Western Atlantic Population Research Articles

Age and growth of grey triggerfish Balistes capriscus from trans-Atlantic populations.

Anthropogenic factors that negatively impact reef fishes can include changes in life-history patterns of fisheries-targeted species. Understanding these impacts on growth and population age structure is essential in the management of exploited populations of fishes. This is the first study to directly compare age and growth for a major fisheries species between east and west populations of a transatlantic reef fish. The main goal of this study was to document age and growth in grey triggerfish Balistes capriscus from coastal waters of Ghana in the Gulf of Guinea (GOG) and compare those with the previous growth studies from that region and with the western Atlantic population. A secondary objective of this study was to evaluate the use of otoliths to age triggerfish and to provide a preliminary comparison with spine-derived age estimates. The results obtained from this study provided an updated understanding of the growth and age structure of the eastern B. capriscus population in GOG. The authors documented that shifts in population attributes occurred for B. capriscus after its major decline in abundance. The differences in physical and biotic characteristics of the East and West Atlantic regions and the differences in collection methods of samples make direct comparisons of growth parameters difficult. Nonetheless, overall differences in maximum sizes and ages were apparent; the western Atlantic population had a larger maximum size and older maximum age. The authors also documented that sagittal otoliths can be used to provide age estimates for triggerfish species, and otoliths as an ageing structure had better between-reader precision compared to dorsal spines.

A Bayesian assessment of the conservation status of humpback whales (Megaptera novaeangliae) in the western South Atlantic Ocean

The population of humpback whales (Megaptera novaeangliae) wintering off the eastern coast of South America is referred to by the International Whaling Commission as ‘Breeding Stock A’ (BSA). This population was heavily exploited in 20th century modern commercial whaling operations. After more than 30 years of protection, its present status remains unknown. A deterministic sex and age-aggregated population dynamics model was used to estimate the pre-exploitation population size (K), the maximum net recruitment rate (rmax), the maximum depletion level (Nmin/K), and other quantities of interest of BSA. Input data included modern whaling catch series, absolute estimates of abundance, observed growth rates and indices of relative abundance. A Bayesian statistical method was used to calculate probability distributions for the model parameters. Prior distributions were set on rmax – an uninformative (Uniform [0, 0.106]) and an informative (Normal [0.067, 0.042]) – and on the population size in 2005 – N2005 (Uniform [500, 22,000]). A total of 10,000 samples were used to compute the joint posterior distribution of the model parameters using the Sampling-Importance-Resampling algorithm. Sensitivity of model outputs to the priors on rmax, a genetic constraint, data inclusion and catch allocation scenarios was investigated. Medians of the posterior probability distributions of quantities of interest for the base case scenario were: rmax = 0.069 (95% probability intervals [PI] = 0.013–0.104), K = 24,558 (95% PI = 22,791–31,118), Nmin/K = 2% (PI = 0.31%–12.5%), N2006/ K = 27.4% (PI = 18.3%–39.5%), N2020/K = 61.8% (PI = 23.8%–88.6%), and N2040/K = 97.3% (PI = 31.6%–99.9%). Despite apparent recovery in the past three decades, the western South Atlantic humpback whale population is still low relative to its pre-exploitation size and requires continued conservation efforts.

Predicting seasonal occurrence of leatherback turtles (Dermochelys coriacea) in eastern Canadian waters from turtle and ocean sunfish (Mola mola) sighting data and habitat characteristics

Part of the western Atlantic population of leatherback turtles (Dermochelys coriacea (Vandelli, 1761)) forage in Canadian waters, where high-use areas have been identified using satellite telemetry and opportunistic sightings. Here, we use sightings of leatherback turtles and ocean sunfish (Mola mola (Linnaeus, 1758)) obtained during a systematic large-scale aerial survey, along with opportunistic turtle sightings, to examine the seasonal occurrence and distribution of leatherback turtles in eastern Canada. Using environmental correlates, we predict the spatial and seasonal development of potentially suitable habitats. All data sets confirmed the presence of leatherback turtles off Nova Scotia during summer. They also highlighted turtle occurrence off southern Newfoundland. Opportunistic sightings suggest a seasonal shift in main turtle concentrations from southwest to northeast, with use of southern Newfoundland waters extending into September. A generalized additive model linking environmental characteristics and turtle observations suggests adding the Grand Banks off Newfoundland and waters east of Anticosti Island in the Gulf of St. Lawrence to the potentially important habitat for leatherback turtles. Direct observations helped delineate habitat currently used by leatherback turtles. In the context of climate change, this modelling approach may improve our ability to forecast changes in turtle habitat suitability and the risks of entrapment or collision associated with potentially changing usage patterns.

