Benthic Flashcards
What is the distribution of sediments?
The distribution of sediments is not uniform and sedimentation rates vary considerably.
What are typical sedimentation rates in different areas?
*0.5-1.0 cm 1000 years-1 in the deep oceans
*10 - 50 cm 1000 years-1 in the continental margins
*>500 cm 1000 years-1 in some bays and deltas
What is the average sediment thickness?
~500m
Why is the sediment thickness more in the Atlantic than the Pacific?
*The Atlantic is about twice that of the Pacific
*The major rivers flowing into the Atlantic extend over more land and carry a much greater sediment load than the equivalent rivers of the Pacific
What is the most important factor in determining sediment thickness?
Time
What is the sediment thickness equation?
sediment thickness = sedimentation rate x time for accumulation
What are the primary factors controlling sediment distribution?
*Age of underlying crust
*Tectonic history of crust
*Structural trends in crust
*Nature and location of sediment source
*Nature of sedimentary processes delivering sediments to centres of deposition
Where are the most abundant sediment deposits?
Along the east and gulf coasts of North America, South china sea and bay of bengal east of india. Most of theses sediments are trapped in estuaries
Where is the youngest rock located?
At the Mid-oceanic ridge where continental plates are pulling apart and new crust is being formed
Where is the oldest rock found?
Along the coastlines of africa and america as old as the jurassic age
How does sediment thickness and seafloor age relate?
*Sediment thickness positively correlates with increasing age of the seafloor
*The thinnest areas of sediment coincide with areas of new seafloor is being generated
How are sediments classified?
The dominant component of their composition
Why are sediments heterogeneous?
Because sediments are always a mixture of different components so are heterogenous in composition and distribution
What are the 4 main types of sediments?
*Lithogenius
*Biogenous
*Hydrogenous
*Cosomogenous
What are the characteristics of lithogeneous sediments?
*Compose up to 75% of all sediment
*formed from weathering and erosion of rocks on land and introduced to ocean by water, winds or ice
*Composition is determined by composition of parent rock
*Typically abundant near to continents, specifically near river mouths, but can be transported to deep ocean via slumps and turbidity flows
What are the characteristics of biogeneous sediments?
*Formed from the insoluble remains/hard parts of organisms
*In shallow water, a majority of these sediments ate the remains of shells
*Most important biogenic minerals are carbonates and biogenic silica (opal) that compose calcareous and siliceous sediments
What are calcareous sediments?
Calcaraous sediments consists of sands and gravel and are common near coral reefs, so coastal environments of the low latitude tropics
What are siliceous sediments?
Siliceous sediments are found near antarctic shelfs and are accumulations of sponges which are silica-based
Where are both calcareous and silious sediment found?
In the open ocean both calcarous and silicous sediment can dominate due to the presence of diatoms (silica), coccolithothores and forams (carbonate)
What are hydrogenous sediments?
*Formed by the precipitation of minerals from the seawater
*The evaporation of water in restricted basins and lagoons can lead to the deposititon of evaporites such as anhydrite and gypsum
*or can be formed as a new mineral as a result of chemical reactions between seawater and sediments that already exist in the ocean floor
What are cosmogenous sediments?
*Sediments are extraterrestrial in nature and are generally like miniature meteroites
*They are the remind of impacts of large bodies of space material (e.g. commets)
What does abundance and distribution of sediments depend on?
Abundance and distribution of sediments on the ocean floor depends on modes of delivery, dilution and destruction.
What is sediment delivery?
The amount of material delivered depends on proximity to source
What is sediment dilution?
The degree of dilution by other components is important
What is sediment destruction?
preservation of sediments is a major issue and is a function of the solubility of minerals
How does latitude impact sediment types?
*There is a gradation of marine sediment types related to latitude
*High latitude, polar regions, are dominated by glacial marine sediment
*Temperate shelves = lithogenous sands and muds from rivers
*Tropical shelves = biogenic calcareous sediment
How does ocean circulation influence the distribution of carbonate and silica rich deposits?
Young, oxygenated water travels polewards from the equatorial Atlantic, cooling en route and sinks at high latitudes forming North Atlantic Deep Water. This dense water, saturated with calcite, forms calcium carbonate in Atlantic marine sediments and flows into the other ocean basins (i.e. first the Pacific and then the Indian Oceans respectively). The Pacific Ocean therefore receives older, deep water rich in carbon dioxide owed to the degradation of organic matter. This acidic deep water results in the dissolution of calcium carbonate in Pacific marine sediments, which are instead dominated by siliceous sediments or clays in oceanic regions of high and low productivity respectively.
What is CCD?
