Body size affects the vertical movement of benthic amphipods through subsurface sediments in response to drying

C Patel,P J Wood,K L Mathers,A N Vadher,C Dwyer

doi:10.1007/s10750-020-04500-x

Abstract

This study aimed to experimentally examine how riverbed drying and different rates of water level reduction influenced the vertical movement of amphipods of various sizes into different subsurface sediment compositions. Using sediment columns (mesocosms) filled with different sized transparent substrates, we explored how varying speeds of drawdown affected vertical movement and stranding of individuals. We hypothesised that: (1) larger individuals would be less able to migrate within subsurface sediments compared to smaller ones; (2) smaller sediment particles would lead to more individuals becoming stranded and; (3) faster rates of water level drawdown would increase the likelihood of individuals becoming stranded above the waterline. Body size significantly influenced the final position of an individual, with smaller individuals accessing deeper sediments more readily. Larger amphipods were more likely to become stranded above the waterline. Amphipods migrated to greater depths during faster water level reduction rates with smaller individuals displaying greater overall movement. Sediment particle size did not influence the ability of amphipods to move vertically into subsurface sediments in response to water level reduction. The results indicate that subsurface sediments may serve as a refuge from surface drying but that both the size of individual invertebrates influences their ability to migrate vertically.

Highlights

The dewatering of benthic sediments has increased globally due to natural events and anthropogenic activities (e.g., Pyne & Poff, 2016; Stubbington et al, 2017; Datry et al, 2018)
Head size was significantly associated with an individual’s final position, with smaller G. pulex individuals accessing deeper sediments more readily
Our findings support our first hypothesis that the vertical movement of G. pulex and D. villosus would vary as a function of their relative body size, with larger individuals being less able to move through subsurface sediments compared to smaller individuals

Summary

Introduction

The dewatering of benthic sediments has increased globally due to natural events and anthropogenic activities (e.g., Pyne & Poff, 2016; Stubbington et al, 2017; Datry et al, 2018). Channel drying and loss of surface water results in distinct species assemblages (Leigh et al, 2016; Bogan et al, 2017; Mathers et al, 2019a), characterised by fauna exhibiting resistance and resilience traits to surface water drying such as use of atmospheric oxygen (Stanley et al, 1994), desiccationresistant life stages (Stubbington et al, 2016), or the ability to rapidly recolonize following the rewetting and resumption of favourable conditions (Vander Vorste et al, 2016a; Paril et al, 2019). The refuge potential may be highly variable depending on water table depth (Vander Vosrte et al, 2016b) and the nature of surface-groundwater exchange (Folegot et al, 2018)

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