Sea surface environment inferred from planktonic foraminifera in the southern South China Sea since the last glacial period

Detailed analyses of planktonic foraminifera at Site 17964 from the southern South China Sea (SCS) disclose that warm-water species have a higher percentage during the Holocene, while temperate-water species have a higher content for the last glacial period. Therefore, the sea surface temperature (SST) is a main factor that affects the foraminiferal assemblage at this site. A remarkable faunal variation at Site 17964 is recognized for Pulleniatina obliquiloculata over the last glacial–interglacial periods: higher P. obliquiloculata content during the glacial period and abrupt drop at the beginning of Termination I (16.5–15 kyr B.P.). The characteristic P. obliquiloculata variation can be correlated with other sites in the southern SCS and thus can be adopted as a stratigraphic tool in the region. A detailed analysis of Orbulina universa shell morphometrics at Site 17964 shows the test size from 0.83 to 1.45 mm and the shell porosity up to 36.7%, much larger than those in the Indian and Atlantic Oceans, which indicates a warmer and less saline surface water in the equatorial–tropical western Pacific. The diameter and shell porosity of O. universa increased from the last glacial to the Holocene, corresponding to the increase of SST recorded by the U^k₃₇ alkenone index. A higher correlation coefficient (89%) between the O. universa test size and SST implies that intraspecific O. universa test size be used as an index of the sea surface temperature in the South China Sea.     

Microsatellite and mitochondrial DNA analyses of the genetic structure of blacktip shark (Carcharhinus limbatus) nurseries in the northwestern Atlantic, Gulf of Mexico, and Caribbean Sea

Abstract We investigated the genetic structure of blacktip shark (Carcharhinus limbatus) continental nurseries in the northwestern Atlantic Ocean, Gulf of Mexico, and Caribbean Sea using mitochondrial DNA control region sequences and eight nuclear microsatellite loci scored in neonate and young-of-the-year sharks. Significant structure was detected with both markers among nine nurseries (mitochondrial PhiST = 0.350, P < 0.001; nuclear PhiST = 0.007, P < 0.001) and sharks from the northwestern Atlantic, eastern Gulf of Mexico, western Gulf of Mexico, northern Yucatan, and Belize possessed significantly different mitochondrial DNA haplotype frequencies. Microsatellite differentiation was limited to comparisons involving northern Yucatan and Belize sharks with nuclear genetic homogeneity throughout the eastern Gulf of Mexico, western Gulf of Mexico, and northwestern Atlantic. Differences in the magnitude of maternal vs. biparental genetic differentiation support female philopatry to northwestern Atlantic, Gulf of Mexico, and Caribbean Sea natal nursery regions with higher levels of male-mediated gene flow. Philopatry has produced multiple reproductive stocks of this commercially important shark species throughout the range of this study.     

Sea surface temperature and the growth of the West Atlantic reef-building coral Montastraea annularis

Relationships were analyzed between sea surface temperature (SST) and annual growth characteristics (density, extension rate and calcification rate) of the Caribbean reef-building coral Montastraea annularis. Colonies were collected from 12 localities in the Gulf of Mexico and the Caribbean Sea. Two well-separated relationships were found, one for the Gulf of Mexico and the other for the Caribbean Sea. Calcification rate and skeletal density increased with increasing SST in both regions, while extension rate tended to decrease. Calcification rate increased ∼0.57 g cm⁻² year⁻¹ for each 1 °C increase in SST. Zero calcification was projected to occur at 23.7 °C in corals from the Gulf of Mexico and at 25.5 °C in corals from the Caribbean Sea. The 24 °C annual average SST isotherm marks the northern limit of distribution of M. annularis. Montastraea annularis populations of the Gulf of Mexico are isolated from those of the Caribbean Sea, and results indicate that corals from the Gulf of Mexico are adapted to growth at lower minimum and average annual SST. Corals from both the Gulf of Mexico and the Caribbean Sea, growing at lower SSTs and having lower calcification rates, extend their skeletons the same or more than those growing at higher SSTs. They achieve this by putting more of their calcification resources into extension and less into thickening, i.e., by sacrificing density.     

