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3 Posts tagged with the coral_reef tag
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Conservation of reef corals of the world: why phylogeny matters


Danwei Huang

Postdoctoral scholar, University of Iowa

 

Friday 18 October 11:00
Sir Neil Chalmers seminar room, Darwin Centre LG16 (below Attenborough studio)


One third of the world's reef-building corals are facing heightened extinction risk from anthropogenic climate change and local impacts. Extinction probabilities aside, species are not equal. Rather, evolutionary processes render each species, or species assemblage in general, unique with a distinctive history that can be characterised for conservation. My research is aimed at quantifying these patterns based on a robust understanding of the coral tree of life. In this talk, I will show that it is critical to consider species' contribution to evolutionary diversity in conjunction with their extinction risk when setting priorities to safeguard biodiversity.

 

My analyses identify the most endangered lineages that would not be given top priority on the basis of risk alone, and further demonstrate that corals susceptible to impacts such as bleaching and disease tend to be close relatives. One of Earth's most threatened reef regions, the Coral Triangle, is also famously the most biodiverse. While competing ideas are plentiful, the dynamics underlying this biogeographic pattern remain poorly understood. Phylogenetic modelling adds a valuable dimension to these explanations, and can help us uncover the evolutionary processes that have shaped coral richness in the hotspot. Indeed, conservation of the world's reef corals requires protecting the historical sources of diversity, particularly the evolutionarily distinct species and the drivers of its geographic diversity gradient.

 

For additional details on attending this or other seminars see http://www.nhm.ac.uk/research-curation/seminars-events/index.html

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Darwin's Corals

Posted by John Jackson Jun 27, 2011

Brian Rosen (Zoology) and Jill Darrell (Palaeontology) have just published a paper on Darwin’s coral specimen collections and specimen lists. Darwin examined coral reefs in detail during the voyage of HMS Beagle, describing the different types of reef and using this information to write one of his early scientific works The Structure and Distribution of Coral Reefs

 

They were invited to present a talk on this subject at a conference on Darwin’s work at the Universita G. d’Annunzio, Chieti-Pescara, in November 2009. The paper deals with the only known Darwin geological collection in the Museum that comprises 29 coral reef specimens (held in Zoology), almost all from Cocos (Keeling) atoll in the Indian Ocean and accompanied by a little known and hitherto enigmatic Coral Reef Specimen List (holograph held in the NHM Library). Darwin mentions his visit to Keeling and interest in corals in a letter to his sister, sent from Mauritius.

 

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Darwin distinguished three primary types of reef: atolls, barrier reefs and fringing reefs, and used his own observations and those from FitzRoy's surveys to explain what he thought were the reasons for the existence of atolls - including Keeling, which he examined in detail.  Darwin noticed that reef-building corals did not grow below a certain depth of water, but that atolls isolated from other rocky islands were reasonably common.  He rejected the idea that gradual sediment buildup had provided foundations, and said that the idea of so many isolated sea-mounts of the right depth in the middle ocean for coral growth could be rejected.  He argued that rocky islands had sunk gradually below the surface, leaving their original coral reefs to keep the same level as the surface of the sea.  Darwin thought that earthquakes might be connected with the sinking islands - he did not know then what we know about plate tectonics, but had developed a keen interest in geological uplift and subsidence in South America on an earlier part of the voyage.

 

Brian and Jill offer for the first time a plausible explanation of the true origin and purpose of this list and set of specimens.  The specimens are unusual, if not unique, in being a small exhibit prepared by Darwin himself, at or before the time he donated them. The most likely occasion for which Darwin prepared his exhibit was that of his first presentation of his famous subsidence theory of coral reefs to the Geological Society of London on May 31st 1837.

 

Rosen B. R & Darrell, J. 2011. A generalized historical trajectory for Charles Darwin’s specimen collections, with a case study of his coral reef specimen list in the Natural History Museum, London. In:  Stoppa, Francesco & Veraldi, Roberto, Eds., Darwin tra scienza, storia e società. 150° anniversario della publicazione di Origine delle Specie [= Darwin in science, history and society. 150th anniversary of the Origin of Species.]  Edizioni Universitairie Romane, Roma, pp.133-198.

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Charles Darwin is best known as an evolutionary biologist but he also had significant success as a geologist.  His first three scientific books after his account of the voyage of the Beagle explored the geology of coral reefs, volcanic islands and South America: The Structure and Distribution of Coral Reefs (1842); Geological Observations of Volcanic Islands (1844); and Geological Observations on South  America (1846).

Dr Brian Rosen, a Scientific Associate in the NHM Department of Zoology, gave an invited public lecture, hosted by the Bermuda Institute of Ocean Sciences (BIOS) in their ‘Distinguished Lecture Series’ in November 2010, entitled ‘Red or Blue? Darwin's Bermuda Dilemma and his Enduring Subsidence Theory of Coral Reefs’, in which he discussed Darwin's ideas and conclusions.

Darwin's subsidence theory of the origin of coral atolls was based on the idea that the world's ocean floors as a whole were subsiding, and that atolls had developed as coral growth kept pace with sea level on the sinking foundations of former volcanoes. The sheer scale and simplicity of Darwin's idea was reflected in his famous coral reef map, on which he shaded atolls and most other oceanic reefs in blue (inferring subsidence), and most reefs elsewhere in red (inferring uplift or stability).

Darwin's theory was initially acclaimed but over time it seemed too revolutionary for many - alternative ideas such as sea level changes were preferred.  However, by the mid twentieth century, it became clear that the reef deposits of most atolls did indeed extend hundreds of metres beneath their surfaces - far deeper than can be explained by glacial sea level changes alone. 

We know now that atolls do form because islands sink gradually as a  consequence of tectonic plate movement.  While Darwin was correct about  the subsidence, tectonic plate movement and sinking as a reason was not proposed until 1912, althougth this was hotly contested until scientific explanation in the 1950s and 1960s.

Although Darwin did not visit Bermuda, he included it in his coral reef book. Bermuda's reefs - being essentially ring-like in arrangement, and with a central lagoon - are atoll-like, but for other reasons Darwin was equivocal about whether it was a true atoll, so he left it uncoloured on his reef map. In his lecture Brian Rosen attempted to resolve Darwin's dilemma, based on the fact that the sea levels at Bermuda have fluctuated over time.