Late Holocene environmental change in Celestun Lagoon, Yucatan, Mexico

Epikarst estuary response to hydroclimate change remains poorly understood, despite the well-studied link between climate and karst groundwater aquifers. The influence of sea-level rise and coastal geomorphic change on these estuaries obscures climate signals, thus requiring careful development of paleoenvironmental histories to interpret the paleoclimate archives. We used foraminifera assemblages, carbon stable isotope ratios (δ13C) and carbon:nitrogen (C:N) mass ratios of organic matter in sediment cores to infer environmental changes over the past 5300 years in Celestun Lagoon, Yucatan, Mexico. Specimens (> 125 µm) from modern core top sediments revealed three assemblages: (1) a brackish mangrove assemblage of agglutinated Miliammina and Ammotium taxa and hyaline Haynesina (2) an inner-shelf marine assemblage of Bolivina, Hanzawaia, and Rosalina, and (3) a brackish assemblage dominated by Ammonia and Elphidium. Assemblages changed along the lagoon channel in response to changes in salinity and vegetation, i.e. seagrass and mangrove. In addition to these three foraminifera assemblages, lagoon sediments deposited since 5300 cal yr BP are comprised of two more assemblages, defined by Archaias and Laevipeneroplis, which indicate marine Thalassia seagrasses, and Trichohyalus, which indicates restricted inland mangrove ponds. Our data suggest that Celestun Lagoon displayed four phases of development: (1) an inland mangrove pond (5300 BP) (2) a shallow unprotected coastline with marine seagrass and barrier island initiation (4900 BP) (3) a protected brackish lagoon (3000 BP), and (4) a protected lagoon surrounded by mangroves (1700 BP). Stratigraphic (temporal) changes in core assemblages resemble spatial differences in communities across the modern lagoon, from the southern marine sector to the northern brackish region. Similar temporal patterns have been reported from other Yucatan Peninsula lagoons and from cenotes (Nichupte, Aktun Ha), suggesting a regional coastal response to sea level rise and climate change, including geomorphic controls (longshore drift) on lagoon salinity, as observed today. Holocene barrier island development progressively protected the northwest Yucatan Peninsula coastline, reducing mixing between seawater and rain-fed submarine groundwater discharge. Superimposed on this geomorphic signal, assemblage changes that are observed reflect the most severe regional wet and dry climate episodes, which coincide with paleoclimate records from lowland lake archives (Chichancanab, Salpeten). Our results emphasize the need to consider coastal geomorphic evolution when using epikarst estuary and lagoon sediment archives for paleoclimate reconstruction and provide evidence of hydroclimate changes on the Yucatan Peninsula.

Thresholds in road network functioning on US Atlantic and Gulf barrier islands

Barrier islands predominate the Atlantic and Gulf coastlines of the USA, where development exceeds national trends. Forward-looking models of barrier island dynamics often include feedbacks with management practices – particularly those aimed at mitigating damage to buildings from natural hazards – and how real estate markets may be linked to barrier island dynamics. However, models thus far do not account for networks of infrastructure, such as roads, and how the functioning of infrastructure networks might influence management strategies. Understanding infrastructure networks on barrier islands is an essential step toward improved insight and foresight into the future dynamics of human-altered barriers. Here, we examine thresholds in the functioning of 72 US Atlantic and Gulf Coast barrier islands. We use digital elevation models to assign an elevation to each intersection in each road network. From each road network we sequentially remove intersections, starting from the lowest elevation. In each network we identify a critical intersection – and corresponding elevation – at which the functioning of the network fails, and we match the elevation of each critical intersection to local annual exceedance probabilities for extreme high-water levels. We find a range of failure thresholds for barrier island road network functioning, and also find that no single metric – absolute elevation, annual exceedance probability, or a quantitative metric of robustness – sufficiently ranks the susceptibility of barrier road networks to failure. Future work can incorporate thresholds for road network into forward-looking models of barrier island dynamics that include hazard-mitigation practices for protecting infrastructure.

