Decades of eelgrass meadow dynamics across the northeast Pacific support seascape-scale conservation

Abstract

Abstract Eelgrass meadows provide vital nearshore habitats and ecosystem services, but they have declined from human stressors and conservation efforts are now widespread. Dynamic ecosystems like eelgrass meadows naturally rearrange as disturbance and recruitment unfold across seascapes. However, some decisions that protect eelgrass only consider extant meadows, thus ignoring the potential for change. Here, we report decades of eelgrass dynamics observed across the northeast Pacific. Our observations support conservation expanded to the seascape scale, which includes potentially inhabitable areas along with extant meadows. We found that total seascape meadow area changed over time, and changes within seascapes were often asynchronous. Some meadows rearranged across seascapes over multiple kilometres and decades. Also, some seascapes compartmentalized meadow collapse, which enabled later recovery, or supported local recruitment that substantially increased total meadow area. These observations were consistent with hierarchical patch dynamics, which promote ecosystem persistence over larger space and time scales. Thus, to enable the dynamics that underpin eelgrass persistence, it is necessary to keep many eelgrass habitat options open across seascapes, rather than protect only extant meadows. Given that dynamic, hierarchical ecosystems are common along marine shorelines, this approach may be effective for both nearshore ecosystems in general and for eelgrass in particular.