MÁRCIA V. REYNIER,*y FREDERICO T. S. TÂMEGA,zx SARAH D. A. DAFLON,y MAURI´CIO A. B. SANTOS,xk RICARDO COUTINHO,x and MARCIA A. O. FIGUEIREDOzxk
yLABTOX–Environmental Analysis Laboratory, University City, Rio de Janeiro, Brazil
zMarine Biodiversity Institute, Rio de Janeiro, Brazil
xDepartment of Oceanography, Almirante Paulo Moreira Marine Research Institute, Arraial do Cabo, Rio de Janeiro, Brazil
kBotanical Garden of Rio de Janeiro Research Institute of Rio de Janeiro, Rio de Janeiro, Brazil
(Submitted 27 May 2014; Returned for Revision 11 July 2014; Accepted 11 February 2015)
Abstract: Discharge of drill cuttings into the ocean during drilling of offshore oil wells can impact benthic communities through an increase in the concentrations of suspended particles in the water column and sedimentation of particles on the seafloor around the drilling installation. The present study assessed effects of water-based drill cuttings, barite, bentonite, and natural sediments on shallow- and deep-water calcareous algae in short-term (30 d) and long-term (90 d) experiments, using 2 species from Peregrino’s oil field at Campos Basin, Brazil: Mesophyllum engelhartii and Lithothamnion sp. The results were compared with the shallow-water species Lithothamnion crispatum. Smothering and burial exposures were simulated. Oxygen production and fluorescence readings were recorded. Although less productive, M. engelhartii was as sensitive to stress as Lithothamnion sp. Mesophyllum engelhartii was sensitive to smothering by drill cuttings, barite, and bentonite after 60 d of exposure and was similarly affected by natural sediments after 90 d. These results indicate that smothering by sediments caused physical effects that might be attributable to partial light attenuation and partial restriction on gas exchange but did not kill the calcareous algae in the long term. However, 1-mo burial by either natural sediments or drill cuttings was sufficient after 60 d for both species to reduce oxygen production, and the algae were completely dead under both sources of sediments. Environ Toxicol Chem 2015;34:1572–1577. # 2015 SETAC
Keywords: Calcareous algae, Sedimentation, Drill cuttings
INTRODUCTION
Rhodolith beds are marine communities dominated by freeliving red calcareous algae [1]. These beds are distributed in tropical and cold temperate oceans, from shallow waters to deep waters exceeding 200 m in depth [2]. In Brazil, rhodolith beds are distributed from the northeast to the south and are the largest extension of calcareous algae carbonate deposits in the world [1,3]. Live rhodolith beds are ecologically important because they support a richer associated community than surrounding gravel and sand bottoms, and some species restricted to this critical habitat are very fragile because of the slow growth rate of the rhodolith-forming calcareous algae species [4]. When living in nearshore, shallow, soft bottoms, rhodoliths are sensitive to sediment disturbance, and decreases in both net and gross production rates have demonstrated that burial by a thin sediment layer has a negative impact on the tested calcareous algae species [5].
Rhodolith beds, therefore, are considered to be good biomonitors because any effects on this biogenic habitat that may pose potential threats to its associated fauna and flora also may alter the surrounding marginal communities [6]. Several areas of the Brazilian coast that contain rhodoliths are exposed to oil and gas extraction activities.
The Peregrino oil field (23º18’0″S, 41º14’0″W and 23º21’0″S, 041º17’0″W) is located in the Campos Basin (Rio de Janeiro, Brazil), a major oil production area approximately 85 km southwest of the Cabo Frio region, at a water depth of 94 m to 106 m [7]. The deep-water rhodolith beds in the Peregrino field are formed by calcareous red algae, the dominant species being Mesophyllum engelhartii and Lithothamnion sp. [7,8]. Rhodoliths are sparsely to densely distributed within a total sampling area of 15 km2 and are associated with limestone gravel [7]. The sparse area is associated with a fine-grain, mobile bottom, and the dense area is associated with a coarse, gravelly bottom [7]. The Peregrino reservoir is located approximately 2300 m below the seabed in relatively heterogeneous, high-permeability, unconsolidated sands that are interbedded with shales and mudstones [9].
The extraction operation involved 2 fixed drilling platforms and a floating production, storage, and offloading vessel [10]. Discharge of drill cuttings into the ocean during drilling of offshore oil wells can affect benthic communities through an increase in the concentrations of suspended particles in the water column and sedimentation of particles on the seafloor around the drilling installation [11]. Drill cuttings are crushed rocks that are brought up to the surface during drilling and are considered inert to the organisms [11]. In Peregrino, the drill cuttings originating from a reservoir section containing hydrocarbon were disposed onshore, whereas the cuttings from the section used with water-based fluids were discharged in the sea [10]. Before disposal, the cuttings are separated from the fluid through sieves of different sizes by gravity [12]. The fluids used in Peregrino were a NaCl/KCl brine-weighted waterbased mud with glycol [9].
Some products used in the drilling activity may adhere to these cuttings, and these products may be toxic to organisms [13]. Barite is a weighting agent, and bentonite is a viscosifier that can form up to 50% of drilling muds. Although they are considered nontoxic to organisms [11,14], these solid […]