Vema Seamount is a seamount in the South Atlantic Ocean. Discovered in 1959 by a ship with the same name, it lies 1,600 kilometres (1,000 mi) from Tristan da Cunha and 1,000 kilometres (620 mi) northwest of Cape Town. The seamount has a flat top at a mean depth of 73 metres (40 fathoms) which was eroded into the seamount at a time when sea levels were lower; the shallowest point lies at 26 metres (14 fathoms) depth. The seamount was formed between 15-11 million years ago, possibly by a hotspot.
The seamount rises high enough that its summit is at shallow depth, allowing sunlight to reach it and thus permitting the growth of kelp and algae. A number of sea animals and fish are encountered on the seamount; active fisheries existed at Vema Seamount and caused the disappearance of some animal species.
Vema Seamount (Africa)
|Summit depth||26 metres (14 fathoms)|
|Summit area||13 square kilometres (5 sq mi)|
|Age of rock||11.00 ± 0.3 million years old|
|Discovered by||RV Vema|
Vema Seamount was discovered by the research ship RV Vema of the Lamont–Doherty Earth Observatory in 1959. Vema is one of the first seamounts to be the subject of scientific study, and the first seamount investigated by scuba divers without special equipment. Vema lies in international waters and its summit is so shallow that it is a navigation hazard to ships.
Vema Seamount lies in the South Atlantic Ocean, 1,600 kilometres (1,000 mi) away from Tristan da Cunha. The cities of Cape Town and Lüderitz lie east-southeast and northeast of Vema, respectively, with Cape Town about 1,000 kilometres (620 mi) distant.
The seamount has a conical shape with a flat top; the shallowest point rises to an elevation of 26 metres (14 fathoms) below sea level and is called Collins Point. At least one source gives a minimum depth of 11 metres (36 ft) for the seamount, while recent bathymetric surveys have found a minimum depth of 21.5 metres (71 ft). The flat top is a summit plateau has a width of 8.0 kilometres (5 mi) and as more recently determined 11 by 8.5 kilometres (6.8 mi × 5.3 mi) at a mean depth of 73 metres (40 fathoms) and has been named Emerson Plateau; it has a vaguely triangular shape pointing west, and Collins Point lies close to the western margin of the Emerson Plateau. Other points on the Plateau also rise to depths of less than 55 metres (30 fathoms). The plateau appears to be a wave-cut platform of Pleistocene age, when sea levels were lower, and is swept by strong ocean currents.
The seamount rises from a depth of 4,600 metres (2,500 fathoms), where it occupies a breadth of 56 kilometres (35 mi) and forms an isolated conical feature. The seafloor from which Vema rises belongs to the abyssal plain of the Cape Basin. From there, the slopes of Vema first rise steeply and feature subsidiary summits; above 130 metres (70 fathoms) depth the slopes flatten.
Volcanic rocks such as tuff as well as calcareous aggregates are found on the plateau. Collins Point is composed of phonolite, which contains aegirine, alkali feldspar, augite and nepheline. Olivine basalt has also been found. A minimum age of 11.0 ± 0.3 has been obtained from samples taken at Collins Point by potassium-argon dating, with another age being 15 million years. Older ages have been obtained deeper on the seamount; a sample from 3,000 metres (9,800 ft) depth gave an age of 18 million years.
Vema is an intraplate volcano and is considered to be the present-day location of a hotspot, the Vema hotspot, although the hotspot itself may have moved farther west (by about 200 kilometres (120 mi)) since when it created the Vema Seamount. Seismic tomography has shown what may be a mantle plume underneath Vema, another theory considers the Vema hotspot is a consequence of the Tristan hotspot shedding a secondary diapir. The hotspot origin of the Vema Seamount is not universally agreed upon. Earlier volcanism caused by the Vema hotspot may have manifested itself in southern Namibia in the form of alkaline volcanics, such as the Klinghardt phonolite, the 49 million years old Dicker Willem volcanic complex or melilites close to the mouth of the Orange River, which are 37 million years old, or even the Karoo-Ferrar large igneous province.
Water temperatures at Vema range between 18–21 °C (64–70 °F), decreasing downwards, and the cold Benguela Current does not reach the seamount. The movement and strength of ocean eddies are altered when they interact with Vema Seamount, with Agulhas eddies often splitting apart at the seamount.
The summit of Vema Seamount is shallow enough that sunlight can reach it, resulting in the growth of various types of algae and seaweeds such as Ecklonia kelp. Such kelp covers large parts of the seamount.