Smalltooth sawfish (Pristis pectinata Latham, 1794) in the Casamance River, Senegal: A historical perspective

Abstract A study of euryhaline elasmobranchs was conducted in the Casamance River, southern Senegal, between June 1974 and October 1975. Data were collected from 159 sawfish, comprising 158 smalltooth sawfish (Pristis pectinata Latham, 1794) and one largetooth sawfish (Pristis pristis Linnaeus, 1758). The mean total rostral tooth count for P. pectinata was 46 (range 41–53), significantly lower than the total tooth counts for the western Atlantic population. No sexual dimorphism in rostral tooth counts was apparent, in contrast to findings from the western Atlantic. The total rostral length averaged 22.9% of the total length. One hundred and forty‐four individuals were caught within the river system itself, all of them were juveniles. Fifteen adults, including the single largetooth sawfish documented during the study, were caught at the river mouth or at sea. Six sawfish, caught between May and July, bore rostral sheaths, indicating that they had recently been born. Although the Casamance and Gambia rivers are only 120 km apart, the findings from this study combined with published data collected from the Gambia River during the same period suggest the partitioning of juvenile habitats by the two sawfish species present in the region, to the level of different river systems. Both species are likely to have used the same coastal habitats as adults. The Casamance River was clearly an important habitat for smalltooth sawfish some 40 years ago, but it is unknown whether the species persists there. Intensive artisanal fisheries for sharks and rays in the region poses a significant threat to any remaining sawfishes, and a challenge for elasmobranch fisheries management.

Mapping and modeling the breeding habitat of the Western Atlantic Red Knot (Calidris canutus rufa) at local and regional scales

ABSTRACT The Western Atlantic population of Red Knot (Calidris canutus rufa) has undergone dramatic declines in recent decades and conservation biologists have sought to improve knowledge about the species' ecology in an effort to understand these declines. One major information gap has been the lack of a detailed understanding of range and habitat use during the breeding season, when the species is distributed sparsely across the Canadian Arctic. Airborne radio-telemetry surveys of Red Knots tagged in Delaware Bay, New Jersey, were conducted across the south and central Canadian Arctic, from Victoria Island in the west to Baffin Island in the east. Intensive field surveys were conducted on Southampton Island, Nunavut, over successive summer field seasons to locate nesting Red Knots and record characteristics of their nesting habitat. Maximum entropy modeling (Maxent) and geographic information system (GIS) data on environmental characteristics were used to predict Red Knot habitat suitability at 2 spatia...

The little shrimp that could: phylogeography of the circumtropical Stenopus hispidus (Crustacea: Decapoda), reveals divergent Atlantic and Pacific lineages.

The banded coral shrimp, Stenopus hispidus (Crustacea: Decapoda: Stenopodidea) is a popular marine ornamental species with a circumtropical distribution. The planktonic larval stage lasts ∼120–253 days, indicating considerable dispersal potential, but few studies have investigated genetic connectivity on a global scale in marine invertebrates. To resolve patterns of divergence and phylogeography of S. hispidus, we surveyed 525 bp of mitochondrial cytochrome c oxidase subunit I (COI) from 198 individuals sampled at 10 locations across ∼27,000 km of the species range. Phylogenetic analyses reveal that S. hispidus has a Western Atlantic lineage and a widely distributed Indo-Pacific lineage, separated by sequence divergence of 2.1%. Genetic diversity is much higher in the Western Atlantic (h = 0.929; π = 0.004) relative to the Indo-Pacific (h = 0.105; π < 0.001), and coalescent analyses indicate that the Indo-Pacific population expanded more recently (95% HPD (highest posterior density) = 60,000–400,000 yr) than the Western Atlantic population (95% HPD = 300,000–760,000 yr). Divergence of the Western Atlantic and Pacific lineages is estimated at 710,000–1.8 million years ago, which does not readily align with commonly implicated colonization events between the ocean basins. The estimated age of populations contradicts the prevailing dispersal route for tropical marine biodiversity (Indo-Pacific to Atlantic) with the oldest and most diverse population in the Atlantic, and a recent population expansion with a single common haplotype shared throughout the vast Indian and Pacific oceans. In contrast to the circumtropical fishes, this diminutive reef shrimp challenges our understanding of conventional dispersal capabilities of marine species.

