Guadalupe Island Research Articles

Mitochondrial Genetic Structure and Matrilineal Origin of White Sharks, Carcharodon carcharias, in the Northeastern Pacific: Implications for Their Conservation.

White sharks (Carcharodon carcharias, WS henceforth) are globally and regionally threatened. Understanding their patterns of abundance and connectivity, as they relate to habitat use, is central for delineating conservation units and identifying priority areas for conservation. We analyzed mitochondrial data to test the congruence between patterns of genetic connectivity and of individual movements in the Northeastern Pacific (NEP) and to trace the matrilineal origin of immature WS from coastal California and Baja California to adult aggregation areas. We analyzed 186 mitochondrial control region sequences from sharks sampled in Central California (CC; n = 61), Southern California Bight (SCB; n = 25), Baja California Pacific coast (BCPC; n = 9), Bahía Vizcaíno (BV; n = 39), Guadalupe Island (GI; n = 45), and the Gulf of California (GC; n = 7). Significant mitochondrial differentiation between adult aggregation areas (CC, GI) revealed two reproductive populations in the NEP. We found general concordance between movement patterns of young and adult WS with genetic results. Young sharks from coastal California and Baja California were more likely born from females from GI. Mitochondrial differentiation of young-of-the-year from SCB and BV suggests philopatry to nursery areas in females from GI. These results provide a genetic basis of female reproductive behavior at a regional scale and point to a preponderance of sharks from GI in the use of the sampled coastal region as pupping habitat. These findings should be considered in Mexican and US management and conservation strategies of the WS NEP population.

Laysan Albatross on Guadalupe Island, México: Current Status and Conservation Actions

Guadalupe Island, off the Baja California peninsula, México, hosts the most important growing Laysan Albatross (Phoebastria immutabilis) breeding colony in the eastern Pacific. Since this seabird's first arrival in 1983, it has been affected by predation from feral cats (Felis catus), present on Guadalupe since the late 19th century. Heavy predation events have been recorded on the island, so we initiated a feral cat control campaign in 2003 and began collecting baseline information for developing an eradication plan. At the same time, we conducted seasonal monitoring of Laysan Albatross reproductive success in order to assess the benefits from control activities. Cat relative abundance on Guadalupe was estimated through spotlight surveys, and control was done at the southernmost end of the island around the 2 locations where Laysan Albatross nest: Colinas Negras and Punta Sur. Laysan Albatross population growth rate was calculated based on the number of reproductive individuals, while breeding success was estimated as the proportion of laid eggs that resulted in fledged chicks. A total of 203 cats were removed from the south end of Guadalupe between 2003 and 2013. During this same period, high reproductive success (0.8) was recorded for Laysan Albatross, suggesting a positive effect of cat control activities. We found significant differences in reproductive success between years with predation and no predation by feral cats. The Laysan Albatross colony on Guadalupe has grown steadily during the past 30 years, increasing from 4 to 143 breeding pairs between 1984 and 2013, respectively, and with a population growth rate of 1.10 between 2004 and 2013.

New record of the basket star Gorgonocephalus eucnemis (Ophiuroidea: Gorgonocephalidae) at the Pacific coast of Mexico

The basket star Gorgonocephalus eucnemis is a common ophiuroid resident of rocky bottoms and artificial substrata at depths of 8 to 1,850 m, and in the eastern Pacific is distributed from the Bering Sea to San Diego, USA. This paper presents a new record of this species obtained with a submersible at Guadalupe Island, Mexico (29.10976°N, −118.25417°W), which extends its distribution range over 400 km, and corresponds to the southernmost site of occurrence of this ophiuroid in the eastern Pacific.

Speciation on oceanic islands: rapid adaptive divergence vs. cryptic speciation in a Guadalupe Island songbird (Aves: Junco).

