Frans Jorissen

Bio: Frans Jorissen is an academic researcher from University of Angers. The author has contributed to research in topics: Foraminifera & Benthic zone. The author has an hindex of 58, co-authored 131 publications receiving 12421 citations. Previous affiliations of Frans Jorissen include University of Bordeaux & Centre national de la recherche scientifique.

Live benthic foraminiferal faunas off Cape Blanc, NW-Africa: Community structure and microhabitats

Abstract: Live (Rose-Bengal stained) benthic foraminifera were studied along a transect across the main area of organic matter deposition in the Cape Blanc upwelling region. The faunal analyses suggest that at the shallowest station (1200 m) the benthic ecosystem is permanently influenced by the upwelling, whereas at the deepest stations (3010 and 2530 m depth) the ocean bottom is subject to significant organic influxes only in summer. The vertical zonation of foraminiferal species in the sediment shows a close correspondence with the depth distribution of oxic respiration, nitrate and sulphate reduction. It is suggested that this linkage is caused by the presence of various stocks of anaerobic and sulphate- and nitrate-reducing bacteria. Deep infaunal foraminiferal species are thought to feed selectively, either on the bacterial stocks or on nutritious particles produced by bacterial degradation of more refractory organic matter. As such, foramininiferal microhabitats are only indirectly controlled by pore water oxygen concentrations.

Seasonal and interannual variability of benthic foraminiferal faunas at 550 m depth in the Bay of Biscay

Abstract: Live benthic foraminiferal faunas were sampled 10 times between October 1997 and April 2000 at a 550 m depth open-slope station in the Bay of Biscay. Duplicate cores for 5 samplings allow distinguishing between spatial and temporal variability of the foraminiferal faunas. Although spatial patchiness of the foraminiferal faunas is substantial, especially in the 63–150 μm fraction, the temporal variability appears to be larger. The foraminiferal patterns are compared with surface water primary production as assessed by the study of available SeaWIFS satellite images. In the study area, the primary production regime is marked by a pulselike and prolonged spring bloom and possibly a short fall bloom. Such periods of elevated chlorophyll-a concentration are followed, after a delay of about 4–6 weeks, by a strong frequency increase of the most opportunistic taxa of benthic foraminifera. Surprisingly, no change of bottom and interstitial water oxygenation and of redox conditions within the sediment is recorded. The small taxa Epistominella exigua, Reophax guttiferus, Bolivina spathulata, Cassidulina carinata and Nuttallides pusillus appear to respond first to a labile organic matter input, by a reproductive event marked by a strong patchy spatial distribution hypothetically resulting of the spatial heterogeneity of organic matter deposits. Uvigerina peregrina and Uvigerina mediterranea, the most opportunistic larger taxa, strongly dominate the >150 μm fraction during eutrophic periods (spring and fall blooms). Intermediate and deep infaunal taxa seem to depend less on fresh organic matter input, even if a small frequency increases are recorded in the >150 μm fraction during the most productive periods; Globobulimina affinis and Melonis barleeanus show reproductive events in rather shallow sediment layers in the more oligotrophic periods of the year. A conceptual model explains the increasing delay in the response to important phytoplankton bloom periods for the successive benthic ecosystem compartments.

Bathymetric distribution and microhabitat partitioning of live (Rose Bengal stained) benthic Foraminifera along a shelf to bathyal transect in the southern Adriatic Sea

Abstract: Rose Bengal stained foraminifera from box cores, collected in the southern Adriatic Sea along a transect ranging from 146 to 1,200 m water depth, have been studied. Total numbers of supposedly deposit-feeding foraminifera decrease in a fairly regular manner with increasing water depth and distance from land, probably as a consequence of a decreasing flux of organic matter. Suspension-feeding astrorhizid taxa have an irregular distribution, apparently not related to water depth. Highest numbers of stained foraminifera are invariably found at the sediment surface, whereas numbers decrease exponentially deeper in the sediment. Although most species have maximum densities near the sediment surface, a few of the rarer species are concentrated at deeper levels in the sediment. The vertical distribution patterns of a number of common species are variable with depth along the transect, apparently determined by several different environmental parameters.

Biofacial patterns in river-induced shelf anoxia

Abstract: Abstract Three areas were studied to assess the effects of riverine input on the marine benthic ecosystem: the Adriatic Sea (with the Po river), the Orinoco-Paria shelf (with the Orinoco and Essequibo rivers) and the northern Gulf of Mexico (with the Mississippi and Rio Grande rivers). In all these areas, the interplay of river-discharge and subsequent transport by surface-water currents has resulted in the deposition of a zone with finegrained, organic-rich sediments parallel to the coast. The foraminiferal associations occupying these mud-belts indicate the occurrence of regular, widespread anoxic or dysoxic conditions at the sediment-water interface. Across the mud belt, benthic foraminifera display a very characteristic zonation, which is essentially the same in all areas studied. In the centre of the zone, low diversity and the presence of opportunistic species indicate a degree of stress. A model which describes the microhabitat occupation within these muddy zones is discussed in some detail. We conclude that the width of the shelf, together with the force of the long-shore current carrying the riverine products into the basin, are essential in determining the occurrence of dysoxic or anoxic conditions while the discharge volume of rivers is a subordinate factor. The chance of anoxia appears to be highest during periods of high sea level, leading to large shelf areas. A final conclusion is that benthic formainifera are excellent tools for determining the occurrence and degree of marine eutrophication induced by the input of polluted river waters.