Genetic population structure in Greenland halibut (Reinhardtius hippoglossoides) and its relevance to fishery management

Exploited marine resources can be managed more effectively when accurate information on geographic population structure is available. Genetic markers offer a powerful tool for fisheries management, because they reveal biologically sound management units. Single nucleotide polymorphisms (SNPs) markers derived from restriction-site associated DNA sequencing (RAD-seq) were developed and used to investigate the stock structure of Greenland halibut (Reinhardtius hippoglossoides). A total of 96 SNPs were analyzed from 384 individuals and eight locations across the Atlantic. Our results suggest a subdivision of Greenland halibut into two populations, an eastern Atlantic population and a western Atlantic population, with a proposed border across the Denmark Strait. In general, Greenland halibut display weak but significant population structure (overall FST= 0.003; p &lt; 0.001), which can be explained by connectivity among populations owing to the migratory behavior or egg and larval drift.

Abundance, Distribution, and Geographic Origin of Non-breeding American Oystercatchers (Haematopus palliatus) in North Carolina, USA

Abstract. American Oystercatchers (Haematopus palliatus) are present in North Carolina, USA, year-round. About 6–7% of the total Western Atlantic population winters in North Carolina. To estimate numbers of American Oystercatchers present during the non-breeding season, four major concentration areas were surveyed in North Carolina, each with multiple roost sites, from 2008–2013. Abundance of American Oystercatchers remained generally stable during the study period. The Lower Cape Fear River area had the greatest number of American Oystercatchers in all seasons. Mean peak abundance was greatest during winter at all concentration areas. Peak winter abundance was 158 at Ocracoke Inlet, 265 in Back Sound, 187 in Masonboro Sound, and 470 on the Lower Cape Fear River. Fall abundance was generally greater than spring abundance at all concentration areas except Masonboro Sound. Most banded individuals observed were marked in North Carolina as chicks or nesting adults, and they exhibited fidelity to concentration...

Abundance and Distribution of American Oystercatchers (Haematopus palliatus) During the Breeding Season in North Carolina, USA

Abstract. The Western Atlantic population of the American Oystercatcher (Haematopus palliatus) is of conservation concern, and much effort has been exerted to determine impacts of conservation efforts and identify important sites that need increased protection within the breeding range. Monitoring numbers of nesting pairs and distribution and habitat selection of nesting pairs provides data for conservation programs. The breeding population of American Oystercatchers in North Carolina has been estimated four times since 2004. Locations of territories and nests were recorded and mapped, and sites were categorized according to habitat type (barrier, dredged-material, or natural sand-shell or marsh island) and management responsibility (Federal, State, Audubon North Carolina, private landowner). Estimates indicate the number of nesting pairs changed slightly: 324 in 2004, 346 in 2007, 373 in 2010, and 351 in 2013. Total numbers of individual American Oystercatchers during the breeding season changed from 703...

Population genetics of the nurse shark (Ginglymostoma cirratum) in the western Atlantic

The nurse shark, Ginglymostoma cirratum, inhabits shallow, tropical, and subtropical waters in the Atlantic and the eastern Pacific. Unlike many other species of sharks, nurse sharks are remarkably sedentary. We assayed the mitochondrial control region and eight microsatellite loci from individuals collected primarily in the western Atlantic to estimate the degree of population subdivision. Two individuals from the eastern Atlantic and one from the Pacific coast of Panama also were genotyped. Overall, the mtDNA haplotype (h = 48 ± 5%) and nucleotide (π = 0.08 ± 0.06%) diversities were low. The microsatellite data mirror the mitochondrial results with the average number of alleles (\( \bar{N}_{A} \) = 9) and observed heterozygosity (\( \bar{H}_{O} \) = 0.58) both low. The low levels of diversity seen in both the mtDNA and the microsatellite may be due to historical sea level fluctuations and concomitant loss of shallow water habitat. Eight of the 10 pair-wise western Atlantic F ST estimates for mtDNA indicated significant genetic subdivision. Pair-wise F ST values for the microsatellite loci indicated a similar pattern as the mtDNA. The western Atlantic population of nurse sharks is genetically subdivided with the strongest separation seen between the offshore islands and mainland Brazil, likely due to deep water acting as a barrier to dispersal. The eastern and western Atlantic populations were closely related. The eastern Pacific individual is quite different from Atlantic individuals and may be a cryptic, sister species.

