Week 21

Question 1

How are marine and estuarine ecosystems organised?

Answer 1

Physical, chemical and biotic factors interact to structure communities.

Question 2

How do habitat templets work?

Answer 2

Communities and species within them can be defined by simple axes so long as they are pertinent to the organisms in question.

Distance / Productivity / Substrate characteristics

Question 3

Disturbance affects parameters (my removing or opening space) indirectly, how?

Answer 3

Any relatively discrete event that removes organisms and opens up space/resources that can be used by others​:

• Predictable: eg tide, waves, seasons​
• Unpredictable: eg boat passage, storms, asteroids​

Question 4

Explain space and time in terms of disturbance?

Answer 4

μm; ms-s; eg chemical reactions, bacterial driven processes​

0.1 – 1m; mins – days; eg bioturbation, feeding pits, diatom mat formation​

100 – 10000m; mo – years; eg hurricane events, iceburg scour​

> 10000m; years – decades; eg volcanic activity, anoxic events, global warming, recolonisation of megafauna​

Question 5

How does disturbance occur by ecosystem engineers?

Answer 5

Individual to population scale – additive effect​

• complete reworking of surface sediment​
• impact upon meiofaunal community​

Question 6

Example of disturbance by ecosystem engineers?

Answer 6

Crabs and flamingos acting as ecosystem engineers by resurfacing the land, which feeds back positively to them allowing their sustained positivity.​

Therefore biology may have more impact than a tide in terms of disturbance.

Question 7

What is the intermediate disturbance hypothesis (IDH) commonly occurring in sea grass or coral reefs?

Answer 7

If disturbance occurs too frequently then few organisms can persist​

If conditions are stable, then specialist organisms dominate through competition​

Thus, species richness is highest at intermediate disturbance frequencies​

Question 8

Currents and Gyres in terms of ecosystem diversity in marine and estuarine ecosystems?

Answer 8

Circulating water masses that restrict particular connectivity at certain areas eg Antarctic circumpolar current​

Important over evolutionary timescales where organisms have tapped into the more efficient transport if they utilise the currents to maintain their life cycle over certain areas eg salmon, tuna, turtles, etc.

Question 9

How can wave energy cause disturbance?

Answer 9

Surface gravity waves caused by friction of wind passing over water.

Wave height ~ length/20

When waves touch the bed, ellipses become compressed into horizontal motion and wave breaks when depth = 4/3 wave height.

Question 10

What may affect water movement, therefore marine and estuarine ecosystems?

Answer 10

gravitational pull of the moon and the sun and the earth rotating produce tides.

Tidal amplitude affected by coastline configuration

Question 11

Movement of water down to tides is responsible for…

Answer 11

A lot of the zonation we see on shore lines.

And this related to the structure and function noticeable in ecosystems (and species that can survive) within the specific zones:
- Littoral
- Infralittoral
- Sublittoral
- Circalittoral
- Offshore circalittoral

Question 12

Mean velocity of water depends upon?

Answer 12

Gravity
Slope
Mean flow depth
Resistance

Typically the faster velocities are near the surface, and due to friction water closer to the bed is slower. Therefore surface velocity isn’t necessarily what organisms on the bed experience making it more habitable.

Question 13

How may shear stress cause disturbance?

Answer 13

Shearing force of water on the bed is dependent upon​: density of water, gravity, hydraulic radius, energy slope.

Proportion of fine particulate matter in the sediment increases downstream because slope and shear stress decrease

Question 14

How does turbidity occur due to water movement.

Answer 14

Turbulence can be made when freshwater meets salt water (eg at an estuary), which will impact the life there both directly and indirectly

Question 15

How does flow of water impact plants/marine life?

Answer 15

Effects of flow on macrophytes / macroalgae

It is evident that environmental pressures placed on an organism can be noticed by its structure eg in sea grass experiencing hydraulic flow.

