Dynamics of the shallow-water fish assemblage of the Patos Lagoon estuary (Brazil) during cold and warm ENSO episodes

In southern Brazil, cold ( La Niña ) and warm ( El Niño ) episodes of the El Niño Southern Oscillation (ENSO) phenomenon cause drought and high rainfall, respectively. The low precipitation and freshwater outflow associated with La Niña during 1995–1996 were associated with an increase in the abundance of marine species in the Patos Lagoon estuary. During the 1997–1998 El Niño , high precipitation and river discharge were associated with low abundance of marine species in the estuary. ANOVA results showed a higher abundance during La Niña than El Niño for estuarine resident (RES) and estuarine dependent (DEP) fishes. During La Niña catch per unit of effort (CPUE) of RES increased from the marine to estuarine area, but during El Niño CPUE increased at the marine area and diminished during summer and autumn in some estuarine sites. DEP fishes had an opposite abundance pattern. During La Niña , these fishes were abundant at the coastal marine area and along some estuarine sites, but during El Niño , CPUE remained almost the same at the marine area but dropped along some estuarine sites. These different abundance patterns for dominant fish groups yielded a positive interaction between stations and climatic events. With higher river discharge and the consequent decline of dominant euryhaline fishes, such as Mugil platanus and Atherinella brasiliensis , freshwater species increased in abundance and richness in the shallow waters of the stuary. The ENSO phenomenon influences precipitation and estuarine salinity in southern Brazil and thereby seems to have a strong influence on recruitment, immigration, and emigration dynamics of fish species living within and adjacent to estuarine habitats.     

Population dynamics of a polychaete during three El Niño events: disentangling biotic and abiotic factors

The macrobenthic community in shallow soft-bottom areas in the Bay of Ancón, Peru, is characterised by low biodiversity due to low oxygen concentrations. During El Niño events, higher temperature and higher concentrations of dissolved oxygen induce a temporary increase in biodiversity. However, the structure and dynamics of the emerging communities vary strongly among events. The reasons for this variation are poorly understood, in particular the relative influence of abiotic vs biotic factors. To disentangle the roles of abiotic and biotic factors, population models based on detailed monitoring data of three El Niño events were developed focused on the population dynamics of one species in the community, the polychaete Sigambra bassi , which showed different responses in different El Niño events. Calculated and observed population dynamics are compared using root mean square deviation (RMSD). The results show that S. bassi abundance can be determined by abiotic environmental conditions. Besides, three biotic factors improved model performance in different El Niño events: negative density dependence in larval settlement, lower carrying capacity in the presence of other species and positive density dependence in adult survival. The results demonstrate how population models can be used to decode information hidden in long-term monitoring data of abiotic and biotic community parameters about factors driving population dynamics.     

Tree mortality due to an El Niño flood along the lower Tana River, Kenya

This study investigated forest tree mortality as a result of the extremely strong 1997–1998 El Niño flood in Tana River, Kenya, directly tested how mortality varied in relation to tree species and diameter at breast height (DBH), and indirectly tested how mortality varied in relation to floodwater depth. The study forest was under 2 m of water for approximately 71 days, from December 1997 until February 1998. Twenty-five liana, subcanopy tree, and canopy tree species were selected based on their importance in the diet of the Tana River mangabey ( Cercocebus galeritus Peters), a critically endangered primate endemic to the Tana River. Reproductive-sized individuals of these species were enumerated in 16.25 ha. I also enumerated trees killed by the El Niño flood, recorded their location in the forest, and measured their DBH. Ninety-two trees in fifteen species were killed by the flood. There were significant differences in mortality by species and by 0.25 ha quadrat. There were negative correlations between number of dead and DBH, number of dead and distance from the river, and per cent of quadrat killed and distance from the river. There appear to have been few long-term consequences of the El Niño flood in the forest or for the mangabeys.     

The effects of seasonal and interannual variability of oceanic structure in the western Pacific North Equatorial Current on larval transport of the Japanese eel Anguilla japonica

As the North Equatorial Current (NEC)–bifurcation is known to be related to El Niño-Southern Oscillation (ENSO) events, the influence of the position of the NEC bifurcation on transport success of the larval Japanese eel Anguilla japonica was investigated. Using a Lagrangian modelling approach, larval transport was simulated and the relative influence of El Niño and La Niña events and the NEC-bifurcation position on the success of particle transport analysed. The number of particles transported from the NEC to the Kuroshio tended to be lowest during El Niño years, and differences between La Niña and regular years were small. The transport success observed in simulations showed some relationships to annual A. japonica glass eel recruitment to Tanegashima Island over 1993 to 2001, but not in 2002. The study shows that particle tracking simulations can be used to improve knowledge of the oceanic migration of A. japonica but further studies are required, including comparisons with the effects on larval survival of fluctuations in temperature and food availability.     

