4 ADAPTATIONS TO SOFT SEDIMENTS

Question 1

What types of sediment are the most representative habitats of the benthos in terms of spatial extent?

Answer 1

Cohesive & non-cohesive

Question 2

Why do organisms adapt to their environment? (4 things)

Answer 2

• RESPOND TO CHANGES IN ECOLOGICAL/ENVIRONMENTAL CONTEXT (climate change, long term pressure of it, short term responses, using marine environment for diff reasons)
• EXPLOIT & DERIVE SUFFICIENT RESOURCES, like food or shelter/camo
• DEFEND OR PROTECT themselves and their resources
• Maximise chances of REPRODUCTIVE SUCCESS (brood eggs to maximise chances)

Question 3

What is adaptation?

Answer 3

Structural, behavioural or physiological/functional change in which a species gains an advantage.

Includes development of special body parts (shape), behavioural traits (defending territories), or physiological processes (anoxia tolerance)

Question 4

Explain the 2 types of adaptation.

Answer 4

1. Ecological adaptation (PHENOTYPIC change; expression of organism)
   - occurs within the lifetime of an individual organism, results from repeated exposure to a naturally occurring challenge (acclimatisation) or a lab/field setting induced challenge (acclimation)
2. Evolutionary adaptation (GENOTYPIC change)
   - occurs within a population over longer timescales (several generations); product of natural selection
   - generally change irreversible either due to imposed natural (nat selection) or experimental conditions (artificial selection)

Question 5

What is the difference between acclimation and acclimatisation?

Answer 5

Acclimation = non-heritable reversible modification that occurs over lifestyle of individual. Generally, a phenotypic response to specific stressor.

Acclimatisation = process where individual adjusts to a challenge in order to maintain performance across range of changing conditions. Generally, a coordinated response to several stressors experienced simultaneously.

Question 6

What is the difference between adaptation and acclimatisation/acclimation?

Answer 6

adaptation = heritable modification that increases fitness of the organism

other 2 = non heritable

Question 7

Why do plastic responses have a cost associated with them, even though metabolic phenotypic plasticity may be the first ‘mechanism’ of response to preserve status quo when species are exposed to a challenge?

Answer 7

• They often require reallocation of energy AWAY from other processes like growth & reproduction

Question 8

Cohesive sediment vs non cohesive functions

Answer 8

Cohesive =

• mainly sessile organisms (muddy)
• fine sediment fractions
• low energy
• sediment profile stable and not prone to flushing
• high organic matter content
• not subject to strong hydrodynamic forcing

Non-cohesive =

• mainly mobile infauna and epifauna (sandy)
• large interstitial pore spaces
• fine sediment fraction removed
• sediment profile dynamic and regularly flushed
• low organic matter content

Question 9

Soft sediment environments are 3D habitats with a vertical dimension that offers new ecospace opportunities & a rel stable environment. What does this mean for environmental gradients and species distributions?

Answer 9

Environ. gradients aren’t as pronounced & sp distributions tend to overlap.

Question 10

Soft sediment environments tend to include a lot of …-sized … fauna and … levels of species …, … and total …

Answer 10

small
mobile
elevated
richness
abundance
biomass

Question 11

In 2D hard substrates, species tend to be … and are subject to a … environment with … buffering capacity.

Answer 11

sessile
variable
low

Question 12

What is the landscape like in non-cohesive sediments? Think wave action, sediment size, organic matter/oxygen content, erosion rate, sediment dwelling organism movement.

Answer 12

Sheltered from wave action, but tidal currents typically high
Dominated by fine sediments, e.g. muds & silts, esp sed grains < 63µm
Small pore/interstitial spaces, so infrequently flushed, high org matter & low oxygen content
Sediment cohesiveness decreases extent & rate of erosion of mudflats
Most of sediment dwelling org’s therefore sessile or discretely sessile burrow dwellers

Question 13

What is the landscape in non-cohesive sediments like? Think about energy levels, sediment type, flushing frequency, org matter/oxygen levels

Answer 13

High energy environments, typically wave swept
Finer fraction of sediment removed
Individual sediment grains typically coarse & surrounded by large pore/interstitial spaces
Sediments therefore regularly flushed, low org matter & high oxygen
Unstable environments, so many of the orgs are mobile burrowers, living intermittently at seafloor & within sediments

Question 14

What are some examples of cohesive and non cohesive sediment organisms?

