shallow seas Flashcards
what is the maximum depth light can penetrate water and what is this zone called
200m
the euphotic zone
what are some physical characteristics of shallow seas/ continental shelves
- highly productive
- responsible for 90% of the worlds fisheries
- high sedimentation rates
- temp varies seasonally
- well mixed
how does the width of continental shelves vary
shelves are wider on passive/ trailing margins compared to being more narrow on leading/active margins
what is the difference between a passive and active margin
passive = A passive margin is the transition between oceanic and continental lithosphere that is not an active plate margin. A passive margin forms by sedimentation
active= An active continental margin is found on the leading edge of the continent where it is crashing into an oceanic plate
what does DOM and DIM stand for
dissolved organic matter
dissolved inorganic matter
what is a benthic community
organisms which live in or very near the substratum (ocean floor)
how are benthic communities classified
1) size
2) location
3) feeding strategies
what are the different sizes of benthic communities
1) macrobenthos = 0.5mm or larger
2) meiobenthos = smaller than 0.5mm
3) microbenthos = smaller than 0.1mm
what are the different classifications of benthic organisms regarding location
1) endobenthos= either buried or partially buried
2) epibenthos = on the surfaces of sediments
3) hyperbenthos= organisms living just above the surface
what are the different feeding strategies
1) suspension feeders
2) deposit feeders
3) herbivores
4) carnivores
5) scavengers
6) filter feeders
give some examples of techniques used to survey shallow water communities
1) van veen grab
2) bottom trawl
3) dredge
4) underwater camera/BRUVS
5) scuba
define recruitment
arrival of new individuals to a population
what are the two phases of coral life cycle
1) pelagic phase
2) benthic phase
outline the pelagic phase of a corals life cycle
1) reproduction forms larvae
2) larvae are then dispersed
outline the benthic stage of a corals life cycle
1) recruits form up to a week after dispersal and grow into juvinles after a few months/years
2) juviniles continue to grow into adults years/ decades after settlement and reproduce
outline some characteristic of softbottom sublittoral communities
- dominate the continental shelf
- unvegetated so most primary productivity from phytoplankton
- environment differs in light, temp and particulate stability
- sessile forms less common
what species use soft bottom or sublittoral areas for fishery gorunds
1) cod which feeds on macrofauna
2) common skate
3) nephrops norbegicus which burrows into soft ground
outline some characteristics of seagrass beds found in soft bottom communties
- marine plants which produce flowers seeds and fruits
- form meadows
- minimum 5% surface irridiance needed
- need calm waters
- very productive
what species can live amongst sea grass beds
- epiphytic algae (a plant which grows on another = epiphytic)
- diatoms
- cyanobacteria
- detritus rich sediments
what percentage of primary production produced by sea grass beds is consumed by herbivores
50%
how much of sea grass meadows have been lost since 1980
40% and around 90% historically with 7% lost each year
what are some characteristics of hard bottom sublittoral communities
- strong currents
- sessile forms may have adaptations to resist drag
- many autotrophs and passive suspension feeders
- high competition for space as highly productive
what is an infralittoral zones
a region of shallow water close to shore typically dominated by algae
what is the circalittoral zone
beyonds the infralittoral and below agal zone dominated by sessile animals
what are some common british kelps
1) saccarina latissima
2) laminaria digitata
3) laminaria hyperborea
outline some characteristics of ginat kelp (macrocystis)
- many leave like fronds up to 5 m long
-stem or stipe up to 30m long - highly productive= growth artes up to 50cm
what is the main predator or giant kelp beds
urchin populations
sea otters eat sea urchins
but sea otter pop in decline
what is a maerl
a group of free living coralline red algae which forms crusts on rocks
outline some characteristics of maerl ecology
- only grows a few mm a year
- very diverse habitat
- require currents
- depth limited at light
what are some threats to maerl
- scallop dredging
- anchors and mooring chains
- eutrophication
- aquaculture
- obstruction to water flow
