Cumulative Impacts in Marine and Coastal Systems: State of the Practice

As human dependence on and use of ocean resources increases, the cumulative stress of those activities has contributed to a decline in the health of ocean and coastal ecosystems. Despite legal mandates requiring resource managers to analyze the combined impacts of these activities on the environment, cumulative effects assessments (CEAs) in coastal and marine ecosystems are often limited in detail and scope. To better understand how practitioners conduct cumulative effects assessments, we disseminated a survey on current practices, challenges, and opportunities for improving CEAs across multiple geographies. The online survey was sent to CEA practitioners in California, United States; British Columbia, Canada; Queensland, Australia; and New Zealand and three focal areas: (1) metrics for determining significance; (2) the use of baselines and thresholds; and (3) the spatial and temporal scale of analysis.

Our Findings and Recommendations

Practitioners face many challenges assessing cumulative effects using current laws and the scientific tools currently available. Overall, we found that practitioners conduct CEAs using the tools and data that are most available to them, creating inconsistent assessment methodologies within and between the geographies we surveyed.

>Define terms: Practitioners differentially define key components of CEAs, including “effect,” “significance,” and “baseline” and would benefit from consistent legal definitions that are based on the best available science.

>Develop indicators and thresholds: Practitioners want additional tools and methods for identifying relevant ecological indicators and thresholds of impact for cumulative effects.

>Rethink spatial scale: Many practitioners conduct CEAs on spatial scales that are misaligned with the proposed project’s current and expected effects and the ecosystem components that are likely to be impacted.

>Increase access to ecological and project data: Practitioners call for shared databases of ecosystem baseline and concurrent projects information so they can better evaluate past, present, and possible future cumulative effects within a geographic region.

>Increase access to resources: Practitioners have limited capacity (e.g., technical tools and time) and limited resources (e.g., funding, staff) to conduct thorough CEAs.

An effort to improve the law, science, and practice of cumulative impact assessment

It is difficult to account for the cumulative effect of multiple stressors that co-occur in space and time. While cumulative effects in marine ecosystems are increasing, we do not fully understand how practitioners are evaluating those impacts. This study is the first effort to document what information is currently being used in assessments and what information is needed to more adequately assess cumulative effects moving forward. In parallel to this study, our team assessed the science and law of CEAs to identify solutions for improving how CEAs are conducted, using the best legal and scientific tools.

The Redondo Beach Pier, power plant and sewage treatment plant.  Photo Credit: © Paula Lauren Gibson, MarinePhotobank.