Answer 14

Cohesive = mud snail, mud shrimp, ragworm

Non-cohesive = lugworm, tellinid bivalves

Question 15

What is the difference in time taken for physiological acclimation and/or adaptation vs behavioural adaptations?

Answer 15

Physiological acclimation/adaptation can take time to develop as individuals adjust to novel conditions.

Behavioural adaptations are expressed as prompt and flexible responses to environmental changes, occurring in particular place at particular time.

Question 16

What are local migrations & altered patterns of activity? What benefits and limitations does this have?

Answer 16

Adaptive responses to a change in circumstance that’s evolved over time & has benefit to the individual.

e.g. species may alter behaviour or relocate in order to track favourable environmental conditions and/or resource availability.

• allows sp to survive in dynamic conditions
• but physiological demands of changing behaviour can result in energetic tradeoffs that compromise overall fitness

Question 17

What are the microphytobenthos?
What is their migration speed?
What happens when the sediment surface is inundated with water?
Why do the microphytobenthos return to the surface at low tide?
What can this do to the sediment surface?

Answer 17

Comprises unicellular eukaryotic algae (mainly diatoms), cyanobacteria, foraminifera and euglenids (flagellates).
They’re motile and can migrate rapidly.
They migrate downwards into sediment to avoid being grazed/washed away.
At low tide, when it coincides with daylight, they go to the surface to photosynthesise.
It can transform the appearance of the sediment surface.

Question 18

What is the name of the internal rhythm, suggested by the cyclical behaviour of the microphytobenthos?

Answer 18

Endogenous rhythms

Question 19

What is the difference between the diatoms found in non-cohesive compared to cohesive sediments? (regarding a cycle)

Answer 19

These diatoms move in a cycle between the sediment and the water surface within the surf zone.

Question 20

How do some surf zone diatoms carry out endogenously controlled vertical migration between water surface during the day and sediment at night? (mucous coat)

Answer 20

Divide to lose their mucous coat and float to the surface waters.
Once carried to outer surf zone by currents, they secrete mucous coat that enables adherence to sediment grains and they sink.
Process repeated so they ride the incoming and outgoing tides to maintain their position.

Question 21

In high energy intertidal shores, is productivity high or low? What does this mean for the predictability of food supply washing onto the surf zone?
What does an individual’s ability to locate food items depend on?

Answer 21

Low.
Results in unpredictable supply of food washing onto surf zone, and can be rapidly relocated by wave action.
Ability to locate food items depends on how it SEARCHES the terrain and how quickly it can TRANSIT to SECURE the food resource.

Question 22

What is the difference in foraging ability between species inhabiting stable environments and species inhabiting physically dynamic habitats?
What is a way that several benthic inverts locate food parcels/prey and transit towards the source of scent?

Answer 22

• species inhabiting physically stable habitats are generally not accomplished foragers
• species inhabiting physically dynamic habitats exhibit range of ADAPTATIONS that allow them to EXPLOIT resources
• several invert’s use CHEMOTAXIS to locate food/prey, and use WAVE-GENERATED FLOW to rapidly transit towards source of scent, assisted by MORPHOLOGICAL ADAPTATIONS that act as a SAIL in the surf

Question 23

What is an example of a species that inhabits the surf and swash zones of south african beaches, which scent decaying carrion? What do they use to surf towards the food parcel?
Why do they migrate with the tides to remain in the swash & saturation zones?
What types of food do they prefer eating?
What other adaptations do they have? (food)

Answer 23

Plough snail Bullia spp
They scent decaying carrion and use enlarged foot morphology to use wave-generated flow to surf towards the food parcel
They risk desiccation if they strand above the waterline
They opt for higher calorific value foods
Survive long periods without food by remaining buried and inactive. They can consume and derive energy from food rapidly and absorb dissolved org matter through their foot.

Question 24

How do bivalve species from dissipative (high energy) beaches vary in shape compared to those from reflective (low energy) beaches?

