Abiotic conditions (e.g., temperature and pH) fluctuate through time in most marine environments, sometimes passing intensity thresholds that induce physiological stress. Depending on habitat and season, the peak intensity of different abiotic stressors can occur in or out of phase with one another. Thus, some organisms are exposed to multiple stressors simultaneously, whereas others experience them sequentially. Understanding these physicochemical dynamics is critical because how organisms respond to multiple stressors depends on the magnitude and relative timing of each stressor. Here, we first discuss broad patterns of covariation between stressors in marine systems at various temporal scales. We then describe how these dynamics will influence physiological responses to multi-stressor exposures. Finally, we summarize how multi-stressor effects are currently assessed. We find that multi-stressor experiments have rarely incorporated naturalistic physicochemical variation into their designs, and emphasize the importance of doing so to make ecologically relevant inferences about physiological responses to global change.

The effects of trawling disturbance on a benthic community were investigated with a manipulative field experiment in a fine muddy habitat that has been closed to fishing for over 25 yr. We examined the effects of extensive and repeated experimental trawl disturbance over an 18 mo period on benthic community structure and also followed the subsequent patterns of recovery over a further 18 mo During the penod of trawl disturbance the number of species and individuals increased and measures of diversity (Shannon's exponential H' and S~rnpson's reciprocal D) and evenness decreased in the trawled area relative to the reference site. The cirratulid polychaetes Chaetozone setosa and Caulleriella zetlandica were found to be most resistant to disturbance. whilst the bivalve Nucula nitidosa and polychaetes Scolopolos armiger and Nephtys cirrosa were identified as sensitive species. Multivariate analysis and abundance biomass comparison plots confirmed that community changes occurred following disturbance. with some differences between treatment and reference sites still apparent after 18 mo of recovery. Physical effects, examined with Side-scan and RoxAnn, were identifiable immediately after disturbance, but were almost indistinguishable after 18 mo of recovery. Such long recovery times suggest that even fishing during a restricted period of the year may be sufficient to maintain communities occupying fine muddy sediment habitats in an altered state.

Summary 1. Spatial management of marine ecosystems requires detailed knowledge of spatio‐temporal mechanisms linking physical and biological processes. Tidal currents, the main driver of ecosystem dynamics in temperate coastal ecosystems, influence predator foraging ecology by affecting prey distribution and ecology. The mechanistic links between tidal currents and how they influence predator–prey behaviour and interactions at a fine scale are poorly understood. 2. Studies of fine‐scale changes in oceanography, prey and predator behaviour with tidal currents require repeated surveys of the same location over brief time‐scales. Such data are highly temporally and spatially autocorrelated and require appropriate analytical tools. 3. We used functional data analysis (FDA), specifically functional principal component analysis (FPCA), to analyse repeated, fine‐scale, survey data collected in the North Sea. FPCA was used to explore the relationship between the behaviour of an important North Sea prey species (sandeel Ammodytes spp.) and a vulnerable surface‐foraging predator (black‐legged kittiwake Rissa tridactyla) with fine‐scale tidally driven changes in bio‐physical characteristics (temperature stratification and maximum subsurface chlorophyll concentration). 4. The FPCA indicated that sandeels were aggregated close to the surface at maximum ebb (ME) currents. Surface‐feeding kittiwakes were also found in highest numbers during ME in locations of both high subsurface chlorophyll concentration and shallow sandeel aggregations. We suggest that the combination of a well‐stratified water column with the movement of tidal currents over uneven topography results in surface aggregations of sandeels which kittiwakes exploit. 5. Synthesis and applications. Functional Data Analysis provides a useful tool for examining spatio‐temporal patterns in natural ecosystems. In combination with fine‐scale repeated survey design, we identified the importance of tide in driving prey behaviour and hence predator foraging behaviour. This has implications both for critical marine habitat identification for Marine Protected Area selection and for fisheries stock assessments. We therefore recommend that tidal aspects should be taken into account when designing marine surveys in temperate coastal ecosystems both to ensure the best identification of critical marine habitat and to improve the accuracy of fish stock assessments.

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