Eg some organisms experience Hydrodynamics and will adapt their body type/features to align to the flow: rheotaxis
Also evident in many fish kind, and all marine/estuarine organisms (form = function)

Question 16

Density of medium (water) affecting ecosystems?

Answer 16

Water is 800-1000x more dense than air ​and at 20oC - it has 50x more viscosity ​

Water density and viscosity varying according to temperature and ionic conc.​

Support for larger organisms​

For a fluid of given dynamic viscosity, motion controlled by velocity and size and quantified by Re: the Reynolds number​

(velocity x size)/dynamic viscosity​

Re < 1000 then seawater is ‘sticky’​

​Interstitial water​

Question 17

How much more dense is water than air, what about visosity? What does this mean for organisms living within it?

Answer 17

Water is 800-1000x more dense than air ​and at 20oC - it has 50x more viscosity ​

Therefore sea water is the best medium for life, despite it being sticky (for cilliates) and so hosts the largest organisms on earth eg The Whale.

Question 17

What is salinity in terms of sea water?

Answer 17

Dissolved ions expressed as:​ mass (mgL-1), ppm or chemical equivalents (meqL-1)​
Total amount of dissolved material in a water sample is the salinity​

​Constancy of seawater allows for determination by measuring a single constituent​
- chlorinity: [Cl-], where salinity = 1.80655 [Cl-] ​
- expressed as ppt or ‰, or now Practical Salinity Units (PSU)​

Salinity in freshwaters highly variable​
- sodium chloride​
- carbonates and hydrocarbonates​

Hypersaline conditions in bays, reef lagoons

Question 18

What are the costs of salinity?

Answer 18

Organisms either maintain body fluids in equilibrium with surrounding medium (osmoconformers) or they osmoregulate

Physiological stress (cost) associated with maintaining fluid balance overcoming osmotic potential (dilute to concentrate)

Question 19

How does salinity change?

Answer 19

From the river mouth to the ocean salinity increases and this level can also change due to:
Seasons, wind, expose of mouth of river, tides.

All of which will affect how freshwater and salt water will mix (causing turbidity) of flow and therefore impacting organisms that live in that area.

Question 20

Who studied Stenohaline vs euryhaline Gammarus spp and impacts of the mixing estuarine zone and the sea with increasing salinity gradients occurrance?

Answer 20

Spooner 1974

Question 21

Solar radiation is important to aquatic systems for two reasons. What are these?

Answer 21

Energy source controlling metabolism through the conversion of solar energy to chemical energy via photosynthesis​

Some radiation is absorbed or dissipated as heat affecting thermal structure and stratification, and circulation patterns​

Question 22

What is the electromagnetic spectrum?

(Don’t need to know everything exact, just a summary will do!)

Answer 22

Light is received as quanta or photons which have wavelength (λ) and amplitude (A)​

Short wavelength, high energy gamma rays (about 100 nm or 1000 Å) ​

Long wavelength, low energy radio and power transmission waves (> 3000 nm or 30,000 Å)​

Visible spectrum is 400 (violet) to 750 nm (red)​

Infrared > 750 nm​

UV < 400 nm (UV-A 315-400 nm, UV-B 280-315 nm) ​

Photosynthetically active radiation (PAR) ie radiant energy 400-700 nm wavelengths ​

Chlorophyll a has absorption peaks at 445 and 660 nm​

Bacteria…​

PAR accounts for about 46-48% of the total energy hitting earth’s surface

Question 23

Formation processes of aquatic systems?

Answer 23

Results from a number of different natural and artificial processes

Causes which bring an ocean basin, lake or river/estuary into being are often interlinked.

Thus waterbodies with similar origins have similar physical characteristics despite being separated by or within continents​

Cascade to biotic similarities; hence often helpful to classify according to causation​

Question 24

Global marine/estuary diversity can be measured using what curve. What is this?

