Lecture Benthic Ecology

Salt marshes are sediment-covered shores

• Salt marshes and estuaries (regions where freshwater and saltwater meet) are highly productive benthic habitats

• Much of this productivity comes from sea grasses, mangroves and other vascular plants

• Salt marshes form in estuaries and are characterized by specialized plants capable of surviving in (and then out of) salt water

Salt marshes: Home Sweet Home

• Salt marshes – via their specialized plants –form protective barriers against erosion, and promote new land formation as plant roots trap sediments on each tidal cycle, and filter out excess nutrients and pollutants

• Salt marshes also provide protective habitat for larval fish species, and provide food and shelter for migratory waterfowl; marsh plants also form the base of the food web via decay

Salt Marshes are Vital Habitats!

http://en.wikipedia.org/wiki/File:Bride-Brook-Salt-Marsh-s.jpg

Classification

Five kingdom system:

Monera Protista FungiPlantae Animalia

Angiosperms Gymnosperms

Distribution: 12 genera of seagrasses (5 in the high latitude and 7 in the low latitude)

• True marine angiosperm• Evolved from shoreline Lillie-like plants~100

mya• Vascular plants reinvaded the seas 3 different

times (algae is nonvascular; i.e., no need for roots to transport water and nutrients)

• Can grow and reproduce while completely submerged under water

Halophila hawaiiana- only form of seagrass in Hawaii

Develop in:• intertidal and shallow subtidal

areas on sands and muds• marine inlets and bays • lagoons and channels, which are

sheltered from significant wave action

1. Help stabilize the sediment

2. Prevents resuspension of sediments in water (water is clearer)

3. Binds substratum, reduces turbidity, and reduces erosion

4. Sediment accumulation slows velocity of incoming water

5. Food for many organisms

6. Refuge for many organisms

Seagrass productivity is highly dependent on a number of factors:• salinity• water temperature• turbidity

This ecosystem is particularly sensitive to degradation due to:• agricultural pollution-run-off of

herbicides• industrial pollution• domestic pollution

Threats to Seagrass Beds

Coral Reef Communities

Hermatypic corals:• possess zooxanthellae• are reef builders

Light: Clear water Warm temperature: 18-32oCLow nutrientsLow productivity in water

Ahermatypic corals:• no zooxanthellae• rely on tentacular feeding• can live in aphotic zone

Cauliflower coral(Pocillopora meaandrina)

6 m

0 m

25 m

13 mLobe coral(Porites lobata)

Finger coral(Porites compressa)

Plate coral(Porites rus)

High light levelsModerate wave energy

Moderate light levelsOccasional storm wave energy

Low light levelsLow wave energy

Very low light, Primarily downwelling No wave energy

Coral Reef Communities

• Corals are animals (Cnidarians) related to anemones and jellyfish

• Most corals secrete hard skeletons of calcium carbonate and produce coral reefs

• An individual coral – known as a polyp – feeds by capturing and eating plankton that drift within reach of their tentacles

• Corals produce sexually and asexually

Hermatypic corals:• possess zooxanthellae• are reef builders

Light: Clear water Warm temperature: 18-32oCLow nutrientsLow productivity in water

Ahermatypic corals:• no zooxanthellae• rely on tentacular feeding• can live in aphotic zone

Coral Reef Communities

• Corals form symbiotic relationships with dinoflagellates, known as zooxanthellae

• Zooxanthellae receive nutrients and shelter from the coral, and photosynthesize, providing the coral with organic compounds

• Zooxanthellae provide corals (otherwise translucent) with their brilliant colors

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Coral reef distribution and diversity

Figure 15-18

Tropical coral reefs support large numbers of species

• Reef-building corals provide substrate for other organisms to attach and hide

• Corals also provide a source of food in otherwise weakly-productive regions

• Coral bleaching (the loss of the symbiotic zooxanthellae in response to environmental stress) may kill the coral, and have devastating impacts on the coral reef community

Coral Bleaching

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Corals are stressed by environmental change

• A water temperature change of only 1°C above the normal summer high temperature for a few weeks leads to coral bleaching– Coral expels zooxanthellae or zooxanthellae expels

itself

• El Niño events can drive coral bleaching• May be reversible – corals can re-aquire new

zooxanthellae if the stress is not too severe

The deep-ocean floor

• Characteristics of the deep ocean:– Absence of sunlight– Temperatures around freezing– Average salinity– High dissolved oxygen– Extremely high pressure– Slow bottom currents (except abyssal storms)– Low food supply

