Benthic Zone part II

Demersal fish
Demersal fish live on or near the bottom of the sea.  Demersal fish are found by the seafloor in coastal areas on the continental shelf, and in the open ocean they are found along the outer continental margin on the continental slope and the continental rise. They are not generally found at abyssopelagic or hadopelagic depths or on the abyssal plain. They occupy a range of seafloors consisting of mud, sand, gravel or rocks.  In deep waters, rattails and brotulas are common, and other well established families are eels, eelpouts, hagfishes, greeneyes, batfishes and lumpfishes. The bodies of deep water benthic fishes are muscular with well developed organs. In this way they are closer to mesopleagic fishes than bathopelagic fishes. In other ways, they are more variable. Photophores are usually absent, eyes and swimbladder range from absent to well developed. They vary in size, with larger species greater than one meter not uncommon.

Deep sea benthic fish are usually long and narrow. Many are eels or shaped like eels. This may be because long bodies have long lateral lines. Lateral lines detect low-frequency sounds, and some benthic fishes appear to have muscles that drum such sounds to attract mates. Smell is also important, as indicated by the rapidity with which benthic fish find traps baited with bait fish.

The main diet of deep sea benthic fish is invertebrates of the deep sea benthos and carrion. Smell, touch and lateral line sensitivities seem to be the main sensory devices for locating these.  Deep sea benthic fish can be divided into strictly benthic fish and benthopelagic fish. Usually strictly benthic fish are negatively buoyant while benthopelagic fish are neutrally buoyant. Strictly benthic fish stay in constant contact with the bottom. They either lie-and-wait as ambush predators or move actively over the bottom in search for food.

Benthopelagic fish
Benthopelagic fish inhabit the water just above the bottom, feeding on benthos and benthopelagic zooplankton. Most dermersal fish are benthopelagic.  They can be divided into flabby or robust body types. Flabby benthopelagic fishes are like bathopelagic fishes, they have a reduced body mass, and low metabolic rates, expending minimal energy as they lie and wait to ambush prey. An example of a flabby fish is the cusk-eel Acanthonus armatus, a predator with a huge head and a body that is 90 percent water. This fish has the largest ears (otoliths) and the smallest brain in relation to its body size of all known vertebrates.  Robust benthopelagic fish are muscular swimmers that actively cruise the bottom searching for prey. They may live around features, such as seamounts, which have strong currents. Examples are the orange roughy and Patagonian toothfish.


Benthic fish
Some fishes don't fit into the above classification. For example, the family of nearly blind spiderfishes, common and widely distributed, feed on benthopelagic zooplankton. Yet they are strictly benthic fish, since they stay in contact with the bottom. Their fins have long rays they use to "stand" on the bottom while they face the current and grab zooplankton as it passes by.  The deepest-living fish known, the strictly benthic Abyssobrotula galatheae, eel-like and blind, feeds on benthic invertebrates.

At great depths, food scarcity and extreme pressure works to limit the survivability fish. The deepest point of the ocean is about 11,000 meters. Bathypelagic fishes are not normally found below 3,000 meters. The greatest depth recorded for a benthic fish is 8,370 m. It may be that extreme pressures interfere with essential enzyme functions.

Benthic fishes are likely to be found, and are more diverse, on the continental slope, where there is habitat diversity and often food supplies. About 40% of the ocean floor consists of abyssal plains, but these flat, featureless regions are covered with sediment and largely devoid of benthic life (benthos). Deep sea benthic fishes are more likely to associate with canyons or rock outcroppings among the plains, where invertebrate communities are established. Undersea mountains (seamounts) can intercept deep sea currents, and cause productive upwellings which support benthic fish. Undersea mountain ranges can separate underwater regions into different ecosystems.




Waystations

1. Seamounts near Tasmania, Austrailia
44 26.1' S; 147 13.7' E (Hill W 1700m)
44 16.7' S; 147 15.6' E (Sister 1, 693m)

Squares indicate seamounts that have been sampled biologically.  Small black dots indicate predicted locations of ~14 000 seamounts.



