Biochemical and Ultrastructural Evidence for the Origin of Whitings: A Biologically Induced Calcium Carbonate Precipitation Mechanism

We propose that Bahamian whitings, floating patches of lime mud, are in part the result of biological precipitation of calcium carbonate induced by picoplankton and cellular components. The cells may act as nucleation sites for crystallization from seawater supersaturated with CaCO3. Our model represents a new hypothesis concerning Bahamian whiting formation and is based on several lines of evidence. Biochemical data suggest that the macromolecules from carbonate suspended in Bahama Banks whitings are distinct from those found in the lime mud sediment producer Penicillus and from bottom sediment. Direct ultrastructural evidence indicates that mineralization occurs on the surfaces of picoplankton cells and degrading organic cellular components. The organic constituents include, but are not restricted to, whole and fragmented algal cells and composite structures ∼20-30 μm in diameter. The observed calcium carbonate crystals are distinct from skeletal debris. Because of the magnitude of the whiting phenomenon, calculations of carbonate sediment production budgets should include the potential contribution of calcium carbonate produced by epicefular precipitation. Knowledge of carbonate mud genesis is critical to interpretation of ancient occurrences of lime mud as well as to understanding ancient and global carbon cycles

Effects of Calcium, Strontium, and Magnesium on the Coccolithophorid Cricosphaera (Hymenomonas) carterae. I. Calcification

The present investigation concerns the effects of calcium, strontium, and magnesium on calcification and mineralogy of the calcified bodies (coccoliths) of the coccolithophorid Cricosphaera (Hymenomonas) carterae. The capacity of cells to calcify in various concentrations of these ions was examined following preliminary decalcification in CO2. At a concentration of 10-2 M Ca, 75% of the cells formed coccoliths within 24 h and almost all cells were recalcified after 2 days. At 10-3 or 10-4 M Ca no recalcification occurred. However, with the addition of Sr to the Ca-deficient media, calcification took place as shown by observations of coccoliths and by analysis of Ca. The percentage of calcified cells increased with increasing concentrations of Sr. Strontium added to a Ca-deficient media was much more effective than an equivalent concentration of Ca. No Sr was deposited in the coccoliths. X-ray analysis demonstrated that calcite was deposited by cells in all concentrations of Ca and Sr at which calcification took place. At concentrations of Mg in the media from 0.0 to 4.2×10-2 M, the cells retained their ability to calcify, although calcification was markedly reduced in the absence of Mg. In low Mg concentrations (1.3×10-4 and 4.2×10-6 M), the coccoliths were 60% calcite and 40% aragonite, and in the absence of Mg, only calcite was formed

Effects of Elevated pCO2 and Irradiance on Growth, Photosynthesis and Calcification in Halimeda discoidea

Ocean acidification (OA) effects on photophysiology and calcification were examined in Halimeda discoidea, a calcifying macroalga that produces tropical reef sediments. Photosynthetic parameters, including maximum photosynthetic rate (Pmax), photosynthetic efficiency (α) and compensating irradiance (Ic) were determined in short-term assays on live thalli after a 10 d exposure to 4 levels of CO2 partial pressures (pCO2; 491, 653, 982 and 1201 µatm) under saturating (300 µmol photons m-2 s-1) and sub-saturating (90 µmol photons m-2 s-1) irradiance in an aquaria study. Morphology of aragonite crystals produced in segments formed on adult thalli was characterized using scanning electron microscopy (SEM). Further, we examined crystal morphology and changes in inorganic content of non-living segments exposed to elevated (1201 µatm) and ambient pCO2 for 27 d to assess OA effects on carbonate sediments generated from H. discoidea. Even though Pmax was higher under elevated pCO2, this photophysiological response did not result in higher calcification rates. Based on crystal measurements and SEM imagery, aragonite crystals within new segments were indistinguishable across pCO2 and irradiance treatments. Under high irradiance, new segments showed a greater investment in organic versus inorganic production. Non-living segments contained narrower crystals after 27 d exposure to elevated pCO2 relative to controls, but differences were small (0.03 µm) and did not contribute significantly to changes in normalized biomass or inorganic content. Based on these results, H. discoidea will likely produce new calcified segments with intact aragonite crystals under year 2100 pCO2 levels at high and low irradiance, while aragonite crystals of the sediment may produce thinner needle carbonate muds

