El Niño effects on the dynamics of terrestrial ecosystems

New studies are showing that the El Ni?o Southern Oscillation (ENSO) has major implications for the functioning of different ecosystems, ranging from deserts to tropical rain forests. ENSO-induced pulses of enhanced plant productivity can cascade upward through the food web invoking unforeseen feedbacks, and can cause open dryland ecosystems to shift to permanent woodlands. These insights suggest that the predicted change in extreme climatic events resulting from global warming could profoundly alter biodiversity and ecosystem functioning in many regions of the world. Our increasing ability to predict El Ni?o effects can be used to enhance management strategies for the restoration of degraded ecosystems.     

The El Niño southern oscillation and malaria epidemics in South America

A better understanding of the relationship between the El Ni?o Southern Oscillation (ENSO), the climatic anomalies it engenders, and malaria epidemics could help mitigate the world-wide increase in incidence of this mosquito-transmitted disease. The purpose of this paper is to assess the possibility of using ENSO forecasts for improving malaria control. This paper analyses the relationship between ENSO events and malaria epidemics in a number of South American countries (Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname, and Venezuela). A statistically significant relationship was found between El Ni?o and malaria epidemics in Colombia, Guyana, Peru, and Venezuela. We demonstrate that flooding engenders malaria epidemics in the dry coastal region of northern Peru, while droughts favor the development of epidemics in Colombia and Guyana, and epidemics lag a drought by 1 year in Venezuela. In Brazil, French Guiana, and Ecuador, where we did not detect an ENSO/malaria signal, non-climatic factors such as insecticide sprayings, variation in availability of anti-malaria drugs, and population migration are likely to play a stronger role in malaria epidemics than ENSO-generated climatic anomalies. In some South American countries, El Ni?o forecasts show strong potential for informing public health efforts to control malaria.     

Effects of El Niño drought on seedling dynamics in a seasonally dry tropical forest in Northern Thailand

As El Niño is predicted to become stronger and more frequent in the future, it is crucial to understand how El Niño-induced droughts will affect tropical forests. Although many studies have focused on tropical rainforests, there is a paucity of studies on seasonally dry tropical forests (SDTFs), particularly in Asia, and few studies have focused on seedling dynamics, which are expected to be strongly affected by drought. Seedlings in SDTFs are generally more drought-tolerant than those in the rainforests, and the effects of El Niño-induced droughts may differ between SDTF and tropical rainforests. In this study, we explored the impact of El Niño-induced drought at an SDTF in northern Thailand by monitoring the seedling dynamics at monthly intervals for 7 years, including a period of strong El Niño. The effects were compared between two forest types in an SDTF: a deciduous dipterocarp forest (DDF), dominated by deciduous species, and an adjacent lower montane forest (LMF) with more evergreen species. El Niño-induced drought increased seedling mortality in both the forest types. The effect of drought was stronger in evergreen than in the deciduous species, resulting in higher mortality in the LMF during El Niño. However, El Niño increased seedling recruitment only in the DDF, mainly because of the massive recruitment of the deciduous oak, Quercus brandisiana (Fagaceae), which compensated for the mortality of seedlings in the DDF. As a result, El Niño increased seedling density in the DDF and decreased it in the LMF. This is the first long-term study to identify the differences in the impacts of El Niño on seedlings between the two forest types, and two leaf habits, evergreen and deciduous, in Southeast Asia. Our findings suggest that future climate change may alter the species composition and spatial distribution of seedlings in Asian SDTFs.     

Drastic effects of El Niño on Galapagos pinnipeds

Summary Population dynamics of pinnipeds living in the tropical upwelling ecosystem of the Galapagos were strongly influenced by the 1982–83 Southern Oscillation-El Niño (EN) event which was the strongest recorded in this century. The Galapagos fur seal (Arctocephalus galapagoensis) population lost the four youngest year classes (1980–1983) almost entirely and approximately 30% of the adult females and non-territorial males. Mortality of large territorial males was almost 100%. Most of the 1982 year class of Galapagos sea lions (Zalophus californianus wollebaeki) died and there was a much lower pup production in the breeding season following EN. Recurrent EN events must strongly influence age structure and average population size of these and other otariid species depending on tropical upwelling ecosystems.     

