Phytoplankton size diversity and ecosystem function relationships across oceanic regions.

Esteban Acevedo-Trejos,Emilio Marañón,Agostino Merico

doi:10.1098/rspb.2018.0621

Abstract

Trait diversity, a key component of biodiversity, mediates many essential ecosystem functions and services. However, the mechanisms behind such relationships at large spatial scales are not fully understood. Here we adopt the functional biogeography approach to investigate how the size composition of phytoplankton communities relates to primary production and export production along a broad latitudinal gradient. Using in situ phytoplankton size distribution data and a trait-based model, we find an increase in the average phytoplankton size, size diversity, primary production and export when moving from low to high latitudes. Our analysis indicates that the interplay between spatio-temporal heterogeneities in environmental conditions and a trade-off between the high affinity for nutrients of smaller cells and the ability to avoid predation by larger cells are the main mechanisms driving the observed patterns. Our results also suggest that variations in size diversity alone do not directly lead to changes in primary production and export. The trade-off thus introduces a feedback that influences the relationship between size diversity and ecosystem functions. These findings support the importance of environmentally mediated trade-offs as crucial mechanisms shaping biodiversity and ecosystem function relationships at large spatial scales.

Highlights

Biodiversity, intended in its broadest sense, is linked to key ecosystem functions and to ecosystem services that are essential to humans [1]
Using in situ size-distribution data and a trait-based model we showed an equatorward decreasing trend in phytoplankton biomass, mean size, size diversity, gross primary production and export
These latitudinal patterns are congruent with the current general understanding of phytoplankton biogeography based on in situ [20,21] and remotely sensed [40,41] data, observations of functional groups based on pigment concentrations [42], and different trait-based modelling applications [43,44]

Summary

Introduction

Biodiversity, intended in its broadest sense (i.e. the variety of species, genes and functional traits in an ecosystem), is linked to key ecosystem functions (e.g. primary production, nutrient cycling and decomposition) and to ecosystem services that are essential to humans (e.g. food production and climate regulation) [1]. Of trade-offs and environmental variability as key mechanisms mediating BP relationships These studies observed that increases in the mean trait value and in the frequency of environmental disturbances (or in the spatial heterogeneity of resources) lead to an increase in phytoplankton production by means of both complementarity and selection. This young area of research combines knowledge of traditional fields such as ecology, biogeography and earth systems science, with the aim of studying the distribution of forms and functions of organisms, populations, communities and ecosystems along large spatial scales [11,12] This new approach uses functional traits as a currency to link different organizational levels (e.g. from organisms to ecosystems [13,14]). Our aim is to provide insights into the mechanisms shaping the patterns of phytoplankton size diversity and ecosystem function (primary production and export) relationships along large spatial scales

Methods

Results

Discussion