Monthly Variability in Florida Bay Benthic Foraminifera Community Structure

Florida Bay is a shallow subtropical estuary, which experiences highly variable environmental fluctuations due to natural forces (hurricanes, climatic variations and sea level rise) and anthropogenic influences (agricultural activity, water management and urbanization). Study of short time-scale variability in benthic community population structure and synchronous environmental change is essential to understanding forcing relationships between environment and its effects on population. Benthic foraminifera assemblage variability is an excellent indicator of environmental change in estuarine and coastal areas because populations may respond relatively quickly on spatial and temporal scales (Alve, 1995). Temporal resolution is enhanced because foraminifera may reproduce as often as 3 months to one year (Murray, 1991). Monthly population sampling from 15 stations throughout Florida Bay is being conducted in a multi-year program begun in January 2004. This includes collection of sediment samples containing benthic foraminifera as well as site measurement of environmental parameters (salinity, temperature, suspended particulate matter, chlorophyll, nutrients, and dissolved organic matter). The objectives of the current study are to examine sites in Florida Bay with enhanced temporal resolution and determine (1) monthly variability in benthic foraminifera species composition, diversity, dominance and abundance; and (2) provide data on the relationship between water quality parameters and these measures of benthic foraminifera community structure. In northeastern Florida Bay (station 1), preliminary results from monthly sampling indicate a temporal inverse relationship between the relative abundance of particular species and increasing salinity to hyper saline (40 o/oo) conditions. The benthic foraminifera community is predominately Ammonia sp., Elphidium sps. and Peneroplis sps. (greater than 60%). Quinqueloculina sps. and Triloculina sps. contribute 40% or less to the total population during each month sampled. Over a twelve month interval an inverse relationship is evident between Peneropolis sps. and Ammonia sp. Peneroplis sps.are more abundant under normal marine conditions, while Ammonia sp. is dominant during low and hyper saline conditions. Elphidium sps. decreased with increasing salinity. Sample collection during 2005, foraminifera enumeration, and data processing is in progress and benthic foraminifera population characteristics are being compared with environmental parameters. These data sets will provide a fundamental baseline from which to evaluate long-term environmental change in Florida Bay and facilitate utilization of benthic foraminifera as proxies of environmental change

Coral Ultrastructural Response to Elevated pCO2 and Nutrients During Tissue Repair and Regeneration

Corals and coral reefs have recently experienced widespread decline attributed to anthropogenic pressure on reef systems. Studies have demonstrated that nutrient and pCO2 stress effect coral growth and calcification, but study of specific effects on coral tissue is lacking. The objective of this research was to examine wound healing in corals and how it is affected by exposure to elevated nutrients and pCO2. Coral tissue repair and regeneration during wound healing in Montastraea cavernosa and Porites astreoides were assessed histologically and ultrastructurally by examining colony fragments exposed to elevated nitrate, phosphate, and pCO2. In M. cavernosa, tissue repair was facilitated by granular amoebocytes, and the zooxanthellae population size increased under enriched nutrient conditions. In P. astreoides, zooxanthellae chloroplasts were markedly abnormal in phosphate-enriched corals, and the concentration of chromophore cells at the healing tissue front was markedly lower under elevated nutrient conditions. The area of wound healed was higher after 14 days under every experimental condition in M. cavernosa compared to P. astreoides. In both species, phosphate enrichment had the most deleterious effect on repair and regeneration

Coccolith Morphology and Paleoclimatology - 2. Cell Ultrastructure and Formation of Coccoliths in Cyclococcolithina leptopora (Murray and Blackman) Wilcoxon and Gephyrocapsa oceanica Kamptner.

Current interest in utilization of coccoliths for paleoclimate reconstruction necessitates background information on environmental limits for growth and coccolith production as well as examination of cell ultrastructure in specimens collected in the field and in cultured representatives. Successful isolation of the two geologically important species Gephyrocapsa oceanica (strain A674) and Cyclococcolithina leptopora (strain A650) allows investigation of ultrastructure in cultured forms. Fine structure of cells and coccoliths was observed in the SEM using critical point dried preparations and ultrastructure was examined with the transmission electron microscope. Coccoliths are formed intracellularly and appear to form within Golgi-derived vesicles located near the nuclear membrane. Formation and development of coccoliths in the two species resemble these processes in Emiliania huxleyi but differ from those of Cricosphaera carterae, notably in the absence of coccolithosomes and scales and in the fact that coccoliths are produced intracellularly one at a time

Insights into Migration and Development of Coral Black Band Disease Based on Fine Structure Analysis

