Marine Invertebrate Assemblages Research Articles

Species diversity, trophic structure, and taxonomic distinctness of molluscan assemblages associated with Sargassum beds in a historically impacted bay

AbstractAnthropogenic impacts on coastal habitats can result in alterations of diversity parameters in marine invertebrate assemblages. Macroalgae beds are highly susceptible to human‐induced disturbances, supporting a great diversity of molluscan species and being ecologically important for coastal ecosystems. This study investigates the diversity alterations on Sargassum‐associated molluscan assemblages from areas with different distances from a main source of pollution within a historically impacted bay in Brazil. In general, sites closer to the pollution source presented lower species diversity, trophic diversity, and taxonomic relatedness among species. Beta diversity among assemblages was highly correlated with environmental differentiations among localities due to heavy metal concentrations in algal tissue. Bittiolum varium was the dominant species and was mainly responsible for differences in community parameters. Several trophic groups were well‐represented in Sargassum‐associated molluscan fauna, but assemblages were mostly dominated by micrograzers. A seasonal trend was observed in diversity alterations, with lower diversity during warm season at most sites except Santa Rita, possibly because it is the site less affected by human impacts. The importance of other environmental variables, such as hydrodynamism, for molluscan composition is also discussed. Our results highlight the potential of Sargassum‐associated molluscan assemblages for the study of impacted areas and reinforce the importance of using multiple community metrics to understand the biodiversity patterns of marine invertebrates under anthropogenic impacts.

Diversity patterns of Middle Permian gastropod assemblages from the Tak Fa Formation, Central Thailand

Middle Permian marine invertebrate assemblages from Central Thailand are strongly dominated by gastropods. Two gastropod assemblages from the Tak Fa Limestone at Khao Noi and Khao Chao Thong of the Nakhon Sawan area are the first Permian ones from Thailand that are analysed regarding diversity and composition based on quantitative data. Both gastropod assemblages, comprising 40 species in total, are dominated by the gastropods Anomphalus sp., Warthia cf. brevisinuata and Glabrocingulum magnum; the genus Anomphalus is especially abundant which is unusual for Permian assemblages. Both studied gastropod assemblages have a similar taxonomic composition and diversity including the same values of diversity indices that indicate a moderate diversity. In addition, rarefaction analyses and rank-abundance distributions also suggest that diversity and structure of both assemblages are the same. The studied assemblage is compared with other Permian gastropod assemblages from Asia (Malaysia, East Timor and Japan). Rarefaction, diversity indices and rank-abundance distributions suggest that the diversity of the studied fauna is distinctly lower than that of the others despite coming from similar depositional environments. This is surprising because the Tak Fa gastropods lived at lower latitudes than the others. This could suggest an inverse diversity gradient in the Palaeo-Tethys, but more evidence is needed to substantiate this assumption. Several Late Palaeozoic and Early Mesozoic fossil assemblages are dominated by gastropods, e.g. those from the Pennsylvanian Buckhorn Asphalt deposit, the Permian from Japan and Malaysia, as well as the Late Triassic Cassian Formation. This shows that at least locally, gastropod dominance is not restricted to modern faunas.

Palaeoecology of tropical marine invertebrate assemblages from Misurina (Late Triassic; Dolomites, Italy)

Palaeoecology of tropical marine invertebrate assemblages from Misurina (Late Triassic; Dolomites, Italy)

The influence of collection method on paleoecological datasets: In-place versus surface-collected fossil samples in the Pennsylvanian Finis Shale, Texas, USA.

There are multiple common methods for collecting fossil material in the field for paleoecological analyses, so it is important to determine if and how different methods may affect the similarities and differences among taxonomic samples. Here, we evaluate the influence of two fossil collection field methods (stratigraphically in-place bulk-sediment versus picking up weathered-out fossils from the ground surface) on paleoecological results, using the Pennsylvanian marine invertebrate assemblages of the Finis Shale in Texas. Based on an informal review of recent paleoecology papers, we observed that the lithology of the study material and the nature of the research question correspond to choice of field collection protocols; however, collection protocols are not always clearly explained or justified in the text of the papers. For the present case study, we collected stratigraphically equivalent samples from three outcrops using both the surface pick-up and in-place bulk sediment methods. We found a difference in the abundance and composition of paleocommunities between these two collection methods. Evidence to support this includes the significant differences between samples using PERMANOVA (p < 0.001), the clear separation in ordination space of samples clustered by sampling method, the significantly higher richness in the surface samples (p < 0.001), and the considerable variation in relative abundances of various taxa and taxonomic groups. Richness and evenness were higher among the surface-collected samples, possibly due to collector bias, weathering artifacts, or spatial and temporal variability. Paleontologists strive to do the best science possible with the material available. Often, paleoecological research methods are limited by time, funding, or the nature of the material. In such cases, we recommend examining both collection methods, even if for only a fraction of the sampling. If only one method is possible, we recommend the use in-place, bulk-collected samples.

