Benthic ecosystems

Question 1

Features of benthic ecosystem?

Answer 1

Lowest tide point to 200m.
0-1500km offshore.
Within euphotic zone.
Water above = neritic zone.

Question 2

Value of benthic ecosystem?

Answer 2

Most heavily exploited area.

Shipping, oil/gas, subsea cables, wind/tidal/wave power, fishing, aquaculture, waste disposal, recreation.

Question 3

Seasonal thermocline?

Answer 3

Nutrients trapped at surface during summer. Surface waters = nutrient-limited. Benthos = O2 limited. Energy reaches seabed as dead matter.

Question 4

Physical forcing on continental shelf?

Answer 4

Scraping of past glacial events (eg: Anglesey).
Currents + waves move sediment = hard-bottom.
Sheltered/deep seas = soft-bottom.
Currents/waves affect rate of food supply to benthos.
Water flow affects body shape (high flow = encrusting, flexible, burrowing, Low flow = delicate, branched).

Question 5

Effect of turbidity on light?

Answer 5

Rivers = turbid = less light.

Algal zonation in deeper, less turbid waters.

Question 6

Different fauna sizes?

Answer 6

Macrofauna, meiofauna, microbiota.

Meiofauna dominate over macrofauna, but more difficult to study.

Question 7

Epibenthic, epibiotic, + infaunal?

Answer 7

Bare rock = anchor for epibenthic macroalgae + soft corals.
High-energy habitats = emergent epibiotic + mobile burrowing animals, + hydrostatic invertebrates.
Low-energy habitats = unicellular algae, burrowing infaunal animals, + hydrostatic invertebrates.

Question 8

Mobile epibenthic biota?

Answer 8

Forage in groups (eg: starfish), move to deep water in winter (eg: spidercrabs), migrate to spawning sites (eg: English Channel plaice migrate to North Sea).
Juveniles have to avoid predators, but bigger adults released from predation.

Question 9

Scavengers?

Answer 9

Predators often scavengers.
Some herbivores scavenge (eg: sea urchins, brittle stars).
More important in polar latitudes (higher mortality).
Amphipods: Macro-invertebrate scavenger. Important in polar shelf seas. Can get large.
Sea mice (Aphrodita): Epifaunal polychaetes. Predate on crabs, worms + scavenge.

Question 10

Importance of grazers?

Answer 10

Control pops = biodiversity.
Herbivorous fish (low latitudes), snails, urchins (high latitudes). 
Carnivorous grazers (nudibranchs on soft corals + sponges).

Question 11

Particle feeders?

Answer 11

Shallow: Feed on phytoplankton. Eg: Oysters, clams, mussels.
Deep: Feed on zooplankton/detritus. Eg: Bryozoans, hydrozoans, sponges.

Question 12

Sediment processors?

Answer 12

Sea urchins + cucumbers.

Question 13

Bioturbation?

Answer 13

Bulldozers (gastropods, sea urchins), feeding pits (starfish, stingrays), burrows (shrimp, fish, polychaetes).
Enhance O2 + nutrient cycling to 2m deep = maintains aerobic bacteria.
Increase surface porosity.

Question 14

Types of habitat on continental shelf?

Answer 14

Sands (47%), muds (37%), broken shell/reef (10%), rocky substrate (6%).
Dominant UK habitat: Sublittoral soft sediment.

Question 15

Hard bottom communities?

Answer 15

Anchorage for sessile biota (macroalgae, encrusting algae, filter feeders (barnacles, anemones, tunicates).
Competition for space.
- Macroalgae pneumatocysts lift them = more space.

Question 16

Boulder reefs?

Answer 16

Nursery ground for commercial fish.

High O2 + food, low predation.

Question 17

Encrusting species?

Answer 17

Sea squirt (Ciona intestinalis) + sponges (Cliona celata).

Question 18

Exposed rocky communities?

Answer 18

Star anemone, sea fans (susceptible to dredging), + ross coral.

Question 19

Brittlestar beds?

Answer 19

High densities live on bedrock, boulders, gravel, or sediment.
Main bed species = Ophiothrix fragilis, + Ophiocominanigra.
20 brittlestar species in UK.

Question 20

Soft bottom communities?

Answer 20

Live in sediment up to 2m deep.
Shallow silt + mudflats dominated by burrowing/sessile suspension feeders (eg: scallops, brittlestars) + detritovores (eg: polychaetes).
Deeper silt dominated by burrowing worms + crustaceans.

Question 21

Physical processes determining soft bottom communities?

Answer 21

Wave action = sand flats = mobile predators/scavengers (eg: crabs, starfish). Round sand easiest to burrow in, + high O2.
Muddy sediment = tight, small grains = less O2 + water = aerobic bacteria can’t consume organic matter in water = stored in sediment.
Bioturbation = O2 enters muddy sediment again.

Question 22

Biogenic reefs?

Answer 22

Aggregations of organisms (eg: bivalves, polychaetes, corals, + calcareous algae/maerl).

Question 23

Maerl beds?

Answer 23

Red seaweed w/ hard skeleton. Needs sunlight = only grows up to 20m deep.

Question 24

Ecosystem engineers?

Answer 24

Cause biologically-mediated habitat modification.
Increase habitat complexity/heterogeneity = higher colonist success + refuge from predators/stresses.
Eg: Tubiculous gregarious polychaete species in soft-bottom sediments increase micro/macro-invertebrate diversity.

Question 25

Sampling benthic ecosystems?

Answer 25

Scuba/manta tow, submarines, sonar, grab/suction sampling, towed cameras, trawling.

Question 26

Biles et al (2002).

Answer 26

Actively burrowing species (eg: N diversicolor) release double ammonia levels into water column than sedentary filter feeders (eg: M edilis). 
Filter feeders (eg: M edulis) remove sediment from water column. C volutator increases sediment in suspension (= increased SA for microbial activity + nutrient cycling). 
Abiotic factors (eg: water flow) affect behaviour of benthic infauna (eg: more suspension feeding in high-flow conditions, deposit feeding in low-flow conditions).

Question 27

Kamenos et al (2004).

Answer 27

Maerl beds not studied as much as mangroves/seagrass.
Easily damaged by dredging.
Pristine maerl beds = nursery for commercial queen scallops + invertebrates (eg: starfish, sea urchins) in Scotland.
Maerl has macro-molecular GABA fraction = chemically-stimulates invertebrate settlement (eg: scallop metamorphosis cues).
Need to study global maerl beds to see if same impact.