Biological ecosystem traits influenced by structural changes in foundation species

Abstract

Foundation species are organisms that modify or create much of the biogenic habitat in an ecosystem. These types of organisms considerably affect biological ecosystem traits because changes that affect their structure or function will affect the entire biotic community associated with that engineered environment. Mangroves are an ideal foundation species to use when exploring structural changes in foundation species and subsequent shifts in ecosystem traits. Mangrove structure can be readily manipulated and simulated, mangrove trees grow quickly, and growth forms are plastic and highly structurally complex. In three studies, I link the habitat structure provided by the red mangrove Rhizophora mangle to biological aspects of its community: 1) R. mangle marine aerial roots influence species interactions in its attendant community, 2) anthropogenic nutrient pollution increases R. mangle canopy habitat but reduces subtidal root habitat, and 3) R. mangle subtidal roots and the epibionts that restructure that root habitat influence marine mangrove communities in the Caribbean.

R. mangle provides virtually the only hard substrate in a soft-sediment environment, requiring sessile benthic invertebrates to settle on mangrove roots in marine mangrove ecosystems. Mangrove root distance from the sea floor influences species interactions, indirectly determining sponge community composition on roots by denying or allowing sea star predators access to root-dwelling sponges.

In coastal areas with anthropogenically enhanced nitrogen levels, this extra nitrogen fertilizes trees. Fertilized trees favor canopy expansion at the expense of marine root growth, producing less marine root biomass over time.

Reduced root and root-dwelling epibiont structure shifts the abundance and diversity of attendant fish and benthic communities using this habitat. Roots and epibionts increase the capacity of marine root habitat to act as a refuge to fishes and they provide food to benthic organisms.

Together, these studies provide new perspectives on how specific elements of biogenecially engineered habitat can affect entire communities.