140
G. Brancato et aI.
and Thysanopoda aequalis. E. hemigibba,
Stylocheiron abbreviatum. E. brevis, in South
Tyrrhenian Sea (cluster T). Lastly, only N. atlantica, S. longicorne and S. maximum showed a similar distribution (duster B). A difference was
noticed with regard to the observations of
Casanova (1968) and Wiebe and D'Abramo
(1972), about T aequalis and E. hemigibba inhabiting the Tyrrhenian Sea, which in our investigation, had an inverted abundance order, the former more abundant than the latter, as shown in
the Table.
The abundance of juvenile stages in comparison with adults showed a marked difference
between two investigated areas. Indeed, for
almost all species. the respective percentages of
juvenile individuals, out of total population, were
higher in the South Tyrrhenian than in Ionian
Sea such as S. abbreviatum (from 77 to 53%), E.
brevis (from 40 to 0%) and T. aequalis (from 80
to 6%). This difference could be correlated with
the different hydrological features of the two
areas, the former being warmer than the latter,
which allows us to suppose that the southern
Tyrrhenian Sea is a nursery area.
Our results on the vertical distribution of the
euphausiid species, confirmed those stated by
Ruud (1936), Casanova (1968) and Andersen and
Sardou (1992). At Tyrrhenian stations, except
station T4 where they concentrated in the upper
layers. all adult euphausiids occurred in deeper
layers than in Ionian ones, according to either the
different temperature and salinity values or the
chlorophyll maximum, while juveniles were usually located at the surface layers. Moreover, during daylight, the highest concentration of
euphausiids was found at the same depth as the
main concentration of zooplankton (Guglielmo
et aI. 1996), suggesting that the maximum prey
occurrence may be more important in determining their depth rather than some physical parameter as for Thysanopoda aequalis and
Euphausia species. Indeed, during the day these
animals usually fed on zooplankton at deeper
layers, but during the night they fed on phytoplankton near the surface as described by
Sameoto et ala (1987). Nematoscelis megalops,
instead, concentrated in deeper layers of
Tyrrhenian Sea than in Ionian Sea, maybe in
relation to the presence of sinking dinoflagellates
coming from Ionian Sea as suggested by
Magazzu and Andreoli (1971); while Stylocheiron
abbreviatum, a detritus feeder (Mauchline and
Fisher 1969), did not migrate, occurring in surface layers down to 200 m.
Summing up, the presence of 11 out of 13
mediterranean species confirmed that the Straits
of Messina hydrographic area has a very considerable richness of euphausiids. In fact the peculiarity of the principal tidal and upwelling currents determine, and maintain through time, the
structure of the zooplankton and micronekton
communities. Many species of euphausiids reach
significant concentrations in the Straits of
Messina which identify this area as a zone of
accumulation that produces a subsequent
"insemination" of the neighbouring Tyrrhenian
and Ionian basins (Guglielmo et a!. 1995a).
Euphausiids are important components of
the pelagic food web, occurring in the diet of
many fish species of high commercial value
(Froglia 1973, 1976) and becoming a part of an
energy flux which also involves mesopelagic fishes (Scotto Di Carlo et ala 1982) and cephalopod
mollusks (Guglielmo et a!. 1995a; Marabello et al.
1996). Moreover since euphausiids are a distinctive group of organisms that live mainly in the
open deep sea, it thus confirms the pelagic nature
of the Straits of Messina waters, the importance
and the peculiarity of this ecosystem in the
frame of Mediterranean Sea.
References
Andersen V, Samou J (1992) The diel migrations and vertical distributions of zooplankton and micronekton in the
Northwestern Mediterranean Sea. 1. Euphausiids, mysids,
decapods and fishes. J Plankton Res 14(8): 1129-1154
Casanova B (1968) Les Euphausiaces de la Mediterranee. In:
Commun Int Explor Sci Mer Mediterr Com Plancton, pp 23-49
Casanova B (1970) Repartition bathymetrique des euphausiaces
dans Ie Bassin ocidentale de la Mediterranee. Rev Trav Inst
Peches Marlt 34: 205-21
Casanova B (1974) Les Euphausiaces de Mediterranee: systematique et developpement larvaire: biogeographie et biologie.
These Doct Etat, Univ Provence, Marseille
Claus C (1863) Dber einige Schizopoden und niedere
Malakostraken Messinas. Z Wiss Zool13: 422-454
Colosi G (1916) Contributo a11a Conoscenza degli Euphausiacei
dello Stretto di Messina. Monitore Zool Ital27: 61-74
Colosi G (1922) Eufausiacei e Misidacei dello Stretto di Messina.
Mem R Com Talassogr Ital,98: 1-22
Froglia C (1973) Osservazioni sull'allmentazione del merluzzo
(Merluccius merluccius L.) nel medio Adriatico. In: Atti V
Congr Nazi Soc Ital BioI Mar, Nardo, pp 327-341
Froglia C (I976) Observations on the feeding of Helicolenus
dactylopterus (Delaroche) (Pisces, Scorpaeoidae) in the
Mediterranean Sea. Rapp Comm int Mer Mediterr 23: 47-48
Genovese S, Guglielmo L, lanora A, Scotto Di Carlo B (1985)
Osservazioni biologiche con il mesoscafo "Forel" nello
Stretto di Messina. Arch Oceanogr Limnol, 20: 1-30
G. Brancato et aI.
and Thysanopoda aequalis. E. hemigibba,
Stylocheiron abbreviatum. E. brevis, in South
Tyrrhenian Sea (cluster T). Lastly, only N. atlantica, S. longicorne and S. maximum showed a similar distribution (duster B). A difference was
noticed with regard to the observations of
Casanova (1968) and Wiebe and D'Abramo
(1972), about T aequalis and E. hemigibba inhabiting the Tyrrhenian Sea, which in our investigation, had an inverted abundance order, the former more abundant than the latter, as shown in
the Table.