Spiny stone or king crab, Lithodes longispina, a species from underwater seamounts south of Tasmania. Hundreds of new species have been discovered on extinct underwater volcanoes, or seamounts, that rise from the sea floor in the Coral Sea and the Tasman Sea between New Caledonia and Tasmania. Many of these creatures have been isolated on their underwater peaks for millions of years with dramatic implications for their conservation.



Caption Typically over 850 vertebrate species live on a seamount, many particular to one mountain.  Many species thought to be extinct have been found: Cataetyx spp. (Bythitidae) and Paralaemonema spp. (Moridae),  and 2 species of Muraenolepis (Muraenolepididae). Within the invertebrate groups thus far examined, as many as 103 species are believed to be new to science.



Fishing with a bulldozer? Pictures before (top) and after (bottom) the trawlers have passed through. Intensive trawl fishing for deep-sea orange roughy near seamounts in recent decades has caused concern.  A 370 square kilometer Marine Protected Area was designated in 1995 to protect 12 seamounts near Tasmania.


2. Cold seep ecology in Sea of Japan (Japan Basin)
39 34' 55" N; 134 34' 11" E
Chemicals don’t only spew out of scalding-hot hydrothermal vents: they also seep from the Earth’s crusts at some locations, at the same temperature as the surrounding seawater.

The deepest cold seep ecosystem discovered so far is located in the Sea of Japan at a depth of 5,000 to 6,500m. Other cold seeps and ‘chemosynthetic biological communities’ have been found in the Gulf of Mexico, the Monterey Canyon off the coast of California, US, and off the coast of Alaska, US.

 Caption  A small bush of tubeworms. When tubeworm bushes are young, only endemic species of animals can colonize them. The presence of the mussels (Bathymodiolis childressi) in the center of the bush means that methane is seeping just below.

Caption The Johnson Sea-Link working near a bush of seep tubeworms. The tubeworms shown here are over 5 feet long and extend far into the sediment below.  Hot vent creatures generally grow fast - giant vent tube worms are one of the fastest-growing animals on Earth. However, their cold seep cousins grow much more slowly. Seep tube worms are thought to live for up to 250 years.

3. Brine pools (NR-1 GC233)
27 45' N; 91 17' W
Since the discovery of vent ecosystems dependent on hydrogen sulfide, scientists have found similar communities living around these so-called "cold seeps." Others have also been found that rely on methane instead of hydrogen sulfide. Some of these are around bizarre deep-sea lakes called "brine pools:" depressions in the sea floor filled with water that has a much higher concentration of salt then the surrounding water. And recently a tube worm community was found living on solid methane hydrate on the ocean floor.



These methane mussels (Bathymodiolus childressi) live at the edge of Brine Pool NR1. The pool of brine in the foreground is nearly four times as salty as seawater and is so dense that the submarine can float on the pool to take pictures such as this.



Listen to Harry Roberts, Mandy Joye, and Gavin Eppard as they witness an underwater wave pass across the surface of the Brine Lake, at the interface between the "lake" and overlying ocean. The wave is caused by pressure exerted by the ALVIN as it sits atop the "lake."


4. Patagonian toothfish
70 S; 150 W

The Patagonian toothfish lives at depths below 2,500m in the Southern ocean. Its tasty flesh fetches prices of up to $35 per kilogram, earning it the name of "white gold" amongst fishers.

5. Antarctic toothfish
77 25' 17" S; 176 08' 33" W
A close relative, the Antarctic toothfish (Dissostichus mawsoni), is found farther south around the edges of the Antarctic shelf; it also lives in the Ross Sea.

6. Extremophiles
http://www.mahalo.com/cold-seep
Entire communities of light-independent organisms - known as extremophiles - develop in and around cold seeps, most relying on a symbiotic relationship with chemoautotrophic bacteria. These prokaryotes, both Archaea and Bacteria, process sulfides and methane through chemosynthesis into chemical energy. More complex organisms, such as vesicomyid clams and siboglinid tube worms use this energy to power their own life processes. In exchange, the microbes are provided with both safety and a reliable source of food. Other microbes form mats that blanket sizable areas.