The impact of El Niño events on populations of mesopelagic hydromedusae

For over 10 years, the midwater ecology group at MBARI has compiled video and accompanying physical data with the ROV Ventana operating in mesopelagic depths of Monterey Bay, CA in order to elucidate patterns in midwater ecology. Two El Niño events have occurred during this time period, in 1991–92 and in 1997–98. The oceanographic metric of spiciness combines temperature and salinity data into one sensitive measurement. Although temperature and salinity measurements alone revealed no clear patterns, clear signals of spiciness were observed that corresponded to water mass intrusions into the deep waters of the bay during the two El Niño events. During these events, some seldom-seen species were observed in high numbers in the midwater, while historically common species became rare. During non-El Niño years, the leptomedusa Mitrocoma cellularia(A. Agassiz, 1865) was common in the surface waters (0–50 m) of Monterey Bay, but it was not abundant at depth, while the trachymedusa Colobonema sericeum Vanhöffen, 1902 was found in relatively high numbers at mesopelagic depths. During the last two El Niño events, M. cellulariawas observed in higher numbers at mesopelagic depths, whereas C. sericeum was scarce. M. cellularia was found in a wider range of temperatures, salinities, and dissolved oxygen values than was C. sericeum. Transport and tolerance hypotheses are proposed to explain differences in the presence and numerical density of the medusae.     

Early-season warning of soybean rust regional epidemics using El Niño Southern/Oscillation information

Soybean rust (SBR) is a disease of significant impact to Brazilian soybean production. Twenty-four locations in a major growing region in southern Brazil, where long-term (30 years) weather information was available, were selected to estimate the risk of SBR epidemics and identify potential predictors derived from El Niño 3.4 region. A rainfall-based model was used to predict SBR severity in an “epidemic development window” (the months of February and March for the studied region) in the time series. Twenty-eight daily simulations for each year-location (n = 720) were performed considering each day after 31 January as a hypothetical detection date (HDD) to estimate a severity index (SBRindex). The mean SBRindex in a single year was defined as the ‘growing season severity index’ (GSSI) for that year. A probabilistic risk assessment related GSSI and sea surface temperatures (SST) at the El Niño 3.4. region (here categorized as warm, cold or neutral phase) in October–November–December (OND) of the same growing season. Overall, the median GSSI across location-years was 34.5%. The risk of GSSI exceeding 60% was generally low and ranged from 0 to 20 percentage points, with the higher values found in the northern regions of the state when compared to the central-western. During a warm OND-SST phase, the probability of GSSI exceeding its overall mean (locations pooled) increased significantly by around 25 percentage points compared to neutral and cold SST phases, especially over the central western region. This study demonstrates the potential to use El Niño/Southern Oscillation information to anticipate the risk of SBR epidemics up to 1 month in advance at a regional scale.     

El Niño effects on soil seed bank dynamics in north-central Chile

The soil seed bank was monitored in four 75×75 m plots over 6 years (1990–1995) in an arid thorn scrub community in north-central Chile. Sixty-six species were identified. Total seed densities ranged from 2,000 to 42,000/m². Average mass of shrub seeds was significantly greater than that of other growth-forms. Between 70 and 90% of the seeds were less than 1 mg, with those in the 0.51–1.00 mg size class being most numerous. Seed densities were highly variable between years as well as within years, but were also closely associated with plant cover patterns and rainfall regime. Higher seed densities were found in wet years, and in samples taken in early summer and early autumn (i.e., after seed set); the lowest seed densities were in late winter (i.e., after annual plant germination). The annual plant species with the highest cover were also the most abundant in the soil seed bank and exhibited the largest seed density fluctuations. In general, seed densities were 5- to 10-fold higher during the 1991–1992 El Niño/southern oscillation (ENSO) years than non-ENSO years, showing the importance of this phenomenon for seed bank replenishment in the arid region of Chile.     

