Decrease In Food Supply Research Articles

Comparative biomass of sediment benthos across a depth transect, Chatham Rise, Southwest Pacific Ocean

The present study examined the partitioning of carbon between benthic meioand macrofauna at sites between 350 and 3100 m water depth across Chatham Rise, Southwest Pacific Ocean. Biomass declined with increasing depth on both sides of the crest, but showed different patterns for each faunal size grouping at the deepest sites. Meiofaunal biomass was highest on the crest and lowest at 2800 m, south of the rise (76 and 8 mg C m–2, respectively), whereas macrofaunal biomass peaked on the southern slope (1169 mg C m–2), with lowest values at the deep northern sites (88 and 116 mg C m–2). Macrofauna dominated total faunal biomass (>80%), although the relative importance of meiofauna increased with increasing depth on the northern side. The meiofauna: macrofauna carbon ratio was correspondingly low across all sites (0.04 to 0.10), except at the deep 3100 and 2300 m northern sites (0.16). These biomass patterns were significantly related to sediment chlorophyll a concentration, indicating greater availability of high-quality (labile) organic carbon. The lack of a shift towards the smaller benthic size class with decreasing food supply at the deep southern site (2800 m depth) appeared to be related to relatively high sediment particulate organic carbon and high calcium carbonate contents, which also influenced meioand macrofaunal biomass. These findings reveal the close link between faunal biomass and food availability in deep-sea habitats and highlight the importance of phytodetritus in structuring benthic assemblages in the Chatham Rise/Subtropical Front region.

Fear for the family has negative consequences: indirect effects of nest predators on chick growth in a farmland bird

Summary 1. The management of habitat structure can limit access to food and can also alter perceived predation risk. Minimising the risk of predation, by changing behaviour, may have negative impacts similar to predation itself across a wide range of species. Predation risk influences the behaviour of adults foraging for altricial young, so that they avoid disclosing the location of their offspring to predators. The consequences of these behavioural changes for offspring are unknown. 2. We investigate whether predator‐induced changes in provisioning rates can have impacts upon avian nestlings through reductions in growth and condition, and whether this is influenced by resource availability, using the declining yellowhammer Emberiza citrinella as a model species. 3. We show a sizeable negative impact of nest predator activity upon brood provisioning rate, indicating that parents can assess nest predation risk and adjust their behaviour accordingly. 4. Chick condition and growth were both negatively influenced by corvid nest predator abundance and positively influenced by food abundance in large broods, suggesting that parents raising large broods in unfavourable conditions were unable to compensate fully for the effect of corvid activity on provisioning rate. 5. In areas of low food availability, corvid abundance was associated with reduced chick growth and condition; in areas of higher food availability no association was found indicating that where food resources are abundant, parents can compensate for reductions in provisioning rate when corvids are active, with no long‐term implications for chicks. 6. Synthesis and applications. We propose a mechanism by which two distinct trends linked with the intensification of agriculture, namely increasing corvid abundance combined with a decreasing food supply, may have indirectly precipitated population declines in farmland passerines through delayed life‐history effects across generations. As the impacts of corvids are reduced where invertebrates are abundant, we suggest that management should concentrate on improving the quality of foraging habitat by creating mosaics of long and short vegetation, rather than on the control of corvids. This will allow adult birds to compensate for the indirect effects of high corvid abundance by increasing their provisioning effort when nest predation risk is low and thus buffer any long‐term consequences for nestlings.

Interactive effects of food availability and aerial body temperature on the survival of two intertidal Mytilus species

Intertidal organisms must episodically contend with the rigors of both the terrestrial and the marine environments. While body temperatures during high tide are driven primarily by water temperature, aerial body temperatures are driven by multiple environmental factors such that temperature of an organism during low tide is usually quite different from air temperature. Thus, whereas decades of research have investigated the effects of water temperature on intertidal species, considerably less is known about the physiological impacts of temperature during aerial exposure at low tide, especially with regard to the interaction of aerial body temperature with other stressors. We examined the interactive effects of aerial body temperature and food supply on the survival of two intertidal blue mussels, Mytilus galloprovincialis and Mytilus trossulus. Survival was monitored for nine weeks using a simulated tidal cycle, with two levels of food and three levels of aerial body temperature (30, 25, and 20 °C). Decreased food supply significantly reduced the survival of mussels, but only under the 30 °C treatment. In the other two thermal regimes there were no significant effect of food on survival. When aerial body temperatures are high, food availability may have a greater effect on intertidal organisms. Decreases in ocean productivity have been linked to increased in ocean temperatures, thus intertidal organisms may become more susceptible to thermal stress as climates shift.

