Distribution of marine cladocerans in the Indian Ocean

Cladocera of the Indian Ocean have been studied, on the basis of samples collected during the International Indian Ocean Expedition (IIOE). Out of a total of 1927 samples, 552 contained Cladocera. Although the distribution of this group is mainly coastal, one species, Evadne tergestina, has been found in oceanic waters also, where it may establish seasonal populations. Evadne spinifera was recorded off the Australian and South African coasts in the southern hemisphere, and in the Northeastern part of the Arabian Sea coastal waters in the northern hemisphere. Podon polyphemoides was reported from a single station in South African waters. Penilia avirostris was found in coastal waters throughout the Indian Ocean. Short-term distribution patterns of E. tergestina and P. avirostris are discussed. The possible value of this group as food for pelagic fishes has been indicated. This work makes clear that adequate sampling in space and time is required along the Continental Shelf of the Indian Ocean in order to obtain more comprehensive information on this group.Visiting Scientist at Indian Ocean Biological Centre, Cochin, India under UNESCO contract SC/2077/70-20579.     

Mitochondrial DNA sequence variation and phylogeography of oceanic insects (Hemiptera: Gerridae: Halobates spp.)

Relatively few insects have invaded the marine environment, and only five species of sea skaters, Halobates Eschscholtz (Hemiptera: Gerridae), have successfully colonized the surface of the open ocean. All five species occur in the Pacific Ocean, H. germanus White also occurs in the Indian Ocean, whereas H. micans Esch- scholtz is the only species found in the Atlantic Ocean. We sequenced a 780 bp long region of the mitochondrial cytochrome oxidase subunit I gene (COI) for a total of 66 specimens of the five oceanic Halobates species. Our purpose was to investigate the genetic variation within species and estimate the amount of gene flow between populations. We defined 27 haplotypes for H. micans and found that haplotype lineages from each of the major oceans occupied by this species are significantly different, having sequences containing five to seven unique base substitutions. We conclude that gene flow between populations of H. micans inhabiting the Atlantic, Pacific, and Indian Ocean is limited and hypothesize that these populations have been separated for 1 to 3 million years. Similarly, there may be limited gene flow between H. germanus populations found in the Pacific and Indian Ocean and between H. sericeus populations inhabiting the northern and southern parts of the Pacific Ocean. Finally, we discuss our findings in relation to recent hypotheses about the influence of oceanic diffusion on the distribution and population structure of oceanic Halobates spp. Received: 29 July 1999 / Accepted: 23 November 1999     

Pelagic biogeography of the South Atlantic Ocean

The biogeography of the South Atlantic was investigated using presence/absence data for euphausiids. Records were taken from recent and historic, as well as published and unpublished data sets. The resulting biogeography is the most complete to date and can be usefully compared with the biogeochemical provinces for the region. A total of six biogeographic provinces were identified from similarity analyses of the 246 five-degree grid squares. These correspond to Antarctic, sub-Antarctic, cold temperate, warm temperate (subtropical) and tropical waters, as well as the Agulhas Current. Congruence with the biogeochemistry of the region is good in the south and emphasises the important determinate role of temperature. However, the biogeography fails to identify coastal and tropical biogeochemical provinces. This can be attributed to the fact that while adjoining areas may share many species in common, their assemblages differ in their quantitative composition. This serves to emphasise differences in provincial functioning. Received: 28 May 1997 / Accepted: 15 July 1997     

Benthic amphipods (Crustacea: Malacostraca) in Icelandic waters: diversity in relation to faunal patterns from shallow to intermediate deep Arctic and North Atlantic Oceans

