Formation of the Isthmus of Panama

The formation of the Isthmus of Panama stands as one of the greatest natural events of the Cenozoic, driving profound biotic transformations on land and in the oceans. Some recent studies suggest that the Isthmus formed manymillions of years earlier than the widely recognized age of approximately 3 million years ago (Ma), a result that if true would revolutionize our understanding of environmental, ecological, and evolutionary change across the Americas. To bring clarity to the question of when the Isthmus of Panama formed, we provide an exhaustive review and reanalysis of geological, paleontological, and molecular records. These independent lines of evidence converge upon a cohesive narrative of gradually emerging land and constricting seaways,withformationof theIsthmus of Panama sensustricto around 2.8 Ma. The evidence used to support an older isthmus is inconclusive, and we caution against the uncritical acceptance of an isthmus before the Pliocene.Facultad de Ciencias Naturales y Muse

Urban coral reefs: Degradation and resilience of hard coral assemblages in coastal cities of East and Southeast Asia

© 2018 The Author(s) Given predicted increases in urbanization in tropical and subtropical regions, understanding the processes shaping urban coral reefs may be essential for anticipating future conservation challenges. We used a case study approach to identify unifying patterns of urban coral reefs and clarify the effects of urbanization on hard coral assemblages. Data were compiled from 11 cities throughout East and Southeast Asia, with particular focus on Singapore, Jakarta, Hong Kong, and Naha (Okinawa). Our review highlights several key characteristics of urban coral reefs, including “reef compression” (a decline in bathymetric range with increasing turbidity and decreasing water clarity over time and relative to shore), dominance by domed coral growth forms and low reef complexity, variable city-specific inshore-offshore gradients, early declines in coral cover with recent fluctuating periods of acute impacts and rapid recovery, and colonization of urban infrastructure by hard corals. We present hypotheses for urban reef community dynamics and discuss potential of ecological engineering for corals in urban areas

Estudio de la deformacion elasto-plástica de láminas planas de acero SAE 1006 y su relación con el proceso de laminación en frío.

Tesis (Magíster en Ingeniería Mecánica) -- Universidad del Norte. Programa de Maestría en Ingeniería Mecánica, 2007.El objetivo de la presente tesis es desarrollar un gráfico que represente la variación del esfuerzo de fluencia contra el porcentaje de deformación del espesor en láminas de acero SAE 1006 y comprobar un método que basado en esta curva sea capaz de predecir teóricamente la fuerza de laminación que se requiere para reducir el espesor deseado de la lámina e igualmente determinar la potencia que se requiere aplicar en los cilindros de laminación para tal efecto. Para lograr el objetivo se laminó en frío una banda en caliente de 2,00 mm. hasta 0.20 mm. utilizando el laminador reversible cuatro en alto de la empresa Acerìas de Colombia en cinco pasadas de reducción y se capturaron muestras de la lámina con el espesor de cada pasada. Se determino con cada muestra su esfuerzo de fluencia y resistencia ultima y se graficaron los datos para obtener la curva deseada. Con el método simplificado de Ekelund se calcularon los valores teóricos de la fuerza de laminación y la potencia de cada pasada y se compararon con los datos reales obtenidos durante la laminación de la bobina de acero analizada, encontrándose diferencias del 5% entre lo real y teórico, validando el método de Ekelund, como método de calculo rápido, que sirve de guía para los diseñadores de laminadores como para el personal de explotación

Coral and micro-benthic assemblages from reef habitats in Moreton Bay

The subtropical coral reefs of Moreton Bay support a rich diversity of corals and micro-benthic organisms. These high-latitude reef communities exist in marginal environments that include relatively cooler, more light-limited, and more variable environmental conditions than those in the tropics. Holocene reef coral communities formed episodically over the Bay’s 7000-year history, with a high degree of persistence in community structure and reef accretion rate until European colonisation of the Queensland coastline. However, during the most recent phase of the Bay’s reef development, reductions in water quality have transformed the Bay’s coral assemblages from predominantly large, fast-growing and branching acroporid corals to predominantly slower growing and smaller massive corals. The modern composition and diversity of benthic foraminiferal and micro-molluscan communities is driven mainly by substrate and water-quality parameters and shows a striking gradient from the variable and stressed water conditions of the western Bay to the more open-marine higher water quality habitats of the eastern Bay, including Myora Reef. Episodic changes also occurred in the Holocene benthic microfaunal composition, confirming the fluctuating nature of the Bay’s marine environments. Recent increases in foraminifera diversity and symbiont-bearing taxa signals a subtle improvement in water quality from the 1970s to 2008; however, for micro-gastropods, comparisons between fossil and modern death assemblages illustrate a decline in the condition of modern Bay habitats. The Holocene variation in the taxonomic composition and diversity of coral and micro-benthic assemblages of Moreton Bay reveals a history of recovery and rapid reef growth. Rapid recovery may still be possible if the causes of anthropogenic degradation are reversed and for this the highest priority is to reduce sediment and nutrient delivery into the Bay’s marine habitats

Patch size drives settlement success and spatial distribution of coral larvae under space limitation

Space availability is a key factor linked to the settlement success of marine invertebrates. Settlement space on coral reefs is predicted to become increasingly fragmented and occupied by competitors under future disturbance regimes, yet how this impacts coral settlement remains largely unknown. We test the effects of space limitation on larval settlement in three common Indo-Pacific corals (Acropora valida, Acropora digitifera and Anacropora spinosa) by manipulating substrate area while maintaining a constant larval supply. Settlement success was highly variable among coral species, with reduced space leading to an up to four-fold increase in settlement of A. valida larvae, a two-fold decrease in settlement of\ua0An. spinosa larvae and no significant effect for A. digitifera. All species displayed similar spatial settlement patterns, whereby larvae settled gregariously irrespective of how much space was available. At the same time, settlers were found to increasingly occur in aggregates (in direct contact with each other) as space decreased. We propose that increased settler aggregations, coupled with settlement intensification for some species, facilitates the formation of chimeras as space becomes limiting. In colonial organisms, the formation of aggregates and particularly chimeric individuals may offset the negative effects of increased competition for space by allowing settlers to rapidly exceed size-escape thresholds, thereby increasing the likelihood of survival

Freshwater input, upwelling, and the evolution of Caribbean coastal ecosystems during formation of the Isthmus of Panama

Caribbean biota underwent major ecological and evolutionary transformation in the Plio-Pleistocene but a lack of detailed paleoenvironmental reconstruction prevents thorough resolution of cause and effect. We quantify levels of upwelling and freshwater input into Caribbean coastal shelf ecosystems over the last ~6 Ma with >3300 stable isotope measurements from 74 fossil serially-sampled gastropods by normalizing δ18O values to open-ocean δ18O from planktonic foraminifera. We find that the influence of Pacific-like upwelling in the southwestern Caribbean (SWC) was low after 4.25 Ma but coastal ecosystems were heavily influenced by seasonal freshening until ~2.5 Ma, after which time low freshwater conditions were established. The origination of modern oligotrophic coastal conditions was therefore a result of oceanographic change causing declining upwelling, and declining nutrients from terrestrial sources. We speculate that a southward shift of the intertropical convergence zone, associated with Northern Hemisphere glaciation, reduced rainfall and terrestrial nutrient input and contributed to biotic turnover in the SWC, including the proliferation of modern reef communities