Marine collections and global digital repositories as source data to assess the effects of habitat condition and biodiversity loss on African Coastal ecosystem functioning and services

Natural history collections (NHC) worldwide contain vast amount of valuable data that can be used to answer a wide range of questions by exploring biodiversity and natural resources records, having an immense potential to contribute to science, policy making and legislating, and to public scientific awareness. Likewise, the development and increase of global and regional biodiversity digital databases (e.g., Global Biodiversity Information Facility - GBIF; Fauna Europaea; Naturdata, etc.), scientific literature and all digital information regarding biodiversity, ecological areas and climate records comprise a huge amount of primary and processed digital ecological data (DED) accessible globally that can be readily used, at no cost, and integrated to further study e.g. biodiversity changes, ecological processes, natural habitat distribution, prioritizing ecosystem management and conservation actions, etc. Marine invertebrate biodiversity contributes to the structure and stability of ecosystem processes such as productivity, ecological networks, as well as nutrient and biogeochemical cycling having also an economic importance as a food source for local populations. Mangroves and seagrasses encompass ecological and socio-economic relevance as they have a preponderant role in marine and coastal ecosystem biodiversity and functioning providing a vast number of goods and services to local populations. Although generally pristine, mangroves and seagrasses in Africa are extremely vulnerable to the increased migration of rural populations to urban coastal areas and to extreme climate events. As a result, human activities such as construction, agriculture and food harvesting, provoke habitat degradation and biodiversity loss which will have further devastating consequences. The degradation and unsustainable use of these ecosystems have major drawbacks to the elimination of extreme poverty because this is one of the key factors that drive environmental degradation and biodiversity loss. The main goal of this work is to use NHC and digital repositories data (including scientific literature) to assess how biodiversity loss and habitat degradation affect ecosystem functioning and services provided by marine invertebrate communities of mangroves and seagrass meadows in the West and East African coast, using the case study of Mozambique and Príncipe’s Island. These will lead to the construction of a comprehensive dataset, an ecological model and a framework adapted to marine invertebrate biodiversity from Mozambique’s (MZ) and São Tomé and Príncipe’s (STP) mangroves and seagrasses as tools:1) integrate and disseminate marine invertebrate biodiversity data gathered along a spatio-temporal scale; 2) compare marine invertebrate assemblies from pristine and impacted habitats in African countries and predict the progress of these communities to habitat degradation and biodiversity loss; and 3) manage ecosystem functioning and services delivered by marine invertebrate assemblages under anthropogenic and environmental pressure scenarios. Specifically this project intends to: compile and integrate the available information contained in NHC and DED to develop a comprehensive spatio-temporal dataset on marine invertebrate biodiversity (e.g. species, number of individuals, local of occurrence and georeferencing, date of collection/observation), as well as mangroves and seagrasses distribution along the Mozambique’s and Príncipe’s coasts; assess different indexes of invertebrate marine biodiversity, biodiversity and habitat spatio-temporal distribution; develop an ecological network approach to assess the functional links of marine invertebrate communities within the studied habitats, and to refine their role in ecosystem functioning, as well as ecosystem services (ES) provided by marine invertebrates in mangroves and seagrasses from MZ and STP; construct a model to evaluate the ecological responses of mangrove and seagrass invertebrate communities to habitat degradation and biodiversity loss and to predict multi-dimensional (spatial, temporal, and social) trade-offs in local/regional ecosystem services along a spatio-temporal gradient; develop a practical framework to manage and preserve ecosystem functioning and services delivered by mangrove and seagrass marine invertebrates under a global change scenario. compile and integrate the available information contained in NHC and DED to develop a comprehensive spatio-temporal dataset on marine invertebrate biodiversity (e.g. species, number of individuals, local of occurrence and georeferencing, date of collection/observation), as well as mangroves and seagrasses distribution along the Mozambique’s and Príncipe’s coasts; assess different indexes of invertebrate marine biodiversity, biodiversity and habitat spatio-temporal distribution; develop an ecological network approach to assess the functional links of marine invertebrate communities within the studied habitats, and to refine their role in ecosystem functioning, as well as ecosystem services (ES) provided by marine invertebrates in mangroves and seagrasses from MZ and STP; construct a model to evaluate the ecological responses of mangrove and seagrass invertebrate communities to habitat degradation and biodiversity loss and to predict multi-dimensional (spatial, temporal, and social) trade-offs in local/regional ecosystem services along a spatio-temporal gradient; develop a practical framework to manage and preserve ecosystem functioning and services delivered by mangrove and seagrass marine invertebrates under a global change scenario.

