Positive and Negative Species Interactions Shape Recruitment Patterns of a Range Expanding Native Alga

Sofie E Voerman,Tim M Glasby,Paul E Gribben

doi:10.3389/fmars.2021.594447

Abstract

A species’ ability to spread is in part governed by the extent to which recipient habitats either resist, tolerate or promote the species’ recruitment. In disturbed marine environments, there is a general trend for the loss of algal canopies, thought to resist invasion, toward algal turf or rock barrens habitat. This study tested whether the spread of the range-expanding native macroalga Caulerpa filiformis was resisted by algal canopies but facilitated by algal turf or barrens habitats. Large-scale field surveys generally supported the predicted recruitment patterns, with C. filiformis recruits being most abundant on turf (but not barrens) and absent under kelp canopies. However, a discrepancy existed between different structural forms of turf, with the positive association holding true only for geniculate corallines, not filamentous turf. Secondly, a laboratory experiment tested whether the physical structure and/or the sediment-trapping properties of coralline turf influenced the recruitment success of C. filiformis. Whilst the structural complexity of turf aided overall recruitment performance (i.e., increased rhizoid production, attachment speed, success, and strength), a positive influence of turf-derived sediment on recruits’ growth was less obvious, at least over 10 days. The high morphological plasticity of C. filiformis propagules resulted in possible benefits of faster or stronger attachment of more developed propagules being only temporary, and that recruitment may be regulated in accordance with habitat preference. Finally, a field experiment confirmed the observed positive role of turf and the negative influence of algal canopies in the short-term, however, adverse environmental conditions in the longer-term resulted in the loss of most fragments. In conclusion, this study demonstrated the importance of both positive and negative species interactions for the recruitment success of a native alga, suggesting that a shift from kelp to turf algae can initiate further community change.

Highlights

Foundation species shape the functioning of entire ecosystems (Stachowicz, 2001)
This study investigated the roles of canopy-forming habitats and less structured habitats, in the recruitment success of C. filiformis
Turf is considered a normal component of the mosaic of shallow rocky reef habitats in New South Wales (NSW) (Underwood et al, 1991; Andrew and Underwood, 1993), turf may represent degraded conditions where has resulted from the loss of canopy-forming algae (Airoldi and Beck, 2007; Filbee-Dexter and Wernberg, 2018)

Summary

Introduction

Foundation species (those that form for example coral reefs, mangrove, and kelp forests) shape the functioning of entire ecosystems (Stachowicz, 2001). Human disturbances acting at a range of scales are eroding the resistance and resilience of foundation species, often leading to phase shifts (or alternative stable states) in which foundation species are lost or replaced by more stress-tolerant species that may differ in their functioning (Hughes et al, 2007; Norström et al, 2009; Montefalcone et al, 2015; O’Brien and Scheibling, 2018). These resulting alternative communities may facilitate further community change (Didham et al, 2007; Tylianakis et al, 2008). Loss of kelp can lead to invasive species becoming dominant on rocky reefs (Valentine and Johnson, 2003; Britton−Simmons and Abbott, 2008; Thompson and Schiel, 2012), or lead to a transition to smaller turf-forming algae (hereafter turf) (Airoldi and Beck, 2007; Connell et al, 2008; Moy and Christie, 2012; Filbee-Dexter and Wernberg, 2018; O’Brien and Scheibling, 2018; Straub et al, 2019)

Methods

Results

Discussion

Conclusion