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By Charles Sheppard

Coral reefs are the most diverse ecosystem in the sea. In some ways they are very robust marine ecosystems, but in other ways, perhaps because of their huge numbers of species, they are very delicate and susceptible to being damaged or killed. On the one hand, healthy reefs are glorious riots of life, and marine scientists have spent several decades unravelling the complicated ways in which they work. On the other hand, at least one third of the world’s reefs have already died — gone for ever in terms of human lifetimes at least — even when the cause of their demise is lifted.

How coral reefs lived and grew right up to the sea surface remained a mystery for years for several reasons. First, where were all their plants? It was known that plants are the world’s food base, yet there were hardly any visible plants, let alone waving fields of them such as the naturalists knew about from their own (mostly cold) Northern shores. The answer is that the main plant base comes from the symbiotic algae living in the cells of reef building corals. This helped answer the second mystery: how could such vibrant reefs live in the nutrient-poor oceans of the tropics? Nutrients, it was known, were needed for plants to grow. But the waters that bathe oceanic reefs in particular were the poorest on Earth in terms of nutrients. The answer was clear once the symbiosis was discovered; there is a very tight cycling of nutrients between the symbiotic components of the coral-algal symbiosis and little ‘leakage’ from the reef into the sea.

There was a third, long running mystery also, namely, how do reefs form? In particular, why do they invariably grow to the surface of the sea from a wide range of depths and, why do they all have rather similar shapes? This was explained in several ways. Firstly it became clear that the Earth’s crust moves, both across oceanic distances over huge time periods, and they move vertically by hundreds of metres. Corals need light (because of their symbiotic algae) so they only live at the contemporary sea level, and the sea level changed hugely over the millennia that corals have lived and made their limestone skeletons. Darwin was the first to deduce this, in particular the importance of growth on subsiding substrates such as volcanoes.

The numerous shapes and kinds of corals, soft corals, and sponges (and many other forms) live together in what has been called a ‘super-symbiosis’ or a ‘super-organism’, terms which, while strictly not true, do give a sense of the intimate linkages that occur between so many of the component groups of species. This may provide one reason why they are, in so many ways, very susceptible to human impacts today. Raised nutrients (e.g. from sewage and shoreline construction) are hugely damaging. Burial of reefs for building on are also fatal to the reefs of course, and, sadly land made by landfill on a reef foundation (something easy to do because reefs are shallow) has a higher economic price when sold for building than the reef did in the first place. Shallow sea and reefs, we might say, become more valuable when they are no longer sea but are converted to expensive, sea-side building land! Eco-nomics and eco-logy have the same root word and should work hand-in-hand, but clearly they don’t, to the detriment of these complex living systems.

Reefs are valuable – but to whom? Reef and beach based tourism forms over half the foreign exchange earnings for many countries. Without reefs to attract tourists, many states would become impoverished; many already are. More importantly (again to whom?) they provide food for huge numbers of coastal dwellers throughout the poorest parts of the world. Not only do fish form the basis for human existence, but so do molluscs, sea cucumbers, octopus… the list is endless. Too many people extracting food from a reef readily collapses the elaborate ecosystem, with the result that there is nothing left for the next year, or the next generation.

Various aspects of climate change are adding to the mix of stresses for reefs. As CO₂ builds up, it warms the oceans, and this has killed off countless areas of reef already or at least added an additional stress. When that gas dissolves in the ocean, the water becomes more acidic, again causing damaging effects, in this case reducing the ability to lay down their limestone skeletons. These are not predicted effects – something for the future. We measure it and know that we are already well along that path.

Coral reefs are a canary in the environmental coal mine, showing us, before any other system can perhaps, what we are doing to the earth today. We know enough of their science now to understand this and avert the problems. What we don’t have is the will to do so. It is no longer a problem of science but of sociology and politics.

Charles Sheppard is Professor in the School of Life Sciences at the University of Warwick. His research focuses mainly on community ecology, particularly on ecosystem responses to climate change. He works for a number of UN, Governmental, and aid agencies to advise on topical marine and costal developmental issues. He is the author or editor of 10 books, including The Biology of Coral Reefs (2009) and Coral Reefs: A Very Short Introduction (2014).

