2. The population was monitored for three years after the mortality events. Availability of pre-event data (1998) allowed comparison of population density and population size structure of the healthy population with those recorded in the three years following the mortality events.3. In 1998, before the two mass mortality events, mean colony density was 33:3 AE 3:7 colonies m À2 and had fallen to 6:7 AE 1:9 colonies m À2 in 2004. 4. In the post-event period the population size structure changed and the modal class of colonies shifted from 16-21 cm to 6-15 cm height.5. In 2004 mortality affected 75 AE 6.4% of colonies. A significant, positive correlation between the extent of damage and colony size was found throughout the monitoring period.6. In the three years following the two mortality events, a small increase in density of recruits and of older undamaged colonies was recorded suggesting that the population was slowly recovering.7. The bathymetric distribution of P. clavata straddles the summer thermocline making this population particularly sensitive to temperature increases. The lack of deeper colonies (less exposed to warming) and the geographical isolation of this population is likely to prevent any substantial external larval supply.8. An increased frequency of mass mortality events associated with ever increasingly high temperature events represent a considerable threat to the persistence of a P. clavata population in the Gulf of La Spezia.

The rapid changes in the climate of Antarctica are likely to pose challenges to living communities, which makes monitoring of Antarctic fauna an urgent necessity. Benthos is particularly difficult to monitor, and is sensitive to local environmental changes. At the same time, long‐term monitoring is complicated by logistical factors. It is therefore urgent to develop advanced instruments to set up autonomous and long‐term monitoring programmes to obtain the lacking biological knowledge needed to understand this complex and remote marine environment. We present a pilot study to set up a non‐invasive and sustainable autonomous monitoring activity in Antarctica, leveraging on a specifically designed automated camera recording, computer vision and machine learning image processing techniques. We also present and analyse the high‐resolution image dataset acquired for an extended period of time encompassing both the summer and the Antarctic night and the corresponding transition periods. The results of this study demonstrate both the effectiveness of such an autonomous imaging devices for acquiring relevant long‐term visual data and the effectiveness of the proposed image analysis algorithms for extracting relevant scientific knowledge from such data. The presented results show how the extracted knowledge discloses dynamics of the observed ecosystems that can be obtained only through continuous observations extended in time, not achievable with the state‐of‐the‐art monitoring approaches commonly implemented in Antarctica. The success of this pilot study is a step towards the collection of continuous data near shore in Antarctic areas and in general in all the remote and extreme underwater habitats. Moreover, the presented stand‐alone and autonomous imaging device can be used for increasing the number of the monitoring sites in remote environments and when complemented with the acquisition of physical and bio‐chemical variables it can be used for obtaining data collections of great scientific value difficult to acquire otherwise.

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In situ time-lapse studies in Polar Regions are uncommon because of the intrinsic limitations of scientific SCUBA diving at sub-zero temperatures and the logistical challenges linked to the deployment of underwater time-lapse systems, which are typically large and heavy. In Antarctica, a number of non-invasive approaches have been adopted to document the behaviour of benthic organisms. For example, in the McMurdo Sound, Ross Sea, Kim et al. (2007) employed time-lapse arrays to study the movement of sea-stars Odontaster validus Koehler in response to organic enrichment, and McClintock et al. (2010) recorded valve clap frequency in scallops Adamussium colbecki (E.A. Smith). At King George Island, Antarctic Peninsula,\ud Schories (unpublished, https://www.youtube.com/watch? v=rKV8s00SFL8) conducted a time-lapse analysis\ud (6 hours) of limpet Nacella concinna (Strebel) and sea urchin Sterechinus neumayeri (Meissner) movement. Here we present a simple and portable time-lapse apparatus, which was tested in TerraNova Bay, Ross Sea, at a depth of 20m below the pack ice

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