Subsurface Deposit Research Articles

Abyssal benthos of the Venezuela Basin, Caribbean Sea: standing stock considerations

Standing stocks of four size classes of benthic organisms were compared among three sedimentary provinces in the Venezuela Basin. Total biomass was dominated by microbiota and filter-feeding glass sponges that were abundant in both macrofaunal and megafaunal size classes. The remaingng biomass was divided among predominantly deposit-feeding meiofauna, macrofauna and megafauna. The concentration of biomass in smaller sized classes in the Venezuela Basin was in general agreement with the results of other deep-sea investigations. By contrast, biomass in shallow-water benthic assemblages is concentrated in the larger sized classes. We postulate that these differences in the distribution of biomass among benthic size classes results, in part, from differences in the quality and quantity of organic matter available to shallow-water and deep-sea communities. Most of the labile organic matter that reaches the deep-sea bottom in the Venezuela Basin is consumed at or near the sediment-water interface by surface deposit-feeding and filter-feeding benthos. Transformation of refractory organic matter into utilizable substrate by bacteria in the upper 10–20 cm of sediment provides a source of food for subsurface deposit feeders. Biological mixing may also play a role in the transfer of recently deposited organic matter to subsurface deposit feeders.

Meiofaunal prominence and benthic seasonality in a coastal marine ecosystem

The muds of a shallow (7 m) site in Narragansett Bay, Rhode Island contained higher abundances of meiofauna (averaging 17×106 individuals per m2 and ash free dry weight of 2.9 g/m2 during a 3 year period) than have been found in any other sediment. The majority of sublittoral muds, worldwide, have been reported to contain about 106 individuals per m2. This difference is attributed primarily to differences in sampling techniques and laboratory processing.Extremely high meiofaunal abundances may have also occurred because Narragansett Bay sediments were a foodrich environment. While the quantity of organic deposition in the bay is not unusually high for coastal waters, this input, primarily composed of diatom detritus, may contain an unusually high proportion of labile organics. Furthermore, meiofauna could have thrived because of spatial segregation of meiofauna and macrofauna. While meiofauna were concentrated at the sediment-water interface, most macrofauna were subsurface deposit feeders. Macrofaunal competition with, and ingestion of meiofauna may thus have been minimized.The seasonal cycles of meiofauna and macrofauna were similar. Highest abundances and biomass were observed in May and June and lowest values in the late summer and fall. Springtime increases of meiofaunal abundance were observed in all depth horizons, to 10 cm. We hypothesize that phytoplankton detritus accumulated in the sediment during the winter and early spring, and that the benthos responded to this store of food when temperatures rose rapidly in the late spring. By late summer, the stored detritus was exhausted and the benthos declined.

A summer benthic survey in Conception Bay, Newfoundland, emphasizing zoogeography of annelids and amphipods

A limited benthic survey was made in August in Conception Bay, Newfoundland, using a 0.2-m2 van Veen grab sampler. Nine stations were sampled in a relatively shallow (62–79 m), soft-bottom (predominantly silt) region with low bottom water (0.2–1.4 °C) and sediment (0.5–2.0 °C) temperatures. Annelids (32 species) and amphipods (18 species) were the common invertebrates collected, with annelids being more numerous, both in numbers of individuals and of species. Deposit-feeding annelids outnumbered carnivores, with subsurface deposit feeders more abundant than surface feeders. Sedentary individuals predominated. Most annelid species had boreal–temperate affinities, with few arctic species being present. Detritivorous amphipods predominated, followed by scrapers and scavengers. Nearly all were burrowers. All the amphipod species were arctic–boreal in distribution and most do not range as far south as do the annelids. Molluscs were small and uncommon and they, like the remaining uncommon components of the biomass, were not identified to any extent.

Stable macrofauna community structure despite fluctuating food supply in subtidal soft sediments of Oslofjord, Norway

At a locality at 32-m depth in Oslofjord, Norway, temperature varied from 4.8° to 9.2°C and salinity varied from 31.2 to 33.3‰ S over a two-year period. There was a peak in chlorophyll a, and C and N in April–June and a smaller peak in November in the sediment. Bacterial numbers showed maxima in July–August and November–December. The macrobenthic fauna was typical of a species-rich and undisturbed boreal community of silt-clay sediments. The community was predominantly composed of surface and subsurface deposit feeders. Over the twoyear period there was little variation in numerical abundance or biomass of the species despite the variation in food input. The lack of seasonality shown by the fauna probably relates to the lack of variability of the physical environment. The mechanism by which this control is achieved, however, is not known. There are large predators/disturbers in the community such as the polychaetes Lumbrineris fragilis, Glycera rouxii, G. alba, Nephthys spp. and the echinoid Brissopsis lyrifera, which probably play an important role in structuring the community.

Volcanic stratigraphy of the Pilot Knob iron deposits, Iron County, Missouri

Two iron deposits, a subsurface deposit of magnetite and a surface deposit of hematite. The bulk of the surface magnetite deposit is a replacement of what originally was a simple cooling unit of an ash-flow tuff. Porosity and permeability were key factors. Because the surface hematite body, which is in approximate updip alignment with the subsurface magnetite deposit, is in reality 240 m stratigraphically higher, a fault is inferred to occur between the two deposits.--Modified journal abstract.