Albatross foraging behaviour: no evidence for dual foraging, and limited support for anticipatory regulation of provisioning at South Georgia

Many pelagic seabirds are thought to regulate reproductive effort by adopting a dual foraging strategy, alternating or mixing short foraging trips over local shelf waters (maximising provi- sioning rates) with longer trips over distant oceanic water (allowing restoration of lost condition). Many species also respond to chick condition, decreasing food supply to over-fed, and sometimes increasing it to under-fed chicks. Analysis of tracking data from 4 albatross species breeding at South Georgia provided evidence that adults responded to prevailing environmental conditions, but did not provide evidence for a dual foraging strategy. Trip durations and maximum foraging ranges tended to follow a positively skewed, unimodal distribution, with the exception of the light-mantled albatross for which no significant modes were apparent. Individual distributions deviated from this, but none were strongly bimodal or showed regular alternation of trip lengths, trip distance or predominant bathy- metric regime. There were significant relationships between meal mass and trip duration, time since the last feed and chick condition on return, reflecting responses to current rather than predicted chick needs. On average, adults returned with smaller meals after 1 to 2 d trips, but otherwise stayed away until a threshold payload was obtained; consequently, provisioning rate (g d -1 ) was much greater after shorter trips. Lack of dual foraging may reflect the diversity of foraging zones available in this highly productive region. By inference, this would mean that adoption of dual foraging elsewhere is a con- sequence of greater heterogeneity in resource availability in waters surrounding those colonies.

Climate Change: Impact on Viral Diseases

Gas emission by humans will change climate, warming by 1.4-5.8°C as predicted at the end of the current cen- tury. Climate oscillations between warm and cold phases (El Nino) add complexity in the field. The effects on health could be thermal stress, extreme weather events, and subsequently emerging infectious diseases. Consequences on food yields, social, demographic and economic imbalances, could also favour contagious diseases. Increasing vector-borne infections could represent a major health concern. Additionally, numerous floods and massive movements of people could facilitate the transmission of water-borne infections. Moreover, decrease in food supply could disorganise populations with crowding and concomitant spreading of transmissible infectious pathogens such as viruses. This short review aims to present the potential viral impact on human health in case of climate change, i.e. increased ar- boviruses, tropical viruses, and viral infections related to overcrowding in poor healthy context.

Patterns of Orthoptera abundance and lesser kestrel conservation in arable landscapes

The lesser kestrel Falco naumanni experienced a marked decline during the second half of the 20th century due to changes in land use that influenced breeding success by reducing the abundance and quality of prey. However, the factors governing spatial and temporal variation of prey abundance around lesser kestrel colonies has not yet been investigated. We sampled Orthoptera abundance in the main crop types and edge habitats surrounding six lesser kestrel colonies in southern Spain. Samplings focused on Orthoptera because they constitute the main prey during the nestling period. Only those Orthoptera species that are known to be preyed by lesser kestrels were considered in this study. We found differences in prey density among localities, and crop types. Semi-natural habitats such as grasslands, fallow land, and field margins held the highest densities. However, prey abundance showed a complex pattern that was not possible to explain solely on the basis of crop composition around colonies. Factors determining productivity in individual fields like soil type and productivity or biocide input, and mean size of agricultural fields contributed to explain this complex pattern of prey abundance. Our results highlight the key role of semi-natural and edge habitats in farmed landscapes as prey reservoirs and corridors. Higher conservation priorities for these habitats are suggested to benefit foraging lesser kestrels, but many other farmland species that also experienced steep population declines due to decreasing food supply resulting from modern agriculture.

Is climate change affecting the population dynamics of the endangered Pacific loggerhead sea turtle?