VARIATION IN TOXIN PRODUCTION OF SYNCHRONIZED CULTURES OF CHRYSOCHROMULINA POLYLEPIS (PRYMNESIOPHYTA)

We studied spatial variability in giant kelp ( Macrocystis pyrifera ) forests at 84 sites along the west coast of North America in order to assess the impacts of the 1997–98 El Niño. Our sites spanned the geographic range of giant kelp in the Northern Hemisphere and were surveyed just before, immediately following, several months after, more than one year after, and nearly two years after the El Niño. Interspersion of sample units allowed us to compare the effects of this disturbance among spatial scales ranging from a few meters to more than a thousand kilometers. Variance components analyses revealed that El Niño shifted the relative importance of factors that regulate giant kelp communities from factors acting at the scale of a few meters (local control) to factors operating at hundreds of kilometers (regional control). Moreover, El Niño resulted in a near-to-complete loss of giant kelp populations throughout nearly two-thirds of the species' range. Evaluation of these effects along with oceanographic data (at the "appropriate" spatial scales), along with closer examination of giant kelp populations in the most severely impacted region (Baja) suggested that the among-region differences in giant kelp survival was due, at least in part, to El Niño-induced differences in ocean climate. Giant kelp recovery following El Niño was also scale-dependent, but driven by factors different from those of the disturbance. Here, we present results for several species of macroalgae in an attempt to relate the importance of El Niño to that of other processes in creating scale-dependent patterns of variability.     

IMPROVED BODY CONDITION OF WEANED HAWAIIAN MONK SEAL PUPS ASSOCIATED WITH EL Niño EVENTS: POTENTIAL BENEFITS TO AN ENDANGERED SPECIES

Efforts to enhance recovery of endangered Hawaiian monk seals ( Monachus schauinslandi ) require an understanding of factors influencing population dynamics. This study examines relationships between body condition and survival of monk seal pups at French Frigate Shoals and Laysan Island and El Niño events. Girth measurements and mass estimates were used as indicators of pup body condition, and survival was evaluated from weaning to age 2. Linear models and logistic regression analysis were used to evaluate El Niño effects. Temporal trends in mean girth, mass, and survival were identified at both study sites. After accounting for temporal trends, girths were 3.7 cm and 2.7 cm greater during El Niño years at French Frigate Shoals and Laysan Island, respectively. Average mass estimates were significantly greater during El Niño years at French Frigate Shoals (2.6 kg increase), but were not significantly different at Laysan Island (1.8 kg increase). Weaned pups born at French Frigate Shoals during El Niño years survived significantly better, but this effect was not detected at Laysan Island. El Niño events probably affect pup condition and survival, but these parameters need to be monitored during future El Niño events to clarify these relationships.     

Effects of large-scale climatic fluctuations on survival and production of young in a Neotropical migrant songbird, the yellow warbler Dendroica petechia

Migrant songbirds are vulnerable to changes in climatic conditions on both the breeding and wintering grounds. For North American Neotropical migrants, the El Niño/Southern Oscillation (ENSO), via its effects on global precipitation and temperature, modulates the productivity of their temperate and tropical terrestrial ecosystems used during the course of their annual cycle. We evaluated how a densely nesting population of yellow warblers Dendroica petechia in a riparian forest in southern Manitoba, Canada, responded to the El Niño/Southern Oscillation (ENSO) between 1992 and 2001. Standardized mist netting was used to estimate apparent annual survival of adults and production of young. Both adult survival and the production of young were positively correlated with the Southern Oscillation Index (SOI). More specifically, values of both these demographic parameters were lowest during El Niño years and highest during La Niña years. These findings demonstrate the influence of climate on populations of Neotropical migrants in North America. The more frequent El Niños predicted to result from future global climate change could negatively affect populations of yellow warblers and other Neotropical migrants breeding in this region.     

