SIO 277 11 01 2007 Christina Tanner Page 1 of 4 The Origin of Deep Sea Fauna Early naturalists presumed the deep sea to be an azoic environment How could life originate and persist in a presumably dark cold pressurized anoxic environment By the mid nineteenth century this theory was rejected with the recovery of life from as deep as 2500m The Norwegian naturalists Michael Sars and his son listed hundreds of invertebrate species collected from the deep sea including the archaic like stalked sea lily Rhizocrinus lofotensis Thomson 1874 The HMS Challenger Expedition from 1872 1876 was expecting to recover archaic life from the deep sea and deduce the origin of life at these extreme depths Instead dredges did not contain archaic life forms and thus initiated further development on identifying the processes leading to the origin of deep sea fauna In the summary reports of the HMS Challenger John Murray concluded that the animals recovered from the deep were not archaic Murray 1895 Rather there were similarities in the taxa found in shallow water high latitude and deep sea habitats Murray postulated that this was an explanation to the origin of deep sea life Animals in shallow waters had submerged into the deep at high latitudes when temperature was isothermal to depth This pattern was described for many sampled organisms For example genera of the class Asteroidea were represented in both the Northern and the Southern latitudes the Holothuroidea had several forms that occurred in the Arctic Sea with conspecifics in the Antarctic and similar patterns were also described in fish decapod crustaceans and hydroids Agassiz 1881 Th el 1882 and Murray 1895 Murray speculated the submergence event leading to the origin of deep fauna 250ma During the Carboniferous Period 300ma sea surface temperatures were globally uniform at 70 F Likewise surface faunas were cosmopolitan from the equator to the poles For example corals were present at all latitudes during the early Mesozoic Period Neaverson 1955 With a uniformity in temperature there would be no deep water formation For this reason Murray proposed the deep sea was anoxic and uninhabitable by life During the Mesozoic Period 250ma there was differential heat input into the surface waters The high latitude waters cooled and were thus denser The submergence of cold high latitude water into the deep sea brought oxygen with it and metazoan life became possible Murray parsed the current ocean fauna into three groups based on life history traits 1 organisms that lack a pelagic larval phase and instead contain pouches to rear young 2 organisms that have pelagic larvae that only appear during spring and summer and 3 organisms that produce a continuous supply of pelagic larvae Accordingly the shallow high latitude and deep sea organisms were defined by group 1 temperate organisms by group 2 and tropical organisms by group 3 As the poles cooled during the Mesozoic Period the animals at the poles either went extinct or their ranges were restricted to low latitudes since their larval life stages could not survive at low temperatures group 1 Animals that were able to restrict their reproductive stage to the summers were able to inhabit mid latitudes and the fauna that could remain at the poles brooded their larvae group 2 The submergence of polar waters into the deep sea took polar animals with them serving as an explanation for the similarity of marine fauna between the deep sea and high latitudes group 3 SIO 277 11 01 2007 Christina Tanner Page 2 of 4 During the mid nineteenth century there were other theories besides Murray s on the origin of fauna in the deep sea However these theories did not persist through the Challenger Expedition s recovery of fauna not endemic to the deep and the advent of embryological investigations Moseley 1880 had regarded the pelagic animals as the original stock from which all other marine animals had sprung Murray 1895 Others including Wallich 1860 postulated that the deep sea fauna had been completely isolated from the rest of the ocean for an extended period due to pressure constraints Therefore the deep sea would contain solely endemic species Murray 1895 Murray s shallow water submergence hypothesis has been shown in various groups of organisms throughout the last century As part of the scientific reports of the Galathea Deep Sea Expedition from 1950 1952 Madsen investigated the origin of Porcellanasteridae a family of asteroid Madsen 1961 Sea stars were collected from widely separated localities and were commonly obtained in dredges from abyssal depths Porcellanasteridae were among the best known deep sea animals with regards to taxonomy and distribution Madsen found that Porcellansteridae are younger than the bathyal and sublittoral faunas suggesting a more recent faunal evolution of shallow water submergence into the deep sea Opposite of shallow water emergence the deep water emergence hypothesis on the origin of fauna in the deep sea has been shown in other groups of organisms Deepwater emergence is a result of animals being highly modified within the deep and radiating into shallow waters Hessler and Thistle 1975 investigated the order Isopoda They argued against Kussakin 1973 in that this group has opposite origins from the deep and radiated into shallow waters This notion is supported by the presence of a diversity center in the deep sea and the lack of eyes in some of the deep Isopoda as well as from some species in shallow waters at high latitudes After a deep sea emergence the shallow species are not capable of successfully recovering such a complex organ Other groups of deep sea fauna do not fit into either of the two previous hypothesis Lipps and Hickman 1982 have concluded that deep sea and Antarctica Foraminifera have their origins by several processes The majority evolved in their respective locations and fewer migrated between the two regions Thus there is no one process identifying the representation of Foraminifera in the deep These early examinations on the origin of deep sea fauna have developed over the last decade with additional studies and technological advancements Young et al 1997 investigated the potential for shallow water echinoids to invade deep waters by looking at the effects of temperature and pressure on larvae They found that larvae were more likely to survive at deep sea pressures and warm temperatures than at shallow water pressures and cold temperatures Accordingly some species have