*Carbonate compensation depth
*The level below there is no calcium carbonate preserved in marine sediments
*Depth at which carbonate input from surface waters is balanced by dissolution in corrosive deep waters
Where is CCD more shallow?
Tends to be shallower in the Pacific versus the Atlntic Icean due to the age and acidity of waters
What is sediment?
*Matter composed of particles which fall by gravitation to the bottom of a liquid
*In reality sediment is more compex and a mixture of inorganic and organic particles, dissolved interstitial gas and fluid phases, an active biota and the mineral solid phase
How is sediment particle size measured?
measured using graded sieves and quantifying the volume retained on each mesh size
What is the Udden-Wenworth grade scale?
*splits up each particle size into different divisons, or grades, to aid descriptions
*built around powers of 2
What is the Krumbein phi (φ) scale?
*distribution between sediment fractions is not equal and the size range of particles span several orders of magnitude
*logarithmic
What are the major size categories?
*gravel (pebbles, cobbles, and boulders)
*sand
*mud (silt and clay)
What are robert folks descriptive metrics?
*descriptors that describe particle shape, form, sphericity, permeability, colour, and texture of particles
What controls local distribution of sediments?
net deposition (e.g. accumulation) vs net erosion
What is the equation for large particles setting velocity?
V=33√d
*V = settling velocity
d =particle diameter
What is the equation for small particles settling velocity?
V=8100d^2
What is he difference between non-cohesive and cohesive sediments?
*Non-cohesive - sand - strong inertial forces
*Chohesive - muds/clays - weak cohesive forces
What is flucculation?
*Condition where small charged particles become attached and form a fragile structure, a floc
What is the interplay of opposing forces?
Van der Waals - attractive forces, of dipoles. The closer the particles the stronger the force
What is electrostatic force?
*repulsion
*The balance of these two forces depends on how the particles react
What occours when particles enter from terrestrial environments?
*the water body carrying the sediment load undergoes a transition, from freshwater to seawater
*Seawater has positive ions, which are attracted to clay, reducing the negative charge of the particle
*Floucculation occurs rapidly at low salities and particle no longe act individually and bind together, acting as a larger particles
What is particle suspension?
They stay in suspension as there is turbulence in the water column lifting them up
What is particle saltation?
*some particles at higher velocity/larger in size get thrown up throught the water column as it has enough inertia behind it.
*These particles are too large to stay in water column through suspension
What is particle bedload transport?
*very large particles roll along bedfloor
*There is enough inertia to push them but not enough to uplift into the water column
What is force of water movement affected by?
*Drag
*Friction (shear stress)
What is drag?
*Drag is related to the cross sectional area of the particle exposed to flow
What is the water force cycle?
*As water passes ove the surface, water particles adjacent to the surface do not move, the no-slip condition
*The next layer of molecules above, are slowed due to the no-slip below
*As we move away from the bed velocity increases and the effect of the ed becomes less dominant
When do different flows occour?
*Laminar flow is only at the leading edge where the water comes in contact with the surface e.g. seafloor, rock, fish
*There is then the transition zone before turbulence
When is shear stress high?
Shear stress is higher in turbulent conditions and the velocity can change very quickly
When does a viscous sub-layer exist?
Thickness is inversely proportional to flow velocity and it depends on the roughness of the bed
When does smooth flow begin to break down?
*D>t/3
*D=particle size diameter
*t-thickness of viscous sub-layer
When is smooth flow destroyed?
D>7t
What are the impacts of too much or too little sediment?
*too much sediment deposition can smother habitats and physically alter the morphology of the benthos
*too little sediment deposition can lead to nutrient depletion and erosion
What happens when you move down the sediment column?
vertical transitions of:
*Oxygen
*Redox
*Sulphide
*Organic matter
What factors influence sampling method?
*Nature and patchiness of target species / or habitat
*Practical considerations
*Questions that the study will address
*Economic considerations
*Previous adopted practice
What is organism lifestyle and interaction with sediment dependent upon?
*Size
*Micro and meio sized animals are associated with individual mineral grains of the sediment, living on particles (micro) or in between particles, respectively (meio)
*Larger organisms (macro & mega) move or manipulate the mineral grains, and either live above or on the sediment, or within the sediment profile
What are the advantages of trawls?
useful for collecting epifaunal organisms, especially species that have a patchy distribution or are rare
What are the disadvantages of trawls?
*the efficiency of sampling is low *faunal returns are generally low in relation to the area swept by the net
*time consuming
What are the advantages of dredges?
*They tend to have modifications aimed to maximise the capture of specific target species, such as ‘teeth’ and larger mesh sizes
*Can cover wide areas in a short amount of time, and can be deployed in most weather conditions
Why are trawls and dredges not quantatative?