The evolutionary divergence of island populations, and in particular the tempo and relative importance of neutral and selective factors, is of central interest to the study of speciation. The rate of phenotypic evolution upon island colonization can vary greatly among taxa, and cases of convergent evolution can further confound the inference of correct evolutionary histories. Given the potential lability of phenotypic characters, molecular dating of insular lineages analyzed in a phylogenetic framework provides a critical tool to test hypotheses of phenotypic divergence since colonization. The Guadalupe junco is the only insular form of the polymorphic dark-eyed junco (Junco hyemalis), and shares eye and plumage color with continental morphs, yet presents an enlarged bill and reduced body size. Here we use variation in mtDNA sequence, morphological traits and song variables to test whether the Guadalupe junco evolved rapidly following a recent colonization by a mainland form of the dark-eyed junco, or instead represents a well-differentiated “cryptic” lineage adapted to the insular environment through long-term isolation, with plumage coloration a result of evolutionary convergence. We found high mtDNA divergence of the island lineage with respect to both continental J. hyemalis and J. phaeonotus, representing a history of isolation of about 600,000 years. The island lineage was also significantly differentiated in morphological and male song variables. Moreover, and contrary to predictions regarding diversity loss on small oceanic islands, we document relatively high levels of both haplotypic and song-unit diversity on Guadalupe Island despite long-term isolation in a very small geographic area. In contrast to prevailing taxonomy, the Guadalupe junco is an old, well-differentiated evolutionary lineage, whose similarity to mainland juncos in plumage and eye color is due to evolutionary convergence. Our findings confirm the role of remote islands in driving divergence and speciation, but also their potential role as repositories of ancestral diversity.

Two-year migration of adult female white sharks (Carcharodon carcharias) reveals widely separated nursery areas and conservation concerns

Satellite tagging programs have provided detailed information about the migratory patterns of northeastern Pacific white sharks, revealing a seasonal migration between a vast offshore region and coastal aggregation sites. Although adult males undergo annual round-trip migrations, photo-identification programs have noted that sexually mature females may only visit coastal aggregation sites once every 2 years, a behavior that is presumably linked to an estimated 18-month gestation period. The whereabouts of females during their full 2-year migration were previously unknown, because of the limited battery capacity of satellite pop-up tags. Through the use of satellite-linked radio-telemetry tags with multi-year tracking capability, we describe the 2-year migratory pattern for four mature female white sharks tagged at Guadalupe Island, Mexico. The 2-year migration comprised four phases: 1) an Offshore Gestation Phase (which had an average duration of 15.5 months; 2) a Pupping Phase, which occurred along the Mexican coast between the months of April and August; 3) a Pre-Aggregation Phase (when the females were in transition between the Pupping Phase and Guadalupe Island; and 4) the Guadalupe Island Aggregation Phase, which began when the mature females arrived at Guadalupe Island between late September and early October. Long-term satellite tracking of mature female white sharks highlighted the connectivity between a single presumed mating site at Guadalupe Island, and two widely separated pupping sites along the Mexican coast. The Offshore Gestation Phase provided evidence that the females remained offshore for up to 16 months during their 2-year migration cycle. The Pupping Phase along the Mexican coast coincided with the seasonal presence of young-of-the-year white sharks along the coast of North America, and with a presumed gestation period of 18 months, this placed mating between October and January, during the period when white sharks are known to be at Guadalupe Island. Tracking data during the time sharks were offshore showed that mature males and females are spatially segregated, except for their concurrent seasonal presence at Guadalupe Island. These discoveries provide important new details about the complete life history of northeastern Pacific white sharks while identifying crucial regions in which young-of-the-year, juveniles and adult females are most vulnerable.

