Principal Scientist: Dr. Adriana Zingone (Stazione Zoologica, Napoli)
Background
The abundance and structure of planktonic communities rapidly respond to environmental changes, and represent synthetic parameters to be used in the interpretation of the dynamics of the pelagic ecosystem. This is particularly true for phytoplankton communities, where the high spatial and temporal variability clearly reflects the fluctuations in environmental factors. This variability affects the patterns of temporal and spatial distribution of zooplankton, which in turn, through the grazing process, can control the size, species composition and fate of phytoplankton, as well as the nature of the organic detritus that supply the microbial regeneration.
Although this concepts have been widely accepted for years, not so much progress has been made to de-codify the information on environment lurking in the variations of planktonic assemblages, which has discouraged further investigations. This has become dramatically apparent in recent years, when few answers, if any, have been given to some urgent questions, about e.g. the predictability of harmful algal blooms, the food availability for fish stocks or the possible effects of climate fluctuations on the structure, biodiversity and functioning of the oceanic ecosystem.
Sensible changes in the pelagic environment have been recorded over the last decades in both Atlantic and Pacific waters, which have highlighted the importance of time-series data as a tool in the assessment of the effects of climatic shifts on the biota (see Mc Gowan, 1990, for a brief review). To formulate predictive models of climate variation impacts on such a complex system as the planktonic system as whole seems to be particularly difficult, due to the numerous non-linear functional relationships between its components which are presently not fully understood. At this stage, it appears more realistic to approach the problem by focusing on patterns of variations for a number of simple, synthetic descriptors of the ecosystem as they relate to equally simple and synthetic parameters which are representative of climatic variations. Plankton long time-series have been shown to be of great value in tracing the influence of climate change on marine communities (e.g. Conover et al. 1995, Le Fevre-Lehoerff et al. 1995, Sournia & Birrien 1995, Southward 1995). The relevance of the analysis of these series to climate change issues has also been emphasized in the frame of the PICES-IOC-SCOR-ICES Global Ocean Ecosystem Dynamics (GLOBEC), particularly by the working group “Time Series and Retrospective Data Analysis”.
Scientific Objectives
Following this approach, we intend to analyze multi-annual time-series of phytoplankton and zooplankton data, which are available for a number of sites scattered along the Italian coasts. An overview of the major part of the series which will be used is provided in the figure, together with the indication of the respective hydrological and hydrochemical data. Altogether these data constitute a conspicuous source of information which however in most cases has only been partially exploited in previous elaboration (e.g. Cataletto et al. 1995, Mazzocchi & Ribera d'Alcala' 1995, Mori et al. 1995).
A main problem in the utilization of these data in the context of the present project could be represented by the location of sampling sites, all very close to the coast, as compared to the area of interest of subprojects A and B, which include open waters where dynamic models have reached a stage of better assessment. However, long-term observations of the same descriptors set against their physical and chemical background will help in distinguishing local phenomena from overall trends on a larger spatial scale. On the other hand, data collected during oceanographic cruises conducted in open waters, which are available for several of the areas taken into consideration, will be utilized to highlight the signal of seasonality against the background of the noise that is typical of coastal areas, due to natural local variability and anthropic effects. Another major limitation of most of the available data-sets is constituted by more or less marked deficiencies in sampling periodicity and/or continuity, which however will be conceivably overcome through the parallel analysis of several different data-sets.
The general aim of this task will be to detect and trace patterns of variations, recurrent at seasonal and/or interannual scale, which are shared by both meteorological and pelagic system components.
The specific objectives of this task include the following:
- To trace the seasonal physiognomy of plankton communities in different hydrographic conditions, to be used as a baseline for future comparison.
- To identify and test different taxonomic and a-taxonomic descriptors of plankton communities that are better fit for showing recurrent patterns or anomalies.
- To identify and test the most appropriate analytical tools to detect the coupling of temporal fluctuations of planktonic species and communities with physical forcing functions driven by meteorological/climatic conditions.
