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Tyrrhenian Sea Associated Investigators: Related Web Sites: The Gulf of Naples, located in the Tyrrhenian Sea at the border between the central and southern regions of the western Mediterranean, has been a study site for investigations on zooplankton taxonomy and distribution since the 19th century (Giesbrecht, 1892). However, only regular sampling, begun in 1984 for the MareChiara time-series, has started to unveil aspects of zooplankton temporal evolution and recurrences in this typical Mediterranean embayment (Mazzocchi and Ribera d Alcala, 1995). This long-term time-series focuses on characterizing the structure of plankton communities, in terms of standing stocks and species composition, and on following their variability at different temporal scales in relation to environmental conditions. Since 2006, the MareChiara time-series has been part of the International network of Long Term Ecological Research (I-LTER; https://www.ilternet.edu). The sampling site is located ca. 3 km from the coastline, near the 75 m isobath (40 48.5'N 14 15'E), and at the boundary between two subsystems whose exchanges are very dynamic: the coastal eutrophic area, influenced by the land run-off from a very densely populated region, and the offshore oligotrophic area, similar to the open Tyrrhenian waters. Sampling has been ongoing since January 1984, with a major interruption from 1993 to 1994. The sampling frequency was fortnightly until 1990 and weekly from 1995 to present (Ribera d'Alcala et al., 2004). Zooplankton samples were collected with two successive vertical tows from a depth of 50 m to the surface with a Nansen net (113 cm diameter, 200 µm mesh). One fresh sample was processed for biomass measurements as dry mass, whereas the other sample was fixed with buffered formaldehyde (2-4% final concentration) for the determination of species composition and abundance. The water column at the site is thoroughly mixed from December to March and stratified during the rest of the year. The annual cycle of depth-integrated temperature (not shown) is characterized by lowest values in March (~14 C) and highest values in September-October (~20 C). Temperature, salinity, and chlorophyll demonstrate high interannual variability. Significant trends during the period 1984-2006 have been recorded in the increasing summer temperatures and in the decreasing annual Chlorophyll a concentrations (Modigh and Castaldo, 2002; Ribera d Alcala et al., 2004; Zingone et al., 2010; M. G. Mazzocchi, pers. comm.). The temperature trends can be seen in the HadISST date-matched and long-term anomalies. The average annual cycles of zooplankton biomass and abundance reveal minima in January and an extended season of high values from April through October, with major peaks in midsummer. The interannual variability of abundance was more pronounced in the first period (1984-1990) than in the second period (1995-2006) of the timeseries, although interannual averages were similar in magnitude. The zooplankton community is numerically dominated by copepods, which account for 61-78% of annual abundance. Cladocerans (with high and steep peaks in summer), tunicates (mainly appendicularians), meroplankton (mainly decapod larvae), and chaetognaths follow the copepods in rank order of abundance. Various other taxonomic groups (e.g. amphipods, ostracods, cnidarians) occur in much smaller numbers and lower frequency. The MareChiara copepod assemblages are highly diversified, with 136 identified species so far and a few unidentified harpacticoids and monstrilloids. The bulk of the copepod abundance consists of small individuals (=1 mm). The species composition changes throughout the year, acquiring a strong seasonal signature (M. G. Mazzocchi, pers. comm.). From spring through autumn, four abundant species peak in succession: Acartia clausi and Centropages typicus in spring-early summer, Pseudocalanus parvus in full summer-early autumn, and Temora stylifera in late summer-autumn. These four calanoids occur throughout the year and, together, represent a fairly stable component of copepod assemblages that account for 47.7% (+/-6.7%) of total copepod abundance from May to October. In late autumn-early spring, when the annual minimal abundance is recorded, copepod assemblages are more diversified than during the rest of the year. The most common genera in this period are the small calanoids Clausocalanus, CaloCalanus, and Ctenocalanus vanus, the cyclopoid Oithona, oncaeids, and corycaeids. The winter-early spring copepod assemblages are further enriched by the regular, although numerically negligible, occurrence of large calanoid species (>1.5 mm total length) that belong to various families that thrive in offshore deeper waters (mainly Nannocalanus minor, Candacia spp., and Pleuromamma spp.). |