Contact : angeline lefran@atu ie Funding : Post - doctoral fellowship ; grant - aid agreement No PDOC/ 23 / 08 / 03 Investigating Irish marine phytoplankton variability through long term monitoring Angéline Cariou - Lefran 1,2 , Dave Clarke 2 , Cóilín Minto 1 , Olga Lyashevska 1 , Deirdre Brophy 1 1 Marine and Freshwater Research Center , ATU, Galway, Ireland 2 Marine Institute, Rinville , Co. Galway, Ireland Context Conclusions Average summer surface chlorophyll - a (2017 - 2021) www.eea.europa.eu/ Ireland’s land temperature anomalies ( 1961 - 1990 baseline ) Our actions have an impact : eg : European regulation on detergent (UE, 1980s) Decrease in P - input by 60% and reduction in chl - a by 28% over 2000 - 2013 in Irish bays and estuaries (Ní Longphuirt & Stengel, 2016) , and western french coast ( Gohin et al., 2019) Not enough in Ireland ’s case As the figure show s here, the chl - a content in Irish waters is still higher than in it’s neighbour country. Agriculture runoffs ar e one of the main cause (EPA, 2025). Climate change facts Temperature and irradiance increase , storms, floods and their associated effects (such as eutrophication, stratification) are directly affecting primary producers as main environmental forcers (Rabalais et al., 2014) This lead to higher risk of Harmful Algal Blooms, mismatch with upper levels recruitment, change in community composition with higher ratio of smaller cells found within phytoplankton ( De Senerpont Domis et al., 2014, Hallegraeff , 2010, Finkel et al., 2010) Met Eireann Today’s change and predictions for climate scenarios +2 ° C (RCP 4.5) and +4 ° C (RCP 8.5) by 2100 Method Results Date Location (/11) Taxa 1 ... Taxa 136 2008 - 01 Cork (abundance 1) ... (abundance 136) ... ... ... ... ... 2022 - 12 Waterford (abundance a) ... (abundance z) Community matrix of monthly average d abundance (cells/L) Box - Cox - chord transformation (logarithmic) applied Distances between cycles can be calculated and visualized on PCoA Eg: 3 cycles = 3 years State succession is shown by arrows linking community composition by similarity creating cyclical trajectories Year 1 Year 2 Year 3 Station 1 Year 1 Year 2 Year 3 Station 2 Cycles can be extracted They are defined by length and shape >> More info can be found on ‘ ecotraj ’ package vignette Cycles shifts compare ecological states from same temporal stages (month ) on different cycles Shannon Waterford Clare Cork SE Donegal Louth Sligo Galway Cork SW National, multi - specific , weekly monitoring time - series from : Temporal and spatial divergence in micro - phytoplankton community structure show local drivers importance There are deep structural changes due to an ongoing modification of environmental characteristics next ? Need to identify environmental drivers , and their role at a local & inter - national scale next ? Examine functional diversity to investigate the extend and effects of those changes on other communities The timing of spring and autumn community structures appear earlier every year in most areas Longer spring period could also explain the increasing diatom maximums in late Winter and Spring (Status report, Marine Institute, 2023) Concur with findings on zooplankton time series from the North Sea 1 3 2 2 Cycle shifts similarities between plankton datasets from the North Sea and Coastal Ireland Despite high variability, t his could indicate longer spring season for phytoplankton Evidence of climate change impacts in western Europe shown on 2 different monitoring programs State succession summary linked with North/South distribution of 11 spatial cyclical trajectories over 15 years. Colours are only associated with stations ID. 1 Dots = All Januaries = Cycles origins Shannon Waterford Clare Cork SE Donegal Louth Sligo Galway Cork SW Distance between annual cycles link spatial community together. We notice that despite their non - connectivity, Sligo and Louth area display similar community composition. This is due to local bay / tide drivers that are shaping community composition. Ireland coastal phytoplankton monitoring ( 2008 - 2022 , 8/11 locations displayed ) North Sea zooplankton from Continuous Plankton Recorder ( 1958 - 2020 , from CETA vignette ) 3 Cyclical Ecological Trajectory Analysis (CETA) ( Djeghri & De Cáceres, in prep ) Handles trajectories presenting regular cyclical dynamics such as seasonality for phytoplankton