The deep seabed was once considered a biological desert. Life, the logic went, was synonymous with light and photosynthesis.The sun powered the planet’s food chains, and only a few scavengers could ply the preternaturally dark abyss.  Then, in 1977, oceanographers working in the deep Pacific stumbled on bizarre ecosystems lush with clams, mussels and big tube worms — a cornucopia of abyssal life built on microbes that thrived in hot, mineral-rich waters welling up from volcanic cracks, feeding on the chemicals that leached into the seawater and serving as the basis for whole chains of life that got along just fine without sunlight.  In 1984, scientists found that the heat was not necessary. In exploring the depths of the Gulf of Mexico, they discovered sunless habitats powered by a new form of nourishment. The microbes that founded the food chain lived not on hot minerals but on cold petrochemicals seeping up from the icy seabed.

A close-up of a new species of tubeworm. Its body holds colonies of microbes that live off hydrogen sulfide -- a highly toxic chemical for land animals that has the odor of rotten eggs -- and supply the tubeworm with energy. The blue stain atop the creature is a dye that scientists applied to gauge the animal's growth. The tubeworm was photographed at a cold seep nearly a mile down.

A group of tubeworms more than a mile down in the gulf. Blind shrimp roam across the worms, looking for food.

A kind of colonial cnidarian -- an animal with stinging cells related to anemones, corals and jellyfish. The cluster of creatures was photographed near a cold seep nearly a mile down.

Here, corals with branching skeletons live atop a cold seep. The corals feed on particles that float through the deep currents, as do brittle stars, which have climbed up the branches to aid their hunt for particulate food.

A unusual species of shrimp moves across a soft coral at a mile-deep cold seep.

A community of seep mussels. Scientists have discovered that this species contains two kinds of microbes in its gills, from which it derives energy. Small anemones and shrimp have colonized the mussel shells, which were photographed at a cold seep 1.4 miles down.


 

                                          

A purple sea cucumber. Scientists have found such animals to be abundant around gulf seeps located at depths greater than half a mile. This animal was photographed at a site 1.4 miles deep.

Squat lobsters on a reef-building hard coral at a cold seep.

An anemone photographed near a cold seep almost a mile down.

A third of a mile down, diverse creatures live atop a cold seep. The community contains old tubeworms (center) surrounded by latecomers, including branching corals, a crab and brittle stars, whose thick arms look like worms. This varied community illustrates a later stage in the development of the dark ecosystem. The microbes -- which live off oil and gas bubbling up from the seabed, becoming the first links of long food chains -- also form a crust on the normally gooey seabed. The hard crust offers attachment points for all the creatures.

Rich benthic community in the European Arctic. Feather stars, basket stars, this particular sea cucumber (all in the group of echinoderms) and anemones prefer hard bottom as a substrate.

Brittle stars dominate vast areas of the investigated Arctic sea floor. The locally high abundance and biomass is determined by the amount of food available and is sustained by only few species.




7. BP Oil spill
26 20' N; 94 30' W
http://www.globalanimal.org/2010/06/22/deep-seabed-creatures-may-be-hit-by-oil-spill-too/5332/

World's richest known concentration of cold seep communities lies in the Gulf of Mexico (1-2 miles underwater).  Scientists are concerned about the effect of the BP oil spill on these communities.

Caption An unfamiliar type of orange anemone living in sediment that has signs of blackish staining from seep petrochemicals. It was photographed at a site 1.4 miles down.

8. Predators
Spider crab (Gulf of Mexico)

Caption A large spider crab crawling over a group of tubeworms. These predators are found throughout the Gulf of Mexico.

Cusk eel 35 43' N; 122 43' W (Davidson seamount, 3300m deep)

The cusk-eel Acanthonus armatus, a predator with a huge head and a body that is 90 percent water. This fish has the largest ears (otoliths) and the smallest brain in relation to its body size of all known vertebrates. These benthopelagic fishes have a reduced body mass, and low metabolic rates, expending minimal energy as they lie and wait to ambush prey. 

Orange roughy

Robust benthopelagic fish are muscular swimmers that actively cruise the bottom searching for prey. They may live around features, such as seamounts, which have strong currents. Examples are the orange roughy (shown here) and Patagonian toothfish.

Eelpout 35.25458 N; 75.51995 W (off Cape Hatteras, NC)

In benthic fishes, swimbladders are usually absent and eyes range from absent to well developed. They vary in size, with larger species greater than one meter not uncommon. The International Eelpout Festival that takes place in February near Walker, Minnesota, celebrates the burbot, which actually a cod-like fish misleadingly known locally as the eelpout.

