Effects of interactions among primary and secondary foundation species on biodiversity and associated community structure

Abstract

A key foundation species, red mangroves (Rhizophora mangle), and secondary foundation species (oysters, sponges, and barnacles) that reside on mangrove prop roots are abundant along the coastline in subtropical Florida. We hypothesized the Foundation Species Interaction Biodiversity (FSIB) model, which explains the relationships between the foundation species. The interactions between the foundation species examined in the FSIB model were mutualistic (+, +), commensal (+, 0), and parasitic (+, −) interactions. We investigated the connections between the primary foundation species (mangroves) and the dominant secondary foundation species to understand the resulting variability in biodiversity within these nearshore ecosystems. Building on existing research, this study introduces the FSIB model, hypothesizing how the nuanced interactions between the primary and secondary foundation species contribute to biodiversity enhancements, a critical area previously underexplored, that will increase biodiversity. It posits that the mutualistic relationship will yield the highest biodiversity, followed by the commensal relationship, and then the parasitic relationship. All three relationships are hypothesized to result in higher diversity compared with an ecosystem lacking a secondary foundation species. The main objective of this research was to assess the predictions of the proposed FSIB model in explaining the composition of benthic communities on red mangrove prop roots. We collected data on epibiont abundance and size, site characteristics, physical and geographical variables (fetch, sediment firmness, distances from inlet and nearest freshwater discharge source, distance to nearest mangrove forest), human disturbance variables, and obtained water quality data (salinity, chlorophyll a, and turbidity). The combined results of diversity metrics, hierarchical cluster analysis, nonmetric multidimensional scaling, and constrained distance-based redundancy analysis indicated that the difference in mangrove prop root communities was largely explained by the location of the communities along the latitudinal gradient and by the presence of secondary foundation species (oysters and sponges). The shift from one secondary foundation species to another had sizable effects on associated species biodiversity, with sites that had multiple secondary foundation species experiencing higher biodiversity than sites with only one secondary foundation species.