The genetic legacy of the Quaternary ice ages

Abstract: Global climate has fluctuated greatly during the past three million years, leading to the recent major ice ages. An inescapable consequence for most living organisms is great changes in their distribution, which are expressed differently in boreal, temperate and tropical zones. Such range changes can be expected to have genetic consequences, and the advent of DNA technology provides most suitable markers to examine these. Several good data sets are now available, which provide tests of expectations, insights into species colonization and unexpected genetic subdivision and mixture of species. The genetic structure of human populations may be viewed in the same context. The present genetic structure of populations, species and communities has been mainly formed by Quaternary ice ages, and genetic, fossil and physical data combined can greatly help our understanding of how organisms were so affected.

Supporting Online Material for Spreading Dead Zones and Consequences for Marine Ecosystems

Abstract: Dead zones in the coastal oceans have spread exponentially since the 1960s and have serious consequences for ecosystem functioning. The formation of dead zones has been exacerbated by the increase in primary production and consequent worldwide coastal eutrophication fueled by riverine runoff of fertilizers and the burning of fossil fuels. Enhanced primary production results in an accumulation of particulate organic matter, which encourages microbial activity and the consumption of dissolved oxygen in bottom waters. Dead zones have now been reported from more than 400 systems, affecting a total area of more than 245,000 square kilometers, and are probably a key stressor on marine ecosystems.

Depletion, Degradation, and Recovery Potential of Estuaries and Coastal Seas

Abstract: Estuarine and coastal transformation is as old as civilization yet has dramatically accelerated over the past 150 to 300 years. Reconstructed time lines, causes, and consequences of change in 12 once diverse and productive estuaries and coastal seas worldwide show similar patterns: Human impacts have depleted >90% of formerly important species, destroyed >65% of seagrass and wetland habitat, degraded water quality, and accelerated species invasions. Twentieth-century conservation efforts achieved partial recovery of upper trophic levels but have so far failed to restore former ecosystem structure and function. Our results provide detailed historical baselines and quantitative targets for ecosystem-based management and marine conservation.

Post-glacial re-colonization of European biota

Abstract: Population structure is the result of both present processes and past history. Molecular markers are proving of great value in describing the former, and it is important to similarly determine the latter in order to understand their respective contributions. The study of palaeo-climates has also advanced significantly, and in particular that of the Pleistocene ice ages, which modified species ranges considerably. The last ice age and rapid post-glacial colonization of Europe is summarized. Possible population genetic consequences of expansion northward from southern refugia, and those of remaining in these mountainous regions are discussed. A series of recent case studies are detailed where DNA sequence information has been used to describe species genetic variation and subdivision across Europe. These include a grasshopper, the hedgehog, oak trees, the common beech, the black alder, the brown bear, newts, shrews, water vole, silver fir and house mice. These molecular data confirm southern peninsulas of Europe as major ice age refugia, and in most cases demonstrate that genetically distinct taxa emerged from them. They can thus define genomic differences and so greatly augment previous fossil data. The refugial genomes contributed differently in various species to the re-colonization of Europe, with three broad patterns described as paradigms—«grasshopper», «hedgehog» and «bear». These different expansion patterns produced clusters of hybrid zones where they made contact, and it is argued that many species genomes may be further cryptically subdivided. A reduction in diversity from southern to northern Europe in the extent of allelic variation and species subdivision is seen; this is attributed to rapid expansion northward and the varied topography of southern refugia allowing populations to diverge through several ice ages. The differences in DNA sequence indicate that some species have been diverging in refugial regions for a few ice ages at most, whilst distinct lineages in other species suggest much more ancient separation.

Climate Change Impacts on Marine Ecosystems

Abstract: In marine ecosystems, rising atmospheric CO2 and climate change are associated with concurrent shifts in temperature, circulation, stratification, nutrient input, oxygen content, and ocean acidification, with potentially wideranging biological effects. Population-level shifts are occurring because of physiological intolerance to new environments, altered dispersal patterns, and changes in species interactions. Together with local climate-driven invasion and extinction, these processes result in altered community structure and diversity, including possible emergence of novel ecosystems. Impacts are particularly striking for the poles and the tropics, because of the sensitivity of polar ecosystems to sea-ice retreat and poleward species migrations as well as the sensitivity of coral-algal symbiosis to minor increases in temperature. Midlatitude upwelling systems, like the California Current, exhibit strong linkages between climate and species distributions, phenology, and demography. Aggregated effects may modify energy and material flows as well as biogeochemical cycles, eventually impacting the overall ecosystem functioning and services upon which people and societies depend.