Understanding the responses of ocean biota to a complex matrix of cumulative anthropogenic change

Oceanic conditions are changing at an unprecedented rate, and these anthropogenically driven changes will intensify into the future. The marine biota will encounter a complex shifting matrix of simultaneous environmental changes-including temperature, pH/pCO(2), nutrients, light, and oxygen-which will be further compounded by concurrent regional and local anthropogenic impacts, such as altered freshwater runoff regimes or biomass harvesting. We are only beginning to grasp the complexity of these interactive changes on ocean biota. To understand the pronounced and/or nonlinear effects of cumulative environmental stresses on organismal fitness and ecosystem functioning, the marine global-change research community can profit from the large body of existing evidence from freshwater lakes or polluted aquatic systems. We explore how the complex environmental changes will affect the biota from primary producers to higher trophic levels in both nearshore and open ocean waters, and conclude by proposing new approaches to address the formidable challenges of this research field. This Theme Section on 'Biological responses in an anthropogenically modified ocean' presents a set of papers that highlights the multiplicity of factors that will alter major biogeochemical and ecological frameworks, and raises awareness of the complexities involved in disentangling the combined effects of global, regional and local anthropogenic change on marine food webs.