Environmental controls on shallow subtidal molluscan death assemblages on San Salvador Island, The Bahamas

Ecological studies that span multiple marine depositional environments frequently find that benthic invertebrate assemblages are correlated primarily with an onshore-offshore gradient. Variability within the same depositional environment is inferred to not result from water depth differences, but other parameters such as substrate consistency and shear stress. Modern studies focusing on assemblage variations within the same depositional environment can identify which variables affecting assemblage compositions are independent of water depth. This study examines the environmental controls on the composition of molluscan death assemblages from the shallow subtidal environments of San Salvador Island. Molluscan assemblages were tabulated from twenty-nine bulk samples collected from four locations around San Salvador Island representing seagrass meadows, open sandflats, and patch reef systems common in the shallow subtidal. In addition, quantitative environmental data for each sample was characterized, including seagrass density, water depth, temperature, pH, dissolved oxygen, and grain-size, as well as qualitative observations of wave energy and bioturbation. Cluster analysis and canonical correspondence analysis (CCA) were performed to identify environmental gradients associated with molluscan assemblage composition. Cluster analysis and CCA Axis 1 identify seagrass coverage and substrate consistency as the primary environmental variables describing molluscan death assemblage compositions. CCA Axis 2 identifies wave energy, bioturbation, and dissolved oxygen as the secondary environmental variables, though the small range of dissolved oxygen values (17–21 mg/L) collected using single, instantaneous measurements make it unclear whether the oxygen gradient is ecologically significant for our time-averaged assemblages. Our analysis demonstrates the variability of assemblages within a single depositional environment, as well as the utility of fine-resolution studies for identifying secondary environmental variables that control the composition of marine invertebrate assemblages.

Influence of setting, sieve size, and sediment depth on multivariate and univariate assemblage attributes of coral reef-associated mollusc death assemblages from the Gulf of Aqaba

Measures of diversity and ecology of marine invertebrate assemblages depend on a variety of factors including environmental conditions and methodological decisions. In this study, the influence of such factors on multi- and univariate assemblage parameters of molluscan death assemblages from the Gulf of Aqaba (Red Sea, Jordan) was evaluated. Sediment samples were collected at two coral reef types, a patch reef at 13 m of water depth characterized by fine-grained sediments and a Millepora-fringing reef with coarse-grained sediments at 5 m of water depth. The upper and lower 10 cm of the sediment column were separately removed and sieved with mesh sizes of 1 and 2 mm. A large dataset of 6400 bivalve and gastropod shells was compiled to evaluate how setting, sediment depth, and sieve size influenced taxonomic composition and species richness, species-abundance patterns and the Shannon–Wiener index, the number of drilled shells per species and drilling frequency (DF) of the assemblage. Setting had the strongest impact on all aspects, followed by sieve size, but sediment depth was insignificant, probably due to complete homogenization of the sediments by reworking and bioturbation. Multivariate assemblage parameters distinguished much better between categories (setting, sieve size) than univariate measures. Sieve size-related disagreements recognized between the two higher taxa are mostly due to the underlying difference in body-size distribution of bivalve and gastropod assemblages. We conclude that species richness and other ecological characteristics of molluscan death assemblages in coral reef-associated sediments will most strongly reflect habitat complexity of the sites chosen, are significantly influenced by methodological decisions (i.e., sieve size), will only poorly preserve temporal patterns, and the results will differ between bivalves and gastropods.

The rise of ocean giants: maximum body size in Cenozoic marine mammals as an indicator for productivity in the Pacific and Atlantic Oceans.

