The fossil record of planktonic foraminifers is a key source of data on the biodiversity and evolution of marine plankton. One of the most distinctive foraminiferal taxa, Orbulina universa, widely used as a stratigraphic and paleoclimatic index, has always been regarded as a single species. Here we present a phylogenetic analysis of Orbulina small subunit rDNA sequences from 25 pelagic stations covering 100°latitude in the Atlantic Ocean. The genetic data reveal the presence of three cryptic species, whose distribution is clearly correlated to hydrographic provinces, and particularly to sea-surface total chlorophyll a concentration. Our results, together with previous studies, suggest that a considerable part of the diversity among planktonic foraminifers has been overlooked in morphological taxonomies. Our data also support the idea that planktonic foraminifers, even if adapted to particular hydrographic conditions, are high-dispersal organisms whose speciation may be similar to that of other high-dispersal taxa in which reproductive mechanisms and behavior, rather than just geographic barriers to dispersal, play key roles in species formation and maintenance.Planktonic foraminifers are unicellular marine zooplankton whose fossil record extends back 160 million years and constitutes a fundamental archive of changes in oceanic biodiversity and paleoceanography. Despite the widespread use of foraminiferal species for paleoceanographic, stratigraphic, and evolutionary research, no large scale genetic studies have been done to develop the species concept among planktonic foraminifers; their diversity has been estimated almost exclusively on the basis of more-or-less subjective morphological classification of the tests (shells), and has never been thought to be extensive in spite of their worldwide distribution. Approximately 50 species are described in the Holocene (1). However, results based on DNA sequences suggest that oceanic biological diversity may have been seriously underestimated (2). In this study, we use molecular tools to examine the questions of planktonic foraminiferal biodiversity, distribution, and speciation in pelagic ecosystems.As a model, we have chosen Orbulina universa d'Orbigny, one of the most commonly encountered planktonic foraminifers inhabiting the surface waters of the World Ocean between 60°N and 50°S. This species appeared in the fossil record 15.4 million years ago and is widely used as a stratigraphic and paleoclimatic index (3). Orbulina has been a focus of evolutionary studies on its origin from trochospirally coiled ancestors (4, 5) and of research on the ultrastructural variability of its last spherical chamber (6, 7). Moreover, it has been used in culture experiments of stable carbon and oxygen isotope, calcium, barium, and cadmium uptake in the test as a proxy for reconstructions of ancient sea surface water temperature and chemistry (8-12). Orbulina universa is considered to be the last representative of a lineage that underwent rapid anagenetic changes at the early/m...

The shallow-water reef coral Goniastrea aspera Verill 1865 has previously been reported to demonstrate differences in within-colony susceptibility to bleaching at elevated sea temperatures; parts of the colony which are exposed to the highest solar radiation are more thermotolerant than areas which are less exposed. In this paper, we show that at elevated experimental sea temperature the 'high light' surfaces lose fewer symbiotic algae, have lower levels of oxidative stress, higher levels of host antioxidant-enzyme copper zinc superoxidase dismutase (CuZnSOD), and host heat-shock proteins 60 and 70, compared to the less exposed surfaces. In addition, 'high light' surfaces show less chronic photoinhibition and greater Photosystem II (PS II) recovery potential when exposed to high irradiance at ambient sea temperature. In contrast, no differences were noted in algal defences (e.g. antioxidant enzymes and stress protein production, and xanthophyll cycling) either at elevated or ambient temperatures. These results are noteworthy because they suggest that corals which acclimatise to high irradiance can, as a result, develop increased thermotolerance which may prevent bleaching at high sea temperatures. Importantly, they also demonstrate the significance of the host tissues in maintaining the intact symbiosis of G. aspera under thermal stress.

Abstract. Concentrations of ammonia / ammonium (NH3/NH4 +) and its methyl-derivatives the methylamines (MAs) were determined in seawater, atmospheric, and rainwater samples during the U.K. Joint Global Ocean Flux Study ARABESQUE program in the Arabian Sea (AugustDecember 1994). In seawater, concentrations of NH3/NH4 + were shown to be 10-100 times greater than those of MAs, of which monomethylamine was the most abundant. Concentrations of all analytes were highest in the productive coastal waters off Oman, and lowest in offshore oligotrophic regimes. Calculations demonstrated that both coastal and offshore waters vented NH3 to atmosphere, and that while coastal waters could act as sources or sinks of atmospheric MAs, offshore waters were a consistent sink. NH3/NH4 + was the dominant atmospheric base, with MAs contributing 16-20% of total measured gaseous base and 5.9-12% of total measured aerosol base (sub-micron). Although photochemical destruction was calculated to be more significant for MAs than for NH3, removal of all species from the atmosphere was dominated by wet deposition. Atmospheric deposition was estimated to fuel less than 1% of the nitrogen requirements of "new" production in oligotrophic regions of the Arabian Sea. With aerosol scavenging calculated to contribute under 0.5% of rainwater NH4 + and MAs, the gas phase was inferred as the dominant source of rainwater MAs and NH4 +. However, equilibria calculations demonstrated rainwater to be undersaturated with respect to gaseous MA and NH3 concentrations, and that paradoxically it was not possible for Henry's law to hold for all analytes simultaneously.

No abstract

No abstract