In many diverse ecosystems, ranging from natural surfaces in aquatic ecosystems to the mammalian gut and medical implants, bacterial populations and communities exist as biofilms. While the process of biofilm development has been well-studied for those produced by unicellular bacteria such Pseudomonas aeruginosa, little is known about biofilm development associated with filamentous microorganisms. Black band disease (BBD) of corals is characterized as a polymicrobial biofilm (mat) community, visually-dominated by filamentous cyanobacteria. The mat migrates across a living coral host, completely lysing coral tissue and leaving behind exposed coral skeleton. It is the only known cyanobacterial biofilm that migrates across a substratum, thus eliciting questions about the mechanisms and unique characteristics of this system. Fragments of the coral Montastraea annularis, five artificially infected with BBD and two collected from a naturally BBD-infected colony, were used to address these questions by detailed examination using scanning and transmission electron microscopy (SEM and TEM). In areas close to the interface of coral tissue and the mature disease band two types of clusters of cyanobacteria were observed, one with random orientation and one with parallel orientation of filaments. The latter exhibited active secretion of extracellular polysaccharide (EPS) while the randomly oriented clusters did not. Within the well developed band cyanobacterial filaments were observed to be embedded in EPS and were present as layers of filaments in parallel orientation. These observations suggest that BBD cyanobacteria orient themselves and produce EPS in a sequential process during migration to form the complex BBD matrix

Benthic Foraminifera from the NECOP Study Area Impacted by the Mississippi River Plume and Seasonal Hypoxia

Benthic foraminifera influenced by the Mississippi River plume and seasonal hypoxia were assessed from Louisiana inner-continental shelf sediment samples. Surface foraminifera assemblages were representative of in-situ populations as established by staining techniques. Community diversity and richness/evenness analyses indicate three regimes: high stress (sediment dominated), intermediate stress (hypoxia dominated), and low stress (low sediment accumulation/high oxygen). Epistominella vitrea and Buliminella morgani are useful tracers of rapid sediment accumulation rate and hypoxia. A bottom-water productivity signal west of the Mississippi River plume is indicated by benthic and planktic foraminifera abundance peaks. Surface benthic foraminifera trends are utilized to interpret changes in historical community structure from hypoxic-area sediments deposited since the turn of the century. The hypoxia-tolerant species Buliminella morgani increases markedly upcore, while hypoxia intolerant species decrease or disappear. Diversity and dominance trends temporally correspond to a dramatic increase in U.S. fertilizer application. The results of this study have application to paleoenvironmental research spanning longer geologic timescales. The documented relationships between population structure and stressors in river-dominated marine systems may provide a useful analog for recognition of these conditions in the fossil record

Primary Utricle Structure of Six Halimeda Species and Potential Relevance for Ocean Acidification Tolerance

Variations in utricle morphology may be responsible for different tolerances to ocean acidification (OA) within the macroalgal genus Halimeda, an important sediment producer on reefs. However, differences in species’ utricle morphology and their relationship to calcification and crystal formation have not been well articulated. In the present study, we characterized the utricle morphologies of six Halimeda species. Primary utricle ultrastructure was quantitatively and qualitatively compared to tissue inorganic content and crystal microstructure. Morphologies differed across species and several morphometric relationships were revealed. Primary utricle size (r2=0.70) and diffusion pathway length (r2=0.87) had inverse relationships with inorganic content based on regression analyses, and corresponded to crystal microstructure form. Species with large utricles and long diffusion pathways contained more narrow (~0.15 μm) aragonite needles and minimal micro-anhedral crystal formations. In contrast, species with small utricles and short diffusion pathways elucidated aggregates of micro-anhedral crystals and wider aragonite needles (~0.30 μm). Species’ utricle characteristics generally corresponded to specific evolutionary lineages. Thus, characteristics of Halimeda utricle morphology may control long-term adaptive responses to OA, an idea articulated in the broader literature

Carbonate Deposits in Marine Fish Intestines: A New Source of Biomineralization

Marine teleostean fish are hypo-osmotic to seawater. As part of a multiorgan osmoregulatory strategy they drink seawater and selectively absorb water and minerals across the intestinal epithelium. Notably, divalent cations (Ca2+ and Mg2-) are left behind. We report here that in the gulf toadfish, Opsanus beta, the ionic by-products of osmoregulation in the intestine contribute to de novo formation of a carbonate mineral, tentatively identified as calcian kutnohorite. Our data suggest that intestinal mineralization is a general feature of osmoregulation in marine teleosts and that this process is an unrecognized and possibly substantial source of marine carbonate sediments