Functional diversity of reef molluscs along a tropical-to-temperate gradient

Matthew Floyd,Masaru Mizuyama,Brigitte Sommer,Mark Gr Miller,Masami Obuchi,Iori Kawamura,James D Reimer,Maria Beger,Hiroki Kise

doi:10.1007/s00338-020-01970-2

Abstract

Global warming is leading to range shifts of marine species, threatening the structure and functioning of ecological communities and human populations that rely on them. The largest changes are seen in biogeographic transition zones, such as subtropical reef communities, where species range shifts are already causing substantial community reorganisation. This causes functional changes in communities over subtropical latitudes, though a baseline functional understanding remains elusive for many taxa. One key marine taxon are molluscs, which provide many ecosystem services, are important prey for fishes and are also fisheries targets themselves, but remain largely unstudied. Here, we examine the trait composition, functional diversity, and functional redundancy of mollusc assemblages along the tropical-to-temperate transition in Japan (25° to 35° Northern latitude). Specifically, we use a trait database of 88 mollusc species from 31 subtropical reefs along the Pacific coast of Japan to show that trait composition of mollusc assemblages changes continuously along the latitudinal gradient. We discover that functional diversity of mollusc assemblages decreases with increasing latitude, a pattern associated with declines in functional dispersion. Moreover, we find a clear distinction between tropical and subtropical mollusc assemblages, with substrate-attached, suspension feeding bivalves more abundant in the tropics and free-living gastropod grazers more prevalent at higher latitudes. Our trait-based evidence in this study shows a contraction and almost complete shift in the functioning of marine mollusc assemblages at biogeographic transition zones and our trait database facilitates further study. Our findings provide evidence of the changing taxonomic and functional composition of extant mollusc communities with latitude, pointing to potential pertinent changes and tropicalisation of these communities with rapid ocean warming.

Highlights

The diversity of species and their traits are directly related to ecosystem stability and ecological functioning (Hooper et al 2005; Hughes et al 2017)
We discover that functional diversity of mollusc assemblages decreases with increasing latitude, a pattern associated with declines in functional dispersion
The functional diversity of communities decreases with latitude, in concert with loss in functional dispersion, whereas gradients in functional richness are independent of latitude

Summary

Introduction

The diversity of species and their traits are directly related to ecosystem stability and ecological functioning (Hooper et al 2005; Hughes et al 2017). Localised extinctions of native species can lead to the loss of important ecosystem functions such as food provision (Micheli et al 2014), and are projected for many coral reef ecosystems (Pratchett et al 2018). Because of this, evaluating changes in ecosystem function with trait-based approaches is an important tool to help understand ecosystem stability (Worm et al 2006). Trait-based approaches link directly to ecological functions (Mouillot et al 2013, 2014), and changes in functioning over time can be better understood by considering current functional differences over spatial gradients such as latitude. Considering the large diversity of organisms inhabiting reef assemblages, there is a need to assess the trait-based responses to environmental stressors for other key taxa (Przeslawski et al 2008)

Methods

Results

Conclusion