Number of species Marine ecosystems 6: Deep Sea Delimited by the photic zone (200m) and the bottom of the ocean Mesopelagic Ocean depths 200-1000m Below 1000m Unique features Lack of primary production by photosynthesis Organisms depend on food produced in the epipelagic that sinks into the deep waters Only 20% of the food reaches the mesopelagic Only 5% of the food sinks to the bottom Dim light up to 1000m, complete darkness below that depth Temperature Main thermocline is present in the mesopelagic Relatively constant at the ocean depths, below 1000m About 35 F = 2 C Plankton Without primary producers Zooplankton dramatically decreases below 1000m Deep sea benthos Shallow-water benthos Number of individuals With food in short supply Biodiversity (number of species) Decreases by 10 times at 500m Decreases by 100 times at 4000m 1
Oxygen - Amount of O 2 + O 2 minimum layer Mesopelagic why the minimum layer? Respiration Bacterial decay Ocean depths Less food and organisms O 2 is used up slowly Animal adaptations Huge gills Inactivity Hemoglobin that works well at very low O 2 conc. why more oxygen than in the mesopelagic? Deep water has a different origin 1. Overturn and mixing: That reaches the bottom Takes place at Antarctica and Greenland 2. Global thermohaline circulation Moves the water into the deep layers of the others oceans Pressure Increases one atmosphere for every 10 meters depth 1 atm = 14.7 lb/in2 DEPTH ATM lb/in 2 10 1 14.7 200 20 294 500 50 735 1000 100 1470 4000 400 5880 0.63 tons 2.63 tons Difficulties bringing deep sea organisms to the surface Organisms have pressure-dependent physiology Ex: Swim bladders: Gas-filled sacs for buoyancy Gas volume is controlled through metabolism (energy!) Fish cannot have fast changes in depth (pressure) 2
Mesopelagic Organisms Zooplankton Squids Copepods Krill (Euphausiacea) Comb jellies & Jellyfish crustaceans Ostracods Arrow worms (Chaetognata) Midwater fish Size is generally small: 2 to 10 cm Bristlemouth & lanternfish account for 90% in numbers Cyclothone signata (bristlemouth) Is the most abundant fish on earth Adaptations of Mesopelagic Organisms Some species do vertical migrations to feed at night in the epipelagic Others species stay always in the mesopelagic Adaptations depend on the lifestyle Reduce the energy requirements Mouths: Large, Extensible jaws Big and sharp teeth To compensate for this They have soft, weak bones And no defensive structures like spines and scales that may increase the weight 3
Very well developed eyes Abnormally big Very sensitive Tubular eyes Good for upward and downward vision (directional vision) Counter shading Dorsal part is dark, ventral part is silvery Coloration Transparency is common in the upper part of the mesopelagic Copepods, shrimps, jellyfish, Silvery color is more common in the middle mesopelagic Red color is common in the deep ocean A 2 nd retina located on the side compensates for lateral vision Red color does not penetrate the water, animals having a red color appear completely black in the deep ocean Reduction of the silhouette Bioluminescence Photophores Are light-emitting organs found in many species of fish and invertebrates In other cases, symbiotic bacteria generate the light Counter illumination Photophores located on the underside The light closely matches the background and helps the animal blend with the background Lure for mating / hunting / escaping Angler fish have symbiotic bacteria and use bioluminescence to attract potential mates or to attract preys Copepods, squids, ostracods: use the bioluminescence to avoid predators 4
Adaptations of Deep sea pelagic fish The energy saving adaptations are more accentuated in the deep ocean Bioluminescence is not used for counterillumination Why? There is no sunlight to create a silhouette! Extensible jaws Expandable stomachs In order to ingest preys that are sometimes bigger than the predator! Differences between Midwater and Deep sea fish (2) (3) (1) (3) Organ systems Generally poor developed in deep-sea fish to maximize energy-saving (1) Amount of photophores Deep-sea fish do not need bioluminescence for counterillumination (2) Gills filaments Mesopelagic fish have normally a higher metabolism But dissolved oxygen can be in short supply when compared to the deep ocean Reproductive adaptations in the Deep-Sea Hermaphroditism The ability to breed is guaranteed is both individuals can produce sperm and eggs Male parasitism Males of Angler fish are small and attached permanently to the female, using her resources but being themselves a permanent source of sperm 5
Differences between Midwater and Deep sea fish Deep-Sea bottom organisms Food is always in shortage But bottom organisms have more time to look for it Sea star and Brittle stars Most invertebrates Are deposit feeders Sea cucumbers Spiny crab Fish Are mainly scavengers 6
Seamounts, Hydrothermal Vents, and Cold Seeps Seamounts Are individual volcanoes on the ocean floor 30,000 1,000? They are areas of high production that support commercially important fisheries and coral mining Why are seamounts so productive? Have strong localized currents and upwellings Plankton biomass is high because of this And in time supports a very rich ecosystem May have a high degree of endemism, Centers of speciation May act as "stepping stones" for the dispersal of coastal species. Hydrothermal Vents Seawater penetrates into the ocean crust, becomes heated, reacts with the oceanic crust, and rises to the seafloor Cold seeps Mostly located along continental margins Hydrogen sulfide (H 2 S) and methane (CH 4 ) seep out from the sea floor Bacteria and Archaea Use these compounds to chemosynthesize Usually as symbionts of other organisms Huge productivity without sunlight! Hot water contains lots of hydrogen sulfide (H2S) Same results than in cold seeps! 7