Rapp. Comm. int. Mer Médit., 36,2001
157
Introduction
The transparent exopolymer particles (TEP) play an important role
in the formation of marine snow (1) and probably also in the mucilage
events (2) that have occurred frequently in the Adriatic since 1989 and
were particularly intense in the northern part (3). It was hypothesized
that mucilage events can develop when the concentration of microag-
gregates with enhanced stickness properties (including TEP) rise
above a «critical» level (4). To verify those assumptions, the distribu-
tions, seasonal changes, and properties of TEP were studied in two
areas of the northern Adriatic with different eutrophication degree.
Materials and methods
Samples were collected from March to December 2000 at stations
SJ101, 12 Nm off the Po River delta, Italy (44° 59,9' N; 12° 49,8' E),
and SJ107, 13 Nm off Rovinj, western Istrian coast, Croatia, (45° 2,8'
N; 13° 19,0' E). The total TEP concentrations (xanthan equivalent)
were measured by the alcian-blue spectrophotometric method (5). The
particle abundances and total areas were determined with a light
microscope on filters stained with alcian blue (1). Salinity was mea-
sured by a high precision laboratory salinometer, temperature with
reversing thermometers, and the phytoplankton abundance was deter-
mined by the Uthermöl method from samples preserved with neutral-
ized lugol. The results were compared using the Spearman's rank cor-
relation test.
Results and discussion
The occurrence of TEP was extremely variable and, surprisingly,
the mean values for the period March-December 2000 did not differ
substantially between the investigated stations (Tab. 1), although the
in?uence of nutrient rich freshwaters were much more marked at sta-
tion SJ101. Increases in TEP concentration at this station during the
spring and summer were due to phytoplankton blooms in surface lay-
ers with significantly lowered salinity (Fig. 1). In contrast, a much
higher freshwater input during October did not induce a correspond-
ing phytoplankton (and TEP) production, probably due to light limita-
tion in turbid waters. Remarkably, at station SJ107 extremely high
TEP concentrations (up to 2500µg xanth.equiv.L
-1
) were measured in
June in surface layers with low phytoplankton abundance, although
their salinity was significantly reduced.
Table 1. Concentrations, abundances and total surface areas of
TEPat stations SJ101 and SJ107.
SJ107
SJ101
nMeanC.V.RangenMeanC.V.Range
Concentration553091274-2498503221119-2000
xanthan equiv.µgL
-1
)
Abundance545.3770.9-28509.1700.8-30
(N°*10
6
L
-1
)
Total surface area547179878-37745098511472-
6255
(mm
2
L
-1
)
Moreover, all TEP parameter values (total concentration, abun-
dance, and surface area) were inversely correlated with salinities at
both stations (statistical significance at least at p<0.05), but different
results were obtained when comparisons with temperatures and
diatomsabundances were made. While significant positive correla-
tions (p<0.01) were found at station SJ101, no evident relationships
were noted at station SJ107.
These results suggest that TEP production occurs mainly in the
more eutrophic western part of the northern Adriatic. Horizontal
advection would represent the principal mechanism of TEP accumula-
tion in the more oligotrophic eastern areas, assuming that their resi-
dence times are longer than for their producers (phytoplankton).
Finally, unexpectedly weak correlations were observed when the
total TEP concentrations were compared with the abundance and total
surface area values. This may be related to contamination of samples
by gel substances that can also react with the alcian blue. In fact, a
mucilage event occurred in June and July 2000, with formation of
aggregates up to several meters in length in the upper water column
(CMR, unpub. data).
References
1. Alldredge A.L., Passow U., Logan B.E., 1993. The abundance and
significance of a class of large, transparent organic particles in the ocean.
Deep-Sea Research, 40: 1131-1140
2. Alldredge A.L., 1999. The potential role of particulate diatom exudates
in forming nuisance mucilaginous scams. Ann. Ist. Super. Sanita, 35:
397-400
3. Degobbis D.; Malej A., Fonda-Umani S., 1999. The mucilage
phenomenon in the northern Adriatic. A critical review of the present
scientific hypotheses. Ann. Ist. Super. Sanita, 35: 373-381.
4. Zutic V., Svetlicic V., 2000. Interfacial processes. In: P.J.Wangersky
Handbook of Environmental Chemistry, Marine Chemistry 5(Part D),
Springer-Verlag Berlin-Heidelberg-NewYork:149-165
5. Passow U., Alldredge A., 1995. A dye-binding assay for the
spectrophotometric measurement of transparent exopolymer particles
(TEP).Limnol. Oceanogr., 40:1326-1335.
PRODUCTION OF TRANSPARENT EXOPOLYMER PARTICLES (TEP)
IN THE NORTHERN ADRIATIC SEA DURING 2000
Tomislav Radic*, Dragica Fuks, Danijela Miokovic, Mirjana Najdek and Danilo Degobbis
Center for Marine Research Rovinj, Rudjer Boskovic Institute, Rovinj, Croatia
Abstract
The distribution, seasonal changes and properties of transparent exopolymer particles (TEP) were studied in two areas of the northern
Adriatic with different degrees of eutrophication. Preliminary results suggested that TEP formation occurs mainly in the more eutrophic
western part of the northern Adriatic while horizontal advection probably represents the principal mechanism of TEP accumulation in the
more oligotrophic eastern part.
Key words: TEP, organic matter, phytoplankton, Adriatic Sea
Figure 1. Temporal distribution of TEP(µgL
-1
xanthan equiv.) at
stations SJ101 and SJ107.
