**1. Introduction**

Environmental management and the preservation of biodiversity are widely considered priorities in the context of accelerating global changes affecting the physical and biological resources of our planet. This Special Issue focuses on "Coastal and Aquatic Ecosystems". The coastal region is a transition area between terrestrial and marine ecosystems. This transition area is now considered an important component of the biosphere, in terms of ecosystem diversity, and the provision of resources and services. Moreover, the coastal region is home to a significant number of distinct biological communities, including coral reefs, mangroves, salt meadows and wetlands, phanerogam meadows, kelp forests, estuarine assemblages or coastal lagoons, forests, and grasslands. The diversity of coastal ecosystems is directly threatened by human activity. It is estimated that 60% of the world's population lives on or near the coast, and economic development stresses the coastal environment. Coastal ecosystems are undergoing permanent changes in production rates, organism abundance, and community structure.

Achieving sustainable coastal zone management poses particularly significant challenges as the pressures of a growing human population, multiple development pressures, pollution from land-based sources, and unsustainable exploitation of natural resources are felt on many of the world's coasts. Remote sensing meets this challenge by offering a wide range of standard products on environmental coastal conditions, thanks to various state-of-the-art sensors. The development of innovative methods based on integrating multi-source, multi-resolution, and multi-temporal images offers promising prospects for considering the different scales of ecosystems. Consequently, the products derived from remote sensing contribute to the development of temporal and spatial indicators for better knowledge and management of coastal and aquatic ecosystems. This Special Issue includes original environmental research using satellite data processing—optical or radar—addressing coastal and aquatic ecosystem monitoring on different spatial and temporal scales.
