Bio-Mineralogy: the influence of the mineral composition of hard substrates on marine benthic organisms and communities distribution.

Studying the interactions between environmental variables and marine organisms is fundamental to understanding these delicate dynamic balances at different space-time scales. These processes are in constant mutual influence since the biotic compartment undergoes abiotic factors but simultaneously modifies the environmental parameters through their own physiological activities. Nevertheless, each of these drivers, taken individually, is the result of precise balances involving single organisms, communities or entire ecosystems, and multiple environmental parameters can be directly correlated with each other. In an age of climate change such as the one we live in, a multidisciplinary approach to the study of the environments and marine organisms appears essential to understand the potential effect of a single part of the system on the others and, consequently, to try to relate to each other, all of these, to optimally manage ecosystems and safeguarding habitats. Benthic marine species, both sessile for the entire duration of their life cycle or linked to the seabed only for part of it, undergo the effect of physic-chemical changes in the water column and through their adaptations can oppose or support them, sometimes exploiting them to advantage, thanks to their resilience and resistance. On the other hand, the same substrate can be modified by different processes of various nature (mechanical, physical, chemical, biological), thus becoming an essential element that can influence the phases of colonization and consequent larval settlement, on the development of the single organism, and the entire benthic community, up to the point of characterizing the submerged landscape. Furthermore, all these aspects have both a very different spatial and temporal scale; therefore, the observation of the interaction phenomena between organisms and environmental variables requires very different approaches, often conducted step by step, to isolate the effect of a single factor and, where this is not possible, mitigate the interaction. The substrate characteristics have already been considered in many scientific fields, ranging from engineering to ecology, highlighting innovative aspects and conflicting conclusions. Furthermore, the interest in bio-mineralogy, i.e., the study of the interaction between the organism and the mineralogical composition of the substrate, began to emerge at the end of the last century, focusing on the toxic effect of the quartz present in the dissolved sediment on colonization phase of the associated fauna. Since then, numerous studies have deepened this area of research, investigating the hard substrates of various kinds and the structure of the communities settled there. Here, the continuation of this research has attempted to define what effects the substrate can have at different ecological scales (from the single organism to the community, up to the landscape), examining different types of rocks and highlighting affinities between similar lithotypes. Due to their natural geological conformation, the Ligurian coast and the Sardinian context of the Tavolara Marine Protected Area - P.ta Coda Cavallo have been investigated. Particularly, this last locality presents, on a reduced spatial scale, the variability of substrates as well as environments of great environmental value. These contexts have proved to be optimal for expanding knowledge on the effect of the mineralogical composition of lithotypes on the distribution and abundance of benthic organisms, pointing out the crucial role of encrusting coralline algae in stabilising substrates. In a second analysis, the survey made it possible to characterize ecologically and deepen the knowledge on the distribution and the state of health and conservation of priority habitats of great environmental value, currently under-valued and subject to substantial impacts by fisheries, indicating new more suitable for the management of these by the competent Bodies.