Analysis of the re-colonization of San Benito Archipelago by Guadalupe fur seals (Arctocephalus townsendi)

Exploitation of the Guadalupe fur seal (GFS) during the XVIII and XIX centuries almost extirpated the species. GFS were distributed from the Revillagigedo islands (Mexico) to the gulf of Farallones (USA). At present, reproductive colonies are found at Guadalupe Island and San Benito Archipelago (SBA). The aim of this work was to analyze the process of re-colonization and the current status of GFS at SBA. The first births and the occupation of the west island of the SBA are also reported. Census data from 1997 to 2007 indicated an annual growth rate for the population of 21.6%. The population size, growth tendency of the colony, reproductive biology, and food preferences were also studied. A total of 2,227 GFS were counted at SBA. Three squid species (Loligo opalescens, Onychoteuthis banksii, Dosidicus gigas) were found to be the main dietary components. Territoriality, activity patterns, and reproductive behavior were similar for the seals from Guadalupe Island and SBA. The mean growth rate for pups from SBA was calculated and compared to that of the pups at Guadalupe Island (SBA: 6.7 ± 1.4 kg, 68.9 ± 2.64 cm; Guadalupe Island: 5.9 ± 0.5 kg, 67.29 ± 4.3 cm). The length of food foraging trips by females was measured, suggesting that the SBA colony is probably near an important feeding area. Maternal care patterns could indicate different strategies of nursing-foraging trips between the SBA and Guadalupe Island. The population of fur seals at SBA is expected to increase as there are no limitations in terms of reproductive space or available food resources in the area.

Legacy and contemporary persistent organic pollutants in North Pacific albatross

Here we report the first measurements of polybrominated diphenyl ethers (PBDE 47, 99, and 153) alongside 11 organochlorine pesticides (OCPs) and 28 polychlorinated biphenyls (PCBs) in the plasma of albatross from breeding colonies distributed across a large spatial east-west gradient in the North Pacific Ocean. North Pacific albatross are wide-ranging, top-level consumers that forage in pelagic regions of the North Pacific Ocean, making them an ideal sentinel species for detection and distribution of marine contaminants. Our work on contaminant burdens in albatross tissue provides information on transport of persistent organic pollutants (POPs) to the remote North Pacific and serves as a proxy for regional environmental quality. We sampled black-footed (Phoebastria nigripes; n = 20) and Laysan albatross (P. immutabilis; n = 19) nesting on Tern Island, Hawaii, USA, and Laysan albatross (n = 16) nesting on Guadalupe Island, Mexico. Our results indicate that North Pacific albatross are highly exposed to both PCBs and OCPs, with levels ranging from 8.8 to 86.9 ng/ml wet weight and 7.4 to 162.3 ng/ml wet weight, respectively. A strong significant gradient exists between Laysan albatross breeding in the Eastern Pacific, having approximately 1.5-fold and 2.5-fold higher levels for PCBs and OCPs, respectively, compared to those from the Central Pacific. Interspecies levels of contaminants within the same breeding site also showed high variation, with Tern black-footed albatross having approximately threefold higher levels of both PCBs and OCPs than Tern Laysan albatross. Surprisingly, while PBDEs are known to travel long distances and bioaccumulate in wildlife of high trophic status, we detected these three PBDE congeners only at trace levels ranging from not detectable (ND) to 0.74 ng/ml wet weight in these albatross.

A first estimate of white shark, Carcharodon carcharias , abundance off Central California

The decline of sharks in the global oceans underscores the need for careful assessment and monitoring of remaining populations. The northeastern Pacific is the home range for a genetically distinct clade of white sharks (Carcharodon carcharias). Little is known about the conservation status of this demographically isolated population, concentrated seasonally at two discrete aggregation sites: Central California (CCA) and Guadalupe Island, Mexico. We used photo-identification of dorsal fins in a sequential Bayesian mark-recapture algorithm to estimate white shark abundance off CCA. We collected 321 photographs identifying 130 unique individuals, and estimated the abundance off CCA to be 219 mature and sub-adult individuals ((130, 275) 95% credible intervals), substantially smaller than populations of other large marine predators. Our methods can be readily expanded to estimate shark population abundance at other locations, and over time, to monitor the status, population trends and protection needs of these globally distributed predators.

