| Popis: |
In this book chapter, we review and discuss the resistance of marginal reefs and their potential as refugia. Marginal reefs (MRs) greatly differ from each other owing to their diverse biogeographic conditions and the different environmental parameters under suboptimal conditions to which they are subjected (e.g., temperature, depth, extreme pH, siltation, nutrients, and turbidity). The bulk of suboptimal conditions represent unsuitable environments for most species, which are filtered out by natural selection, resulting in two conspicuous characteristics of marginal reefs: low biological richness and dominance of stress-tolerant species. Moreover, this low diversity could result in a low ecological redundancy in several functions, which would lead these functions to a status close to collapse when faced with the loss of one or more of their species. Thus, the loss of one or more functions could result in a persistent phase shift. In contrast, tolerant species have high environmental plasticity and can live in a wide range of one parameter. In other words, although these reefs have a lower functional redundancy, their species are usually more resistant to one or even several environmental parameters under suboptimal conditions (e.g., heatwaves and/or moderate turbidity). In this scenario, a plethora of different MR conformations (e.g., turbid-zone, high-latitude and high-temperature reefs, and mesophotic coral ecosystems) is presented, some of which are considered as potential short-term refuge, but restricted to adapted species. In parallel, other MRs could also take some climatic refugees by shifts in species distribution in the Anthropocene. Nevertheless, most MRs are threatened by multiple chronic and acute stressors, including long-term warming, invasive species, heatwaves, overfishing, acidification, bottom trawling, weakening of benthic-pelagic coupling, plastic and organic pollution, oil spills, sea-level rise, and increased siltation. Therefore, the resistance and refugia potential of MRs will be lower than expected because they are under severe anthropogenic pressure and are ecologically distinct ecosystems from the shallow-water coral reefs under optimal conditions. Thus, the heterogeneous set of MRs actually represents limited long-term refugia, and their resistance and recovery potential will be lost if resilience-based management actions at the local and global scale are not urgently adopted. We highlight the importance of maintaining pathways of connectivity, reducing reef stressors, and also protecting the endemism hotspots, unique diversity of marginal reefs, and their few functional groups. |