Answer 24

Hypsographic curve​ Cumulative percentage of the Earth below a given elevation​ ~71% is below sea level ~45% abyssal; ~25% slope​ Rise in sea level of 100m would reduce land area by ~5%​

Question 25

What is the approximate volume as a percentage in each of the defined aquatic systems?

Answer 25

Oceans = 96.5%* Glacial ice = 1.8% Groundwater = 1.7% Freshwater lakes = 0.008% Saline lakes = 0.006% Atmosphere = 0.001% Rivers = 0.0001%*

Question 26

What is 'dynamic' water?

Answer 26

Does not consider water movement on a global scale​ ​All connected via an active hydrological cycle​ Movement represented generally anticlockwise​ Some mechanisms act in a reverse direction; most important as dashed lines​ Precipitation on ocean surface negligible in terms of biology​

Question 27

The majority of ocean habitat is what?

Answer 27

'open' ocean eg water column or pelagic habitat. Different mechanisms operating at different depths result in relatively discrete environments separated by depth​ eg temperature, light, oxygen etc​ Despite being ‘connected’, barren-ness of pelagic zone hinders or prevents movement of most organisms as it creates a behaviour barrier – space effect​

Question 28

What is Pelagic habitat structure?

Answer 28

physical & chemical structure ‘typically’ homogenous in horizontal dimension​: ​- vertical heterogeneity associated with chemical and thermal stratification​ ​- energy flow largely through phytoplankton & bacterial pathways

Question 29

What is benthic habitat structure?

Answer 29

substantial heterogeneity in horizontal & vertical dimensions:​ - physical – substrate, debris, macrophytes​ - chemical – steep gradients associated with O2​ ​- energy flow arguably more complex:​ = Primary Production from microphytobenthos, macrophytes, periphyton, chemosynthesis​ = allochthonous inputs from estuaries​ and out into the sea = sedimentation of pelagic Primary Production​

Question 30

Benthic versus pelagic

Answer 30

More complex habitat ie a coral reef compared to an empty fish bowl!

Question 31

What is the depth zonation of the pelagic?

Answer 31

Simplistic​ Photic zone in open waters much greater than nearshore (neritic)​ Epipelagic, Mesopelagic, Bathypelagic, Abyssalpelagic, Hadalpelagic

Question 32

Depth zonation: Vertical distributions of limiting parameters (eg Oxygen minimum zones, temperature, , etc) can result in what?

Answer 32

Habitat squeeze with consequences for fauna Therefore habitat is restricted. May be permanent or seasonal in terms of space and time

Question 33

How is pelagic all connected at surface ocean circulation?

Answer 33

Currents are generated by wind friction​ Thus global pattern of currents reflects that of atmospheric movement​ ‘Piling’ of water on the down current side​ ​Counter currents​ Land masses interfere​

Question 34

How is pelagic all connected at deep ocean circulation?

Answer 34

Deep currents are independent of the surface​ Initiated by surface waters cooling at high latitudes downwelling​ In most of the oceans, the water in contact with the abyssal plain is Antarctic Bottom Water downwelling from Ross & Weddell Seas​

Question 35

Why may deep ocean currents be failing?

Answer 35

Antarctic Circumpolar Current (ACC), 5x stronger than the Gulf Stream, 100x stronger than the Amazon​ Driven by Freshwater from melting Antarctic ice​ diluting saltwater​ and cool water moving away from the continent ​ACC 20% slower by 2050​ Negative feedback​ = acting as a buffer zone to the Antarctic to keep warmer water at bay and so effects of climate change. But if this is breaking down, it will increase the effects of the 'buffer zone'. ​(Sohail et al, 2025​)

Question 36

How is pelagic all connected at localised connectivity at 'edges'?

Answer 36

Upwelling & downwelling against the land connect water masses and habitats ​

Question 37

What are fronts in terms of marine and estuarine biology? What can these fronts be mapped to show?