Plastid DNA Diversity Is Higher in the Island Endemic Guadalupe Cypress than in the Continental Tecate Cypress

Background Callitropsis guadalupensis (Guadalupe cypress) is endemic to Guadalupe Island, Mexico, where it is the dominant species of the only forest. The species has suffered declining numbers following the introduction of goats to the island over 150 years ago. Callitropsis guadalupensis is closely related to Callitropsis forbesii (Tecate cypress), distributed in small isolated populations in mainland Baja California and southern California. The objective of the present study was to compare the genetic diversity of the island endemic to the continental species.Methodology/Principal FindingsWe measured genetic diversity in Callitropsis guadalupensis (n = 54) from Guadalupe Island and in Callitropsis forbesii (n = 100) from five populations in mainland Baja California. The plastid DNA trnS-trnG spacer and the trnL-trnF region were chosen for characterization. Thirty-four haplotypes were observed, of which six were shared between both species. One of these haplotypes was also shared with three other species, Callitropsis lusitanica, Callitropsis montana, and Callitropsis stephensonii. Haplotype diversity (h) and nucleotide diversity (π) were significantly higher for Callitropsis guadalupensis (h = 0.698, π = 0.00071) than for Callitropsis forbesii (h = 0.337, π = 0.00024).Conclusions/Significance Callitropsis guadalupensis shows no evidence of a founder effect or of a genetic bottleneck, and can be added to a growing list of insular species with higher genetic diversity than their mainland relatives.

Isolation of microsatellite loci from Rhamnus pirifolia

Rhamnus pirifolia Greene (Rhamnaceae), the island redberry, is a small evergreen tree endemic to the California Channel Islands and Guadalupe Island, Mexico. Nine polymorphic microsatellite loci were isolated from the taxon and were screened for variability in populations from three California Channel Islands. Moderate levels of variability were observed, with mean numbers of alleles per locus ranging from 1.3 to 4.7. The mean observed and expected heterozygosities ranged from 0.01 to 0.53 and 0.01 to 0.56, respectively. These new loci will be useful in conservation genetic and evolutionary studies within Rhamnus.

Sampling procedures and species estimation: testing the effectiveness of herbarium data against vegetation sampling in an oceanic island

Questions: What is the relationship between species assemblages in herbarium collections and species abundances in the field, and how trustworthy are herbarium data in vegetation science? Location: Guadalupe Island, Baja California, Mexico. Methods: We compared species-abundance distribution and evenness in 110 vegetation plots in Guadalupe Island against data from four herbaria. We tested whether the relative frequencies derived from herbarium specimens differed significantly from species frequencies in the field. We compared the rarefaction curves for both field and herbarium data sets, and tested whether taxonomic collectors accumulated new species at a higher rate than that observed in ecological plot sampling. Results: At any given sampling effort, the total number of observed species was higher in herbarium data. The relative abundance of common species in the field was higher, and the evenness of the distribution was lower, than in herbarium data. There was no significant correlation between species abundances in the field and in the herbaria. By selectively targeting rare species, collectors accumulate previously unseen species much faster than through ecological sampling. Conclusions: Because collectors aim for the rarer species and avoid the more common ones, the relative abundance of species in herbarium collections cannot be interpreted as a predictor of their true abundance in the field. Any statistical procedure that requires the sample to be representative of the true abundance distribution is likely to show errors when applied to herbarium data. However, because collectors actively search for rare species their rate of species accumulation is higher and their floristic lists are more complete than those obtained through ecological field sampling.