The loggerhead sea turtle is an endangered species exposed to many anthropogenic hazards in the Pacific. It is widely held that pelagic longline fisheries pose the major risk for Pacific loggerheads but the effects of other risk factors such as human-induced global climate change have rarely been considered. So we used generalised additive regression modelling and autoregressive-prewhitened cross-correlation analysis to explore whether regional ocean temperatures affect the long-term nesting population dynamics for the 2 Pacific loggerhead genetic stocks (Japan, Australia). We found that both Pacific stocks have been exposed to slowly increasing trends in mean annual sea surface temperature in their respective core regional foraging habitats over the past 50 years. We show that irrespective of whether a population was decreasing or increasing that there was an inverse correlation between nesting abundance and mean annual sea surface temperature in the core foraging region during the year prior to the summer nesting season. Cooler foraging habitat ocean temperatures are presumably associated with increased ocean productivity and prey abundance and consequently increased loggerhead breeding capacity. So warming regional ocean temperatures could lead to long-term decreased food supply and reduced nesting and recruitment unless Pacific loggerheads adapt by shifting their foraging habitat to cooler regions. So the gradual warming of the Pacific Ocean over the past 50 years is a major risk factor that must be considered in any meaningful diagnosis of the long-term declines apparent for some Pacific loggerhead nesting populations.

Depth-related changes in the arctic epibenthic megafaunal assemblages of Kangerdlugssuaq, East Greenland

The effects of depth-related differences in environmental factors (pressure, hydrography, habitat and disturbance) on the benthic megafauna at the mouth of Kangerdlugssuaq Fjord in Arctic Greenland were investigated using a towed camera platform and autonomous underwater vehicle photographs. Large reductions in faunal density (60,132 to 1881 individuals ha−1) and increases in diversity (H′=0.93–2.54), through increases in richness (ES(220)=7.6–18.8) and reductions in dominance (Berger–Parker index=0.77–0.38) were found between 270 and 720 m water depth. Assemblages were separated into distinct shallow, intermediate and deep faunas by multivariate community analysis. In the shallower sites there were high levels of iceberg disturbance, directly reducing diversity as well as creating a complex, patchy environment inhabited by high densities of mobile suspension-feeding epifauna. In the deeper areas there was small-scale disturbance from the deposition of drop stones, but at a relatively low frequency and magnitude, which allowed increased species diversity. Proportions of deposit-feeding epifaunal and infaunal taxa rose with depth, as indicated by an increase with depth in faunal traces. Decreases in faunal density probably resulted from decreased food supply with depth.

ECOLOGICAL DISTRIBUTION OF BENTHIC FORAMINIFERA, OFFSHORE NORTHEAST NEW ZEALAND

Northeast of New Zealand, nine benthic foraminiferal associations are recognized and mapped (50–3800 m depth) based on cluster analysis of faunal census data (>63 μm, 235 species, 56 samples). Similar associations are identified using cluster analysis based on the presence or absence of species. Canonical correspondence analysis shows that the associations correlate most strongly with factors related to water depth, especially decreasing food supply (organic carbon flux) with increasing depth. The depth-stratified distribution of lower bathyal to abyssal (>1000 m) associations accords well with the deep water masses, and is attributed in part to lower oxygen concentrations in the bottom waters. The two deepest associations, dominated by Alabaminella weddellensis , Epistominella exigua , Bulimina marginata f. aculeata , Globocassidulina subglobosa , and Oridorsalis umbonatus , underlie the oxygen minimum zone of Circumpolar Deep Water. A mid-lower bathyal association dominated by Cassidulina carinata , Alabaminella weddellensis , Abditodentrix pseudothalmanni , and Trifarina occidentalis , underlies Antarctic Intermediate Water. In addition to their bathymetric stratification, mid shelf to upper bathyal (50–600 m) associations also show latitudinal variation that may reflect differences in terrigenous mud (abundant Eilohedra vitrea ), bottom current strength, food supply (more abundant Cassidulina carinata ) and nutrient remineralization on the seafloor. At depths of 50 m depth) is similar off northeast (235 species) and eastern (246 species) New Zealand and higher than off the west coast (150 species).