Answer 24

High energy/dissipative = blade shaped (burrow fastest)

Low energy/reflective = uniform and wedge-shaped

Question 25

How does surfing and rapid burrowing behaviour serve as an adaptation to save energy?

Answer 25

• by avoiding desiccation and exposure to air

- as metabolic rates (i.e. respiration, filtration and excretion) are increased in higher temps

Question 26

How do the donax serra clams vary in morphological features in the cold benguela current compared with the warm province agulhas current? (shape)

Answer 26

Cold = more rounder, flatter & less wedge-shaped

Question 27

How do mole crabs of the genus Emerita thrive in the unstable sediments within the highly dynamic swash zone? (burying, relocating, feeding, antennae direction of respiratory current of water)

Answer 27

• bury extremely rapidly
• individuals relocate as the sand shifts
• rapidly filter feed when submerged
• antennae adapted for filtering food from water & transporting it to the mouth
• direction of respiratory current of water changed from that of other decapods and flows from anterior to posterior

Question 28

Many physical & ecological processes exhibit variability, on a daily, seasonal or yearly time scale that can mean individuals need to adjust their behaviour & timing of activity to coincide with phases that benefit them most.
What are some examples of forcing that can impose cyclic behaviour on burrowing species?

Answer 28

Tides
Diurnal light changes
Temperature changes
Lunar & seasonal weather patterns

Question 29

Many physical factors, biotic interactions, and internal cues control cyclic behaviour.
Many benthic species, incl those inhabiting shelf & deep sea, exhibit cyclic behaviour.
What are some examples of this behaviour, including species?

Answer 29

Nocturnal circadian rhythm; common amphipod talitrus saltator has endogenous rhythm of 24.5hrs. Species uses light for navigation, orientating to silhouettes of sand dunes to maintain shore position. Foraging at night avoids solar radiation exposure, desiccation and visual predators like birds.

Diurnal circadian rhythm; gastropod Philine aperta, foraging activity seems to coincide with day time illumination levels.

Tidal rhythm; ophiuroid Amphiura filiformis, burrowing brittlestar, cyclic behaviour pattern related to tidal phase; alternates between deposit feeding at depth and filter feeding in water column by elevating arms into passing currents.

Lunar and semi-lunar cycle; mud shrimp Corophium volutator exhibits endogenous circa tidal rhythm of swimming activity that varies seasonally & over spring to neap tide cycle. Semi-lunar reproductive cycle in summer but rhythmicity becomes obscure in early spring and summer & shifts to lunar cycle in cooler season, matching changes in egg development duration which is prolonged by lower temps.

Tidal, diel and semi lunar changes in faunal assemblage; different tidal migration modes between species; shift in community composition occurred between spring and neap tides, suggesting lunar influence.

Question 30

Phys & chemical environ conditions place physiological constraints on where & how individuals can occupy space
What are some examples of how benthic invertebrates construct various biogenic features to modify, or otherwise exploit, their immediate environment, allowing ecospace to be modified?

Answer 30

• burrow architecture; U shaped burrows in cohesive sediments vs I or J shaped in non-cohesive, due to small particle size of surrounding sediment in muds preventing burrow water penetration of the burrow wall.
• burrow morphology; burrow diameter, orientation, inclination, branching & volume offer potential source of phenotypic variation. e.g. burrow shape may relate to body size & ecological setting (like vegetation type, environ conditions or disturbance)
• mucous secretions and tube lining; many sp construct mucous lined burrows or tubes made from membranous secretions or calcareous materials, or by cementing sand grains/selected fragments together. Serve to protect the occupant, act as lair for prey, facilitate attachment to substrata, / provide stable & regulated environ in sandy/muddy substrates. Tubes are sites of higher microbial activity that can elevate pH within burrow lumen and deplete sulphur in adjacent sediment, promoting favourable biogeochem conditions.
• biogenic features and hydrodynamic; dense aggregations of various tube worms stabilise sediments & generate oases for benthic communities that are different & often more diverse/abundant than those of surroundings. Projecting tubes within a stand produce vortex patterns which may alter resuspension of sediment particles & alter character of seafloor.
• pits and food; mounds & pits generated by reworking activities alter topography of sediment. Depressions act as traps for detrital material.
• environmental control; behavioural & physiological adaptations to regulate internal environment of burrow system. Allows exploitation of otherwise uninhabitable areas. e.g. low oxygen levels adaptations, exposed to hypoxia, hypercapnia, and sulphide at depth e.g. pleopod beating increases in thalassinidean shrimps at low oxygen partial pressures, switch from aerobic to anaerobic

Question 31

Species must also respond to biological factors & changes in community dynamics, as well as the phys environment.
What are the behavioural alterations in response to these stimuli, which can lead to phenotypic expression?

