Abstract
Seagrasses – a group of foundation species in coastal ecosystems – provide key habitat for diverse and abundant faunal assemblages and support numerous ecosystem functions and services. However, whether the habitat role of seagrasses is influenced by seagrass diversity, by dominant species or both, remains unclear. To that end, we sought to investigate the specific seagrass characteristics (e.g., species diversity, seagrass traits) that influence tropical fish assemblages, and place this in the context of small-scale fishery use. We surveyed seagrass variables at 55 plots, nested within 12 sites around Zanzibar (Tanzania) in the Western Indian Ocean, and used Baited Remote Underwater Video (BRUV) systems to assess fish assemblages across plots. Using linear mixed models, we reveal that seagrass structural complexity and depth were the best predictors of fish abundance, with higher abundance occurring in deeper meadows or meadows with high canopy, leaf length and number of leaves per shoot. Moreover, an interaction between seagrass cover and land-use was the best predictor of fish species richness, where sites closer to human impacts were less affected by cover than sites with lower human impact. Overall, models with seagrass species richness or functional diversity as predictors poorly explained fish assemblages. Fish taxa that were important for small-scale fishery sectors (e.g., emperors, snappers, rabbitfish, and parrotfish) were primarily driven by seagrass structural complexity. Our results provide a unique analysis of the relationship between seagrass habitat and its associated fish assemblages in that we show that seagrass species diversity had little effect on seagrass fish assemblages, which instead appear driven by specific seagrass traits and seagrass cover. If conserving high value species that support adjacent fisheries is the priority for protecting seagrass meadows, then seagrass areas should be chosen with high cover and structural complexity that are in deeper waters. Any conservation measures also need to balance the needs of fishers that use the resources supported by seagrasses.
Highlights
Foundation species like trees, corals and seagrasses play a pivotal role in driving ecosystem functions and services globally (Angelini et al, 2011), notably by facilitating the creation of habitats
The upper subtidal areas are comprised of C. serrulata, T. hemprichii, H. ovalis and Syringodium isoetifolium, shifting to C. serrulata, T. hemprichii, H. ovalis, S. isoetifolium and Thalassodendron ciliatum before being often dominated by T. ciliatum and Enhalus acoroides, growing in monospecific or mixed strands, in deeper areas
We compared seven models testing the influence of seagrass meadow variables on fish abundance (MaxN), along with a null model
Summary
Foundation species like trees, corals and seagrasses play a pivotal role in driving ecosystem functions and services globally (Angelini et al, 2011), notably by facilitating the creation of habitats. The ‘mass ratio’ hypothesis proposes that ecosystem functions, like complex habitats favoring high biodiversity, are primarily determined by the functional traits of dominant species within the community (Grime, 1998). In order to manage ecosystems for the services they provide, it is vital to understand how biodiversity drives ecosystem functions (e.g., whether it is species composition or diversity, or both), especially in the context of global change (Benkwitt et al, 2020). While the topic has become a heated debate, especially with regards to terrestrial ecosystems (Picasso, 2018), meta-analyses of hundreds of experiments in terrestrial (Cardinale et al, 2011) and marine ecosystems (Gamfeldt et al, 2015) suggest that both the species composition and diversity can jointly influence ecosystem functions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
