Biofilms are matrix‐enclosed communities that represent the most dominant and active mode of microbial life on Earth. Because biofilms are inherently more productive than any equivalent planktonic community, they are of great relevance to all environments they inhabit. However, their existence and importance are still poorly known by the general public, conservation practitioners and environmental policymakers. Most micro‐organisms of multicellular organisms (including humans, animals and plants) occur in the form of true biofilms or biofilm‐like structures that play vital roles in their development, physiology and immunity. Conversely, some biofilms can have a negative effect on host health. Biofilms growing on non‐biological surfaces are essential components of many terrestrial and marine ecosystems: they form the basis of food webs and ensure nutrient cycling and bioremediation in natural systems. However, environmental biofilms can promote the persistence of human pathogens, produce harmful toxins, foul and corrode surfaces in natural and man‐made settings; all of which can have significant health and economic implications. There is a knowledge gap about the roles of biofilms in the epidemiology of wildlife emerging infectious diseases, yet these pose a major threat to public health, biodiversity and sustainability. The drivers of global environmental change all affect biofilm structure and functions. The consequences for host and ecosystem health are, however, poorly understood. While the concept of a healthy microbiome (as opposed to dysbiosis) is emerging in medicine and conservation biology, the concept of a healthy biofilm remains to be defined in environmental sciences. Here, we use an integrative approach to (a) review current knowledge on the roles of biofilms growing on biological and non‐biological interfaces for the health of multicellular organisms and ecosystems, and (b) provide future research directions to address identified knowledge gaps. Giving the biofilm life‐form its full importance will help understand the effects of global environmental change on these communities and, in turn, on human, animal, plant and ecosystem health.

Compensatory recruitment is a key demographic mechanism that has allowed the coexistence of populations of susceptible amphibians with Batrachochytrium dendrobatidis (Bd), a fungus causing one of the most devastating emerging infectious disease ever recorded among vertebrates. However, the underlying processes (e.g. density‐dependent increase in survival at early life stages, change in reproductive traits) as well as the level of interpopulation variation in this response are poorly known. We explore potential mechanisms of compensatory recruitment in response to Bd infection by taking advantage of an amphibian system where male reproductive traits are easy to quantify in free‐living populations. The Southern Darwin's frog Rhinoderma darwinii is a vocal sac‐brooding species that exhibits a high susceptibility to lethal Bd infection. Using a 7‐year capture–recapture study at four populations with contrasting Bd infection status (one high prevalence, one low prevalence and two Bd‐free populations), we evaluated whether Bd‐positive populations exhibited a higher adult recruitment and a higher male reproductive effort than Bd‐negative populations. We also estimated population growth rates to explore whether recruitment compensated for the negative impacts of Bd on the survival of adults. In addition, we evaluated a potential demographic signal of compensatory recruitment (i.e. positive relationship between the proportion of juveniles and Bd prevalence) in response to Bd infection using raw count data from 13 R. darwinii populations. The high Bd prevalence population exhibited the highest male reproductive effort and the highest recruitment among the four monitored populations. This led to a growing population during the study period despite high mortality of adult hosts. In contrast, males from the population with low Bd prevalence had a low reproductive effort and this population, which had the lowest adult recruitment, was declining during the study period despite adults having a higher survival in comparison to the high Bd prevalence population. We also found a demographic signal of compensatory recruitment in response to Bd infection in our broader analysis of 13 R. darwinii populations. Our study underlines the importance of interpopulation variation in life‐history strategies on the fate of host populations after infectious disease emergence. Our results also suggest that an increase in reproductive effort can be one of the processes underlying compensatory recruitment in populations of Bd‐susceptible amphibians.