5 FAUNAL MEDIATION OF ECOSYSTEM PROCESSES

Question 1

What is benthic-pelagic coupling?
What do the fluxes of material across the sed-water interface & mechanisms that mediate and constrain the fluxes play a prominent role in?

Answer 1

At the sediment-water interface, dynamic exchanges of energy, mass and nutrients occur via a multitude of diverse pathways.
2-way flux between benthos & overlying water column
Plays prominent role in functions from nutrient cycling to energy transfer in food webs, and collectively are of global significance.

Question 2

What are the 3 successive stages of benthic-pelagic coupling?

Answer 2

1) deposition of non-living org matter to the seabed
2) mineralisation of material within the seabed
3) release of nutrients back into overlying water column

Question 3

In temperature latitudes, seasonal patterns in productivity have what impact in both shallow and deep sea environments?

Answer 3

Elicit a seasonal pattern of faunal activity in both shallow and deep sea environments.

Question 4

Most benthic systems are detritus based. What does this mean? What is the food normally in the form of?

Answer 4

Benthos derives food and energy typically in form of detritus and debris from elsewhere (usually through horizontal and vertically derived subsidies).
Organic carbon

Question 5

Where are the areas of highest flux recorded?

Answer 5

• Centres of coastal upwelling & on continental shelves

- Essentially where we observe high rates of primary production & seasonality

Question 6

What is the nature of the flux of living organisms that undertake a range of diel, seasonal and ontogenetic migrations that collectively link organisms on the seafloor with those at the surface.

Answer 6

Bi-directional

Question 7

What are the 3 examples of the bi-directional flux of living organisms that undertake a range of diel, seasonal & ontogenetic migrations that link the organisms on the seafloor with those surface:

Answer 7

• Active movement without a life-form shift. e.g. regular diel vertical migrations, seen in many plankton species
• Active movement WITH a life-form shift. Ontogenetic movement includes egg & larval release. Org’s can broadcast spawn their gametes/sex cells into water column. Benthic environments can act as storage banks for young stages of water column species & vice versa.
• Passive events. Transfer of individuals can occur in extreme events like storms or submarine landslides, or when associated w upwelling from deep-sea canyons or other topographical features, vents & seeps. Intense human activities, like fishing and dredging also important tin exacerbating benthic-pelagic exchange.

Question 8

What is the importance of how invertebrate fauna mediate recycling of nutrients and flux of materials across the sediment-water interface?

Answer 8

• global carbon budgets

- biogeochemical budgets

Question 9

What is bioturbation?

Answer 9

the biogenic alteration of sediments

refers to modification of sediment habitat through the action of organisms that can obscure primary stratigraphic features & create other secondary structure.

Question 10

What organisms did Darwin conclude to be the most important organisms for the history of the world?

Answer 10

Soil and sediment dwelling invertebrates/infaunal organisms

Question 11

How did Darwin argue worms to be the cause of the layer of lime being situated at 3 inches depth after 15 years?

Answer 11

• Worms deposit new soil on the surface
• sorting soil with finer particles towards the surface and coarser material at depth
• causing whatever was on top to slowly submerge

Question 12

What observations did Charles Davison 1891 make with regards to lugworms?

Answer 12

• Calculated that lugworms were responsible for bringing 1911 tons sediment acre -1 year -1
• a volume 136x more than weight of soil brought up by earthworms as reported by darwin

Question 13

What observations did Charles Davison 1891 make with regards to lugworms?

Answer 13

• Calculated that lugworms were responsible for bringing 1911 tons sediment acre -1 year -1
• a volume 136x more than weight of soil brought up by earthworms as reported by darwin

Question 14

What two factors are important for the sediment disturbance of earthworms?

Answer 14

• density

- season

Question 15

What did Othenio Abel’s book Vorzeitliche Lebensspuren (= Ancient Traces of Life) outline? What do they include?

Answer 15

Outlined importance of trace fossils in determining the lifestyle & behaviour of extinct fauna.
Included fossilised tracks, trails, burrows, borings, nests, injuries and eggs.

Question 16

What was Richter & the Senckenberg Society & German Navy’s station “Senckenberg am Meer” (Senckenberg by the Sea) founded with the aim of? What was it based on the principle of?

Answer 16

Studying animal-sediment relationships in the Wadden Sea.