Answer 37

Where two different water messes meet (may also be classified as an 'edge') - Can be mapped to show differentiation in temperature, plant primary production, etc.

Question 38

What water process is important for marine predator feeding?

Answer 38

Mass water movements (disturbance), for example more copepods/algae/plankton will more likely be found where the water currents/circulations mix (and where freshwater may meet sea water).

Question 39

What water process is important for migrating animals?

Answer 39

Mass water movements for these animals to complete their life-cycle. Eg Fish that reside in estuaries, move to a current to aid travel to a warmer place to hatch, before moving through another circulation current to another continent, or migrate back to the estuary. Efficient to aid weaker swimming states (eg larvae) and allows less food consumption. If these streams collapse it will affect other marine organisms that utilise these currents to migrate and complete life cycles.

Question 40

Pelagic habitat summary?

Answer 40

Relatively simple structured mostly by physicochemical qualities, hence ‘barren’ – little life​ Where that life is found tends to be at a disturbance or edge

Question 41

What is the difference between arctic and antarctic ice habitats?

Answer 41

Arctic = Forms on the edge of many continents. Lots of freshwater run off from the land masses in the arctic so its more fresh, 'old' and cold in its formation Antarctic = Forms on the edge of the Antarctic ocean. Formed on a seasonal basis where the salt sea water will freeze, 'new' and relatively warm formation.

Question 42

What % of benthos oceanic habitat is deep sea floor / abyssal plain?

Answer 42

~45% and is relatively poorly connected and relatively few organisms persist there.

Question 43

What % of benthos oceanic habitat is ocean ridges?

Answer 43

~33% and can be considered as 'new' sea floor with clear lines of volcanic activity Study: 40day scientific cruise recorded 160 newly recorded species and potentially 50 new to science. - This may be driven by primary production where zonation is evident to provide nutrients, etc (due to methane seep, hydrothermal vents) for species.

Question 44

Oceanic benthos habitats: the continental shelf and slope?

Answer 44

Continental shelf and slope can be extremely dynamic​ ~20% of bed surface​ ‘Width’ determined by plate characteristics​ ​ Upper continental shelf comprises accumulated material from ‘land’ ​ relatively unstable and thus likely to move downslope​ generate turbidity currents

Question 45

The coastal zone makes up what % of oceanic benthos?

Answer 45

~3%​ Most diverse in terms of habitats… in the smallest area​ ​- Inter-tidal zone​ - Coral reefs​ - Estuaries​ - Coastal wetlands​ Considered to be ‘Well connected’​ habitats (access light, nutrients, energy, etc)

Question 46

What processes affect water distribution and light penetration, and how is irradiance at different depths calculated?

Answer 46

Reflection / Scattering / Absorption​ Irradiance – # of photons passing a unit area (mE s-1m-2) ​ Light Attenuation ​ Iz = Io e-kz​ Where: ​ - Io is irradiance at surface ​ - Iz is the irradiance at depth z​ - k is the extinction coefficient​ Measure k directly using a photometer or estimate from Secchi depth where k = 1.7zs​ ~53% of total light energy transformed to heat within top meter

Question 47

How is light penetration different in the open ocean versus in coastal waters?

Answer 47

Light penetration different in open vs coastal ocean waters because turbidity drives molecules from the land to water, causing a decrease in light penetration in coastal areas compared to open ocean.

Question 48

Colour and transparency is described by what?

Answer 48

Dissolved molecules/particles (eg carbon) in the ocean at the time. So we describe turbidity not colour. True colour is mostly impacted by DOC (dissolved carbon molecules)

Question 49

Different names for zonation of light penetration?

Answer 49

Sunlight zone = Euphotic zone Twilight zone = Dysphotic zone Midnight zone = Aphotic zone (Biodiverse and bio phosphorescence examples of life here and show strange evolutionary behaviour to increase survival/reproductive success.)

Question 50

What is Boyle's law? What does it explain?