Genetic connectivity of lionfish (Pterois volitans) in marine protected areas of the Gulf of Mexico and Caribbean Sea

Lionfish (Pterois volitans) have rapidly invaded the tropical Atlantic and spread across the wider Caribbean in a relatively short period of time. Because of its high invasion capacity, we used it as a model to identify the connectivity among nine marine protected areas (MPAs) situated in four countries in the Gulf of Mexico and the Caribbean Sea. This study provides evidence of local genetic differentiation of P. volitans in the Gulf of Mexico and the Caribbean Sea. A total of 475 lionfish samples were characterized with 12 microsatellites, with 6–20 alleles per locus. Departures from Hardy–Weinberg equilibrium (HWE) were found in 10 of the 12 loci, all caused by heterozygous excess. Moderate genetic differentiation was observed between Chiriviche, Venezuela and Xcalak, México localities (F_ST = 0.012), and between the Los Roques and the Veracruz (F_ST = 0.074) sites. STRUCTURE analysis found that four genetic entities best fit our data. A unique genetic group in the Gulf of Mexico may imply that the lionfish invasion unfolded both in a counterclockwise manner in the Gulf of Mexico. In spite of the notable dispersion of P. volitans, our results show some genetic structure, as do other noninvasive Caribbean fish species, suggesting that the connectivity in some MPAs analyzed in the Caribbean is limited and caused by only a few source individuals with subsequent genetic drift leading to local genetic differentiation. This indicates that P. volitans dispersion could be caused by mesoscale phenomena, which produce stochastic connectivity pulses. Due to the isolation of some MPAs from others, these findings may hold a promise for local short‐term control of by means of intensive fishing, even in MPAs, and may have regional long‐term effects.     

Mitochondrial DNA genome evidence for the existence of a third divergent lineage in the western Atlantic Ocean for the bull shark (Carcharhinus leucas)

We report for the first time a highly divergent lineage in the Caribbean Sea for the bull shark (Carcharhinus leucas) based on the analysis of 51 mitochondrial DNA genomes of individuals collected in the western North Atlantic. When comparing the mtDNA control region obtained from the mitogenomes to sequences reported previously for Brazil, the Caribbean lineage remained highly divergent. These results support the existence of a discrete population in Central America due to a phylogeographic break separating the Caribbean Sea from the western North Atlantic, Gulf of Mexico and South America.     

Late neogene biostratigraphy and stable isotope stratigraphy of a drilled core from the Gulf of Mexico

Late Neogene stable isotope stratigraphy and planktonic foraminiferal biostratigraphy have been examined in a high sedimentation rate core (E67-135, Shell Oil Co.) drilled at 725 m water depth in the De Soto Canyon, Gulf of Mexico. The 305 m core contains sections that are Late Miocene, Early Pliocene, Late Pliocene, and Quaternary in age, and is rich in well-preserved assemblages of planktonic foraminifera.A biostratigraphy has been established based on the ranges of 34 selected species of foraminifera. The core 3orrelates with sections from the Gulf of Mexico, the Caribbean Sea, and the subtropical North and South Atlantic Oceans using, as datums, the evolutionary appearances of Globorotalia miocenica Palmer and Globorotalia margaritae evoluta Cita, the extinction of Globorotalia miocenica and the first appearance of Globorotalia truncatulinoides (d'Orbigny).Oxygen and carbon isotope stratigraphy is based on analysis of the benthonic foraminifer, Uvigerina d'Orbigny. Isotopic trends are similar to those observed in the Pacific and Atlantic Oceans. From Early Pliocene to Late Pleistocene time, average δ¹⁸O values increase (2.42‰ to 3.36‰) and exhibit a wider range of values (0.71‰ in Early Pliocene compared to 1.65‰ in Late Pleistocene sediments), probably reflecting Late Neogene climatic deterioration. The ratio ${}^{13}\text{C}{}^{12}\text{C}$ decreases significantly by ?0.21‰ from the Late Miocene to the Early Pliocene. A decrease in δ¹³C is observed in other cores and is probably related to changing oceanic circulation patterns in Late Miocene time.     