Patterns in diversity, species replacement and species composition of gammaridean amphipods (Crustacea: Malacostraca) were studied in two areas on different sides of the Greenland–Iceland–Faeroe Ridge. One was sited south of the Ridge in the North Atlantic Ocean off southern Iceland and the other north of the Ridge in the Arctic Ocean (subarctic and arctic waters of the Iceland Sea) off northern Iceland. Samples were taken with a Rothlisberg–Pearcy epibenthic sled within the depth range of about 50 to 1200 m at a total of 28 stations. In all 21 150 individuals were found belonging to 156 species. Of these 102 were found in the northern area with 64 of the species restricted to this area. In all 94 species were found in the southern area with 52 of the species restricted to this area. This suggests a similar regional diversity, but a different faunal composition. The amphipods showed similar species replacement patterns with depth on both sides of the Ridge, while the diversity patterns differed between the areas. In the North Atlantic the number of species increased with depth, while in the Arctic there seemed to be no pattern at all. It is suggested that diversity patterns of amphipods on each side of the Ridge are shaped by different factors, and these may not be the same as those determining diversity patterns of other groups in the area. Salinity (as indicative of water masses) was found to be the most important environmental variable in explaining the species composition when both areas were considered, suggesting a number of contributing factors (adaptation to water masses, dispersal, etc.). Water temperature was the most important variable in explaining the variance in the species composition in the northern area, while depth was the most important variable in explaining the variance in the species composition of the southern area. Received: 9 March 1997 / Accepted: 10 December 1997     

Distribution of coccolithophores in marginal seas along the western Pacific Ocean and in the Red Sea

The distribution of coccolithophores was studied in the neritic environment along the western margin of the Pacific Ocean: the Inland Sea of Seto, Yellow Sea, East China Sea, South China Sea, Java Sea, Timor Sea, Arafura Sea and Gulf of Carpentaria. The coccolithophore community in the Red Sea was also studied for comparison with the Pacific marginal seas. With minor exceptions, the coccolithophore communities were very similar throughout the neritic areas investigated, but differed completely from the pelagic community in three aspects. Firstly, almost all neritic coccolithophores, regardless of species, suffered various degrees and forms of malformation with relation to the morphology of their coccoliths, while such malformation was rare in the pelagic population. Nitrogen deficiency may cause such malformation. Secondly, the diversity of species in these marginal seas was much lower than in the pelagic environment, although no species was found to be exclusively neritic. Emiliania huxleyi, usually ubiquitous in oceanic areas and in various neritic environments of higher latitudes, was scarce, while Gephyrocapsa oceanica dominated the flora throughout the studied areas. Finally, the horizontal and vertical distributions of the neritic populations were sporadic compared to those of the rather uniform pelagic environments.     

Concentrations of V,Cr, Mn,Fe, Ni,Co, Cu,Zn, As and Cd in mesopelagic crustaceans from the North East Atlantic Ocean

Specimens of oceanic decapods, mysids and euphausiids, collected from the North East Atlantic Ocean during July 1985, were analysed for V, Cr, Mn, Fe, Ni, Co, Cu, Zn, As and Cd. Measurement of the metals was carried out using two techniques: inductively-coupled plasma-source mass spectrometry (ICP-MS) and atomic absorption (AAS). With the exception of the iron data, good agreement was observed between the data from the two techniques. Baseline-metal data are presented for the species measured, along with any effects of animal size on metal concentration. The data presented for oceanic animals from different trophic levels are important in studies of metal fluxes and for the assessment of markers within the food web in the oceans.     

Afro-Eurasia and the Americas present barriers to gene flow for the cosmopolitan neustonic nudibranch Glaucus atlanticus

