Abstract
Coastal regions are subject to various forms of environmental impacts, such as spills of crude oil and associated products, with a wide range of effects on benthic biodiversity. This study characterized the patterns of recolonization of the macrofauna associated with the brown alga Sargassum cymosum(C. Agardh), on fronds contaminated by diesel oil in a small-scale field experiment. We collected 40 fronds of S. cymosum from an algal bed in southeastern Brazil and defaunated each frond by immersion in fresh water. Half of the fronds were then immersed in seawater (control group) and the other half in a mixture of 50% diesel oil and 50% seawater (impacted group). The test fronds were returned to the algal bed, and natural recolonization took place over a period of 12 days. Samples of the vagile macrofauna were taken randomly at three-day intervals over the course of the recolonization period. No significant differences in the densities of most taxa were found between the impact treatment (IG) and control treatment (CG). At the end of the recolonization period (day 12), the faunal composition of the treated fronds was very similar to the natural conditions, indicating a high rate of community recovery and suggesting that benthic associations can be rather resilient to diesel-oil impacts on a small scale.
Highlights
The phytal community associated with marine macrophytes is highly diverse in composition, and in the characteristics of the species that constitute it (JACOBUCCI & LEITE 2002)
Half of the fronds were immersed in seawater and the other half in a mixture of 50% diesel oil and 50% seawater
No significant differences in the densities of most taxa were found between the impact treatment (IG) and control treatment (CG)
Summary
The phytal community associated with marine macrophytes is highly diverse in composition, and in the characteristics of the species that constitute it (JACOBUCCI & LEITE 2002). The phytal supports large faunal densities and species richness (SCHNEIDER & MANN 1991), because of the large number of microhabitats offered (WALTHERS & WETHEY 1996) and the interactions among macrophytes, epiphytic algae and invertebrates, functioning on many different spatial and temporal scales (JERKANOFF et al 1996, DUFFY & HAY 2000) Polluting agents such as petroleum and its derivatives have various impacts on biodiversity, that is, through physical, environmental or toxic effects (KENNISH 1997). The effects of oil on biodiversity have been investigated after accidental spills These investigations basically explain biological patterns after the disturbance, or compare affected and unaffected areas (SANDERS et al 1980) by means of estimaties of mortality and resistance of the communities (GESTEIRA & DAUVIN 2000). Such events are by their nature unpredictable, and experimental control and establishment of causeand-effect relationships between the impact and the biological responses are unfeasible
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