Introduction and state of the art:

 

Shallow coastal habitats such as estuarine  and continental shelf soft-sediments represent some of our most valued ecosystems [1] but increasingly experience multiple stressors along with the expanding human population in the coastal environment [2]. For example, eutrophication-induced oxygen deficiency is a widespread threat to coastal and estuarine ecosystems and communities [3]. In addition, these ecosystems are vulnerable to variation in climatic conditions. The enhanced emission of greenhouse gasses (e.g. CO2) have raised global sea surface temperatures (SST) at approximately 0.13 °C per decade since the current period of climate warming began in the mid 1980s and climate models suggest that patterns of mean and extreme SST will alter across the globe, including the shallow coastal habitats [4]. In addition, ocean CO2 absorption alters sea water carbonate chemistry and pH, with temperate shallow marine ecosystems currently experiencing an order of magnitude faster decrease in pH (i.e. ocean acidification) as compared to global estimates [5, 6]. This unprecedented fast rate of acidification affects, among others, species condition and physiology, and benthic ecosystem processes, e.g. [7, 8].  The abovementioned stressors (hypoxia, seawater temperature rise and acidification) will likely instigate change in a whole range of interaction strengths on the population and ecosystem level with vast repercussions for overall ecosystem functioning and stability, including change in trophic interactions, species physiology and distributions. Moreover, these stressors do not act in isolation and additive, synergistic or antagonistic effects of these concurrent climate and non-climate stressors may therefore be expected. 

 

The prediction of ecosystem responses to stressors requires understanding of the dynamics and functioning of species populations in the ecosystem, in particular how these patterns and processes are influenced by varying degrees in forcing of interactive stressors. The ability of organisms to perform essential tasks such as avoiding predation, competing with other individuals, and obtaining food is, by definition, dependent upon the behaviours that they perform. Hence any stressor-induced disruption to these behavioural processes has the potential to influence both individual fitness and population success.  Moreover, changes in key species behaviour can determine functions such as recruitment, emigration and immigration, and cycling of energy, all of which affect community dynamics and thus general ecosystem stability [9].  Consequently, investigation of the single and combined effects of stressors on the condition and behaviour of ecosystem key species, and the feedback processes with components of their ecosystem, have been put forth to improve our understanding of the mechanisms that underpin resilience to change in environmental forcing [10, 11]. 

 

A key area of behaviour that might change in response to environmental stressors is the ability to detect and evade predators. This behaviour is often highly repeatable among individuals, but this repeatability is known to be reduced in response to stress. Conversely, a degree of intra-individual variation in behaviour (IIV) is believed to be adaptive, since unpredictable individuals may be harder to capture. A recent study on the effect of temperature has shown that at elevated temperatures IIV is increased [12], possibly as a consequence of the greater risk of capture due to increase in foraging requirements at higher metabolic rates. Factors that reduce metabolism, or reduce the ability to respond to cues [13] could therefore lead to reduced IIV, a level of behaviour that has only recently been investigated in marine animals [14]. However, linking behavioural change to diversity and functioning in marine sediments is particularly challenged due to the benthic living (and thus behavior) of infaunal invertebrates.  Nonetheless, the behaviour of these organisms, e.g. feeding, bioturbation and bio-irrigation, influences diversity and essential ecosystem functions such as energy cycling and sediment transport processes [15, 16]. Recently, behaviour-specific pressure wave-forms within the sediment porewater were shown instrumental to document a variety of benthos behavioural activities into detail over a long period, including e.g. siphon movement, burrow pumping, feeding, sediment excavation and burrowing in a few, but functionally different, macrobenthic species (i.e. shallow living filter feeders and (sub)surface deposit feeders)[17, 18].  Consequently, the application of this technique enables linking change in benthos-mediated diversity and ecosystem functioning to detailed insights in behavioural change.

 

Aims and methodology:

 

This project aims at further the understanding of the mechanisms that underpin the (future) functioning and diversity of marine soft-sediment ecosystems by means of laboratory experiments that shed light into how benthic key species alter their contribution to ecosystem functioning resulting from a hypothesized behavioural response to different degrees of multiple interactive stressors: hypoxia, temperature rise and acidification of seawater. 

 

Specifically, hydraulic behavioural signatures and IIV in behaviour of the shallow burrowing filter feeder C. edule and surface deposit feeder M. balthica, and the free moving omnivorous N. diversicolor will be documented under different conditions of seawater pH, temperature and dissolved oxygen which will be obtained using state-of-the-art techniques (e.g. controlled N2 and CO2 bubbling). These species have different feeding and sediment reworking modes, have been proven to maintain good condition in the laboratory for sufficient long time, and are known to alter functioning of shallow coastal sediments, e.g. sediment-water exchange of nutrients. This project will therefore, for the first time, provide direct mechanistic linkages between ecosystem functioning and species behaviour under stress by the simultaneous recording of (1) benthos behaviour using non-destructive pressure sensors, and (2) ecosystem properties, e.g.  macrofaunal, meiofaunal and microbial community composition, and fluxes of carbon, nitrogen and oxygen across the sediment-water interface. 

 

References to the subject proposal:

 

[1]Snelgrove, P.V.R., 1999. Bioscience 49, 129-138; [2]Airoldi, L., Beck, M.W., 2007. Oceanography and Marine Biology, Vol 45, 345-405; [3]Diaz, R.J., Rosenberg, R., 2000. Science 321, 926-929; [4]IPCC, 2007. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp; [5]Provoost, P., et al., 2010. Biogeosciences 7, 3869-3878; [6]Wootton, J.T., et al., 2008. Proceedings of the National Academy of Sciences of the United States of America 105, 18848-18853; [7]Kroeker, K.J., et al., 2010. Ecology Letters 13, 1419-1434; [8]Van Colen, C., et al., 2012. Plos One 7, e446555; [9]Thrush, S.F., et al., 2009. Proceedings of the Royal Society B-Biological Sciences 276, 3209-3217; [10]Russell, B.D., et al., 2012. Biology Letters 8, 164-166; [11]Wernberg, T., et al., 2012. Global Change Biology 18, 1491-1498; [12]Briffa, M., et al., in press. Animal behaviour; [13]Briffa, M., et al., 2012. Marine Pollution Bulletin 64, 1519–1528; [14]Stamps, J.A., et al. 2012. Animal behaviour 83, 1325-1334; [15] Braeckman, U,. et al., 2010. Marine Ecology Progress Series 422: 179-191; [16]Van Colen et al. 2012 Plos One 7, e49795; [17] Woodin, S.A., et al., 2010. Integrative and Comparative Biology 50, 176-187; [18]Wethey, D.S., et al., 2008. Journal of Marine Research 66, 255-273.