Abiotic and Biotic Interactions Control Ruppia maritima Life History Development Within a Heterogeneous Coastal Landscape

Abstract

Habitat-forming submerged aquatic vegetation (SAV) in estuaries increasingly depend on sexual recruitment from propagules for population sustainability under varying conditions from climate and human-induced changes. Seed recruitment requires successful transitions through multiple life history stages, but few studies have examined abiotic and interspecies interactions on multiple life stages in SAV. A series of field experiments in Florida Bay quantified impacts of abiotic (salinity, temperature, light, sediment nutrients) and biotic (interspecific SAV interactions) factors on seedlings, adult individuals (genets), and shoots (ramets) of the SAV Ruppia maritima. Five study sites were established at the Everglades-Florida Bay ecotone, where seed recruitment sustains R. maritima. Seedling survival was low (≤ 16%), and further reduced under low light, P-limitation and competition with the macroalga Chara hornemannii. Significantly high genet survival and vegetative and sexually reproductive shoot production (4400 m−2 and 300 m−2, respectively) were found at a site where nutrients (P) were sufficient, when C. hornemannii was absent and light levels were three-times higher during the dry season (~ 14000 lumens m−2; December–March) than any other time of year. At P-limited sites, vegetative shoot production occurred with adequate light (> 20,000 lumens m−2) at stable salinities (CV 0.5) where 30–45-day averages remained < 15. However, variable or elevated salinity delayed vegetative shoot production ~ 60 days, suggesting salinity stress limits asexual reproduction. Understanding how light and P-limitation, salinity stress, and competition controls R. maritima recruitment in the Everglades is essential to its management for restoration and climate change.