Federica G. Pannacciulli

Phylogeography on the rocks: The contribution of current and historical factors in shaping the genetic structure of Chthamalus montagui (Crustacea, Cirripedia)

The model marine broadcast-spawner barnacle Chthamalus montagui was investigated to understand its genetic structure and quantify levels of population divergence, and to make inference on historical demography in terms of time of divergence and changes in population size. We collected specimens from rocky shores of the north-east Atlantic Ocean (4 locations), Mediterranean Sea (8) and Black Sea (1). The 312 sequences 537 bp) of the mitochondrial cytochrome c oxidase I allowed to detect 130 haplotypes. High within-location genetic variability was recorded, with haplotype diversity ranging between h = 0.750 and 0.967. Parameters of genetic divergence, haplotype network and Bayesian assignment analysis were consistent in rejecting the hypothesis of panmixia. C. montagui is genetically structured in three geographically discrete populations, which corresponded to north-eastern Atlantic Ocean, western-central Mediterranean Sea, and Aegean Sea-Black Sea. These populations are separated by two main effective barriers to gene flow located at the Almeria-Oran Front and in correspondence of the Cyclades Islands. According to the ‘isolation with migration’ model, adjacent population pairs diverged during the early to middle Pleistocene transition, a period in which geological events provoked significant changes in the structure and composition of palaeocommunities. Mismatch distributions, neutrality tests and Bayesian skyline plots showed past population expansions, which started approximately in the Mindel-Riss interglacial, in which ecological conditions were favourable for temperate species and calcium-uptaking marine organisms.

Bioerosive and bioprotective role of barnacles on rocky shores

Bioerosion and bioprotection (bio-remodeling) is the action exerted by biota colonizing rocky shores. It represents an important component among processes responsible for shaping coastal landforms, and a clear evidence of interaction between the biosphere and the solid earth. Barnacles extensively colonize the midlittoral belt of rocky shores in the Mediterranean Basin. Previous research, mostly based on laboratory evidence, suggests that barnacles are bioprotectors, in that they protect the rock surface from different types of physical and chemical weathering. In this paper, we present the results of a field experiment carried out at different spatial scales at two study areas along the moderately energetic and microtidal coast of NW Italy. Barnacles were removed from the sandstone bedrock in replicated plots (manipulated plots) arranged according to a hierarchical spatial design. After four months rock hardness was tested on each plot with both Schmidt hammer and Equotip Piccolo devices, as well as on a corresponding number of control plots. Data were processed by means of a multifactorial analysis of variance (ANOVA). In control plots, rock hardness tested with Schmidt hammer exceeded that measured in previously manipulated plots. Testing with Equotip yielded the opposite results. This experimental evidence confirmed that barnacles play a bio-protective role in the midlittoral at sub-surficial level, while adding the key aspect that this effect is generalizable to spatial scales ranging from a few centimeters up to tens of kilometers. In addition, our results showed, for the first time, that at surface level they can simultaneously act as bioeroders, likely causing corrosion of the rock surface by fostering dissolution of the sandstone carbonate matrix.