- it is not possible to know how much of the seafloor has been sampled.
*The length of tow can be standardised to allow a semi-quantitative estimate of the area sampled
What are bottom sledges?
Designed to sample epifauna and the water immediately above the seafloor - the ‘suprabenthos’
What are the disadvantages of bottom sledges?
*Epibenthic sleds are only semi-quantitative
*Reduced coverage
*low efficiency
*readily filled with sediment if pilot not experienced or sea conditions not favourable
What are the advantages of bottom sledges?
*Epifaua and suprabenthic organisms
*good on uneven substrates (where trawl nets and dredges are prone to entanglement)
What are grabs?
*The most common sampling method for obtaining macrofauna inhabiting sediment
*General penetration depths of 5-10cm
*Grabs are designed for collecting soft to medium hard sediment, such as muddy-sand and sand. Grabs tend to over penetrate in gravels and under penetrate in muds
What are the disadvantages of grabs?
Grabs do leave significant elements of the fauna, in particular mobile epifauna and deeper dwelling macrofauna.
What are the advantages of grabs?
Grabs are quantitative, and a standard component of most benthic surveys.
What are the advantages of box corers?
*Extensively used in shelf and deep sea regions
*quantitative
*return relatively undisturbed large samples
*Retains the sediment-water interface and overlying water
What are the disadvantages of box corers?
*Difficult to operate
*Only used in calm conditions
*limited spatial coverage
*large and expensive
What are corers?
Corers work by driving a tube into the sediment profile, either using gravity or mechanical assistance, to retrieve an intact column of sediment
What is the Craib corer?
designed to take a single vertical intact core within a removable acrylic core-line
What is the difference between lightweight corers and multicorers?
Multicorers tend to be larger, so retrieve longer and larger diameter cores relative to single corers
How are faunal samples processed?
*a compromise between the efficiency of the mechanical process and how that process affects the condition of the fauna
*Rigorous sieving with high powered hoses will help with rapid processing but is likely to lose or overly damage fauna, making identification and enumeration difficult
*Once sediment has been removed, the faunal returns is rinsed into a suitable container and immediately preserved in either 70% industrial methylated spirit (IMS) or 4% formaldehyde
How long should samples be stored?
minimum of 3 months to stabilise the biomass (replacement of tissue water with the preservative)
What is SPI?
Sediment profile imaging (assessing benthic habitat condition and observing subsurface macrofaunal behaviour)
What are the advantages of SPI?
provides a rapid, non-invasive means to observe invertebrate-sediment behaviour and interactions below the sediment-water interface
What are the disadvantages of SPI?
*images only reflect the immediate environment in contact with the face-plate
*Limited to soft-medium sediments, *deployment demands calmer weather conditions
What is important to study design?
*Samples should be a random sample of the total population of interest
*A larger sample size = more confidence that effect of treatment rather than due to chance
What is pseudoreplication?
your actual sample size is smaller than what you think you have
What was recognised in relation to assemblages in 1870?
there was recognition the there is an interaction between fauna and sediment in the environment
What is an assemblage?
*a group of organisms occurring in a particular environment, presumably interacting with each other and the environment, and separable by means of ecological survey from other groups
*assemblage and community are used interchangably
What did Peterson do in relation to classifying assemblages?
- he developed the grab in order to standardize sample retrieval
*made the transition from qualitative to quantitative sampling
What were Petersons ideas in relation to classifying assemblages?
*assemblages could be described by their characterising species
*Constancy and dominance were the two most important features defining a characterising species
*Petersen applied his characterising species rules to his data to demonstrate the utility of the approach, and defined 7 major community types
What were pertersons 7 community types pattern?
The 7 community types patterns broadly matched types of sediments, prevailing currents and other environmental variables, so investigators could start to draw conclusions and/or present hypotheses about what might be happening with respect to fisherie
What was the limitation of peterson?
did not take into account that species responded to their immediate environment
What are Jones’ zoogeographical regions?
*Arctic (-2 to 7˚C)(northern)
*Atlantic boreal (3 to 16˚C) (southern UK to Arctic)
*separated the Atlantic into two regions, Arctic and Atlantic boreal clusters. The Arctic cluster was cooler than the Atlantic boreal, but there was an overlap in temperature and the distribution of species that was difficult to justify as a sensible means of separation
What did Jones’ zoogeographical arctic region describe?
- 4 associations:
*Shallow water (Macoma)
*Offshore sand (Venus)
*Offshore muddy-sand (Astarte)
*Deep mud (Foraminifera)
What did Jones’ zoogeographical atlantic region describe?
