Plankton in the open Mediterranean Sea: a review

Abstract. We present an overview of the plankton studies conducted during the last 25 years in the epipelagic offshore waters of the Mediterranean Sea. This quasi-enclosed sea is characterized by a rich and complex physical dynamics with distinctive traits, especially in regard to the thermohaline circulation. Recent investigations have basically confirmed the long-recognised oligotrophic nature of this sea, which increases along both the west-east and the north-south directions. Nutrient availability is low, especially for phosphorous (N:P up to 60), though this limitation may be buffered by inputs from highly populated coasts and from the atmosphere. Phytoplankton biomass, as chl a, generally displays low values (less than 0.2 μg chl a l−1) over large areas, with a modest late winter increase. A large bloom (up to 3 μg l−1) is observed throughout the late winter and spring exclusively in the NW area. Relatively high biomass values are recorded in fronts and cyclonic gyres. A deep chlorophyll maximum is a permanent feature for the whole basin, except during the late winter mixing. It is found at increasingly greater depths ranging from 30 m in the Alboran Sea to 120 m in the easternmost Levantine basin. Primary production reveals a west-east decreasing trend and ranges between 59 and 150 g C m−2 y−1 (in situ measurements). Overall, the basin is largely dominated by small autotrophs, microheterotrophs and egg-carrying copepod species. The microorganisms (phytoplankton, viruses, bacteria, flagellates and ciliates) and zooplankton components reveal a considerable diversity and variability over spatial and temporal scales, although the latter is poorly studied. Examples are the wide diversity of dinoflagellates and coccolithophores, the multifarious role of diatoms or picoeukaryotes, and the distinct seasonal or spatial patterns of the species-rich copepod genera or families which dominate the basin. Major dissimilarities between western and eastern basins have been highlighted in species composition of phytoplankton and mesozooplankton, but also in the heterotrophic microbial components and in their relationships. Superimposed to these longitudinal differences, a pronounced biological heterogeneity is also observed in areas hosting deep convection, fronts, cyclonic and anti-cyclonic gyres or eddies. In such areas, the intermittent nutrient enrichment promotes a switching between a small-sized microbial community and diatom-dominated populations. A classical food web readily substitutes the microbial food web in these cases. These switches, likely occurring within a continuum of trophic pathways, may greatly increase the flux towards higher trophic levels, in spite of the apparent heterotrophy. Basically, the microbial system seems to be both bottom-up and top-down controlled. A "multivorous web" is shown by the great variety of feeding modes and preferences and by the significant and simultaneous grazing impact on phytoplankton and ciliates by mesozooplankton.

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Plankton in the open Mediterranean Sea: a review

Biogeosciences Discussions ◽

10.5194/bgd-6-11187-2009 ◽

2009 ◽

Vol 6 (6) ◽

pp. 11187-11292 ◽

Cited By ~ 7

Author(s):

I. Siokou-Frangou ◽

U. Christaki ◽

M. G. Mazzocchi ◽

M. Montresor ◽

M. Ribera d'Alcalá ◽

...

Keyword(s):