Inter-hemispheric synchrony of forest fires and the El Niño-Southern Oscillation

Fire histories were compared between the south-western United States and northern Patagonia, Argentina using both documentary records (1914–87 and 1938–96, respectively) and tree-ring reconstructions over the past several centuries. The two regions share similar fire–climate relationships and similar relationships of climatic anomalies to the El Niño–Southern Oscillation (ENSO). In both regions, El Niño events coincide with above-average cool season precipitation and increased moisture availability to plants during the growing season. Conversely, La Niña events correspond with drought conditions. Monthly patterns of ENSO indicators (southern oscillation indices and tropical Pacific sea surface temperatures) preceding years of exceptionally widespread fires are highly similar in both regions during the 20th century. Major fire years tend to follow the switching from El Niño to La Niña conditions. El Niño conditions enhance the production of fine fuels, which when desiccated by La Niña conditions create conditions for widespread wildfires. Decadal-scale patterns of fire occurrence since the mid-17th century are highly similar in both regions. A period of decreased fire occurrence in both regions from c. 1780–1830 coincides with decreased amplitude and/or frequency of ENSO events. The interhemispheric synchrony of fire regimes in these two distant regions is tentatively interpreted to be a response to decadal-scale changes in ENSO activity. The ENSO–fire relationships of the south-western USA and northern Patagonia document the importance of high-frequency climatic variation to fire hazard. Thus, in addition to long-term trends in mean climatic conditions, multi-decadal scale changes in year-to-year variability need to be considered in assessments of the potential influence of climatic change on fire regimes.     

Subsistence Economies and the Origins of Andean Complex Societies

Recent arguments stating that marine resources were relatively unimportant in cultural developments on the coast of Peru during the Preceramic Period are incorrect on several counts. It is shown that the economics and technology of maritime subsistence of coastal Peru are more complex than previously thought, that the nutritional values of terrestrial versus maritime foods are debatable, that the dynamics of El Niño events are complex, and that maritime resources must still be seen as important for Preceramic Period economies. [Central Andes, coastal adaptations, ecological anthropology, origins of complex societies]     

Seasonal, El Niño and longer term changes in flower and seed production in a moist tropical forest

It has recently been reported that humid tropical forests are changing rapidly in response to global anthropogenic change and that these forests experience greater tree mortality and even fire during droughts associated with El Niño events. The former reports are controversial largely because a single method has been used – repeated censuses of tree plots. The latter reports focus on recent extreme El Niño events. Here, we show that flower and seed production both increase during El Niño events in an old-growth tropical forest in Panama. Flower production, but not seed production, has also increased over the past 18 years. The sustained increase in flower production was greater for 33 liana species than for 48 tree species. These results indicate that moderate El Niño events favour seed production, document long-term increases in flower production for the first time, and corroborate long-term increases in the importance of lianas using independent methods. Changes in levels of solar irradiance might contribute to all three patterns.     

Sea-surface temperature estimates in the Southeast Pacific based on planktonic foraminiferal species; modern calibration and Last Glacial Maximum

Estimates of sea-surface temperatures based on foraminiferal faunal species suggest that the Eastern Equatorial Pacific Ocean was 3–5°C cooler during the Last Glacial Maximum (LGM) than at present. Analysis of new cores from the Southeast Pacific reveals a likely source of ice-age cooling in variations of the Peru Current. Off southern Peru, LGM ocean temperatures were 6–8°C cooler than at present, consistent with substantial cooling on land inferred from regional glacier advances and ice-core data. In the Southeast Pacific, ice-age foraminiferal assemblages have good modern analogs, and transfer functions that define assemblages based on ancient samples yield results similar to those based on coretop samples. During the LGM, subpolar species dominate the Eastern Boundary Current off Peru and extend to the equator. In contrast, the range of the equatorial upwelling species remains roughly constant. We infer from these data and a heat budget model that equatorward advection of cool water, more than equatorial upwelling, drove LGM cooling of the Eastern Tropical Pacific Ocean.     

The impact of El Niño events on the pelagic food chain in the northern California Current

The zooplankton of the northern California Current are typically characterized by an abundance of lipid‐rich copepods that support rapid growth and survival of ecologically, commercially, and recreationally valued fish, birds, and mammals. Disruption of this food chain and reduced ecosystem productivity are often associated with climatic variability such as El Niño events. We examined the variability in timing, magnitude, and duration of positive temperature anomalies and changes in copepod species composition in the northern California Current in relation to 10 tropical El Niño events. Measurable impacts on mesozooplankton of the northern California Current were observed during seven of 10 of these events. The occurrence of anomalously warm water and the response of the copepod community was rapid (lag of zero to 2 months) following the initiation of canonical Eastern Pacific (EP) events, but delayed (lag of 2–8 months) following ‘Modoki’ Central Pacific (CP) events. The variable lags in the timing of a physical and biological response led to impacts in the northern California Current peaking in winter during EP events and in the spring during CP events. The magnitude and duration of the temperature and copepod anomalies were strongly and positively related to the magnitude and duration of El Niño events, but were also sensitive to the phase of the lower frequency Pacific Decadal Oscillation. When fisheries managers and biological oceanographers are faced with the prospect of a future El Niño event, prudent management and observation will require consideration of the background oceanographic conditions, the type of event, and both the magnitude and duration of the event when assessing the potential physical and biological impacts on the northern California Current.     