Factors influencing the distribution of Subantarctic deep-sea benthic foraminifera, Campbell and Bounty Plateaux, New Zealand

We investigate the combination of environmental factors that influence the distribution patterns of benthic foraminiferal tests (> 63 μm) in a topographically varied region crossed by both the Subtropical and Subantarctic Fronts, south-east of New Zealand. Seafloor sample sites, extending from outer shelf (50 m) to abyssal (5000 m) depths, are bathed by five different water masses, and receive phytodetritus from Subtropical, Subantarctic and Circumpolar surface water masses. Eight mappable associations are recognised by Q-mode cluster analysis of the benthic foraminiferal census data. Similar associations are identified using cluster analysis based solely on the presence or absence of species. Canonical correspondence analysis and a correlation coefficient matrix were used to relate the faunal data to a set of environmental proxies. These show that factors related to water depth (especially decreasing food supply with increasing depth) are the most significant in determining the overall foraminiferal distribution. Other contributing factors include surface water productivity and its seasonality; bottom water ventilation; energetic state of the benthic boundary layer and resulting substrate texture; and bottom water carbonate corrosiveness. Three shallow-water associations (50–700 m), dominated by Cassidulina carinata, Trifarina angulosa, Globocassidulina canalisuturata, Gavelinopsis praegeri, and Bolivina robusta, occur in coarse substrates on the continental shelf, and on the crests and upper slopes of four seamounts under well-oxygenated, high energy regimes, and high food input. Three mid bathyal to upper abyssal associations (500–3300 m), dominated by Alabaminella weddellensis, C. carinata, and Epistominella exigua, occur in biopelagic sandy mud, beneath a region of strongly seasonal food supply, with their composition influenced by total food flux, ventilation (Oxygen Minimum Zone), and bottom current strength. An unusual lower bathyal association (1200–2100 m), dominated by T. angulosa and Ehrenbergina glabra, occurs in a belt of coarser sandy substrate that runs along the crest of the submarine plateaux slopes beneath the strongly-flowing Subantarctic Front-related currents. A deep abyssal association (3500–5000 m), dominated by Nuttallides umbonifer and Globocassidulina subglobosa, occurs on the abyssal plain beneath oligotrophic lower Circumpolar Water south-east of the Subantarctic Front and is strongly influenced by the cold, carbonate-corrosive conditions. The faunal composition of this subantarctic region is most similar to adjacent southern New Zealand, but with the addition of a few significant Antarctic elements (e.g., E. glabra, Globocassidulina crassa).

Relationships between Biochemical Bone Turnover Markers, Season, and Inflammatory Status Indices in Prepubertal Gambian Boys

Seasonal and interindividual differences in food availability and illnesses cause variations in growth, including bone growth, in children in developing countries. We investigated seasonal differences in biochemical (serum) markers of bone metabolism and relationships between these markers (procollagen type I N propeptide [P1NP], serum C-terminal telopeptide of type 1 collagen [S-CTX]) and serum markers of inflammation (alpha(1)- antichymotrypsin [ACT], C-reactive protein [CRP], sialic acid) in prepubertal Gambian boys. Three seasonal time points were chosen: August, mid-rainy season; October, late rainy season (both are associated with decreased food supply, increased prevalence of infection, reduced weight gain, and stunting); and April, late dry season, when environmental conditions are better and rates of weight gain are higher. The prevalence of raised inflammatory markers was high: 29% of ACT values >0.40 g/L in August, 42% >0.40 g/L in October, and 18% >0.40 g/L in April. Of CRP values, 92-96% were >0.47 mg/L and 30%, 46%, and 18% were >3.95 mg/L in August, October, and April, respectively. Also, 42-52% of sialic acid values were >648 mg/L. Of the bone markers, S-CTX exhibited the highest values in August; P1NP did not vary with season. Inverse relationships between each bone marker and the acute phase markers occurred, with the strongest relationships between P1NP and ACT or sialic acid. We conclude that bone collagen synthesis and turnover are reduced during inflammation in rural Gambian boys. Biochemical indices can provide powerful, single-time point evidence of infection and growth-faltering episodes.