An annotated checklist of the amphibians and reptiles of North Padre Island, Texas, USA, with comparisons to adjacent barrier island and mainland herpetofauna

Padre Island is the world’s longest barrier island and includes the longest stretch of undeveloped barrier island in the world. Largely due to harsh environmental conditions and difficult access, only cursory and incomplete checklists and subjective estimates of abundance have been produced. The results of an inventory of amphibians and reptiles of North Padre Island conducted 2002–2020, including the results of extensive field surveys conducted 2002–2003, are reported herein. Natural history museum and iNaturalist records are summarized and compared among North and South Padre and Mustang islands and the mainland portion of the seven counties in which the islands occur. The conservation status of rare species and extirpation of others is noted. The morphology and taxonomic status of some unique occurrences are discussed. Eleven species of amphibians and 39 species of reptiles presently occur or have occurred naturally or as introduced or accidental species on North Padre Island. Twelve species of amphibians and 50 species of reptiles occur or have occurred on North Padre, South Padre, and Mustang islands. Thirty-one species of amphibians and 93 species of reptiles have been reported from the seven counties in which the islands occur.

Biological Abundance and Diversity in Organic-Rich Sediments From a Florida Barrier Island Lagoon

Organic-rich sediments in estuaries and the coastal ocean are often a product of land clearing, runoff of excess nutrients and other human activities. They can harbor pollutants, oxygen-consuming microbes and toxic hydrogen sulfide (H2S), thereby creating a hostile environment for infauna. In one barrier island lagoon, the Indian River Lagoon (IRL), Florida, layers of organic-rich sediments have increased substantially in thickness and areal extent over the past 60 years. Geochemical properties of these muddy sediments have been described; however, less is known about their habitability. We analyzed infauna and geochemical properties of 102 samples taken during wet and dry seasons at 17 locations spanning 60 km of the lagoon. We quantified infaunal abundance and diversity (Shannon-Wiener, H′) and determined Pearson’s correlation coefficients for effective number of species (ENS = eH′) vs. sediment porosity (ϕ = 0.69–0.95), organic carbon (1–8%), nitrogen (0.1–0.7%), silt + clay (16–99%), porewater H2S (5–3,600 μM), and other environmental variables. Small bivalves accounted for 70% of the organisms collected, followed by gastropods, polychaetes and other biota. The bivalves were predominantly Macoma spp., Mulinia lateralis and Parastarte triquetra with average abundances of 3,896, 2,049, and 926 individuals per m2, respectively. High abundance of some species, such as Macoma, showed that these opportunists had adapted to poor quality sediments. More than two-thirds of the 35 species collected were present at <100 individuals per m2 of sediment. Cluster analysis identified four groups of stations with significantly different geochemical properties. Permutation analyses of variance indicated that the four groups also represented statistically different infaunal communities. Diversity decreased with increasing sediment concentrations of organic carbon, nitrogen and silt + clay; however, community richness at our most prolific station along the perimeter of muddy deposits was ∼7 times lower than found previously in sandy sediments from the IRL. The results identified areas where infaunal communities have experienced the greatest stress due to accumulation of organic-rich sediments. Results from this study help support management plans for remediation of organic-rich mud and improvement of sediment and water quality, especially in areas identified with low ENS.

An Integrated, Probabilistic Modeling Approach to Assess the Evolution of Barrier-Island Systems Over the Twenty-First Century

