Incorporating generalist seagrasses enhances habitat restoration in a changing environment

Coastal habitat-forming species provide protection and essential habitat
for fisheries but their ability to maintain these services are under
threat from novel stressors including rising temperatures. Coastal habitat
restoration is a powerful tool to help mitigate the loss of
habitat-forming species, however, many efforts focus on reintroducing a
single, imperiled species instead of incorporating alternatives that are
more conducive to current and future conditions. Seagrass restoration has
seen mixed success in halting local meadow declines but could begin to
specifically utilize generalist seagrasses with climate change-tolerant
and opportunistic life history traits including high reproduction rates
and rapid growth. Here, we built on decades of successful eelgrass
(Zostera marina) restoration in the Chesapeake Bay by experimentally
testing seed-based restoration potential of widgeongrass (Ruppia maritima)
– a globally distributed seagrass that can withstand wide ranges of
salinities and temperatures. Using field experiments, we evaluated which
seeding methods yielded highest widgeongrass survival and growth, tested
if seeding widgeongrass adjacent to eelgrass can increase restoration
success, and quantified how either seagrass species changes restored bed
structure, invertebrate communities, and nitrogen cycling. We found
widgeongrass can be restored via direct seeding in the fall, and that
seeding both species maximized total viable restored area. Our pilot
restoration area increased by 98% because we seeded widgeongrass in
shallow, high temperature waters that are currently unsuitable for
eelgrass survival and thus, would remain unseeded via only eelgrass
restoration efforts. Restored widgeongrass had higher faunal diversity and
double animal abundance per plant biomass than restored eelgrass, whereas
restored eelgrass produced three times greater plant biomass per unit area
and higher nitrogen recycling in the sediment. Synthesis and
applications: Overall, we provide evidence that supplementing
opportunistic, generalist species into habitat restoration is a proactive
approach to combat climate change impacts. Specifically, these species can
increase trait diversity which, for our study, increased total habitat
area restored - a key factor to promote seagrass beds' facilitation
cascades, stability, and grass persistence through changing environments.
Now, we call for tests to determine if the benefits of restoration with
generalist species alone or in conjunction with historically dominant taxa
are broadly transferrable to restoration in other marine and terrestrial
habitats.