White Shark Offshore Habitat: A Behavioral and Environmental Characterization of the Eastern Pacific Shared Offshore Foraging Area

BackgroundAlthough much is known about the behavior of white sharks in coastal regions, very little is known about their vertical movements offshore in the eastern Pacific where they spend up to five months. We provide the first detailed description of the offshore habitat use of white sharks in the eastern North Pacific.Methodology/Principal FindingsThis study uses 2-min data from four recovered pop-up satellite archival tags deployed at Guadalupe Island (2002 and 2005). Deployments ranged from 5.4 to 8.2 months. Two predominant vertical patterns were described. The first was a bimodal vertical pattern with time spent at the surface and at depth, which was observed while traveling. The second was a repetitive oscillatory diving mode displayed by sharks in the Shared Offshore Foraging Area (SOFA). For all four datasets the average maximum daily dive depths ranged from 442.5 to 492.8 m and were typically associated with dissolved oxygen concentrations of above 1.7 ml L−1. Although infrequent, occasional dives to near 1000 m with a minimum temperature of 3.9°C and a minimum O2 level of 0.3 ml L−1 were observed.Conclusions/SignificanceRecovered pop-up satellite tags from Guadalupe Island white sharks advance our understanding of the vertical habitat use of white sharks while offshore. The bimodal vertical pattern during traveling is most likely related to geolocation. The oscillatory dive pattern is likely associated with foraging. While feeding is not documented, foraging is likely occurring in association with the deep scattering layer. Diving depths were not limited by temperature but were constrained by O2 levels below approximately 1.5 ml L−1. While oxygen may limit the extent of sharks' vertical movements, it will also impact prey distribution. Consequently, the shallow oxygen minimum zone in the SOFA may act to concentrate prey, thus enhancing foraging opportunities in these oligotrophic waters.

Sea stars (Chinodermata: Asteroidea) in rocky reefs of Guadalupe Island, Northwest Mexico.

The objective of the work was to describe the community structure of the stars of sea ​​in Isla Guadalupe, (28° N - 29° N), located west of the Baja California Peninsula. The area was visited in September 2008 and 64 censuses were made in 16 sites (3,200 m2 reviewed), both in shallow areas (0 to 10 m) as deep (11 to 20 m). From the counts, the community descriptors of density and richness, diversity (H') and uniformity (J'). On the island, only the species Astrometis sertulifera, Pisaster giganteus and Linckia columbiae. The NU- The total number of individuals found was seven and given the low abundance, no significant differences were detected between sites or depth levels with any of the indices. There is no explanation for the low number of starfish in the work area, but considering the low numbers of the populations and that Isla Guadalupe is a Biosphere Reserve, it is recommended not to grant permits for the extraction of stars from sea ​​in the area, given that the species found are part of the market for species of ornament.

Migration patterns of white sharks Carcharodon carcharias tagged at Guadalupe Island, Mexico, and identification of an eastern Pacific shared offshore foraging area

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 370:221-237 (2008) - DOI: https://doi.org/10.3354/meps07628 Migration patterns of white sharks Carcharodon carcharias tagged at Guadalupe Island, Mexico, and identification of an eastern Pacific shared offshore foraging area Michael L. Domeier*, Nicole Nasby-Lucas Pfleger Institute of Environmental Research,901-B Pier View Way, Oceanside, California 92054, USA Present address: Marine Conservation Science Institute, 2809 S. Mission Road, Fallbrook, California 92028, USA *Email: ml.domeier@gmail.com ABSTRACT: Pop-up satellite archival tags (PSATs) were used to study the migration patterns and habitat preference of 56 white sharks tagged off Guadalupe Island, Mexico, between 2000 and 2008. Nine tags were recovered, providing 1021 d of high resolution (2 min) archival data. Two individual sharks were tagged in consecutive years, providing 2 yr of tracking data for each individual. White sharks were found to make long-range, seasonal migrations from Guadalupe Island to an offshore pelagic habitat, sometimes traveling as far west as the Hawaiian Islands. The pelagic region inhabited by Guadalupe Island white sharks corresponds with that reported for sharks tagged off central California; thus we have termed it the Shared Offshore Foraging Area (SOFA). Sharks spent at least 5 mo off Guadalupe Island before beginning their migration around 15 February on average (earliest 21 December, latest 5 May). They traveled through a migration corridor in an average time of 16 d at an average speed of 3.2 km h–1 and remained in the SOFA for an average duration of 140 d. Males and females began their offshore migrations around the same time and traveled to the same area, but males were found to return to Guadalupe Island on average around 22 July (earliest 15 July, latest 30 July), while females remained in the SOFA into early autumn. Diving profiles of sharks in the SOFA strongly suggest feeding behavior; however, the targeted prey species are unknown at this time. KEY WORDS: Carcharodon · Migration · Aggregation · Guadalupe Island · White shark · Behavior · Philopatry Full text in pdf format PreviousNextCite this article as: Domeier ML, Nasby-Lucas N (2008) Migration patterns of white sharks Carcharodon carcharias tagged at Guadalupe Island, Mexico, and identification of an eastern Pacific shared offshore foraging area. Mar Ecol Prog Ser 370:221-237. https://doi.org/10.3354/meps07628 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 370. Online publication date: October 28, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