A number of animals inhabit Vema, usually cryptic or encrusting animals. Ascidians, black corals, non-reef building corals including gorgonia and scleractinia, decapods, holothurians, hydroids, polyzoa, rock lobsters (Jasus tristani), sea fans and sponges live on the seamount. Other animals such as bryozoans, echinoderms, gastropods, oysters, pelecypods, serpulids and other worms have also left their traces on Vema. Rock lobsters propagate from Gough Island and Tristan da Cunha to Vema Seamount, while other species appear to originate from South Africa.
Several species appear to be endemic to Vema Seamount, including the sea snail species Austromitra rosenbergi discovered in 2015 and the sponge Strongylodesma areolata described in 1969; it is estimated that about 22-36% of all species at Vema are endemic, similar to the proportion of endemic species at other seamounts of the world. The holothurian Holothuria vemae is named after the seamount, where it was discovered in 1965-1966 as is the sea snail Trivia vemacola.
A number of fish have been encountered at Vema, although most fish species appear to be pelagic species that are not directly bound to the seamount environment. Fishing operations have attracted seabirds to Vema Seamount. Euphausiids and copepods are also found in the waters, including at least one copepod that parasitizes fish. Among the fish species encountered at Vema Seamount are:
Fish on the seamount are commercially fished, with the late 1970s and 1980s seeing the initiation of Mackerel scad and tuna fishing, respectively. Rock lobsters in particular were heavily used; they disappeared from Vema Seamount after overfishing in the 1960s, briefly recovered and then disappeared again by 1981 due to renewed overfishing. The collapse of this fishery is one of the first instances of a seamount fishery collapsing, and has been cited as an example of how fisheries outside of exclusive economic zones end up ungoverned and abused. Today Vema Seamount is closed to fishery by the South East Atlantic Fisheries Organisation, and man-made debris such as crab traps and ropes can be found on Vema Seamount.
Austromitra rosenbergi is a species of sea snail, a marine gastropod mollusk, in the family Costellariidae, the ribbed miters.Hotspot (geology)
In geology, the places known as hotspots or hot spots are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Their position on the Earth's surface is independent of tectonic plate boundaries. There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary. The other hypothesis is that lithospheric extension permits the passive rising of melt from shallow depths. This hypothesis considers the term "hotspot" to be a misnomer, asserting that the mantle source beneath them is, in fact, not anomalously hot at all. Well-known examples include the Hawaii, Iceland and Yellowstone hotspots.Jasus
Jasus is a genus of spiny lobsters which live in the oceans of the Southern Hemisphere. They have two distinct "horns" projecting from the front of the carapace, but lack the stridulating organs present in almost all other genera of spiny lobsters. Like all spiny lobsters, they lack claws, and have long stout antennae which are quite flexible.List of marine bony fishes of South Africa
This is a sublist of the List of marine fishes of South Africa for bony fishes recorded from the oceans bordering South Africa.
This list comprises locally used common names, scientific names with author citation and recorded ranges. Ranges specified may not be the entire known range for the species, but should include the known range within the waters surrounding the Republic of South Africa.
List ordering and taxonomy complies where possible with the current usage in Wikispecies, and may differ from the cited source, as listed citations are primarily for range or existence of records for the region.
Sub-taxa within any given taxon are arranged alphabetically as a general rule.
Details of each species may be available through the relevant internal links. Synonyms may be listed where useful.
Osteichthyes (), popularly referred to as the bony fish, is a diverse taxonomic group of fish that have skeletons primarily composed of bone tissue, as opposed to cartilage. The vast majority of fish are members of Osteichthyes, which is an extremely diverse and abundant group consisting of 45 orders, and over 435 families and 28,000 species. It is the largest class of vertebrates in existence today.
The group Osteichthyes is divided into the ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii). The oldest known fossils of bony fish are about 420 million years old, which are also transitional fossils, showing a tooth pattern that is in between the tooth rows of sharks and bony fishes.List of marine fishes of the suborder Percoidei of South Africa
This is a sub-list of the List of marine Perciform fishes of South Africa for fishes of the suborder Percoidei recorded from the oceans bordering South Africa. This list comprises locally used common names, scientific names with author citation and recorded ranges. Ranges specified may not be the entire known range for the species, but should include the known range within the waters surrounding the Republic of South Africa.
List ordering and taxonomy complies where possible with the current usage in Wikispecies, and may differ from the cited source, as listed citations are primarily for range or existence of records for the region. Sub-taxa within any given taxon are arranged alphabetically as a general rule. Synonyms may be listed where useful.