Answer 31

behavioural plasticity
gregarious behaviour
competition for space and/or food
character displacement
maximising opportunity

Question 32

Explain behavioural plasticity as a behavioural alteration in response to biological factor stimuli/change in community dynamic stimuli. (what is it, innate and learned, feeding styles, thermoregulatory behaviour, competitive interaction/predation)

Answer 32

• org’s vary behaviour in response to environ changes; involves large spectrum of behavioural mechanisms that reflect many physiological patterns
• 2 classes of behavioural plasticity: innate and learned
• innate = occur when modification of behaviour is a result of the evolution at the population scale over multiple generations; predetermined phenotypic trait produced in response to predetermined environ stimulus (e.g. predator recognition)
• learned = occur when modification of behaviour is refined through experience within lifetime of individual (e.g. escape responses, prey capture)
• deposit/suspension feeding alternation, others have multiple feeding strategies as conditions change, foraging in particular areas
• many sp show thermoregulatory behaviour, altering level of burrow ventilation or seasonal relocation to exploit food resources and/or reproduce at appropriate temps
• deposit to filter feeding in resp to changes in tidal associated flow patterns which can alter ecosystem functioning at assemblage level
• change in behaviour to reduce risk of competitive interaction or predation; buries deep and switch to deposit feeding to avoid predation

Question 33

Explain gregarious behaviour as a behavioural alteration in response to biological factor stimuli/change in community dynamic stimuli. (aggregation, reasons for aggregation, disadvantages)

Answer 33

• aggregation - ranges from congregating at unique time/location e.g. for reproduction, or where resources are optimal or preferred across multiple locations
• larvae of many benthic inverts known to be gregarious, but doesn’t automatically mean this occurs in adult stages
• species susceptible to desiccation & dislodgement often aggregate for protection or sharing of food e.g. anemones
• others may gather to maximise resource capture or alter microhabitats e.g. sponges
• or increases chance of survival e.g. urchins and brittlestars
• behaviour of individuals within an aggregation can be more variable & v different to behaviour of individuals in isolation
• costs like reduced growth rates and smaller body size related to intra-specific competitive interactions

Question 34

Explain competition for space/food as a behavioural alteration in response to biological factor stimuli/change in community dynamic stimuli. (competitive displacement, vertical separation of functionally similar species, limitation due to coexistence)

Answer 34

• competitive displacement = removal of a formerly established species from its position/standing as a result of direct/indirect competitive interactions w another species
• tends to occur betw closely related/functionally similar species - but completely exclusion is rare
• vertical separation of what were at face value functionally similar species within sediment profile
• competitive hierarchy over space/resources could determine vert position of individual species
• effects on growth of species due to coexistence

Question 35

Explain character displacement as a behavioural alteration in response to biological factor stimuli/change in community dynamic stimuli.

Answer 35

• character displacement = where differences among similar species whose distributions overlap geographically are accentuated in regions where species co-occur, but are minimised/lost where the sp distributions do not overlap
• ^ populations diverge in phenotype and resource use, thus reducing resource competition & permitting coexistence
• e.g. Hydrobia ulvae and H ventrosa

Question 36

Explain maximising opportunity as a behavioural alteration in response to biological factor stimuli/change in community dynamic stimuli.

Answer 36

• malanid polychaete praxillura maculata constructs multi-spoked membranaceus tube from which it suspends mucous web for increasing particle capture
• some mobile scavengers & decapods exhibit decorating and carrying behaviour, placing and arranging a variety of species on their carapace - reduce risk of predation/maximise prey capture opportunity