Succession of pelagic copepod species in coastal waters off northern Chile: the influence of the 1997–98 El Niño

A 2-year time series (17-d interval) of zooplankton, sampled from June 1996 through January 1998, along with oceanographic data, allowed the study of species abundances and diversity during non-El Niño and El Niño conditions at Mejillones (23° S), northern Chile. A total of 28 species was identified, of which the most abundant were the calanoids Paracalanus parvus, Calanus chilensis, Acartia tonsa, and Centropages brachiatus, the cyclopoid Oithona similis, and the poecilostomatoids Oncaea conifera and Corycaeus typicus. El Niño Southern Oscillation (El Niño) was first detected in the area in May 1997 and persisted until March 1998. We divided the time series into two parts: non-El Niño and El Niño conditions. The number of species significantly increased during El Niño conditions, but total abundance of copepods was greater during non-El Niño conditions. Although some expatriate species appeared during El Niño, such as the harpacticoid Microsetella norvegica and Eucalanus subtenuis, the diversity index of Hulburt was not significantly different between the two periods. Despite the dramatic alteration of oceanographic conditions during the El Niño period, we concluded that the community of pelagic copepods was not subject to drastic changes either in total abundance or in structure.     

Repercussions of El Niño: drought causes extinction and the breakdown of mutualism in Borneo

Figs (Ficus spp.) and their species-specific pollinators, the fig wasps (Agaonidae), have coevolved one of the most intricate interactions found in nature, in which the fig wasps, in return for pollination services, raise their offspring in the fig inflorescence. Fig wasps, however, have very short adult lives and hence are dependent on the near-continuous production of inflorescences to maintain their populations. From January to March 1998 northern Borneo suffered a very severe drought linked to the El Niño-Southern Oscillation event of 1997-1998. This caused a substantial break in the production of inflorescences on dioecious figs and led to the local extinction of their pollinators at Lambir Hills National Park, Sarawak, Malaysia. Most pollinators had not recolonized six months after the drought and, given the high level of endemism and wide extent of the drought, some species may be totally extinct. Cascading effects on vertebrate seed dispersers, for which figs are often regarded as keystone resources, and the tree species dependent on their services are also likely. This has considerable implications for the maintenance of biodiversity under a scenario of climate change and greater climatic extremes.     

“El Niño” events recorded in dry-forest species of the lowlands of northwest Peru

The northwest coast of Peru (5°S, 80°W) is very sensitive to and impacted by the climate phenomenon El Niño-Southern Oscillation (ENSO). Though mainly desert, this warm, dry region contains an equatorial dry forest. We report the first dendrochronological studies from this region and identify several species that have dendrochronological potential. Short ring-width chronologies of Palo Santo (Bursera graveolens) show a well-developed response to the ENSO signal over the last 50 years and good inter-site correlations. Preliminary isotopic studies in Algarrobo (Prosopis sp.) also show evidence of the 1997–98 El Niño event. ENSO events have a strong effect on the variability in the growth of several species and thereby on the economy of rural communities where the wood is used for housing, cooking, furniture, tools, fodder and medicinal uses. The extensive use of wood in archeological sites also offers the possibility of ultimately developing longer records for some of these species.     

Effects of the 1991-92 El Niño on scleractinian corals of the Costa Rican central Pacific coast

