318
G. Mancinelli etal.
effects were also evaluated by thalli visual analysis. percent total ash content and ash content of
fragments free from fouling colonisers.
Materials and Methods
A survey of the epifaunal assemblage associated
with Gracilaria verrucosa in the Lesina Lagoon
at the time of the present study showed that
three species of vagile mesograzers - the isopods
Idotea baltica Pallas and Sphaeroma serra tum
Fabricius, and the amphipod Gammarus insensibilis Stock - together accounted for ca. 90% of
the total number of epifaunal organisms found
on the macro alga (Mancinelli. unpublished
data). Our findings corresponded with previous
investigations on the Lesina Lagoon epifauna
(De Benedictis et a1. 1996; Dinardo et al. 1997).
The encrusting bryozoan Conopeum seurati
Canu and the filamentous macro epiphyte
Enteromorpha intestinalis (L.) Link. were
observed as the prevailing fouling colonizers of
the macro alga. At the site chosen for the manipulation experiment, I. baltica, G. insensibilis and
S. serratum together acconted for 92.7 ± 2.8% of
epifaunal organisms sampled on Gracilaria, corresponding to a total density of 5.3 ± 0.6 individuals g-l algal wet weight. C. seurati represented the dominant fouling colonizer.
The manipulation experiment was done using
cages. They consisted of cylindrical polyethylene
frames (0 25 cm,60 cm high), with the bottom
covered with a lO-rom nylon mesh. One day prior
to the experiment, fouling-free G. verrucosa turfs
of similar branching and size were collected and
stored overnight in oxygenated tanks containing
defaunated lagoon water.
On 4 May 1998, randomly chosen turfs free
from fouling bryozoans and grazing damage
were blotted dry, singularly weighted (1.787 ± 0.1
g. mean wet weight ± 1 SE), and carefully tied
with nylon threads to the bottom of the cages.
Invertebrates were excluded or allowed access to
the macro alga in three 'cage' treatments: (1) no
exclusion, Gracilaria in open frames without
mesh that allowed access to all invertebrates ("C"
treatment); (2) total exclusion, Gracilaria in
frames covered with small nylon mesh (0.22 rom
mesh size) that prevented invertebrates access
("F" treatment) and (3) partial exclusion,
Gracilaria in frames covered with large mesh (2
mm) allowing access to juveniles and immature
stages of the three species dominating the epifauna (UM" treatment).
A total of 27 enclosures were randomly
attached to wooden sticks embedded in the bottom mud at the same depth at which thalli fragments were sampled.
Wet weight and percent ash content of
Gracilaria turfs were determined after 5, 15 and
28 day. At each sampling time, three replicates of
each treatment were retrieved, and the algal samples were rinsed in deionized water to eliminate
macrofauna and residual salts. tapped in blotting
paper and wet-weighted. They were successively
oven-dried for 96 h at 60°C, weighted (dry
weight, DW) and ignited (450°C, 6 h, to avoid
carbonate volatilization; Rosa et al. 1994).
Fouling-free algal subsamples were taken from
each turf and subjected to the same procedure.
Growth rates of Gracilaria were measured
from increases in turf wet weight and presented
as percent growth per day according to the formula G = [(WI - Wo}l/t - 1] x 100 (Penniman et aL
1986). where G = percent increase in wet weight
per day, W 0 = initial weight, and WI = weight after
t days. Percent ash content of samples was calculated as the percent ratio between DW after
and before ignition. For parametric statistical
analysis. all percentages were normalised as
x = arcsin...J PIIOO.
Results and Discussion
Gracilaria demonstrated in the control treatment no significant variations in G values during
the study (I-way ANOVA, F = 0.67, NSj min, 10.49
± 0.18%; max: 12.23 ± 0.39 % d- 1 ). In contrast, in
both partial and total faunal exclusion treatments, Gracilaria showed negative variations in
"G" values (Fig. 1). In particular, whereas no difference was found among treatments after 5 d (1way ANOVA. F = 0.92, NS), after 15 d and 28 d the
observed negative variations were statistically
significant (F=18.09, p
p
differences occurred between exclusion treatments at day 15 and 28 (I-way ANOVA, contrast
analysis 15 d : "F" and "M" treatments vs. "C") F =
32.26, p
= 5.03. NS). After 15 and 28 days it was also possible in "M" and "F" treatments to detect a signif-
G. Mancinelli etal.
effects were also evaluated by thalli visual analysis. percent total ash content and ash content of
fragments free from fouling colonisers.