A re-description of the eastern Pacific swellshark, Cephaloscyllium ventriosum (Garman 1880) (Chondrichthyes: Carcharhiniformes: Scyliorhinidae), with comments on the status of C. uter (Jordan & Gilbert 1896)

The genus Cephaloscyllium Gill 1862 (Chondrichthyes, Carcharhiniformes, Scyliorhinidae), arguably has one representative species in the eastern Pacific, C. ventriosum (Garman 1880). While the C. ventriosum holotype was collected from central Chile, a dubious species, C. uter, (Jordan & Gilbert 1896) was described from California. Garman (1913) classified C. uter as a junior synonym of C. ventriosum. This study marks the first morphometric and meristic analysis comparing the holotype of C. ventriosum from Chile with California Cephaloscyllium specimens and presents a revision of the genus for the eastern Pacific. Based on a comparison of morphometric and meristic data from specimens collected from Monterey, California; Santa Catalina Island, California; Santa Barbara, California; Guadalupe Island, Mexico; and Valparaiso, Chile, it is concluded that the California and Chilean Cephaloscyllium species represent a single, wide-ranging species, C. ventriosum.

Guadalupe Island: Lost paradise recovered? Overgrazing impact on extinction in a remote oceanic island as estimated through accumulation functions

Guadalupe Island, an oceanic island in the northwest of Mexico, is an outlier of the California Floristic Province that has been disturbed by introduced goats for more than a century, with dramatic effects of goats on plant communities and local species extinctions. In 2004 the island went through a successful eradication program. Since then, six previously unrecorded species have been discovered and four supposed extinct species have been found again. Quantifying the true species richness of the island at the time of eradication, to set a benchmark for the future monitoring of this large-scale natural experiment, is both a challenge and a necessity. For this purpose, we estimated (a) current and (b) accumulated historical plant species richness of the island through accumulation functions. Estimation of current species richness was based on the geographical accumulation process of species richness (80 species) obtained from sampling 110 (50 m × 2 m) transects distributed along the island in year 2004. Historical species richness was estimated through the temporal accumulation of species richness (119 species) from botanical records (1,960 specimens reviewed) between 1875 and 2000. The predicted value of historical richness (213 species) is similar to known historical records (218 species), but estimation of current richness (203 species) is significantly higher than accepted extant plant richness (187 species). Our results suggest that currently there may be more plant species living in the island than estimated through recent botanical exploration. Future monitoring of the island as it recovers will clarify this hypothesis.

The Rediscovery and Status of Dissanthelium californicum (Poaceae) on Santa Catalina Island, California

Dissanthelium californicum (Nutt.) Benth. (Poaceae) is an annual grass known only from Santa Catalina and San Clemente Islands, off the coast of Southern California, USA, and Guadalupe Island, off the coast of Baja California, Mexico. It had not been recorded since Blanche Trask collected it in 1903 on San Clemente Island, and was therefore considered to be extinct, possibly as a result of overgrazing by introduced goats on these islands. During monitoring by the Catalina Island Conservancy from March through July 2005, D. californicum was discovered growing in seven diverse and widely spread locations on Santa Catalina Island. The rediscovery may be a result of the removal of feral goats and pigs from the island, record-breaking rainfall, and increased exploration of remote areas. A revised description of the species and a summary of its habitat preferences are provided. Thorough monitoring and surveying of known and potential locations will be necessary to better determine the conservation status of the species.

