Metals in bivalve mollusks from the jaco scar seep, pacific, Costa Rica

Abstract

Deep sea-research has made significant discoveries thanks to the availability of high resolution bathymetric mapping and vehicles able to reach hydrothermal vents and cold seeps. The Pacific continental margin of Costa Rica includes cold seeps that are inhabited by vesicomyid clams, which are expected to accumulate metals. Data on metals from cold seep clams are scarce. Thus, the objective of this study is to present the concentrations of Al, Cd, Cu, Fe, Pb, Mn, Ni, Sb and Zn in samples from seven clams, a mussel, sediment, and a rock, together with clam morphometric data. The bivalves (Archivesica sp.?) were collected in 2005 at a depth of 1 888 m on the Jaco Scar (09o06' N - 84o50' W) during DSRV Alvin dive 4 129. Metals were analyzed by Flame Atomic Absorption Spectrometry (FAAS) and Graphite Furnace (GFAAS). Concentrations are in µg/g dry weight. The order of decreasing maximm concentrations and range in tissues of seven clams, were: Zn (43.4 - 266.3) > Fe (27.2 - 100.0) > Al (5.0 - 69.9) > Cd (0.1 - 12.2) > Sn (2.8 - 9.5) > Cu (4.0 - 7.3) > Mn (1.1 - 2.2) > Pb (0.2 - 0.8) > Ni (0.19 - 0.58). The gills had the maximum concentrations of Fe and Al. Maximum concentrations in the only mussel specimen collected, were: Zn (80.4 - gills), Fe (70.6 - gills), Cu (31.0 - gills), Al (26.6 - gills), Sn (4.8 - mantle), Mn (1.7 - mantle), Ni (0.97 - muscle), Pb (0.7 - muscle), Cd (0.57 - gills). The sediment sample had: Al (40 800), Fe (26 500), Mn (72.0), Zn (64.7), Cu (29.4), Ni (19.3), Sn (15.5), Pb (2.98), Cd (0.16). A rock fragment had: Fe (15 650), Al (9 240), Mn (170), Sn (99.5), Zn (36.5), Ni (20.4), Cu (13.4), Pb (1.6), Cd (traces). Clam gills concentrated metals such as Fe and Al. Fe was below the range reported for hydrothermal vent clams, while concentrations of other metals were near the lower range. Fe, Cd, Mn, and Pb in mussel tissues were lower than those in mussels from hydrothermal vent sites, while Cu and Zn were within the range. Metals in the sediment and rock samples appeared very rich in certain metals like Al and Fe and very poor in others, such as Cd. There is a paucity of information on metals and pollutants in clams and other macrofaunal species from Costa Rican cold seeps. Data presented herein must be complemented with future studies conducted jointly on the geochemistry, biology, and management of these deep-sea systems.