University of Plymouth PEARL https://pearl.plymouth.ac.uk Faculty of Science and Engineering School of Biological and Marine Sciences 2011-09-15 Effects of ocean acidification on marine biodiversity and ecosystem function Barry, JP http://hdl.handle.net/10026.1/1314 Oxford University Press All content in PEARL is protected by copyright law. Author manuscripts are made available in accordance with publisher policies. Please cite only the published version using the details provided on the item record or document. In the absence of an open licence (e.g. Creative Commons), permissions for further reuse of content should be sought from the publisher or author. OUP CORRECTED PROOF – FINAL, 08/11/2011, SPi CHAPTER 10 Effects of ocean acidifi cation on marine biodiversity and ecosystem function J ames P . B arry, S tephen W iddicombe, and J ason M . H all- S pencer be diffi cult to detect amidst the variability associ- 10.1 Introduction ated with other human and non-human factors, and The biodiversity of the oceans, including the strik- the greatest impacts are expected to occur as acidifi - ing variation in life forms from microbes to whales cation intensifi es through this century. and ranging from surface waters to hadal trenches, In theory, large and rapid environmental changes forms a dynamic biological framework enabling the are expected to decrease the stability and produc- fl ow of energy that shapes and sustains marine eco- tivity of ecosystems due to a reduction in biodiver- systems. Society relies upon the biodiversity and sity caused by the loss of sensitive species that play function of marine systems for a wide range of serv- important roles in energy fl ow (i.e. food web func- ices as basic as producing the seafood we consume tion) or other processes (e.g. ecosystem engineers; or as essential as generating much of the oxygen we Cardinale et al. 2006 ). In practice, however, most breathe. Perhaps most obvious is the global seafood research concerning the biological effects of ocean harvest totalling over 100 Mt yr –1 (82 and 20 Mt in acidifi cation has focused on aspects of the perform- 2008 for capture and aquaculture, respectively; FAO ance and survival of individual species during 2009 ) from fi shing effort that expands more broadly short-term studies, assuming that a change in indi- and deeper each year as fi shery stocks are depleted vidual performance will infl uence ecosystem func- ( Pauly et al. 2003 ). Less apparent ecosystem services tion. By their nature, controlled experimental linked closely to biodiversity and ecosystem func- studies are limited in both space and time, and thus tion are waste processing and improved water may not capture important processes (e.g. acclima- quality, elemental cycling, shoreline protection, rec- tization and adaptation, multispecies biological reational opportunities, and aesthetic or educational interactions, chronic low-level impacts) that can experiences ( Cooley et al. 2009 ). ultimately play large roles in the response of marine There is growing concern that ocean acidifi cation systems to ocean acidifi cation. This ‘scaling up’ caused by fossil fuel emissions, in concert with the from individual- to ecosystem-level effects is the effects of other human activities, will cause signifi - most challenging goal for research on the potential cant changes in the biodiversity and function of effects of ocean acidifi cation. marine ecosystems, with important consequences To plan for the future, society needs information to for resources and services that are important to understand how ocean acidifi cation and other envi- society. Will the effects of ocean acidifi cation on eco- ronmental changes will affect fi sheries, aqua culture, systems be similar to those arising from other envi- and other services deriving from the effi cient func- ronmental perturbations observed during human tion of marine ecosystems. The infl ux of fossil fuel or earth history? Although changes in biodiversity CO2 into the upper ocean from the atmosphere is and ecosystem function due to ocean acidifi cation altering the chemistry of ocean waters at a faster have not yet been widely observed, their onset may rate and greater magnitude than is thought to have 192 OUP CORRECTED PROOF – FINAL, 08/11/2011, SPi EFFECTS OF ACIDIFICATION ON MARINE BIODIVERSITY AND ECOSYSTEMS 193 occurred on earth for at least a million years and per- tems in a region), or functional diversity (the number haps as much as 40 Myr ( Pelejero et al. 2010 ; see of functional roles performed by the species present) Chapter 2 ). In this chapter, the infl uence of this (see Fig. 10.1 ; Petchey and Gaston 2006 ). Biodiversity important change in ocean chemistry on the biodi- is a dynamic feature of natural systems, refl