Temporal and spatial variability in stable isotope ratios of SPM link to local hydrography and longer term SPM averages suggest heavy dependence of mussels on nearshore production

Temporal changes in hydrography affect suspended particulate matter (SPM) composition and distribution in coastal systems, potentially influencing the diets of suspension feeders. Temporal variation in SPM and in the diet of the mussel Perna perna, were investigated using stable isotope analysis. The δ13C and δ15 N ratios of SPM, mussels and macroalgae were determined monthly, with SPM samples collected along a 10 km onshore–offshore transect, over 14 months at Kenton-on-Sea, on the south coast of South Africa. Clear nearshore (0 km) to offshore (10 km) carbon depletion gradients were seen in SPM during all months and extended for 50 km offshore on one occasion. Carbon enrichment of coastal SPM in winter (June–August 2004 and May 2005) indicated temporal changes in the nearshore detrital pool, presumably reflecting changes in macroalgal detritus, linked to local changes in coastal hydrography and algal seasonality. Nitrogen patterns were less clear, with SPM enrichment seen between July and October 2004 from 0 to 10 km. Nearshore SPM demonstrated cyclical patterns in carbon over 24-h periods that correlated closely with tidal cycles and mussel carbon signatures, sampled monthly, demonstrated fluctuations that could not be correlated to seasonal or monthly changes in SPM. Macroalgae showed extreme variability in isotopic signatures, with no discernable patterns. IsoSource mixing models indicated over 50% reliance of mussel tissue on nearshore carbon, highlighting the importance of nearshore SPM in mussel diet. Overall, carbon variation in SPM at both large and small temporal scales can be related to hydrographic processes, but is masked in mussels by long-term isotope integration

Ranging patterns of bottlenose dolphins living in oceanic waters : implications for population structure

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Marine Biology 156 (2008): 179-192, doi: 10.1007/s00227-008-1075-z.Very little is known about the ecology of common bottlenose dolphins (Tursiops truncatus) living in oceanic waters. This study investigated the ranging and residence pattern, of bottlenose dolphins occurring in the Azores (Portugal), the most isolated archipelago in the North Atlantic. Data were collected during standardized boat-based surveys conducted over a 6-year period in an area of approximately 5,400 km2 (main study area). To investigate the extent of movements of individual animals. non-systematic surveys were also conducted outside this area. Only 44 individuals out of 966 identified were frequently sighted within and between years. The remaining individuals were either temporary migrants from within or outside the archipelago, or transients. Resident dolphins showed strong geographic fidelity to the area. Long-distance movements (of almost 300 km), consistent with foraging or exploratory trips. were observed among non-resident dolphins. Home range size was estimated for 31 individuals sighted ≥ 10 times. Range areas of these dolphins varied in size and location, but considerable overlap was observed in the areas used, suggesting the absence of habitat partitioning between resident and non-resident dolphins. Estimates of home range size of bottlenose dolphins in the Azores were found to be considerably larger than those previously reported for this species. It is hypothesized that dolphins living in the Azores carry out extensive movements and have large home ranges in response to the lower density and patchy distribution of prey compared to other areas. The extensive ranging behaviour and the lack of territoriality provide an opportunity for interbreeding between dolphins associated with different islands, thus preventing genetic differentiation within the population of the Azores.This researd was funded by the Portuguese Science and Technology Foundation (FCT). under the CETAMARH project (POCTI/BSF/38991/01 ), by an EU-LlFE program (B4-3200/98/ 509), and by an Interreg program (Interreg IIIBMAC/4.2/A2). We are also grateful to FCT for funding M. A. S. doctoral grant (SFRH/BD/ 8609/2002) and post-doctoral grams (SFRH/BPD/29841/2006), and S. M. M. and M. I. S. research grams through the CETAMARH projec

Sex ratios of loggerhead sea turtles Caretta caretta during the juvenile pelagic stage

Sex ratios are a fundamental trait for species reproduction. In species with temperature-dependent sex determination (TSD), sex ratios are not necessarily even, which has important demographic consequences. We examined the sex ratio of juvenile pelagic stage loggerhead turtles Caretta caretta offshore Madeira Island, North Eastern Atlantic, using laparoscopy and histology. The overall sex ratio was 2:1 (F:M), significantly different from an even sex ratio. Although there was no apparent temporal variation, sex ratios among size classes were significantly different. The sex ratio of juveniles was compared with known sex ratios for the putative source rookery and found to be similar to the subadults’ sex ratio, but significantly less female-biased than the hatchlings sex ratio. This suggests overestimation of hatchlings sex ratios and/or, less likely, differential mortality of females during the first months of life. Alternatively, the Madeira Island aggregation may be recruiting males from other geographical sources such as the Mediterranean and the Cape Verde