Food Web ◽

Mediterranean Sea ◽

Deep Convection ◽

Trophic Levels ◽

Grazing Impact ◽

Late Winter ◽

Amazon Forest ◽

Chl A ◽

Spatial And Temporal Scales ◽

The Mediterranean

Abstract. We present an overview of the plankton studies conducted during the last 25 years in the epipelagic offshore waters of the Mediterranean Sea. This quasi-enclosed sea is characterized by a rich and complex physical dynamics that includes unique thermohaline features, particular multilayer circulation, topographic gyres, and meso- and sub-mesoscale activity. Recent investigations have basically confirmed the long-recognised oligotrophic character of this sea, which enhances along both the west-east, and the north-south directions. Nutrient availability is low, especially for phosphorous (N:P up to 60), although limitation may be relaxed by inputs from highly populated coasts and from the atmosphere. Phytoplankton biomass as chl-a, generally displays low values (less than 0.2 μg chl-a l-1) over large areas, with a modest late winter increase. A large bloom (up to 3 μg l-1) throughout the late winter and early spring is only observed in the NW area. Relatively high biomass peaks are also recorded in fronts and cyclonic gyres. A deep chlorophyll maximum is a~permanent feature for the whole basin (except during the late winter mixing). It progressively deepens from the Alboran Sea (30 m) to the easternmost Levantine basin (120 m). Primary production reveals a similar west-east decreasing trend and ranges from 59 to 150 g C m-2 y-1 (in situ measurements). Overall the basin is largely dominated by small-sized autotrophs, microheterotrophs and egg-carrying copepod species. The phytoplankton, the microbial (both autotrophic and heterotrophic) and the zooplankton components reveal a considerable diversity and variability over spatial and temporal scales, the latter less explored though. Examples are the wide diversity of dinoflagellates and coccolithophores, the multifarious role of diatoms or picoeukaryotes, and the distinct seasonal or spatial patterns of the species-reach copepod genera or families which dominate in the basin. Major dissimilarities between western and eastern basins have been highlighted in species composition of phytoplankton and mesozooplankton, but also in the microbial components and in their relationships. Superimposed to these longitudinal differences, a pronounced biological heterogeneity is also observed in areas hosting deep convection, fronts, cyclonic and anti-cyclonic gyres or eddies. There, the intermittent nutrient enrichment promotes switches from a small-sized microbial community to diatom-dominated populations. A classical food web is ready to substitute the microbial food web in these cases. These switches, likely occurring within a continuum of trophic pathways, may greatly enhance the flux towards high trophic levels, in spite of an apparent heterotrophy. Basically, the system seems to be top-down controlled and characterised by a ‘multivorous web’, as shown by the great variety of feeding modes and preferences and by the significant and simultaneous grazing impact on phytoplankton and ciliates by mesozooplankton. ‘La Mediterrània, o almenys la seva zona pelàgica, seria comparable a una Amazònia marina.’ (Margalef, 1995) (The Mediterranean, or at least its pelagic zone, would be like a marine version of the Amazon forest.)

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Mesoscale variations in the assemblage structure and trophodynamics of mesozooplankton communities of the Adriatic basin (Mediterranean Sea)

10.5194/bg-2021-240 ◽

2021 ◽

Author(s):

Emanuela Fanelli ◽

Samuele Menicucci ◽

Sara Malavolti ◽

Andrea De Felice ◽

Iole Leonori

Keyword(s):

Food Web ◽

Food Webs ◽

Mediterranean Sea ◽

Environmental Variables ◽

Complex Structure ◽

Assemblage Structure ◽

Trophic Levels ◽

Ecosystem Functions ◽

Food Web Structure ◽

Adriatic Basin

Abstract. Zooplankton are critical to the functioning of ocean food webs because of their utter abundance and vital ecosystem roles. Zooplankton communities are highly diverse and thus perform a variety of ecosystem functions, thus changes in their community or food web structure may provide evidence of ecosystem alteration. Assemblage structure and trophodynamics of mesozooplantkon communities were examined across the Adriatic basin, the northernmost and most productive basin of the Mediterranean Sea. Samples were collected in June–July 2019 along coast-offshore transects covering the whole western Adriatic side, consistently environmental variables were also recorded. Results showed a clear separation between samples from the northern-central Adriatic and the southern ones, with a further segregation, although less clear, of inshore vs. off-shore stations, the latter mostly dominated in the central and southern stations by gelatinous plankton. Such patterns were mainly driven by chlorophyll-a concentration (as a proxy of primary production) for northern-central stations, i.e. closer to the Po river input, and by temperature and salinity, for southern ones, with the DistLM model explaining 46 % of total variance. The analysis of stable isotopes of nitrogen and carbon allowed to identify a complex food web characterized by 3 trophic levels from herbivores to carnivores, passing through the mixed feeding behavior of omnivores, shifting from phytoplankton/detritus ingestion to microzooplankton. Trophic structure also spatially varied according to sub-area, with the northern-central sub-areas differing from each other and from the southern stations. Our results highlighted the importance of environmental variables as drivers of zooplanktonic communities and the complex structure of their food webs. Disentangling and considering such complexity is crucial to generate realistic predictions on the functioning of aquatic ecosystems, especially in high productive and, at the same time, overexploited area such as the Adriatic Sea.