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Image credit: Iolanda reef in Ras Muhammad nature park (Sinai, Egypt), By Mikhail Rogov, CC-BY-SA-3.0 via Wikimedia Commons

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By Rachael A. Bay

For tigers, visiting your neighbor is just not as easy as it used to be. Centuries ago, tigers roamed freely across the landscape from India to Indonesia and even as far north as Russia. Today, tigers inhabit is just 7% of that historical range. And that 7% is distributed in tiny patches across thousands of kilometers.

Habitat destruction and poaching has caused serious declines in tiger populations – only about 3,000 tigers remain from a historical estimate of 100,000 just a century ago. Several organizations are concerned with conserving this endangered species. Currently, however, all conservation plans focus increasing the number of tigers. Our study shows that, if we are managing for a future with healthy tiger populations, we need to look beyond the numbers. We need to consider genetic diversity.

Genetic diversity is the raw material for evolution. Populations with low genetic diversity can have lower health and reproduction due to ‘inbreeding effects’. This was the case with the Florida panther – in the early 1990s there were just 30 Florida panthers left. Populations with low genetic diversity are also vulnerable when faced with challenges such as disease or changes in the environment.

Photo by Rachael A. Bay

Luckily for tigers, they don’t have low genetic diversity. They have very high genetic diversity, in fact. But the problem for tigers is that losing genetic diversity happens more quickly in many small, disconnected populations than in one large population. The question is: how can we keep that genetic diversity so that tigers never suffer the consequences of inbreeding effects.

We used computer simulations to predict how many tigers we would need in the future to keep the genetic diversity they already have. Our study shows that without connecting the small populations, the number of tigers necessary to maintain that variation is biologically impossible. However, if we can connect some of these populations – between tiger reserves or even between subspecies – the number of tigers needed to harbor all the genetic variation becomes much smaller and more feasible. Case studies have shown that introducing genetic material from distantly related populations can hugely benefit the health of a population in decline. In the case of the Florida panther, when individuals from another subspecies were introduced into the breeding population, the numbers began to rise.

We do need to increase the number of tigers in the wild. If we can’t stop poaching and habitat destruction, we will lose all wild tigers before we have a chance to worry about genetic diversity. But in planning to conserve this majestic animal for future generations we should make sure those future populations can thrive – and that means trying to keep genetic variation.

Rachael A. Bay is a PhD candidate at Stanford University, and co-author of the paper ‘A call for tiger management using “reserves” of genetic diversity’, which appears in the Journal of Heredity.

Journal of Heredity covers organismal genetics: conservation genetics of endangered species, population structure and phylogeography, molecular evolution and speciation, molecular genetics of disease resistance in plants and animals, genetic biodiversity and relevant computer programs.

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Image credit: Tigers at San Francisco Zoo. Photo by Rachael A. Bay. Do not reproduce without permission.

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By Rebecca Cramp

In recent decades, the extraordinarily rapid disappearance of frogs, toads, and salamanders has grabbed the attention of both the scientific community and concerned citizens the world over. Although the causes of some of these losses remain unresolved, the novel disease chytridiomycosis caused by the skin-based fungus Batrachochytrium dendrobatidis (Bd), has been identified as the causative agent in many of the declines and extinctions worldwide. Bd is now regarded as being responsible for the greatest disease-driven loss of vertebrate biodiversity in recorded history.  Like other entirely cutaneous microbes, interactions with the skin of its host determine how and under what conditions the fungus can induce disease.

The skin plays an important role in immune defence. In the first instance, skin acts as a physical barrier against microbes and pathogens. It also produces anti-microbial skin secretions and supports a large microbial community made up of good (commensal), bad (pathogenic) and indifferent (neither good nor bad; having no discernable effect) microbes. Like most animals, the outer skin layer of amphibians is shed (sloughed) on a regular basis—as often as daily to every couple of weeks. However, unlike mammals, amphibians shed (and often eat) the entire outer skin layer in one piece.  Therefore, anything adhering to or within that outer layer would be lost from the body every time the animal sloughs it skin. As such, regular sloughing could play a role in regulating the abundance and persistence of microbes (including Bd) at the body’s surface. To date, however, the potential for regular skin sloughing to serve as an immune defense strategy in amphibians has been largely overlooked.