Based on the principle that “the present is the key to the past”

Question 17

Why was Heezen and Hollister’s 1972 book significant?

What did this mean for the state of studies at the time?

Answer 17

Contained almost 600 images providing a visual perspective of the deep sea floor.
Included images of faunal traces, burrows and mounds in what was unseen detail, and unknown species.
Studies remained largely qualitative with few quantitative studies.

Question 18

Since the intro of the term by Richter & despite recognition of the importance of a wide range of faunal activities, bioturbation has become synonymous with…

Answer 18

redistribution of particles and, to a lesser extent, fluids by macroinvertebrates.

Question 19

What does the bulk of the sediment profile consist of, despite recognition of several sediment phases?

Answer 19

Mineral particulates and interstitial water

Question 20

What are the 2 primary transport processes that can be identified at expense of considering other faunal mediated processes?

Answer 20

Movement of particles (reworking activity)

Water and solute transport (ventilation/bioirrigation)

Question 21

What is bioadvection & biodiffusion

Answer 21

Bioadvection = non-local transport of fluid/particles

Biodiffusion = local transport of fluid/particles

Question 22

What are the 2 main transport processes?

Answer 22

i) particle reworking, the movement/transport of sediment particles
ii) ventilation, the movement/transport of interstitial porewater & solutes. tends to be used to describe physical mechanism of burrow flushing.

Question 23

When the process of burrow ventilation has geochemical consequences, what is it usually referred to as?

Answer 23

Bioirrigation, although this term is used interchangeably with ventilation.

Question 24

What factor determines burrowing success? How else can species facilitate burrowing?

Answer 24

Mechanical properties of sediment & variation in species morphology & behaviour can determine burrowing success.

Sp can facilitate burrowing through mucous production, contraction/expansion of the body or hydrostatic skeleton.

Question 25

What are the three methods of burrowing?

Answer 25

1. by fracture
2. by fluidisation
3. by plastic rearrangement of sediment particles

Question 26

Explain burrowing by fracture (anchor, wedge)

Answer 26

• burrowers use mechanically efficient system referred to as CRACK PROPAGATION
• alternating ‘anchor’ system of burrowing serves as wedge to extend the crack shaped burrow

Question 27

Explain burrowing by fluidisation.

Answer 27

• burrowers deform sediment by fluidisation.
• atlantic razor clam burrows by expanding & contracting its valves to fluidise the surrounding sediment
• uses an order of magnitude less energy than would be needed to push the clam directly into the sediment - known to burrow >70cm depth

Question 28

Explain burrowing by plastic arrangement of sediment particles.

Answer 28

• Armandia brevis, mud burrowing opheliid polychaete, uses curvature of undulating body to rearrange particles within sediment profile
• this mode of burrowing may be common in v small non-peristaltic species of worm

Question 29

What 5 behaviours of benthic-dwelling invertebrates play a signficant role in redistribution of pore water fluids and sediment particles?

Answer 29

Burrowing
Feeding
Irrigation
Construction
Locomotory activities

Question 30

What are some of the different methods used to quantify particle reworking?

Answer 30

• radionuclides
• chlorophyll a
• heavy minerals
• metal doped sediment
• glass beads
• luminophores

Question 31

What is the method of choice for quantifying redistribution of particles?
What method has been used the most?
What is used for most short term experiments?

Answer 31

• use PARTICULATE TRACERS
• like darwin used powdered chalk to track earthworm activity
• radionuclide tracers been used most, but integrate over long time periods
• for most short term experiments: fluorescent dyed particles (luminophores)

Question 32

Which method used to be favoured for measuring burrow ventilation?
What is an alternative?
What is the most recent, more sophisticated technique?

Answer 32

1. glass tube systems where pressure head could be measured
2. use clearance rate of species based on reduction of algal cells, bromide, or a dye like rhodamine
3. Positron emission tomography & computed tomography (PET/CT) to provide fully quantitative description of ventilation in lugworm in 4 dimensions

Question 33

What are the two dividing lines that classify the many connections between the great number of model types developed to describe sediment mixing?
Which 3 criteria provide quantitative basis to decide whether a process should be modelled as L/NL?