A new type of test wall in the Late Cretaceous (Late Santonian-Campanian) heterohelicid planktic foraminifera

The first Cretaceous serial planktic foraminifer (family Heterohelicidae Cushman, 1927) with simple-ridged test wall is reported from the uppermost Santonian-lower Campanian sediments of the Deep Sea Drilling Project Site 463 (Mid-Pacific Mountains, equatorial Central Pacific). Hendersonites pacificus n. sp. is characterized by the reduced ornamentation over the last pairs of chambers and strong peripheral costae lining the periphery with test wall flexure. This species evolved from H. carinata (Cushman, 1938) of the upper Santonian-Campanian, a frequently reported species from the Atlantic Ocean, Gulf of Mexico and Western Tethyan Realm.     

First report of a sleeper shark (Somniosus sp.) in the southern Colombian Caribbean

A sleeper shark, genus Somniosus, was observed in the Colombian Caribbean. A Remote Operated Vehicle (ROV) recorded a sleeper shark specimen during an inspection while drilling a hydrocarbon exploratory well at 1,820 m water depth. This is the first record of a sleeper shark for the southern Colombian Caribbean. The previous most southern records of Somniosid sharks in the tropical and subtropical western Atlantic came from the western and northern Gulf of Mexico, and from Cuba.     

Placing the Floridian marine genetic disjunction into a regional evolutionary context using the scorched mussel, Brachidontes exustus, species complex

The well-documented Floridian Gulf/Atlantic marine genetic disjunction provides an influential example of presumed vicariant cladogenesis along a continental coastline for major elements of a diverse nearshore fauna. However, it is unclear if this disjunction represents a local anomaly for regionally distributed morphospecies, or if it is merely one of many such cryptic phylogenetic splits that underlay their assumed genetic cohesiveness. We aimed to place the previously characterized scorched mussel Gulf/Atlantic genetic disjunction into a regional phylogenetic perspective by incorporating genotypes of nominal conspecifics sampled throughout the Caribbean Basin as well as those of eastern Pacific potential geminate species. Our results show it to be one of multiple latent regional genetic disjunctions, involving five cryptic Caribbean species, that appear to be the product of a long history of regional cladogenesis. Disjunctions involving three stem lineages clearly predate formation of the Isthmus of Panama and of the Caribbean Sea, although four of the five cryptic species have within-basin sister relationships. Surprisingly, the Atlantic clade was also found to be widespread in the southern Caribbean, and ancestral demography calculations through time for Atlantic coast-specific genotypes are consistent with a northward range extension after the last glacial maximum. Our new data seriously undermine the hypothesis of a Floridian vicariant genesis and imply that the scorched mussel Gulf/Atlantic disjunction represents a case of geographic and temporal pseudocongruence. All five Caribbean Basin cryptic species exhibited an intriguing pattern of predominantly allopatric distribution characterized by distinct geographic areas of ecological dominance, often adjoining those of sister taxa. This pattern of distribution is consistent with allopatric speciation origins, coupled with restricted postspeciation range extensions. Several lines of indirect evidence favor the hypothesis that the predominantly allopatric distributions are maintained over evolutionary time scales, primarily by postrecruitment ecological filters rather than by oceanographic barriers to larval-mediated gene flow.     

Spawning ofConger oceanicus andConger triporiceps (Congridae) in the Sargasso Sea and subsequent distribution of leptocephali

Synopsis Distribution of leptocephali ofConger in the Western North Atlantic Ocean was studied using specimens from our collections, specimens from other collections, and various existing collection records. The presence of leptocephali ofConger oceanicus andConger triporiceps < 30 mm long over deep water in the southwestern Sargasso Sea in autumn and winter implies a protracted spawning period there. The subtropical convergence zone, meandering east-west across the Sargasso Sea, is probably the northern limit of spawning of both species. Spawning may also occur close to the Bahamas and Antilles.C. triporiceps may spawn also in the Caribbean Sea judging by the capture of small leptocephali in the western Caribbean and of the more southerly continental distribution of its juveniles. The claim of Johannes Schmidt in 1931 that the EuropeanC. conger spawns across the North Atlantic into the western Sargasso Sea is probably incorrect, because leptocephali ofConger are rare in the eastern Sargasso Sea and becauseC. triporiceps, with myomere numbers overlapping those ofC. conger, was recently described in the western North Atlantic. With increasing size, leptocephali ofC. oceanicus and a portion ofC. triporiceps spread westward and northward in the Florida Current and Gulf Stream, but larger leptocephali especially ofC. triporiceps are found also in the Caribbean and Gulf of Mexico. Spawning ofC. oceanicus in the Sargasso Sea indicates that adults cross the Florida Current-Gulf Stream, and successful leptocephali cross the current in the opposite direction to colonize juvenile habitat on the continental shelf, a migratory pattern similar to that of the American eelAnguilla rostrata (Anguillidae).     

