Analysis of Antarctic benthos dynamics and spatial patterns based on non-destructive techniques and image analysis: development of an integrated monitoring toolkit and general protocols

Introduction- First chapter introduces the Antarctic coastal marine environments, as part of the intriguing and challenging “puzzle” that scientific community is committed to resolve, represented by Antarctica and its changes. A brief glimpse on two of the main drivers influencing benthic communities dwelling in these areas, the sea-ice and the substrate, is given, with a special eye on the unresolved aspects of their influence on marine organisms and on the effect of their variations. Some of the major challenges of scientific researches in such extreme and fragile environment is highlighted together with an overview on ongoing and proposed strategies of the Scientific Committee on Antarctic Research (SCAR). Especially focusing on monitoring perspective, the essential requirement of the establishment of permanent sites and of specially protected areas is discussed. Later on, an overview on the study site and its inhabiting key species is presented. Recent advances in underwater technologies confer the opportunity to overcome previous technical limitations and to improve our capacity of investigation in similar areas. Between emerging techniques, non-destructive image-based ones are introduced in their theoretical aspects. Another pivotal aspect of monitoring is the strategy of sampling, one of the major issues on which relies the reliability of a monitoring project. Preliminary considerations on the relevance of choice of the best sampling design are described. Materials and Methods- Second chapter describes the methodologies used to collect, elaborate and analyse data obtained from images. Firstly, field operations are described, corresponding to well-established protocol of nondestructive image-based SCUBA-operated sampling on shallow rocky bottoms. A particular attention is provided to the use made of sampled materials during the in-silico procedures. This is a newness element of this project, providing one of the first examples of application of some emerging image-based techniques in Antarctica. The informative potential that archived and new SCUBA-operated videos are able to store up about epifaunal communities composition and structure has been exploited by applying photogrammetric reconstruction and measurements. Due to the dated format of older videos, a procedure of adaptation to new applications was needed. In order to better explain these steps, a brief and simply panoramic on some major features of, as defined, ‘historical’ videos is given. Thanks to the proposed in-silico procedures, it has been possible to describe three-dimensional features of seafloor and dwelling organisms, also from videos not specifically meant for this purpose. Later in the chapter, it is shown how spatial information about specimens distribution has been obtained thanks to a variety of GIS tools. Finally, it is supplied a summary of the statistical analyses used to the multiple aims of: i) exploring data, ii) describing macrobenthic populations and their spatial distribution, iii) deriving best sampling design for key species, iv) producing comparisons across years (thanks to two temporal repetitions) and sites. Results- Third chapter reports the main results deriving from the different ‘fields of study’ of the research, including: i) a first section, specifically focusing on the photogrammetric output, with a special eye on the issues related to the use of ‘historical’ materials, as the used video samples were defined; and ii) a second, more ecological, section, reporting the results from counting procedures and spatial statistical analyses. The taxonomical composition of the megabenthic community is described: extendedly, in form of list of taxa that was possible to distinguish and eventually recognize at the lower taxonomical level as possible; and synthetically, by the estimation of biodiversity indices. The small-scale spatial pattern analysis is, then, reported, highlighting the distribution and neighbour estimates of different taxa. Sampling strategy has different outcomes if applied to organisms with different distributions and, thus, when it is advisable to preventively study these spatial aspects. In our case, statistical analyses on sampling simulation suggest specific combinations of sample size and sampling scheme for the main keyspecies analysed. Finally, the results of the trial linear regression model between the distribution of the sea urchin Sterechinus neumayeri (Meissner, 1900) and of the encrusting algae Corallinales are reported, confirming the need of a major number of covariates in order to understand distributional pattern shaping factors. Discussion- The final outcomes of the study are reviewed, according to the original aims and with the major issues of the research. The interpretation of some of the results is particularly investigated. The future perspectives are also mentioned, in many of the possible fields of improvement. Conclusions- Due to the overall value of the proposed methodological approach and of the results of the study, they are presented as contibution to the definition of a standardized protocol of monitoring techniques for the Antarctic benthos, in the perspective of a shared international collaboration.