The economic efficiency of a time–area closure to protect spawning bluefin tuna

Summary 1. Spatial management measures, such as time–area closures, offer a widely advocated strategy for managing bycatch in fisheries and fisheries that impact particular life‐history stages, like spawning. The effectiveness of proposed management strategies can be evaluated across different policy dimensions of which we focus on one – maximising total profit. We examine whether a time–area closure presents an economically efficient means to manage bycatches of Atlantic bluefin tuna Thunnus thynnus on their spawning ground in the Gulf of Mexico by longline fishermen targeting yellowfin tuna T. albacares. 2. We combine a behavioural representation of bluefin migration with population dynamic models for the two species and an economic representation of relevant fisheries and solve for optimal, equilibrial management strategies. 3. The models predict the western Atlantic bluefin population is close to open access harvesting conditions, and that rebuilding the bluefin population would increase overall economic revenues from the fisheries by 460%, regardless of the specific actions taken in the Gulf. 4. Time–area closures in the Gulf are predicted to be economically costly if there is little scope for recovery of the bluefin stock. However, the models predict such closures would offer limited economic benefits if there were a broader commitment to rebuild the bluefin population. 5. Synthesis and applications. Technological advances and improvements in our understanding of the life history of these and other species make increasingly precise spatial effort control possible in many fisheries. The case study illustrates when such management measures would maximise fisheries profits while accounting for population dynamics and differences in mortality from different fisheries. However, the case study also highlights that the more elementary policy challenge of preventing overfishing has still often to be overcome.

Effective size closely approximates the census size in the heavily exploited western Atlantic population of the sandbar shark, Carcharhinus plumbeus

The sandbar shark, Carcharhinus plumbeus, is a long-lived species with low lifetime fecundity that is heavily fished in the western North Atlantic. Inshore nursery grounds increase survivorship of sandbar shark pups and the principal nurseries are in the mid-Atlantic region. We calculated effective number of breeders (Nb) and effective population size (Ne) for adults utilizing the nursery grounds of the Delaware Bay and the Eastern Shore of Virginia by genotyping 902 animals across five cohorts at eight microsatellite loci. Estimates of Nb and Ne were compared to estimates of census size (Nc) of cohorts obtained from Delaware Bay. The estimated Ne/Nc and Nb/Nc ratios were 0.45 or higher whether the Delaware Bay cohorts were considered as distinct year classes or combined. This is in contrast to estimated Ne/Nc ratios in other exploited marine fishes, which are several orders of magnitude smaller. Instead, the Ne/Nc ratio of sandbar sharks is similar to that found in marine and terrestrial mammals.

Bioaccumulation of persistent organic pollutants in female common dolphins ( Delphinus delphis) and harbour porpoises ( Phocoena phocoena) from western European seas: Geographical trends, causal factors and effects on reproduction and mortality

Concentrations of polychlorinated biphenyls (PCBs) in blubber of female common dolphins and harbour porpoises from the Atlantic coast of Europe were frequently above the threshold at which effects on reproduction could be expected, in 40% and 47% of cases respectively. This rose to 74% for porpoises from the southern North Sea. PCB concentrations were also high in southern North Sea fish. The average pregnancy rate recorded in porpoises (42%) in the study area was lower than in the western Atlantic but that in common dolphins (25%) was similar to that of the western Atlantic population. Porpoises that died from disease or parasitic infection had higher concentrations of persistent organic pollutants (POPs) than animals dying from other causes. Few of the common dolphins sampled had died from disease or parasitic infection. POP profiles in common dolphin blubber were related to individual feeding history while those in porpoises were more strongly related to condition.