Hagfish 69N 72W (off Baffin Island, Canada)

Caption Deep sea benthic fish are usually long and narrow. Many are eels or shaped like eels. This may be because long bodies have long lateral lines. Lateral lines detect low-frequency sounds, and some benthic fishes appear to have muscles that drum such sounds to attract mates. Smell is also important, as indicated by the rapidity with which benthic fish find traps baited with bait fish.

Spiderfish 31 33' S; 159 05' E (800 m deep)

Caption  A benthopelogic fish that prefers the sea bottom. The nearly blind spiderfish use  long rays on their fins to "stand" on the bottom while they face the current and grab zooplankton as it passes by. 

9. Hadeep Project
40 07' N; 144 19' E
A UK-Japan team found the 17-strong shoal at depths of 7.7km (4.8 miles) in the Japan Trench in the Pacific and captured the deep sea animals on film. The scientists have been using remote-operated landers designed to withstand immense pressures to comb the world's deepest depths for marine life.  Monty Priede from the University of Aberdeen said the 30cm-long (12in), deep-sea fish were surprisingly "cute."

The fish, known as hadal snailfish (Pseudoliparis amblystomopsis), can be seen darting about in the darkness of the depths, scooping up shrimps. the fish are rushing around, feeding accurately, snapping at prey coming past.  Because the fish live in complete darkness, they use vibration receptors on their snouts to navigate the ocean depths and to locate food.

Caption The Hadeep project, which began in 2007, is a collaboration between the University of Aberdeen's Oceanlab and the University of Tokyo's Ocean Research Institute to explore the Japan Trench and aims to expand our knowledge of biology in the deepest depths of the ocean.

10. Deepest fish?
19 50' 09" N; 66 45' 16" W


The record for the deepest fish goes to a species of cusk eel (Abyssobrotula galatheae). It was dredged from the bottom of the Puerto Rico Trench at a depth of 8,368m in 1970. The species name refers to the research ship Galathea, which captured the first specimens.


11. Bathydemersal fish
30 0' N; 125 0' E

Bathydemersal fish inhabiting Okinawa Trough at a depth range of 910 - 990 m.  Upper half of body depressed, snout strongly depressed. Eye small, developed at upper surface of head. Head and body covered with tiny scales. Skin very thick. Three gill rakers developed on 1st gill arch.

12. Mid-Atlantic Ridge
0 N; 18 W

Scientists just completed the last leg of MAR-ECO - an international research program, part of the Census of Marine Life, which is enhancing our understanding of the occurrence, distribution and ecology of animals along the Mid-Atlantic Ridge between Iceland and the Azores.  Dr Andrey Gebruk, Shirshov Institute, Moscow, said: “We were surprised how species, elsewhere considered rare, were found in abundance on the Mid Atlantic Ridge and we were finding new species up to the last minute of last dive in the voyage.”

Caption Giant seastar.  This specimen of Hymenaster regalis with R=160 mm is a remarkable representative of the collection retrieved by the James Cook ECOMAR expedition in 2009. This is the biggest specimen ever recorded for this species. Also in the collection five species of Hymenaster were found. In total 15 species of this genus occur in the Atlantic. 

 Caption Sea cucumbers, or holothurians, normally seen crawling incredibly slowly over the flat abyssal plains of the ocean floor, were found on steep slopes, small ledges and rock faces of the underwater mountain range. Researchers were also surprised to see that they were very able and fast moving swimmers and unique video sequences were recorded of swimming holothurians.

13. Opening scene




Phosphorus cycle
Phosphorus cycles thorugh the aquatic community when organinsms die and release inorganic phosphorus.
Unlike carbon and nitrogen, the phosphorus cycle is not a true cycle.  There is a great deal of phosphorus lost.  Phosphorus has a tendency to wind up at the bottom of the ocean.  Once at the bottom the phosphorus ions are lost to the world.

 
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Marine Snow

As a weather forcast, one should expect a continuous shower of "marine snow."

The "snow" is a composition of: dead or dying animals and plants (plankton), protists, sand, soot, fecal matter, and other inorganic dust. This 'snow' is the main food source for all benthic organisms.