Large consumers have ecological influence disproportionate to their abundance, although this influence in food webs depends directly on productivity. Evolutionary patterns at geologic timescales inform expectations about the relationship between consumers and productivity, but it is very difficult to track productivity through time with direct, quantitative measures. Based on previous work that used the maximum body size of Cenozoic marine invertebrate assemblages as a proxy for benthic productivity, we investigated how the maximum body size of Cenozoic marine mammals, in two feeding guilds, evolved over comparable temporal and geographical scales. First, maximal size in marine herbivores remains mostly stable and occupied by two different groups (desmostylians and sirenians) over separate timeframes in the North Pacific Ocean, while sirenians exclusively dominated this ecological mode in the North Atlantic. Second, mysticete whales, which are the largest Cenozoic consumers in the filter-feeding guild, remained in the same size range until a Mio-Pliocene onset of cetacean gigantism. Both vertebrate guilds achieved very large size only recently, suggesting that different trophic mechanisms promoting gigantism in the oceans have operated in the Cenozoic than in previous eras.

Eurydesma–Lyonia fauna (Early Permian) from the Itararé group, Paraná Basin (Brazil): A paleobiogeographic W–E trans-Gondwanan marine connection

Here, the biocorrelation of the marine invertebrate assemblages of the post-glacial succession in the uppermost portion of the Late Paleozoic Itararé Group (Paraná Basin, Brazil) is for the first time firmly constrained with other well-dated Gondwanan faunas. The correlation and ages of these marine assemblages are among the main controversial issues related to Brazilian Gondwana geology. In total, 118 brachiopod specimens were analyzed, and at least seven species were identified: Lyonia rochacamposi sp. nov., Langella imbituvensis (Oliveira),? Streptorhynchus sp.,? Cyrtella sp., Tomiopsis sp. cf. T. harringtoni Archbold and Thomas, Quinquenella rionegrensis (Oliveira) and Biconvexiella roxoi Oliveira. The presence of Tomiopsis sp. cf. T. harringtoni and the bivalve Atomodesma (Aphanaia) orbirugata (Harrington) in the Teixeira Soares beds plus Myonia argentinensis (Harrington) and Heteropecten paranaensis Neves et al., both of which recorded in deposits in the Teixeira Soares and Mafra beds (Butiá), suggests a biocorrelation with the Eurydesma fauna from the Bonete Formation, Sauce Grande-Colorado Basin, Argentina. Furthermore, the presence of Lyonia Archbold and Praeundulomya cf. subelongata Dickins in the Taciba Formation indicates affinities with deposits in the Lyons Group, Carnarvon Basin, and the Fossil Cliff Member, Perth Basin (Western Australia), suggesting a late Asselian–early Sakmarian age. Even more importantly, the collected data suggest the existence of an W–E trans-Gondwanan marine seaway between the Paraná (Brazil), Sauce Grande-Colorado (Argentina), Huab (Hardap shale of the Dwyka Group, Aranos area, Namibia, southwest Africa), the Carnavon (Western Australia) basins, and beyond eastward to the Cimmerian region. A V proto-rift system through two major axes of extensional basin development facilitated the W–E marine connection. Main axes formed by a north-northwesterly trending axis paralleling the future South Atlantic and a broadly north-northeasterly trending line of separation related to the future Indian Ocean. This proto-rift system coupled with a sea-level rise of at least 100m, favored the establishment of a long narrow shallow seaway, allowing the exchange of Eurydesma fauna between eastern and western Gondwana.

Biodiversity of an unknown New Zealand habitat: bathyal invertebrate assemblages in the benthic boundary layer

For the first time in New Zealand waters, marine invertebrate assemblages from the benthic boundary layer were sampled as part of a broad scale national biodiversity programme, Ocean Survey 2020. Macrobenthic assemblages were collected from ∼1 m above the seafloor at 16 sites on the Chatham Rise and five sites on the Challenger Plateau to the east and west of New Zealand. Depths ranged from 218 to 1,239 m. Nearly 80 000 individual organisms were caught and identified to 33 higher taxonomic groups. Taxa of the supra- and epibenthos as well as taxa with suprabenthic affinities were encountered. Relative abundance and taxonomic richness of the invertebrates between the Chatham Rise and the Challenger Plateau were compared. The crustacean superorder Peracarida proved to be a good group to be representative for abundance patterns of the benthic boundary layer. The peracarid order Tanaidacea was identified to species level, showing high species richness, with 77% of the species being new to science. The observed high levels of biodiversity and high abundances, particularly of copepods and peracarid crustaceans, suggest that this component of the marine fauna, in the benthic boundary layer plays a significant role in ecosystem functioning of New Zealand waters.