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Deep Ocean Physical Environment

• Bathal, abyssal, hadal zones• Light absent below 1000 meters• Temperature usually between -1.8°C and

3°C• High oxygen• High pressure• Abyssal storms – affect bottom currents

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Deep Ocean Food Sources and Species Diversity

• No primary productivity• Only 1 – 3% of euphotic

food present• Special adaptations for

detecting food• Species diversity

equivalent to rain forest

Deep-sea hydrothermal vent biocommunities

• Found in deep water near black smokers along the mid-ocean ridge

• Do not rely on food from sunlit surface waters• Organisms include:

– Tube worms– Clams– Mussels– Crabs– Microbial mats

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Deep-Sea Hydrothermal Vent Biocommunities

• Discovery – Alvin in 1977

• Galapagos Rift in Pacific Ocean

• Water temperature 8–12°C (46–54°F)

• Chimney vents, hot acidic water – Black smokers

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Locations of Hydrothermal Vent Communities

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Chemosynthesis • Microscopic archaea – thrive on hydrogen sulfide

from vents– Manufacture sugar, carbon dioxide, and dissolved oxygen

• Base of hydrothermal vent food chain

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Hydrothermal Vent Species• Giant tubeworms• Giant clams• Giant mussels• Crabs• Microbial mats• Life supported by

chemosynthesis

Phylum Annelida 30

Family Siboglinidae• Defining characteristic

– Gut tissue forms an organ (trophosome) that becomes filled with chemosynthetic bacteria

– Segmentation confined to small rear portion of animal (the opisthosoma)

• Small intriguing class of tube dwelling worms found throughout the worlds oceans

All 120 species are marine and can be found in high concentrations on hydrothermal vents

Clade Siboglinidae (Phylum Pogonophora)

Ridgea spRiftia pachyptila

Giant tube worms (Vestimentifera)

Riftia pachyptila

trophosome

Phylum Annelida 33

Trophosome• The major organs (gonads

and trophosome) are found in the coelom

• The trophosome of all species contains closely packed bacteria and play a crucial role in nutrition

• The last segment is the opisthosoma, which has many segments and septa like polychaetes

Phylum Annelida 34

Chemosynthetic Bacteria

• The most interesting aspect of pogonophora is the lack of a digestive system– Bacteria in the

trophosome fix the chemicals leaving the vents

– The bacteria can occur at concentrations of 10 billion per gram of trophosome tissue

Figure 8.1 The effects of competition and predation on barnacle distribution in Scotland. Ci, intraspecific competition; C2, interspecific competition between Chthamalus an6 Balanus, D, desiccation; P, predation by Nucella, a predatory snail. The widths of the distribution bars indicate relative abundance; the widths of the mortality bars indicate relative importance of the factors concerned. Note that the upper limits of distribution for both species are determined by physical factors (i.e. tolerance to dessication). Snail predation andintraspecific competition for space are the major causes of mortality for Balanus, and both factors become increasingly important at lower tidal levels. For Chthamalus, the major cause of mortality of newly settled larvae is intraspecific competition for space with thefaster-growing Balanus. Few Chthamalus larvae settle below mean tide level, but those that do are eliminated by predation and interspecific competition.

When the top predator is removed, competition for space is intensified and, in this region, Mytilus californianusovergrows and outcompetes all other macrobenthos to take over the available space throughout most of the mid-intertidal zone. Pisaster is referred to as a keystone species

An idealized diagram of the distribution of freshwater, brackish-water, and marine animals relative to salinity. (Numbers of species given in relative units.)

The biomass on the sea floor tends to decrease with depth faster than it

does with distance from shore.• The benthic food chains largely depend upon

food from the surface which reaches the bottom.• Characteristics of the benthic organisms include:

year-round reproduction, smaller broods, slow growth, and longer life.

• Diversity of the benthos is greater than expected because the high predation rate prevents any group from dominating through competitive

13-2 Biology of the Open Ocean and the Deep Sea

• Four traits common to all abyssal depths are: perpetual darkness., low temperature, high hydrostatic pressure, and sparse food supply.

• Rate of bacterial decay is greatly reduced under high hydrostatic pressure.

• This means that organic material that settles onto the sea floor remains for a long time before it decays and is thus more likely to be consumed.

13-2 Biology of the Open Ocean and the Deep Sea