Today we have a guest post from Dr. Peter Tomiak who delves into the life and death of corals…
I completed my undergraduate degree in Biology and Geology at the University of Bristol in 2008. Subsequently I undertook a sponsored internship with Save The Elephants, in Samburu National Park Kenya, before starting a short term position alongside Prof. Adrian Lister at the Natural History Museum, London, constructing a database of radiocarbon dates for extinct Pleistocene mammals. At this point I moved away from terrestrial mammals, and into the marine realm. I completed my PhD, examining the nature and applications of coral skeleton, within the Earth Sciences Department at Bristol University in 2013 (funded by the Natural Environmental Research Council and an additional Wingate Scholarship), and then continued with my research as a postdoctoral researcher at the university into 2014. Over the past 6 months, I have been travelling throughout South and North America, performing volunteer work at several State and National Parks along the way. I enjoy spending time in the natural environment and am very enthusiastic about conservation. In my spare time, I enjoy wildlife photography, SCUBA, live music and playing or watching football.
En masse, the aragonite (a polymorph of calcium carbonate) skeleton deposited by the living component of a coral, the polyp, provides the structural framework of coral reefs. This “convergence” of the geological, chemical and biological worlds necessitates a truly interdisciplinary approach to reef studies. In my (undoubtedly biased) opinion, this makes coral reefs a particularly interesting, if somewhat daunting subject of study. However, it is unquestionably an extremely important field; reefs support a huge diversity of marine life, being considered as the “rainforests of the oceans”. Additionally, they provide coastal protection and a food source for local populations, and generate large revenues through fishing and tourism.
Opportunities to dive amongst corals whilst doing a PhD in the U.K are rare; most samples are delivered to you in boxes. However, the International Coral Reef Symposium 2012 took place in Cairns (Australia) allowing for some dive-time on the Great Barrier Reef. Credit: Peter Tomiak
Unfortunately, many experts now believe that the future of coral reefs is looking rather bleak. In addition to “local” pressures, such as more intensive fishing practices, it is very likely that climate change will cause significant transformations to the reef community. Recently, the impacts of ocean acidification (the reduction in pH of the ocean waters over an extended period, primarily caused by uptake of CO2 from the atmosphere), on both the living and mineral components of reefs, has also been the subject of intense study. The situation is complicated by the intimate relationship that exists between the reef building coral (the “host”) and the photosynthetic symbiotic algae that reside within the coral tissue; when attempting to forecast the effects of anthropogenic changes in oceanic conditions, researchers must consider the impacts upon both.
In fact, it is increasingly apparent that in order to accurately predict the response of corals to such pressures, we must first establish a better appreciation of the mechanisms involved in skeletal formation (“calcification”). Researchers have now established that skeletal formation in corals, as is the case for other calcifying organisms, is biologically controlled, involving a set of organic molecules collectively termed the “organic matrix”, which subsequently becomes incorporated and preserved within the skeleton. Despite over 40 years of investigation, the true nature and importance of this organic matrix, which only represents a small fraction of the skeleton, remains enigmatic; however, it is very likely to be of fundamental importance to the calcification process and therefore deserves further exploration.
When coral dies, however, not all is lost; whilst the living tissue of the polyp degrades relatively quickly, the skeleton persists, and, over extended time periods, may be uplifted by tectonic or isostatic forces, above the current sea-level. Preservation of the skeleton in the geological record can provide a tantalising window into the period during which it was formed.
For example, because the tissue of reef building corals contains photosynthetic algae, thereby limiting the coral host to shallow well-lit surface waters, fossil specimens of known age can be used to constrain palaeo sea-level (provided that any uplift of the sample is corrected for). Reconstructing palaeo sea-level fluctuations facilitates estimates of global ice volume associated with variations in global climate, thereby helping to establish the timing of past glacial and interglacial periods.
In addition, information regarding the prevailing environmental conditions during coral growth is stored as isotopic and chemical signatures within the skeleton. This skeletal archive of data can even be exploited in colonies that are still growing; some coral colonies continue to precipitate new material over several centuries. Researchers use analytical techniques such as mass spectrometry to determine the geochemical signatures of coral skeleton, which are in turn utilised as proxies for an assortment of environmental conditions, including surface seawater pH, temperature, salinity and sediment flux.
Acropora palmata skeleton; when living, each coral polyp resides within a single “tube” or corallite and forms new skeleton at its base. Credit: Peter Tomiak
Accurate dating of the fossil skeleton is a prerequisite for all such applications. Various techniques including radiocarbon dating and electron spin resonance have been used in attempts to date fossil coral, although Uranium-series (U-series) isotopic analysis is by far the most commonly applied. However, whilst the efficiency, analytical precision and age-range of U-series have improved significantly in recent decades, the field is still undermined by a poor understanding of the sensitivity of this dating technique to diagenetic mechanisms* that afflict the coral skeleton after its formation. Ironically, a major contributor to our ignorance is the rejection, prior to analysis, of coral samples demonstrating visual evidence of diagenetic alteration. Further study into the impacts of diagenetic change on U-series analyses is certainly required, but exploring the use of complementary chronometers also seems prudent. One contender is Amino Acid Racemisation (AAR) dating, which has experienced recent methodological advancements, but as of yet, has not been thoroughly examined in fossil coral. AAR is a time-dependent degradation reaction that occurs when amino acids (the building blocks of protein), become isolated within the organic matrix of the coral skeleton. Therefore, in contrast to many dating techniques in which the organic matrix is often considered a source of contamination and annoyance, this technique actively exploits the biological component of the skeleton.
This is an “introduction” to coral studies, which concentrates upon research topics that I examined during my PhD and does not include comment upon many other important areas of coral research. Furthermore, coral, of course, represents just one component of the complex reef ecosystem. More information on Coral Reef Research at Bristol (CRAB) can be found at http://www.bristol.ac.uk/biology/research/ecological/coral/ .
Appendix
At times, undertaking a PhD with a multi-disciplinary nature can be difficult; I often found myself stumbling into unfamiliar terrain. However, this is typical of most PhDs in the Earth Sciences department, which cannot easily be “shoe-horned” into a single subject. However, being part of a university, particularly one where the various departments are located within close proximity, offers the opportunity to exploit the vast data-bank of knowledge within different research groups. Neither you, nor your supervisor, can be an expert on everything; I found that humbly requesting help or advice from others with different areas of expertise can save time and potentially lead to rewarding inter-departmental collaboration.
If you have any questions feel free to email Pete at petertomiak at hotmail.com