*Described 3-tiered hierarchy:
*Shallow water & brackish
*Offshore communities
*Deep communities
What were Thorson’s ideal rules?
*Allowed a binary ‘yes’/’no’ decision as to whether a species would be classified as a characterising or not
*down to percentage of hauls present and percentage of total biomass
Created 7 communities but they can each be defined by more than 1 species (in comparrison to peterson)
What is a conspicuous species?
present all of the time
Why do organisms adapt to their environment?
*To respond to changes in ecological or environmental context
*To exploit and derive sufficient resources, such as food or shelter/camouflage
*To defend or protect themselves and their resources
*To maximise chances of reproductive success
What is adaptation?
structural, behavioral or physiological/functional change in which a species gains an advantage, including the development of special body parts, behavioral traits or physiological processes (tolerance to anoxia, production of slime)
What are the 2 types of adaptation?
*ecological adaptation
*evolutionary adaptation
What is ecological adaptation?
occurs within the lifetime of an individual organism; results from repeated exposure to a naturally occurring challenge (acclimatisation)
What is evolutionary adaptation?
*genotypic change
*occurs within a population over longer time-scales (several generations); product of natural selection. Facilitates an enhanced ability, or fitness, to survive and reproduce.
*Generally, change is not reversible either due to imposed natural (natural selection) or experimental conditions (artificial selection).
What is acclimation?
the non-heritable reversible modification that occurs over the lifetime of an individual. Generally, a phenotypic response to a specific stresso
What is acclimatisation?
the process by which an individual adjusts to a challenge in order to maintain performance across a range of changing conditions. Generally, a coordinated response to several stressors experienced simultaneously
What is the landscape of cohesive sediments?
*Dominated by fine sediments
*Cohesive muddy shores tend to be sheltered from wave action, however tidal currents are typically high
*Small pre/interstitial spaces so infrequently flushed
*High organic matter
*Low oxygen content
*Cohesiveness allows for stable burrows for animals
*Most organisms sessile burrow dwellers
What is the landscape of non-cohesive sediments?
*High energy environments
*Typically wave swept
*Individual sediment grains are typically coarse and surrounded by large pore spaces
*Regularly flushed
*Low organic matter
*High oxygen content
*Mobile borrowers that live intermittently at seafloor and within sediments
What is cohesive sediment burrowing technique?
*Burrow ventilation causes water to flow through the burrow
*Diffusion across burrow walls
*Diffusive vertical transport through sediment interstitial space
What is non-cohesive burrowing technique?
*Burrow ventilation causes water to flow through the burrow
*Diffusion across burrow walls
*Advective vertical transport through sediment interstitial spaces
What causes local migration?
Adaptive response to a change in circumstance that has evolved over time and has benefit to the individual
e.g.resource availability
What are microphytobenthos?
*They inhabit the sediment-water interface and uppermost few millimetres of the sediment profile in the photic zone
*Mainly found in cohesive sediments
What is the migration of microphytobenthos?
*When the surface of the sediment is inundated with water, the microphytobenthos migrate downwards into the sediment to avoid being grazed and/or washed away
*at low tide, the microphytobenthos return to the surface to photosynthesise.
What is the migration of microphytobenthos in non-cohesive sediments?
*move in a cycle between the sediment and the water surface within the surf zone
*endogenously controlled vertical migration between the water surface during the day and the sediment at night and a horizontal movement between the surf zone during medium to high energy conditions and the nearshore during calm periods
How do non-cohesive microphytobenthos diatoms surf tides?
*Individuals divide to lose their mucus coat and float to the surface waters. *Once they are carried to the outer surf zone by the currents, they secrete a mucus coat that enables adherence to sediment grains and they sink.
*The process is repeated so that the diatoms ride the incoming and outgoing tides to maintain their position
What is burrow architecture?
Muds are cohesive elastic solids, whereas granular sands form a non-cohesive porous matrix. Infaunal invertebrates that burrow through sediments therefore face different mechanical challenges that can lead to a variety of burrowing strategies and architectures.
What physical mechanism drives the maintenance of burrows?
Active burrow ventilation
What is the architecture of cohesive sediments?
*In muds, the small particle size of the surrounding sediment means burrow water cannot penetrate the burrow wall, other than by diffusional transfer and the vast majority of the volume must be actively removed via the burrow opening at the surface
*burrows in cohesive sediments tend to be U-shaped or have multiple openings to the surface
What is the architecture of non-cohesive sediments?
*In sands, ventilation flows can penetrate the surrounding sediment and enter the interstitial pore spaces via the terminal end of the burrow.
*burrows in non-cohesive sediments can be I- or J-shaped
What are mucous lined burrows formed from?
*membranous secretions or *calcareous materials
*cementing sand-grains or selected fragments together
What is the purpose of mucous lined burrows/ tubes?
*protect the occupant
*act as a lair for catching passing prey
*facilitate attachment to various substrata
*provide a stable and regulated environment
How do mucous lined tubes produce favorable biogeochemical conditions?
They are sites of enhanced microbial activity that can elevate pH within the burrow lumen and deplete sulphur in adjacent sediment
What is behavioral plasticity?
*organisms changing there behaviour
*there are 2 classes - innate and learning
What are innate behavioral responses?
occur when the modification of behaviour is the result of evolution at the population scale over multiple generations
What are learning behavioural responses?
occur when a modification of behaviour is refined through experience within the lifetime of an individual
How do species adjust their behaviour in response to environmental stimuli?
*adjust their behaviour in response to environmental stimuli
*Change due to tidal flow
*Change to reduce competitive interaction or predation by burrowing deeper
Why might species aggregate/show gregarious behaviour?
*reproduction
*Maximise resource capture
*Protection
*Sharing of food
What are the negatives of gregarious behaviour?
reduced growth rates and smaller body size related to intra-specific competitive interactions
What is character displacement?
When species distribution overlap populations can diverge in phenotype and resource use reducing resource competition
What is benthic-pelagic coupling>
It follows that fluxes of materials across the sediment-water interface
What are the stages of benthic-pelagic coupling?
*deposition of non-living organic matter to the seabed
*mineralisation of material within the sediment
*release of nutrients back into the overlying water column
How does flux and primary productivity relate?
Areas of high flux overlie areas of high primary production and seasonality
Where does the highest flux occour?
centres of coastal upwelling and continental shelves
What are causes of benthic-pelagic exchange?
*Active movement without a life-form shift e.g. diel vertical migrations
*Active movement with a life-form shift e.g. storage banks for young stages of water column species
*Passive events e.g. extreme weather and human activities like dredging
What is bioturbation?
*The biogenic alteration of sediments
*Transport processes by animals including particle reworking and burrow ventilation
What makes up the sediment profile?
*mineral particulates
*interstitial water
What are the 2 primary transport processes?
*Movement of particles - reworking activity
*water and solute transport - ventilation/bioirrigation
What is bio-advection?
non-local transport of fluid/particles
What is biodiffusion?
local transport of fluid/particles
What does burrow flushing do?
*Part of bioirrigation/ventilation
*Replenishes supply of dissolved oxygen, removes metabolites, temp control
How do species burrow?
*production of mucus *contraction/expansion of the body *hydrostatic skeleton
What is burrowing by fracture?
crack propagnation uses an alternating ‘anchor’ system where burrowing serves as a wedge to extend the crack-shaped burrow
What is burrowing by fluidisation?
Burrowers deform the sediment by fluidisation. Uses less energy than needed to directly push the organism into the sediment
What is burrowing by plastic rearrangement of sediment particles?
Curvature of undulating bodies rearrange particles within the sediment profile
How do you quantify bioturbation?
Particle redistribution is mostly quantified by applying fluorescent dyed particle tracers e.g. rhodamine that can be visualised under UV light
What is tracer type determined by?
If a species ventilates its burrow diffusively or advectively
What is a biodiffusion coefficient?
*Db
*Measures the rate of bioturbation as it is a series of small particle displacement events
*Units = cm^2 year^-1
What classifications do bioturbation models use?
*Mechanistic process (local/non-local)
*Mathematical process (discrete/semi-discrete/continuous)
What is the biodiffusive model?
*Describes patterns of tracer profiles
*Applies Fick’s Law of diffusion to simulate particle dispersal by analogy with diffusive heat transport and calculates a biodiffusion coefficient, Db
What are the 7 modes of bioturbation?
*Epifaunal
*surficial modifiers
*Biodiffusers
*gallery biodiffusers
*upward conveyors
*downward conveyors
*Regenerators
In an ‘average’ community, we would expect to see representatives from all of these bioturbation modes
What are water interface sediments characterised by?
sediments are characterised by a thin superficial layer where oxygen is the terminal electron acceptor and aerobic autotrophic and heterotrophic bacteria predominate
What is the oxidised layer?
*Above the redox potential discontinuity (RPD) transition, the sediment is anoxic, although it remains oxidised due to the presence of other electron acceptors (e.g. nitrate, manganese oxides, and iron oxides). *These oxidised sediment horizons are characterised by a distinct brown to brown-grey colouration
*usually support the highest amounts of bacterial activity
What is the redox potential discontiunity boundary (RPD)?