Mixing rates in weakly differentiated stocks of greater amberjack (<Emphasis Type="Italic">Seriola dumerili</Emphasis>) in the Gulf of Mexico

The greater amberjack (Seriola dumerili) is a commercially and recreationally important marine fish species in the southeastern United States, where it has been historically managed as two non-mixing stocks (Gulf of Mexico and Atlantic). Mark-recapture studies and analysis of mitochondrial DNA have suggested the two stocks are demographically independent; however, little is currently known about when and where spawning occurs in Gulf of Mexico amberjack, and whether stock mixture occurs on breeding grounds. The primary objective of this study was to quantify stock mixture among breeding populations of amberjack collected from the Atlantic and Gulf of Mexico. Genetic data based on 11 loci identified very low, though statistically significant differentiation among Gulf of Mexico samples (G_ST = 0.007, \(G_{{{\text{ST}}}}^{\prime }\) = 0.009; all P?=?0.001) and between reproductive adults collected from two spawning areas (G_ST = 0.007, \(G_{{{\text{ST}}}}^{\prime }\) = 0.014; all P?=?0.001). Naïve Bayesian mixture analysis supported a single genetic cluster [p(S|data)?=?0.734] whereas trained clustering (using Atlantic and Gulf spawning fish) gave the highest support to a two-cluster model (p(S|data)?=?1.0). Our results support the argument that the genetic structuring of greater amberjack is more complex than the previously assumed two, non-mixing stock model. Although our data provide evidence of limited population structure, we argue in favour of non-panmixia among reproductive fish collected from the Gulf of Mexico and Florida Keys.     

Forecasting lionfish sources and sinks in the Atlantic: are Gulf of Mexico reef fisheries at risk?

Invasive lionfish (Pterois volitans/miles complex) now permeate the entire tropical western Atlantic, Caribbean Sea, and Gulf of Mexico, but lionfish abundance has been measured only in select locations in the field. Despite its rapid range expansion, a comprehensive meta-population analysis of lionfish ‘sources’ and ‘sinks’ and consequentially the invader’s potential abundance and impacts on economically important, sympatric reef fishes have not been assessed. These data are urgently needed to spatially direct control efforts and to plan for and perhaps mitigate lionfish-caused damage. Here, we use a biophysical computer model to: (1) forecast larval lionfish sources and sinks that are also delineated as low to high lionfish ‘density zones’ throughout their invaded range, and (2) assess the potential vulnerability of five grouper and snapper species—Epinephelus morio, Mycteroperca microlepis, Epinephelus flavolimbatus, Lutjanus campechanus, and Rhomboplites aurorubens—to lionfish within these density zones in the Gulf of Mexico. Our results suggest that the west Florida shelf and nearshore waters of Texas, USA, and Guyana, South America, function both as lionfish sources and sinks and should be a high priority for targeted lionfish control. Furthermore, of the five groupers and snappers studied, the high fishery value E. morio (red grouper) is the Gulf of Mexico species most at risk from lionfish. Lacking a comprehensive lionfish control policy, these risk exposure data inform managers where removals should be focused and demonstrate the risk to five sympatric native groupers and snappers in the Gulf of Mexico that may be susceptible to dense lionfish aggregations, should control efforts fail.     

