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Marine Ecology > The Benthic Realm > Flashcards

The Benthic Realm Flashcards

1
Q

Physical factors that shape benthic community structure?

A

Proximity to land and Depth

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2
Q

Aspects of Depth that affect benthic community:

A
  1. Temperature
  2. waves and currents affecting the bottom surface (tides strong in narrow inlets, stirs up sediment, prevents stratification)
  3. Salinity
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3
Q

Aspects of Land Proximity that affect benthic community:

A
  1. High Sedimentation
  2. Nutrient runoff

rates of sedimentation influenced by water movement

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4
Q

Lithogenous sediment

A

produced by weathering of rocks, most sediment on continental shelf

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5
Q

Biogenous sediment

A

skeletons and shells of organisms

- can be silicious or calcareous

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6
Q

siliceous ooze

A

found under diatom-rich waters, contains silicon-based shells
[diatoms and radiolarians]
sun Antarctica and central-west Pacific

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7
Q

calcareous ooze

A

contains the remains of CaCO3 shells
[coccolithophores, foramnifiera]
more common in shallow waters than deeper waters (pressure forces CaCO3 out of solution)

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8
Q

Substrate size determines community structure

A
  • Larger particles settle rather quickly from moving water
  • Finer particles remain suspended and only settle in quiet water
  • Sandy (47%) and muddy (37%) substrates dominate the benthos
    of the world
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9
Q

Soft bottomed Communities

A
  • Conditions more stable than soft bottomed intertidal
  • Species tend to occur in patches due to microenvironments
  • Vast majority lack seaweeds and seagrasses (unvegetated)
  • 4 groups of animals dominate: polychaetes, molluscks, echinoderms, and
    crustaceans
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10
Q

Primary nutrient source

A

Detritus

- little to no primary production on shelf seabed

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11
Q

Deposit feeders

A

feed on deposits of organic matter on or in the sediment
- mostly burrowing polychaetes: trumpets, bamboo, and lugworms
- also sea urchins, heart urchins, sand dollars, echiurans, peanut worms, sea cucumbers, ghost shrimp
Dominant in muddy sediments because more detritus settles due to low turbulence

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12
Q

Bioturbation

A

organisms stir up and oxygenate sediments

- uncovers and oxygenates deeper sediments, buries epifauna

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13
Q

suspension feeders

A

feed on particles suspended in the water column (includes filter feeders)
- dominant on sandy bottoms
[sea pens and pansies can be found in dense stands]

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14
Q

active suspension feeders

A

use active pumping or sweeping motion to move water toward mouth

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15
Q

passive suspension feeders

A

use mucus or cilia to move suspended particles to mouth

- may include clams that are filter feeders like razor clams, quahog clams, and cockles [some clams are deposit feeders]

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16
Q

Tube builders

A

many are deposit feeders

- help stabilize substrate making it more suitable for suspension feeders

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17
Q

epifaunal deposit feeders

A

amphipods, small crustaceans, brittlestars

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18
Q

epifaunal scavengers

A

crabs, snails, shrimp, starfish

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19
Q

Grazers

A 
some fish (blennies), gastropods, and sea urchins
- Nudibranchs graze on encrusting bryozoan, soft corals, and sponges
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20
Q

soft bottom predators

A
  • burrow through sediment to get prey/catch prey on the surface
  • whelks and moon snails drill holes into prey shells
  • sea stars and predatory amphipods (feed on settling larvae)
  • fish are common predators (demersal carnivores like rays, skates, and flounders)
  • pelagic species of squid, cuttlefish
    [extra-oral digestion]
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21
Q

Near shore sediments

A
  • <30 m often distributed by wave action
  • highly mobile, robust scavengers dominate epifauna (crabs, amphipods, starfish)
  • highly mobile, short-lived ploychaetes and burrowing bivalves dominate infauna

[beyond this, sessile organisms begin to appear]

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22
Q

deep water sediments

A
  • > 50 m can allow silt and clay to settle
  • epifauna is sparse (mainly anemones and sea pens)
  • typically burrowing megafauna dominated by crustaceans and echiurans
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23
Q

Deep sea floor (physical/chemical factors)

A
  1. Light
  2. Temperature
  3. Dissolved Oxygen
  4. Bottom Currents
  5. Hydrostatic Pressure
  6. Sediment
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24
Q

Light (Deep sea floor factor)

A
  • non-existent in aphotic zone of the deep sea

- only bioluminesence

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25
Q

Temperature (Deep sea floor factor)

A
  • low and constant, average at 2 C (-1 to 4 C)

- exceptions are the Red Sea and Mediterranean Sea

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26
Q

Dissolved Oxygen (Deep sea floor factor)

A
  • relatively constant; approx. 0.5 mg/L below 2000m
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27
Q

Bottom Currents (Deep sea floor factor)

A
  • tidal currents (bidirectional): can reach base of the continental slope in areas
  • Unidirectional: thermohaline currents and Coriolis currents
28
Q

