Mesophotic Coral Ecosystems in the Eastern Tropical Pacific: The current state of knowledge and the spatial variability of their depth boundaries.

In the Eastern Tropical Pacific (ETP), Mesophotic Coral Ecosystems (MCEs) are limited by oceanographic conditions and are thought to be mostly absent. However, considering the currently discussed more flexible approach to define mesophotic boundaries, based on light availability, we performed a systematic search to assess their current state of knowledge. Using MODIS-Aqua satellite data (Kd490), we calculated the mesophotic boundaries in the ETP, based on optical depths, and performed a bibliographic search of studies carried out at those depths, including those present in turbid waters with KdPAR values up to 0.2 m-1. Seventy-seven papers on MCEs research were compiled in this review, recording a total of 138 species. The studies focus almost exclusively on taxonomy, ecosystem function, and reviews, indicating the need for future research regarding aspects, such as structuring environmental variables, molecular ecology, and natural resource management. Furthermore, remote sensing data show that there exists a high spatial variability of water transparency in the ETP, resulting in significant differences in KdPAR between oceanic and continental locations, mostly related to the occurrence of seasonal upwelling in the latter. Based on KdPAR, we estimated the mesophotic depth boundaries (z10%, z1%, z0.1%) for specific locations within the ETP and found that MCEs can potentially occur as shallow as 13-15 m in coastal regions. Also, we compared the calculated boundaries with the respective deepest records of light-dependent corals. With one exception, the presence of the corals was restricted to the upper mesophotic subzone (z10%-z1%), which agrees with reports for other regions, showing that light availability is one of the main drivers for the bathymetric distribution of MCEs and can be used as a first approach to identify their potential presence, though other local factors (e.g., geomorphology, temperature, internal waves) should also be considered, as they can cause shifts in depth limits.

Designing connected marine reserves in the face of global warming.

Marine reserves are widely used to protect species important for conservation and fisheries and to help maintain ecological processes that sustain their populations, including recruitment and dispersal. Achieving these goals requires well-connected networks of marine reserves that maximize larval connectivity, thus allowing exchanges between populations and recolonization after local disturbances. However, global warming can disrupt connectivity by shortening potential dispersal pathways through changes in larval physiology. These changes can compromise the performance of marine reserve networks, thus requiring adjusting their design to account for ocean warming. To date, empirical approaches to marine prioritization have not considered larval connectivity as affected by global warming. Here, we develop a framework for designing marine reserve networks that integrates graph theory and changes in larval connectivity due to potential reductions in planktonic larval duration (PLD) associated with ocean warming, given current socioeconomic constraints. Using the Gulf of California as case study, we assess the benefits and costs of adjusting networks to account for connectivity, with and without ocean warming. We compare reserve networks designed to achieve representation of species and ecosystems with networks designed to also maximize connectivity under current and future ocean-warming scenarios. Our results indicate that current larval connectivity could be reduced significantly under ocean warming because of shortened PLDs. Given the potential changes in connectivity, we show that our graph-theoretical approach based on centrality (eigenvector and distance-weighted fragmentation) of habitat patches can help design better-connected marine reserve networks for the future with equivalent costs. We found that maintaining dispersal connectivity incidentally through representation-only reserve design is unlikely, particularly in regions with strong asymmetric patterns of dispersal connectivity. Our results support previous studies suggesting that, given potential reductions in PLD due to ocean warming, future marine reserve networks would require more and/or larger reserves in closer proximity to maintain larval connectivity.

Operationalizing the social-ecological systems framework to assess sustainability.

Environmental governance is more effective when the scales of ecological processes are well matched with the human institutions charged with managing human-environment interactions. The social-ecological systems (SESs) framework provides guidance on how to assess the social and ecological dimensions that contribute to sustainable resource use and management, but rarely if ever has been operationalized for multiple localities in a spatially explicit, quantitative manner. Here, we use the case of small-scale fisheries in Baja California Sur, Mexico, to identify distinct SES regions and test key aspects of coupled SESs theory. Regions that exhibit greater potential for social-ecological sustainability in one dimension do not necessarily exhibit it in others, highlighting the importance of integrative, coupled system analyses when implementing spatial planning and other ecosystem-based strategies.

Like a rolling stone: the mobility of maerl (Corallinaceae) and the neutrality of the associated assemblages.

Beds of nonattached coralline algae (maerl or rhodoliths) are widespread and considered relatively species rich. This habitat is generally found in areas where there is chronic physical disturbance such that maerl thalli are frequently moved. Little is known, however, about how natural disturbance regimes affect the species associated with maerl. This study compared the richness, animal abundance, and algal biomass of maerl-associated species over a two-year period in a wave-disturbed bed and a sheltered maerl bed. Changes in associated species over time were assessed for departures from a neutral model in which the dissimilarity between samples reflects random sampling from a common species pool. Algal biomass and species richness at the wave-exposed site and on stabilized maerl at the sheltered site were reduced at times of higher wind speeds. The changes in species richness were not distinguishable from a neutral model, implying that algal species were added at random to the assemblage as the level of disturbance lessened. Results for animal species were more mixed. Although mobile species were less abundant during windy periods at the exposed site, both neutral and non-neutral patterns were evident in the assemblages. Artificial stabilization of maerl had inconsistent effects on the richness of animals but always resulted in more attached algal species. While the results show that the response of a community to disturbance can be neutral, the domain of neutral changes in communities may be relatively small. Alongside non-neutral responses to natural disturbance, artificial stabilization always resulted in an assemblage that was more distinct than would be expected under random sampling from a common pool. Community responses to stabilization treatments did not consistently follow the predictions of the dynamic equilibrium model, the intermediate disturbance model, or a facilitation model. These inconsistencies may reflect site-specific variation in both the disturbance regime and the adjacent habitats that provide source populations for many of the species found associated with maerl.