Stable isotope composition of particulate organic matter and zooplankton in North-East Brazilian shelf waters

Particulate organic matter (POM) and zooplankton (> 300 mu m) were sampled at 15 stations along five transects off north-Eastern Brazil during the dry season. Additionally, samples were taken from the Itamaraca Estuarine Syst em (IES), near Recife, for comparison. The data on naturally occurring stab le isotopes suggest that export of POM from the IES was restricted to the r eef line. This was evident by a maximum of delta(13)C on the inshore shelf (app. 6 to 15 km offshore). There was no measurable estuarine influence on delta(13)C of POM and zooplankton on the shelf. No significant differences were observed in delta(13)C and delta(15)N between the samples taken at she lf stations off Pernambuco and Ceara states, although mangrove cover in Per nambuco is more than 10 times higher than in Ceara. delta(13)C values of sh elf zooplankton varied between -19.8 and -16.3 parts per thousand PDB. The difference in delta(13)C between zooplankton and POM was 4.2 +/- 1.8 parts per thousand. Decapod crustacean larvae showed delta(13)C values between -1 9.8 and -17.2 parts per thousand PDB. Copepods had delta(13)C values betwee n -19.5 and -18.7 parts per thousand PDB. The differences in delta(13)C bet ween copepods and chaetognaths found inshore and offshore were 1.1 and 1.0 parts per thousand PDB, respectively. After "C/N-correcting" delta(13)C val ues, zooplankton still had significantly higher values than POM. POM delta( 15)N varied between 1.6 and 5.6 parts per thousand. Zooplankton was signifi cantly higher in N-15 compared with POM at estuarine and shelf stations. Th e difference in delta(15)N was 3.2 parts per thousand. Decapod larvae showe d relatively low delta(15)N values (similar to or even lower than zooplankt on subsamples), indicating a relatively low trophic position. delta(13)C va lues of decapod larvae were generally close to the values measured for the oceanic copepod community indicating a similarity in the utilization of pel agic primary carbon sources.