Adaptation of reef and mangrove sponges to stress: evidence for ecological speciation exemplified by Chondrilla caribensis new species (Demospongiae, Chondrosida)

Sponges (Porifera) in mangroves have adapted to a wide range of environmental parameters except for extended periods of exposure to freshwater or air. Many marine mangrove islands are located in the shallow backwaters of coral reefs in Belize and elsewhere in the Caribbean and have a mean tidal range of only 15 cm. They are densely populated by sponges, mostly attached to subtidal red-mangrove stilt roots and peat banks lining tidal channels. Some species are endemic to mangroves, others are immigrants from nearby reefs. Mangrove endemics endure environmental hardships, such as occasional exposure to air during spring tides, temperature and salinity extremes, fine sediments, even burial in detritus. Reef immigrants into mangroves enjoy protection from spongivores that do not stray into the swamp but they eventually succumb to environmental stress. There is evidence exemplified by the common demosponge Chondrilla aff. nucula, that sponges flourishing in both mangrove and reef habitats may develop separate ecologically specialized and reproductively isolated populations. Such processes can lead to genetic modifications and thus serve as mechanisms for ecological speciation. Because Chondrilla nucula Schmidt was first described from the Mediterranean Sea, it was long suspected that the western Atlantic population may be a separate species. New morphological and molecular evidence prompt us to describe it under a new name, Chondrilla caribensis, with two ecological forms, forma caribensis from mangroves and lagoons, and forma hermatypica from open reefs.

Fatal enterocolitis in harbour seals (Phoca vitulina) caused by infection with Eimeria phocae

Coccidiosis due to Eimeria phocae infection has been described in harbour seals (Phoca vitulina) from the western Atlantic population, but not in any detail in seals from the eastern Atlantic...

Relative growth and size at first maturity of the deep water shrimp,Heterocarpus Ensifer (Decapoda, Pandalidae) from the southern Gulf of Mexico

The pandalid shrimp, Heterocarpus ensifer occurs on continental slopes over the eastern and western Atlantic, and over some portions of the Indian and Pacific oceans. Despite its wide distribution, studies on the biology of this species are scant. In particular, there is no information on morphometric relationships or reproductive issues from any western Atlantic population. Although the general morphology of males and females of H. ensifer appears similar, we hypothesized that size at the onset of sexual maturity (SOM) and sexual dimorphism of H. ensifer could be examined with morphometric analyses, using those body dimensions most commonly measured in shrimp: carapace length (CL), body length (BL), rostral length (RL), and body weight (BW). We examined 754 H. ensifer from the southern Gulf of Mexico. SOM, determined through sequential reduced major axis regressions of BL, RL, relative rostral length (RRL = RL/CL), and BW against CL, was 23-24 mm CL in females and 21-22 mm CL in males. These sizes closely matched those of the smallest ovigerous females and the smallest males with appendices masculinae. Juveniles of both sexes showed similar morphometry and allometries, but ontogenetic allometry and morphometric sexual dimorphism occurred after maturity. In particular, the positive relationship (with negative allometry) between RL and CL shown in juveniles was lost after SOM in females and changed to enantiometry in males, despite a wide dispersion of data. The rostral polymorphism may be related to the protracted, year-round reproductive activities of this Gulf of Mexico population. Morphometric techniques may be useful to compare populations of if. ensifer from disparate locations.

Reproductive biology of the school shark, Galeorhinus galeus, off Argentina: support for a single south western Atlantic population with synchronized migratory movements

synopsis We sampled school sharks, Galeorhinus galeus, in Anegada Bay, Argentina, to investigate reproductive ecology. Males dominated the catches in October and April, while females were more abundant than males from November to March. Males were estimated to mature at a smaller size (108-119 cm total length) than females (mean 125 mm total length). Differences between fecundity and fertility were not dependent on mother size. The largest embryos were found in late October and November, coinciding with ovulation. This indicates that gestation lasts about 12 months. Embryonic growth was best described by a Gompertz model. Four groups of females were recognized: (1) juveniles up to 129 cm TL, with translucent-to-white ovarian follicles; (2) mature, non-pregnant, pre-ovulatory females with yellow ovarian follicles and low gonadosomatic index (GSI); (3) mature non-pregnant ovulating females with large yellow ovarian follicles, high GSI; and (4) pregnant females carrying near term embryos, with minute ovarian follicles. These observations support a 3-year female reproductive cycle. The patterns of occurrence, reproductive condition, and embryonic growth of school sharks in northern Argentina are complementary to those from southern Brazil, supporting the hypothesis that there is a single large population of school sharks in the south western Atlantic.

