AN IN-SITU EXPERIMENT ON TEMPERATURE SENSITIVITY OF NEARSHORE TEMPERATE BENTHIC FORAMINIFERA

The Benthic Foraminifera Temperature Experiment (BFTREX) is an in situ experiment that tested the response of nearshore benthic foraminifera l species to a +4 degrees C offset in ambient bottom water temperature , A local Bedford Basin (Halifax Harbour) foraminiferal population col onized eight 56 cm x 56 cm pans that were placed in a water depth of 7 m. Four of the pans were heated by a computer controlled system that maintained the temperature of their contained substrate material (fine sterile sand) at +4 degrees C above natural ambient temperature. The experiment was run from July, 1990 to October, 1991 (462 days). The se quence of colonization by foraminifera appeared to be generally simila r in heated and unheated pans, and for both the 0-1 cm and 1-3 cm sedi ment depth intervals over the 15-month operational period. During the summer of 1991, the population density in the 0-1 cm layer of the heat ed substrate was lower than in the unheated substrate. Statistical ana lysis (ANOVA) of living foraminiferal data at the species level indica ted that: (1) of the six species that showed a difference between heat ed and unheated pans, only one (Textularia gracillima) preferred heate d pans, and the two most abundant species in the natural environment ( Eggerella advena and Lepidodeuterammina ochracea) preferred unheated p ans; and (2) four of the six species that exhibited a difference betwe en heated and unheated pan populations are arenaceous types. Three of these six also showed a significant ''heat x time'' hypothesis, sugges ting a change in temperature preference that appears to be seasonally- dependent (e.g., T. gracillima showed a preference for heated pans dur ing the colder seasons). These observations suggest that some species in the living population may preferentially colonize shallower or deep er water habitats in response to interannual variations of bottom wate r temperature.