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Interactive effects of temperature and light during deep convection: a case study on growth and condition of the diatom Thalassiosira weissflogii

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu218 ◽

2014 ◽

Vol 72 (6) ◽

pp. 2061-2071 ◽

Cited By ~ 11

Author(s):

B. Walter ◽

J. Peters ◽

J. E. E. van Beusekom ◽

M. A. St. John

Keyword(s):

Primary Production ◽

Deep Convection ◽

Growth Conditions ◽

Interactive Effects ◽

Light Conditions ◽

Thalassiosira Weissflogii ◽

Pulsed Light ◽

Low Light ◽

Chl A ◽

The North

Abstract Aim of this study was to expose phytoplankton to growth conditions simulating deep winter convection in the North Atlantic and thereby to assess changes in physiology enabling their survival. Growth rate, biochemical composition, and photosynthetic activity of the diatom Thalassiosira weissflogii were determined under two different light scenarios over a temperature range of 5–15°C to simulate conditions experienced by cells during winter deep convection. These metrics were examined under a low light scenario (20 µmol m−2 s−1, 12/12 h light/dark), and compared with a scenario of short light pulses of a higher light intensity (120 µmol m−2 s−1, 2/22 h light/dark). Both experimental light conditions offered the same daily light dose. No growth was observed at temperatures below 8°C. Above 8°C, growth rates were significantly higher under low light conditions compared with those of short pulsed light exposures, indicating a higher efficiency of light utilization. This could be related to (i) a higher content of Chl a per cell in the low light trial and/or (ii) a more efficient transfer of light energy into growth as indicated by constantly low carbohydrate levels. In contrast, pulsed intense light led to an accumulation of carbohydrates, which were catabolized during the longer dark period for maintaining metabolism. Light curves measured via Chl a fluorescence indicated low light assimilation for the algae exposed to short pulsed light. We postulate that our trial with short light pluses did not provide sufficient light to reach full light saturation. In general, photosynthesis was more strongly affected by temperature under pulsed light than under low light conditions. Our results indicate that model estimates of primary production in relation to deep convection, which are based on average low light conditions, not considering vertical transportation of algae will lead to an overestimation of in situ primary production.

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Oxygen budget of the north-western Mediterranean deep- convection region

Biogeosciences ◽

10.5194/bg-18-937-2021 ◽

2021 ◽

Vol 18 (3) ◽

pp. 937-960

Author(s):

Caroline Ulses ◽

Claude Estournel ◽

Marine Fourrier ◽

Laurent Coppola ◽

Fayçal Kessouri ◽

...

Keyword(s):

Dissolved Oxygen ◽

Mediterranean Sea ◽

Atmospheric Oxygen ◽

Deep Convection ◽

Western Mediterranean ◽

Biogeochemical Model ◽

The North ◽

Oxygen Budget ◽

The Mediterranean ◽

North Western

Abstract. The north-western Mediterranean deep convection plays a crucial role in the general circulation and biogeochemical cycles of the Mediterranean Sea. The DEWEX (DEnse Water EXperiment) project aimed to better understand this role through an intensive observation platform combined with a modelling framework. We developed a three-dimensional coupled physical and biogeochemical model to estimate the cycling and budget of dissolved oxygen in the entire north-western Mediterranean deep-convection area over the period September 2012 to September 2013. After showing that the simulated dissolved oxygen concentrations are in a good agreement with the in situ data collected from research cruises and Argo floats, we analyse the seasonal cycle of the air–sea oxygen exchanges, as well as physical and biogeochemical oxygen fluxes, and we estimate an annual oxygen budget. Our study indicates that the annual air-to-sea fluxes in the deep-convection area amounted to 20 molm-2yr-1. A total of 88 % of the annual uptake of atmospheric oxygen, i.e. 18 mol m−2, occurred during the intense vertical mixing period. The model shows that an amount of 27 mol m−2 of oxygen, injected at the sea surface and produced through photosynthesis, was transferred under the euphotic layer, mainly during deep convection. An amount of 20 mol m−2 of oxygen was then gradually exported in the aphotic layers to the south and west of the western basin, notably, through the spreading of dense waters recently formed. The decline in the deep-convection intensity in this region predicted by the end of the century in recent projections may have important consequences on the overall uptake of atmospheric oxygen in the Mediterranean Sea and on the oxygen exchanges with the Atlantic Ocean, which appear necessary to better quantify in the context of the expansion of low-oxygen zones.

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Phytoplankton temporal dynamics in the coastal waters of the north-eastern Adriatic Sea (Mediterranean Sea) from 2010 to 2017

Nature Conservation ◽

10.3897/natureconservation.34.30720 ◽

2019 ◽

Vol 34 ◽

pp. 343-372 ◽

Cited By ~ 6

Author(s):

Federica Cerino ◽

Daniela Fornasaro ◽

Martina Kralj ◽

Michele Giani ◽

Marina Cabrini

Keyword(s):

Mediterranean Sea ◽

Seasonal Cycle ◽

Phytoplankton Community ◽

Spring Bloom ◽

Temporal Dynamics ◽

Late Winter ◽

Research Station ◽

Phytoplankton Assemblages ◽

The North ◽

Long Term Ecological Research

Phytoplankton community structure was analysed from 2010 to 2017 at C1-LTER, the coastal Long-Term Ecological Research station located in the Gulf of Trieste, which is the northernmost part of the Mediterranean Sea. Phytoplankton abundance and relevant oceanographic parameters were measured monthly in order to describe the seasonal cycle and interannual variability of the main phytoplankton taxa (diatoms, dinoflagellates, coccolithophores and flagellates) and to analyse their relationship with environmental conditions. Overall, phytoplankton abundances showed a marked seasonal cycle characterised by a bloom in spring, with the peak in May. During the summer, phytoplankton abundances gradually decreased until September, then slightly increased again in October and reached their minima in winter. In general, the phytoplankton community was dominated by flagellates (generally <10 µm) and diatoms co-occurring in the spring bloom. In this period, diatoms were also represented by nano-sized species, gradually replaced by larger species in summer and autumn. Phytoplankton assemblages differed significantly between seasons (Pseudo-F = 9.59; p < 0.01) and temperature and salinity were the best predictor variables explaining the distribution of the multivariate data cloud. At the interannual scale, a strong decrease of the late-winter bloom was observed in recent years with the spring bloom being the main phytoplankton increase of the year.

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A high resolution reanalysis for the Mediterranean Sea

10.5194/egusphere-egu21-11420 ◽

2021 ◽

Author(s):

Romain Escudier ◽

Emanuela Clementi ◽

Mohamed Omar ◽

Andrea Cipollone ◽

Jenny Pistoia ◽

...

Keyword(s):

High Resolution ◽

Mediterranean Sea ◽

Large Scale ◽

Thermohaline Circulation ◽

Deep Convection ◽

Horizontal Resolution ◽

Continuous Increase ◽

The Past ◽

The Mediterranean

In order to be able to predict the future ocean climate and weather, it is crucial to understand what happened in the past and the mechanisms responsible for the ocean variability. This is particularly true in a complex area such as the Mediterranean Sea with diverse dynamics such as deep convection and thermohaline circulation or coastal hydrodynamics. To this end, effective tools are reanalyses or reconstructions of the past ocean state.&#160;Here we present a new physical reanalysis of the Mediterranean Sea at high resolution, developed in the Copernicus Marine Environment Monitoring Service (CMEMS) framework. The hydrodynamic model is based on the Nucleus for European Modelling of the Ocean (NEMO) combined with a variational data assimilation scheme (OceanVar).The model has a horizontal resolution of 1/24&#176;&#160;and 141 vertical z* levels and provides daily and monthly 3D values of temperature, salinity, sea level and currents. Hourly ECMWF ERA-5 atmospheric fields force the model and daily boundary conditions in the Atlantic are taken from the global CMCC C-GLORS reanalysis. 39 rivers model the freshwater input to the basin plus the Dardanelles. The reanalysis covers 33-years, initialized from SeaDataNet climatology in January 1985, getting to a nominal state after a two-years spin-up and ending in 2019. In-situ data from CTD, ARGO floats and XBT are assimilated into the model in combination with satellite altimetry data.This reanalysis has been validated and assessed through comparison to in-situ and satellite observations as well as literature climatologies. The results show an overall improvement of the skill and a better representation of the main dynamics of the region compared to the previous, lower resolution (1/16&#176;) reanalysis. Temperature and salinity RMSE is decreased by respectively 12% and 20%. The deeper biases in salinity of the previous version are corrected and the new reanalysis present a better representation of the deep convection in the Gulf of Lion. Climate signals show continuous increase of the temperature due to climate change but also in salinity.The new reanalysis will allow the study of physical processes at multi-scales, from the large scale to the transient small mesoscale structures.

