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Isle of Wight sized reef found by seabed mappers

05 December 2011

A string of new discoveries by seabed habitat mappers around the world seem to bear out the old adage - that we know more about the surface of Mars than we do about the Earth's seabed.

In UK waters, recent work by Cefas scientists has revealed an extensive system of rocky ridges in the central English Channel. Previously, the mapped area was thought to contain little or no rock outcrops.

So the mappers were surprised to find a "reef" that is about four times the size of the Isle of Wight. As remarkable as that is, the reef is also important for another reason: it supports a large variety of marine animals. The abundant fauna includes sponges, bryozoans, anemones and sea-squirts.

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Markus Diesing, of Cefas' Marine Habitats and Mapping team said: "We used a combination of existing data and new survey information, collected on our research vessel, the Cefas Endeavour, to outline and characterise the area of rock ridges.

"These extend over 1,100 square kilometres of seabed, some 30 kilometres south of the Isle of Wight. The reef rests at depths between 40 and 100 metres below the surface, so it isn't hazardous to shipping."

Multi-beam sonar shows a complex of rock formations exposed at the seabed - with ridges up to 4 metres high - generally running in an east-west direction. Underwater video and seabed photographs reveal the detailed physical nature of the seabed and show the range of animals that live there.

Multi-beam of underwater river, Channel

Multi-beam sonar image showing some of the rock ridges in the central English Channel and the path of an ancient river that has cut through them. The scale shows water depth in metres.

The feature, now known as the Wight-Barfleur Reef (PDF), is currently under consideration for protection under the European Union's Habitats Directive as part of a European network of Marine Protected Areas, known as Natura 2000.

This particular discovery has recently been published as a case study in a major new book called Seafloor Geomorphology as Benthic Habitat - GeoHab Atlas of Seafloor Geomorphic Features and Benthic Habitats.

The atlas provides a synthesis of current knowledge in relation to seabed geomorphology as benthic habitat and presents a total of fifty-seven case studies from around the world. 

It seems there is still plenty to explore and discover here on Earth.

Seabed fauna Benthic fauna, Channel

1. Sponges (Porifera) are collections of cells that can be organised into a variety of shapes. They live attached to rock and feed by filtering particles out of the water. There are many encrusting forms in the UK, but the massive forms such as the large white or grey "Elephant's Hide" sponge (Pachymatisma johnstonia, not shown in this image) are relatively uncommon.

2. Bryozoans (Ectoprocta) are colonies of "zooids", small individuals about the size of a grain of sugar that are not quite independent from each other. They live in a matrix of individual chambers and different groups of zooids perform different functions for the colony (e.g. feeding, excretion, reproduction). The colonies live attached to rocks and there are many forms in UK waters. The "Hornwrack" (Flustra foliacea) was very common on the rock ridges.

3. Anemones (Actiniaria) are individual soft-bodied animals with a central mouth surrounded by a ring of tentacles armed with stinging cells. They usually live attached to rocks with their tentacles spread wide waiting for prey items to brush into them.

4. Sea-squirts (Ascidiacea) have sac-like bodies with a primitive backbone and are typically about the size of a grape. They live attached to rocks and can be solitary, gregarious (living in groups) or colonial. They pump seawater through their body cavity and filter out tiny particles of food.

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Last Modified: 27 April 2014