Horizontal Distribution of Deep Sea Microplankton: A New Point of View for Marine Biogeography

Jessica Vannini,Salvatore Moscatello,Letterio Guglielmo,Lidia Yebra,Genuario Belmonte,Antonia Granata

doi:10.3390/w13091263

Abstract

An investigation on microplankton composition and spatial distribution has been carried out around Italian seas. The analysis of 53 samples, collected in 2017 at two depths in 27 different stations, has led to a scenario of horizontal distribution of microplankton. Dinophyta and Ciliophora were chosen as representatives of the whole microplankton community. A total of 60 genera were identified. Cluster analysis of data regarding taxa presence and abundance led us to recognize that similarities between surface stations were more evident than those between deep ones. Furthermore, we conducted an inter-annual comparison with available data from the South Adriatic Sea (2013, 2015). The higher dissimilarity between deep sea samples was also confirmed in a relatively smaller geographic area. The dissimilarity of deep-sea samples does not correspond to a higher habitat diversification, in terms of abiotic parameters. It has been suggested that the negligible biological connectivity in the deep, for those micro-organisms not able to perform wide spatial migrations, could produce such a biological diversification.

Highlights

Microplankton is considered fundamental for pelagic marine ecosystem functioning [1]; this notwithstanding, studies on this marine compartment are still largely insufficient
Dale [7] and Taylor [8] calculated that only 13–16% of about 2000 marine Dinophyta species were known to produce resting stages, and this trait of the life cycle has been described only in 3 species of marine Ciliophora Oligotrichida from a total of 141 known species [9,10,11]
The present study aims to compare the horizontal variability of surface microplankton with that of deep waters, to verify if the mesophotic community assemblages can be partitioned in local subcommunities, in some way corresponding to those of the surface or, on the contrary, if a possibly different geographic distribution of microplankton at different water depths exists and why

Summary

Introduction

Microplankton is considered fundamental for pelagic marine ecosystem functioning [1]; this notwithstanding, studies on this marine compartment are still largely insufficient. Thanks to the presence of resting stages, locally even more abundant than corresponding active stages [4], microplankton organisms are considered to be geographically widespread and sometimes present everywhere [5,6] This generalization, derives mainly from studies of freshwater organisms, and knowledge of adaptation and distribution mechanisms of unicellular organisms in the sea abruptly decreases from the coastline towards the pelagic habitat. Microplankton, in addition, performs vertical migration only for short distances [13] not comparable to vertical daily migrations of hundreds of meters typical of mesoplanktonic crustaceans, and/or horizontal movements of kms typical of nekton These facts strongly suggest the isolation of local communities. If such a supposition is correct, microplankton distribution might be characterized by a geographic partitioning someway independent of abiotic features

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Conclusion