Inter-specific and inter-individual trait variability matter in surface sediment reworking rates of intertidal benthic foraminifera

Noémie Deldicq,Vincent M P Bouchet,Laurent Seuront

doi:10.1007/s00227-021-03908-w

Abstract

Although benthic foraminifera are an important component of meiofauna and contribute to carbonate production and carbon/nitrogen cycles, their role in bioturbation processes remains poorly known. Five dominant intertidal benthic foraminiferal species were recently classified into functional bioturbator groups according to their sediment reworking mode and intensity. Our study aimed at identifying potential drivers (i.e. size and/or travelled distance) of species-specific surface sediment reworking rate. The travelled distance and surface sediment reworking rate of Haynesina germanica, Cribroelphidium williamsoni, Ammonia tepida, Quinqueloculina seminulum and Miliammina fusca were assessed through image analysis. Our results show that the surface sediment reworking performed by these species is not size-dependent, but dependent on their motility traits through interspecific differences in the travelled distance. Smaller species (i.e. Quinqueloculina seminulum and Haynesina germanica) contributed more to surface sediment reworking than larger ones (i.e. Ammonia tepida, Cribroelphidium williamsoni and Miliammina fusca). These observations stress the critical role of motion behaviour in surface sediment reworking processes by intertidal foraminifera. Finally, we stress that the high inter-individual variability observed in conspecific motion behaviour may be important to decipher the role of foraminifera in sediment bioturbation. Noticeably, the species characterized by a strong inter-individual variability are also the species that have the highest surface sediment reworking rates. This last observation may inform on the species-specific phenotypic plasticity and, therefore, the potential for the functional role of these species to be maintained in their natural environment. This is particularly relevant in an era of global change where ecosystem balance is increasingly threatened by various stressors such as heat-waves, ocean acidification and pollution.

Highlights

Bioturbation activities of benthic fauna contribute to the structure and functioning of most marine soft-sediment ecosystems; see Kristensen et al (2012) for a review
These observations strongly suggest that the role of meiofauna in bioturbation processes needs to be urgently considered in studies dealing with benthic ecosystem functioning as they play an important role in soft sediment ecosystems (Näslund et al 2010; Nascimento et al 2012; Bonaglia et al 2014, 2020)
The specific objectives of the study were (i) to estimate individual surface sediment reworking rate of five dominant intertidal foraminifera species in temperate intertidal mudflats, (ii) to understand how morphological traits or those related to their displacements would influence SSRRi and (iii) to further link these traits and SSRRi intensity to the functional groups recently introduced for benthic foraminifera

Summary

Introduction

Bioturbation activities of benthic fauna contribute to the structure and functioning of most marine soft-sediment ecosystems; see Kristensen et al (2012) for a review. Beyond the fact that they may be more abundant, diverse and resilient than macro-invertebrates (Gerlach 1978; Bouchet et al 2018, 2020), their contribution to sediment reworking and bio-irrigation is non-negligible compared to the one of macroinvertebrates (Rysgaard et al 2000; Gross 2002; Näslund et al 2010; Bonaglia et al 2014; Bouchet and Seuront 2020) Through their movement and feeding activity, meiofaunal organisms further structure and constrain microbial communities that are crucial for organic matter mineralization (De Mesel et al 2004; Moens et al 2005; Nascimento et al 2012). These observations strongly suggest that the role of meiofauna in bioturbation processes needs to be urgently considered in studies dealing with benthic ecosystem functioning as they play an important role in soft sediment ecosystems (Näslund et al 2010; Nascimento et al 2012; Bonaglia et al 2014, 2020)

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