Barrier-island systems, spanning ∼7% of the world’s coastlines, are of great importance to society because not only they provide attractive, liveable space for coastal communities but also act as the first line of defense from coastal storms. As many of these unique coastal systems are affected by both oceanic and terrestrial processes, it is necessary to consider the holistic behavior of applicable terrestrial and coastal processes when investigating their evolution under plausible future scenarios for climate change, population growth and human activities. Such holistic assessments, also accounting for uncertainties, can readily be achieved via reduced-complexity modeling techniques, owing to their much faster simulation times compared to sophisticated process-based models. Here, we develop and demonstrate a novel probabilistic modeling framework to obtain stochastic projections of barrier-island evolution over the twenty-first century while accounting for relevant oceanic and terrestrial processes under climate change impacts and anthropogenic activities. The model is here demonstrated at the Chandeleur islands (Louisiana, United States) under the four Intergovernmental Panel on Climate Change (IPCC) greenhouse gas emission scenarios (i.e., Representative Concentration Pathways 2.6, 4.5, 6.0, and 8.5) with results indicating that there are significant uncertainties in projected end-century barrier-island migration distance and available barrier freeboard under the high emission scenario RCP 8.5. The range of uncertainties in these projections underscores the value of stochastic projections in supporting the development of effective adaptation strategies for these fragile coastal systems.

Studies in New Zealand Oligocene and Miocene Plant Macrofossils

<p>Assemblages of fossil leaves ranging in age from Upper Oligocene to Upper Miocene or Lower Pliocene have been examined from localities in Southland, Central Otago, the Dunedin area, the Buller region and Great Barrier Island. Nearly 200 form taxa have been recognized so far; of these 52 are figured and described and the remainder are included in an illustrated catalogue. Conifers, Casuarinaceae and Nothofagus spp. are discussed in detail. Thirteen new species are named and described: Gleichenia southlandica, Hypolepis maruiensis, Blechnum maruiense, Dacrydium (Lagarostrobos) franklinoides, Microcachrys imbricata, Phyllocladus strictus, Libocedrus compressa, Nothofagus southlandica, Gymnostoma stellata, Gymnostoma crassa, Casuarina avenacea, Metrosideros diffusoides and ? Eucalyptus roxburghiensis. Six new species are described but not named as more detailed study is still proceeding. A further ten new form taxa are identified to genus level only. The fossil flora from the Kaikorai Valley, Dunedin, originally described by Oliver (1936) is revised and Blechnum proceroides, Nothofagus pinnata, N. australis, N. kaikoraiensis and Ripogonum latipetiolatum are new names arising from this revision. The fossil assemblages from Southland and Central Otago are derived from heath, swamp and forest communities developed on an early to mid Tertiary peneplain. In contrast the fossil floras of the Buller region reflect predominantly forest vegetation developed on young soils of a prograding coastal floodplain backed by rapidly rising fault block ranges, while the fossil floras of Dunedin and Great Barrier Island reflect vegetation periodically affected by volcanic activity. Late Oligocene and Miocene climates throughout New Zealand appear to have been humid and at least as warn as Auckland today, although conditions on the east coast of the South Island may have been cooler and drier than on the west. The sediment containing the Landslip Hill fossil flora is interpreted as a silcrete and resembles similar deposits in Australia. The uncompressed state of the fossils and the preservation of turgid cell structures indicates early silica cementation in a surface or near-surface environment, probably as a result of direct precipitation of silica from ground water. The present-day New Zealand flora appears to be derived in part from the late Cretaceous flora of coastal eastern Gondwanaland. Other south-west Pacific floras may stare a similar origin, and may also have contributed to the New Zealand flora following fragmentation of the continental margin. The distribution of New Zealand Tertiary plants, as far as it is known, is consistent with my inferred paleogeography.</p>

