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What controls animal size in the sea?

What controls animal size in the sea? 

Supervisors: Dr David Aldridge (Department of Zoology), Professor Lloyd S Peck (British Antarctic Survey), Dr Elizabeth M Harper (Department of Earth Sciences)


Scientists have been fascinated for over a century about why animals are larger in some parts of the world than others, and in some historical periods than others. The trend to large size towards the poles (Bergman’s rule) and to increasing size in lineages over geological time (Cope’s rule) are two of the most well known. Such trends are clear in some groups, especially amphipod and isopod crustaceans and pycnogonids, but also in sponges, polychaetes and even some protozoans. Over the last 2 decades oxygen has been identified as being important in setting size limits that an aquatic taxon can attain (Chapelle & Peck 1999, 2004), but it does not dictate the size of the vast majority of species.  Thus the largest sea spiders may not be able to grow larger in their given environment, but most sea spiders in that region are smaller than the largest species and their size is dictated by a complex set of factors, mostly ecological. These are thought to include taxon diversity (competition), temperature, resource availability (primarily food) and bauplan. In recent years there has been a debate in the literature as to the mechanism whereby oxygen limits maximum attainable size, with variations in ambient concentration, oxygen use via temperature effects on ectotherm metabolic rate, solubility and partial pressure being seen as important (e.g. Verberk & Atkinson 2013).  This project will investigate variation in size of marine ectotherms in relation to a range of environmental and physical factors.


What the project will involve: the project could take a variety of different directions including extracting data on animal size for a given taxon across a wide range of environments and correlating these changes with environmental factors, either across the globe currently and/or across geological time periods. It could also involve conducting experiments holding and breeding animals in manipulated experimental conditions to identify effects on size



Chapelle, G., Peck, L.S. (1999) Polar gigantism dictated by oxygen availability.  Nature, 399: 114-115; Chapelle, G., Peck L.S., (2004) Amphipod crustacean size spectra: new insights in the relationship between size and oxygen. Oikos 106: 167-175; Verberk & Atkinson 2013 Why polar gigantism and Palaeozoic gigantism are not equivalent: effects of oxygen and temperature on the body size of ectotherms. Functional Ecology 27, 1275–1285.