Functional traits and diversity of intertidal seaweeds: from individuals to communities

Abstract

Marine producers such as seaweeds and seagrasses support a wide range of coastal ecosystem functions and services worldwide. As marine assemblages face accelerating environmental change, there is a growing need to understand and predict ecosystem-level consequences from changes in community composition and diversity. Functional traits facilitate the link between species identity and ecosystem processes and functions. My research aimed to elucidate patterns, processes, and possible ecosystem effects of community assembly of seaweeds. More specifically, I investigated how multiple aspects of the functional diversity of seaweeds vary across an environmental gradient, from low to high shore. With collaborators, I developed an extensive database of functional traits. I then applied this trait data to community surveys across intertidal rocky shores in south Wales, UK. Scaling from individuals to communities, I investigated the taxonomic, functional, and phylogenetic structure of assemblages. Among the main findings are that 1) within morpho-functional groupsthe most common approach in seaweed functional ecologythere is substantial variation in traits, which demonstrates how much information is gained by moving from grouping approaches to measured traits; 2) functional diversity of seaweeds declines alongside species richness across the intertidal gradient in a scale-dependent way; 3) changes in dominant traits between intertidal zones represent shifts in ecological functions; and 4) phylogenetic diversity of the largest algae clade (Rhodophyta) did not accurately describe how functionally different species are, although it provided additional insights into their ecology. Collectively, results show that seaweed traits can improve our understanding of the assembly of these highly diverse marine producers, while bringing a new perspective to the well-studied seaweed intertidal zonation. Table of Contents Chapter 1. General Introduction .