Deep-sea Ecosystems

Question 1

Describe the deep-sea environment

Answer 1

• Mean depth of oceans: 3.2km
• 60% of earth surface > 1000 m
• T= 4-5 ºC
• S = 35
• No light
• high pressure (1 atm 10m -1)
• Low food availability
• seasonality small
• O2 limiting (biological uptake small)

like a dark, empty pressurized fridge

very little is known about it as < 20.000 m2 quantitatively sampled

Question 2

How does food get into the deep sea?

Answer 2

• Single most imporatant factor affecting organism abundance
• Dependent on sedimentation from the euphotic zone
• Phytoplankton settling velocity ~ 1 m d -1, zooplankton fecal pallets 100 m d-1
• particles subjected to bacterial decay < 1% organic content
• 1-3% of surface production reaches the deep sea
• most of the deep sea lies beneath unproductive surface waters

food exponentially declines with greater depth which effects organism density and biomass

Question 3

Describe the hypothesis put forward to explain high species diversity in deep-sea sediments

Answer 3

Diversity comparable to tropical rainforests and coral reefs

Intermediate disturbance hypothesis (Grassle & Morse-Porteous 1987)

three disturbances

1. Patchy food supply

Marine snow, fish falls create microhabitats

Infrequent and unpredictable means on one group can dominate

2. Biological disturbance

Small disturbances (eg fecal mounds, tracks) create habitat heterogeneity

3. Lack of barriers to larval dispersal

Larvae have a long pelagic period

Environment constant

Lack of predation

Question 4

How are hypothermal vents formed?

Answer 4

Continental plates moving apart allow magma to get close to the sea floor where it heats up the water that seeps through cracks. The hot water rises with minerals that create the dark color (iron-zinc, sulfides, calcium sulfates, copper-iron)

Question 5

How are hydrothermal vent communities productive?

Answer 5

• High abundance of hydrogen sulfide
• energy fixed by chemsoynthetic bacteria
• only ecosystem in the world not driven by sunlight
• oxygen and hydrogen sulfide required simultaneously
• given the concentration of raw material not surprising secondary production is so high

I Dispersal of bacteria in vent plume – ingested by grazers

II Suspension feeder loop

III Microbial mats grazed by invertebrates

IV Symbiotic relationship between bacteria and invertebrates (worms & clams)

Question 6

What is an endosymbiotic relationship?

Answer 6

Bacteria living in the gills of organisms around the vents supply the host with nutrients -> endosymbiotic relationship with chemosynthetic bacteria

Vent tube worms - Rifta pachyptila

1.5 m long in < 2 a

Adults have no gut

Special hemoglobin