Rapp. Comm. int. Mer Médit., 36,2001
302
Hermesinum adriaticumZach. species has uncertain taxonomic
position (Incertae sedis; 1) due to the presence of a siliceous skeleton
inside its cells, two unequal ?agella and a nucleus with condensed
chromosomes similar to that of Euglenophyceae.
H. adriaticumis known both as a tropical and temperate species.
Highest known concentrations (up to 380,000 cells/L) were associated
with a marked chemocline at the H2S boundary in the Narragansett
Bay (USA; 2) and in the Lake Rogoznica (small salty lake on the cen-
tral eastern Adriatic coast; 3) in summer. In the northern Adriatic Sea,
since 1906 (4), H. adriaticumhas not been reported, although the
Centre for Marine Research in Rovinj continuously collected phyto-
plankton data since 1972. The Hermesinum species was found only in
the western coastal part of the Otranto Strait (5) and in the offshore
southern Adriatic along “profile” Dubrovnik-1000m isobath (3), when
its appearance was correlated with the in?ow of eastern Mediterranean
waters with temperatures above 13.8°C and salinity above 38.6‰,
providing evidence of subtropical microplankton winter migration into
Adriatic. Immigration brought by natural anomalies in the current
transport is a frequent reason for the appearance of new species in
plankton communities, as already observed in the northern Adriatic
(6).
Seawater samples for analysis of microphytoplankton composition
were collected from 1/1/1998 to 31/12/1999 on 11 stations, using Van-
Dohrn bottles, and preserved with Lugol solution (neutralised with
sodium-acetate). On 7 stations additional samples were taken and pre-
served with 2% neutralised formaldehyde solution. Cell counts were
performed by the Utermöhl method (7). The investigated region
included open waters as well as coastal belt of the northern Adriatic
including Limski kanal (Fig. 1).
Figure 1. Map of the study area with sampling stations.
H. adriaticumspecies was found in summer and autumn months
(Tab. 1), mostly in the 0-10 m layer, in low concentrations, ranging
generally from 40-800 cells/L. Higher values (up to 6400 cells/L) were
found on August 24th, 1999 in the surface layer of the area 22 km
south-east off the river Po delta.
Table 1. Records ofHermesinum adriaticumin the Northern
Adriatic in 1998 and 1999.
The hypothesis that the appearance of H. adriaticumin the northern
Adriatic in 1998 and 1999 was due to higher than usual northward
advective transport of oligotrophic southern Adriatic waters was veri-
fied principally from higher salinity and transparency, as well as min-
imum values of plankton abundance and oxygen production and con-
sumption in 1998 and 1999. It may also indicate an intrusion of east-
ern Mediterranean water masses into Adriatic. This in?ow appeared to
be more intensive in 1999 than in 1998.
Assuming that the origin of the observed H. adriaticumare coastal
environments in the warmer and saltier eastern Mediterranean (3), this
species could be used as an indicator of enhanced intrusions of these
waters in the Adriatic, up to its northernmost part.
References
1 - Corliss J.O., 1994. An interim utilitarian ("userfriendly") hierarchial
classification and characterization of the protists. Acta Protozool., 33 : 1-
51.
2 - Hargraves, P. E., Miller, B. T., 1974. The ebridian Flagellate
Hermesinum adriaticumZach.Arch. Protistenk. Bd., 116 : 280-284.
3 - Vilicic, D., Marasovic, I., Kuspulic, G., 1997. The Heterotrophic
Ebridian Micro?agellate Hermesinum adriaticumZach. in the Adriatic
Sea.Arch. Protistenkd., 147 : 373-379.
4 - Zacharias, O., 1906. Eine neue Dictyochide aus dem Mittelmee :
Hermesinum adriaticumn. g., n. sp. Arch. Hydrobiol. Plankton,1 : 394-
398.
5 - Caroppo, C., Fiocca, A., Sammarco, P., Magazzu, G., 1999. Seasonal
Variations of Nutrients and Phytoplankton in the Coastal SW Adriatic
Sea (1995-1997). Botanica Marina, 42 : 389-400.
6 - Krcinic, F., Precali, R., 1997. On the occurrence of oceanic tintinnines
with particular consideration of the species Amphorides laackmanni
(Jörgensen, 1924), (Ciliophora, Oligotrichida, Tintinnina) in the Northern
Adriatic Sea. Marine Ecology, 18(1) : 67-81.
7 - Utermöhl, H., 1958. Zur Vervollkomnung der Quantitativen
Phytoplankton Methodik. Mitt. Int. Ver. Limnol., 9 : 1-38.
UNUSUAL OCCURRENCE OF THE MICROFLAGELLATE HERMESINUM ADRIATICUM ZACH.
IN THE NORTHERN ADRIATIC SEA IN 1998 AND 1999
Danijela Miokovic
1
, Damir Vilicic
2
, Marija Crncevic
3
*, Zrinka Buric
2
1
Institute Rudjer Boskovic, Center for Marine Research, Rovinj, Croatia - miokovic@cim.irb.hr
2
Faculty of Science, Department of Botany, University of Zagreb, Croatia
3
Polytechnics of Dubrovnik, Croatia
Abstract
Hermesinum adriaticumZacharias (Incertae sedis) is a rare heterotrophic micro?agellate that has been described for the first time in the
northern Adriatic in 1906, but since then it wasn’t recorded in this region until the summer of 1998 and summer and autumn of 1999.
Keywords : plankton, Adriatic Sea
Date
Stationdepth/mcells/L
09/06/98
SJ107
10
200
17/08/98
SJ108
10
400
10/06/99
SJ107
0
740
24/08/99
SJ108
0
800
24/08/99
SJ108
5
6400
24/08/99
SJ108
10
3200
24/08/99
SJ108
20
800
01/09/99
LKE01
10
400
01/09/99
LKE03
10
40
01/09/99
LKE03
16
200
08/09/99
SJ107
20
200
18/12/99
A13
24
370
