Changes in biodiversity, including those due directly and indirectly to outbreaks of indigenous species, invasions by alien species and changes in distribution, can have major implications for the functioning of marine ecosystems. Changes in ecosystem functioning can, in turn, impact strongly on services and direct economic benefits to society, such as productive fisheries, aquaculture and tourism. For example, invasive gelatinous zooplankters such as Mnemiopsis may be changing foodwebs, reducing survival of larval fish and damaging fisheries. Likewise, introduced seaweeds can alter the structure and functioning of benthic assemblages.
In global terms, a substantial research effort is underway to develop a body of ecological theory to characterise and explain relationships between biodiversity and ecosystem functioning. Relevant research is, however, fragmented and has tended to focus on tractable model systems rather than changes in biodiversity that are directly relevant to society and environmental management. Synthesis is needed to clarify the extent to which general theoretical models are applicable in different environmental contexts. Research to date has focussed primarily on species-level diversity emphasising individual differences among taxa and localities. This does not offer an intuitive, quantifiable link to ecosystem functioning and services which would provide clearer direction for scientific-based management of marine ecosystems.