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Dispersal is more intense in the ocean than on land because most marine taxa present planktonic life stages that are transported by currents even without specific morphological traits. Thus, species dispersal shapes the distribution of biodiversity along seascapes and drives the composition of biodiversity assemblages. To identify marine assembling zones which characterise spatial areas particularly prone to receive and retain similar animal assemblages from the regional pool of species through passive dispersal, we propose a community‐based approach grounded on Lagrangian simulations of plankton dispersal. This novel approach was applied to communities (coast, outer shelf, slope, seamounts and islands; 0–80 m depth) of the Tropical Southwestern Atlantic and used to assess connectivity pathways. For that, we classified the modelled particles in 15 categories according to biological traits (planktonic life duration and spawning habitat) of representative planktonic communities. From the hierarchical clustering of the multivariate matrix containing the amount of arriving particles from each category in each cell we defined 14 assembling zones. Results highlighted that the assembling zones were mostly shaped by the degree of exposure to currents and the presence of mesoscale features (eddies, recirculation) derived from the interaction between these currents and coastlines. The boundaries, dispersal and connectivity patterns of these zones consistently align with local and regional in situ spatial distribution and abundance patterns of organisms, and provide an appropriate basis for the formulation of ecological hypotheses in the metacommunity framework to be tested in situ, such as the balance between species sorting and mass effect assembling archetypes. This approach, when coupled with the knowledge of other processes shaping communities' structure and distribution, provides important insights for regions and animal groups for which knowledge is limited or absent, a

The edible sea urchin (Paracentrotus lividus) is of significant economic importance due to high demand for its consumption in various Mediterranean countries. This echinoderm plays a crucial ecological role by regulating the dynamics of seaweed and seagrass through its grazing behaviour. The abundance of sea urchin is variable in time and space, but it is currently potentially declining in the Mediterranean Sea, and likely to be negatively affected by global change. Therefore, gaining a more comprehensive understanding of sea urchin larval dispersal patterns over an extended period could contribute to our understanding of how their dynamics relate to population connectivity. To investigate the trajectories of larval dispersal of this sea urchin in the Northwestern Mediterranean Sea, we combined a Lagrangian model (Ichthyop) with a hydrodynamic model (MARS3D). This study covered the years 2010–2018 and aimed to quantify the connectivity between the preferred habitats of the sea urchin (seagrasses and rocky substrates). The present study explores seasonal variations in dispersal routes and habitat connectivity relationships for two spawning scenarios identified in the literature (spring and autumn). The results enable us to identify dispersal routes, and their regularity over time. They highlight a consistent connection between Sardinia, Corsica, and the coastlines of the Ligurian and Tyrrhenian Seas, indicating a lack of genetic structuring within the edible sea urchin population in this area, particularly in Corsica. The connectivity matrices confirm the observed dispersal trajectories and highlight certain areas of significant and enduring local retention over time. The results also reveal minimal seasonal variability. Conversely, interannual variability appears pronounced, particularly in relation with trends in the warming of surface waters in the Mediterranean, which seem to impact the dispersal routes taken by P. lividus larvae. Lastly, a connectivity map was c

Detailed knowledge on connectivity, i.e. the exchange of marine organisms among geographically separated populations, is essential for effective marine spatial planning strategies and the design of marine protected areas (MPAs) in coastal ecosystems. Coastal waters around southern Africa are characterized by complex oceanographic processes that strongly influence connectivity, challenging the design and management of marine ecosystems. Here we reviewed connectivity studies conducted across 25° of latitude on both the southeastern and southwestern sides of Africa based on biophysical modelling, ecological and molecular approaches, and identified 7 corridors and 8 barriers recognized to influence marine connectivity for a variety of vertebrate and invertebrate taxa of commercial and ecological interest. These corridors and barriers were generally consistent across studies, species and methodological approaches, and were reflected in marine bioregion breaks. Nevertheless, life history traits appear to be important to understanding why some corridors and barriers may be notable for some species and life stages and not for others. Our review underlines the value of including studies from different disciplines in order to have a broad view of marine connectivity, and, in particular, the complementarity of larval-dispersal biophysical models and seascape genetics is emphasized. The corridors and barriers to connectivity identified in this review represent baselines to critically assess existing MPAs and prioritize new spatial management efforts to mitigate human impacts on marine ecosystems.

