Thermal stress assessment using carbon and oxygen isotopes from Scleractinia,Rocas Atoll,northeastern Brazil

More than 430 C and O isotope analyses were carried out on carbonates from six coral species collected during June 1995, July 1998 and February 1999 at Rocas atoll, offshore northeastern Brazil: Siderastrea stellata Verrill 1868, Porites branneri Rathbum 1887, Porites astreoides Lamarck 1816, Mussismilia hispida Verrill 1902, Madracis decactis Lyman 1859 and Montastrea cavernosa Linnaeus 1886. Samples were collected in pools within the ring of the atoll, at water depths from 1.0 to 7.0 m. Oxygen isotope chemistry demonstrated that the studied species experienced several periods of bleaching; calculated temperature for one species vary, suggesting important changes within the time scale of coral growth. The species P. branneri, P. astreoides, M. cavernosa and the Brazilian endemic species M. hispida registered temperature variations during coral growth more accurately than did S. stellata and M. decactis. Carbon isotope behaviour in coral skeletons of the species examined at this atoll seems to have maintained a close relationship between density and/or zooxanthelar productivity: the greater the algal density, the heavier the δ¹³C values in skeletons.