The Hidden Forests Below: A Review of the Ecology and Evolution of Wood Falls on the Deep Seafloor

Abstract

Wood falls—parcels of wood that sink to the deep-sea floor—represent unique and dynamic ecosystems that support a highly diverse and evolutionarily distinct assemblage of faunal communities. The fauna inhabiting wood falls exhibit a high degree of endemism, with many species using the wood not only as a substrate and habitat but also as a direct or indirect source of organic matter. Xylophagous species play a critical role in breaking down the wood, creating complex food webs and contributing to nutrient cycling in the deep-sea environment. The composition of faunal communities associated with sunken wood is influenced by several factors, including the physical properties of the wood itself, such as species, mass, and surface area, as well as environmental conditions like water depth, geographic location, and the stage of ecological succession. These factors interact to shape the biodiversity and ecological processes within wood falls, making them temporally and spatially finite habitats. Their distinct boundaries and lifespans are tightly linked to the rate of wood degradation, primarily driven by specialized wood-boring organisms. Despite their ecological significance, most knowledge about wood-fall ecosystems comes from experimental studies rather than from observations of naturally occurring wood falls. This has left significant gaps in our understanding of the natural variability and ecological roles of these systems in the deep sea. The scarcity of natural wood-fall records poses challenges for fully grasping their contribution to deep-sea biodiversity, carbon cycling, and biogeography. In this review, we synthesize the current state of knowledge on wood-fall ecosystems. We also explore the potential applications of wood-fall research in broader ecological, industrial, and environmental contexts. Wood falls offer valuable insights into deep-sea ecosystem functioning, biodiversity maintenance, and species evolution.