On the time-scale of deglaciation: Atlantic deep-sea sediments and gulf of Mexico

Deglaciation as seen in the δ¹⁸O record of deep-sea sediments starts about 14,000 yrs. ago. Measured bulk ¹⁴C ages are too old by 1000–2000 yrs. in the central Atlantic compared with ages derived from climate correlation. This conclusion rests on the observation that deglaciation occurs in two major steps, separated by a pause, and on the hypothesis that this pause is correlative to the Younger Dryas cold period. The Gulf of Mexico record is readily correlated with the deep-sea record if it is assumed that the appearance of Globorotalia menardii is retarded with respect to the tropical Atlantic, by about 2000 yrs. The major meltwater spike then dates near 9000 yrs. ago, rather than at 13,500 yrs. B.P. (as assumed by Kennett and Shackleton, 1975) or 11,500 yrs. B.P. (as in Emiliani et al., 1975).     

Coccolithophores in the equatorial Atlantic Ocean: response to seasonal and Late Quaternary surface water variability

The present study was initiated to ascertain the significance of coccolithophores as a proxy for paleoceanographic and paleoproductivity studies in the equatorial Atlantic. Data from a range of different samples, from the plankton, surface sediments as well as sediment cores are shown and compared with each other.In general, the living coccolithophores in the surface and subsurface waters show considerable variation in cell numbers and distribution patterns. Cell densities reached a maximum of up to 300×10³ coccospheres/l in the upwelling area of the equatorial Atlantic. Here, Emiliania huxleyi is the dominant species with relatively high cell numbers, whereas Umbellosphaera irregularis and Umbellosphaera tenuis are characteristic for oligotrophic surface waters. Although they are observed in high relative abundances, these species only occur in low absolute numbers. The lower photic zone is dominated by high abundances and considerable cell numbers of Florisphaera profunda.The geographical distribution pattern of coccoliths in surface sediments reflects the conditions of the overlying surface water masses. However, abundances of the oligotrophic species Umbellosphaera irregularis and Umbellosphaera tenuis are strongly diminished, causing an increase in relative abundance of the lower photic zone taxa Florisphaera profunda and Gladiolithus flabellatus.During the past 140,000 years the surface water circulation of the equatorial Atlantic has changed drastically, as can be seen from changes in the coccolithophore species composition, absolute coccolith numbers, as well as coccolith accumulation rates. Significant increases in coccolith numbers and accumulation rates is observed in the southern equatorial Atlantic during the last glacial interval (oxygen isotope stages 2–4), which we attribute to enhanced upwelling intensities and advection of cool nutrient rich waters at this site. In the western equatorial Atlantic we observe an opposite trend with decreasing numbers of coccoliths during glacial periods, which probably is caused by a deepening of the thermocline.     

Studies in conservation genetics of tarpon (Megalops atlanticus) — V. Isolation and characterization of microsatellite loci

The tarpon, Megalops atlanticus, supports important recreational fisheries in the Atlantic Ocean, Caribbean Sea and Gulf of Mexico. Declines in segments of these fisheries have prompted questions concerning genetic stock structure in this species. Preparatory to a survey of genetic variation in tarpon, 15 microsatellite markers were isolated. The number of alleles per locus ranged from two to 10 and observed heterozygosity ranged from 0.091 to 0.765, providing potentially useful markers for the detection of within‐ and among‐population genetic variability.     

Horizontal Movements,Migration Patterns,and Population Structure of Whale Sharks in the Gulf of Mexico and Northwestern Caribbean Sea