- To build up an accessible, intercalibrated database including phytoplankton and zooplankton long-term data from Italian coastal areas and provide guidance to data set interpretation
- To develop an intercalibrated strategy of observation of plankton dynamics to be followed in long-term monitoring researches related to climatic changes during the future national programs
Subtasks:
C.1.1. Data inventory
C.1.2. For each hydrographic season, data will be pooled together as extensively as possible, depending on the coherence of data sets, to obtain a series of most probable seasonal physiognomies for phyto- and zooplankton communities in different areas and hydrographic conditions.
C.1.3. For each database, key elements (species, species-groups, functional groups, etc.) will be selected based on both their relative importance and the possibility of tracing them in the years.
C.1.4. The possible use of synthetic descriptors of the whole community (e.g. diversity, dominance and similarity) will be tested in relation to environmental factors on different temporal scales. Besides traditionally used indexes, the possible use of complementary indexes taking into account non-taxonomic characteristics of the populations (e.g. size, shape, feeding and reproductive habits) will also be
considered.
C.1.5. Chlorophyll concentration and zooplankton biomass will be used to synthetically define the trophic situation. Time-series satellite images such as CZCS will be utilized to integrate the above mentioned descriptive elements in a general context and gain information on the temporal evolution and spatial extension of local events.
C.1.6. Among parameters of meteorological variation, light availability will be chosen as factor directly influencing the development of phytoplankton populations. Temperature and salinity will be mainly considered as tracer of hydrographic conditions and indirectly affecting plankton populations. Other parameters such as winds, rains and storms and their periodicity will be taken into account for their disturbance role. The access to such meteorological data, as well as their strategy of utilization, will profit by advice and cooperation from participants to the other subprojects of SINAPSI.
C.1.7. To provide a common background for the planned activities, the same strategy and format for the archiving and analysis will be agreed upon and adopted for the different databases available for phytoplankton and zooplankton. Species lists will be reviewed in the light of the recent taxonomic literature, and a common language to indicate supra-specific taxa will be agreed upon.
An important area of research is to link variations in indices of planktonic systems (i.e., abundance, biomass) to climatic patterns. Some of the Italian time series provide several year records with associated hydrographic information, and are therefore suitable for a more in depth analysis aimed to evaluate the relationship with physical and climatic factors. For example, the 10 year (interrupted) ichthyo- and zooplankton series of Litorale Chiavari (1985-apr 89, dec 90-dec 95) covers the same time period as the Corsica Channel current and temperature time series (1985-summ88, spring 90-present). It has been seen that the physical interannual patterns in the Corsica Channel are associated to biological changes in Ligurian Sea marine species (Astraldi et al.,. 1995), while their association to the North Atlantic Oscillation is currently under study (Vignudelli et al., 1998). Thus, analysis of these time series would: a) link the Plankton Subproject (C) to the Physical Variability Subproject (B); and b) evaluate the association of coastal planktonic systems to the western Mediterranean circulation and to climatic factors, such as the North Atlantic Oscillation, which are possibly driving it. These analyses could be expanded to the time series of the Gulf of Naples in order to evaluate the presence of common signals in the Thyrrenian Sea (e.g., abundance, diversity response to cold, warm years) and the lag relationship. Similar analyses could be made in the other long time series (e.g., Gulf of Trieste, Sinigallia) in order to verify the existence (or not) of a larger scale (Eastern/Western Mediterranean) response. The results could be verified on shorter time series.
Task C.2: Response of the marine biota to physical forcing variability’s
Principal Scientist : Dr. Marco Zavatarelli (IMGA-CNR, Bologna)
Introduction
The researches comprised within the framework of this subtask will focus on the dynamical adaptations of marine organisms and ecosystems to time variations in the physical characteristics of the environment. The time scales considered vary from the seasonal to the interannual for the modeling studies of the ecosystem dynamics of the Mediterranean and Adriatic Seas, while the research connected with the adaptations of fishes to an increased penetration of ultra-violet radiation into the ocean touches an issue connected with a possible long term change related with the decreased concentration of stratospheric ozone which might determine a change in the behavior of the fish species considered.
