Ecology of Deep Oceans: Hadal Trenches

Abstract

The majority of the Earth is covered by ocean which itself averages greater than 3500 m deep. It is comprised mainly of the vast deep ocean plains, which span a depth range of 2000–6000 m. The maximum depth of the ocean however is nearly 11 000 m deep. These extremely deep areas are a result of tectonic plate convergence where an oceanic plate is subducted beneath a neighbouring continental plate. This subduction forms extraordinarily deep trenches which comprise what is known as the ‘hadal zone’. The hadal zone (6000–11 000 m) is therefore encompassed by clusters of disjunct and often extremely isolated deep trenches and troughs. The morphology of these habitats had provided a setting where environmental conditions (hydrostatic pressure and food supply) differ greatly from the majority of the deep‐sea and has resulted in high levels of species endemism at the greatest depths. Key Concepts: The deepest biozone in the oceans is the hadal zone (6000–11 000 m deep). The hadal zone is comprised mainly of deep trenches formed by tectonic convergence. The trench environment is characterised by high hydrostatic pressure, low temperatures, the absence of light and a limited food supply. Trench topography provides a unique setting with regard to food supply input because organic matter (food) is accumulated at the deepest trench axis. High levels of species endemism are observed in trenches as a result of their geographical isolation. Physiological adaptation to high pressure and low food supply is an essential prerequisite for survival in the trenches. Most metazoan taxa are represented in these deep trenches. Until recently, the technical challenges of studying the hadal zone were responsible for a dearth of information regarding the ecology at these depths. Research into the ecology of the hadal zone is in its infancy relative to shallower biozones.

A three-dimensional mapping of the ocean based on environmental data

“…A total of 102 depth zones extend to 5,500 m. The depth intervals are as follows: 5 m (from 0 m to 100 m), 25 m (from 100 m to 500 m), 50 m (from 500 m to 2,000 m), and 100 m (from 2,000 m to 5,500 m). The deepest points for which data are available do not necessarily represent the actual depth of the water column because the 5,500 m lower limit of the WOA data is approximately half of the maximum depth of the ocean (Jamieson, 2011). However, the 5,500 m lower limit does substantially exceed the mean depth (3,682.2 m) of the ocean as reported in the review by Charette and Smith (2010).…”

Molecular adaptation in the world's deepest‐living animal: Insights from transcriptome sequencing of the hadal amphipod Hirondellea gigas

“…Organic debris falling from the upper layers is the main carbon source of the hadal zone (Blankenship & Levin, ; Sainte‐Marie, ), which implies that food in hadal trenches is much more limiting than that in shallower regions. These harsh living conditions and remoteness from ocean surface form a unique extreme environment with endemic faunal community (Jamieson, ). Hadal trenches is one of the habitats with least understanding on the planet (Jamieson, ).…”

“…These harsh living conditions and remoteness from ocean surface form a unique extreme environment with endemic faunal community (Jamieson, ). Hadal trenches is one of the habitats with least understanding on the planet (Jamieson, ). Studying the molecular adaptation of endemic animals living in the deepest point, the Challenger Deep, can shed light on the secrets to life living in hadal trenches.…”

Single Cells within the Puerto Rico Trench Suggest Hadal Adaptation of Microbial Lineages

“…Most hadal zones are true trenches, lying within convergent margins where an oceanic plate is subducted below an oceanic or continental plate (1). Extreme environmental conditions, such as a lack of sunlight, magmacrustal physical and chemical interactions, near-freezing temperatures, and high pressure, give rise to unique ecosystems with distinct biological diversity (2).…”