El Niño,Climate, and Cholera Associations in Piura,Peru, 1991–2001: A Wavelet Analysis

In Peru, it was hypothesized that epidemic cholera in 1991 was linked to El Niño, the warm phase of El Niño–Southern Oscillation. While previous studies demonstrated an association in 1997–1998, using cross-sectional data, they did not assess the consistency of this relationship across the decade. Thus, how strong or variable an El Niño–cholera relationship was in Peru or whether El Niño triggered epidemic cholera early in the decade remains unknown. In this study, wavelet and mediation analyses were used to characterize temporal patterns among El Niño, local climate variables (rainfall, river discharge, and air temperature), and cholera incidence in Piura, Peru from 1991 to 2001 and to estimate the mediating effects of local climate on El Niño–cholera relationships. The study hypothesis is that El Niño-related connections with cholera in Piura were transient and interconnected via local climate pathways. Overall, our findings provide evidence that a strong El Niño–cholera link, mediated by local hydrology, existed in the latter part of the 1990s but found no evidence of an El Niño association in the earlier part of the decade, suggesting that El Niño may not have precipitated cholera emergence in Piura. Further examinations of cholera epicenters in Peru are recommended to support these results in Piura. For public health planning, the results may improve existing efforts that utilize El Niño monitoring for preparedness during future climate-related extremes in the region.     

Variation in a sparrow's reproductive success with rainfall: food and predator-mediated processes

From 1997 to 1999, we monitored the reproductive success of individual rufous-crowned sparrows (Aimophila ruficeps) in coastal sage scrub habitat of southern California, USA. Annual reproductive output of this ground-nesting species varied strongly with annual variation in rainfall, attributed to the El Niño-Southern Oscillation. Birds fledged 3.0 young per breeding pair in 1997, when rainfall was near the long-term mean, 5.1 offspring per pair in 1998, a wet El Niño year, and 0.8 fledglings per pair in 1999, a dry La Niña year. Variation in many components of reproductive output was consistent with the hypothesis that food availability was positively correlated with rainfall. However, the factor most responsible for the high reproductive output in 1998 was low early season nest predation which, combined with favorable nesting conditions, enabled more pairs to multiple-brood. Cool, rainy El Niño conditions may have altered the activity of snakes, the main predator of these nests, in the early season of 1998. Overall, more of the annual variation in fecundity was attributable to variation in within-season components of reproductive output (mean number of nests fledged per pair) than to within-nest components (mean brood size). Annual variation in rufous-crowned sparrow fecundity appears to be driven primarily by food resource-mediated processes in La Niña years and by predator-mediated processes in El Niño years.     

Effects of warm sea-surface temperature anomalies on the blue petrel at the Kerguelen Islands

Several long-term studies on Southern Ocean seabirds and seals have suggested a possible link between major declines in breeding performance and El Niño Southern Oscillation events. We report that the breeding performances and body condition of the blue petrel (Halobaena carulea) on the Kerguelen Islands is depressed by episodic, warm sea-surface temperatures (SSTs) in the winter before breeding. Lagged cross correlations between SSTs in the Kerguelen sector and the Southern Oscillation Index indicate that warm SSTs were found south of Kerguelen Islands within a year of, and between 4.2 and 5.4 years after, an El Niño event took place. These results can be discussed with respect to the recently described Antarctic Circumpolar Wave that drives climatic anomalies eastward around the Southern Ocean.     

Climate shifts the interaction web of a marine plankton community

Climatic effects in the ocean at the community level are poorly described, yet accurate predictions about ecosystem responses to changing environmental conditions rely on understanding biotic responses in a food‐web context to support knowledge about direct biotic responses to the physical environment. Here we conduct time‐series analyses with multivariate autoregressive (MAR) models of marine zooplankton abundance in the Northern California Current from 1996 to 2009 to determine the influence of climate variables on zooplankton community interactions. Autoregressive models showed different community interactions during warm vs. cool ocean climate conditions. Negative ecological interactions among zooplankton groups characterized the major warm phase during the time series, whereas during the major cool phase, ocean transport largely structured zooplankton communities. Local environmental conditions (sea temperature) and large‐scale climate indices (El Niño/Southern Oscillation) were associated with changes in zooplankton abundance across the full time series. Secondary environmental correlates of zooplankton abundance varied with ocean climate phase, with most support during the warm phase for upwelling as a covariate, and most support during the cool phase for salinity. Through simultaneous quantitation of community interactions and environmental covariates, we show that marine zooplankton community structure varies with climate, suggesting that predictions about ecosystem responses to future climate scenarios in the Northern California Current should include potential changes to the base of the pelagic food.     