*the zone separating the surficial aerobic sediment from the underlying anaerobic basement
*an area of high bacterial activity with sulphide-oxidizing bacteria prevalent
How does abundance and grain size relate with aerobic and anaerobic microbes?
microbial abundance is negatively correlated with increasing grain size because there is a greater surface area available in fine sediments relative to that of coarse sediments
How is abundance related to organic carbon and nitrogen?
For sediment organic carbon and nitrogen content, microbial abundance is strongly and positively correlated
How is abundance and redox potential related?
no relationship with redox potential (Eh), as both aerobic and anaerobic microbes respond and effect redox conditions in a variety of ways
What is the diagenetic sequence
oxygen, nitrate, manganese, iron, sulphate, methane, co2
What are taxon based approaches to compare how species effect and respond to abiotic and biotic conditions?
*compare species assemblages in relation to environmental conditions (does not prove causation)
What are trait based approaches to compare how species effect and respond to abiotic and biotic conditions?
how the components of biodiversity influence ecosystem properties
What are functional traits?
define species in terms of their ecological roles - how they interact with the environment and with other species
What is a trait?
any feature at any level of organisation that is measurable at the level of the individual
What is a functional effect trait?
any trait which alters specific community or ecosystem properties
What is a functional response trait?
any trait responding to external forcing that alters the performance or fitness of an individual
What is functional redundancy?
Overlap of how species in the same assemblage contribute or respond in the same way as other species
What is a functional group?
a set of organisms sharing similar responses to the environment and have similar effects on ecosystem processes (e.g. bioturbation) and functioning (e.g.productivity)
What is biological trait analysis?
allowed functional group allocation to be based on an extended series of life history, morphological, and behavioural characteristics
What were the 3 key developments in benthic ecology?
*1st - recognition that fauna occurred in zones or regions (These were also divided into smaller divisions - facies)
*2nd - described / categorised fauna occurring in zones
*3rd - organisms-sediment interactions
What are organism-sediment relations?
*Organisms change the chemistry and physical character of the sediment through their burrowing and feeding activities.
*This forms an infaunal assemblage that reflects the interactions between temporal, environmental, and biological variation
What did Gray (1974) do?
Attempted to relate individuals, populations and communities to sediments. His view was that larvae or adults selected suitable sites for settlement, the population modifies the sediment, in turn, leading to temporal and spatial changes in which species survive
What was Gray’s (1974) summary?
sequential sequence of larval responses to stated stimuli
What was the difference between Gray (1974) and Rhoads (19740)?
Rhoads viewpoint was similar to Gray, but he emphasised post-settlement processes and species-sediment interactions
What did Rhoads (1974) do?
*Rhoads (1974) made the leap from Thorson’s homogeneous “parallel communities” to heterogeneous communities that were modified by the biology
*Rhoads took the view that assemblages were not just a product of wider environment, but actively modify their own local environment
Why was Rhoads (1974) successful?
The development of the sediment profile imaging camera - he could make direct observations
What was Rhoads (1974) summary?
*organism-sediment interactions were important in influencing the stability of seafloor, substratum patchiness and particle size which, in turn, effect species diversity and habitat properties
* faunal activity could control an entire biodeposition and/or resuspension cycle
What are phenomenological models of benthic succession
Ecological succession, or how biological communities re‐assemble following natural or anthropogenic disturbance
What is the mechanistic basis for species distribution?
Species functional traits that influence fitness or performance provide a mechanistic basis for understanding patterns of species distribution because species turnover occurs through environmental filtering
What did Pearson (1976)?
*The faunal and sedimentary changes that occur with distance from the point of organic loading, recognising four stages
*Summarised the effects of organic enrichment on sediment quality (mainly in terms of redox potential) and community composition.
What are the 4 stages of organic loading, Pearson (1976)?
*grossly polluted, through polluted and transitory, before returning to normal (unenriched)
*benthic organic enrichment caused a predictable and sequential changing in the characteristics of the resident macrofauna and associated sedimentary environment
What is Pearsons (1976) effects of organic enrichment on sediment quality and community composition?
*the first scenario represents a heavily organically enriched location where there is poor flushing capacity and all oxygen is used up by microbial decomposition
*second scenario - there is some exchange of water but oxygen consumption remains high reducing the oxidised depth of the sediment
*third - the system has a plentiful supply of oxygen and water exchange and organic matter is dispersed over a wide area, allowing a mature faunal assemblage to develop
What was the success of Pearson (1976)?
By putting faunal responses and tolerances together with amount of organic enrichment and local conditions, it was now possible to predict the ecological outcome
What is succession in the Baltic (Rymohr)?
