Aspects of recent benthic foraminifera from Port Darwin, Northern Territory

Abstract

Eighty-nine species and subspecies of Recent foraminifera from fifty-one stations in Port Darwin are identified and distinguished -as tropical species from the Indo-Pacific region. The Port Darwin environment is basically estuarine, but it is subject to tidal changes of depths of up to 8 m, and this .causes a tidal stream in the main harbour channel with·velocities of up to 3 knots. Consequent reworking and deposition of large volumes of sediment takes place on the banks of the main channel and beyond the harbour mouth. There are wide tidal flats within the harbour where estuarine conditions prevail and as well there are several coral reefs within the precincts of Port Darwin. Discrimination of foraminiferal biotopes shows five major environments: tidal flat biotope, channel floor biotope, coral reef biotope, shallow subtidal biotope and offshore biotope The tidal flat biotope and the coral reef biotope are distinguished by their faunas which are thought to closely represent the living faunas. Analysis of the other biotopes is hampered by the reworking of sediment, and with it the redistribution of some foraminiferal species with rugged tests, particularly Quinqueloculina philippinensis -(Cushman), and the scouring of sediment from the main harbour channel. These biotopes resemble more closely thanatocoeneses, and it is found that mathematical methods are unable to discriminate the biotopes adequately. The foraminifera from Port Darwin show close affinities to the North Queensland and the Western Australian faunas from the same environment. The re-establishment of the fauna since post-glacial times may have been dominated by Western Australian types but subsequent mixing with North Queensland types in the past 8 000 years since the final breaching 9£ Torres Strait barrier has produced a fauna of reasonable continuity from North Queensland to tropical Western Australia. This agrees with current biogeographical thinking which no longer discriminates between the Solanderian and Damperian Provinces. Show more