Coral reef resilience to thermal stress in the Eastern Tropical Pacific.

Coral reefs worldwide are threatened by thermal stress caused by climate change. Especially devastating periods of coral loss frequently occur during El Niño-Southern Oscillation (ENSO) events originating in the Eastern Tropical Pacific (ETP). El Niño-induced thermal stress is considered the primary threat to ETP coral reefs. An increase in the frequency and intensity of ENSO events predicted in the coming decades threatens a pan-tropical collapse of coral reefs. During the 1982-1983 El Niño, most reefs in the Galapagos Islands collapsed, and many more in the region were decimated by massive coral bleaching and mortality. However, after repeated thermal stress disturbances, such as those caused by the 1997-1998 El Niño, ETP corals reefs have demonstrated regional persistence and resiliency. Using a 44 year dataset (1970-2014) of live coral cover from the ETP, we assess whether ETP reefs exhibit the same decline as seen globally for other reefs. Also, we compare the ETP live coral cover rate of change with data from the maximum Degree Heating Weeks experienced by these reefs to assess the role of thermal stress on coral reef survival. We find that during the period 1970-2014, ETP coral cover exhibited temporary reductions following major ENSO events, but no overall decline. Further, we find that ETP reef recovery patterns allow coral to persist under these El Niño-stressed conditions, often recovering from these events in 10-15 years. Accumulative heat stress explains 31% of the overall annual rate of change of living coral cover in the ETP. This suggests that ETP coral reefs have adapted to thermal extremes to date, and may have the ability to adapt to near-term future climate-change thermal anomalies. These findings for ETP reef resilience may provide general insights for the future of coral reef survival and recovery elsewhere under intensifying El Niño scenarios.

The Eastern Tropical Pacific coral population connectivity and the role of the Eastern Pacific Barrier.

Long-distance dispersal is believed to strongly influence coral reef population dynamics across the Tropical Pacific. However, the spatial scale and strength at which populations are potentially connected by dispersal remains uncertain. To determine the patterns in connectivity between the Eastern (ETP) and Central Tropical Pacific (CTP) ecoregions, we used a biophysical model incorporating ocean currents and larval biology to quantify the seascape-wide dispersal potential among all population. We quantified the likelihood and determined the oceanographic conditions that enable the dispersal of coral larvae across the Eastern Pacific Barrier (EP-Barrier) and identified the main connectivity pathways and their conservation value for dominant reef-building corals. Overall, we found that coral assemblages within the CTP and ETP are weakly connected through dispersal. Although the EP-Barrier isolates the ETP from the CTP ecoregion, we found evidence that the EP-Barrier may be breached, in both directions, by rare dispersal events. These rare events could explain the evolutionary genetic similarity among populations of pocilloporids in the ecoregions. Moreover, the ETP may function as a stronger source rather than a destination, providing potential recruits to CTP populations. We also show evidence for a connectivity loop in the ETP, which may positively influence long-term population persistence in the region. Coral conservation and management communities should consider eight-key stepping stone ecoregions when developing strategies to preserve the long-distance connectivity potential across the ETP and CTP.

Efecto de bordessobre el proceso de descomposición de hojarasca en bosque nublado / Edge Effect on the Decomposition Process of Leaf Litter in Cloud Forest

Los fragmentos de bosque están delimitados por bordes y rodeados de matriz circundante. La interacción entre estas comunidades disímiles en estructura y composición, se define como efecto de borde. Este fenómeno genera localmente cambios abióticos y bióticos alterando procesos ecosistémicos del suelo. Para determinar la existencia de este efecto sobre la descomposición de hojarasca y sus factores de control, se seleccionaron dos fragmentos de bosque nublado en la Sabana de Bogotá. En cada fragmento se trazaron transectos con longitud de 64 m en dirección oriente-interior y occidente-interior, donde se dispusieron en siete distancias desde el borde experimentos de descomposición de hojarasca con duración de 90 y 180 días. En cada transecto y distancias se estimaron el porcentaje de descomposición y humedad de hojarasca, densidad de vegetación, densidad de hongos anamorfos y relación carbono:nitrógeno. Se determinaron la distancia máxima del efecto de borde sobre la descomposición y su interacción con la orientación, distancia y factores reguladores. Se evidenció un efecto de la orientación cardinal del borde sobre la descomposición y sobre sus factores reguladores. En las zonas de borde oriental se presentó un efecto de borde marcado sobre la humedad de hojarasca hasta los 7 m y sobre la densidad de vegetación hasta los 30 m. En los fragmentos de bosque la descomposición fue regulada por la humedad y la relación C:N de la hojarasca. La poca penetración del borde sugiere efectos menores sobre el ciclaje de nutrientes, proporcionando un valor adicional a la conservación de fragmentos pequeños.

Forest fragments are physically delimited by edges and encircled by a surrounding matrix. The interaction between these communities dissimilar in structure and composition is defined as the edge effect. This occurrence generates local abiotic and biotic changes altering soil ecosystem processes. To determine the existence of the effect on leaf litter decomposition and its control factors, two fragments of cloud forest in the southwest region of the Bogotá Savannah were selected. Within each, two 64 m long transects were laid out bearing east and west from edge to center respectively, a leaf litter decomposition experiment of a 90 to 180 day duration was set up at seven distances measured from the starting point of each transect. The percentage of leaf litter moisture and decomposition, vegetation density, anamorphic fungi density and carbon:nitrogen ratio were estimated at each point. The maximum distance of the edge effect on the decomposition was determined, and the interaction between orientation, distance and the regulating factors of the decomposition process were ascertained. The results established an effect of the cardinal orientation of the edge on the decomposition and its regulating factors. Marked edge effects on leaf litter moisture extending up to 7 m and up to 30 m on vegetation density were displayedin Eastern border areas. In forest areas, decomposition was regulated by leaf litter moisture and its C:N ratio. The limited penetration of edge effect suggests minor effects regarding nutrient cycles and provides justification and additional value to the use of small fragments.