Coral communities on the central Pacific coast of Costa Rica were affected during the 1991-92 El Ni?o warming event. More than 57% of all observed colonies at three localities (Parque Nacional Manuel Antonio, Punta Cambutal, and Parque Marino Ballena) were bleached. Mortality during this El Ni?o was much lower (approximately 9%) than in previous events. Psammocora spp. accounted for approximately 66% of dead corals, while massive (Porites lobota, Pavona spp.) and branching (Pocillopora spp.) for approximately 34%. Our results suggest that the observed bleaching in P. lobata was related to zooxanthellar densities and not to changes in pigment concentrations: only chlorophyll a varied between normally pigmented and bleached colonies at one locality (Ballena). Site differences in zooxanthellar densities or their pigment concentrations, may not be the result of the bleaching event itself, because a percentage of dead corals and zooxanthellar densities of bleached colonies seems to follow a trend with the exposure to tidal regimes and currents at each site. Local oceanographic conditions can be influencing the zooxanthellar densities and their response to the warming, together with intrinsic differences between colonies as well. The impact of this event can be considered serious given the short period of time that elapsed between El Ni?o related mortalities and the slow reefs recovery, the mode of reproduction of reef building species, and the anthropogenic-originated disturbances which affect the coral communities and reefs of the Costa Rican central Pacific coast.     

El Niño 1997-1998 impact on the plankton dynamics in the Gulf of Nicoya, Pacific coast of Costa Rica

The impact of the El Ni?o 1997-1998 phenomenom on plankton dynamics was studied during 1997 at the Punta Morales estuary, Gulf of Nicoya, Pacific coast of Costa Rica. The study covered dry season/transition and the rainy season. Phytoplankton (microphytoplankton > 30 microm and nanophytoplankton) were collected at two depths (50 and 10% light incidence) using a 5 L Niskin bottle, and samples taken to determine chlorophyll a. Temperature, salinity, oxygen, and Secchi depth were measured. Horizontal sub-surface zooplankton hauls were conducted with a conic zooplankton net of 0.49 m diameter and 280 microm mesh width, supplied with a flowmeter. Surface sea water temperature average was 29.9 +/- 0.9 degrees C, with a maximum of 31.5 degrees C in April and a minimun of 28 degrees C in March and October. Chlorophyll a concentration (phytoplankton net) averaged 3.1 +/- 1.7 mg/m3, with higher values during the rainy season and lower values during the transition. Nanophytoplankton chlorophyll a concentration averaged 2.5 +/- 1.2 mg/m3, with a maximum during the transition season. For both fractions there were significant differences between transition and rainy seasons, and for nanophytoplankton between dry and transition seasons (p < 0.05). In the last case, differences were explained by temperature. Herbivorous copepods dominated the abundance and biomass of zooplankton, with a biomass maximun of 167.3 in October and a minimun of 7.1 mg DW/m3 in December. These values are higher than those found some years ago in the same zone and those reported for some places in the Caribbean. The El Ni?o 1997-1998 phenomenon in the plankton dynamics appears to have produced a change in the phytoplankton structure. This is the first attempt to evaluate the possible impact of El Ni?o on the plankton dynamics of the Pacific coast of Central America.     

Lesions in octocorals of the Costa Rican Caribbean During The 2015–2016 El Niño

Coral Reefs - Emerging infectious diseases affecting marine ecosystems are increasing worldwide. Nevertheless, there are very few histopathological analyses describing the tissue damage associated...     

El Niño as a Window of Opportunity for the Restoration of Degraded Arid Ecosystems

Most arid ecosystems have suffered from severe overexploitation by excessive wood harvesting, overgrazing, and agriculture, resulting in depletion of vegetation biomass and soil erosion. These changes are often difficult to reverse due to positive feedbacks that tend to stabilize the new situation. In this paper, we briefly review evidence for the idea that different states in these ecosystems might represent alternative equilibria and present a graphic model that summarizes the implications for their response to changing environmental conditions. We show how, in the light of this theoretical framework, climatic oscillations such as El Niño Southern Oscillation (ENSO) could be used in combination with grazer control to restore degraded arid ecosystems. We also present evidence that, depending on grazing pressure, ENSO episodes can trigger structural and long-lasting changes in these ecosystems.     

