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Recent New Zealand shallow-water benthic foraminifera: Taxonomy, ecologic distribution, biogeography, and use in paleoenvironmental assessment

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  • Geomarine Research

Abstract

ABSTRACT Ecologic distribution of brackish water foraminifera Census data on 89 species of benthic foraminiferal tests from 131 samples from brackish water environments throughout New Zealand are analysed by cluster and correspondence analyses. Ten brackish water faunal associations are recognised. When mapped in study areas they can be seen to inhabit distinct estuarine and tidal inlet environments. The associations are characterised by Trochamminita salsa, Haplophragmoides wilberti, Trochammina inflata, Jadammina macrescens, Miliammina fusca, Elphidium excavatum and Ammonia parkinsoniana, on their own or in combinations. Canonical correspondence analysis indicates that the factors most influential in determining the faunal distribution in brackish environments are, in descending order of importance: salinity, tidal exposure, and presence of intertidal vegetation. Associations characterised by agglutinated species occur in the more extreme brackish water environments - in the least saline environments and also above mean high water. Ecologic distribution of normal marine salinity foraminifera Census data on 327 species of benthic foraminiferal tests from 197 samples from shallow water (<100 m), normal marine environments around New Zealand are analysed by cluster and correspondence analyses. Eighteen faunal associations inhabiting distinct coastal environments are recognised. The associations are characterised by various combinations of species of Elphidium, Haynesina, Pileolina, Rosalina, Gaudryina, Notorotalia, Planoglabratella, Quinqueloculina, Cibicides, Zeaflorilus, Virgulopsis, Patellinella, Nonionellina, Trifarina, Bulimina and Cassidulina. Canonical correspondence analysis indicates that the following factors in decreasing order of importance are most influential in determining the faunal distribution in normal marine environments: factors linked to depth, factors linked to wave and current energy, factors linked to biogeography, bottom water oxygen concentrations and substrate type. Taxonomy 419 species are listed from shallow water (<100 m) around New Zealand. The 233 most common or distinctive species are fully illustrated and their diagnostic features outlined. Four new species are described: Glabratellina kermadecensis n.sp., Neoconorbina cavalliensis n.sp., Pileolina gracei n.sp. and Notorotalia hornibrooki n.sp.. Frequency of species occurrence To assess species frequency, species duration and biogeography, we used a data set containing the presence/absence records of 353 species in 50 composite shallow water localities from around the New Zealand region. The frequency of species occurrence follows a log series curve with 35% of the species occurring rarely (1-2 localities) and 20% occurring commonly (>16 localities). Rotaliinid species have the greatest frequency of occurrence (35% are common), whereas lageninids and textulariinids have the greatest number of rare species (44%, 55%). Unlike reported North American results, there appears to be no significant difference in the percentage of endemic or cosmopolitan species that are rare or common. Species duration 128 Recent benthic species (36%) have a recorded New Zealand fossil record (50% of rotaliinids, <35% of other suborders). One species first appears in each of the late Cretaceous and Paleocene, 22 in Eocene, 25 in Oligocene, 67 in Miocene, 14 in Pliocene, 4 in Pleistocene, with major influxes in the latest Eocene-early Oligocene, and early Miocene (31 species each). Species with a fossil record have a mean partial species duration of 21 m.yrs. Deeper water species (live dominantly >100 m) have a longer mean duration (24 m.yrs.), than dominantly shallow species (20 m.yrs.) or brackish species (9 m.yrs.). Commonly occurring species have a far greater percentage with a fossil record (55%) than rarely occurring species (19%). Contrary to findings elsewhere, the rarely occurring species with a fossil record have a longer mean duration (27 m.yrs.) than the intermediate class (21.5 m.yrs.) and the common class (15.5 m.yrs.). 66% of the 50 endemic New Zealand species have a fossil record (mean duration 14 m.yrs.), whereas only 40% of the 180 cosmopolitan species have a New Zealand fossil record (mean duration 25 m.yrs.). Biogeography Fifty percent of our species are cosmopolitan, 14% endemic and 10% have a South-west Pacific distribution. All 21 brackish-restricted species are cosmopolitan. There is one endemic genus (Zeaflorilus) and one third of the endemic species belong to three genera - Notorotalia (6 spp.), Pileolina (5 spp.) and Quinqueloculina (5 spp.). New Zealand appears to be the centre of greatest diversity for the former two genera. 