Jan-Claas Dajka

Helmholtz Institute for Functional Marine Biodiversity

Thermally induced mass coral bleaching is globally responsible for major losses of coral cover. Coral recovery from mass coral disturbances like the 2016 bleaching event hinges on successful recruitment of new coral colonies to the existing population. Juvenile corals as a life history stage represent survival and growth of new recruits. As such, h...

Herbivory is a key process on coral reefs, which, through grazing of algae, can help sustain coral‐dominated states on frequently disturbed reefs and reverse macroalgal regime shifts on degraded ones. Our understanding of herbivory on reefs is largely founded on feeding observations at small spatial scales, yet the biomass and structure of herbivor...

Social–ecological systems (SES) exhibit complex cause‐and‐effect relationships. Capturing, interpreting, and responding to signals that indicate changes in ecosystems is key for sustainable management in SES. Breaks in this signal–response chain, when feedbacks are missing, will allow change to continue until a point when abrupt ecological surprise...

Despite an increasing understanding of the issue of marine pollution, humanity continues on a largely unsus-tainable trajectory. This study aimed to identify and classify the range of scientific studies and interventions to address coastal and marine pollution. We reviewed 2417 scientific papers published between 2000 and 2018, 741 of which we anal...

Cell size is a master trait in the functional ecology of phytoplankton correlating with numerous morphological, physiological, and life‐cycle characteristics of species that constrain their nutrient use, growth, and edibility. In contrast to well‐known spatial patterns in cell size at macroecological scales or temporal changes in experimental conte...

Thresholds and tipping points are frequently used concepts to address the risks of global change pressures and their mitigation. It is tempting to also consider them to understand biodiversity change and design measures to ensure biotic integrity. Here, we argue that thresholds and tipping points do not work well in the context of biodiversity chan...

The current policy and goals aimed to conserve biodiversity and manage biodiversity change are often formulated at the global scale. At smaller scales however, biodiversity change is more nuanced leading to a plethora of trends in different metrics of alpha diversity and temporal turnover. Therefore, large‐scale policy targets do not translate easi...

The Wadden Sea became a UNESCO World Heritage Site in 2009 owing to its geographical and ecological importance. Given its status and its global recognition, academic understanding of, and engagement with, a diverse set of stakeholders is crucial to the sustainability of the Wadden Sea and the wildlife that inhabit its transnational boundaries. As s...

The sustainable management of water resources is required to avoid water scarcity becoming widespread. This article explores the potential application of a social-ecological framework, used predominantly in the fields of ecology and conservation, as a tool to improve the sustainability and resilience of water resources. The “red-loop green-loop” (R...

1. Extensive and dense macroalgal fields can compromise the ecosystem function of habitat mosaics on reefs owing to their limiting effect on patch connectivity. Macroalgae can maintain and increase their dominance with effective self-reinforcing feedback mechanisms. For example, macroalgae can form dense beds, supressing coral settlement and grazin...

There is an assumption that tropical sea urchins are macroalgal grazers with the ability to control macroalgal expansion on degraded coral reefs. We surveyed abundances of Echinothrix calamaris, an urchin species common in the western Indian Ocean on 21 reefs of the inner Seychelles and predicted their density using habitat predictors in a modellin...

Coral reefs are degrading under global stressors that are increasing in frequency and severity as the Anthropocene accelerates. My thesis contributes to our scientific understanding of the dynamics that govern degraded coral reef states. More specifically, I contribute to our understanding of feedback processes on degraded coral reefs in conceptual...