El Niño,volcanism, and global climate

The June 1991 eruption of Mt. Pinatubo in the Philippines produced one of the greatest volcanic aerosols in the last hundred years. The estimated net decrease of radiation may have peaked at 10% in the tropics. What was the impact of the Pinatubo aerosol on regional and global climate? Besides the expected net cooling of the average global surface temperature, correlation studies indicate that other types of climate anomalies may also be expected. These include the appearance of an El Niño event, decreased Indian monsoon rainfall, fewer tropical storms in the north Atlantic Ocean in 1991–1993, and normal to above normal winter rainfall in California in 1991/92, all of which were observed. A proposed physical mechanism for the almost-simultaneous occurrence of this constellation of climate anomalies is presented. The results of correlation studies between low-latitude volcanic aerosols and the El Niño/Southern Oscillation are presented in some detail as one example. The correlation between Indian monsoon rainfall and tropical storms in the north Atlantic Ocean is also shown and is updated for the most recent 5 years.     

Aboveground Forest Carbon Dynamics in Papua New Guinea: Isolating the Influence of Selective-Harvesting and El Niño

Assessment of forest carbon (C) stock and sequestration and the influence of forest harvesting and climatic variations are important issues in global forest ecology. Quantitative studies of the C balance of tropical forests, such as those in Papua New Guinea (PNG), are also required for forest-based climate change mitigation initiatives. We develop a hierarchical Bayesian model (HBM) of aboveground forest C stock and sequestration in primary, selectively harvested, and El Niño Southern Oscillation (ENSO)-effected lowland tropical forest from 15 years of Permanent Sample Plot (PSP) census data for PNG consisting of 121 plots in selectively harvested forest, and 35 plots in primary forest. Model parameters indicated: C stock in aboveground live biomass (AGLB) of 137 ± 9 (95% confidence interval (CI)) MgC ha^?1 in primary forest, compared with 62 ± 18 MgC ha^?1 for selectively harvested forest (55% difference); C sequestration in primary forest of 0.23 ± 1.70 MgC ha^?1 y^?1, which was lower than in selectively harvested forest, 1.12 ± 3.41 MgC ha^?1 y^?1; ENSO-induced fire resulted in significant C emissions (?6.87 ± 3.94 MgC ha^?1 y^?1). High variability between PSPs in C stock and C sequestration rates necessitated random plot effects for both stock and sequestration. The HBM approach allowed inclusion of hierarchical autocorrelation, providing valid CIs on model parameters and efficient estimation. The HBM model has provided quantitative insights on the C balance of PNG’s forests that can be used as inputs for climate change mitigation initiatives.     

Mass Mortality of Coral Reef Ascidians Following the 1997/1998 El Niño Event

In April/May each year from 1995 to 2000, ascidians were sampled randomly with 35 1m² quadrats from three different reef habitats (intertidal reef tops, coastal reef walls and shallow-bank reefs) at four replicate localities (Praia do Forte, Itacimirim, Guarajuba and Abai) in northern Bahia (Brazil). As the sampling period included the 1997/1998 El Niño event, the most severe on record, for the first time these results allow a quantitative assessment of the impact of this major environmental stressor on the biodiversity of associated coral reef ascidians. Across all reef habitats, 22 ascidian species were recorded from three different orders (Aplousobranchia, Phlebobranchia and Stolidobranchia). After El Niño, all species showed significantly altered densities (ANOVA, F=602.90, p<0.0001); many species were absent from the reefs within 2 years of the El Niño period, but densities of Lissoclinum perforatum (all reefs) and Echinoclinum verrilli (subtidal reefs) increased significantly from 1998 onwards. Univariate and multivariate analyses confirmed that significant changes in assemblage composition had occurred. BIOENV analysis identified turbidity, mean temperature and cloud cover as the main factors best explaining these assemblage changes. Our results suggest that although the 1997/1998 El Niño had a differential effect on the species contributing to the ascidian assemblage of Brazilian coral reefs, most species disappeared and those remaining are likely to enhance reef degradation through their bioeroding activities.     