Aquatic invertebrate responses to fish presence and vegetation complexity in Western Boreal wetlands, with implications for Waterbird productivity

Aquatic invertebrates are essential to wetland function, serving as the key trophic link between primary producers, fish, and waterfowl in boreal wetlands. We studied how both aquatic vegetation complexity and prevalence, and fish presence, could be used to predict the distribution of invertebrate biomass in 24 wetlands of the Western Boreal Forest (WBF). The percent volume occupied by aquatic plants was significantly positively associated with overall invertebrate biomass per liter (P = 0.009). Particular invertebrate functional feeding groups were correlated with types of aquatic macrophyte architecture; herbivorous invertebrate biomass (mg/L) was greater in more complex aquatic environments, and predatory invertebrate biomass was greater in environments with simple plant architecture. Wetlands inhabited by Brook Stickleback (Culaea inconstans) had reduced invertebrate biomass of the predatory, non-predatory (excluding omnivores), and gatherer/collector functional feeding groups. Gatherer/collector, predator, shredder, and piercer invertebrate groups were negatively correlated with dissected leaved plant dominance in those wetlands without fish. These invertebrate groups comprise the bulk of invertebrate protein available to nesting hen mallards and their ducklings. We suggest that the presence of stickleback and/or dominance of dissected leaved plants in the wetlands of the WBF results in decreased food supply for hatchling waterfowl.

NATURALIZED POPULATIONS OF OYSTERS, CRASSOSTREA GIGAS ALONG THE SOUTH AFRICAN COAST: DISTRIBUTION, ABUNDANCE AND POPULATION STRUCTURE

Abstract The Japanese oyster Crassostrea gigas forms the mainstay of the South African oyster farming industry. Despite having been cultured along the South African coast for 30 years, this is the first record of naturalized populations of this well known global invader from the region. DNA sequence data confirmed the presence of C. gigas in the Breede and Goukou estuaries. Populations of 184,206 ± 21 058.9 (SE), 876 ± 604.2 (SE) and 1 228 ± 841.8 (S.E.) individuals were recorded in the Breede, Goukou and Knysna estuaries respectively. No C. gigas were recorded from the open coast. The condition index of oysters in the Goukou and Knysna estuaries differed significantly from those in the Breede Estuary (Kruskal-Wallis ANOVA H = 48.249, P 0.05). The lower condition index recorded in the Breede Estuary is believed to reflect decreased food supply as a result of the large C. gigas population prese...

Cretaceous/Paleogene boundary bathyal paleo-environments in the central North Pacific (DSDP Site 465), the Northwestern Atlantic (ODP Site 1049), the Gulf of Mexico and the Tethys: The benthic foraminiferal record

Uppermost Maastrichtian benthic foraminiferal assemblages (> 63 μm) are diverse, indicating mesotrophic conditions in lower bathyal DSDP Hole 465A (Hess Rise, central North Pacific), in 4 lower bathyal land sections in central-East and Northeastern Mexico, and in the upper to middle bathyal Agost section (Tethys area, Southeastern Spain). They indicate more eutrophic conditions in lower bathyal ODP Hole 1049C (Blake Nose, Northwestern Atlantic). Benthic foraminifers did not suffer significant extinction at the K/Pg boundary, but diversity and heterogeneity of the assemblages and the percentage of infaunal morphogroups decreased drastically in all sections, with the exception of DSDP Hole 465A where the percentage of infaunal taxa increased. These faunal changes probably reflect the effect on the benthic faunas of a widespread decrease in the food supply to the sea floor, as a result of the collapse of primary productivity at the K/Pg boundary. The decrease in food supply apparently affected the benthic faunas least at more eutrophic NW Atlantic ODP Site 1049 and at Pacific DSDP Site 465, which is distal from the impact site of the K/Pg bolide on the Yucatan Peninsula. At these sites the faunas recovered within the Parvulorugoglobigerina eugubina Biozone (∼ 100 ky), although diversity and heterogeneity remained low through the early Danian, possibly indicating environmental stress. This stress might be related to a high or fluctuating food supply by primary producers that could not easily be used by the benthos, such as various bloom species of dinoflagellates. Benthic assemblages recovered more slowly (∼ 300 ky) in the Mexican and Spanish sections. Low oxygen conditions after the K/Pg boundary could be inferred from the benthic assemblages at Agost (Southeastern Spain) only. A short episode of hypoxia, however, may be obscured at Pacific DSDP Hole 465A by drilling disturbance, and in the Mexican sections and Hole 1049C by incomplete sections due to downslope transport. Benthic foraminiferal assemblages thus appear to have been affected by the collapse of primary productivity at the K/Pg boundary to a different extent in different regions, and took different lengths of time for their recovery after the boundary.

