Atmospheric Deposition Effects on Plankton Communities in the Eastern Mediterranean: A Mesocosm Experimental Approach

Tatiana M Tsagaraki,Manolis Tsapakis,Michael D Krom,Anastasia Tsiola,Christos Panagiotopoulos,Barak Herut,Travis B Meador,Stella Psarra,Tsuneo Tanaka,Kalliopi Violaki,Eyal Rahav,Nikolaos Nikolioudakis,Anna Lagaria,Antonia Giannakourou,Alexandra Gogou,Paraskevi Pitta,Soultana Zervoudaki,Epaminondas D Christou,Maria Luiza Pedrotti ,María Luz Fernández De Puelles ,Ilana R Berman Frank ,Nikos Papageorgiou

doi:10.3389/fmars.2017.00210

Abstract

The effects of atmospheric deposition on plankton community structure were examined during a mesocosm experiment using water from the Cretan Sea (Eastern Mediterranean), an area with a high frequency of atmospheric aerosol deposition events. The experiment was carried out under spring-summer conditions (May 2012). The main objective was to study the changes induced from a single deposition event, on the autotrophic and heterotrophic surface microbial populations, from viruses to zooplankton. To this end, the effects of Saharan dust addition were compared to the effects ofmixed aerosol deposition on the plankton community over 9 days. The effects of the dust addition seemed to propagate throughout the food-web, with changes observed in nearly all of the measured parameters up to copepods. The dust input stimulated increased productivity, both bacterial and primary. Picoplankton, both autotrophic and heterotrophic capitalized on the changes in nutrient availability and microzooplankton abundance also increased due to increased availability of prey. Five days after the simulated deposition, copepods also responded, with an increase in egg production. The results suggest that nutrients were transported up the food web through autotrophs, which were favored by the Nitrogen supplied through both treatments. Although, the effects of individual events are generally short lived, increased deposition frequency and magnitude of events is expected in the area, due to predicted reduction in rainfall and increase in temperature, which can lead to more persistent changes in plankton community structure. Here we demonstrate how a single dust deposition event leads to enhancement of phytoplankton and microzooplankton and can eventually, through copepods, transport more nutrients up the food web in the Eastern Mediterranean Sea.

Highlights

Mineral dust is an important driver of biogeochemical cycles in the surface ocean and an integral component of the landatmosphere-ocean system (Mahowald et al, 2005, 2008; Bryant, 2013)
The questions we aimed to address with the present experiment, with regards to the Eastern Mediterranean were: (I) how does a single dry deposition event affect the microbial food web, from viruses to zooplankton; and (II) does the source of dust make a difference to the type and magnitude of change observed
The impact of Saharan dust and mixed aerosol deposition on plankton communities was examined in the Eastern Mediterranean

Summary

Introduction

Mineral dust is an important driver of biogeochemical cycles in the surface ocean and an integral component of the landatmosphere-ocean system (Mahowald et al, 2005, 2008; Bryant, 2013). Of iron through atmospheric deposition to the ocean is well-documented and considered one of the main sources of this critical trace element to large ocean areas (Jickells, 2005 and references therein). It is a major reason why large areas of the global ocean are not Fe limited, as mineral dust provides sufficient iron to support primary productivity. Insoluble mineral apatite may drop through the surface layers without interacting with the biota but after acidification processes in the atmosphere, mainly interaction with pollutants such as NOx and SOx, it is converted into bioavailable phosphate (Nenes et al, 2011; Stockdale et al, 2016). Atmospheric aerosols contain important amounts of DON and DOP with largely unknown bioavailability (Markaki et al, 2010)

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