Plankton response in post regime shift conditions: the Gulf of Trieste ...

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the Gulf of Trieste, North Adriatic Sea case study. Plankton community composition contributes to shape the structure of the pelagic food web and the pathways ...
Plankton response in post regime shift conditions: the Gulf of Trieste, North Adriatic Sea case study Lipizer M.1, Cabrini M. 1, Cataletto B. 1, Cerino F. 1, Del Negro P. 1, Fonda Umani S. 2, Fornasaro D. 1, Giani M. 1, Kralj M. 1, Monti M. 1, Mosetti R. 1, Solidoro C. 1 1OGS

- Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Trieste, Italy 2 Dipartimento di Scienze della Vita – University of Trieste, Italy

Regime shift: Plankton community composition contributes to shape the structure of the pelagic food web and the pathways of matter and energy cycling in the marine ecosystem. Temporal modifications in the composition and relative abundance of different planktonic compartments result from the synergy of multiple environmental as well as anthropogenic drivers, which in case of abrupt and substantial changes, may determine regime shifts in the state of the ecosystem which may ultimately have important implications on food web integrity and on ecosystem services.

Regime 1

Regime 2

Regime 3

Regime 1

Regime 2

Regime 3

During the last decades, in which the whole northern Adriatic has been experiencing cultural oligotrophication, several regime shifts have been documented in the planktonic ecosystem of the Gulf of Trieste and of the North Adriatic (Cabrini et al., 2012; Conversi et al., 2010; Maric et al., 2012; Mozetic et al., 2012).

1. Are regeneration and/or recovery paths evident following the last observed regime shifts? 2. Are there indications that novel ecosystems will develop? 3. What are the potential implications, human costs and benefits of alternate stable states or novel systems? Microzooplankton

Regime 1

 Time series (March 1986– December 2014) of monthly surface phytoplankton abundance from C1-LTER station in the Gulf of Trieste, North Adriatic Sea  Time series (January 1999 – December 2014) of monthly surface microzooplankton abundance  Time series (March 1986– December 2014) of monthly hydrological parameters and Isonzo River discharge (data from: ARSO, Slovenia)  Time series (April 1997 – December 2014) of monthly surface nutrient concentrations  Regime shift tested according to sequential t-test analysis (STARS), developed by Rodionov (2004) and modified by Rodionov and Overland (2005). The selected cut-off length L is 10 years and probability level was set at p = 0.05.

Total abundance: 1.958.000

Regime 2

Total abundance: 183.000

Regime 3

Total abundance: 958.600

Differences in phytoplankton composition and total abundance (cell/l) in the 3 regimes

Dinoflagellates of high concern: Increased frequency of possible harmful algae

 Correlation analysis between plankton abundances (Log – transformed) and abiotic factors carried out using STATISTICA 7.1 Stat Soft. Software.

Modifications in nutrient availability (annual median)  Two main contrasting regime shifts are recognized during the 1986 – 2014 time series (1995 and 2009/2010)  The last regime is characterized by a «recovery» of trophic conditions (plankton abundance, nitrogen, silicate) References: Cabrini M., Fornasaro D., Cossarini G., Lipizer M., Virgilio D. 2012 Phytoplankton temporal changes in a coastal Northern Adriatic site during the last 25 years. Estuarine, Coastal and Shelf Science, Special Issue: North Adriatic doi: 10.1016/j.ecss.2012.07.007 Conversi, A., Fonda Umani, S., Peluso, T., Molinero, J. C., Santojanni, A., & Edwards, M. (2010). The Mediterranean Sea regime shift at the end of the 1980s, and intriguing parallelisms with other European basins. PLoS One, 5(5), e10633. Mozetič, P., Francé, J., Kogovšek, T., Talaber, I., & Malej, A. (2012). Plankton trends and community changes in a coastal sea (northern Adriatic): bottom-up vs. top-down control in relation to environmental drivers. Estuarine, Coastal and Shelf Science, 115, 138-148. Rodionov, S., 2004. A sequential algorithm for testing climate regime shifts. Geophysical Research Letters 31, L09204.

Rodionov, S.N., Overland, J.E., 2005. Application of a sequential regime shift detection method to the Bering Sea. ICES Journal of Marine Science 62, 328-332.

 The new regime is different from the “starting point” (differences in plankton relative abundance, increase in Dinoflagellate, differences in nutrient availability and ratios) and seems to be a novel ecosystem  The novel system is characterized by risk of higher frequency of occurrence of possible Harmful Algal species which may have important implications on food-web integrity and ecosystem services