Human impacts and ecosystem services: Insufficient research for trade-off evaluation

In order to perform a science-based evaluation of ecosystem service tradeoffs, research is needed on the impacts to ecosystem services from multiple human activities and their associated stressors ('impact-pathways'). Whereas research frameworks and models abound, the evidence-base detailing these pathways for trade-off evaluation has not been well characterized. Toward this end, we review the evidence for impact-pathways using estuaries as a case study, focusing on seagrass and shellfish. Keyword searches of peer-reviewed literature revealed 2379 studies for a broad suite of impact-pathways, but closer inspection demonstrated that the vast majority of these made connections only rhetorically, and only 4.6% (based on a subset of 250 studies) actually evaluated impacts of stressors on ecosystem services. Furthermore, none of the reviewed studies tested pathways based on metrics of ecosystem services value that are most relevant to beneficiaries. Multi-activity tradeoff evaluation and management will require a concerted effort to structure ecosystem-based research around impact-pathways.