Pelagic species have been traditionally thought to occupy vast, genetically interconnected, geographic ranges in an essentially homogeneous environment. Although this view has been challenged recently for some mesopelagic planktonic taxa, the population structure of hyponeustonic (surface-drifting) species remains unknown. Here, we test the hypothesis of panmixis in Glaucus atlanticus, a cosmopolitan neustonic nudibranch, by assessing the genetic differentiation of multiple representatives from a global neustonic sampling effort. Specimens were collected from all subtropical oceanic gyre systems (North Atlantic, South Atlantic, North Pacific, South Pacific, and Indian Ocean). We sequenced a fragment of the mitochondrial cytochrome oxidase I gene for 98 individuals and performed population structure, differentiation (analysis of molecular variance, spatial analysis of molecular variance, F _ST, Jost’s D), and molecular clock analyses. Our results indicate that G. atlanticus is not globally panmictic, but that populations appear to be panmictic within ocean basins. We detected several topologically ectopic haplotypes in the Atlantic Ocean, but the molecular clock analysis indicates that these have diverged from closely related Indo-Pacific haplotypes over 1.2 MYA, coinciding with cooling in waters around in the southern tip of Africa and resulting oceanographic changes. These data and the fact that G. atlanticus is not known from polar latitudes suggest that gene flow between ocean basins is hindered by physical barriers (supercontinents) and water temperatures in the Arctic and Southern Oceans.     

Coexistence of oceanic predators on wintering areas explained by population-scale foraging segregation in space or time

Ecological niche theory predicts segregation mechanisms that mitigate potential competition between closely related organisms. However, little is known outside the breeding season, when central-place foraging animals may move on larger scales. This study tested for segregation mechanisms within the same 2007 inter-breeding period on three neighboring populations of avian predators from the southern Indian Ocean: Eastern Rockhopper Penguins Eudyptes filholi from Crozet and Kerguelen and Northern Rockhopper Penguins E. moseleyi from Amsterdam. Using state-of-the-art geolocation tracking and stable isotope analysis techniques, we quantified and compared the ecological niches in time, space, and diet. The three populations showed large-scale movements over deep oceanic waters near the Subantarctic Front, with generally little individual variation. The two neighboring populations of Eastern Rockhopper Penguins showed strikingly distinct distribution in space, while foraging in similar habitats and at the same trophic level (crustacean-eaters). In contrast, Northern Rockhoppers showed marked spatial overlap with birds of the sibling Eastern species, but their temporal delay of two months enabled them to effectively avoid significant overlap. Our results highlight parsimonious mechanisms of resource partitioning operating at the population level that may explain how animals from neighboring localities can coexist during the nonbreeding period.     

Oceanographic characteristics of areas used by Cory’s shearwaters during short and long foraging trips in the North Atlantic

Many breeding seabird species are central-place foragers and constrained to find productive prey patches within their foraging ranges. We assessed how different populations of a pelagic seabird species, the Cory’s shearwater Calonectris diomedea, breeding in oceanic and neritic conditions, cope with these constraints in the North Atlantic, during both incubation and chick-rearing periods. We analysed 237 foraging trips to study the movements and oceanographic characteristics of foraging habitats of seven different populations of Cory’s shearwaters. Generally, oceanic populations exhibited higher foraging effort, by travelling more time and to more distant areas, and larger home ranges and feeding areas, than the neritic population (i.e. breeding on an island within the Portuguese continental platform). On their short trips (i.e. ≤4 days), birds from the different populations fed mostly in shallower waters around the colony. During long trips (i.e. ≥5 days), feeding areas of both oceanic and neritic populations were characterized by high concentration values of chlorophyll-a, low sea-surface temperature and shallower habitats, with oceanic populations of the Azores exploiting areas north of the islands over known seamounts and frontal regions. Birds from other oceanic population (Selvagens) also exploited the African continental shelf system on their long trips. The home ranges of the different populations overlapped widely, but there was a general spatial segregation in terms of the core feeding areas at the population level. Core feeding areas and areas of foraging overlap between different populations should be important to inform conservation management measures, such as the definition of Marine Important Bird Areas for seabirds over the North Atlantic.     

