Intertidal Seaweeds Modulate a Contrasting Response in Understory Seaweed and Microphytobenthic Early Recruitment

José A Zertuche-González,Lydia Ladah,Schery Umanzor

doi:10.3389/fmars.2018.00296

Abstract

Recruitment is a fundamental step upon which all subsequent interactions within a community occur. We explored how the attenuation of physical conditions by seaweed plots comprised of either Chondracanthus canaliculatus, Pyropia perforata, Sylvetia compressa or a mixed aggregation, at varying densities (average 1199, 816 and 408 in. m-2), affected recruitment of seaweeds and microphytobenthic organisms in the understory, and if physical factors modulate their abundance and distribution. We outplanted macroscopic seaweeds in the intertidal and measured changes in understory irradiance, particle retention, and bulk water flow. Both factors influenced physical conditions below the canopy. However, only canopy density had a significant effect on recruitment. The low-density treatments showed greater abundance of seaweeds, with the opposite found for microphytobenthic organisms. The recruitment processes of seaweeds and microphytobenthic organisms, however, appeared to be independent of each other and were not due to competition. We conclude that it is crucial to consider microscale biological interactions, which are rarely addressed when assessing recruitment processes of benthic primary producers.

Highlights

Abiotic factors can affect both the distribution and abundance of organisms, modulating community structure (Crain and Bertness, 2006)
Higher abundances of seaweed recruits occurred underneath canopy treatments with the least attenuated physical conditions, whereas the MPB showed the lowest abundance under these conditions
Our results indicate that the attenuation of physical factors driven by macroscopic seaweeds influences the abundance and distribution of seaweed and MPB recruits differently

Summary

INTRODUCTION

Abiotic factors can affect both the distribution and abundance of organisms, modulating community structure (Crain and Bertness, 2006). We evaluated the factors that could be affecting the patterns of distribution and abundance of seaweed recruits underneath manipulated canopies in the intertidal compared to MPB settlement. Evidence shows that there are multiple factors, both inherent and external to the species, that can influence successful settlement and recruitment of early stages. External factors such as particle movement resulting in sedimentation, siltation, scour or increased turbidity might affect early settlers by either preventing or enhancing their survival. Particle movement resulting in complete burial or sand scour can, have a positive outcome for some algal species such as Rhodomela, Penicillus, and Halimeda, allowing their colonization of areas where other species would not thrive (Hurd et al, 2014) Substrate properties such as its topography and stability can greatly enhance or reduce successful seaweed recruitment. We determined if seaweed recruitment was correlated to the attenuation of bulk water flow, particle transport, and irradiance driven by the experimental canopies

MATERIALS AND METHODS

RESULTS

DISCUSSION