Answer 50

The volume of a given quantity of gas at constant temperature varies inversely with pressure. This law is an explanation for challenges of aphotic zone in ocean = organisms do not suffer decompression gasses.

Question 51

How does the ionic character of water influence its density in relation to temperature, and at what temperature is water densest?

Answer 51

​Ionic character of water affects how its density reacts to temperature​ Water densest at 4oC; changes in density per degree are slight around this point​ At higher temperatures, changes in density per degree become increasingly large

Question 52

What are the characteristics of the layers in a stratified water column where wind and wave stress are minimal?

Answer 52

- Where or when wind / wave stress is minimal​ - Upper part – well mixed – epilimnion​ - This floats on colder, denser hypolimnion​ (aka thermocline) - Between the two is a stratum of thermal discontinuity – the metalimnion​ - Typically >1oC m-1

Question 53

What are the structural and global significance of sea ice, and how does it form?

Answer 53

Sea ice / pack ice has structural properties for the local habitat​ also important in driving global ocean thermohaline circulation patterns via deep water masses​ Seawater freezes at -1.8oC (Eicken 2003)​ Crystals rise and aggregate into slicks of grease ice​ period of inoculation​ Forming Pancake ice or Congelation ice ​

Question 54

What are the characteristics and changes in brine channels in sea ice, and how do they affect salinity?

Answer 54

Semi-solid matrix permeated by pores or brine channels​ Hypersaline conditions as salts expelled (Krembs et al 2000)​ ‘Cold’ ice – less volume in channels; salinity higher​ ‘Old’ ice – loss of brine due to expulsion and gravity

Question 55

What occurs when melting of sea ice happens?

Answer 55

​Upon ice break or melt​ Freshwater lens can stabilise water column – effective frontal system algal blooms from ice matrix inoculum​ Aggregation into marine snow​ Crustacean grazing – repackaging as faecal pellets flux of 660 mgCm-2d-1 (Cadee 1992) Possible impact of 'pulse' on the benthos

Question 56

What factors contribute to oxygen availability in aquatic environments, and how do organisms adapt?

Answer 56

Uneven distributions of O2 in aquatic environments (seawater 20% less)​ ​Many morphological, biochemical and behavioural adaptations ​ ​1% oxygen by volume compared to ~21% in air​ 100m increase in altitude reduces solubility by about 1.4%

Question 57

Example where O2 intake adaptations has occurred in marine organisms: sea worms

Answer 57

Cellular exchange of O2 and CO2 require gaseous diffusion across a boundary, thus protists and small metazoans use their entire SA

Question 58

Example where O2 intake adaptations has occurred in marine organisms: whales

Answer 58

These organisms may face decompression gases compared to fish and worms as they have complex breathing systems (eg lungs)

Question 59

How does the temperature range and stability in aquatic environments affect aquatic life?

Answer 59

Aquatic life typically experiences a narrower range of temperatures and more stable thermal regimes compared to terrestrial systems. This temperature stability impacts key biological processes such as metabolic rate, growth, development and final body size. They adapt their features for the purpose of function.

Question 60

Explain the ratio of salinity : temperature : oxygen impacting marine organisms

Answer 60

All of these impact life in marine ecosystems contributing to life forms able to survive there.

Question 61

How does water's tendency to form hydrogen bonds at the water-air boundary relate to surface tension and the communities associated with it?

Answer 61

Water's tendency to form hydrogen bonds with itself creates a high surface tension at the water-air boundary. This physical property supports entire communities, collectively known as the neuston, which inhabit this boundary layer: - Epineuston live on or above the water surface. - Hyponeuston reside just below the surface

Question 62

How does the water-sediment boundary contribute to benthic habitats and biological diversity?

Answer 62

The water-sediment boundary exhibits differing properties, creating opportunities for significant biological contributions This boundary supports the benthos, organisms that inhabit the sediment, by providing complex and varied habitats that accommodate diverse life forms.