Latitudinal variation in local interactions and regional enrichment shape patterns of marine community diversity

While communities are shaped by both local interactions and enrichment from the regional species pool, we propose a hypothesis that the balance of these forces shifts with latitude, with regional enrichment dominating at high latitudes and local interactions dominating at low latitudes. To test this hypothesis, we conducted a latitudinal-scale experiment with marine epifaunal communities. In four regions of the North Atlantic Ocean and Caribbean Sea, we used mimics of ecosystem engineers to manipulate biogenic structural complexity. We iteratively evaluated diversity patterns of experimental communities up to one year after deployment. Additional data were also collected from one of our tropical sites 2.5 years after initial deployment. As hypothesized, we found a reciprocal latitudinal gradient in the effects of the structurally complex mimics and regional enrichment. In the tropics, local diversity was always higher in association with the mimics than in exposed areas that were more open to predation. This effect was consistent across two spatial scales and beyond the one-year timescale of the experiment. In temperate communities, no consistent effects of the mimics on diversity were observed. However, the proportion of species from the regional species pool that were present at the local scale increased from the tropics to the temperate zone, consistent with the hypothesis that higher-latitude communities may experience greater influence from the regional species pool than communities at low latitudes. This study represents the first large-scale experimental demonstration that suggests that the relative impact of local interactions and regional enrichment on community diversity may depend on latitude.     

A comparative survey of neuston: geographical and temporal distribution patterns

Neuston samples were collected from 149 stations during a voyage west from Fiji to the Bay of Biscay from August 1979 through November 1980. The neustonic fauna was counted and assigned to 50 species groups, chosen to represent the most numerous animals in the hauls. Analyses of neustonic concentration and population structure showed regional and temporal differences in the fauna. Permanent inhabitants of the surface waters, the euneuston, were most numerous in the open tropical waters of the Central Indian Ocean. In contrast, the temporary neuston, which was composed of juveniles, vertical migrants and the uppermost individuals from deeper populations, attained its greatest concentration in the upwelling region of the Somali Current and at inshore stations around the Indonesian archipelago and in the Gulf of Aden and Red Sea. Heavy rains adversely affected the neuston, possibly by diluting the surface waters. Both neustonic groups were sparsely represented in the cooler waters of the Mediterranean Sea and the eastern Atlantic Ocean. At night considerable immigration occurred into the neustonic zone, and the mean faunal density at dusk was 21 times greater than was found at mid-day. Surface waters were inhabited by the developmental stages of many species, and eggs and juveniles of both vertebrates and invertebrates were consistently present in the hauls.     

Isotopic niches of emperor and Adélie penguins in Adélie Land,Antarctica

The emperor and Adélie penguins are the only two species of penguins that co-occur at high-Antarctic latitudes. We first measured and compared their isotopic niches on the same year in Adélie Land in spring, when the two species co-exist. Emperor and Adélie penguins segregated by their blood isotopic signatures, with adult δ¹³C values (−24.5 ± 0.2 and −25.4 ± 0.2‰, respectively) suggesting that emperor penguins foraged in more neritic waters than Adélie penguins in spring. At that time, difference in their δ¹⁵N values (4.1‰, 12.0 ± 0.4 vs. 7.9 ± 0.1‰) encompassed more than one trophic level, indicating that emperor penguins preyed mainly upon fish (and squids), while Adélie penguins fed exclusively on euphausiids. Second, we compared the food of breeding adults and chicks. The isotopic signatures of adults and chicks of emperor penguins were not statistically different, but δ¹⁵N value of Adélie penguin chicks was higher than that of adults (10.2 ± 0.8 vs. 9.0 ± 0.2‰). The difference showed that adult Adélie penguins captured higher trophic level prey, i.e. higher-quality food, for their chicks. Third, the isotopic signatures of Adélie penguins breeding in Adélie Land showed that adults fed on Antarctic krill in oceanic waters in spring and shifted to neritic waters in summer where they preyed upon ice krill for themselves and upon fish and euphausiids for their chicks. A comparison of isotopic niches revealed large overlaps in both blood δ¹³C and δ¹⁵N values within the community of Antarctic seabirds and pinnipeds. The continuum in δ¹⁵N values nevertheless encompassed more than one trophic level (5.2‰) from Adélie penguin and crabeater seal to the Weddell seal. Such a broad continuum emphasizes the fact that all Antarctic seabirds and marine mammals feed on varying proportions of a few crustacean (euphausiids) and fish (Antarctic silverfish) species that dominate the intermediate trophic levels of the pelagic neritic and oceanic ecosystems.     