*Rymohr identified two additional stages that reflected the regular hypoxia and long term anoxia regions of the Baltic (Stages IV and v)
*Similar transitions take place on much shorter timescales in areas that undergo seasonal hypoxia
What was Rymohrs baltic stage IV?
assemblages are characterized by longer periods of anoxia, and the formation of bacterial mats (Beggiatoa spp.) at the sediment surface. These are normally intermittent, and the assemblage is not regarded as a successional end-point.
What was Rymohrs baltic stage V?
represents the complete break-down of the macrobenthic community due to long-term (years-decades) hypoxia, which results in lamination of the sediment through lack of bioturbation.
What are the 9 stages of organism-sediment interactions from right to left?
*redox potential discontinuity
*Stage -1
*Stage 0
*Stage 1
*Bioturbation
*Peak of opportunists
*Ecotone point
*Stage 2
*Stage 3
What is Redox potential discontinuity in organism-sediment interactions cycle?
*All marine sediments are anoxic at depth below the sediment-water interface.
*The transition zone separating the surficial aerobic sediment from the underlying anaerobic basement is the redox potential discontinuity (RPD)
*The relative position of the RPD is a function of dissolved oxygen, diffusive flux, temperature, infaunal mixing, and the biological and chemical oxygen demand associated with organic matter degradation.
*At high levels of impact, the consumption of electron acceptors is sufficient to cause an encroachment of the RPD towards the sediment surface.
What is stage -1 in organism-sediment interactions cycle?
*Complete break-down of the macrobenthic community due to long-term hypoxia
*resulting in lamination of the sediment through lack of bioturbation.
*There may be no sedimentary redox discontinuity as the boundary between negative and positive conditions may lie in the water colum
What is stage 0 in organism-sediment interactions cycle?
*Characterized by longer periods of anoxia, and the formation of bacterial mats (Beggiatoa spp.) at the sediment surface.
*The RPD-layer is at the sediment/water interface
*macrofauna is generally lacking.
What is stage 1 in organism-sediment interactions cycle?
*the sediment content of labile organic matter has declined and the formerly anoxic or hypoxic sediment has given way to oxic conditions in the uppermost layers of the profile.
*This enables small ‘opportunistic’ species that have a physiological requirement for sediment containing high levels of organic matter to colonise the surface layer.
*The bioturbatory activities of these infauna start to significantly modify the physical, chemical, and biological nature of the deposit and pave the way for other species to establish.
What is bioturbation in organism-sediment interactions cycle?
*The formation of holes, tubes and burrows, and the biologically mediated circulation and incorporation of oxygenated water into the sediment serve to stimulate aerobic microbial breakdown of organic material
*increase the depth of oxygenated sediment
What is peak of opportunists in organism-sediment interactions cycle?
The first species to be encountered tended to be small and few then, some short distance away, community abundances rise and then fall dramatically
What is the ecotone point in organism-sediment interactions cycle?
Species richness and abundance begin to increase towards the ecotone point, a transitional zone poor in species richness, biomass and abundance.
What is stage 2 in organism-sediment interactions cycle?
*Bioturbation allows further colonisation of a greater variety of species and the macrofaunal assemblage enters a ‘transitory’ phase of succession that is unfavourable for ‘pioneer’ population persistence. Species that characterise the transitory include suspension and deposit feeding bivalves, conveyor belt’ polychaetes, and relatively immobile holothurians.
What is stage 3 in organism-sediment interactions cycle?
*A more complicated and persistent faunal assemblage forms and evolves towards a ‘normal’ or ‘equilibrium’ or ‘climax’ community status.
*Sediments at ‘equilibrium’ are characterised by “burrow complexes of large species intermingled with smaller tube dwelling and burrowing species” that together depress and maintain the RPD at depths in excess of 10 cm
What is a stressor?
any physical, chemical or biological factor that requires a compensation response by affected organisms, thus placing constraints on the productivity and development of ecosystems
What doe the effect of an individual stressor depend on?
intensity, frequency and duration of stress, and can lead to either semi-permanent or permanent ecological adjustments
What are the different interactions of multiple stressors?
*synergistic, a&b > a + b
*antagonistic, a&b < a + b
*Additive, a+b
What is the most common interaction of multiple stressors?
synergistic
What are the major categories of human activities resulting in ocean stresses?
*Pollution
*unsustainable resource use
*habitat fragmentation and destruction
*species invasions
*climate change
What are different human benthic pressures?
*Resource exploitation
*Waste disposal and pollution
*Nutrient loading and hypoxia
*Offshore construction and man-made objects
*Sound and vibration
*Chemicals and pharmaceuticals
How is resource exploitation a benthic pressure?