Percoidei is one of 18 suborders of bony fishes in the order Perciformes. Many commercially harvested fish species are contained in this suborder, including the snappers, jacks, whitings, groupers, basses, perches, and porgies.List of marine gastropods of South Africa
This list of marine gastropods of South Africa attempts to list all of the sea snails and sea slugs of South Africa, in other words the marine gastropod molluscs of that area. This list is a sub-list of the List of marine molluscs of South Africa.
The gastropods (), more commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca, called Gastropoda. This class comprises snails and slugs from saltwater, from freshwater, and from the land. There are many thousands of species of sea snails and slugs, as well as freshwater snails, freshwater limpets, and land snails and slugs.
The class Gastropoda contains a vast total of named species, second only to the insects in overall number. The fossil history of this class goes back to the Late Cambrian. , 721 families of gastropods are known, of which 245 are extinct and appear only in the fossil record, while 476 are currently extant with or without a fossil record.
Gastropoda (previously known as univalves and sometimes spelled "Gasteropoda") are a major part of the phylum Mollusca, and are the most highly diversified class in the phylum, with 65,000 to 80,000 living snail and slug species. The anatomy, behavior, feeding, and reproductive adaptations of gastropods vary significantly from one clade or group to another. Therefore, it is difficult to state many generalities for all gastropods.List of submarine volcanoes
A list of active and extinct submarine volcanoes and seamounts located under the world's oceans. There are estimated to be 40,000 to 55,000 seamounts in the global oceans. Almost all are not well-mapped and many may not have been identified at all. Most are unnamed and unexplored. This list is therefore confined to seamounts that are notable enough to have been named and/or explored.Macrorhynchia filamentosa
Macrorhynchia filamentosa, the smoky feather hydroid, is a colonial hydroid in the family Aglaopheniidae.Outline of oceanography
The following outline is provided as an overview of and introduction to Oceanography.Planar hydroid
The planar hydroid (Sertularella arbuscula) is a branching colonial hydroid in the family Sertulariidae.Pycnotheca mirabilis
Pycnotheca mirabilis, The feathery hydroid, is a colonial hydroid in the family Kirchenpaueriidae.
Feathery hydroids are often white and grow in crowded colonies resembling upright feathers. The stems may grow to 3 cm in total height. The reproductive bodies are found at the base of the stems and resemble beehives.This colonial animal is found off the South African coast from False Bay to KwaZulu-Natal, as well as around the Indo-Pacific rim and Vema Seamount. It lives from the subtidal to 50 m under water. This species eats microplankton.RV Vema
The research vessel Vema was a three-masted schooner of the Lamont Geological Observatory (now the Lamont-Doherty Earth Observatory [LDEO]), a research unit of Columbia University. The 202 ft (62 m). waterline vessel, with her almost indestructible Swedish wrought iron hull, became renowned as one of the world’s most productive oceanographic research vessels. The ship had been first sailed for pleasure under the name Hussar, and after her career as a research vessel entered a new career as the cruising yacht Mandalay.Thuiaria articulata
Thuiaria articulata, the jointed hydroid or sea spleenwort, is a branching colonial hydroid in the family Sertulariidae.Vema
Vema may refer to:
Prolaya Vema Reddy, the first king of the Reddy dynasty in Andhra Pradesh, India
A Greek pace (unit of length)
Research Vessel Vema, a research ship of the Lamont-Doherty Earth Observatory used by J. Lamar Worzel and Marie Tharp, and some ocean phenomena discovered using it:
Vema (genus), a genus of Monoplacophoran molluscs
The Vema Seamount, a seamount in the South Atlantic Ocean at 31°38' S 8°20' E.
The Vema hotspot, a hotspot (geology)
The Vema Fracture Zone a fracture zone in the equatorial Atlantic OceanWalvis Ridge
The Walvis Ridge (walvis means whale in Dutch and Afrikaans) is an aseismic ocean ridge in the southern Atlantic Ocean. More than 3,000 km (1,900 mi) in length, it extends from the Mid-Atlantic Ridge, near Tristan da Cunha and the Gough Islands, to the African coast (at 18°S in northern Namibia). The Walvis Ridge is one of few examples of a hotspot seamount chain that links a flood basalt province to an active hotspot. It is also considered one of the most important hotspot tracks because the Tristan Hotspot is one of few primary or deep mantle hotspots.