A qualitative and quantitative analysis of the evolution of macroalgal vegetation on an artificial reef with anti-grazing nets (Loano-Ligurian Sea)

Abstract

To evaluate the effect of grazing by sea urchins on the development of vegetation, plastic netting (65 × 45-mm mesh) was stretched over the horizontal surfaces of two out of four cubes of a Loano artificial reef pyramid and held slightly above the surface. The macroalgal population of the horizontal surfaces of the four cubes was seasonally sampled over one and a half years. A qualitative analysis based on a floristic survey of all species present did not reveal significant differences between treatments. However, the quantitative analysis of the algal community based on biomass samples revealed marked differences. Before starting the experiment, fresh and dry weights of the vegetation of all four cubes were of comparable magnitude, while after deployment of the netting, biomass on the two surfaces protected by the net was always significantly higher than in the controls throughout the sampling period. The relative increase seems related to the mechanical effect of the netting in reducing the predatory pressure caused by sea urchins. © 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved.