251 2010 14 Deep Sea Ecosystems I

8/12/2019 251 2010 14 Deep Sea Ecosystems I

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Deep Sea BiologyLife under the photic zone



Our knowledge of deep-sea systems is recentand incomplete

• Not lifeless as thought 200 years ago• Shells first dredged from abyss in 1846

• Challenger expedition, 1873-1876 – Animals from 5500 m

• 1967: first quantitative measure of deep

sea diversity by Hessler & Sanders• 2006: Venter sampling of microorganisms



Microbial diversity in pelagic ecosystems

“We estimate there are at least 25,000different kinds of microbes per litre ofseawater,” says Sogin. “But I wouldn't besurprised if it turns out there are 100,000 ormore.”





Definitions and limits

• “Deep sea” = all environments below thecompensation depth (below Photic Zone)

• Up to 10,000 m• Water column + Benthic habitats• Some organisms are “depth specialists”

but others move > 1,000 m vertically





Most important gradients in environment

• Source of light switches from ambient tobiotic

• Pressure increases 1 atmosphere for each10 m of depth

• Density of food for filter feeders declinesuntil collected on and in sediments

• Depth of minimum oxygen is atintermediate depths (oxygen minimum)







Adaptations to decreasing light, cont.

• Eye structure

– mesopelagic: large relative to body size

– bathyal: small eyes or blind



Consequences of changing pressure

• Difficulties in conducting experiments andobserving organisms

• How do we know?

• Enzyme efficiency can be pressure sensitive – protein stability varies with pressure

• Lipid “fluidity” varies with pressure • Calcium carbonate solubility increases with

pressure



Pressure-dependent growth experiment



Patterns in food density

• In water column, average amount ofbiomass declines with depth

• At bottom, marine snow accumulates

• Average particle size varies, withincreasing “patchiness” with depth

• EXCEPT for ecosystems that aredominated by chemosynthetic bacteria – vent ecosystems – cold seep ecosystems



Deep Sea food sources



Consequences of lower food density toorganisms (reproductive)

• Decreasing densities of populations – consequences for finding mates, sociality

•Decreasing availability of food for offspring – migrations to surface waters, or . . . – delayed reproduction & smaller repro effort – more parental care – slow embryological development



Example of reproductive migration



Consequences of lower food density toorganisms (ecological & physiological)

• Tendency for smaller body size as depthincreases (but reversed for bathyal spp.)

• Chemosensory acute to locate patchy food• Large mouths to use wide range of food• Lower metabolic rates (reduced mobility)

– but high mobility for bathyal species• Slow growth, but high longevity

• How does this influence “sustainable yield”?



Deep sea benthos: characteristics

• Early sampling limited by technology – Suggested low density – Suggested low diversity

• Increasing sampling intensity & with lessdamage – Low density generally was correct

– But High Diversity



Deep Sea Benthic diversity• In & on sediments• Dominated by “ macrofauna ”

– Defined by size (> 300 μm but too small to beidentified by photographs)

– Include polychaetes, molluscs, crustaceans,echinoderms

• Estimated to include between 500,000 and10,000,000 species – Program to inventory under way (CeDAMar or

“Census of Diversity of Marine Life”)



Ecological importance of macrofauna

• Nutrient cycling at ecosystem level• Food resource for commercially important

species

• Pollutant metabolism• Dispersion & bural• Energy cycling• Influence sediment structure & turnover



Why so many species of macrofauna?

• Why would we expect low diversity?• Apparently low variety of habitats so

apparently low number of different niches

• Low rate of input for new energy/nutrients• “Competitive exclusion principle” predicts

low diversity



What ecological mechanisms would explainhigh diversity?

• H1: Niches are defined by more dimensionsthan sediment type – Location within sediments (e.g., vary in O 2)

– Other organisms create “biotic” variation • H2: Competition is not a major factor – Predator influence – Disturbance influence

• H3: Local diversity may be low but regionaldiversity can be high – This is multiplied by a very large area of habitat



Sediment variation – “Bioturbation”

Box Core from 1900 m

Variable sediment surface frombiological activity: 1100 m

Documents

251 2010 14 Deep Sea Ecosystems I