**Preface to "Freshwater Macroinvertebrates: Main Gaps and Future Trends"**

Being also known as "the blue planet", Earth is almost entirely covered with water. Nonetheless, only a small percentage (2.2% of the total) is freshwater. Of this, less than a third is available for living organisms. Facing raising threats posed by global changes, freshwaters are nowadays an increasingly rare, precious, and non-renewable resource, which should not be wasted.

Macroinvertebrates are ubiquitous organisms found in both fresh and brackish waters all around the globe, from streams of different sizes to lakes, wetlands, ponds, river estuaries, and lagoons. They are often unevenly distributed and relatively difficult to sample, especially in deep sediments where they play a crucial role in linking sediments and their processes to the food webs. Therefore, their species richness and their function are mostly neglected until the ecosystems show visible environmental modifications. Indeed, several factors impact species assemblages locally and globally: nitrogen deposition, salinity and temperature increase, pollution (e.g., pesticides and heavy metals), introduction of alien species, floods or droughts.

Hence, we developed the idea of a Special Issue that dealt with freshwaters and macroinvertebrates, with the aim of describing recent developments in biomonitoring of lakes and rivers, and of identifying future scientific developments to provide data and updates to politicians, water managers, technicians of environmental agencies, and researchers. The involvement of everyone is a key factor in planning and developing future activities for its management and fair and sustainable use.

Freshwater ecology used several approaches to study and sample macroinvertebrates, to develop metrics and indices to be used to evaluate the ecological status of the environments they inhabit, to standardize the sampling and the classification of water status. Moreover, problem-solving solutions arise from the development of experimental designs useful to monitor the presence or the absence of macroinvertebrates or their abundances. This Special Issue presents the past and current knowledge on freshwater macroinvertebrates to understand their role as providers of ecosystem services, to highlight the effects of global changes on their community structure, and to underline major gaps in their study. A special emphasis is dedicated to their value as biological indicators of environmental change for the assessment of water ecological status and human risk.

The papers submitted highlight that: i) the Water Framework Directive could have a worldwide application in its general term to obtain robust and shareable data; ii) diatoms could be used in biomonitoring programs supporting researchers with information that provides a different and integrated perspective with respect to the sole use of macroinvertebrates; iii) data sharing is a useful tool to derive larger scale analyses and distribution patterns of macroinvertebrate assemblages under climatic change stress, reducing at once costs and time for river ecology research; iv) alien species introduction causes a redistribution of species within ecosystems, but can be used to promote mitigation and conservation actions on native species or allow the development of new sampling strategies for large and deep lakes to obtain robust information on littoral occurrence of species; and v) researchers should focus their research also on cave organisms to solve the uncertainties linked to their poor taxonomic identification, sampling difficulty, biogeographic distribution, and richness contributing to solve Linnean, Wallacean, and Racovitzan shortfalls.

All the previous statements highlight that invertebrates are often neglected in biodiversity conservation policies that must be therefore implemented in order to contrast the current loss of biodiversity, to favor the achievement of the quality objectives of the Water Framework Directive, and to find mitigating solutions for the effects of anthropogenic pressures on aquatic ecosystems.

> **Angela Boggero, Laura Garzoli** *Editors*
