CORDIS - EU research results

Continuous measurements of plankton and environmental variables: towards assessment of phytoplankton community response to environmental change

Final Report Summary - CONPLANK (Continuous measurements of plankton and environmental variables: towards assessment of phytoplankton community response to environmental change)

The aim of the project CONPLANK (Continuous measurements of plankton and environmental variables: towards assessment of phytoplankton community response to environmental change) is to use a multidisciplinary approach to assess phytoplankton diversity, variability and dynamics in relation to physical, biological and chemical factors at relevant ecosystem timescales. Phytoplankton dynamics are highly variable in coastal ecosystems because physical, chemical and biological influences are forced in complex ways. Many important processes that influence coastal phytoplankton dynamics are episodic (e.g. hurricanes, storms and droughts). However, phytoplankton variability at short-term scales is poorly understood.

The main objectives of the project were:

1) To characterize the diversity of the phytoplankton community at relevant scales
2) To identify the phytoplankton variability, and shifts in species diversity and abundance at relevant timescales
3) To evaluate possible mechanisms by which environmental factors affect phytoplankton community

The following were the main results according to the above objectives (note that final analyses are still ongoing):

An important part of the project was devoted to gain experience with the Imaging FlowCytobot (IFCB), an instrument that combines microscopy and flow cytometry to produce images of phytoplankton cells, thereby providing taxonomically resolved estimates of phytoplankton abundance with fine temporal resolution. Images and associated data generated by the IFCB were processed and analyzed. Automated classification of the images was performed, evaluated and corrected in order to obtain more accurate estimations. Overall, the automated classification and correction accuracy across all categories was 77%.

Data on the phytoplankton community obtained with two IFCB instruments was analyzed. The phytoplankton time series of the IFCB deployed at Port Aransas (Texas, USA) was analyzed together with high-frequency environmental data. In addition, spatial data of the phytoplankton community measured with a lab version of the IFCB during two cruises carried out in the Northwestern Gulf of Mexico were analyzed together with environmental variables. Results of the analysis of the ICFB phytoplankton time series at Port Aransas revealed that the majority of species do not show seasonality in cell abundance. The species that showed seasonality had mainly an oceanic origin. The phytoplankton community showed responses to 3 main episodic environmental drivers: tropical cyclones, upwelling events and droughts. Tropical cyclones produced rapid responses with increased cell abundance in a large number of species and considerable changes in community composition. Interestingly, the species that dominated reached the largest cell abundance of all the IFCB time series and caused deviations in the annual averages.

Upwelling events caused notable increases in cell abundance of particular diatom species. High abundances of the same diatom species were detected during the spatial surveys in the Northwestern Gulf of Mexico, suggesting that the phytoplankton response to the upwelling events is a large-scale response in this area. This is the first study to show the influence of upwelling events on the phytoplankton community in the Northwestern Gulf of Mexico.

Contrastingly, severe droughts that affected Texas revealed a detrimental effect in the phytoplankton community, as revealed by the acute decrease in cell abundances and in biodiversity of species during the droughts.

Other high-resolution instruments were used during this project. Data on suspended particles size recorded with a laser scattering instrument (LISST-100X) and simultaneous fluorescence measurements from Palma Bay (Balearic Islands, Spain) were analyzed in combination with observations of nutrient concentrations and ocean currents. To distinguish the phytoplankton fraction from non-algal components in the suspended particulate matter, a statistical approach based on canonical correlation analysis was developed and applied to the suspended particle and fluorescence data. Data on phytoplankton size structure showed heterogeneous distribution driven by ocean currents at relatively large scales (1–10 km). This preferential concentration mechanism may have important ecological impacts from the phytoplankton level to the whole ecosystem.

To understand the response of the community to biogeochemical perturbations, data on the phytoplankton community at Maó harbor (Balearic Islands, Spain) was analyzed together with measurements of estuarine flow, nutrient concentrations and alkaline phosphatase activity (APA, indicative of use of organic phosphorous (P)) of phytoplankton. The identification of species-specific P requirements and assimilation capabilities in the phytoplankton community of Maó harbor revealed that dinoflagellate species expressed higher APA than diatoms. In some particular species, cells expressed high APA even under conditions of inorganic P availability. These results emphasize the importance of identifying the species-specific traits in order to evaluate the response of phytoplankton to biogeochemical perturbations.

In addition, information on phytoplankton diversity was obtained using several molecular techniques: single-cell PCR and Next Generation Sequencing (Illumina sequencing). The ribosomal DNA sequences (18S, ITS-5.8S and 28S regions) of phytoplankton cells obtained during this project and the inference of phylogenetic trees revealed the identification of a new dinoflagellate species and the detection of previously unknown dinoflagellate cryptic species (morphologically undistinguishable but different DNA sequences). To investigate the phytoplankton diversity in several different coastal habitats of Palma Bay, the 18S ribosomal gene was sequenced using Illumina. Coastal waters of the Balearic Islands are considered pristine due to the low impact of terrestrial input. However, they are anthropogenically influenced due to high tourism pressure. This study is still ongoing, and expected results will improve our knowledge on how diversity relates to biogeochemical processes and anthropization in the marine environment.

The results of this project increase our knowledge on the responses of the phytoplankton community to environmental changes at high-resolution timescales. Despite that alteration of the magnitude and frequency of episodic events is considered one of the consequences of future global climate change, the potential effects of such changes in coastal ecosystems are not fully understood. The results of this project provide new perspectives to the understanding of the timing and occurrence of phytoplankton blooms in the coastal ecosystems, which is essential for the appropriate management of fisheries and marine resources. In addition, a deeper understanding on the diversity of phytoplankton and its relation with biogeochemical processes and anthropization will improve assessment of the human impact in marine ecosystems functioning, and thus contribute to improve policy making in the future.

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