Studies in New Zealand Oligocene and Miocene Plant Macrofossils

<p>Assemblages of fossil leaves ranging in age from Upper Oligocene to Upper Miocene or Lower Pliocene have been examined from localities in Southland, Central Otago, the Dunedin area, the Buller region and Great Barrier Island. Nearly 200 form taxa have been recognized so far; of these 52 are figured and described and the remainder are included in an illustrated catalogue. Conifers, Casuarinaceae and Nothofagus spp. are discussed in detail. Thirteen new species are named and described: Gleichenia southlandica, Hypolepis maruiensis, Blechnum maruiense, Dacrydium (Lagarostrobos) franklinoides, Microcachrys imbricata, Phyllocladus strictus, Libocedrus compressa, Nothofagus southlandica, Gymnostoma stellata, Gymnostoma crassa, Casuarina avenacea, Metrosideros diffusoides and ? Eucalyptus roxburghiensis. Six new species are described but not named as more detailed study is still proceeding. A further ten new form taxa are identified to genus level only. The fossil flora from the Kaikorai Valley, Dunedin, originally described by Oliver (1936) is revised and Blechnum proceroides, Nothofagus pinnata, N. australis, N. kaikoraiensis and Ripogonum latipetiolatum are new names arising from this revision. The fossil assemblages from Southland and Central Otago are derived from heath, swamp and forest communities developed on an early to mid Tertiary peneplain. In contrast the fossil floras of the Buller region reflect predominantly forest vegetation developed on young soils of a prograding coastal floodplain backed by rapidly rising fault block ranges, while the fossil floras of Dunedin and Great Barrier Island reflect vegetation periodically affected by volcanic activity. Late Oligocene and Miocene climates throughout New Zealand appear to have been humid and at least as warn as Auckland today, although conditions on the east coast of the South Island may have been cooler and drier than on the west. The sediment containing the Landslip Hill fossil flora is interpreted as a silcrete and resembles similar deposits in Australia. The uncompressed state of the fossils and the preservation of turgid cell structures indicates early silica cementation in a surface or near-surface environment, probably as a result of direct precipitation of silica from ground water. The present-day New Zealand flora appears to be derived in part from the late Cretaceous flora of coastal eastern Gondwanaland. Other south-west Pacific floras may stare a similar origin, and may also have contributed to the New Zealand flora following fragmentation of the continental margin. The distribution of New Zealand Tertiary plants, as far as it is known, is consistent with my inferred paleogeography.</p>

Loss of Genetic Diversity with Captive Breeding and Re-Introduction: A Case Study on Pateke/Brown Teal (Anas chlorotis)

<p>Pateke/brown teal (Anas chlorotis) have experienced a severe population crash leaving only two remnant wild populations (at Great Barrier Island and Mimiwhangata, Northland). Recovery attempts over the last 35 years have focused on an intensive captive breeding programme which breeds pateke, sourced almost exclusively from Great Barrier Island, for release to establish re-introduced populations in areas occupied in the past. While this important conservation measure may have increased pateke numbers, it was unclear how much of their genetic diversity was being retained. The goal of this study was to determine current levels of genetic variation in the remnant, captive and re-introduced pateke populations using two types of molecular marker, mitochondrial DNA (mtDNA) and microsatellite DNA. Feathers were collected from pateke at Great Barrier Island, Mimiwhangata, the captive breeding population and four re-introduced populations (at Moehau, Karori Wildlife Sanctuary, Tiritiri Matangi Island and Mana Island). DNA was extracted from the base of the feathers, the mitochondrial DNA control region was sequenced, and DNA microsatellite markers were used to genotype individuals. The Great Barrier Island population was found to have only two haplotypes, one in very high abundance which may indicate that historically this population was very small. The captive breeding population and all four re-introduced populations were found to contain only the abundant Great Barrier Island haplotype as the vast majority of captive founders were sourced from this location. In contrast, the Mimiwhangata population contained genetic diversity and 11 haplotypes were found, including the Great Barrier Island haplotype which may have been introduced by captive-bred releases which occurred until the early 1990s. From the microsatellite results, a loss of genetic diversity (measured as average alleles per locus, heterozygosity and allelic richness) was found from Great Barrier Island to captivity and from captivity to re-introduction. Overall genetic diversity within the re-introduced populations (particularly the smaller re-introduced populations at Karori Wildlife Sanctuary, Tiritiri Matangi Island and Mana Island) was much reduced compared with the remnant populations, most probably as a result of small release numbers and small population size. Such loss of genetic diversity could render the re-introduced populations more susceptible to inbreeding depression in the future. Suggested future genetic management options are included which aim for a broader representation of genetic diversity in the pateke captive breeding and release programme.</p>