Mass Movement Effects on a Bathyal Macrofaunal Population, California Borderland: ABSTRACT

The benthic macrofauna of Santa Cruz basin, a dysaerobic bathyal basin in the California borderland, is subject to frequent substrate disturbances that erode the muddy surficial deposits, bury more deeply burrowing infauna, and transport shallow-water fauna to deeper environments. The effects on infaunal distributions have been examined through trophic-group and life-habit analyses. X-ray radiography and textural distributions of surficial sediments recovered at 211 box-core stations are complemented by acoustic profiling records. These data indicate that the basin is presently filling by both hemipelagic sedimentation and gravity-induced mass movements. Failures are frequent, and many dislocations involve the uppermost 1 cm of the sediment pile. A single ridge-crest to basin-floor transect of 10 stations has been quantitatively analyzed for macrofauna (> 0.5 mm). Species richness, density, and standing crop decrease from the ridge crest across the slope and fluctuate on the basin floor proper. Polychaetous annelids dominate the benthic macrofauna; crustaceans are second in abundance on the slopes, and mollusks are second on the basin floor. The sand-and-gravel covered crest is equally partitioned by epifaunal suspension feeders and surface-deposit feeders. In comparison, the silty slope is dominated by infaunal, surface, and subsurface deposit feeders. Upper slope populations are evenly divided among sessile and motile species; motile species become more common toward the base of the slope. The basin floor is dominated by motile, infaunal surface-deposit feeders. Substrate instability produces confused and patchy End_Page 441------------------------------ trends at the slope-basin floor boundary. For example, population explosions of the oweniid Myriochele at the base of the slope suggests opportunism related to substrate instability. Significant macrofaunal populations are supported throughout this environment. Repeated disturbance by mass movements produces a downslope trend toward an infaunal, motile life habit. End_of_Article - Last_Page 442------------

Spatial dispersion of benthic Foraminifera in the abyssal central North Pacific 1

Five 0.25‐m2 box cores (four open cores and one vegematic core subdivided in situ into 25 contiguous 10‐ × 10‐cm subcores) reveal that populations of benthic agglutinated Foraminifera in the central North Pacific are extremely abundant and diverse. As many as 120 species and 10,310 total fragments occur in a single open core, and the Foraminifera outnumber all metazoan taxa combined by at least an order of magnitude. Significant patchiness occurs on both the between‐core scale of kilometers and the within‐core scale of centimeters. Few species occurred in all cores and those that did were not abundant. Hierarchical classification and multiple discriminant analysis on the resultant subcore groups in the vegematic core suggest potential interactions between certain species of Foraminifera and such external variables as surface deposit feeders, subsurface deposit feeders, carnivores, filter feeders, biogenic surface structure, and manganese nodules. Multiple regressions of foraminiferan species against all the external variables substantiate the existence of patterns of association. Foraminifera are important components of the benthic fauna, acting, among other things, as predators and disturbance agents. It may well be that they have a more significant effect on the structure and dynamics of deep‐sea henthic communities than have any of the metazoan macrofaunal taxa that are the usual objects of deep‐sea studies.

Food-chain relationships in subtidal silty sand marine sediments and the role of meiofauna in stimulating bacterial productivity.

From bibliographic data the biomass correlations (organic dry weight) are constructed for the subsurface layer of a hypothetical 30 m deep silty sand station: 200 μg/ml macrofauna (including 120 μg/ml subsurface deposit feeders), 50 μg/ml meiofauna, 20 μg/ml Foraminifera, 1 μg/ml Ciliata and Flagellata, and 100 μg/ml bacteria. ATP-biomass is discussed.Meiofauna and Foraminifera contribute with 30 and 12% to the living biomass in the sediment, and it is assumed that their contribution to the food of deposit-feeding macrofauna is of a similar percentage. This is corroborated by productivity estimations.Bacteria are the main food of deposit feeding macrofauna, meiofauna, and microfauna. From different calculations it becomes evident that the productivity of bacteria in the sediment is far below figures achieved in experimental cultures: the conclusion is that sediment bacteria, in general, do not live under good environmental conditions.A rather large part of the bacterial population in the sediment seems to be in the stationary phase of life, and only a fraction of the total population exhibits high metabolic rates and rapid duplications. Only these active bacteria are of importance for the breakdown of relatively refractive organic matter in the sediment.In soft bottom marine sediments where the input of organic matter is higher than the remineralization rate, benthic animals stimulate by their activities and by nutrient cycling the decomposition of detritus via bacteria. Though meiofauna, in principle, feeds upon the same food resource as macrofauna, there is no real competition for food, because meiofaunal animals by their activities and by excreting metabolic end products induce a bacterial productivity which would not be there without them, and feed on it. There are a few examples where more specialized interactions exist between benthic animals and bacteria; these interactions have been termed "gardening". They could be highly important in the benthic ecosystem.

Variable features on Mars. VI. An unusual crater streak in Mesogaea

An unusual, prominent dark streak located in Mesogaea (near 8°N, 191°W) is described. Its appearance is unlike that of most dark streaks on Mars, many of which have ragged outlines, are variable on short time-scales, and are presumed to be erosional. The Mesogaea streak has a tapered, smooth outline, and no changes within it were observed. We suggest that this streak is depositional and that the low-albedo material originated within the associated crater itself. The source area is identified with a compact, low-albedo region on the crater floor. Two possible origins for the dark material are suggested: (1) deflation from a recently exposed, relatively unconsolidated subsurface deposit, and (2) production of ash by a volcanic vent.