ecting versity and function of marine ecosystems is consid- the continual evolutionary response of species in a ered, from basic physiological responses of individual region to selection across a broad range of environ- organisms and species, to the potential changes in mental and ecological pressures. Biodiversity can various ocean environments. expand and contract as species diversity or other elements of biological diversity are created, main- 10.2 Biodiversity and ecosystem tained, or lost to extinction. function The function of ecosystems is wholly dependent on biodiversity that allows energy to fl ow through The term biodiversity is broadly defi ned, and used trophic webs and biological networks. Moreover, to characterize aspects of the biological complexity the stability and resilience of ecosystem functions, of natural systems. Often cast simply as the number from nutrient cycling and energy fl ow, to the of species in a region (i.e. species richness ), biodiver- population dynamics of species, are thought to be sity has a far larger scope that spans the variation sensitive to the loss of biodiversity caused by per- within and among systems and organisms over turbations of both human and non-human origin. multiple scales and levels of genetic, organismal, This concept has long been considered theoreti- ecological, or ecosystem diversity. Measures of bio- cally, with more diverse and trophically complex diversity attempt to estimate the richness and even- systems expected to be more stable and resistant ness of biological characteristics at different levels, to perturbations. Species complementarity (different such as species richness and species diversity (the species have similar ecological roles) and species number and evenness of species in a region), taxo- redundancy (different species perform the same nomic diversity (not just species richness, but diver- function) are thought to provide ‘insurance’ for sity at higher taxonomic levels), genetic diversity ecosystem function in diverse systems by promot- (genetic variation in a population or species), habitat ing functional diversity and maintaining energy or ecosystem diversity (range of habitats or ecosys- fl ow among trophic levels (i.e. ecosystem function) Figure 10.1 Species diversity does not necessarily represent functional diversity. Note that both groups have equal species richness and diversity (a single individual from each of eight molluscan species), but the group on the right has greater taxonomic distinctness and functional diversity. Photo R. M. Warwick. OUP CORRECTED PROOF – FINAL, 08/11/2011, SPi 194 OCEAN ACIDIFICATION upon a reduction or loss of species in response to ture) are intolerable. Range shifts along other environmental variation or other factors ( Loreau gradients in pH or carbonate saturation (e.g. depth- et al. 2001 ). related or horizontally in coastal regions) may also Field studies in terrestrial and marine ecosystems be possible. over the past two decades have provided both sup- Whether marine organisms, from microbes to port (e.g. Steneck et al. 2002 ) and moderate contro- long-lived megafauna, will be able to acclimatize or versy concerning the diversity–stability concept adapt to future ocean acidifi cation is an important, ( Loreau et al. 2001 ; Cardinale et al. 2006 ). The contro- but unresolved, question. Acclimatization is the versy relates, in part, to the disproportionate role of process by which individuals adjust to environmen- key species in many systems studied, without which tal changes (i.e. physiological adjustment). This stability is reduced. This issue may be important in may result in a change in energy costs (positive or several marine ecosystems where key prey species negative) associated with living. Adaptation is the (e.g. pteropods, krill, anchovies, and squid in coastal adjustment of species to environmental change systems) or taxa that play an important structural between generations, through natural selection of role (e.g. habitat-forming corals) can be critical individuals tolerant of new conditions. Tolerance or resources for other taxa. Thus, reduced biodiversity acclimatization by at least some individuals in the due to the loss of prey taxa or habitat-forming spe- population allows for adaptation, assuming that the cies may not have large effects on energy fl ow or tolerant traits are heritable and suffi cient time is ecosystem function and stability, so long as key spe- available for selection to increase the frequency of cies that maintain the functional diversity of the tolerant genotypes through multiple generations. If system are relatively unaffected ( Tilman et al. 1997 ). individuals in most populations are able to acclima- Although this debate continues, a recent examina- tize