Journal of the Marine Biological Association of the United Kingdom

Research Article

Effects of oil drilling activity on the deep water megabenthos of the Orinoco Fan, Venezuela

Daniel O.B. Jonesa1 c1, Juan J. Cruz-Mottaa2, David Bonea3 and Janne I. Kaariainena1

a1 National Oceanography Centre, European Way, Southampton, SO14 3ZH, UK

a2 Departamento Estudios Ambientales, Universidad Simón Bolívar, Caracas, Venezuela

a3 Departamento Biología de Organismos, Universidad Simón Bolívar, Caracas, Venezuela

Abstract

The response of a deep-water megafaunal assemblage to sedimentation disturbance from hydrocarbon drilling was investigated using remotely operated vehicle video off the Atlantic coast of Venezuela. This was the first assessment of megafauna in bathyal waters in this region. A two-way analysis of variance (ANOVA) design was used to assess patterns in density and assemblage structure both temporally, before and after the drilling event, and spatially, at different distances from the disturbance. High levels of sedimentation occurred within a radius of 20 to 50 m from the drilling site. Megafaunal densities were reduced with high levels of disturbance (from 0.60 m−2 to 0.17 m−2 <20 m from the drilling site). The responses of motile and sessile fauna were different. Sessile fauna were most common (77% total) and reflected trends for total density. Motile megafaunal density was generally higher after drilling (up to double the pre-drill density). Species richness was reduced by disturbance and proximity to the disturbance. Multivariate ANOVA revealed significant differences in assemblage composition with distance and before and after drilling but no interaction. This was most likely a result of variable species-specific responses to disturbance. Megafaunal densities were generally much higher than reported densities from comparable depths in the Gulf of Mexico or from deeper locations in the Caribbean Sea. The responses to sedimentation disturbance were generally less obvious than observed elsewhere and may result from the fauna being adapted to the naturally high levels of sedimentation deriving from the Orinoco River.

(Received November 03 2010)

(Accepted June 15 2011)

(Online publication August 19 2011)

Correspondence:

c1 Correspondence should be addressed to: D.O.B. Jones, National Oceanography Centre, European Way, Southampton, SO14 3ZH, UK email: dj1@noc.soton.ac.uk