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Benthic Environment. BENTHIC CREATURES. In the early 1800s Edward Forbes noticed that the majority of marine life was found in the surface layers – and concentrations decreased with depth. He assumed that the depths of the ocean were devoid of life.
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BENTHIC CREATURES In the early 1800s Edward Forbes noticed that the majority of marine life was found in the surface layers – and concentrations decreased with depth He assumed that the depths of the ocean were devoid of life During the same period, Sir John Ross and Sir James Clark Ross examined grab samples taken in the Arctic & Antarctic Their conclusion: life exists in all levels of the ocean even the deep sea floor
BENTHIC CREATURES Of the 250,000 known marine dwelling species, more than 98% inhabit the ocean floor Ranging from sandy and rocky shores to the abyssal plains, the seabed provides a wide range habitats with varied physical conditions Distribution of benthic biomass correlates with photosynthetic productivity in surface waters Which in turn depends on temperature, currents, upwellings etc.
ROCKY SHORES These are often covered with animals living on the ocean floor = EPIFAUNA These organisms are either attached to the seabed, or move over it The rocky shore can be divided into the SPRAY ZONE (above the spring high tide) and the INTERTIDAL ZONE This latter zone can be further divided: HIGH TIDE ZONE – relatively dry, covered only in highest tides MIDDLE TIDE ZONE – alternately wet & exposed LOW TIDE ZONE – only exposed in lowest tides
ADPTATIONS FOR THE ROCKY SHORE HAZZARD: DRYING OUT IN LOW TIDE Ability to seek shelter or withdraw into shell Thick exterior/exoskeleton to prevent water loss HAZZARD: STRONG WAVE ACTIVITY Strong holdfasts (algae) or attachment threads (mussels) to stop being washed away Multiple legs, tube feet (starfish) or muscular foot (gastropods) to attach to the rocky surface Hard structures adapted to withstand wave action
ADPTATIONS FOR THE ROCKY SHORE HAZZARD: PREDATORS DURING LOW TIDE Firm attachment (mussels) Stinging cells (anemones) Camouflage (sea slugs) Squirt ink (octopi & cuttlefish) Break off body parts and regrow them later (starfish) HAZZARD: DIFFICULTY IN FINDING MATES Produce large numbers of eggs & sperm (urchins) Massive penises [5x body length] (barnacles)
ADPTATIONS FOR THE ROCKY SHORE HAZZARD: RAPID CHANGES IN TEMPERATURE, SALINITY, pH and OXYGEN AVAILABILITY Withdraw into shell -minimizing exposure (barnacles) Physiology adapted to withstand changes in temperature, pH etc HAZZARD: LACK OF ATTACHMENT SITES Attach to other organisms (coral, bryzoans)
SPRAY ZONE Also called the SUPRALITTORAL ZONE Organisms must be able to withstand long dry periods Most species have shells (e.g. Littorina – periwinkle or Acmaea – limpet) Often find rock lice or sea roaches (isopoda, crustacea; Ligia) These hide in rocky crevices by day and scavenge at night Not much algae found in spray zone
HIGH TIDE ZONE Also called the UPPER LITTORAL ZONE Many species here also have shells You find some barnacles, but not many (they need to be submerged to feed & breed) Some seaweeds can be found eg Fucus (cool climates) and Pelvitica (warm climates) These seaweeds have extra thick cellulose cell walls to reduce water loss at low tide Many SESSILE organisms also attach onto these seaweeds (eg Bryozoans)
MIDDLE TIDE ZONE Also called the MIDLITTORAL ZONE More algae and more soft-bodied organisms A much greater biomass in this zone than the previous two – therefore more competition for attachment sites Acorn barnacles (Balanus) and goose-necked barnacles (Pollicipes), as well as various mussel species are common (e.g. Mytilus, Modiolus) Carnivorous snails and starfish feed on the mussels, and some worms and crustaceans may be found amongst the mussels Crevices in the rocks may trap seawater forming TIDE POOLS
TIDE POOLS Tide pools contain a wide diversity of species Particularly abundant are sea anemones (cnidarians – relative of jellyfish) Sea anemones are shaped like a sac. With tentacles surrounding the mouth of the sac – these are covered in stinging cells (NEMATOCYSTS) Hermit crabs are frequently found in rock pool – their vulnerable rear ends are protected by empty gastropod shells Sea urchins may also graze on algae in rock pools – they have a 5-toothed mouth at the bottom of their spherical, spine-covered shells
LOW TIDE ZONE Also called the LOWER LITTORAL ZONE Algae (not animals) dominate this almost continually submerged zone Red, green and brown macroalgae can be found in this zone. Animals tend to live on and around this algae Shore crabs are frequently found in this zone, scavenging or grazing on algae Sea slugs or NUDIBRANCHS feed on a variety of sessile organisms Sea cucumbers and tube worms filter feed amongst the algae