High genetic homogeneity of an intertidal marine invertebrate along 8000 km of the Atlantic coast of the Americas

Phallusia nigra is a cosmopolitan solitary ascidian with a distinct niger-blue tunic that is considered to be an easy diagnostic feature, even in the field. The wide geographic distribution of this species may have been a result of the overconfidence of taxonomists and ecologists in the assignment of unknown specimens to this species, based on this simple diagnostic character. Indeed, there seems to be a correlation between cosmopolitanism and the presence of few, but very conspicuous diagnostic characters in benthic invertebrate species. Almost invariably, genetic studies have demonstrated that the cosmopolitanism of those species is artificial and that, rather, they are made up of groups of morphologically very similar, but genetically distinct, species. Thus, we decided to verify the specific status of Western Atlantic populations of P. nigra, from Miami (USA) to São Paulo (southeastern Brazil) by estimating genetic variation and population structure levels along the entire range of this ascidian in the Western Atlantic. The analysis of 10 allozyme systems shows high levels of mean heterozygosity ( H=0.28) so that P. nigra has genetic variation levels more related with other invertebrates than to their, phylogenetically closer, chordate relatives (that show lower levels of heterozygosity). The genetic structure of the population was relatively high ( F ST=0.083) for conspecific populations, but much lower than what would be expected if they belonged to different species. High levels of gene identity also indicate that the Western Atlantic population of P. nigra constitutes a single species. This result suggests an extremely high dispersal capability of the larvae of this ascidian or a relatively recent range expansion of its populations. Since this species is commonly found in harbors, the anthropogenic transport (p.e., in ballast water) may have contributed for the observed genetic homogeneity.

A Commentary on Western Atlantic Bluefin Tuna Assessments

Abstract Intense fishing for bluefin tuna Thunnus thynnus in the western Atlantic Ocean began in the 1960s, when landings peaked at nearly 20,000 metric tons (mt). During the 1970s, landings averaged about 5,000 mt. The International Commission for the Conservation of Atlantic Tunas (ICCAT) established a total allowable catch (TAC) of 1,160 mt in 1982 and has set limits ranging from 1,995 to 2,660 mt annually since. The Commission's assessments indicate that unrestricted fishing through the 1960s and 1970s resulted in a sharp decline in abundance, primarily because heavy fishing on young fish wasted potentially good recruitment. Since the late 1980s, ICCAT management has stabilized the western Atlantic population, and recently there are signs of improvement. Resource assessments and management of western Atlantic bluefin tuna are subjects of severe controversy. Two of the most controversial issues are the stock assessment implications of fish migrations between the western and eastern Atlantic management ...

Progenesis in Late Eocene populations of Subbotina linaperta (Foraminifera) from the western Atlantic

It has been argued that the successive appearance of a distinct set of test morphologies by planktic foraminifera represents evidence for the multiple evolution of mechanical optima ( Steineck and Fleisher, 1978). However, morphometric, isotopic and biostratigraphic analyses of the globigerine species Subbotina linaperta from Middle-Late Eocene Atlantic Ocean deep sea cores suggests that changes in developmental pathways may also play an important role in planktic foraminiferal evolution. During a period of prolonged and global change in the Middle-Late Eocene marine environment, at least one western Atlantic population of S. linaperta was characterized by a marked decrease in mean test size that persisted throughout the remainder of this species' teilzone. In addition, this Late Eocene population exhibited anomalous relative abundances and a pronounced change in depth habitat when compared to conspecific populations in the Gulf of Mexico and South Atlantic. Quantitative morphometric analyses indicate the observed size reduction to be a secondary result of selection for the ontogenetically accelerated attainment of sexual maturity; a mode of developmentally mediated evolution termed progenesis. The temporal persistence of this progenetically dwarfed population throughout the remainder of the Late Eocene at this locality serves to illustrate the potential of this evolutionary mechanism to produce sustained morphological and ecological changes within populations of marine plankton as well as implying that this population was at least partially isolated from the general circulation of the Gulf Stream during this time interval. In addition, similarities between the nature of phenotypic change in this population and the common anecdotal observation of test size reduction in a number of planktic foraminiferal lineages at the Cretaceous-Tertiary boundary and during the Paleogene-Neogene faunal transition suggest that selection for different developmental patterns may provide an alternative explanation for the reappearance of simple globigerine morphotypes after major planktic foraminiferal extinction events.