CHAPTER 41
Indirect Control of Vagile Epifauna on Gracilaria verrucosa (Hudson)
Papenfuss* Growth: a Field Study in the Lesina Lagoon (FG), Italy
G. Mancinelli, P. Polimeno, and L. Rossi
ABSTRACT
The effect induced by vagile macrofauna on the growth of the Rhodophyta Graci/aria verrucosa
(Huds.) was evaluated in the Lesina Lagoon {southern Italy} through an in situ manipulation
experiment. Percent wet weight daily growth rates and percent ash content of pre-weighted G.
verrucosa thalli were monitored for 28 days in enclosures made of nets with fine (220 pm,"F"
treatment) and medium mesh (2000 pm, UM" treatment). Both partial and total faunal exclusion
treatments showed a significant negative variation of daily growth rates together with evident
fouling phenomena confirmed by the percent total ash content analysis on Graci/aria samples. A
further analysis on ash content of thalli fragments free from fouling organisms excluded any
effective variation of macroalgal tissue ash content. The study highlighted a significant effect
induced by vagile epifauna on G. verrucosa growth, accomplished through an indirect control on
fouling organisms. Our results support, besides regeneration phenomena of nutrients necessary
for growth induced by particulate detritus processing (widely documented in the literature), the
hypothesis of a further, positive action of herbivorous-detritivorous macrofauna on macroalgal
populations in salt marsh and coastal environments. The results, moreover, suggest a potentially
effective control method on the quality of Grad/aria, which is extensively used as an agar source.
Introduction
In estuarine and coastal environments, macroalgae are comI1lonly associated with a diverse
assemblage of small invertebrates, many of
which are potential consumers of their host
plants. Collectively referred to as "mesograzers"
(Hayet a!. 1987), these small herbivores include
amphipods (Duffy 1990; Poore 1994) and
isopods (Arrontes 1990). Despite their high
abundance, often in the order of thousands per
square metre of substratum (Healy and O'Neill
1984), the way in which vagile macrofauna affect
algal growth is poorly understood (Brawley
1992). Mesograzers inhabiting macroalgae have
the opportunity to feed not only on their host
plant but also on a large spectrum of fouling
organisms. usually exerting a detrimental effect
on algal growth rates (Wahl 1989). Therefore, the
trophic activity displayed by mesograzers has
great significance for host plant fitness and
development patterns: in fact, they may affect
their host both indirectly through removal of the
fouling colonisers, or directly through consumption of the host plant tissues.
The present study investigated the effects
induced by vagile macrofauna on the growth of
the Rhodophyta Gracilaria verrucosa CRuds.) in
the Lesina Lagoon (FG), Italy. In an experimental site characterised by the co-occurrence of the
red macro alga with high densities of benthic
macrocrustaceans, the effective impact of epifauna on daily growth rates of pre-weighted
Gracilaria living thalli was examined in an situ
manipulation experiment involving the use of
partial and total exclusion cages. Macrofaunal
* According to Steentoft et aI. (1995) the correct name of this species is Gradlariopsis longissima (S.G. Gmelin) Steentoft, Irvine
L.M. and Farnham w.P.
Dipartimento di Genetica e Biologia Molecolare, Sezione Ecologia, Universita di Roma "La Sapienza", Via dei Sardi 70,00185
Roma,ItaIy
P.M. Faranda, L. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
© Springer-Verlag Itilia 2001
Indirect Control of Vagile Epifauna on Gracilaria verrucosa (Hudson)
Papenfuss* Growth: a Field Study in the Lesina Lagoon (FG), Italy
G. Mancinelli, P. Polimeno, and L. Rossi
ABSTRACT
The effect induced by vagile macrofauna on the growth of the Rhodophyta Graci/aria verrucosa
(Huds.) was evaluated in the Lesina Lagoon {southern Italy} through an in situ manipulation
experiment. Percent wet weight daily growth rates and percent ash content of pre-weighted G.
verrucosa thalli were monitored for 28 days in enclosures made of nets with fine (220 pm,"F"
treatment) and medium mesh (2000 pm, UM" treatment). Both partial and total faunal exclusion
treatments showed a significant negative variation of daily growth rates together with evident
fouling phenomena confirmed by the percent total ash content analysis on Graci/aria samples. A
further analysis on ash content of thalli fragments free from fouling organisms excluded any
effective variation of macroalgal tissue ash content. The study highlighted a significant effect
induced by vagile epifauna on G. verrucosa growth, accomplished through an indirect control on
fouling organisms. Our results support, besides regeneration phenomena of nutrients necessary
for growth induced by particulate detritus processing (widely documented in the literature), the
hypothesis of a further, positive action of herbivorous-detritivorous macrofauna on macroalgal
populations in salt marsh and coastal environments. The results, moreover, suggest a potentially
effective control method on the quality of Grad/aria, which is extensively used as an agar source.
Introduction
In estuarine and coastal environments, macroalgae are comI1lonly associated with a diverse
assemblage of small invertebrates, many of
which are potential consumers of their host
plants. Collectively referred to as "mesograzers"
(Hayet a!. 1987), these small herbivores include
amphipods (Duffy 1990; Poore 1994) and
isopods (Arrontes 1990). Despite their high
abundance, often in the order of thousands per
square metre of substratum (Healy and O'Neill
1984), the way in which vagile macrofauna affect
algal growth is poorly understood (Brawley
1992). Mesograzers inhabiting macroalgae have
the opportunity to feed not only on their host
plant but also on a large spectrum of fouling
organisms. usually exerting a detrimental effect
on algal growth rates (Wahl 1989). Therefore, the
trophic activity displayed by mesograzers has
great significance for host plant fitness and
development patterns: in fact, they may affect
their host both indirectly through removal of the
fouling colonisers, or directly through consumption of the host plant tissues.
The present study investigated the effects
induced by vagile macrofauna on the growth of
the Rhodophyta Gracilaria verrucosa CRuds.) in
the Lesina Lagoon (FG), Italy. In an experimental site characterised by the co-occurrence of the
red macro alga with high densities of benthic
macrocrustaceans, the effective impact of epifauna on daily growth rates of pre-weighted
Gracilaria living thalli was examined in an situ
manipulation experiment involving the use of
partial and total exclusion cages. Macrofaunal
* According to Steentoft et aI. (1995) the correct name of this species is Gradlariopsis longissima (S.G. Gmelin) Steentoft, Irvine
L.M. and Farnham w.P.
Dipartimento di Genetica e Biologia Molecolare, Sezione Ecologia, Universita di Roma "La Sapienza", Via dei Sardi 70,00185
Roma,ItaIy
P.M. Faranda, L. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
© Springer-Verlag Itilia 2001