The origin of the Southern Ocean marine fauna

Abstract

Current knowledge of the break-up of Gondwana during the Tertiary indicates that shallow water marine habitats may have been present continuously, and on occasions were considerably more extensive than at present. Although direct fossil evidence is sparse after the Eocene, geophysical evidence suggests that shallow waters have been present since the late Mesozoic, and possibly much longer. The break-up of Gondwana was accompanied by a more or less steady lowering of both surface and bottom temperatures in the Southern Ocean from about 15°C in the Late Cretaceous to the present range of roughly +2 to −1.8°C. Microfossils in deep-sea drilling cores indicate that temperature drops were particularly sharp in the early Oligocene ( c. 38 Ma), mid-Miocene (10–14 Ma) and Pliocene ( c. 4 Ma BP). Geological evidence suggests that the Drake Passage opened, and the present oceanographic regime established, about 25–30 Ma BP. This is now known to be about the time of full-scale development of the East Antarctic ice cap. Subsequently ice sheets extended across, and deeply eroded, the continental shelves but the effects of these glacial maxima on the marine biota are not fully understood. Late Cretaceous/early Tertiary marine fossils from the James Ross Island group indicate a diverse shallow water marine fauna, including two groups notably lacking in diversity in the living fauna: decapods and teleost fish. In several genera occurrences in this fauna predate first occurrences in lower latitudes by as much as 40 Ma, suggesting the possibility that a number of groups originated at high southern latitudes. The living fauna exhibits a high biomass in many areas, and within-site diversity can be as high as anywhere in the world. Some individual taxonomic groups, however, (notably bivalves and gastropods) have a lower diversity than in the tropics, supporting the concept of a latitudinal cline in diversity. Studies of physiological adaptation to temperature suggest that the decline in seawater temperature during the Cenozoic has not presented a particularly severe evolutionary problem. The reasons for the absence of large decapods and the low diversity of fish in the present fauna are unclear. Most of the biological features of the modern fauna are more likely a response to the seasonality of the ecosystem rather than low temperature per se . Overall the evidence suggests that the present Southern Ocean shallow water marine fauna largely evolved in situ, having been present since at least the Late Cretaceous, and possibly much longer. Some groups have invaded, for example along the Scotia arc, but the isolation of the Southern Ocean by the present oceanographic regime and the limited dispersal ability of many forms means that exchange with lower latitudes is very slow.

Patrones de diversidad y estructura genética en especies antárticas y subantárticas de Nacella (Nacellidae)

“…La divergencia molecular entre linajes de Antártica y Sudamérica estaría relacionada a cambios importantes ocurridos en el OA asociados a la evolución del Arco de Escocia y a la profundización del Paso de Drake a mediados del Mioceno (Dalziel et al 2013). Junto a todos estos procesos geológicos y oceanográficos, el cambio climático ha tenido un gran rol en el OA desde el Cenozoico modelando la abundancia, estructura y distribución de su biota (Clarke & Crame, 1989Aronson et al 2007). El tercer periodo de marcados cambios en el OA ocurre durante el Cuaternario cuando la alternancia entre periodos glaciales e interglaciales afectaron en gran medida la estacionalidad e intensidad de la formación de hielo marino, así como también la posición de la ACC (Gersonde et al 2005;Kemp et al 2010).…”

The megazoobenthos of the Scotia Arc islands

“…The Scotia Arc, a series of trenches and elevations spreading over more than 1,500 km between the southern tip of South America and the Antarctic Peninsula (Acosta et al, 1989) constitutes a particularly important area for understanding the history of the Southern Ocean marine fauna (Clarke and Crame, 1989).…”

Nuclear and Mitochondrial Gene Data Support Recent Radiation within the Sea Spider Species Complex Pallenopsis patagonica

“…Therefore, paradoxically the Southern Ocean has emerged from being regarded as a biodiversity sink to a center of marine biodiversity in the past two decades. This phenomenon of high in situ species diversity has been termed the Antarctic diversity pump (sensu Clarke and Crame, 1989).…”

“…Several processes have been discussed as drivers fueling this diversity pump (Clarke and Crame, 1989). In this context, molecular data have led to a paradigm shift: Most of the cryptic species have rendered the distribution ranges of formerly described species from broad (i.e., circum-Antarctic) to small and allopatric (Lörz et al, 2009;Held, 2014).…”