Phytoplankton Phenology in the Coastal Zone of Cyprus, Based on Remote Sensing and In Situ Observations

Abstract

Alterations in phytoplankton biomass, community structure and timing of their growth (phenology), are directly implicated in the carbon cycle and energy transfer to higher trophic levels of the marine food web. Due to the lack of long-term in situ datasets, there is very little information on phytoplankton seasonal succession in Cyprus (eastern Mediterranean Sea). On the other hand, satellite-derived measurements of ocean colour can only provide long-term time series of chlorophyll (an index of phytoplankton biomass) up to the first optical depth (surface waters). The coupling of both means of observations is essential for understanding phytoplankton dynamics and their response to environmental change. Here, we use 23 years of remotely sensed, regionally tuned ocean-colour observations, along with a unique time series of in situ phytoplankton pigment composition data, collected in coastal waters of Cyprus during 2016. The satellite observations show an initiation of phytoplankton growth period in November, a peak in February and termination in April, with an overall mean duration of ~4 months. An in-depth exploration of in situ total Chl-a concentration and phytoplankton pigments revealed that pico- and nano-plankton cells dominated the phytoplankton community. The growth peak in February was dominated by nanophytoplankton and potentially larger diatoms (pigments of 19’ hexanoyloxyfucoxanthin and fucoxanthin, respectively), in the 0–20 m layer. The highest total Chl-a concentration was recorded at a station off Akrotiri peninsula in the south, where strong coastal upwelling has been reported. Another station in the southern part, located next to a fish farm, showed a higher contribution of picophytoplankton during the most oligotrophic period (summer). Our results highlight the importance of using available in situ data coupled to ocean-colour remote sensing, for monitoring marine ecosystems in areas with limited in situ data availability.

Annual cycle of mesozooplankton at the coastal waters of Cyprus (Eastern Levantine basin)

“…This could also be triggered by the coastal upwelling present during the summer, southern of Cyprus, and/or the proportion of nanophytoplankton and picophytoplankton, among them. Demetriou et al. (2022) , based on phytoplankton sample analysis from the same stations, reported that during the stratified period (May–December) in southern stations AKR and VAS, the percentage of nanophytoplankton was higher, thus nanophytoplankton dominated over picophytoplankton.…”

Research progress in calculating net community production of marine ecosystem by remote sensing

“…For example, Lewis et al (2016) divided the Arctic Ocean three bio-optical provinces, which are mainly influenced by rivers and carried materials (such as colored dissolved organic matter) and found that different regions have their own most suitable ocean color algorithms for chlorophyll. In terms of time, one approach is to study marine phytoplankton phenology through the use of remote sensing; for example, along the coast of the Mediterranean Sea, the growing season of phytoplankton starts in November and reaches its peak in February, with an average duration of about four months (Demetriou et al, 2022). Racault et al (2012) pointed out that the growing season of phytoplankton in different marine areas around the world is influenced by factors such as light, nutrient supply, and climate patterns (El Niño and La Niña).…”

Atlas of phytoplankton phenology indices in selected Eastern Mediterranean marine ecosystems

“…The phenology algorithm that was implemented in the current study was based on the cumulative sums of anomalies method, which utilizes a threshold criterion 8 , 16 , 22 , 25 , 129 . To construct the climatological seasonal cycles, we calculated the weekly means for each 7-day bin over the 23 years spanning the period from 1997 to 2020.…”