Whale sharks, Rhincodon typus, aggregate by the hundreds in a summer feeding area off the northeastern Yucatan Peninsula, Mexico, where the Gulf of Mexico meets the Caribbean Sea. The aggregation remains in the nutrient-rich waters off Isla Holbox, Isla Contoy and Isla Mujeres, Quintana Roo for several months in the summer and then dissipates between August and October. Little has been known about where these sharks come from or migrate to after they disperse. From 2003–2012, we used conventional visual tags, photo-identification, and satellite tags to characterize the basic population structure and large-scale horizontal movements of whale sharks that come to this feeding area off Mexico. The aggregation comprised sharks ranging 2.5–10.0 m in total length and included juveniles, subadults, and adults of both sexes, with a male-biased sex ratio (72%). Individual sharks remained in the area for an estimated mean duration of 24–33 days with maximum residency up to about 6 months as determined by photo-identification. After leaving the feeding area the sharks showed horizontal movements in multiple directions throughout the Gulf of Mexico basin, the northwestern Caribbean Sea, and the Straits of Florida. Returns of individual sharks to the Quintana Roo feeding area in subsequent years were common, with some animals returning for six consecutive years. One female shark with an estimated total length of 7.5 m moved at least 7,213 km in 150 days, traveling through the northern Caribbean Sea and across the equator to the South Atlantic Ocean where her satellite tag popped up near the Mid-Atlantic Ridge. We hypothesize this journey to the open waters of the Mid-Atlantic was for reproductive purposes but alternative explanations are considered. The broad movements of whale sharks across multiple political boundaries corroborates genetics data supporting gene flow between geographically distinct areas and underscores the need for management and conservation strategies for this species on a global scale.     

Population structure of the dusky pipefish (Syngnathus floridae) from the Atlantic and Gulf of Mexico,as revealed by mitochondrial DNA and microsatellite analyses

Aim To elucidate the historical phylogeography of the dusky pipefish (Syngnathus floridae) in the North American Atlantic and Gulf of Mexico ocean basins. Location Southern Atlantic Ocean and northern Gulf of Mexico within the continental United States. Methods A 394‐bp fragment of the mitochondrial cytochrome b gene and a 235‐bp fragment of the mitochondrial control region were analysed from individuals from 10 locations. Phylogenetic reconstruction, haplotype network, mismatch distributions and analysis of molecular variance were used to infer population structure between ocean basins and time from population expansion within ocean basins. Six microsatellite loci were also analysed to estimate population structure and gene flow among five populations using genetic distance methods (F_ST, Nei’s genetic distance), isolation by distance (Mantel’s test), coalescent‐based estimates of genetic diversity and migration patterns, Bayesian cluster analysis and bottleneck simulations. Results Mitochondrial analyses revealed significant structuring between ocean basins in both cytochrome b (Φ_ST = 0.361, P < 0.0001; Φ_CT = 0.312, P < 0.02) and control region (Φ_ST = 0.166, P < 0.0001; Φ_CT = 0.128, P < 0.03) sequences. However, phylogenetic reconstructions failed to show reciprocal monophyly in populations between ocean basins. Microsatellite analyses revealed significant population substructuring between all locations sampled except for the two locations that were in closest proximity to each other (global F_ST value = 0.026). Bayesian analysis of microsatellite data also revealed significant population structuring between ocean basins. Coalescent‐based analyses of microsatellite data revealed low migration rates among all sites. Mismatch distribution analysis of mitochondrial loci supports a sudden population expansion in both ocean basins in the late Pleistocene, with the expansion of Atlantic populations occurring more recently. Main conclusions Present‐day populations of S. floridae do not bear the mitochondrial DNA signature of the strong phylogenetic discontinuity between the Atlantic and Gulf coasts of North America commonly observed in other species. Rather, our results suggest that Atlantic and Gulf of Mexico populations of S. floridae are closely related but nevertheless exhibit local and regional population structure. We conclude that the present‐day phylogeographic pattern is the result of a recent population expansion into the Atlantic in the late Pleistocene, and that life‐history traits and ecology may play a pivotal role in shaping the realized geographical distribution pattern of this species.     

A new sponge-inhabiting amphipod species (Crustacea, Gammaridea, Sebidae) from the Veracruz Coral Reef System, southwestern Gulf of Mexico

A new species of the genus Seba Bate (Amphipoda: Sebidae) is described from the Veracruz Coral Reef System, Veracruz, south-western Gulf of Mexico. The specimens were found in association with a sponge, Ircinia fistularis, at depths from 8 to 10 m. Seba alvarezi n. sp. can be distinguished from closely related species mainly by the presence of a short, two-articulated accessory flagellum, three apical setae on article 3 of the mandible palp, and by the absence of apical setae on the inner lobe of maxilla 1. The new species is compared to closely related species in the family, and an identification key to the species of Seba known from the Gulf of Mexico and the Caribbean Sea is given.