Materials and Methods
A survey of the epifaunal assemblage associated
with Gracilaria verrucosa in the Lesina Lagoon
at the time of the present study showed that
three species of vagile mesograzers - the isopods
Idotea baltica Pallas and Sphaeroma serra tum
Fabricius, and the amphipod Gammarus insensibilis Stock - together accounted for ca. 90% of
the total number of epifaunal organisms found
on the macro alga (Mancinelli. unpublished
data). Our findings corresponded with previous
investigations on the Lesina Lagoon epifauna
(De Benedictis et a1. 1996; Dinardo et al. 1997).
The encrusting bryozoan Conopeum seurati
Canu and the filamentous macro epiphyte
Enteromorpha intestinalis (L.) Link. were
observed as the prevailing fouling colonizers of
the macro alga. At the site chosen for the manipulation experiment, I. baltica, G. insensibilis and
S. serratum together acconted for 92.7 ± 2.8% of
epifaunal organisms sampled on Gracilaria, corresponding to a total density of 5.3 ± 0.6 individuals g-l algal wet weight. C. seurati represented the dominant fouling colonizer.
The manipulation experiment was done using
cages. They consisted of cylindrical polyethylene
frames (0 25 cm,60 cm high), with the bottom
covered with a lO-rom nylon mesh. One day prior
to the experiment, fouling-free G. verrucosa turfs
of similar branching and size were collected and
stored overnight in oxygenated tanks containing
defaunated lagoon water.
On 4 May 1998, randomly chosen turfs free
from fouling bryozoans and grazing damage
were blotted dry, singularly weighted (1.787 ± 0.1
g. mean wet weight ± 1 SE), and carefully tied
with nylon threads to the bottom of the cages.
Invertebrates were excluded or allowed access to
the macro alga in three 'cage' treatments: (1) no
exclusion, Gracilaria in open frames without
mesh that allowed access to all invertebrates ("C"
treatment); (2) total exclusion, Gracilaria in
frames covered with small nylon mesh (0.22 rom
mesh size) that prevented invertebrates access
("F" treatment) and (3) partial exclusion,
Gracilaria in frames covered with large mesh (2
mm) allowing access to juveniles and immature
stages of the three species dominating the epifauna (UM" treatment).
A total of 27 enclosures were randomly
attached to wooden sticks embedded in the bottom mud at the same depth at which thalli fragments were sampled.
Wet weight and percent ash content of
Gracilaria turfs were determined after 5, 15 and
28 day. At each sampling time, three replicates of
each treatment were retrieved, and the algal samples were rinsed in deionized water to eliminate
macrofauna and residual salts. tapped in blotting
paper and wet-weighted. They were successively
oven-dried for 96 h at 60°C, weighted (dry
weight, DW) and ignited (450°C, 6 h, to avoid
carbonate volatilization; Rosa et al. 1994).
Fouling-free algal subsamples were taken from
each turf and subjected to the same procedure.
Growth rates of Gracilaria were measured
from increases in turf wet weight and presented
as percent growth per day according to the formula G = [(WI - Wo}l/t - 1] x 100 (Penniman et aL
1986). where G = percent increase in wet weight
per day, W 0 = initial weight, and WI = weight after
t days. Percent ash content of samples was calculated as the percent ratio between DW after
and before ignition. For parametric statistical
analysis. all percentages were normalised as
x = arcsin...J PIIOO.
Results and Discussion
Gracilaria demonstrated in the control treatment no significant variations in G values during
the study (I-way ANOVA, F = 0.67, NSj min, 10.49
± 0.18%; max: 12.23 ± 0.39 % d- 1 ). In contrast, in
both partial and total faunal exclusion treatments, Gracilaria showed negative variations in
"G" values (Fig. 1). In particular, whereas no difference was found among treatments after 5 d (1way ANOVA. F = 0.92, NS), after 15 d and 28 d the
observed negative variations were statistically
significant (F=18.09, p
differences occurred between exclusion treatments at day 15 and 28 (I-way ANOVA, contrast
analysis 15 d : "F" and "M" treatments vs. "C") F =
32.26, p
= 5.03. NS). After 15 and 28 days it was also possible in "M" and "F" treatments to detect a signif-