Hydrostatic Pressure (Deep sea floor factor)

A
  • tremendous, constant pressure; compresses gases

- pressure likely limits depth range for most species

29
Q

sediment (Deep sea floor factor)

A
  • mostly soft sediment with consistent physio-chemical properties
  • clay particles and inorganic substances found under oligotrophic waters
  • hard substrate is uncommon
30
Q

Deep Sea primary production

A
  • rare and mostly limited to hydrothermal vents and cold seeps
  • vast majority of the deep sea is allochthonous
31
Q

Particulate Organic Matter (POM)

A
  • very little of surface primary production reaches sea floor
  • marine snow
  • important food input to sea floor
32
Q

Dissolved Organic Matter (DOM)

A
  • DOM in sediment can be 10x higher than that of water
  • can be a significant portion of some species’ nutrients
  • created mainly by metazoan metabolic processes, bacteria, and decay
33
Q

deep sea oxygen and metabolism

A
  • oxygen consumption is less than 100-fold less than at shelf depths
  • bacterial uptake is 2% of the rate on shelf bottoms
  • complex animal activity, benthic biomass is low, poor fish muscle mass, slower metabolic rates, not constantly using energy to swim
34
Q

trends in biomass, abundance, and size

A
  • # of individual organisms (density) and total biomass show a sharp decline with depth
  • megafauna show clearest decrease
  • very little change in bacteria
  • more organisms per unit area in shallow water
35
Q

Macrobenthos trends

A
  • show mean decrease in mean size with depth as do meiofauna
  • some species show opposite trend (fish [avg] get bigger with depth, large fish tend to be very old w/ slow growth rates)
36
Q

Deep sea Diversity patterns

A
  • do not show linear relationship with depth (peak around 2000m, parabola)
  • quantitative samples suggest consistent ratio of # of species to # of individuals in an area regardless of depth
37
Q

Latitudinal trends

A
  • apparent in isopods, gastropods, and bivalves
  • higher diversity at tropics than poles
  • deep sea diversity may be higher in southern than northern hemisphere
  • small # of samples limit conclusions
38
Q

soft sediment trends

A
  • communities differ despite similar sediment composition with latitude
  • prominent in North Atlantic
    1. isolation of deep sea communities leads to increased speciation
    2. deep ocean is constant over geologic time, stable, low extinction rates
    [shelf is more variable, ice ages, sea level changes, storms)
39
Q

Microbes of the deep sea

A
  • play a major role in deep-sea carbon and nutrient cycles
  • bacteria abundant in the deep sea
  • pressure and cold do slow their growth (take 1000x longer to decompose food, optimized to use organic matter in low concentrations)
  • archaea are as abundant as bacteria
  • viruses are key driver of microbial ecosystem (kill 80% of bacteria/archaea, release DOC that other microbes take up)
40
Q

deep sea benthic organisms

A
  • composition of smaller organisms (meiofauna <0.5mm, macrofauna >0.5mm) are similar to equivalent to sediment samples in shallow waters
  • macrofauna: polychaetes, bivalves, cumaceans, amphipods
  • meiofauna: nematodes, copepods, foramnifera
41
Q

Sessile Megafauna

A
  • 2 groups of Cnidarians belonging to Anthozoa are abundant in soft sediment habitat of the deep sea (sea fans [Gorgonians] sea pens [Pennatulids])
  • anchored in sediment via stalk with feeding and reproductive zooids held above fine sediment
  • also sponges and glass sponges
42
Q

deep water corals

A
  • occur worldwide, often on seamounts
  • present between 800-1300m
  • lack zooxanthellae, feed with tentacles
  • hard substrate attachment
  • abundant in North Atlantic, Gulf of Mexico, North Pacific, northern coast of S. America, and Northwest Africa
  • reefs of hard and soft corals, sponges
43
Q

deep water coral mounds

A
  • found at depths of > 1000 m
  • associated with bottoms often with glacial rock deposits, upon which mounds form
  • dominated by calcareous corals, but coral whips and sea fans are also common along w/ hundreds of invertebrate species
  • also attract fish and in danger from deep-sea trawlers
  • acidification is still an issue, slow growing, endemism suggected
44
Q

Sedentary Megafauna

A
  • larger organisms that live below sediment surface
  • mostly unknown
  • Echiurans (spoon worms) are a major group that lives permanently in burrows and uses long proboscis to feed on surface detritus
45
Q

Mobile Megafauna

A
  • many groups, but 3 are most prevalent (Echinoderms [all classes], Brittlestars [Ophiuroidea], sea cucumbers [Holothuroidea])
  • significant bioturbators
  • can form herds that move across the sea bed together (resource partitioning)
46
Q

Deep sea Crustaceans

A
  • decapod crustaceans
  • squat lobsters are predominant reptant (walking) decapods and occur in large densities
  • crabs are rare except for red crabs (Geryon and Chaceon)
  • prawns are common (large compared to shallow species, red in color)
47
Q

Deep sea fish

A
  • benthopelagic fish swim just above the sea floor, diverse, elongated body form
  • rays, hagfish, flatfishes (flounders, monkfish), rat tails
  • use lipid stores instead of air-filled swim bladders to remain above the sea floor, others reduce body density
48
Q

Deep sea gigantism

A
  • trend of increasing body size as depth increases

- most notable in squids, isopods/amphipods, and some crustaceans

49
Q

Xenophyohores

A
  • large, single-celled protists found on the deep sea floor
  • multiple nuclei
  • dense aggregation provide habitat (refuge, nursery, larval settlement, elevated suspension feeders)
  • found in areas with enhanced organic input
  • can be dominant species in South Pacific (97% of biomass)
  • “they are just one of those strange, mysterious things living in the ocean in houses made of poop”
50
Q

Seamount Heights

A
  1. seamounts
  2. abyssal hills
  3. abyssal knolls
51
Q

Seamounts

A
  • relatively isolated underwater mountains of volcanic origins (single or chains)
  • can be 1 km or more but don’t break surface
  • dominated by sessile inverts, fishes, mobile inverts, and abundant coral species
  • high endemism likely
  • in danger from trawling, can support fisheries for a short time but not sustainable
  • creates upwelling and downwelling
  • 21% of sea floor
52
Q

Food Falls

A
  • whole bodies of dead animals and large fractions of plants can sink to sea floor
  • whale falls provide a significant source of nutrients when available
  • may also provide a route for dispersal of deep sea species
53
Q

Food Fall Stages

A
  1. mobile scavenger stage
  2. enrichment stage
  3. sulfophilic stage
  4. reef stage
54
Q
  1. Mobile scavenger stage
A
  • dominated by mobile scavengers (hagfish, crabs, rat tails, sleeper sharks, amphipods) which consume soft tissue
  • drawn in by scent
  • feast or famine
  • can consume enough material to survive for a year
55
Q
  1. Enrichment stage
A
  • dominated by aggregations of polychaete worms, crustaceans, and snails
  • most scavengers are gone, smaller may remain, small opportunistic detritus feeders
56
Q
  1. Sulfophilic stage
A
  • break down lipids in bones
  • supports other species
  • osedox worms burrow roots into bone and extract fats w/ red plumes that act as gills
  • lasts 10-50 years
  • chemosynthetic bacteria, bacterial mats, mussels, tube worms
57
Q
  1. Reef Stage
A
  • provides a hard substrate for sessile species to colonize
58
Q

Hydrothermal Vents

A
  • found in regions with high tectonic activity (mid-ocean ridges), ephemeral in nature
  • 1st seen in 1977, Galapagos Rift, Alvin submersible
  • giant tube worms, dense mussels, shrimp, crabs, fishes, clams
  • Pacific vents: tube worms, clams, unusual snails
  • Mid-Atlantic vents: Rimacaris shrimp
59
Q

Hydrothermal Vent formation

A
  • sea water trickles down through cracks and fissures and is heated to high temperatures
  • heated sea water then emerges from chimney containing minerals (hydrogen sulfide) used by vents communities
  • chemosynthesis allows for primary production (symbiosis w/ bacteria/archaea)
60
Q

Black Smokers

A
  • hotter and larger in size
  • most common
  • release sulfur and iron which precipitate out as iron monosulfide (has black color) when warm water hits cooler water creating black “smoke” effect
61
Q

White smokers

A
  • cooler and generally smaller
  • located further away from an active rift
  • mainly release barium, calcium, and silicon
  • support snails, sponges, deep corals, and others but not in the abundance as black smokers
  • thick mats of chemosynthetic archaea/bacteria seen in some areas that use carbonate minerals instead of sulfide minerals
62
Q

Vestimentiferan tube worms

A
  • characterize Pacific vent communities
  • 1-2 m long, members of Polychaeta
  • attach to vent, lack mouth and digestive system
  • have specialized organ called “trophosome” that houses chemosynthetic bacteria that supply carbon to the tube worm
63
Q

Cold Seeps

A
  • occur at fissures or cracks in the seafloor that are caused by the movement of the earth’s tectonic plates
  • hydrogen sulfide, methane, and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool
  • typically dominated by bivalves with symbiotic chemosynthetic bacteria
64
Q

Dispersal from vents

A
  • vents are ephemeral structures that form and collapse with changing geologic events
  • vents usually <10 m apart; if dispersal was limited, extensive genetic variation would occur between vents
  • 2 models of gene flow
65
Q

Stepping stone model (dispersal)

A
  • assumes most gene flow occurs between neigboring vents

[Riftis fits this model]

66
Q

Island model (dispersal)

A
  • suggests long-distance dispersal and mixing of larvae

[Bathymodiolus fits this model]

67
Q

Submarine Canyons

A
  • canyons found on continental slopes
  • estimated 9000, covering 11% of slopes
  • upwelling and downwelling
  • sheer rock face
  • areas of complex topography

Marine Ecology (3 decks)

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