FOOD FOR THE CITIES: URBAN AGRICULTURE IN DEVELOPING COUNTRIES

FOOD FOR THE CITIES: URBAN AGRICULTURE IN DEVELOPING COUNTRIES

Natural variation in a metallothionein-like protein in Tubifex tubifex in the absence of metal exposure

Concentrations of a metallothionein-like protein (MTLP) in Tubifex tubifex were consistent throughout the various life stages with no significant variation associated with reproductive stage. The mean concentration from cocoon through 10 weeks of age was 2.5 (±0.6) nmol MTLP/g. T. tubifex was subjected to a number of potential environmental stressors to determine whether MTLP production could be induced in the absence of metal exposure. There were no significant differences in the concentrations of MTLP between the controls and worms subjected to decreased food supply, increased handling, or reduced dissolved oxygen at a given exposure temperature. However, at 12°C T. tubifex had significantly ( P<0.01) higher MTLP than T. tubifex held at 23°C. There were also significant differences in wet weight and reproduction at the two temperatures, which may have implications for the levels of MTLP.

Benthic response to ice-edge-induced particle flux in the Arctic Ocean

With the aims of investigating the response of the smallest benthic biota to a strong ice-edge-related input of phytodetritus, and of registering supposed lateral transportation processes of phytodetrital matter with northerly direction under the ice, we analysed a number of abiotic and biotic parameters in surface sediments from the northern Fram Strait. Two transects of 14 stations in total were made. One transect, crossing the Fram Strait from the east to the west, followed mainly the ice edge. The second transect extended latitudinally in a northerly direction, starting in ice-free areas, passing the ice edge, and ending in heavy ice-covered areas, approximately 100 nm north of the ice edge. Stations along this transect were sampled at almost constant water depths to avoid depth-related influences in our investigations. Results showed the expected high phytodetritus concentrations in the ice-edge vicinity. Concentrations of sediment-bound plant pigments were approximately 5 times higher than in ice-covered areas, indicating a very strong phytodetritus input. With increasing distance from the highly productive areas at the ice edge, we found significantly decreasing concentrations of phytodetrital input to the seafloor in a northerly direction. Within the foraminiferans, generic diversity was clearly reduced in the area of strong phytodetritus deposition. Along the latitudinal transect, out of the direct ice-edge influence, foraminiferal diversities slowly increased within increasing distance from the ice edge. The integration of results from earlier foraminiferal investigations, from stations further to the north, indicates a once more decreasing diversity with continually decreasing food supply.

Phylogeny of Mammalian metabolism

Mammals are at the end of a gradual metabolic evolution in the course of which the step from anaerobic to aerobic cellular metabolism and the transition from water to land life formed the basis for an increase in metabolic rate (from brady- to tachymetabolism). The increased metabolic rate and the resulting endogenous heat production were the preconditions for enhanced long-term performance as well as for homeothermy which allowed mammals and birds to invade temperate zones. However, the underlying increase in membrane permeability also results in an increased energy demand (for membrane pump activity) which leads to the reduced hypoxia tolerance of mammals and requires a permanent substrate supply. As an adaptation to a seasonal discrepancy between increased thermoregulatory energy demand and decreased food supply, some small mammals apparently extended the newly evolved non-REM-sleep into hibernation. Mammalian hibernation is characterized by a profound metabolic reduction which is influenced by acidosis and limited to a tolerable degree by maintained thermoregulation. The lower limit of cooling seems to be determined by a critical minimal metabolic rate which is common to all mammals. The higher the normothermic metabolic rate, the lower is the temperature at which this minimal metabolic rate is reached. Since specific (i. e., weight-corrected) basal metabolic rate increases with decreasing body mass, small mammals exhibit a higher hypothermia tolerance than larger ones. On the other hand, the metabolic decrease to a uniform minimal level reflects an inactivation of the overall metabolic size relationship and, thus, forms a counterpart to the metabolic increase from a lower fetomaternal to the higher size-related level, occurring after birth. The postnatal metabolic increase which favours the onset of thermoregulation, parallels the increase in oxygen tension at the transition from fetal to adult circulation and, thus, probably enables mammalian neonates to readjust their metabolic needs in response to hypoxia. There is increasing evidence that, similar to the step from anaerobiosis to aerobiosis, the increase in metabolic rate resulting from any increase in oxygen supply is a general principle of evolution that, apart from its further adaptive benefits, protects tissues from oxygen excess and subsequent oxidative stress.

