## 3 Results
### Phytoplankton and Ciliate Dynamics  
Chlorophyll \(a\) concentrations in Lough Feeagh ranged from 0.76 to 2.61 \(\upmu\)G Chl _a_-L\({}^{-1}\), Shannon diversity ranged from 1.02 to 2.66, and phytoplankton community biovolume ranged from 97.81 to 539.74 mm\({}^{3}\)-m\({}^{-3}\) during the study period (April to October 2018). Increases in phytoplankton biovolume occurred as soon as St increased above 400 J-m\({}^{-2}\), which was a consequence of the warm  
Figure 5: **(A)** TN:TP nutrient ratios of Lough Feeagh (blue circles) and loadings to Lough Feeagh (black squares) and (**B**) Lough Feeagh N:P nutrient imbalances (seston N:P minus zooplankton community N:P) from April to October 2018. Ratios are performed in molar units. Dotted red lines indicate the Storm Hector event and solid red lines indicate when the Feeagh water column returned to more stable stratification conditions. and calm meteorological conditions. In addition, from the end of May to mid-June (pre-storm period), Chl \(a\), phytoplankton and ciliates biovolume quickly increased to maximum values of 1.93 \(\mathrm{\SIUnitSymbolMicro m}\)\(a\)-L\({}^{-1}\) and 325.97 mm\({}^{3}\)-m\({}^{-3}\), respectively. However, phytoplankton diversity decreased 2.5-fold during the first heatwave at the beginning of June (Figure 6). From April to the end of May (mean \(\pm\) SD, n = 5), the system was clearly dominated by Bacillariophyta (diatom bloom), with a biovolume of 134.48 \(\pm\) 73.48 mm\({}^{3}\)-m\({}^{-3}\) (71.96 \(\pm\) 13.86% of relative biovolume) in the top 6 m water column (Figure 6A), but also at deeper layers (12 m and 25 m), with an average biovolume of 259.11 mm\({}^{3}\)-m\({}^{-3}\) (86.95%) for that specific day (Figure 7, 28 th May pre-storm). On the 12 th June, just before Storm Hector, and at the end of the first heat wave, Cryptophyta, Euglenophyta and ciliates increased their biovolume to 92.28 mm\({}^{3}\)-m\({}^{-3}\) (28.31%), 43.95 mm\({}^{3}\)-m\({}^{-3}\) (13.48%) and 69.08 mm\({}^{3}\)-m\({}^{-3}\) (21.19%), respectively. In turn, Bacillariophyta biovolume decreased to 105.09 mm\({}^{3}\)-m\({}^{-3}\) (32.24%). Specifically, there was a relatively large and rapid increase in _Plagioselmis nannoplanctica_ (Crysophyta), _Trachelomonas volvocina_ (Euglenophyta) and _Strobilidium_ sp. (large ciliates), decreasing Shannon diversity index from 2.51 to 1.02 (Figure 6A). After the Storm Hector event (12 days post-storm), although there was a recovery in phytoplankton Shannon diversity to maximum values of 2.35, Chl \(a\), phytoplankton and ciliate biovolume decreased, dropping to the minimum values for the study period (0.98 \(\mathrm{\SIUnitSymbolMicro m}\)\(a\)-L\({}^{-1}\) and 171.1 mm\({}^{3}\)-m\({}^{-3}\), respectively; Figure 6). By comparing phytoplankton community changes between the 12 th (pre-storm period) and the 26 th (intermediate period) June, it was observed that Cryptophyta and ciliates decreased to biovolumes of 24.72 mm\({}^{3}\)-m\({}^{-3}\) (14.45%) and 19.50 mm\({}^{3}\)-m\({}^{-3}\) (11.40%), respectively, while Chlorophyta biovolume started to increase to 44.00 mm\({}^{3}\)-m\({}^{-3}\) (25.71%) in the top 6 m layers (Figure 6A). From July onwards, the system restabilised and remained stratified until the autumn turnover period at the end of September (Figure 3). These repeated warm and calm conditions at a later stage of the phytoplankton seasonal dynamics resulted in another increase in Chl \(a\) concentrations, reaching a maximum of 2.61 \(\mathrm{\SIUnitSymbolMicro m}\)\(a\)-L\({}^{-1}\) in August, but coinciding with another Shannon diversity minimum (1.22) on the 10 th July (Figure 6), when the system was dominated by _Plagioselmis nannoplantica_ in the Cryptophyta group and _Botryococcus brunni_ in the Chlorophyta group. Immediately following the restabilisation period (10 th July), there was an increase in Chlorophyta biovolume to 113.03 mm\({}^{3}\)-m\({}^{-3}\) (33.39%) and, again, Cryptophyta biovolume increased to 110.30 mm\({}^{3}\)-m\({}^{-3}\) (32.58%).