Do marine rooted plants grow in sediment or soil? A critical appraisal on definitions, methodology and communication

Mangroves, saltmarsh plants and seagrasses grow in coastal areas near the land-ocean interface. Marine scientists normally identify the substratum in which these plants grow as sediments. For half a century, sediments supporting emergent vegetation have been described by pedologists and some ecologists as soils. However, more recently, some pedologists began to suggest that subtidal marine substrata should be “subaqueous soils.” This followed a change in the definition of soil in the 2nd (1999) edition of Soil Taxonomy by the US Department of Agriculture. These developments have caused concerns among many coastal marine scientists, and have led to the emergence of serious and important questions which we address in this paper. We conclude that the terms “sediment” and “soil” to describe the substrata in coastal environments vegetated by mangrove forests, saltmarshes and seagrass beds are not mutually exclusive. Coastal marine substrata will still be denoted sediments by most marine scientists. Pedologists should recognize and affirm the appropriateness of this historical convention, while they at the same time for specific purposes can use the term “soil” when justifiable according to the definition. Furthermore, research methodology must be appropriate to the environments under study and recognize the uniqueness of these water saturated and largely anoxic environments. This is critical to avoid flawed and incomparable results and to facilitate better communication among scientists working in the coastal zone. A mutual awareness and appreciation among involved communities will help to avoid confusion and improve the understanding among the marine and soil researchers studying these systems. We hope that these ideas can be adopted by the marine and terrestrial scientific communities and look forward to further cooperation through a continued positive dialogue.