Graduate Thesis Or Dissertation
 

Two zoogeographic studies of deep sea benthic gammarid amphipods

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  • Two separate studies on the distribution of gammarid amphipods in the bathyal and abyssal benthic environments demonstrated that different assemblages could be found at a single depth over distances on the order of 100 kilometers. These studies evaluated changes in the species composition and relative abundance of the amphipod assemblage utilizing samples collected with an epibenthic sled. The amphipod faunas of the San Diego Trough and Tanner Basin were compared utilizing 18 epibenthic sled hauls. These two bathyal basins of the Continental Borderland off Southern California are very similar in their environments and both have a bottom depth close to 1250 meters. The amphipod fauna from each basin was characterized by comparing the percentage each species comprised of the total amphipod fauna, the frequency of occurrence of each species, and the rank order of abundance of species. The large differences observed in the structure of the amphipod assemblage between the two basins can probably be attributed to different sources of food in the two basins. Nineteen sled hauls were collected at two stations on Cascadia Abyssal Plain located off the Oregon coast at 2800 meters depth. The two stations were representative of the near shore and offshore portions of this abyssal plain. The amphipod assemblages were found to be very different at these two stations, despite their similar depths and physical environments. Geological evidence indicated that the sources of food to the sea floor at these two stations were likely to be very different. It was this difference in food input that seemed most likely to be the cause of the faunal difference. These studies of "mesoscale" zoogeography have added a new element of complexity to our understanding of factors controlling animal distributions in the deep sea benthos, because they have demonstrated that different assemblages can be found at the same depth in the same geographic region. The results suggest that the quality and quantity of food supplied to the deep sea floor may play a major role in controlling the composition of the fauna.
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