Revision of Flabelliderma Hartman, 1969 (Polychaeta: Flabelligeridae)

The flabelligerid genus Flabelliderma Hartman, 1969 is redefined and its type species is re‐established. In comparison with Flabelligera Sars, 1829, the diagnostic features include the fusion of papillae forming tubercles, often adhering sediment particles, and notopodial lobes forming large ovoid lobes. Four species are described and presented as new combinations, and three others were previously undescribed; thus the species included are F. papillosa (Essenberg, 1922) from southern California, F. berkeleyorum n. sp. from Washington, F. claparedei (de Saint‐Joseph, 1898) from the Bay of Biscay, F. gourdoni (Gravier, 1906) from Antarctica, F. lighti n. sp. from Guadalupe Island, western Mexico, F. ockeri n. sp. from southern California, and F. pruvoti (Fauvel, 1930) from New Caledonia.

Persistent organic pollutants carried by synthetic polymers in the ocean environment

Thermoplastic resin pellets are melted and formed into an enormous number of inexpensive consumer goods, many of which are discarded after a relatively short period of use, dropped haphazardly onto watersheds and then make their way to the ocean where some get ingested by marine life. In 2003 and 2004 pre-production thermoplastic resin pellets and post-consumer plastic fragments were collected and analyzed for contamination for persistent organic pollutants (POPs). Samples were taken from the North Pacific Gyre, and selected sites in California, Hawaii, and from Guadalupe Island, Mexico. The total concentration of PCBs ranged from 27 to 980 ng/g; DDTs from 22 to 7100 ng/g and PAHs from 39 to 1200 ng/g, and aliphatic hydrocarbons from 1.1 to 8600 μg/g. Analytical methods were developed to extract, concentrate and identify POPs that may have accumulated on plastic fragments and plastic pellets. The results of this study confirm that plastic debris is a trap for POPs.

Drilling the Crust at Mid-Ocean Ridges: An "In Depth" Perspective

In April 1961, 13.5 m of basalts were drilled off Guadalupe Island about 240 km west of Mexico's Baja California, together with a few hundred meters of Miocene sediments, in about 3500 m of water. This fi rst-time exploit, reported by John Steinbeck for Life magazine, aimed to be the test phase for the considerably more ambitious Mohole project, whose objective was to drill through the oceanic crust down to Earth's mantle (Lill and Bascom, 1959; Bascom, 1961). Born in the late 1950s, the Mohole project unfortunately ended in muddy waters and was terminated by the United States Congress in 1965 (Shor, 1985; Greenberg, 1971). Undeterred, the scientifi c community rallied again to launch the Deep Sea Drilling Project (DSDP) in 1968, followed by the Ocean Drilling Program (ODP) in 1985, and the Integrated Ocean Drilling Program (IODP) in 2003. These programs have provided solutions to some of the most pressing and interesting problems in ocean and earth science (see, for example, Oceanography 19-4, December 2006).the early 1970s, almost 15 years after the fi rst Mohole attempt, attendees of a Penrose fi eld conference (Conference Participants, 1972) formulated the concept of a layered oceanic crust composed of lavas, underlain by sheeted dikes, then gabbros (corresponding to the seismic layers 2A, 2B, and 3, respectively), which themselves overlay mantle peridotites. Deep drilling into the oceanic crust would provide the ground truth for the Penrose model; the fl ame of the Mohole project still burned. This article draws from results of more than 30 years of ocean drilling at mid-ocean ridges or in older igneous oceanic crust and briefl y reviews some important milestones that improved understanding of crustalaccretion processes at mid-ocean ridges. Figure 1 shows the locations of the numerous DSDP, ODP, and IODP expeditions to which we refer; Table 1 lists site locations.