Preprint volume - SIBM

Pre-print Volume – Posters
PLANKTON COMMITEE
polyhaline (18-30). Both reactive phosphorus (RP) and dissolved inorganic nitrogen
(DIN) concentrations displayed high values with minima in May and a significant
increase in autumn (October - November 2008), when chlorophyll a concentrations
were relatively low (0.5-7.6 µg l -1 ). The highest value of chlorophyll a was measured in
February (57.8 µg l -1 ). The lagoon of Caorle showed always lower chlorophyll a values
than the Po Delta lagoons, where, the concentrations were often >10 µg l -1 from
February to August. In the Caorle lagoon, phytoplankton community was dominated by
diatoms in May 2008, with the highest mean abundance (22.0×10 6 cells l -1 ). Flagellates
were dominant or abundant as diatoms, represented by the pennate forms, which are
typical of benthic habitats. Centric diatoms were represented by the pelagic
Thalassiosira spp., even if it has been frequently recorded in the sediments (Facca and
Sfriso, 2007). Except for May 2008, during the other observations, the mean
abundance did not exceed 4.0×10 6 cells l -1 . Conversely in the communities of the Po
Delta lagoons centric colonial and pelagic diatoms often were found. The main bloom
was recorded in February 2008 due to Skeletonema marinoi (up to 77.0×10 6 cells l -1 ).
However, so far in May and August 2008 the mean cell abundance remained in the
order of 10 7 cells l -1 , even though the contribution was mainly due to Chaetoceros spp.
(May and August) and Cerataulina pelagica (May). The only exception was a
punctiform dinoflagellate bloom with value of 13.7×10 6 cells l -1 dominated by a
mixture of armoured and naked forms. In autumn, the abundance drastically decreased
being in the order of 10 6 cells l -1 . In such period, the contribution of diatoms became
almost negligible and the community was mainly constituted by flagellates, such as
cryptophytes.
Conclusions – Nutrient concentrations were high enough to guarantee phytoplankton
blooms, which were mainly driven by temperature, light availability, water column
turbidity and hydro-dynamism. Thus the enriched nutrient Po Delta lagoons, for most
of the year, were in persistent blooming conditions, due to pelagic colonial diatoms, as
it is normally observed in the coastal belt of the Adriatic Sea (Bernardi Aubry et al.,
2004), whereas the trophic level of the Caorle lagoon was generally lower and the
community was dominated by resuspended benthic diatoms. Such data represented the
first description of the phytoplankton in the area and may be used to verify the WFD
requirements.
References
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Phytoplankton succession in a coastal area of the NW Adriatic over a 10-years sampling period
(1990-1999). Cont. Shelf Res., 24/1: 97-115.
FACCA C., SFRISO A. (2007) – Epipelic diatom spatial and temporal distribution and relationship
with the main environmental parameters in coastal waters. Estuar. Coast. Shelf Sci., 75: 35-49.
HOLM-HANSEN O., LORENZEN C.J., HOLMES R.W., STRICKLAND J.D.H. (1965) -
Fluorometric determination of chlorophyll. J. Cons. Explor. Mer., 30: 3-15.
STRICKLAND J.D.H., PARSON T.R. (1972) – A Practical Handbook of Seawater Analyses. Fish.
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UTERMÖHL H. (1958) - Zur Vervollkomnung der quantitativen Phytoplankton-Methodik. Mitt. Int.
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