The abundance of juvenile stages in comparison with adults showed a marked difference
between two investigated areas. Indeed, for
almost all species. the respective percentages of
juvenile individuals, out of total population, were
higher in the South Tyrrhenian than in Ionian
Sea such as S. abbreviatum (from 77 to 53%), E.
brevis (from 40 to 0%) and T. aequalis (from 80
to 6%). This difference could be correlated with
the different hydrological features of the two
areas, the former being warmer than the latter,
which allows us to suppose that the southern
Tyrrhenian Sea is a nursery area.
Our results on the vertical distribution of the
euphausiid species, confirmed those stated by
Ruud (1936), Casanova (1968) and Andersen and
Sardou (1992). At Tyrrhenian stations, except
station T4 where they concentrated in the upper
layers. all adult euphausiids occurred in deeper
layers than in Ionian ones, according to either the
different temperature and salinity values or the
chlorophyll maximum, while juveniles were usually located at the surface layers. Moreover, during daylight, the highest concentration of
euphausiids was found at the same depth as the
main concentration of zooplankton (Guglielmo
et aI. 1996), suggesting that the maximum prey
occurrence may be more important in determining their depth rather than some physical parameter as for Thysanopoda aequalis and
Euphausia species. Indeed, during the day these
animals usually fed on zooplankton at deeper
layers, but during the night they fed on phytoplankton near the surface as described by
Sameoto et ala (1987). Nematoscelis megalops,
instead, concentrated in deeper layers of
Tyrrhenian Sea than in Ionian Sea, maybe in
relation to the presence of sinking dinoflagellates
coming from Ionian Sea as suggested by
Magazzu and Andreoli (1971); while Stylocheiron
abbreviatum, a detritus feeder (Mauchline and
Fisher 1969), did not migrate, occurring in surface layers down to 200 m.
Summing up, the presence of 11 out of 13
mediterranean species confirmed that the Straits
of Messina hydrographic area has a very considerable richness of euphausiids. In fact the peculiarity of the principal tidal and upwelling currents determine, and maintain through time, the
structure of the zooplankton and micronekton
communities. Many species of euphausiids reach
significant concentrations in the Straits of
Messina which identify this area as a zone of
accumulation that produces a subsequent
"insemination" of the neighbouring Tyrrhenian
and Ionian basins (Guglielmo et a!. 1995a).
Euphausiids are important components of
the pelagic food web, occurring in the diet of
many fish species of high commercial value
(Froglia 1973, 1976) and becoming a part of an
energy flux which also involves mesopelagic fishes (Scotto Di Carlo et ala 1982) and cephalopod
mollusks (Guglielmo et a!. 1995a; Marabello et al.
1996). Moreover since euphausiids are a distinctive group of organisms that live mainly in the
open deep sea, it thus confirms the pelagic nature
of the Straits of Messina waters, the importance
and the peculiarity of this ecosystem in the
frame of Mediterranean Sea.
References
Andersen V, Samou J (1992) The diel migrations and vertical distributions of zooplankton and micronekton in the
Northwestern Mediterranean Sea. 1. Euphausiids, mysids,
decapods and fishes. J Plankton Res 14(8): 1129-1154
Casanova B (1968) Les Euphausiaces de la Mediterranee. In:
Commun Int Explor Sci Mer Mediterr Com Plancton, pp 23-49
Casanova B (1970) Repartition bathymetrique des euphausiaces
dans Ie Bassin ocidentale de la Mediterranee. Rev Trav Inst
Peches Marlt 34: 205-21
Casanova B (1974) Les Euphausiaces de Mediterranee: systematique et developpement larvaire: biogeographie et biologie.
These Doct Etat, Univ Provence, Marseille
Claus C (1863) Dber einige Schizopoden und niedere
Malakostraken Messinas. Z Wiss Zool13: 422-454
Colosi G (1916) Contributo a11a Conoscenza degli Euphausiacei
dello Stretto di Messina. Monitore Zool Ital27: 61-74
Colosi G (1922) Eufausiacei e Misidacei dello Stretto di Messina.
Mem R Com Talassogr Ital,98: 1-22
Froglia C (1973) Osservazioni sull'allmentazione del merluzzo
(Merluccius merluccius L.) nel medio Adriatico. In: Atti V
Congr Nazi Soc Ital BioI Mar, Nardo, pp 327-341
Froglia C (I976) Observations on the feeding of Helicolenus
dactylopterus (Delaroche) (Pisces, Scorpaeoidae) in the
Mediterranean Sea. Rapp Comm int Mer Mediterr 23: 47-48
Genovese S, Guglielmo L, lanora A, Scotto Di Carlo B (1985)
Osservazioni biologiche con il mesoscafo "Forel" nello
Stretto di Messina. Arch Oceanogr Limnol, 20: 1-30