Answer 33

discrete/semi-discrete/continuous
local/nonlocal

frequency, symmetry and length

Question 34

Under natural conditions, what do most modes of sediment reworking meet the condition for, but violate additional assumptions of the biodiffusion model?
What is this referred to?

Answer 34

Non local exchange formalism

Biodiffusion paradox

Question 35

What is the most widely applied model to describe patterns of tracer profiles?

Answer 35

The biodiffusive model.
Applies Fick’s law of diffusion to simulate particle dispersal by analogy with diffusive heat transport & calculates biodiffusion coefficient, Db.

Question 36

What is the biodiffusion coefficient, Db?

Answer 36

The rate at which the variance of particle location changes over time, where the variance is a measure of the spread of particles in a tracer profile and is proportional to the squared velocity of the diffusing particle.

Question 37

What does the biodiffusion model assume?
Why is the validity of these assumptions unlikely?
What has been developed in response? What do these allow?

Answer 37

That particles experience a random walk with a fixed step length (small) and fixed step frequency (often)
But given the wide range of spatio-temporal scales on which particles are displaced by organisms, validity of these assumptions are unlikely
Non-local bioturbation models been advanced in response, which allow long-range mass transfer betw spatially separated layers within the sediment

Question 38

What are the 7 modes of bioturbation that reflect the mechanistic basis of how particles are transported?

Answer 38

• epifaunal
• surficial modifiers
• biodiffusers
• gallery biodiffusers
• upward conveyors
• downward conveyors
• regenerators

Question 39

What else do we need to think about other than transport mechanisms?

Answer 39

1. burrow ventilation rates
2. burrow morphology & complexity
3. burrow characteristics
4. burrow surface area

Question 40

Functioning of most of the global ocean seafloor depends largely upon the addition of what and what to the sediment water interface, and the subsequent what & what achieved by microbial-faunal coupling?

Answer 40

oxygen and organic matter

organic remineralisation and nutrient processing

Question 41

In the water column inventory, what do bacterial assemblages in open oceanic waters range from? Where are comparatively higher numbers of bacteria typically found?

Answer 41

10^2 to 10^6 cells per ml, although elevated numbers reported in eutrophic coastal waters.
Unpolluted sediments.

Question 42

In general, sediments are characterised by a … superficial layer where … is the terminal electron acceptor and … … and … bacteria predominate

Answer 42

thin
oxygen
aerobic autotrophic
heterotrophic

Question 43

In general, sediments are characterised by a … superficial layer where … is the terminal electron acceptor and … … and … bacteria predominate

Answer 43

thin
oxygen
aerobic autotrophic
heterotrophic

Question 44

Above the redox potential discontinuity transition, the sediment is …, although it remains … due to the presence of other electron acceptors (e.g. nitrate, mn oxides, and ion oxides). These oxidised sediment horizons are characterised by a distinct … to …-… colouration and usually support the … amounts of bacterial activity

Answer 44

anoxic
oxidised
brown
brown-grey
highest

Question 45

The redox potential discontinuity boundary transition, the zone separating the surficial … sediment from the underlying … basement, is also an area of … bacterial activity with …-… bacteria of the genera Beggiatoa and Thiovulum particularly prevalent

Answer 45

aerobic
anaerobic
high
sulphide-oxidising

Question 46

Below the RPD, some fermentation & … of organic compounds occur, but … reduction prevails as the dominant bacterial process.
Here, the activities of … reducing bacteria outcompete … and … bacteria in all but the deepest sediment.

Answer 46

methanogensis
sulphate
sulphate
fermenting
methanogenic

Question 47

Biogenic structures, like …, …, … and … disrupt the layered sediment profile that would otherwise form. … of burrow systems in particular can dramatically change … composition and activity and determine which … pathways dominate.

Answer 47

burrows, tubes, mounds and pits
Ventilation
microbial
diagenetic

Question 48

Significant numbers of … reducing bacteria, mostly found in the … layers below, are also present in the surficial … layer of sediments persisting in localised spots, or …, and utilising the … availability of substrate from the surrounding sediment.

Answer 48

sulphate
reduced
microniches
high

Question 49

The abundance of microbes is strongly correlated with … variables. When aerobic and anaerobic microbes are considered together, … abundance is … correlated with increasing grain size bc there is a … surface area available for fine sediments rel. to that of coarse sediments.

Answer 49

environmental
microbial
negatively
greater