Continuous plankton records: Geographical variations in numerical abundance,biomass and production of euphausiids in the North Atlantic Ocean and the North Sea

Geographical variations in the numbers, biomass and production of euphausiids and the contribution of common species to the total are described from samples taken during 1966 and 1967 in the North Atlantic Ocean and the North Sea by the Continuous Plankton Recorder at 10 m depth. Euphausiids were most abundant in the central and western North Atlantic Ocean and the Norwegian Sea. Thysanoessa longicaudata (Krøyer) was numerically dominant. Biomass was greatest in the Norwegian Sea and the north-eastern North Sea where Meganyctiphanes norvegica (M. Sars) accounted for 81 and 59%, respectively, of the total biomass. Production was highest off Nova Scotia and in Iberian coastal waters; the dominant species were T. raschi (M. Sars) in the former area and Nyctiphanes couchi (Bell) in the latter. The mean P:B ratios were correlated with temperature.     

A model of area fidelity,nomadism, and distribution patterns of loggerhead sea turtles (<Emphasis Type="Italic">Caretta caretta</Emphasis>) in the Mediterranean Sea

Sea turtle tagging carried out in Italy in the period 1981–2006 resulted in 125 re-encounters of loggerhead turtles (Caretta caretta) after a mean of 2.5 years, from different marine areas in the Mediterranean. At first finding, turtles ranged 25–83 cm of curved carapace length. Data were analyzed according to size, area, habitat type, season, in order to provide indication of movement patterns. When integrated with other information, results indicate that: (1) a part of turtles in the oceanic stage show a nomad behavior with movements among different oceanic areas; (2) another part show fidelity to an oceanic area; (3) turtles in the neritic stage show fidelity to neritic areas, and once settled to one area, change to other neritic areas is unlikely; (4) nomad oceanic turtles are significantly larger than sedentary ones, and also larger than turtles found in neritic areas; it is hypothesized that these could be Atlantic turtles that eventually leave the Mediterranean; (5) ecological transition from oceanic to neritic habitats occurs at a wide range of sizes, and some turtles may have a very brief oceanic stage; (6) turtles in the oceanic stage are more likely to recruit to neritic areas close to their oceanic areas than to distant ones; (7) part of turtles from some Mediterranean nesting beaches might frequent a relatively limited area range, including both oceanic and neritic areas; (8) in most of the Mediterranean, latitudinal seasonal migrations are unlikely. A general model of movement patterns of loggerhead turtles in the Mediterranean is proposed.     

