Misplaced Pages

#715284

30-522: Westonoceratidae are exogastric, mostly compressed, Discosorida of moderate size from the Middle Ordovician to the Lower Silurian . The siphuncle is typically close to the convexly curved outer margin of the phragmocone – the chambered part of the shell – taken to be ventral but may be more central in some genera. Connecting rings are thin to moderately thick with inflated bullettes grasping

60-495: A decrease in benthic macroinvertebrate biomass, which lead to the disappearance of food sources into the substrate. Because the benthic system regulates energy in aquatic ecosystems, studies have been made of the mechanisms of the benthic zone in order to better understand the ecosystem. Benthic diatoms have been used by the European Union's Water Framework Directive (WFD) to establish ecological quality ratios that determined

90-411: A great variety of physical conditions differing in: depth, light penetration and pressure. Depending on the water-body, the benthic zone may include areas that are only a few inches below the surface. The continental shelf is a gently sloping benthic region that extends away from the land mass. At the continental shelf edge, usually about 200 metres (660 ft) deep, the gradient greatly increases and

120-503: A rapidly expanding siphuncle with segments that extend into the adjacent chambers, and parietal deposits within the siphuncle that overlap to form endocones. The Discosorida include these families, more or less in phylogenetic sequence beginning with the oldest: These form three basin evolutionary lineages. The first, formed by the Reudemannoceratidae, Cyrtogomphoceratidae, and Phragmoceratidae, are fundamentally endogastric with

150-400: Is known as the continental slope. The continental slope drops down to the deep sea floor. The deep-sea floor is called the abyssal plain and is usually about 4,000 metres (13,000 ft) deep. The ocean floor is not all flat but has submarine ridges and deep ocean trenches known as the hadal zone . For comparison, the pelagic zone is the descriptive term for the ecological region above

180-466: Is not easy to map or observe these organisms and their habitats, and most modern observations are made using remotely operated underwater vehicles (ROVs), and rarely submarines . Benthic macroinvertebrates have many important ecological functions, such as regulating the flow of materials and energy in river ecosystems through their food web linkages. Because of this correlation between flow of energy and nutrients, benthic macroinvertebrates have

210-655: Is recommended in the European Union benthic monitoring program (by Kelly 1998 for the United Kingdom then in the EU and for the EU as a whole by CEN 2003 and CEN 2004) and in some United States programs (by Moulton et al. 2002). Benthic gross primary production (GPP) may be important in maintaining biodiversity hotspots in littoral zones in large lake ecosystems . However, the relative contributions of benthic habitats within specific ecosystems are poorly explored and more research

240-552: The Plectronoceratida rather than through the more developed Ellesmerocerida , as did the other orders. Finally and most diagnostic, discosorids developed a reinforcing, grommet -like structure in the septal opening of the siphuncle known as the bullette, formed by a thickening of the connecting ring as it draped around the folded back septal neck. The origin of the Discosorida is unknown, thought at one time to be directly from

270-656: The Plectronocerida . Evolution within the order begins with the lower Middle Ordovician Reudemannoceratidae and from there diverges into three main lineages. Questionable discosorids have been reported as early as the Middle Tremadocian - near the start of the Ordovician, however the first bona fide examples date to the Middle Ordovician. The diversification of the Discosorida, in terms of genera, peaked at

300-466: The water column ; even within the benthic zone variations in such factors as light penetration, temperature and salinity give rise to distinct differences, delineated vertically, in the groups of organisms supported. Many organisms adapted to deep-water pressure cannot survive in the upper parts of the water column: the pressure difference can be very significant (approximately one atmosphere for each 10 meters of water depth). Many have adapted to live on

330-452: The Discosorida resembled the Oncocerida , which lived about the same time, but evolved from a completely different stock. The two convergent groups differ in their internal detail. Benthic The benthic region of the ocean begins at the shore line ( intertidal or littoral zone ) and extends downward along the surface of the continental shelf out to sea. Thus, the region incorporates

