Page 2 - Bracciali_2016

C. Bracciali et al. / Marine Environmental Research 113 (2016) 116e123 117
sensu Rosenweig and Lomolino, 1997; Lefebvre et al., 1997)by was a sheltered site exposed to the north-east and characterized by
which they are able to live along a gradient of different environ- a gently sloping bottom and a maximum depth of 20 m. In contrast,
mental conditions (Losos et al., 2004). Here, we used a classical Punta Basana was situated on the southern coast, where study site
morphometric analysis (Cheverud et al., 1983) to test whether two is exposed to the main current of the open sea Sicilian Strait, and
different hydrodynamics conditions elicited different expressions characterized by a steeply sloped bottom and a maximum depth of
in functional trait patterns in a zooplanktivorous model fish, 40 m. The hypothesis of different hydrodynamics was generated
Chromis chromis. (Actinopterygii: Perciformes: Pomacentridae; from the observation made at the beginning of 2007 that two sites
Fasola et al., 1997; Guidetti, 2000), at small spatial scale (few kms). had different water current velocities when a Valeport current
Damselfish is an useful model for this purpose as it is a strictly meter was kept in situ in both sites for four days in three occasions
territorial non-migratory species (the home range is thought to be (January, March and June 2007). This field dataset was later used to
only few hundreds of meters from where they build their nests; validate seasonal hydrodynamics patterns as downloaded from
Picciulin et al., 2004) that abundantly inhabits Mediterranean MyOcean daily database (http://marine.copernicus.eu). Field
subtidal habitats from few meters to more than 35 m (Aguzzi et al., observed and satellite derived hydrodynamics data were highly
2013). It reproduces in summer up early autumn in Southern confident and two sites resulted to have water current velocity on
1
Mediterranean, diurnally relies on zooplankton, spends most day- average 10.1 ± 4.9 cm s 1 and 17.2 ± 5.2 cm s , respectively in
time for food searching at the middle column (Pinnegar et al., 2007; Cammello Bay (hereafter LOW-HYDRO) and Punta Basana (here-
Bracciali et al., 2012, 2014). As most zooplanktivorous fish, after HIGH-HYDRO) (Table 1). Contextually, to test the hypothesis
C. chromis has limited energetic reserves and need to feed contin- that different hydrodynamics would have been able to generate
uously (Boddeke, 1963; Charnov et al., 1976) during both larval/ different trophic conditions affecting functional and life history
juvenile (Macpherson and Raventos, 2005) and adult (Dulcic and traits in damselfish, experimental trophic conditions were set by
Kraljevic, 1995) stages. Thus, local oceanographic conditions measuring some water column variables. Water samples were
affecting food availability may emerge as primary factors indirectly collected through a Niskin bottle at middle water column (~10 m) to
influencing life history of this species (Macpherson and Raventos, measure suspended chlorophyll-a, total (TSM), inorganic (ISM) and
2005). Here, we hypothesized that hydrodynamics at small organic matter (POM). Once brought back to the laboratory, water
spatial scale (at the scale of km) plays a role of effector in deter- samples were filtered on Whatman GF-F 0.45 mm fiberglass filters
mining both individual growth (via food encountering-energetic and stored at 20 C. POM was estimated by ignition loss and

costs ratio) and body shape e by affecting swimming perfor- chlorophyll-a through the classical acetone extractive method, ac-
mance and water column position in our Mediterranean cording to details reported in many companion studies (e.g. Sar a
damselfish. et al., 1999, 2003; 2011). Unfortunately, we did not collect
zooplankton at the time of this study, and then the chosen water
column variables indirectly described the amount of suspended
2. Materials and methods food available for zooplanktivorous species as damselfish. Thus, we
did some assumptions to support our experimental hypothesis, as
2.1. Study area and a-priori oceanographic contextualization follows (i) chlorophyll-a concentration, a proxy of the phyto-
plankton biomass, can be in turn used as a proxy of trophic sub-
The study was conducted in the Egadi Marine Protected Area, on strates for zooplankton (e.g. ciliates; Stromberg et al., 2009) and (ii)
the Island of Marettimo (Egadi Archipelago, western Sicily) in two some zooplankton species, such as cladocerans and copepods being
areas with different hydrodynamic conditions located less than the main feeding resource to C. chromis, have similar fatty acids
5.0 km from one another (Fig. 1). Cammello Bay on the north coast

Fig. 1. Location of the Island of Marettimo. The map shows the position of the LOW-HYDRO site of Cammello Bay and the HIGH-HYDRO site of Punta Bassana.