ENVIRONMENTAL-CONTROL OF LIVING SYMBIOTIC AND ASYMBIOTIC FORAMINIFERA OF THE CALIFORNIA CURRENT

Plankton tows from the northern California Current constrain biological and physical influences on living planktonic foraminifera. In this region, the dominant factors controlling the size and distribution of symbiotic and asymbiotic species are light and food. Food decreases offshore. Light, needed for symbiont photosynthesis, increases offshore as water turbidity lessens. Asymbiotic foraminifera (e.g., right-coiling Neogloboquadrina pachyderma, Globigerina quinqueloba, and Globigerina bulloides), which survive by grazing, dominate the coastal fauna. The most abundant of these species, right-coiling Neogloboquadrina pachzyderma, did not change in size in response to increasing food. Species that benefit from symbiont photosynthesis (Orbulina universa, Neogloboquadrina dutertrei, Globigerinoides ruber, and Globigerinita glutinata) dominate the offshore fauna. Individuals of these species are rare and have smaller shells in turbid waters where light is limited. G. ruber, which is near its thermal tolerance limit of approximate to 14 degrees C, is the only species to demonstrate a clear temperature response. Although temperature may control a foraminiferal species' distribution near the limits of its thermal tolerance, food and light appear to provide the primary control under more favorable thermal conditions. We infer that gradients in food and light can result in quantifiable sedimentary patterns related to oceanic productivity through changes in plankton biomass and turbidity.