Affinity of the benthic foraminifer Cassidulinoides parkeriana (Brady) for whale-falls: evidence from off western Vancouver Island, British Columbia, Canada

Abstract

A partial skeleton of a blue or fin whale, estimated to have been 16.5 m in length and thought to have been lying on the seafloor for less than 10 years, was observed at a depth of 1288 m off western Vancouver Island, British Columbia, Canada (48.68 N, 126.84 W). Four push cores were taken at the site, three (15-26 cm in length) directly under caudal vertebrae and one 18 cm long, considered a reference, 15 m away, in order to characterize changes in the benthic foraminiferal assemblage due to the whale-fall. A Q-mode cluster analysis identified four groupings, separating the surface and deeper samples of both the whale-fall and reference cores. The results of a metric multi-dimensional scaling plot and permutational multivariate analysis of variance test of the surface samples also suggest there was a significant difference between the whale-fall and reference core benthic foraminiferal faunas. No endemic species were recovered. Downcore samples below 6 cm in the whale-fall and reference cores were characterized by common Uvigerina peregrina, Pseudoparrella pacifica, Bolivina spissa, Bulimina striata, and Takayanagia delicata. In contrast, Cassidulinoides parkeriana, which typically is a minor component of benthic foraminiferal assemblages, dominated the upper 6 cm of the whale-fall cores, whereas the low oxygen-tolerant species T. delicata dominated the same interval in the reference core. The dramatic increase in abundance of C. parkeriana in the upper sediments below this whale-fall, as well as at the Torishima Seamount whale-fall site off Japan, indicate that it is an opportunistic species well adapted to taking advantage of unpredictable and highly localized tropic windfalls such as whale-falls. To our knowledge, this is the first benthic foraminiferal species shown to increase dramatically in abundance in the presence of a whale-fall. Additionally, modern fragments of whale bones occurring as deep as 12 to 15 cm downcore at the western Vancouver Island site demonstrate the effect of bioturbation by invertebrate scavengers that consume whale carcasses, indicating that detailed biostratigraphic records below whale-falls should be interpreted with caution.