Long-term changes in a benthic assemblage associated with artificial reefs

Abstract

The aim of the study was to evaluate the long-term development of a hard bottom benthic assemblage over a period of 20 years in an area off the mouth of a large river. The artificial reef of Fregene was selected because benthic assemblage data were available for the period 1981-1992. This artificial reef is located in the mid Tyrrhenian Sea, 5 nautical miles north of the two mouths of the Tevere River (Latium, Italy) and 1.5 nautical miles offshore from Fregene (Rome, Italy). The artificial reef was deployed in March 1981 for fisheries enhancement in 10-14 m of water on a sandy-silty seabed. The Tevere River carries suspended materials and a heavy load of organics since it transports Rome's effluent, resulting in the eutrophic state of area waters. Benthic sampling was conducted in 2001 by SCUBA diving; two standard surfaces of 400 cm 2 were scraped from the vertical walls of the same uppermost block in four different periods. All organisms were identified and counted. The methodology used is the same as that adopted in the previous periods, so that the 2001 data could be compared with past collected data. The benthic assemblage was analysed by cluster analysis using the Bray-Curtis index and clustered using the group average clustering algorithm. The SIMPER procedure was used to identify those taxa that characterize each station group identified by cluster analysis. Changes in benthic assemblages and hydrological trends of the Tevere River were investigated using the cumulative sum series method. The 20-year development of the benthic community, starting from the new substratum, is composed of different phases characterised by different benthic assemblages. In particular five different phases were distinguished: 1. Pioneer species recruitment (May 1981-June 1981); 2. Mytilus galloprovincialis (mussel) dominance (August 1981-November 1983; 3. M. galloprovincialis regression (July 1984-October 1985; 4. M. galloprovincialis absence (91-92); 5. Bryozoans bioconstruction dominance (2001). The dynamic succession of the observed benthic assemblages exhibited a good relation with the Tevere River flow. The Tevere River flow, and the subsequent sedimentation process, seems to have strongly influenced the benthic assemblage succession of the Fregene artificial reef.

Colonization of an artificial reef in south-west England—ex-HMS ‘Scylla’

“…Our account of the types of species colonizing ‘Scylla’ and the length of time taken for the community to reach a composition that appeared stable is broadly similar to that of other long-term studies of artificial reefs. Species with larvae or spores in the water at the time of placement are likely to settle almost immediately and be conspicuous after a few days or weeks (tube worms, barnacles and hydroids on ‘Scylla’, on the basalt reef described by Leewis & Hallie, 2000 and from concrete structures off the west coast of central Italy: Nicoletti et al , 2007). Some mobile species such as fish, crustaceans and echinoderms may also encounter and colonize the reef very soon after placement.…”

“…Studies of colonization have been undertaken worldwide and often involve deployment of concrete structures with an associated programme of monitoring settlement (see, for instance: papers in Jensen et al , 2000; Moura et al , 2007; Nicoletti et al , 2007; Relini et al , 2007). In the north-east Atlantic, the biogeographical area in which the study described here was undertaken, colonization on oil industry structures and, more recently, offshore wind farm pilings and other energy devices has been studied.…”

Expected Effects of Offshore Wind Farms on Mediterranean Marine Life

“…However, the establishment of mussel beds on artificial structures in the Mediterranean may be highly localized, as several artificial structures showed no such dominance [117,[121][122][123] or highly variable results [124]. The only long-term data set on a concrete artificial reef (20 years) reported five distinct phases of species assemblage: dominance of pioneer species, mussel dominance, mussel regression, mussels absence, and finally dominance of bryozoan bio-constructions [125]. Differences in the material used for offshore structures may have a significant effect on climax community composition; the two offshore, steel study sites in the Mediterranean offshore steel structures were both dominated by bivalves after 52 and 70 months [119,121].…”

Long-term changes of fish assemblages associated with artificial reefs off the northern coast of Rio de Janeiro, Brazil

“…Long‐term studies allow detection of the effects of slow‐acting processes, revealing subtle but consistent biological trends. In contrast, brief ‘snap‐shots’ are often unable to detect these changes and thus may lead to incorrect conclusions regarding dynamics of the ecological systems (Nicoletti et al., ). Few studies on artificial reefs, however, have addressed temporal changes of fishes attracted over extended (i.e.…”