Abstract
We investigated the plankton community composition and abundance in the urban marine environment of Thessaloniki Bay. We collected water samples weekly from March 2017 to February 2018 at the coastal front of Thessaloniki city center and monthly samples from three other inshore sites along the urban front of the bay. During the study period, conspicuous and successive phytoplankton blooms, dominated by known mucilage-producing diatoms alternated with red tide events formed by the dinoflagellates Noctiluca scintillans and Spatulodinium pseudonoctiluca, and an extensive mucilage aggregate phenomenon, which appeared in late June 2017. At least 11 known harmful algae were identified throughout the study, with the increase in the abundance of the known harmful dinoflagellate Dinophysis cf. acuminata occurring in October and November 2017. Finally, a red tide caused by the photosynthetic ciliate Mesodinium rubrum on December 2017 was conspicuous throughout the sampling sites. The above-mentioned harmful blooms and red tides were linked to high nutrient concentrations and eutrophication. This paper provides an overview of eutrophication impacts on the response of the unicellular eukaryotic plankton organisms and their impact on water quality and ecosystem services.
Highlights
On a global scale, the rate of coastal urbanization will increase rapidly in the decades, and in combination with climate change is projected to result in an increased risk of coastal eutrophication [1,2].Sewage inputs from coastal cities that are transported directly to coastal waters can act synergistically with land-based sources and river run-off causing high levels of nutrients [3,4]
Remarkably high values were recorded for all nutrients on 22 March 2017 in the White Tower (WT), (SiO4 : 10.17 μmol L−1 ; PO4 : 9.54 μmol L−1 ; NO2 : 0.77 μmol L−1 ; NO3 and NO2 : 7.53 μmol L−1 ; NH4 : 160.3 μmol L−1 ; POP: 42.1 μmol L−1 ), followed by high values of most nutrients during the sampling on 28 June 2017 in WT and Music Hall coast (MH), 20 September 2017 in all sites, and 10 January 2018 in WT
In the majority of the samples, phytoplankton abundance, and nutrient concentrations indicated high eutrophic conditions and bad environmental status according to the implementation of the EU WFD and the EU MSFD
Summary
The rate of coastal urbanization will increase rapidly in the decades, and in combination with climate change is projected to result in an increased risk of coastal eutrophication [1,2].Sewage inputs from coastal cities that are transported directly to coastal waters can act synergistically with land-based sources and river run-off causing high levels of nutrients [3,4]. The global Indicator for Coastal Eutrophication Potential (ICEP) analyses indicate that the potential for coastal eutrophication continuously grows worldwide [2]. Worldwide eutrophication has led to phytoplankton abundance and biomass increase [5,6,7], while more coastal harmful algal blooms (HABs), with more toxic species, have been linked with eutrophication phenomena [8,9]. Numerous examples of linkages between nutrient loading and coastal phytoplankton blooms and mucilagine aggregate phenomena [10,11] include the involvement of harmful species, i.e., the diatom Pseudonitzschia spp. in the Gulf of Mexico [12], the dinoflagellates Prorocentrum sp., and Karenia mikimotoi along the coast of.
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