El Niño in the warm tropics: local sea temperature predicts breeding parameters and growth of blue-footed boobies

1. There is increasing interest in the impacts of El Ni?o Southern Oscillation (ENSO) on reproduction of apical predators such as seabirds and marine mammals. Long-term studies documenting ENSO effects on reproduction of seabirds in the warm tropics are scarce, and differential sensitivity of breeding parameters to ENSO has rarely been explored. 2. Analysis of 18 years of breeding data from a colony of the blue-footed booby Sula nebouxii (Milne-Edwards) showed a delay in onset of breeding when the global Southern Oscillation Index was negative; each unit of the atmospheric pressure differential (hPa) across the Pacific Ocean meant a delay of 7 days. 3. ENSO conditions also produced declines in breeding participation, clutch size, brood size, hatching success and fledging success, especially when surface waters surrounding the colony were warmer during winter and spring. Each additional degree (°C) of water temperature produced a reduction of 0.45 fledglings per nest. Different breeding parameters were sensitive to ENSO indices in different blocks of months. 4. Warming of local waters during the winter was associated with decline in ocean productivity in the current year and the following year, consistent with ENSO impacts on breeding parameters being mediated by effects on local productivity and prey availability. However, there was no evidence of lagged effects of ENSO on any breeding parameter. 5. Comparison of 5 years revealed that when local surface waters were warm, chicks grew more slowly, but no effects of ENSO on weight and size of eggs were evident in data of 9 and 7 years, respectively. 6. Our findings extend evidence of impacts of ENSO on seabird reproduction to the eastern tropical Pacific and indicate that several breeding parameters of blue-footed boobies (but not egg size) are affected in the short term by ENSO conditions, particularly by local anomalies in sea surface temperature associated with decline in ocean productivity.     

Impact of the 1998 El Niño event on a Lake Charr, Salvelinus Namaycush, Population Recovering from Acidification

This study provides a case history of the impact of the 1998 El Ni no event on a lake charr population in a shallow (maximum depth = 13m) lake in the southern boreal shield ecozone of Ontario. The lake lost its native charr population by acidification from air-borne pollutants in the 1950–1960s. A naturally reproducing population was re-established through hatchery stocking after the water quality improved in the 1980s. The warm years triggered by the El Ni no event exposed fish to bottom water temperatures of 20°C for several weeks and resulted in the loss of all hatchery-reared juveniles that were released in 1998. A few adults survived the warm years by making use of cold water refuge areas (groundwater seepage). This study shows how climate change can eliminate charr populations at the margins of their range. It also illustrates the potential confounding effects of climate warming on aquatic ecosystems already subject to other stressors.     

El Niño droughts and their effects on tree species composition and diversity in tropical rain forests

In this study I investigated the effects of the extreme, 1997/98 El Niño related drought on tree mortality and understorey light conditions of logged and unlogged tropical rain forest in the Indonesian province of East Kalimantan (Borneo). My objectives were to test (1) whether drought had a significant effect on tree mortality and understorey light conditions, (2) whether this effect was greater in logged than in undisturbed forest, (3) if the expected change in tree mortality and light conditions had an effect on Macaranga pioneer seedling and sapling densities, and (4) which (a)biotic factors influenced tree mortality during the drought. The 1997/1998 drought led to an additional tree mortality of 11.2, 18.1, and 22.7% in undisturbed, old logged and recently logged forest, respectively. Mortality was highest in logged forests, due to extremely high mortality of pioneer Macaranga trees (65.4%). Canopy openness was significantly higher during the drought than during the non-drought year (6.0, 8.6 and 10.4 vs 3.7, 3.8 and 3.7 in undisturbed, old logged and recently logged forest, respectively) and was positively correlated with the number of dead standing trees. The increase in light in the understorey was accompanied by a 30 to 300-fold increase in pioneer Macaranga seedling densities. Factors affecting tree mortality during drought were (1) tree species successional status, (2) tree size, and (3) tree location with respect to soil moisture. Tree density and basal area per surface unit had no influence on tree mortality during drought. The results of this study show that extreme droughts, such as those associated with El Niño events, can affect the tree species composition and diversity of tropical forests in two ways: (1) by disproportionate mortality of certain tree species groups and tree size classes, and (2) by changing the light environment in the forest understorey, thereby affecting the recruitment and growth conditions of small and immature trees.