The influence of canopy algae on vertical patterns of distribution of low-shore assemblages on rocky coasts in the northwest Mediterranean

Canopy-forming algae have been shown to play a fundamental role in the maintenance of understorey assemblages on rocky shores. In the Mediterranean, low-shore habitats are often monopolised by canopy algae of the genus Cystoseira and, in particular, by the species Cystoseira amentacea var. stricta. Alternatively, low-shore habitats are dominated by turf-forming algae and/or mussels. Previous studies showed that loss of Cystoseira, by natural or anthropogenic disturbances, resulted in the increase of turfing algae. Here, we propose that turf-forming algae may act as colonisers from nearby habitats, specifically from lower portions of the shore. The following hypotheses were tested to investigate this proposition: (1) in presence of Cystoseira, the assemblage living under its canopy will be distinct, in terms of composition and structure, from that found lower on the shore, (2) if the canopy of Cystoseira was removed, the differences between the two assemblages would decrease or disappear, (3) the effects of the canopy would be more important than other causes of variability at the spatial scale investigated (hundreds to thousands of metres), and (4) that effects of removal of the canopy would be consistent through time. These hypotheses were tested by means of a canopy removal experiment, involving several spatial and temporal repetitions of the manipulation.The assemblage underneath the canopy of Cystoseira was distinct from that found immediately lower on the shore, but when the canopy was removed there were no differences between the two. The effects of the canopy were consistent at the spatial and temporal scales investigated. Several species living under the canopy disappeared and were replaced by turf-forming species, resulting in a homogenisation of the two habitats and in a drastic loss of habitat diversity. This study shows that Cystoseira can be considered a habitat-forming species, responsible for the maintenance of two distinct low-shore assemblages. In this light, its importance should be taken into account by policies aiming to preserve biodiversity on rocky shores.     

Variability at different spatial scales of a coralligenous assemblage at Giannutri Island (Tuscan Archipelago,northwest Mediterranean)

This study was carried out on the rocky cliffs of Giannutri Island (Tyrrhenian Sea, Italy) to test the hypothesis that coralligenous assemblages are consistent within the bathymetric range considered (25–35 m depth) over three different spatial scales (1000 m, 100 m and 10 m). A multi-factorial sampling design was used to assess patterns of vertical distribution in the studied area. Data on the percent cover of algae and invertebrates were collected at three depths (25, 30 and 35 m) using a photographic method, and percentage cover was obtained using a visual method. Analysis of the results using ANOVA indicated that the distribution and abundance of algae and some invertebrates of the sublittoral assemblages are clearly heterogeneous. Algae, sponges and bryozoans showed significant variability in distribution and abundance at different depths, but this variability was not consistent amongst transects. Ascidians did not show any variability, while the abundance of anthozoans differed significantly amongst transects. We concluded that heterogeneity in the distribution and abundance of the taxa analysed is related to the smallest spatial scale investigated (10's of m). Some of the possible causes of the observed variability are discussed.     

Continuum and discrete approach in modeling biofilm development and structure: a review

Journal of Mathematical Biology - The scientific community has recognized that almost 99% of the microbial life on earth is represented by biofilms. Considering the impacts of their sessile...