Monitoring international migration flows in Europe. Towards a statistical data base combining data from different sources

The paper reviews techniques developed in demography, geography and statistics that are useful for bridging the gap between available data on international migration flows and the information required for policy making and research. The basic idea of the paper is as follows: to establish a coherent and consistent data base that contains sufficiently detailed, up-to-date and accurate information, data from several sources should be combined. That raises issues of definition and measurement, and of how to combine data from different origins properly. The issues may be tackled more easily if the statistics that are being compiled are viewed as different outcomes or manifestations of underlying stochastic processes governing migration. The link between the processes and their outcomes is described by models, the parameters of which must be estimated from the available data. That may be done within the context of socio-demographic accounting. The paper discusses the experience of the U.S. Bureau of the Census in combining migration data from several sources. It also summarizes the many efforts in Europe to establish a coherent and consistent data base on international migration. The paper was written at IIASA. It is part of the Migration Estimation Study, which is a collaborative IIASA-University of Groningen project, funded by the Netherlands Organization for Scientific Research (NWO). The project aims at developing techniques to obtain improved estimates of international migration flows by country of origin and country of destination

Estimates of fish and coral larvae as nutrient subsidies to coral reef ecosystems

Nutrient subsidies are essential for the functioning of many ecosystems. A long‐standing conundrum in coral reef ecology is how these systems can be among the most productive globally, but persist in nutrient‐poor conditions. Here, we investigate the importance of the larvae of fishes and corals and gametes of corals as nutrient subsidies for coral reefs. We provide evidence that fish larvae may be an ecologically important source of exogenous nutrients. We found that at the high end of mean estimates of fish larval supply rates, larvae can replace the nutrients in the entire fish community (estimated from Caribbean coral reefs) in 28 and 434 d for nitrogen (N) and phosphorus, respectively. Coral larvae, on the other hand, appear to represent only a fraction of the nutrients supplied by the larval fish community. In contrast, coral gametes provide substantial pulses of recycled nutrients during synchronous spawning events. Within a single night, gametes from coral spawning events can produce nutrient fluxes that represent 13 and 64 times the amount of N and carbon, respectively, stored in coral reef fish communities. Our analysis suggests that larvae and/or gametes of fishes and corals may represent an important, but previously underappreciated, source of nutrients to coral reefs that warrant inclusion into models of nutrient dynamics and ecosystem function.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/144262/1/ecs22216_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144262/2/ecs22216.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144262/3/ecs22216-sup-0002-AppendixS2.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144262/4/ecs22216-sup-0001-AppendixS1.pd

Nitrogen pollution interacts with heat stress to increase coral bleaching across the seascape

Climate change is increasing the frequency and magnitude of temperature anomalies that cause coral bleaching, leading to widespread mortality of stony corals that can fundamentally alter reef structure and function. However, bleaching often is spatially variable for a given heat stress event, and drivers of this heterogeneity are not well resolved. While small-scale experiments have shown that excess nitrogen can increase the susceptibility of a coral colony to bleaching, we lack evidence that heterogeneity in nitrogen pollution can shape spatial patterns of coral bleaching across a seascape. Using island-wide surveys of coral bleaching and nitrogen availability within a Bayesian hierarchical modeling framework, we tested the hypothesis that excess nitrogen interacts with temperature anomalies to alter coral bleaching for the two dominant genera of branching corals in Moorea, French Polynesia. For both coral genera, Pocillopora and Acropora, heat stress primarily drove bleaching prevalence (i.e., the proportion of colonies on a reef that bleached). In contrast, the severity of bleaching (i.e., the proportion of an individual colony that bleached) was positively associated with both heat stress and nitrogen availability for both genera. Importantly, nitrogen interacted with heat stress to increase bleaching severity up to twofold when nitrogen was high and heat stress was relatively low. Our finding that excess nitrogen can trigger severe bleaching even under relatively low heat stress implies that mitigating nutrient pollution may enhance the resilience of coral communities in the face of mounting stresses from global climate change

Is coral richness related to community resistance to and recovery from disturbance?

More diverse communities are thought to be more stable-the diversity-stability hypothesis-due to increased resistance to and recovery from disturbances. For example, high diversity can make the presence of resilient or fast growing species and key facilitations among species more likely. How natural, geographic biodiversity patterns and changes in biodiversity due to human activities mediate community-level disturbance dynamics is largely unknown, especially in diverse systems. For example, few studies have explored the role of diversity in tropical marine communities, especially at large scales. We tested the diversity-stability hypothesis by asking whether coral richness is related to resistance to and recovery from disturbances including storms, predator outbreaks, and coral bleaching on tropical coral reefs. We synthesized the results of 41 field studies conducted on 82 reefs, documenting changes in coral cover due to disturbance, across a global gradient of coral richness. Our results indicate that coral reefs in more species-rich regions were marginally less resistant to disturbance and did not recover more quickly. Coral community resistance was also highly dependent on pre-disturbance coral cover, probably due in part to the sensitivity of fast-growing and often dominant plating acroporid corals to disturbance. Our results suggest that coral communities in biodiverse regions, such as the western Pacific, may not be more resistant and resilient to natural and anthropogenic disturbances. Further analyses controlling for disturbance intensity and other drivers of coral loss and recovery could improve our understanding of the influence of diversity on community stability in coral reef ecosystems