Indirect Control of Vagile Epifauna on Gracilaria verrucosa (Hudson) Papenfuss Growth: a Field Study in the Lesina Lagoon (FG), Italy
The effect induced by vague macrofauna on the growth of the Rhodophyta Gracilaria verrucasa (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. verrucasa thalli were monitored for 28 days in enclosures made of nets with fine (220 μm “F” treatment) and medium mesh (2000 μ, “M” 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 Gracilaria 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 Gracilaria, which is extensively used as an agar source.
KeywordsSalt Marsh Daily Growth Rate Indirect Control Fouling Organism Agar Source
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