Trophic strategies of euphausiids in a low-latitude ecosystem

Vertical distribution, diet, and morphology of adults were examined in 27 species of euphausiids occurring in the upper 1000 m in the eastern Gulf of Mexico. Vertical distribution patterns were similar to those found in the central ocean gyres and oceanic equatorial waters of the Atlantic, Indian and Pacific Oceans. Most species migrated vertically from their daytime depths of 300 to 600 m to the upper 300 m at night. Exceptions were the non-migrating species of Stylocheiron, which remained in the epipelagic zone day and night, and Nematobrachion boopis, which remained in the mesopelagic zone. Based on gut-contents analysis, the Gulf euphausiids were largely zooplanktivorous, with cyclopoid and calanoid copepods being the most common items in stomachs. ostracods were especially common in the stomachs of Thysanopoda spp. and phytoplankton in the guts of Euphausia spp. Nearly every species' diet contained a considerable amount of olive-colored debris, which may have been marine snow generated in the epipelagic zone. Cluster analysis grouped the euphausiids into nine diet guilds. Euphausiids with a generalized morphology (i.e., spherical eyes, uniform thoracic appendages) tended to group together and demonstrated little variety in stomach contents among species. Euphausiids with a specialized morphology (i.e., bilobed eyes, elongate thoracic appendages) showed considerable variety in stomach contents among species, and several species had diets that were highly specific. Many of the species that had similar gut contents fed on prey of different sizes, as indicated by the width of the calanoid copepod mandibles found in stomachs. Principal-components analysis of seven morphological characters yielded species groups that were similar, but not identical, to those generated by cluster analysis of stomach contents data. We inferred from this that morphological characters partly determine diet, but that behavior is also important. Using the 20 most abundant species and 3 niche parameters, we attempted to identify the degree of separation among euphausiids based on the level of overlap in vertical distribution and diet composition, and on differences in mean prey size. Overlap of <60% in vertical distribution or diet composition was considered to indicate distinction of that parameter. Of 190 total species pairs, only 4 pairs did not demonstrate niche separation in at least one of these categories. We found that differences in these niche parameters were greatest among species with a specialized morphology and least among species that were morphologically generalized.     

Satellite tracking reveals a dichotomy in migration strategies among juvenile loggerhead turtles in the Northwest Atlantic

Few data are available on the movements and behavior of immature Atlantic loggerhead sea turtles (Caretta caretta) from their seasonal neritic foraging grounds within the western north Atlantic. These waters provide developmental habitat for loggerheads originating from several western Atlantic nesting stocks. We examined the long-term movements of 23 immature loggerheads (16 wild-caught and seven headstart turtles) characterizing their seasonal distribution, habitat use, site fidelity, and the oceanographic conditions encountered during their migrations. We identified two movement strategies: (1) a seasonal shelf-constrained north–south migratory pattern; and (2) a year-round oceanic dispersal strategy where turtles travel in the Gulf Stream to the North Atlantic and their northern dispersal is limited by the 10–15°C isotherm. When sea surface temperatures dropped below 20°C, neritic turtles began a migration south of Cape Hatteras, North Carolina (USA) where they established fidelity to the waters between North Carolina’s Outer Banks and the western edge of the Gulf Stream along outer continental shelf. Two turtles traveled as far south as Florida. Several turtles returned to their seasonal foraging grounds during subsequent summers. Northern movements were associated with both increased sea surface temperature (>21°C) and increased primary productivity. Our results indicate strong seasonal and interannual philopatry to the waters of Virginia (summer foraging habitat) and North Carolina (winter habitat). We suggest that the waters of Virginia and North Carolina provide important seasonal habitat and serve as a seasonal migratory pathway for immature loggerhead sea turtles. North Carolina’s Cape Hatteras acts as a seasonal “migratory bottleneck” for this species; special management consideration should be given to this region. Six turtles spent time farther from the continental shelf. Three entered the Gulf Stream near Cape Hatteras, traveling in the current to the northwest Atlantic. Two of these turtles remained within an oceanic habitat from 1 to 3 years and were associated with mesoscale features and frontal systems. The ability of large benthic subadults to resume an oceanic lifestyle for extended periods indicates plasticity in habitat use and migratory strategies. Therefore, traditional life history models for loggerhead sea turtles should be reevaluated.     

Global population divergence of the sea star Hippasteria phrygiana corresponds to the onset of the last glacial period of the Pleistocene

Genetic structure and connectivity of populations of the globally distributed and eurybathic sea star Hippasteria phrygiana (Parelius 1768) were studied in 165 individuals sampled from three oceanic regions: the North Pacific Ocean, the South Pacific Ocean (considered to include the adjacent regions of the Southern Ocean and the southern Indian Ocean) and the North Atlantic Ocean. A nuclear gene region (ATP synthase subunit α intron #5, ATPSα) and a mitochondrial gene region (cytochrome oxidase subunit I, COI) were amplified and sequenced. Significant heterogeneity was detected in an AMOVA analysis among the three sampled oceanic regions for COI, but not for ATPSα. Neither gene showed significant genetic heterogeneity within the North Atlantic, as assessed by ΦST values. Significant heterogeneity was detected for COI (but not ATPSα) in the North Pacific, but the converse was true in the South Pacific. Coalescent simulations suggested that the three regions have been diverging with little or no gene flow for the past 50–75,000 years, a time frame that corresponds to the onset of the last glacial period of the Pleistocene. A possible genetic signature of recent population expansion (or non-neutrality) was detected for each gene in the North Pacific, but not in the other two oceanic regions.     