SANDY (SEDIMENT-COVERED) SHORES Most organisms that inhabit sediment covered shores are INFAUNA burrowing into the sediment Although these shore have lesser diversity of species than rocky shores, the actual biomass of organisms is usually much greater Sediment-covered shores include: Beaches Salt marshes Mud flats
SANDY SHORES ZONATION The zones for sandy beaches are the same as rocky beaches: supralittoral, high/middle/low tide zones. These zones are more apparent in steep sandy shores In flat sandy shores (e.g. mud flats), there may be extremely large middle tide zones, with little evidence of the other zones Both species diversity and biomass increase the closer you are to the sea
SANDY SHORE ADAPTATIONS Very different adaptations are required for sandy shores, compared to rocky shores BURROWING: allows organisms to hide and shelter within (moist) sediments Many species have specialized mouthparts, legs, or muscular feet to help them burrow FILTER FEEDING: organisms buried in the sediment extrude organs to collect food items suspended in the seawater e.g. the fan like ‘nets’ of sea pens e.g. siphon tubes of clams – suck in seawater
SANDY SHORE ADAPTATIONS DEPOSIT FEEDING: feeding on dead and decaying matter, or organic matter covering sediments. Some eat sediment – and their digestive system extracts the organic matter Others are adapted to detect (smell/taste) decaying matter on the sediment surface PREDATION: carnivorous organisms seek out other animals. e.g. The starfish Astropecten burrows into the sand and pries open buried shellfish
SHALLOW OFFSHORE OCEAN FLOOR (SUBLITTORAL ZONE) Extends from the low (spring) tide line to the edge of the continental shelf Usually covered in sediment and has a low-moderate diversity of species Diversity is lowest UNDER upwelling areas –nutrients and taken to the surface Productivity is high in surface waters – high level of dead and decaying matter raining down from the surface This matter decomposes → uses up oxygen → anoxic conditions & low diversity
SHALLOW OFFSHORE OCEAN FLOOR (SUBLITTORAL ZONE) In rocky areas of the seabed is usually an abundance of macroalgae This seaweed attaches to the rocky substrate with a HOLDFAST The STIPES (stems) and BLADES (leaves) of the seaweed are lifted towards the surface (and sunlight) by gas-filled floats =PNEUMATOCYSTS Some grow to lengths of 30m or more (e.g. Macrocystis – brown bladder kelp KELP FORESTS → habitats for other organisms
DEEP OCEAN FLOOR Includes: BATHYL, ABYSSAL & HADAL zones Light is absent below 1000m Temperature: 3oC to -1.8oC Oxygen concentrations in water are high PRESSURE: Ocean ridges – 200 atmospheres / 2940 lbs/square inch Abyssal plains – 300-500 atmospheres / 4410-7350 lbs/square inch Trenches – >1000 atmospheres / >14,700 lbs/square inch Most areas are covered with a layer of clay and/or ooze ABYSSAL STORMS (eddies) rage in some areas for weeks at a time
DEEP OCEAN FLOOR Except around hydrothermal vents etc. all nutrients fall from the surface layers Only 1%-3% of the food produced in the upper layers reach the deep ocean floor Adaptations for creatures in this environment tend to revolve around chemically detecting food It was thought that species diversity in/on the deep ocean seabed was low Although patchy – diversity can be very high One study noted 898 infauna species in 21 square meters of seabed – 460 were new species
HYDROTHERMAL VENTS As mentioned previously – there are newly discovered phenomena Large (>1m) tube worms (e.g. Riftia) often predominate Giant clams (e.g. Calypotogena), mussels, white crabs (e.g. Brachyura) also common Biomass around a hydrothermal vent can be 1000x greater than the rest of the deep seabed The producers of these communities are chemosynthetic Archaea (like bacteria) 6H2S + 6H2O + 6CO2 + 6O2 → C6H12O6 + 6H2SO4 hydrogen sulfide glucose sulfuric acid
LOW TEMPERATURE SEEPS Another newly discovered phenomena 1984 – a hypersaline (46.2 ppt) pool was found on the seabed at a depth of 3km Unlike hydrothermal vents, the temperature of the water was cool (<0oC) The water flowed out from fractures in a limestone escarpment Associated with the seep were mats of chemosynthetic Archaea These provide nutrients for starfish, brittlestars, clams, mussels, shrimp, crabs, sea anemones, tube worms and fish
HYDROCARBON SEEPS Also discovered in 1984 Trawls in waters of 600-700m in the Gulf of Mexico found species similar to hydrothermal vents – despite being much shallower Subsequently similar communities were found in depths down to 2.2 km These communities were associated with seeping methane (CH4) Chemosynthetic Archaea used methane instead of / as well as hydrogen sulfide to produce nutrients
SUBDUCTION ZONE SEEPS Also discovered in 1984 A community was found around a subduction zone off the coast of Oregon Water is squeezed out of seabed sediment being folded into the crust, and seeps out in certain locations on the seabed The water temperature is only 0.3oC warmer than the bottom waters But the seeping water contains methane (probably produced from decomposing material in the sediments) Several similar subduction zone communities have been found (1.3km – 5.5 km deep)