Carcasses on the coastline: measuring the ecological fidelity of the cetacean stranding record in the eastern North Pacific Ocean

To understand how well fossil assemblages represent original communities, paleoecologists seek comparisons between death assemblages and their source communities. These comparisons have traditionally used nearshore, marine invertebrate assemblages for their logistical ease, high abundance, and comparable census data from living communities. For large marine vertebrates, like cetaceans, measuring their diversity in ocean ecosystems is difficult and expensive. Cetaceans, however, often beach or strand themselves along the coast, and archived data on stranded cetaceans have been recorded, in some areas, over several decades. If the stranding record is interpreted as a death assemblage, then the stranding record may represent a viable alternative for measuring diversity in living communities on directly adjacent coastlines. This study assessed the fidelity of the cetacean stranding record in the eastern North Pacific Ocean. The living community in this region has been studied for over 100 years and, recently, extensive and systematic live transect surveys using ship-based observing platforms have produced a valuable source of live diversity data. Over this same period, the U.S. Marine Mammal Stranding Program has collected and archived a record of cetacean strandings along the U.S. Pacific coastline, providing an ideal death assemblage for comparison. Using fidelity metrics commonly used in marine invertebrate taphonomy, I determined that the stranding record samples the living cetacean community with high fidelity, across fine and coarse taxonomic ranks, and at large geographic scales (&gt;1000 km of coastline). The stranding record is also richer than the live surveys, with live-dead ratios between 1.1 and 1.3. The stranding record recovers similar rank-order relative abundances as live surveys, with statistical significance. Also, I applied sample-based rarefaction methods to generate collector's curves for strandings along the U.S. Pacific Coast to better evaluate the spatiotemporal characteristics of the stranding record. Results indicate that saturation (i.e., sampling &gt;95% assemblage) at species, genus, and family levels occurs in less than five years of sampling, with families accumulating faster than species, and larger geographic regions (i.e., longer coastlines) accumulating taxa the most rapidly. The high fidelity of the stranding record, measured both in richness and by ranked relative abundance, implies that ecological structure from living cetacean communities is recorded in the death assemblage, a finding that parallels marine invertebrate assemblages, though at far larger spatial scales. These results have implications for studying cetacean ecology in both modern and ancient environments: first, these results imply that the stranding record, over sufficiently long time intervals, yields a richer assemblage than using line-transect methods, and faithfully records aspects of community structure; and second, these results imply that geochronologically well-constrained fossil cetacean assemblages might preserve ecologically relevant features of community structure, depending on depositional and taphonomic conditions.

The impact of lithification on the diversity, size distribution, and recovery dynamics of marine invertebrate assemblages

Lithified marine sediments are not equitably distributed through time, raising the possibility that lithification masks biological signals when data from unlithified and lithified sediments are compared or combined. Using mollusk-dominated assemblages from the early Cenozoic of the Gulf Coastal Plain, we find that lithification conceals small taxa, decreases taxonomic resolution, and exacerbates the undersampling of rare taxa. Lithified assemblages appear less diverse and have less even abundance distributions than coeval unlithified samples. These limitations cannot be overcome by standardization procedures, nor are they likely to be circumvented by collecting larger samples. The effects of this bias, however, can be mitigated by restricting analyses to a single lithification state or to specific size classes. Since lithification selectively obscures small taxa, the magnitude of this bias will be most severe when organisms are particularly small, such as in the aftermath of mass extinctions. In the study area, lithification artificially protracts the recovery period following the Cretaceous-Paleogene mass extinction by ~7 m.y.

