Spatial and temporal variability and bloom formation of the potentially toxic diatom Pseudo-nitzschia spp. was investigated weekly to monthly from October 2009 to October 2010 in a eutrophic estuary, the Golden Horn. Pseudo-nitzschia spp. were detected in 195 of 512 samples (38%) collected throughout the year. Two species, P. calliantha and P. pungens, were identified based on the SEM examination. Blooms of Pseudo-nitzschia occurred in the lower and middle estuary in January and May. The bloom in January mainly comprised P. calliantha. In the bloom in early May, P. calliantha made up 72% of the Pseudo-nitzschia cells and P. pungens 28%. However, the contribution of P. pungens increased to 83% in late May. The Pseudo-nitzschia blooms occurred at low temperature (9–15°C) and moderate salinity (17–18), and for P. calliantha a significant negative correlation was found with temperature and a significant positive correlation with salinity. The percentage of Pseudo-nitzschia cells decreased gradually from lower to upper estuary (59–14%), correlating with a decrease in Secchi depth (5.5–0.5 m). Principal components analyses (PCA) were used to explore the spatial and temporal variability of environmental factors in relation to Pseudo-nitzschia abundances, and showed that NH4, pH, Secchi depth and DO values were the most important factors reflecting spatial differences, while temperature, salinity, Chl-a and Si:N were more important factors showing temporal differences. High abundances of P. pungens correlated mainly with pH, Secchi depth and DO values, whereas P. calliantha also correlated with NO3 + NO2. Low light availability due to high concentrations of suspended material and very variable environmental conditions (e.g. pH, DO and NH4) may have limited growth of Pseudo-nitzschia in the upper estuary. Regular monitoring of Pseudo-nitzschia is important for improving the understanding of the influence of environmental parameters on bloom dynamics in the study area.

From September 2000 to September 2001 the concentration of chlorophyll a, and the abundance and composition of the phytoplanktonic community was studied in a neritic station of the Mallorca Channel (Western Mediterranean). Sampling was performed approximately every 12 days. Chlorophyll a concentration and phytoplankton abundance reached maxima of 1.79 μg L−l and 352 cells mL−1, respectively. It was a relatively productive period, as a result of the high convective mixing in winter and the prevalence of northern waters during most of the cycle. Phytoplankton proliferations (chlorophyll a concentration >1 mg L−1) were detected in January, February, March and June. Those blooms mainly happened under the influence of northern waters, with the exception of the February proliferation, when mixing conditions were found. During bloom conditions it highlights the presence of coccolithophores as proliferation precursors. During no-bloom situations the phytoplankton community was mainly constituted by nanoplanktonic flagellated forms. The Winter Mixing period was dominated by different groups of nanoflagellates, including coccolithophores, undetermined flagellates and dinoflagellates. However, in the most oligotrophic conditions (from April until November) dinoflagellates were clearly dominant, except in the DCM in summer where diatoms prevailed.

In September 2014 an unusual mixture of ctenophores was recorded at Arboretet, south-western Norway and at Flødevigen, near Arendal on the south coast of Norway. In addition to the invasive American lobate ctenophore, Mnemiopsis leidyi, the common northern lobate ctenophore Bolinopsis infundibulum and the cydippid Pleurobrachia pileus, two beroid ctenophores, were noted – Beroe cucumis and Beroe gracilis. The latter species had not been documented before in Norwegian waters.

Even though very few biological data on dinoflagellates from Iraqi aquatic ecosystems are available to date, there are none on the genus Scrippsiella. For this reason, the survey was conducted along four sites in the Shatt Al-Arab River between November 2009 and July 2010. A dense population of Scrippsiella-like dinoflagellate was observed in the studied samples during November and December 2009. Less dense population of the same taxon was encountered in the downstream sites in July 2010. Based on observations of thecal plate pattern in epifluorescence microscopy, the species was attributed to Scrippsiella trochoidea. The occurrence of S. trochoidea is reported for the first time in Iraqi waters from a wide range of temperature (17.9°C–35.2°C) and salinity (2.3–16.7).

Aequorea pensilis was recorded for the first time in massive quantities on 17 August 2013 at Damb, Sonmiani; however, only a few stranded specimens were collected from Clifton on 2 December 2012. Both these localities are on the Pakistan coast. These findings suggest that, A. pensilis has been established in this region. This report also provides the first record of A. pensilis from Pakistan and is the first report of a hydroidomedusa from the region. This species is distributed in the Atlantic and Indo-Pacific Oceans, and the Mediterranean Sea.

We describe here the limnological characteristics of the Santillana Reservoir (Spain) and study the phytoplankton distributionduring a typical growing season (July to November). The reservoir is a eutrophic stratified waterbody in central part of Spain,in which the average phytoplankton biomass in summer is higher than 20 µg chlorophyll a 1-1. Maximum phytoplankton biomassin 1999 occurred between the end of summer and the beginning of autumn (September-October). Cyanobacteria, that weregenerally prevalent in phytoplankton community, clearly dominated during the peak of phytoplankton biomass. Microcystiswesenbergii was dominant amongst the cyanobacteria and represented almost 100 % of the biomass at the time of maximumphytoplankton value. The importance of environmental variables triggering cyanobacterial bloom events is discussed. Ourresults indicate that neither temperature nor N/P ratio are related to the bloom development. However, high nutrient concentration(ammonium in particular) and stability of the watercolumn seems to coincide with the maximum abundance of Microcystis wesenbergii.

Daily integrals of photosynthesis by a cyanobacterial bloom in the Baltic Sea, during the summer of 1993, were calculated from the vertical distributions of light, temperature and the organisms in the water column and from photosynthesis/irradiance curves of picoplanktonic and diazotrophic cyanobacteria isolated from the community. The distribution of chlorophyll a in size-classes < 20 μm and > 20 μm was monitored over 9 days that included a deep mixing event followed by calm. Picocyanobacteria formed 70% of the cyanobacterial biomass and contributed 56% of the total primary production. Of the filamentous diazotrophs that formed the other 30%, Aphanizomenon contributed 28% and a Nodularia-containing fraction 16% of the primary production. For the whole population there was little change in standardized photosynthetic O2 production, which remained at about 31 mmol m−2 before and after the mixing event. There were differences, however, between the classes of cyanobacteria: in picocyanobacteria primary production hardly changed, while in Aphanizomenon it increased by 2·6 and in Nodularia it fell below zero. Total phytoplankton photosynthesis was strongly dependent on total daily insolation with the compensation point at a photon insolation of 22·7 mol m−2 d−1. Similar analyses of N2 fixation showed much less dependence on depth distribution of light and biomass: Aphanizomenon fixed about twice as much N2 as Nodularia their; their fixation exceeded their own N demand by about 12%. Together, these species contributed 49% of the total N demand of the phytoplankton population. Computer models based on the measured light attenuation and photosynthetic coefficients indicate that growth of the cyanobacterial population could occur only in the summer months when the critical depth of the cyanobacteria exceeds the depth of mixing.