Late Quaternary deep-sea ostracodes in the polar and subpolar North Atlantic: paleoecological and paleoenvironmental implications

Two sediment cores from the northern North Atlantic, one from the Iceland Plateau and one from the Rockall Plateau, were investigated in order to examine the response of deep-sea benthic ostracodes to climate-related environmental changes since marine isotope stage (MIS) 7. Ostracode fauna was divided into three factor assemblages by using Q-mode factor analyses and diversity was calculated using the Shannon–Wiener index. The Iceland Plateau revealed an ‘interglacial assemblage’ dominated by Henryhowella, a transitional assemblage dominated by Eucythere, and a ‘background assemblage’ that consists of the common taxa Krithe and Cytheropteron. The presence of Henryhowella is linked to conditions that prevailed during the peak interglacial periods (MIS 5e and 1), characterized by increased food supply, well-oxygenated bottom water, and lateral advection. The presence of Eucythere, mainly during the interstadial periods, appears to be related to slightly increased food supply, whereas the ‘background assemblage’ is considered to be opportunistic and able to cope with decreased food supply as interpreted for glacial times. On the Rockall Plateau the opportunistic ‘background assemblage’ (consisting mainly of Krithe, Argilloecia, and Cytheropteron) shows no obvious relation to climate changes. The ‘interglacial assemblage’ consists of several taxa dominated by Pelecocythere but, as on the Iceland Plateau, it also contains Henryhowella. The third assemblage is the ‘glacial assemblage’ that consists of a variety of taxa, several of which are known from the modern Arctic Ocean and the Greenland Sea shelf. Thus, this assemblage indicates glacial conditions on the Rockall Plateau that are comparable to those found in the present-day Arctic Ocean. Diversity calculations revealed higher ostracode diversities in glacial than in interglacial episodes in both cores and particularly high diversities during periods of increased input of iceberg-rafted debris (IRD) in the Rockall Plateau core. Both cores reveal lower surface-water productivity during the glacial compared to the interglacial periods and particularly low productivity during the IRD events, as inferred from carbonate contents. We assume, therefore, that ostracode diversity in the study areas is negatively correlated with food flux.

Benthic foraminifera at the Cretaceous-Tertiary boundary around the Gulf of Mexico

Cretaceous-Tertiary (K-T) boundary sections in northeastern Mexico contain marly formations separated by a controversial clastic unit. Benthic foraminifera in seven sections indicate middle and lower bathyal depths of deposition for the marls, with the exception of the upper bathyal northernmost section. Mixed neritic-bathyal faunas were present in the clastic unit, indicating redeposition in the deep basin by mass-wasting processes resulting from the K-T bolide impact in the Gulf of Mexico. Benthic foraminifera in the Mexican sections, and at other deep-sea locations, were not subject to major extinction at the time of impact, but there were temporary changes in assemblage composition. Benthic faunas indicate welloxygenated bottom waters and mesotrophic conditions during the late Maastrichtian and increased food supply during the latest Maastrichtian. The food supply decreased drastically just after the K-T boundary, possibly because of the collapse of surface productivity. Cretaceous and early Paleogene benthic foraminifera, however, did not exhibit the benthic-pelagic coupling of present-day faunas, as documented by the lack of significant extinction at the K-T collapse of surface productivity. Much of the food supplied to the benthic faunas along this continental margin might have been refractory material transported from land or shallow coastal regions. The decrease in food supply at the K-T boundary might be associated with the processes of mass wasting, which removed surface, food-rich sediment. Benthic faunas show a staggered pattern of faunal recovery in the lowermost Paleogene, consistent with a staged recovery of the vertical organic flux but also with a gradual buildup of organic matter in the sediment.