Recent years have seen a rapid expansion in the ability of earth system models to describe and predict the physical state of the ocean. Skilful forecasts ranging from seasonal (3 months) to decadal (5-10 years) time scales are now a reality. With the advance of these forecasts of ocean physics, the first generation of marine ecological forecasts has started to emerge. Such forecasts are potentially of great value in the management of living marine resources and for all of those who are dependent on the ocean for both nutrition and their livelihood; however, this is still a field in its infancy. We review the state of the art in this emerging field and identify the lessons that can be learnt and carried forward from these pioneering efforts. The majority of this first wave of products are forecasts of spatial distributions, possibly reflecting the inherent suitability of this response variable to the task of forecasting. Promising developments are also seen in forecasting fish-stock recruitment where, despite well-recognized challenges in understanding and predicting this response, new process knowledge and model approaches that could form a basis for forecasting are becoming available. Forecasts of phenology and coral-bleaching events are also being applied to monitoring and industry decisions. Moving marine ecological forecasting forward will require striking a balance between what is feasible and what is useful. We propose here a set of criteria to quickly identify "low-hanging fruit" that can potentially be predicted; however, ensuring the usefulness of forecast products also requires close collaboration with actively engaged end-users. Realizing the full potential of marine ecological forecasting will require bridging the gaps between marine ecology and climatology on the one-hand, and between science and end-users on the other. Nevertheless, the successes seen thus far and the potential to develop further products suggest that the field of marine ecological forecasting can be expected to flourish in the coming years.

Global patterns of planktonic diversity are mainly determined by the dispersal of propagules with ocean currents. However, the role that abundance and body size play in determining spatial patterns of diversity remains unclear. Here we analyse spatial community structure - β-diversity - for several planktonic and nektonic organisms from prokaryotes to small mesopelagic fishes collected during the Malaspina 2010 Expedition. β-diversity was compared to surface ocean transit times derived from a global circulation model, revealing a significant negative relationship that is stronger than environmental differences. Estimated dispersal scales for different groups show a negative correlation with body size, where less abundant large-bodied communities have significantly shorter dispersal scales and larger species spatial turnover rates than more abundant small-bodied plankton. Our results confirm that the dispersal scale of planktonic and micro-nektonic organisms is determined by local abundance, which scales with body size, ultimately setting global spatial patterns of diversity.

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Autonomous Reef Monitoring Structures (ARMS) have been applied worldwide to characterize the critical yet frequently overlooked biodiversity patterns of marine benthic organisms. In order to disentangle the relevance of environmental factors in benthic patterns, here, through standardized metabarcoding protocols, we analyse sessile and mobile (<2 mm) organisms collected using ARMS deployed across six regions with different environmental conditions (3 sites × 3 replicates per region): Baltic, Western Mediterranean, Adriatic, Black and Red Seas, and the Bay of Biscay. A total of 27,473 Amplicon Sequence Variants (ASVs) were observed ranging from 1,404 in the Black Sea to 9,958 in the Red Sea. No ASVs were shared among all regions. The highest number of shared ASVs was between the Western Mediterranean and the Adriatic Sea (116) and Bay of Biscay (115). Relatively high numbers of ASVs (103), mostly associated with the genus Amphibalanus, were also shared between the lower salinity seas (Baltic and Black Seas). We found that compositional differences in spatial patterns of rocky-shore benthos are determined slightly more by dispersal limitation than environmental filtering. Dispersal limitation was similar between sessile and mobile groups, while the sessile group had a larger environmental niche | 4883