SECTION 10

#1732877284716

360-517: The ability to influence food resources on fish and other organisms in aquatic ecosystems . For example, the addition of a moderate amount of nutrients to a river over the course of several years resulted in increases in invertebrate richness, abundance, and biomass . These in turn resulted in increased food resources for native species of fish with insignificant alteration of the macroinvertebrate community structure and trophic pathways. The presence of macroinvertebrates such as Amphipoda also affect

390-526: The beginning in the Middle Ordovician (modern Darriwilian stage) followed by a decline in the Upper Ordovician (modern Sandbian and Katian stages) only to peak again in the Middle Silurian. Afterwards their diversity declined drastically and remained low until their end in the late Devonian. Some were endogastrically curved, with the lower, siphuncle side concave, others were exogastrically curved with

420-519: The beginning of the Middle Ordovician , through the Silurian , and into the Devonian . Discosorids are unique in the structure and formation of the siphuncle , the tube that runs through and connects the camerae (chambers) in cephalopods, which unlike those in other orders is zoned longitudinally along the segments rather than laterally. Siphuncle structure indicated that the Discosorida evolved directly from

450-418: The benthic food chain ; most organisms in the benthic zone are scavengers or detritivores . Some microorganisms use chemosynthesis to produce biomass . Benthic organisms can be divided into two categories based on whether they make their home on the ocean floor or a few centimeters into the ocean floor. Those living on the surface of the ocean floor are known as epifauna . Those who live burrowed into

480-969: The benthic zone. The microbes found in the benthic zone, specifically dinoflagellates and foraminifera , colonize quite rapidly on detritus matter while forming a symbiotic relationship with each other. In the deep sea, which covers 90–95% of the ocean floor, 90% of the total biomass is made up of prokaryotes. To release all the nutrients locked inside these microbes to the environment, viruses are important in making it available to other organisms. Modern seafloor mapping technologies have revealed linkages between seafloor geomorphology and benthic habitats, in which suites of benthic communities are associated with specific geomorphic settings. Examples include cold-water coral communities associated with seamounts and submarine canyons, kelp forests associated with inner shelf rocky reefs and rockfish associated with rocky escarpments on continental slopes. In oceanic environments, benthic habitats can also be zoned by depth. From

510-400: The benthos, including the water column up to the surface. At the other end of the spectrum, benthos of the deep ocean includes the bottom levels of the oceanic abyssal zone . For information on animals that live in the deeper areas of the oceans see aphotic zone . Generally, these include life forms that tolerate cool temperatures and low oxygen levels, but this depends on the depth of

540-439: The deposition of organic matter, and bacterial communities. The amount of material sinking to the ocean floor can average 307,000 aggregates per m per day. This amount will vary on the depth of the benthos, and the degree of benthic-pelagic coupling. The benthos in a shallow region will have more available food than the benthos in the deep sea. Because of their reliance on it, microbes may become spatially dependent on detritus in

570-457: The dominance of certain types of algae in Benthic ecosystems as well. In addition, because benthic zones are influenced by the flow of dead organic material , there have been studies conducted on the relationship between stream and river water flows and the resulting effects on the benthic zone. Low flow events show a restriction in nutrient transport from benthic substrates to food webs, and caused

600-649: The ecological status of lakes in the UK. Beginning research is being made on benthic assemblages to see if they can be used as indicators of healthy aquatic ecosystems. Benthic assemblages in urbanized coastal regions are not functionally equivalent to benthic assemblages in untouched regions. Ecologists are attempting to understand the relationship between heterogeneity and maintaining biodiversity in aquatic ecosystems. Benthic algae has been used as an inherently good subject for studying short term changes and community responses to heterogeneous conditions in streams. Understanding

