The northern Adriatic ecosystem: deep time in a shallow sea
F.K. McKinney Columbia University Press , 2007 ; 299 pp . ISBN 978-0-231-13242-8 . Hardback : GBP 38.50 .
The topic of this book meshes perfectly with the title and subtitle of this journal: ‘Marine Ecology: an evolutionary perspective’. In an age when global change is the catchword, those who study long-term trends and analyse data over evolutionary time scales often take home a lot of trophies. In the field of marine ecology, what better background can one have than being a palaeontologist with one foot squarely doing research in modern seas? Frank McKinney, a world-leading bryozoan specialist and distinguished evolutionary paleobiologist who has worked for many years at the Adriatic Sea, is the right person at the right time.
This book builds on the premise that bottom-dwelling sea life has evolved from the Paleozoic prevalence of stationary suspension-feeders on the sediment surface to bottom-dwelling animals living predominantly in or seeking temporary refuge within the sediment. McKinney proposes that the northern Adriatic is a natural, living laboratory in which to test that shift. Accordingly, the northern Adriatic can improve our understanding of the benthic ecosystems of ancient shallow seas and their ecological evolution.
Three major hypotheses have been forwarded to explain this ecological shift from Paleozoic to modern evolutionary faunas: increased predation pressure, increased bioturbation and increased nutrient contents. McKinney tests these hypotheses in the northern Adriatic Sea, primarily using a huge data set of grab samples; he selectively supports his conclusions by case studies here and elsewhere. He documents this shift based not on taxonomic but on ecological entities involving megaguilds (e.g. endobenthos, epibenthos, bioturbators, suspension feeders, detritus feeders, omnivores, carnivores), defined according to life habits (substrate relations and feeding strategies).
McKinney begins by outlining the ‘long-term changes in shallow marine life’, an admirable and beautifully illustrated introduction to this topic for marine scientists. This is followed by chapters dealing with the geography of the northern Adriatic Sea, the geological origin of the Adriatic, physical oceanography, nutrients and pelagic biology, Pleistocene and Holocene sediments, before coming to the lengthiest chapter, the benthic ecosystem. The next chapter treats the fossilization potential of northern Adriatic benthos. The detailed information in each of these chapters is very practically condensed in a ‘summary/implications’ form. These chapters all weave a well-thought-out and structured story that leads to the key chapter ‘Paleontological implications’, which presents the actual quantitative evaluation of his data set. For his synthesis, McKinney was able to use one of the major plus points of the Adriatic – that it has been studied by marine scientists for centuries. Thirty pages of references reflect the major effort that McKinney has made to summarize available information.
McKinney’s synthesis is based on a perceived ecological gradient from Paleozoic-style surface-dwelling communities in the east to modern communities living almost exclusively in the sediment in the west. It relies heavily on Aristotle Vatova’s Van Veen grab samples from the 1930s and 1940s. The grab sampling approach, however, has drawbacks, which are exemplified by the great contrast between Vatova’s classification (based on infauna species) and the later designation gained using underwater camera sleds and intensive SCUBA-diving-supported field work (which showed the widespread occurrence of a high biomass macro-epibenthic community). This discrepancy is also evident in McKinney’s benthic biomass graph (Fig. 7.2): the northernmost Adriatic is illustrated as having 30 g·m−2 as opposed to the average of 200–370 g·m−2 detected – for the macroepibenthos alone – by the methods of later authors.
In evaluating the reasons behind the faunal transition from an epifauna-dominated east to an infauna-dominated west, McKinney concludes that nutrient content and predation intensity (lower predation leads to epifauna-dominated communities) are the primary sources of variation, downplaying water depth, sediment composition and rates, as well as bioturbation.
This conclusion will no doubt stir debate among others who, as McKinney, are ‘passionate about the northern Adriatic’. The present reviewers, for example, would tend to see the above east–west gradient explained in the framework of sedimentation rates (bedload and suspension load), hypoxia/anoxia, and the stable substrata that epifauna need for settlement and growth on soft bottoms. McKinney himself pinpoints what we consider to be the underlying truth – although it runs counter to his oligotrophic versus eutrophic line of argumentation: ‘epibenthos in general track finer-grained soft sediments in the northern Adriatic’ and ‘all that is required in the proper environment, regardless of texture of the substrate, is the presence of local hard substrata, such as shells or shell fragments on which growth can begin’ (p. 232). McKinney’s treatment of sediment grain size and his consideration of the roles of bioturbation and predation levels in the northern Adriatic can also be discussed at length.
This book was prickling to read. Its scope clearly extends to all readers – paleontologists and marine scientists alike – interested in the ecology and evolution of shallow seas. Everyone we discussed the book with already has or plans to order it, and everyone had excited opinions about how their areas of specialty were presented. The northern Adriatic – as a degraded shallow sea – does indeed have a lot to tell us both about coastal ecosystems and about ourselves. Although some points may be controversial, no one will soon write a more coherent, comprehensive, interdisciplinary account than Frank McKinney.
