Ocean dredging was an

oceanography Oceanography (), also known as oceanology and ocean science, is the scientific study of the oceans. It is an Earth science, which covers a wide range of topics, including ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamic ...

technique introduced in the nineteenth century and developed by naturalist

Edward Forbes Edward Forbes FRS, FGS (12 February 1815 – 18 November 1854) was a Manx naturalist. In 1846, he proposed that the distributions of montane plants and animals had been compressed downslope, and some oceanic islands connected to the mainlan ...

. This form of

dredging Dredging is the excavation of material from a water environment. Possible reasons for dredging include improving existing water features; reshaping land and water features to alter drainage, navigability, and commercial use; constructing da ...

removes substrate and fauna specifically from the

marine environment Marine habitats are habitats that support marine life. Marine life depends in some way on the saltwater that is in the sea (the term ''marine'' comes from the Latin ''mare'', meaning sea or ocean). A habitat is an ecological or environmental ...

. Ocean dredging techniques were used on the HMS Challenger expeditions as a way to sample marine sediment and organisms. Eke Möbius ship dredging near Cuxhaven

History

Edward Forbes

would lay out the dredged material on the deck to examine, preserve and study it. The practice was chronicled in a remembrance of Forbes by

William Jerdan William Jerdan FSA (16 April 1782 – 11 July 1869), Scottish journalist, was born at Kelso, Scotland. During the years between 1799 and 1806, he spent short periods in a country lawyer's office, a London West India merchant's counting hou ...

in his 1866 book ''Men I Have Known''.

HMS ''Challenger''

Ocean dredging was a common sampling technique used on the

Challenger expedition The ''Challenger'' expedition of 1872–1876 was a scientific program that made many discoveries to lay the foundation of oceanography. The expedition was named after the naval vessel that undertook the trip, . The expedition, initiated by Wil ...

. The expedition, led by oceanographer John Murray and chief scientist Charles Wyville Thomson, set sail in 1872 and returned to England in 1876. The ship was equipped with 34 dredges and 20 dredge nets, completing 133 dredges at 111 stations during the 4 year long expedition. Thomson and Murray detail the following instructions for surveying dredged organisms: Britannica Dredge and Dredging 17

"Examine mud brought up by dredge from different depths for living
diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
s; examine also for the same purpose the stomachs of '' Salpae'' and other marine animals."

The expedition successfully dredged, collected, and preserved marine sediments, plants, algae, and invertebrates. The Challenger expedition is attributed to discovering approximately 4,700 new marine species and expanding the current knowledge of ocean sediments and geology.

Seafloor effects

Ocean dredging can negatively affect

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

ecosystems. When dredging equipment is moved along the seafloor, habitat-forming epifauna is damaged or removed. As emergent

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and sec ...

sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

s, and

seagrasses Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the orde ...

are damaged there is less habitat complexity for juvenile fishes to find protection in. Dredging also removes the

sand waves A sand wave is a lower regime sedimentary structure that forms across from tidal currents. Formation Sand waves are formed through the action of the wind or water (through waves or tidal currents). Sand waves form also underwater. See also ...

in which juvenile

Atlantic cod The Atlantic cod (''Gadus morhua'') is a benthopelagic fish of the family Gadidae, widely consumed by humans. It is also commercially known as cod or codling. The top 2–6 cm of marine substrate is disturbed during dredging, which can have negative impacts on deposit feeders, nutrient flux, and burrowing species. Dredging is often banned or highly restricted within

marine protected areas Marine protected areas (MPA) are protected areas of seas, oceans, estuaries or in the US, the Great Lakes. These marine areas can come in many forms ranging from wildlife refuges to research facilities. MPAs restrict human activity for a conserv ...

in order to protect recovering ecosystems.

Equipment used

Dredging in the marine environment can be carried out with a variety of equipment, depending on the purpose of the dredge. If the purpose is to remove sand or redistribute sediment, then a

dredge drag head {{unreferenced, date=July 2018 A dredge drag head is used by a trailing suction hopper dredger to collect sand from the sea floor. The dredge drag head is a steel structure that is connected to the dredger by a suction pipe. Supported by the g ...

attached to a

trailing suction hopper dredger A trailing suction hopper dredger is a ship that has a full sailing capacity used to maintain navigable waterways, deepening the maritime canals that are threatened to become silted, to construct new land elsewhere or to replace sand eroded by ...

ship is used. A

fishing dredge A fishing dredge, also known as a scallop dredge or oyster dredge, is a kind of dredge which is towed along the bottom of the sea by a fishing boat in order to collect a targeted edible bottom-dwelling species. The gear is used to fish for scallo ...

(also known as a scallop dredge) is used for collecting edible species of oysters,

mussels Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which ...

scallops Scallop () is a common name that encompasses various species of marine bivalve mollusks in the taxonomic family Pectinidae, the scallops. However, the common name "scallop" is also sometimes applied to species in other closely related famil ...

clams Clam is a common name for several kinds of bivalve molluscs. The word is often applied only to those that are edible and live as infauna, spending most of their lives halfway buried in the sand of the seafloor or riverbeds. Clams have two ...

, and

crabs Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

from the seafloor. PSM V06 D022 Vessels dredging for oysters

References

Oceanography {{ocean-stub