Marine biogeographical structure in two highly dispersive gastropods: implications for trans‐Tasman dispersal

AbstractAim Recent genetic and ecological studies of marine invertebrate species with planktotrophic larvae have inferred high rates of gene flow across wide oceanic barriers. We therefore aim to test for the genetic signature of long‐distance dispersal in two widespread and abundant marine gastropod taxa.Location The intertidal and shallow subtidal zones of southern Australia and New Zealand (NZ), which house similar marine invertebrate assemblages despite being separated by the 2000‐km‐wide Tasman Sea.Methods We used mtDNA cytochrome oxidase I gene sequence analysis of two gastropod genera exhibiting trans‐Tasman distributions, namely Austrolittorina (Littorinidae) (139 specimens; 28 localities) and Scutus (Fissurellidae) (154 specimens; 32 localities). The cool‐temperate Australian (A. unifasciata; S. antipodes) and NZ (A. antipodum; S. breviculus) taxa within each genus are morphologically similar but of uncertain taxonomic status.Results The mtDNA analyses indicate major trans‐Tasman genetic discontinuities for both gastropod genera, with no evidence of recent or ongoing intercontinental gene flow. Although both Scutus and Austrolittorina show significant east–west structure within southern Australia – consistent with recent studies of regional marine phylogeography – neither taxon exhibits significant differentiation within NZ.Main conclusions Morphologically conserved but biogeographically disjunct gastropod populations may exhibit striking phylogeographic discontinuities, even when dispersal abilities appear to be high. On the basis of these data we reject recent calls for the synonymy of NZ and Australian lineages.

Marine invertebrate assemblages from the Late Pennsylvanian (Virgilian) Holder Formation, Dry Canyon, Sacramento Mountains, south-central New Mexico

Marine invertebrate assemblages from the Late Pennsylvanian (Virgilian) Holder Formation, Dry Canyon, Sacramento Mountains, south-central New Mexico

DIRECT AND INDIRECT EFFECTS OF REPEATED POLLUTION EVENTS ON MARINE HARD-SUBSTRATE ASSEMBLAGES

Testing the effects on organisms of a constant exposure to toxicants in uniform environments is unlikely to reflect accurately the majority of toxicant exposures in the field, and environmental managers need tools to help predict impacts especially of pulse toxicant inputs into highly variable natural environments. We investigated the effect of pulse copper pollution events on the development of sessile marine invertebrate assemblages at two sites in Port Phillip Bay, Victoria, Australia. Using a field dosing technique we created localized 2-d copper pollution events close to settlement plates. Pulses were delivered every 2, 4, 8, or 16 wk for the duration of the 16-wk experiments, and the assemblages allowed to develop under these dosing regimes. Pulse pollution events dramatically altered the assemblages at both sites predominantly through a direct negative effect on the densities of large space-occupying tunicates. Most other taxonomic groups responded positively to multiple copper pulses, which was considered a density-mediated indirect effect of the toxicant. In particular, organisms known to be good colonizers but poor competitors for space such as serpulid polychaetes occurred in densities an order of magnitude higher on plates exposed to copper pulses. The responses of the assemblages were predominantly independent of the frequency of pulse pollution events, although a single pulse exposure at the beginning of the experiment had no observable effect when censused at week 16. The impact of these transient pollution events were manifest as changes in the structure of invertebrate assemblages and could persist for some time after the agent of disturbance was removed. The effects of a single pulse copper pollution event on an established (8-wk-old) assemblage were evident for at least a further 8 wk after it occurred.

Stratigraphy and paleoceanography of Pliocene deposits of Karaginsky Island, eastern Kamchatka, U.S.S.R.

The lithology and paleontology of Pliocene deposits from Karaginsky Island, off eastern Kamchatka Peninsula, U.S.S.R., are described in order to provide a paleoceanographic reconstruction of this region of the eastern North Pacific Ocean. The stratigraphic sequence is divided into three suites — the Limimtevayamian, the Ust-Limimtevayamian, and the Tusatuvayamian, which correspond to three standard Pacific diatom zones — the Thalassiosira oestrupii, Neodenticula koizumi-N. kamtschatica, and N. koizumi. The entire sequence is further subdivided into six members and 18 distinct beds on the basis of molluscan assemblages and three members and seven beds on the basis of benthic foraminiferal assemblages. Marine ostracodes are described from the Limimtevayamian suite. The marine invertebrate assemblages from Karaginsky Island provide evidence that: (1) ocean water temperatures were warmer than today about 4 Ma and again about 3.5-3.0 Ma; (2) several Arctic-Atlantic species of molluscs and ostracodes migrated to the eastern North Pacific between 4.2−3.0 Ma, presumably through the proto-Bering Strait; (3) many species found in the Karaginsky Island Pliocene represent Pacific taxa which migrated through the Arctic into the North Atlantic during the late Pliocene.