Latitudinal consistency of biomass size spectra - benthic resilience despite environmental, taxonomic and functional trait variability

Mikołaj Mazurkiewicz,Maria Włodarska-Kowalczuk,Barbara Górska,Paul E Renaud

doi:10.1038/s41598-020-60889-4

Mikołaj Mazurkiewicz, Maria Włodarska-Kowalczuk + Show 2 more

Open Access

https://doi.org/10.1038/s41598-020-60889-4

Copy DOI

Abstract

Global warming is expected to cause reductions in organism body size, a fundamental biological unit important in determining biological processes. Possible effects of increasing temperature on biomass size spectra in coastal benthic communities were investigated. We hypothesized higher proportions of smaller size classes in warmer conditions. Soft bottom infauna samples were collected in six Norwegian and Svalbard fjords, spanning wide latitudinal (60–81°N) and bottom water temperature gradients (from −2 to 8 °C). Investigated fjords differed in terms of environmental settings (e.g., pigments or organic carbon in sediments). The slopes of normalised biomass size spectra (NBSS) did not differ among the fjords, while the benthic biomass and NBSS intercepts varied and were related to chlorophyll a and δ13C in sediments. The size spectra based on both abundance and biomass remained consistent, regardless of the strong variability in macrofauna taxonomic and functional trait composition. Variable relationships between temperature and body size were noted for particular taxa. Our results indicate that while benthic biomass depends on the nutritional quality of organic matter, its partitioning among size classes is consistent and independent of environmental and biological variability. The observed size structure remains a persistent feature of studied communities and may be resilient to major climatic changes.

Highlights

Global warming is expected to cause reductions in organism body size, a fundamental biological unit important in determining biological processes
In a gradient related to river influence, normalised biomass size spectra (NBSS) slopes for deltaic macrofauna decreased from −0.5 in river mouth to −1.0 in the plume area[13]
Size structure was a conservative feature of benthic communities of undisturbed soft bottom sediments

Summary

Introduction

Global warming is expected to cause reductions in organism body size, a fundamental biological unit important in determining biological processes. Size spectra may be powerful indicators of ecosystem functioning (e.g., productivity) and environmental changes (e.g., anthropogenic disturbances)[9,10] Despite their widespread and growing use in pelagic studies, size spectra remain rarely explored in marine benthos, mostly due to methodological difficulties and time consuming laboratory sample processing (measurements of hundreds of specimens). In subsidized systems like deep-sea detritus-based benthic communities or estuaries with high allochthonous inputs from land, a slower biomass decrease with body size (NBSS slope coefficient >−1) may be observed[19,20]. In such systems size structure does not reflect trophic relationships because organisms share the same base of resources. The role of size in determining ecosystem functioning, and the possibility that climate change may potentially shift community size structure suggests this is an important (but largely neglected) characteristic of ecosystems

Objectives

Methods

Results

Discussion

Conclusion