630-598: The genus Teichertoceras , a derivative of Ulrichoceras . One goes simply from Westonoceras to Winnipegoceras . The other goes from Faberoceras to Clarkesvillia to Glyptodendron . Faberoceras may also have given rise to Hecatoceras and Reedsoceras and is the likely source for the Lowoceratidae. Two other genera are included, but are separately derived from Ulrichoceras . These are Sinclairoceras and Simardoceras . Discosorida Discosorida are an order of cephalopods that lived from

SECTION 20

#1732877284716

660-456: The ocean floor are known as infauna . Extremophiles, including piezophiles , which thrive in high pressures, may also live there. An example of benthos organism is Chorismus antarcticus . Sources of food for benthic communities can derive from the water column above these habitats in the form of aggregations of detritus , inorganic matter, and living organisms. These aggregations are commonly referred to as marine snow , and are important for

690-471: The potential mechanisms involving benthic periphyton and the effects on heterogeneity within a stream may provide a better understanding of the structure and function of stream ecosystems. Periphyton populations suffer from high natural spatial variability while difficult accessibility simultaneously limits the practicable number of samples that can be taken. Targeting periphyton locations which are known to provide reliable samples – especially hard surfaces –

720-710: The previous septal foremina. Parietal deposits within the siphuncle from endocones in advanced genera and cameral deposits are found in some. The Westonoceratidae are derived from the Cyrtogomphoceratidae through the cyrtogomphoceratid, Ulrichoceras . In turn, the Westonoceratidae gave rise to a small group of discosorids, the Lowoceratidae , which form an intermediary step before the Discosoridae . Two principal lineages have been identified, both stemming from

750-528: The same side convex. In some, the aperture was a simple opening. In others, it became contracted into a pattern of slits. In earlier, Ordovician forms, the bullette became quite large and readily noticeable. In later forms, the bullette became reduced, in some to the point of being vestigial. The Discosoridae, one of the last families to evolve, found in Silurian and questionably in Devonian rocks, are characterized by

780-664: The shallowest to the deepest are: the epipelagic (less than 200 meters), the mesopelagic (200–1,000 meters), the bathyal (1,000–4,000 meters), the abyssal (4,000–6,000 meters) and the deepest, the hadal (below 6,000 meters). The lower zones are in deep, pressurized areas of the ocean. Human impacts have occurred at all ocean depths, but are most significant on shallow continental shelf and slope habitats. Many benthic organisms have retained their historic evolutionary characteristics. Some organisms are significantly larger than their relatives living in shallower zones, largely because of higher oxygen concentration in deep water. It

810-538: The siphuncle near the inside or longitudinally concave curvature. The second, formed by the Westonoceratidae, Lowoceratidae, and Discosoridae, are fundamentally exogastric with the siphuncle near the outside or longitudinally convex curvature, although the Discosoridae are somewhat different. The third, consisting of the Mandaloceratidae and Mesoceratidae are basically straight (orthoconic). Families differ primarily in

840-536: The structural details of the siphuncle and in the nature of the aperture. Discosorids were probably benthic forms that crawled over the bottom in search of food or safety, or hovered close to the bottom. The general orientation during life was most likely head down, with the aperture of the shell facing the general direction of the sea floor and shell carried above. Nothing is known of what the animal itself may have looked like; how many tentacles they had and relative length or how well they may have seen. In general form

870-442: The substrate (bottom). In their habitats they can be considered as dominant creatures, but they are often a source of prey for Carcharhinidae such as the lemon shark . Because light does not penetrate very deep into ocean-water, the energy source for the benthic ecosystem is often marine snow . Marine snow is organic matter from higher up in the water column that drifts down to the depths. This dead and decaying matter sustains

900-440: The water. As with oceans, the benthic zone is the floor of the lake, composed of accumulated sunken organic matter . The littoral zone is the zone bordering the shore; light penetrates easily and aquatic plants thrive. The pelagic zone represents the broad mass of water, down as far as the depth to which no light penetrates. Benthos are the organisms that live in the benthic zone, and are different from those elsewhere in

#715284