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Effects of environmental variability on different trophic levels of the North Atlantic food web

Marine Ecology Progress Series ◽

10.3354/meps10180 ◽

2013 ◽

Vol 477 ◽

pp. 15-28 ◽

Cited By ~ 35

Author(s):

VH Paiva ◽

P Geraldes ◽

V Marques ◽

R Rodríguez ◽

S Garthe ◽

...

Keyword(s):

Food Web ◽

North Atlantic ◽

Environmental Variability ◽

Trophic Levels ◽

The North ◽

The North Atlantic

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Major contribution of prokaryotes to carbon fluxes in the pelagic microbial food webs of the Mediterranean Sea

Advances in Oceanography and Limnology ◽

10.4081/aiol.2016.5799 ◽

2016 ◽

Vol 7 (1) ◽

Cited By ~ 5

Author(s):

Luca Zoccarato ◽

Anna Malusà ◽

Serena Fonda Umani

Keyword(s):

Food Web ◽

Mediterranean Sea ◽

Trophic Levels ◽

Trophic Conditions ◽

Major Pathway ◽

Carbon Transfer ◽

Wide Range ◽

Autotrophic Biomass ◽

Heterotrophic Prokaryotes ◽

The Mediterranean

In this study, we carried out dilution experiments at the surface and in the mesopelagic and bathypelagic layers at 15 sites in the Mediterranean Sea that covered a wide range of trophic conditions. The main aim was to test the hypothesis that prokaryotes, and particularly heterotrophic prokaryotes, are pivotal in sustaining both nanoplankton and microzooplankton energy requirements at all of the considered trophic states. These data highlight that bacterivory is the major pathway of organic carbon transfer in the oligotrophic and meso-eutrophic environments. The microzooplankton mostly feed on prokaryotes, directly or indirectly (through nanoplankton exploitation), rather than on microalgae. Under eutrophic conditions, herbivory is the main trophic pathway; however, the heterotrophic prokaryotes always represent an important source of carbon. The lowest food-web efficiency (i.e., ratio between productivity of the highest trophic level and productivity of the lower trophic levels) was determined for the eutrophic status due to possible grazer satiation, which translates into an excess of autotrophic biomass available for export or transfer to higher trophic levels. The food-web efficiency is higher under mesoeutrophic and oligotrophic conditions, where the main pathway is bacterivory. In the mesopelagic and bathypelagic layers, only nanoplankton predation on heterotrophic prokaryotes was investigated. The food-web efficiency in these layers was relatively high and nanoplankton appear to efficiently exploit the available biomass of heterotrophic prokaryotes.

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Dominant aquatic species and their hydrological niches in freshwater ecosystems in a developing city

Marine and Freshwater Research ◽

10.1071/mf18336 ◽

2019 ◽

Vol 70 (5) ◽

pp. 615

Author(s):

S. Yang ◽

T. Pan ◽

X. Wang ◽

Y. Sun ◽

Y. Zhang ◽

...

Keyword(s):

Food Web ◽

Water Resource Management ◽

Keystone Species ◽

Aquatic Organisms ◽

Freshwater Ecosystems ◽

Trophic Levels ◽

Food Web Structure ◽

Spatial And Temporal Scales ◽

Web Structure ◽

Jinan City

Maintenance of appropriate hydrological niches is crucial to aquatic organisms. This study identified keystone species using the Ecopath with Ecosim food web model for hydrological niche analysis in Jinan City, the first pilot city of the Water Ecological Civilisation Project in China. The niche breadth of keystone species was analysed using Levins’ breadth model. Results revealed 35 keystone species in the aquatic ecosystems of Jinan City, including 5 phytoplankton, 7 zooplankton, 9 zoobenthos and 14 fish species. Streamflow was the most important hydrological factor affecting the phytoplankton, zooplankton, zoobenthos and fish communities in the study area, and excess variation in streamflow had an adverse effect on the normal evolution of the four biotic communities. We found that: (1) higher trophic levels in the food web contained more keystone species in the corresponding community; (2) carbon is an important element constraining the food web structure, and the magnitude of its effect on energy flow determines the degree of importance of the keystone species in the food web; and (3) changes to the survey season and at the spatiotemporal scale will have strong effects on the results of hydrological niche analysis and, to reduce these effects, it will be important to lengthen the spatial and temporal scales to cover both dry and flood seasons in the future. These results may provide an important basis for decision making regarding ecological scheduling and remediation of rivers in the study area, and potentially regions worldwide, thus facilitating aquatic ecological remediation and sustainable water resource management.

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