A green tree frog. Photo by Ed Meyer.

To test the hypothesis that sloughing in plays a role in the management of cutaneous microbe abundance, we investigated changes in the number of cultivable cutaneous bacteria on the ventral and dorsal body surfaces of the Green tree frog (Litoria caerulea) with sloughing. Effects of temperature on sloughing periodicity were also investigated in order to determine how the efficacy of sloughing in regulating microbial infection might vary with climate and season. Our study showed that sloughing massively reduced the overall abundance of bacteria, in some cases by as much as 100%. In addition, temperature had a marked effect on sloughing periodicity, with animals in cooler temperatures having a much longer time between sloughs compared with animals at held higher temperatures.

Most importantly however, we found that the extended time between sloughs in animals in the cold treatments allowed skin microbe numbers to increase to levels in excess of those seen in animals in the warm treatment. These data suggest that for pathogens that like relatively cooler conditions (like Bd), the effect of temperature on host sloughing frequency may allow pathogen numbers to build up to such a degree that fatal disease occurs.

What does it all mean, though? Firstly, the epidemiology of skin based diseases like Bd could be in part attributed to the effects of temperature on host sloughing periodicity particularly when disease outbreaks occur in cool habitats and/or at cooler times of year. Secondly, differences between species in the frequency of sloughing could influence pathogen establishment and go some way to explaining why some amphibian species are more resistant to cutaneous pathogens than others. Thirdly, the ability of commensal (good) bacteria to protect against pathogens may be reduced in frog species which slough frequently as commensal bacteria would also be lost from the skin with sloughing, unless they are able to recolonise the skin rapidly.

Understanding the role the skin plays as the first bastion of defense against external pathogens is vitally important as the rate of emergence of both novel and pre-existing infectious diseases is predicted to skyrocket in the future as a result of anthropogenic climate change.

Dr Rebecca Cramp is a Research Officer at The University of Queensland in the laboratory of Professor Craig Franklin. Rebecca has diverse research interests and is currently working on several projects including a study of disease susceptibility in frogs, the control of ion regulation in acid-tolerant amphibian larvae and the effects of environmental stressors on immune function in amphibian larvae. She is a co-author of the paper ‘First line of defence: the role of sloughing in the regulation of cutaneous microbes in frogs‘, which appears in the journal Conservation Physiology.

Conservation Physiology is an online only, fully open access journal published on behalf of the Society for Experimental Biology. Biodiversity across the globe faces a growing number of threats associated with human activities. Conservation Physiology publishes research on all taxa (microbes, plants and animals) focused on understanding and predicting how organisms, populations, ecosystems and natural resources respond to environmental change and stressors. Physiology is considered in the broadest possible terms to include functional and mechanistic responses at all scales.

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Image credit: A green tree frog. Photo by Ed Meyer. Do not reproduce without permission.

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By Mark van Kleunen

Conservation physiology was first identified as an emerging discipline in a landmark paper by Wikelski and Cooke, published in Trends in Ecology and Evolution in 2006. They defined it as “the study of physiological responses of organisms to human alteration of the environment that might cause or contribute to population decline”. Although the case studies and examples presented by Wikelski and Cooke focused on wild animals, they indicated already that conservation physiology should be applicable to all taxa. With the launch of the journal Conservation Physiology – one year ago – this taxonomic inclusiveness was made more explicit, and the definition was broadened to “an integrative scientific discipline applying physiological concepts, tools and knowledge to characterizing biological diversity and its ecological implications; understanding and predicting how organisms, populations and ecosystems respond to environmental change and stressors; and solving conservation problems across the broad range of taxa (i.e. including microbes, plants and animals)”.

Although the definition of conservation physiology, and also the journal with the same name, covers in principle all taxa, plants (and also microbes, and among animals the invertebrates) are still clearly underrepresented. Of the 32 papers that were published in the journal in 2013, only three (9%) focussed on plants. This underrepresentation of plants, however, appears to be a general trend in conservation science, as the journal Conservation Biology had only ten out of 93 contributed papers (11%) focussing on plants in 2013. The journal Biological Conservation did a bit better with 59 out of 309 regular papers (19%) focussing on plants in 2013. Given the importance of plants as primary producers, which are indispensable for all other organisms, and the fact that 10,065 of the 21,286 species (47%) assessed by the IUCN Red List as globally threatened are plants, they clearly deserve more attention in the field of conservation physiology, and conservation science in general.

