2700: deep ocean- shelf to slope habitats

submerged benthic zones

the continental shelf is the submerged edge of a continental plate (34-450 miles from the shoreline)

shelf extends from the low tide line to the shelf break

continental shelf is typically ~0.1 degree

continental slope is steeper, varying between 4-25 degrees

slope has a big drop off, greatly affects organisms due to loss of light

continental rise has a slope between 0.5-1 degrees

rise leads to abyssal plain

atlantic shelf goes further out compared to pacific

western north atlantic

shelf extends ~300 km from coast

shelf is gateway to deep ocean

break occurs around 430 km

most of the atlantic (by area) is abyssal plain

plain is scarce in nutrients and biodiversity

shelf included subtidal habitats within estuaries, kelp forests, reefs

life on continental shelf

biologically rich (by # of species)

also an area of potential natural resources like oil and natural gas, fisheries

in the 50’s UN created EEZ, 200 nautical miles out

properties of continental shelf

temp varies less than estuaries, more than deep ocean

• many estuarine organisms migrate to shelf in winter to avoid colder temps

water column is well mixed

• this affects not only the temp of the water, but also affects the nutrients available in the water

• nutrients are continuously mixed and redistributed

the shelf-deep sea (slope gradient

supply of food particles to the deep sea vary by:

1. distance from shore (areas closer to shore have more nutrients, more 1 degree productivity)

2. depth and time of travel material from surface to bottom (decomposition and scavenging)

   1. primary productivity that happens here has a lot of particles sink to the bottom

quantity of primary productivity in surface waters (subtropical gyres vs equator)

input of organic matter

from water column, declines with depth and distance from shore:

• continental shelf sediment organic matter = 2-5%

• open ocean sediment organic matter = 0.5-1%

• open ocean abyssal bottoms beneath gyre centers < 0.25%

  • pulses of organic matter to sediment can create biogenic sediment?

sediments tend to be dominated by inorganic mud in deeper systems

how do we measure particle flux?

multiple ways

see if they are productive areas

moored traps

• funnel

surface tethered traps

• easier to access

• cheaper

freely drifting neutrally buoyant sediment trap

particle size influences sinking rates

majority of organic material includes phytoplankton cells, bits of dead zooplankton, and fecal pellets

particles 0.1-1 pm would theoretically take years to reach deep sea

50-500 pm particles could make it to the bottom in days to weeks

food availability is patchy

food includes:

• large food falls like whales, large pelagic fish carcasses

• large kelp fragments

• trees carried via river

deep sea benthos

dominated by scavengers and deposit feeders

deposit feeders make sediment watery and unstable. incresing liklihood of turbidity near S-W interface

• an ex of trophic group amensalism

bacteria decompose organic matter much slower

• likely due to extreme pressure (barophilic bacteria) and temp (genetically isolated from shelf bacteria)

either rly big or little organisms

home to a wide variety of meiofauna living above or within sediment, feeding on bacteria, small scavengers and predators

many organism are large- deep sea gigantism

some organisms grow larger (but due to slow growth, long lifespans, reproduce later in life, few, large, well-developed eggs)

deep sea gigantism

cold temps allow more growth time between juvenile to reproducing time

resource scarcity

large bodies hold more energy and can buffer against large gaps in meals

reduced predation- less life, dark, less likely to encounter another organism

a good subtidal benthos sampler should:

1. sample a large enough area to be representative

2. sample a defined area and uniform depth below the sediment-water interface

3. sample uniformly in differing bottom substrata

4. have a closing device to prevent washout of specimens as sampler is brought to surface

5. bring samples to boat intact

methods for subtidal benthos sampling

dredges

sleds

grabs

corers

dredges

heavy metal frames with cutting edges that dig into sediment

anchor dredges- collects infaunal animals within a specific depth range

detrimental to sediment

sleds

dredges with ski-lke runners that allow only shallow sampling of sediment

grabs

samples that sample only a defined area at a time

Peterson grabber

corers

small tubes that are dropped into sediment (useful for microbiota, sediment samples)

box corer

sampling the deep sea benthos

visual observations are crucial to observe living organisms

observations and sampling can be done by submersibles, both manned and unmanned

deep sea environments must be less diverse if they receive less food right?

• sample benthos to find out

• use expensive robots to get videodeep or grab samples and do genomics

deep sea biomass and biodiversity

originally looked at by Sander et al 91965)

established a transect from Martha’s vinyard to bermuda

used bottom sampler comparable among sites

biomass decreased with depth…

• deeper locations had higher species richness

problems estimating deep sea biodiversity

1. some environments are more difficult to sample

2. only a few representative samples may be available

3. samples are expensive to collect

4. no environment can be sampled exhaustively

• in order to compare diversity, one can compare rarefaction curves as opposed to the absolute number of species

• allows us to compare a sample with 20 inds to one with 1000

• curves are developed by repeat random sampling of each sample

biodiversity max at 2000 m

biodiversity increases w depth, then declines with increasing depth below 2000 m

trend found in temperate and tropical regions

carnivorous animals are less frequent deeper than 2000 m

whats going on at 2000 m?

1. environmental stability

   1. stability of temp reduces extinction events

2. greater age of the deep sea

   1. species accumulate over longer time, shelf has been covered and uncovered over time

   2. deeper than 2000 m, pop size is so small that extinctions is frequent

3. particles size diversity is greater at depths of 1500 m, so deposit feeders are likely to be more diverse

   1. trend applies to many feeding types

4. submarine canyons on slope may create geological “islands” over short distances, encouraging speciation

   1. makes barrier for species

diversity also changes with latitude

one of the most pervasive gradients

number of species increases towards the equator

gradient tends to apply to many taxonomic levels

deep-sea biodiversity also changes with latitude

a surprise, since there’s no major environmental gradient at depth

trend is more pronounced for N. hemi

increase in diversity at equator areas

take home: biodiversity gradients

between-ocean differences

within-ocean differences

inshore-estuarine habitats

deep-sea diversity gradient

between ocean gradients

pacific biodiversity generally greater than atlantic, owing to older age, stable environment

within-ocean differences

from a central high of biodiversity in the SW pacific, diversity declines with increasing latitude away form the center

similar trend in other oceans

inshore-estuarine habitats

estuaries tend to be lower in diversity than continental shelf marine habitats

deep-sea diversity gradient

diversity increases relative to relative shelf habitats with a max of ~2000 m, then decreases toward abyssal depths