Late Quaternary uplift and subsidence of the west coast of Tanna, south Vanuatu, southwest Pacific: U-Th ages of raised coral reefs in the Median Sedimentary Basin

Twelve Late Quaternary TIMS U-Th ages are reported here from 10 coral samples collected in situ from five transgressive coral/algal raised reefs (height: max. 113 m, min. 8 m) and two raised lagoonal deposits (height: max. 18 m, min. 8 m) along and near the west coast of Tanna, which lies in the Median Sedimentary Basin of South Vanuatu, southwest Pacific. These reefs and raised lagoonal deposits represent several age groups: (i) 215 ka (marine oxygen-isotope stage 7) penultimate interglacial (highest elevation and oldest); (ii) one lagoonal deposit of ca 127 ka (marine oxygen-isotope stage 5e); (iii) three last interglacial reefs with ages 102, 89 and 81 ka (representing marine oxygen-isotope stages 5c, 5b and 5a, respectively, of the latter part of the last interglacial); (iv) a lagoonal deposit with a 92 ka age (5b); and (v) a Holocene reef (age >5.7-5.0 ka) (lowest elevation and youngest). A ca 4.9 ka regressive reef (at elevation of 1.5 m above sea-level) is consistent with an island-wide 6.5 m uplift (probably largely coseismic), and a probable further island-wide uplift occurred in the late Holocene. The U-series ages taken together with the heights of transgressive reefs show that uplift since 215 ka was, on average, at similar to0.52 mm/y; although since 5 ka the uplift rate was, on average, similar to1.6 mm/y (the assumption being that a 1.5 m above sea-level reef has a coseismic origin). Elevation of transgressive reefs 5a, 5b and 5c and their ages indicates an island-wide subsidence during the period ?124-89 ka (i.e. Late Quaternary uplift/subsidence was jerky). Late Quaternary uplift/subsidence on the northwest coast of Tanna is considered to be due to irregular thicknesses of crust being subducted beneath Tanna.

Overlapping species boundaries and hybridization within the Monastraea "annularis" reef coral complex in the Pleistocene of the Bahama Islands

Recent molecular analyses indicate that many reef coral species belong to hybridizing species complexes or "syngameons." Such complexes consist of numerous genetically distinct-species or lineages, which periodically split and/or fuse as they extend through time. During splitting and fusion, morphologic intermediates form and species overlap. Here we focus on processes associated with lineage fusion, specifically introgressive hybridization, and the recognition of such hybridization in the fossil record. Our approach involves comparing patterns of ecologic and morphologic overlap in genetically characterized modern species with fossil representatives of the same or closely related species. We similarly consider the long-term consequences of past hybridization on the structure of modern-day species boundaries. Our study involves the species complex Montastraea annularis s.l. and is based in the Bahamas, where, unlike other Caribbean locations, two of the three members of the complex today are not genetically distinct. We measured and collected colonies along linear transects across Pleistocene reef terraces of last interglacial age (approximately 125 Ka) on the islands of San Salvador, Andros, and Great Inagua. We performed quantitative ecologic and morphologic analyses of the fossil data, and compared patterns of overlap among species with data from modern localities where species are and are not genetically distinct. Ecologic and morphologic analyses reveal "moderate" overlap (>10%, but statistically significant differences) and sometimes "high" overlap (no statistically significant differences) among Pleistocene growth forms (= "species"). Ecologic analyses show that three species (massive, column, organ-pipe) co-occurred. Although organ-pipes had higher abundances in patch reef environments, columnar and massive species exhibited broad, completely overlapping distributions and had abundances that were not related to reef environment. For morphometric analyses, we used multivariate discriminant analysis on landmark data and linear measurements. The results show that columnar species overlap "moderately" with organ-pipe and massive species. Comparisons with genetically characterized colonies from Panama show that the Pleistocene Bahamas species have intermediate morphologies, and that the observed "moderate" overlap differs from the morphologic separation among the three modern species. In contrast, massive and columnar species from the Pleistocene of the Dominican Republic comprise distinct morphologic clusters, similar to the modern species; organ-pipe species exhibit "low" overlap (

Bryophyte propagule banks in a feldmark on subantarctic Macquarie Island

Subantarctic Macquarie Island has substantial areas of feldmark on its plateau above 200 m altitude. Samples of the substrate (5.5 cm in depth) from bare areas of feldmark contained viable propagules of bryophyte species found at adjacent and distant sites on the island. In laboratory conditions propagules of 15 bryophyte taxa germinated, allowing interpretation of reasons for bare patches in feldmark: bryophytes were successful at colonizing stable ground but when surface movement was present, burial and/or damage of propagules and young plants prevented colonization. Spherical moss polsters found in cryoturbatic areas in feldmark, however, represent a growth form that can tolerate surface movement. A conceptual model illustrating processes associated with colonization dynamics of bryophytes on feldmark terraces is presented. Ten of the 15 germinated taxa were nonlocal taxa which currently grow in plant communities at lower and hence warmer altitudes on Macquarie Island. The presence of viable propagules of these taxa provide an immediate and constant potential for dramatic vegetation change with climate change.