Conservation science has many important, frequently intertwined, sub-disciplines, including among others conservation policy, conservation genetics and conservation physiology. The strength of physiology, and thus of conservation physiology, is that it focusses on the mechanisms underlying patterns by identifying cause-and-effect relationships, preferably through experimentation. Physiology is directly related to the functioning and function of plants. This means that physiological knowledge is imperative for understanding the habitat requirements of endangered native plants and of potentially invasive exotic plants, and the ecological impacts of invasive exotic plants and migrating native plants. An accessory advantage of working with plants is that they lend themselves extremely well for experimental studies, as they are sessile, can easily be marked, and frequently can be grown in large numbers under greenhouse or garden conditions. Plants are thus ideal objects for conservation physiological studies.

Given that plants are underrepresented, a logical question is what kind of plant studies fall under the umbrella of conservation physiology. The three reviews on plants that were published in Conservation Physiology in 2013 do a great job in setting the scene. Hans Lambers and colleagues reviewed the research on phosphorus-sensitive plants in a global biodiversity hotspot. Many of these species are threatened by the introduced pathogen Phytophthora cinnamomi and by eutrophication; the latter partly due to large-scale application of phosphite-containing fungicides (biostats) that are used to fight the pathogen. This illustrates how one conservation measure may cause undesired side effects. Physiological understanding of how phosphite functions could help to develop alternative fungicides with less negative side effects. Fiona Hay and Robin Probert reviewed recent research on seed conservation of wild plant species. They clearly make the case that if we want to preserve genetic material of wild plant species in ex-situ seed banks for conservation purposes, physiological research is imperative for developing optimal storage, germination and growth conditions. Last but not least, Jennifer Funk reviewed research on physiological characteristics of exotic plant species invading low-resource environments. Prevention of invasions and mitigation of the impacts of invasions requires physiological research that resolves the question whether exotic species manage to invade low-resource environments through enhanced resource acquisition, resource conservation or both. These three reviews thus illustrate already three important plant-related topics in conservation physiology: causes of threat of native plants, ex-situ conservation, and invasive exotic plants.

An important topic that hasn´t been covered yet in the journal Conservation Physiology is how plants will respond to climate change. As physiology underlies the fundamental niche of a species, physiological studies can inform predictive models on potential responses of plants to climate change. Related topics are how endangered and invasive plant species will respond to increased CO₂ levels, and how their vulnerability to diseases may change under novel climatic conditions. Furthermore, as we seem to miserably fail in reducing greenhouse-gas emissions, it becomes also more likely that governments will start to implement climate engineering methods to reduce incoming solar radiation or atmospheric CO₂ levels. Undesired ecological side effects of these methods will raise novel conservation issues for which physiological knowledge will be imperative. Other topics that haven’t been covered yet are physiological responses of plants to pollution, and how endangered species that are difficult to propagate from seeds could be multiplied using tissue culture or other techniques. Obviously, the list of potential topics that I have mentioned here is far from exhaustive, but I hope it illustrates that many of the plant-related topics on which many of us work already or will work in the future fit within the discipline of conservation physiology.

Mark van Kleunen is a Professor of Ecology at the University of Konstanz. His research focusses on invasiveness of exotic plants, plant responses to global change and life-history evolution. This blog post is an adapted version of his editorial ‘Conservation Physiology of Plants‘ in the journal Conservation Physiology.

Conservation Physiology is an online only, fully open access journal published on behalf of the Society for Experimental Biology. Biodiversity across the globe faces a growing number of threats associated with human activities. Conservation Physiology publishes research on all taxa (microbes, plants and animals) focused on understanding and predicting how organisms, populations, ecosystems and natural resources respond to environmental change and stressors. Physiology is considered in the broadest possible terms to include functional and mechanistic responses at all scales.

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Image credit: California wildflowers. By Rennett Stowe. CC-BY-2.0 via Wikimedia Commons

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