Task C.2.1 Modeling the marine pelagic primary production response to seasonal and interannual changes in physical forcing
Responsible: Dr. M.Zavatarelli (IMGA-CNR, Bologna)
Background
A correct description and interpretation of the marine ecosystem dynamics requires information about the marine physical environment. It is rather straightforward to associate the primary production processes with the (seasonally varying) input of short wave energy available, the gravity related sinking of biomass outside the euphotic zone and with the seasonal cycle of the vertical thermal stratification of the water masses. Consideration of these environmental physical factors has led to a large number of 1-D ecological models where the ecosystem dynamics is coupled with a physical model reproducing the seasonal thermocline development and decay as a function of the surface (heat flux and wind stress) physical forcing.
However, horizontal advective and diffusive mass transport processes at large and intermediate scale play certainly a considerable role in setting the overall characteristics of a specific marine ecosystems as well as its trophic state: the general oligotrophy of the Mediterranean Sea represents a striking example of the role that large scale circulation plays on the ecosystem dynamics. Moreover, interdisciplinary studies carried out in the framework of the GLOBEC project have shown the close connection between the spatial variability of the primary production processes and mesoscale motions. Thus, ecological models coupled with 3-D general circulation models can be a valuable tool for the comprehension of the links between the circulation characteristics of a specific basin and the pelagic ecosystem structure and dynamics, providing information about the role that different scales of spatial and temporal variability in the physical forcing play in determining the trophic conditions of a basin.
Scientific Objectives
On the basis of the above considerations we plan to investigate the response of the Mediterranean pelagic ecosystems dynamics to temporal and spatially varying physical forcing by means of coupled ecosystem models having different degrees of spatial resolution and of ecological complexity. The focus will be on the overall Mediterranean basin and on the Adriatic Sea basin. The main scientific objectives are:
C.2.1. To improve the representation of the seasonal cycle of the primary production processes of the whole Mediterranean Sea at the climatological level.
C.2.2. Begin to investigate the response of the Mediterranean pelagic ecosystem to interannually varying physical forcing
C.2.3. Simulate the climatological and interannually varying dynamics of the Adriatic Sea benthic pelagic system
C.2.4. Carry out simulation experiments devoted a general assessment of the possible ecosystem response to long term trends in the forcing functions by setting a series of long term variations scenarios.
C.2.5 Understand the influence of mesoscale processes in determining the coastal circulation of the Western Adriatic Sea through numerical simulations with realistic and idealized models.
C.2.6 Modeling the role played by the mesoscale circulation on the ecosystem dynamics of the Northern and Middle Adriatic Sea.
Experiments concerning the whole Mediterranean basin will be carried out by the OGS-DOGA team with the aggregated ecosystem model coupled with the MOM Mediterranean circulation model. The objective is the study of the impact of the variability of the terrestrial and atmospheric inputs on the Mediterranean ecosystem function at medium to long time by setting scenarios of changes based on different hypotheses of long term trends in the Mediterranean forcing functions.
Adriatic Sea ecosystem simulations will be performed by the coupling of the Princeton Ocean Model (POM) with the ERSEM (European Regional Seas Ecosystem Model,) by the IMGA-CNR group, and with a simpler ecological model with only four state variables by the ISDGM-CNR group. The IMGA CNR group will carry out simulation of the whole Adriatic Sea ecosystem dynamics, while the ISDGM-CNR group will focus on the Northern and Middle Adriatic Sea through a nested model procedure. Simulations devoted to the study of the interannual variability of the Adriatic Ecosystem in response to the Atmospheric forcing will be carried out by forcing the coupled model with the data obtained from the ECMWF daily synoptic analyses for the period 1987-1995. Interannual variations in the river runoff will be also taken into account.
