winter and lower textural range in summer, but with high seasonal variability of mean grain size. The mega-earthquake and subsequent tsunami that hit the study area in February 2010 led to short-term changes in morphodynamics, mainly beach slope and granulometry, but beaches tended to regain conditions similar to those prior to the earthquake, showing an apparent high resilience to this strong natural perturbation.

Studies on population abundance variations at different temporal scales contribute to the understanding on how these populations change over time and what are the factors influencing those variations. We analyzed daily, monthly and annual haul-out abundance patterns of South American sea lions (SASL, Otaria flavescens) in 2 breeding colonies of the north of Chile. Additionally we analyzed the effect of El Nino events on the sea lions' annual patterns. The abundance of sea lions in Punta Negra (PN) decreased from 1994 to 2011, whereas in Punta Patache (PP) increased, although the number of pups was proportionately low. Our results indicated a strong effect of El Nino over the abundance of sea lions, especially for females + juveniles in PN. The haul-out monthly abundance of females and juveniles increased during austral winter months, whereas adult and subadult males did not show a clear pattern. Finally, the haul-out abundance tended to increase throughout the day reaching a maximum by late afternoon, especially for females and juveniles. No di fference in daily patterns between breeding and non-breeding seasons for any of the sex/age classes was found. This study shows that the number of animals in the PP and PN breeding colonies presented annual, monthly and daily periodiciti es, and that these periodicities are conditioned by both intrinsic (e.g., breeding period) and extrinsic (e.g., time of day, El Nino) factors. On an annual basis, our results indicate that even at a local scale, SASL population trends at 2 colonies may be different.

Studies on population abundance variations at different temporal scales contribute to the understanding on how these populations change over time and what are the factors influencing those variations. We analyzed daily, monthly and annual haul-out abundance patterns of South American sea lions (SASL, Otaria flavescens) in 2 breeding colonies of the north of Chile. Additionally we analyzed the effect of El Nino events on the sea lions' annual patterns. The abundance of sea lions in Punta Negra (PN) decreased from 1994 to 2011, whereas in Punta Patache (PP) increased, although the number of pups was proportionately low. Our results indicated a strong effect of El Nino over the abundance of sea lions, especially for females + juveniles in PN. The haul-out monthly abundance of females and juveniles increased during austral winter months, whereas adult and subadult males did not show a clear pattern. Finally, the haul-out abundance tended to increase throughout the day reaching a maximum by late afternoon, especially for females and juveniles. No difference in daily patterns between breeding and non-breeding seasons for any of the sex/age classes was found. This study shows that the number of animals in the PP and PN breeding colonies presented annual, monthly and daily periodicities, and that these periodicities are conditioned by both intrinsic (e.g., breeding period) and extrinsic (e.g., time of day, El Nino) factors. On an annual basis, our results indicate that even at a local scale, SASL population trends at 2 colonies may be different.

Sand crabs belonging to the genus Emerita are the dominant species on sandy beaches of the Pacific and Atlantic coasts of America. The success of this genus has been attributed to the great phenotypic plasticity of life history traits that enables them to cope with swash climate variability from beach to beach. The burrowing rate and variation in carapace shape of Emerita analoga from south-central Chile were studied on a series of five sandy beaches with contrasting reflective-intermediate swash conditions (harsher swash to benign swash). Environmental sampling was carried out monthly from September 2009 to November 2010, while biological experiments were conducted in September and October 2010. A combination of field experiments, geometric morphometric tools and multivariate analysis was used to assess the relationship between burrowing behavior and carapace shape with variables of swash climate. Our results showed that (1) body shape of E. analoga is directly affected by the frequency of effluent line crossing, (2) burrowing rate of E. analoga is affected directly by shape variability, (3) burrowing rate is affected directly and indirectly by the swash climate variables: frequency of effluent line crossing and mean grain size of sediment. Thus, the physical conditions in the intertidal zone may be the main environmental constraints determining cephalothorax shape, with a wider cephalothorax on beaches with finer sand and more benign physical dynamics, and a narrower shape on beaches with coarser sand and harsher physical dynamics. The latter phenotype (narrower shape) probably allows compensating the high difficulty of burying in coarser sediments.

On February 27, 2010, the world's sixth strongest earthquake on record (8.8 M (w)) and tsunami hit central Chile. We assess the response of the epibenthic macrofaunal community following this event in Coliumo Bay, one of the areas most affected by this mega-perturbation. The indicators of aggregate and compositional variability show that 3 years after this event, the community appears to have undergone the following dynamics: (1) At an inter-annual timescale, the community (both in density and biomass) shifted through different structures with apparent directionality; (2) Oceanographic and biological seasonality had a strong cyclical influence on the inter-annual community response; (3) There was spatial homogenization of the community over time (i.e., recovery of diversity), probably promoted by the ecological functionality of scavenger species (i.e., crab Cancer coronatus and snail Nassarius spp.) and by the proportional increase in non-dominant species; (4) Bathymetry and bottom dissolved oxygen also played significant roles in the spatial structure of this community; (5) Three years after the perturbation, total density and total community biomass were still considerably below those described under unperturbed conditions, mainly associated with the decrease in density and biomass of dominant species. Therefore, in spite of this apparent community compositional recovery, the aggregate variability currently remains below the levels reported prior to the effect of the mega-earthquake and tsunami. These results provide evidence that supports both the Cross-Scale Resilience Hypothesis and the Response Diversity Hypothesis.

The sandcrab Emerita analoga is the dominant species inhabiting sandy beaches along the Pacific coast of the American continent. In our study, 10 sandy beaches were sampled seasonally from 2006 to 2011, including coastal planktonic sampling from 2006 to 2008. Two major population cores were detected, the first one in the northern part of the study area and the second in the area immediately to the south of the Itata River mouth. Zoeal stages were found along the entire coastal zone. Highest densities and recruitment were found during spring and summer of each year. PLS regression indicated that source–sink habitat proxies correlated positively with morphodynamic parameters; while beach slope and total organic matter were negatively correlated. These results agree with the source–sink hypothesis, finding higher densities of adults, recruits and cohort recurrence on open coast beaches with milder physical dynamics. Furthermore, a hypoxic event and a mega-earthquake/tsunami negatively affected recruitment at the inter-annual scale.

The Humboldt Current System (HCS) has one of the three most important oxygen minimum zones (OMZ) of the global ocean. Several studies have looked at the macrofaunal benthic assemblages inhabiting the continental shelf and shallow bays off central-southern Chile associated with low oxygen areas, but little is known about open coast macrofaunal communities within this zone, which are frequently subjected to the low oxygen conditions of Equatorial Subsurface Waters (ESSW). In order to assess local and mesoscale coastal macrofauna dynamics, the sampling area (ca. 40 linear km) was divided into seven local zones (Cobquecura, southern Cobquecura, northern Itata, Itata River mouth, external, southern Itata, and Coliumo). Eight oceanographic cruises were carried out between May 2006 and February 2008 covering 16 coastal sampling sites, between 36°07'S and 36°30'S. The macrofaunal assemblage was dominated by polychaetes, crustaceans, and mollusks. Our results suggest a high degree of temporal faunal stability on the mesoscale in soft bottom communities along the open coast, given the persistence of a faunal assemblage dominated by organisms tolerant of low oxygen conditions. While there is some local variability in community attributes, the main structuring factor for soft bottom communities in the shallow coastal area off central-southern Chile is the seasonal intrusion of low oxygen ESSW.