Present-day genetic composition suggests contrasting demographic histories of two dominant chaetognaths of the North-East Atlantic, <Emphasis Type="Italic">Sagitta elegans</Emphasis> and <Emphasis Type="Italic">S. setosa</Emphasis>

Sagitta elegans and S. setosa are the two dominant chaetognaths in the North-East (NE) Atlantic. They are closely related and have a similar ecology and life history, but differ in distributional ranges. Sagitta setosa is a typical neritic species occurring exclusively above shelf regions, whereas S. elegans is a more oceanic species with a widespread distribution. We hypothesised that neritic species, because of smaller and more fragmented populations, would have been more vulnerable to population bottlenecks resulting from range contractions during Pleistocene glaciations than oceanic species. To test this hypothesis we compared mitochondrial Cytochrome Oxidase II DNA sequences of S. elegans and S. setosa from sampling locations across the NE Atlantic. Both species displayed very high levels of genetic diversity with unique haplotypes for every sequenced individual and an approximately three times higher level of nucleotide diversity in S. elegans (0.061) compared to S. setosa (0.021). Sagitta setosa mitochondrial DNA (mtDNA) haplotypes produced a star-like phylogeny and a uni-modal mismatch distribution indicative of a bottleneck followed by population expansion. In contrast, S. elegans had a deeper mtDNA phylogeny and a multi-modal mismatch distribution as would be expected from a more stable population. Neutrality tests indicated that assumptions of the standard neutral model were violated for both species and results from the McDonald-Kreitman test suggested that selection played a role in the evolution of their mitochondrial DNA. Congruent with these results, both species had much smaller effective population sizes estimated from genetic data when compared to census population sizes estimated from abundance data, with a factor of ~10⁸–10⁹ difference. Assuming that selective effects are comparable for the two species, we conclude that the difference in genetic signature can only be explained by contrasting demographic histories. Our data are consistent with the hypothesis that in the NE Atlantic, the neritic S. setosa has been more severely affected by population bottlenecks resulting from Pleistocene range shifts than the more oceanic S. elegans.     

The spatial ecology of juvenile loggerhead turtles (Caretta caretta) in the Indian Ocean sheds light on the “lost years” mystery

While our understanding of the early oceanic developmental stage of sea turtles has improved markedly over recent decades, the spatial context for this life history stage remains unknown for Indian Ocean loggerhead turtle populations. To address this gap in our knowledge, 18 juvenile loggerheads were satellite tracked from Reunion Island (21.2°S, 55.3°E) between 2007 and 2011. Nine turtles swam north toward Oman (20.5°N, 58.8°E), where one of the world’s largest rookeries of loggerheads is located. Three individuals traveled south toward South Africa and Madagascar, countries that also host loggerhead nesting grounds. Fourteen of the transmitters relayed diving profiles. A dichotomy between diurnal and nocturnal diving behavior was observed with a larger number of shorter dives occurring during the day. Diving behavior also differed according to movement behavior as individuals spent more time in subsurface waters (between 10 and 20 m) during transit phases. The study provides an understanding of the oceanic movement behavior of juvenile loggerheads in the Indian Ocean that suggests the existence of an atypical trans-equatorial developmental cycle for the species at the ocean basin scale in the Indian Ocean. These results address a significant gap in the understanding of loggerhead oceanic movements and may help with the conservation of the species.