38% of the endemic species occur commonly around New Zealand with many as characterising species of faunal associations - Spiroplectinella proxispira, Elphidium novozealandicum, Nonionellina flemingi, Notorotalia finlayi, Pileolina zealandica, Virgulopsis turris, Zeaflorilus parri. All the New Zealand brackish and mid shelf faunal associations occur overseas, but 13 of the 16 normal marine salinity, inner shelf associations appear to be restricted to New Zealand. Most endemic species are widespread around New Zealand with just 6 having distributions restricted to a single province - Glabratellina kermadecensis (Kermadecian), Discorbinella deflata (Moriorian), Fissurina baccata, Elphidium excavatum f. oirgi, Pileolina calcarata, P. harmeri (Aupourian). A simplified version of the composite locality presence/absence data set on New Zealand’s normal marine, shallow water foraminifera was analysed by clustering Jaccard coefficients. Six mappable biogeographic provinces were identified from the resulting dendrogram - Kermadecian, Aupourian (north-east North Island), New Zealand (most of the three main islands), Fiordland, Moriorian (Chatham Islands) and Antipodean (Subantarctic Islands). These foraminiferal provinces are closely similar to the classic, molluscan-defined marine provinces, except that the classic Cookian and Forsterian Provinces are combined into the New Zealand Province and a separate Fiordland Province is recognised. Another minor difference is that the Far North and Waitemata Harbour are excluded from the foraminiferal Aupourian province and group with the New Zealand Province. The number of shallow water benthic foraminiferal species present in the Fiordland and outlying island provinces is considerably fewer than in the two mainland provinces, because of less extensive study, reduced range of habitats, less likelihood of successful trans-oceanic dispersal (islands), young age of island group (Kermadecian), or cooler water (Fiordland, Antipodean). Diversity decreases from north to south in the well-studied mainland provinces, with 304 species in Aupourian and 270 in the New Zealand. Thirty warm, shallow-water species are restricted to the Aupourian Province, which is strongly influenced by the warm East Auckland Current, and a further 8 species are restricted to the Aupourian plus the Kermadecian. Few species are restricted to the other provinces - Kermadecian (6), New Zealand (9), Fiordland (0), Moriorian (1) and Antipodean (0). The pattern of brackish water foraminiferal biogeography in New Zealand differs from that of the normal marine species and appears to be more similar to that displayed by terrestrial plants and animals. Dispersal Our results show that there are two groups of shallow water foraminiferal species. One group has been able to rapidly disperse widely around the world, crossing oceanic barriers of up to 1500 km width (Tasman Sea), whereas the other group (including the New Zealand endemics) have not successfully dispersed to other countries. Transport on the feet or feathers of migratory wading seabird is postulated as the most likely dispersal mechanism for the cosmopolitan brackish foraminiferal fauna. Trans-oceanic current transport of suspended juveniles is the most favoured dispersal mechanism for the majority of the widespread normal marine, shallow water species, possibly assisted at times by “island-hopping” across the wider oceanic barriers. We infer from their modern New Zealand distribution patterns that three species (Elphidium vellai, Virgulinella fragilis, Siphogenerina raphana) have been introduced in ships’ ballast water within the last century or so. A fourth (Spiroloculina carinata) may also but is less certain. Paleoenvironmental assessment A multiplicity of physical and biological factors determine the modern ecologic distribution patterns of foraminifera. The correlation of some of these factors with the presence or abundance of certain foraminiferal taxa or associations has been documented in modern faunas and may be used to assess the paleoenvironment of fossil foraminiferal faunas. The validity of this uniformitarian approach is largely accepted for the Quaternary and Neogene but becomes less reliable going back in time through the Paleogene and Cretaceous. Fossil foraminiferal faunas can provide assessments, at varying levels of accuracy, of a number of paleoenvironmental factors of value to geological, paleoclimatic and paleoceanographic studies. Planktic foraminiferal percentage, maximum size, encrustation, diversity, coiling ratios and taxonomic census data can be used to estimate oceanicity and paleotemperature and to give an indication of water depth. Benthic foraminiferal diversity and composition by suborder sometimes provide a general indication of the past environment, but the benthic taxonomic composition and recognition of faunal associations allow more detailed assessments of water depth, intertidal level, salinity, exposure to water turbulence, bottom oxygen concentrations, water temperature and carbon flux. Charts and tables summarising the correlation between modern foraminifera and a number of these factors are presented to assist in paleoenvironmental assessments. Post-mortem faunal changes, such as test breakdown, dissolution, winnowing, bed-load transport and reworking, can modify the composition of foraminiferal faunas and affect paleoenvironmental assessments. These changes may be recognised by study of the preservational state and test size distribution and composition of the benthic foraminifera and be useful in refining the paleoenvironmental assessment. A method for rapid paleoenvironmental assessment of individual fossil faunas is outlined, based largely on an estimate of the planktic percentage and identification of the dominant benthic taxa or faunal association. Keywords. Foraminifera; shallow water; brackish environments; shelf environments; systematics; species frequency; species duration; dispersal mechanisms; biogeography; benthic foraminiferal associations; ecologic distribution; paleoenvironmental assessment; New Zealand; Cavalli Islands; Helena Bay; Waitemata Harbour; Great Barrier Island; Pauatahanui Inlet; Wanganui Bight; Queen Charlotte Sound; Oparara Inlet; Purakanui Inlet; Port Pegasus
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