Response of a rocky intertidal ecosystem engineer and community dominant to climate change

To evaluate how climate change might impact a competitively dominant ecological engineer, we analysed the growth response of the mussel Mytilus californianus to climate patterns [El Niño-Southern Oscillation, Pacific Decadal Oscillation (PDO)]. Mussels grew faster during warmer climatic events. Growth was initially faster on a more productive cape compared to a less productive cape. Growth rates at the two capes merged in 2002, coincidentally with a several year-long shift from warm to cool PDO conditions. To determine the mechanism underlying this response, we examined growth responses to intertidal sea and air temperatures, phytoplankton, sea level and tide height. Together, water temperature (32%) and food (12.5%) explained 44.5% of the variance in mussel growth; contributions of other factors were not significant. In turn, water temperature and food respond to climate-driven variation in upwelling and other, unknown factors. Understanding responses of ecosystem engineers to climate change will require knowing direct thermal effects and indirect effects of factors altered by temperature change.     

Occurrence and distribution of Vibrio cholerae in the coastal environment of Peru

The occurrence and distribution of Vibrio cholerae in sea water and plankton along the coast of Peru were studied from October 1997 to June 2000, and included the 1997-98 El Ni?o event. Samples were collected at four sites in coastal waters off Peru at monthly intervals. Of 178 samples collected and tested, V. cholerae O1 was cultured from 10 (5.6%) samples, and V. cholerae O1 was detected by direct fluorescent antibody assay in 26 out of 159 samples tested (16.4%). Based on the number of cholera cases reported in Peru from 1997 to 2000, a significant correlation was observed between cholera incidence and elevated sea surface temperature (SST) along the coast of Peru (P < 0.001). From the results of this study, coastal sea water and zooplankton are concluded to be a reservoir for V. cholerae in Peru. The climate-cholera relationship observed for the 1997-98 El Ni?o year suggests that an early warning system for cholera risk can be established for Peru and neighbouring Latin American countries.     

Spatiotemporal fire occurrence in Borneo over a period of 10 years

South-east Asia's tropical rainforests are experiencing the highest rate of deforestation worldwide and fire is one of the most important drivers of forest loss and subsequent carbon dioxide emissions. In this study, we analyzed all fire events in Borneo recorded by satellites over a period of 10 years. About 16.2 Mha, which corresponds to 21% of the land surface, have been affected by fire at least once and 6% more than one time. During El Niño conditions, which cause prolonged droughts in the region, the fire-affected area was on average three times larger than during normal weather conditions. Similarly, fires in forests affected 0.3 Mha in normal years and 1 Mha during El Niño years. Carbon rich peat swamp forest ecosystems were most severely affected. There is a pronounced difference in fire occurrence between different countries and provinces in Borneo although ecosystem and land use are very similar across the island. Compared with Sarawak, Sabah (Malaysia) and Brunei the relative annual fire-affected area in Kalimantan, the Indonesian part of Borneo, was on average five times larger. During El Niño conditions the fire-affected area increased only in Kalimantan and not in Brunei and the Malaysia. A similar pattern was observed in National Parks. This suggests, that El Niño related droughts are not the only cause of increased fire occurrence and do not necessarily lead to a higher number of fire events. These results improve our understanding of existing fire regimes and drivers of fire in SE Asian tropical ecosystems and may help to better protect the remaining rainforests.     

Vietation changes over three decades on Santa Fe Island, Galhpagos, Ecuador

Changes in mortality and turnover of selected woody plants which dominate and characterise the arid vegetation of the island of Santa Fe, Galapagos, have been studied regularly during the period 1972–2003. After the eradication of feral goats from Santa Fe in 1971, the vegetation started to recover. The previously threatened small tree Scalesia helleri ssp. helleri recovered and some recruitment of the dominant trees Opuntia echios var. barringtonensis and Bursera graveolens took place. The dominant shrub species Cordia lutea, Encelia hispida and Lantana peduncularis increased in number, whereby the shrub layer is becoming denser and the structure of the predominant dry season deciduous steppe forest vegetation is changing. The strong impact of El Niño on the survival and recruitment of Opuntia indicates that recovery of Opuntia-dominated vegetation should be viewed on a time-scale of perhaps 150 years or more, in correspondence with the long life-expectancy of adult Opuntia individual. It is suggested that recruitment and survival of Opuntia may be hindered if future El Niño events are to occur with increased strength, and that this would alter the aspect of the Santa Fe vegetation.