Biophysical models are often used to estimate larval dispersal patterns for the assessment of marine metapopulation spatial structure. However, comparisons of these models with field observations are relatively rare, and the extent to which models reproduce true marine connectivity patterns is unclear. We developed a biophysical model for larvae of the blacktail seabream Diplodus capensis (Sparidae), an abundant recreational and subsistence fishery species along the south-east coast of South Africa, and compared outputs from various configurations of that model to results from a field study conducted in a large regional embayment (Algoa Bay). Seasonal patterns of dispersal and recruitment produced by the model agreed best with field observations when thermal constraints on spawners and larvae were included. Spatial gradients in settling larvae also matched well, with the model capturing observed high settler densities within the lee of a major headland. Nevertheless, stronger spatial gradients were observed in larval densities from the field study when compared with model results, which may be explained by behavioural post-settlement processes. Model-based dispersal patterns revealed up to 5 subpopulations along the southern coast, with barriers to connectivity between subpopulations generally linked to hydrographic features. Overall, our results suggest that thermally mediated spawning behaviour, physical transport and post-settlement processes all play important roles in determining marine connectivity for the blacktail seabream. Refining physiological larval constraints may be an important component that needs to be considered going forward.

Purse-seine fisheries use drifting Fish Aggregating Devices (dFADs), human-made floating objects, to facilitate the capture of tropical tunas. Currently, the majority of dFADs are constructed primarily of highly durable non-biodegradable materials and there is no legal obligation to recover dFADs after deployment, leading to beaching events and potentially negative environmental impacts. We assessed beachings as a function of intra- and inter-annual trends, water depth, distance from land, seasonality, and benthic habitat within the local context of the Seychelles Archipelago using trajectories of dFADs deployed by French purse seiners over 2008-2020. Overall, 3842 beaching events associated with 2371 distinct dFAD tracking buoys were identified. Beachings occurred most frequently during the winter monsoon (December-March). Due to the shallow Mahe Plateau, beachings occurred in both nearshore (<= 5 km from land) and offshore (> 5 km) regions, predominantly in estimated depths less than 60 m. Despite representing < 20% of overall mapped habitat, the benthic habitat "Coral/Algae" had the highest beaching rate (35.3% of beachings), and therefore, beachings pose a significant concern for conservation. Our results provide a detailed view of the spatio-temporal pattern of beachings in the Seychelles, supporting the development of mitigation and prevention methods to reduce marine debris and perturbations to the marine environment.

Natural floating objects (FOBs) have always been a major component of the habitat of pelagic species. Since the 1990s, the number of FOBs in the open ocean has increased greatly as a result of the introduction of fish aggregating devices (FADs) by the industrial tropical tuna purse seine vessels. These changes, and their potential impacts on the species that associate with FOBs, remain poorly understood. Using fisheries observer data, data from satellite-linked tracking buoys attached to FOBs and Lagrangian simulations, this study quantifies the temporal changes in the density and spatial distribution of FOBs due to the use of FADs in the Indian Ocean (IO) between 2006 and 2018. From 2012 to 2018, the entire western IO is impacted, with FADs representing more than 85% of the overall FOBs, natural FOBs less than 10%, and objects originating from pollution 5%. Results also suggest that both FADs and natural FOBs densities are lower in the eastern IO, but this initial investigation highlights the need for further studies. Our study confirms that FADs have greatly modified the density and spatial distribution of FOBs, which highlights the need to investigate potential consequences on the ecology of associated species.