Ocean acidification and warming will lower coral reef resilience

Ocean warming and acidification from increasing levels of atmospheric CO₂ represent major global threats to coral reefs, and are in many regions exacerbated by local‐scale disturbances such as overfishing and nutrient enrichment. Our understanding of global threats and local‐scale disturbances on reefs is growing, but their relative contribution to reef resilience and vulnerability in the future is unclear. Here, we analyse quantitatively how different combinations of CO₂ and fishing pressure on herbivores will affect the ecological resilience of a simplified benthic reef community, as defined by its capacity to maintain and recover to coral‐dominated states. We use a dynamic community model integrated with the growth and mortality responses for branching corals (Acropora) and fleshy macroalgae (Lobophora). We operationalize the resilience framework by parameterizing the response function for coral growth (calcification) by ocean acidification and warming, coral bleaching and mortality by warming, macroalgal mortality by herbivore grazing and macroalgal growth via nutrient loading. The model was run for changes in sea surface temperature and water chemistry predicted by the rise in atmospheric CO₂ projected from the IPCC's fossil‐fuel intensive A1FI scenario during this century. Results demonstrated that severe acidification and warming alone can lower reef resilience (via impairment of coral growth and increased coral mortality) even under high grazing intensity and low nutrients. Further, the threshold at which herbivore overfishing (reduced grazing) leads to a coral–algal phase shift was lowered by acidification and warming. These analyses support two important conclusions: Firstly, reefs already subjected to herbivore overfishing and nutrification are likely to be more vulnerable to increasing CO₂. Secondly, under CO₂ regimes above 450–500 ppm, management of local‐scale disturbances will become critical to keeping reefs within an Acropora‐rich domain.     

Ordovician and Silurian brachiopods from graptolitic shales and related deep-water argillaceous rocks

Ordovician and Silurian graptolitic shales and deep-water mudstones contain a sparse fauna of clustered, minute shells which are commonly believed to have been epiplankton attached to seaweed. Modern deep-water organisms may preferentially attach to local firm areas on the soft sediment. It is suggested that the Ordovician and Silurian shells may also have been benthic animals attached to local firm regions of the sea floor. These substrates might have included algal fronds which had fallen to the bottom.     

Neuroendocrinology of Teleosts

The nucleus preopticus has been shown to receive afferent inputfrom certain cranial nerves and the spinal cord. In addition,the nucleus preopticus and its tracts can synthesize and transporthormones about as rapidly as a mammal can. The nucleus preopticusis functionally involved in the spawning reflex behavior. The hypothalamic control of each of the adenohypophysial hormonesis discussed. There is conflicting and incomplete evidence forthe control of melanocyte-stimulating hormone (MSH), prolactin,and somatotropin. Secretion of prolactin and MSH may each becontrolled by an inhibitory factor. Corticotropin secretionhas been shown to be controlled by corticotropin releasing factor(CRF). There is a negative fedback effect by cortisol on thepituitary to suppress corticotropin secretion. Gonadotropinsecretion is controlled by gonadotropin releasing factor (GRF).A part of the nucleus lateralis tuberis is involved in the controlof gonadotropin secretion. A great deal of indirect evidenceindicates that a thyrotropin inhibitory factor (TIF) controlsthyrotropin secretion. There is a negative feedback effect bythyroxine on the pituitary to suppress thyrotropin secretionand a positive feedback effect on the hypothalamus to stimulateTIF secretion. The above findings are restricted to only one or two speciesin each instance. It is not known how general the above mechanismsof control are found throughout the teleosts.