*bottom fishing
*deep sea mining of metals from nodule grounds
What is the impact of bottom fishing?
*Fishing gear has a direct physical effect on the seabed
*effects include scraping and ploughing, sediment resuspension, and physical destruction
What is the impact of mineral extraction?
*the accelerating progress of new technologies is increasing the demand for rare metals used in the electronics industry
Where are manganese nodules most abundant?
*70% in Atlantic
*These conttain less ore because the sedimentation rate is faster - more sediment mixed into nodule, less metal.
How are diamonds a exploited benthic resource?
*mined from the ocean floor
*Diamonds are eroded from land and deposited into the ocean by rivers. *Only the best diamonds survive this transport process, so the quality of ocean diamonds tends to be very high
How is waste disposal and pollution a benthic pressure?
*Radioactive waste disposal
*Sewage dumping
*Marine litter (rafting of species on floating litter has the potential to introduce species to new regions )
How is nutrient loading and hypoxia a benthic pressure?
*increases in anthropogenic nitrogen and phosphorus loading
*when in excess can lead to eutrophication and hypoxia
What are the impacts of low oxygen levels on benthic environments?
*Low oxygen levels can reduce survival and growth and alter behaviour of individual organisms.
*As oxygen declines, shifts in benthic successional stage occur
How is Offshore construction and man-made objects a benthic pressure?
*ship wrecks (and fuel impact)
*Offshore structures (act as islands by being a substratum leading to more suspension feeding over deposit feeding)
How is sound and vibration a benthic pressure?
The oceans are full of natural sounds (waves, currents, earthquakes, biology) creating soundscapes that provide essential information for marine fauna, but increasingly human activity has added considerable amounts of noise and vibration.
How are chemicals and pharmaceuticals benthic pressures?
*Uptake can occur by ingestion or diffusion across cell membranes/gills
*Once within the body, chemicals are transported to target tissues
*leading to metabolizing and detoxification processes leading to the excretion of toxic chemicals
What is benthic carbon sequestration?
One of the options to reduce atmospheric carbon dioxide is storage in deep sea benthic environments. CO2 pumped into ocean may return to surface after >500 years, but the view is that this is a long delay that provides sufficient time for future generations to solve the problem of reducing CO2 output
What are the depths for different forms of CO2?
*0-500m - gas
*>500m and >11ºC - liquid
*130-350m and <11ºC - solid and gaseous
*>400m and <11ºC - solid and liquid
*Deep sea - solid from freezing
What are sector-pressure impact chains?
An ecological characteristic (e.g. a species or feature of an ecosystem) can be impacted by multiple sectors and multiple pressures
What is good habitat quality from an environmental management viewpoint?
that state in which the components and processes remain well within the specified limits of system integrity selected to assure that there is no diminution in the capacity of the system to render its basic services to society
What is good habitat quality from an biological integrity viewpoint?
a water body should have the ability to support “a balanced, integrated, adaptive community of organisms
What is good habitat quality from an ecological health viewpoint?
a biological system … can be considered healthy when its inherent potential is realized, its condition is stable, its capacity for self-repair when perturbed is preserved, and minimal external support for management is needed
What does species response to stress vary with?
*Abiotic and biotic context
*life stage
*phylogeny
*severity and frequency of stressor
* where the pollutant is active within the organism
What is the response to stress in an unmanaged system?
Trajectory has two phases; stimulation as stress starts, increasing stress causes decline in ecosystem properties
What is the response to stress in a managed system?
Trajectory has three phases; stimulation as stress starts, increasing stress causes decline, followed by recovery due to reduced stress following management intervention
Why measure macrobenthos?
*the lifespan of many species (ranging from a few months to a few years) allows community structure to integrate and reflect sources of stress over time
*reside at the sediment-water interface where many pollutants concentrate
*taxonomically diverse, consisting of species that that exhibit different tolerances to stress
How does benthic habitat quality relate to sediment or substrate type?
The consideration of substrate in this way equates habitat only with the three dimensions of topography plus sediment textural characteristics.
What are the 8 factors for non-biological assessments?
- Dominance of reductionist viewpoints across disciplines
- Limited legal and regulatory programs
- Lack of clear definition of biological integrity
- Indices to assess biological integrity
- Region based quantitative definitions of ecological health
- Standardisation of field methods
- Linking field measurements to enforceable management options
- Need for cost effective approaches
What is the organism-sediment index (OSI)?
The apparent mean redox potential discontinuity depth in the sediment, the presence of sedimentary methane, dissolved oxygen immediately above the sediment-water interface and successional stage
What is the Benthic Habitat quality (BHQ)
Same as OSI but emphasises the presence of fauna
