Soft Sediment Adaptations Flashcards

This set of 30 flashcards covers the lecture content on adaptations in soft sediment marine environments, including physiological, morphological, and behavioral traits across sandy and muddy shores.

What sediment types are the most representative habitats of the benthos

Cohesive and non-cohesive

What four reasons may species adjust to their environment over short and longer timescales

To respond to changes in ecological or environmental context

To exploit and derive sufficient resources, such as food, shelter/camouflage

To defend or protect themselves and their resources

To maximise the chances of reproductive success

What is adaptation

The structural, behavioural or physiological/functional change in which a species gains an advantage, including the development pf special body parts, behavioural traits or physiological processes

This change is not reversible

What are the two types of adaptation

Ecological adaptation and evolutionary adaptation

How is ecological adaptation distinguished from evolutionary adaptation?

Ecological adaptation involves phenotypic change within an individual's lifetime; results from repeated exposure to a naturally occurring challenge (acclimatisation) or a lab/field setting induced challenge (acclimation).

Evolutionary adaptation involves genotypic change over several generations within a population and is the product of natural selection or artificial selection.

How does the sabellid polychaete Amphiglena mediterranea exhibit ecological adaptation to naturally occurring $CO_2$ vents?

This species lives in carbon dioxide vents, which lower the pH of the water, and exhibit high rates of metabolism to compensate for $pCO_2$-induced hypoxaemia

These rates return to normal once the organism is removed from the vents, indicating it is acclimated rather than adapted.

What characterizes the physiological state of Playnereis dumerilii living in $CO_2$ vents?

It is genotypically adapted to elevated $pCO_2$

Its metabolic rate remains high even after being removed from the vents.

What is the primary difference between acclimation and acclimatisation?

Acclimation is the non-heritable reversible modification that occurs over the lifetime of an individual. Generally, a phenotypic response to a specific stressor

Acclimatisation is the process by which as 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 a significant energetic cost associated with metabolic phenotypic plasticity?

It requires the reallocation of energy away from other critical processes such as growth and reproduction.

What are the physical characteristics of grains in non-cohesive sediments?

They are typically coarse grains with large pore/interstitial spaces that are regularly flushed.

What are the physical characteristics of grains in cohesive sediments?

They are usually fine-grained, compact, and have smaller pore spaces that retain water.

Are non-cohesive sediments high or low energy environments

High energy environments

Are cohesive sediments high or low energy environments

Low energy environments (sheltered from wave influence but still tidally influenced)

Are non-cohesive sediments stable or unstable

Unstable

Are cohesive sediments stable or unstable

Stable

What kind of organisms are in non-cohesive sediments and what is their motility

Mobile infauna and epifauna

What kind of organisms are in cohesive sediments and what is their motility

Sessile and discretely sessile infauna

Do non-cohesive sediments have a low or high oxygen content

High oxygen content

Do cohesive sediments have a low or high oxygen content

Low oxygen content

Do cohesive sediments have a low or high organic matter content

High

Do non-cohesive sediments have a low or high organic matter content

Low organic ma

What grain size threshold defines the fine sediments in cohesive muddy shores?

$< 63\,\mu\text{m}$.

Describe the burrowing technique in cohesive sediments

Burrow ventilation causes water to flow through the burrow

Diffusion across burrow walls

Diffuse vertical transport through sediment interstitial space

Describe the burrowing technique in cohesive sediments

Burrow ventilation causes water to flow through the burrow

Diffusion across burrow walls

Advective vertical transport through sediment interstitial spaces

Why is vertical zonation typical of rocky shores not clearly visible in soft sediment systems?

Because soft sediments are 3-dimensional habitats where species distributions overlap and many animals live beneath the surface or move cyclically.

What do the microphytobenthos inhabit

The sediment-water interface and uppermost few millimetres of the sediment profile in the photic zone

What organisms comprise the microphytobenthos community?

Unicellular eukaryotic algae, cyanobacteria, foraminifera, and euglenids.

Are the microphytobenthos motile

Yes, they are motile

How do microphytobenthos respond when the sediment surface is inundated with water?

They migrate downwards into the sediment (as little as $4\,mm$) to avoid being washed away.

How does the primary productivity of microphytobenthos compare to terrestrial plants?

They convert solar energy into biomass at a rate around $10$ times greater than terrestrial plants.

How much $CO_2$ can be fixed per $1\,kg$ of microalgae biomass?

Up to $1.83\,kg$.

How do diatoms founds in found in sheltered beaches move

Move in a cycle between the sediment and the water surface within the surf zone

What migration do some surf-zone diatoms undertake

An 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 mucus coated individual diatoms move in the surface-zone

Individuals divide to loose 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 enable adherence to sediment grains and they sink.

The process is repeated so the diatoms ride the incoming and outgoing tides to maintain their position

Why is migration important for the microphytobenthos

It provides then protection from grazers and maximises the period over which photosynthesis can take place

This allows them to store sufficient energy in order to survive the extended period in the dark and to grow

What morphological adaptation helps the plough snail Bullia transit towards food scents?

An enlarged foot that acts as an underwater sail in the surf.

Why do plough snails migrate with the tides

They risk desiccation if they are stranded above the waterline

How long can a plough snail Bullia survive without food while remaining buried?

$120\,\text{days}$.

How do clams from the cold province (Benguela current) and warm province (Agulhas current) differ

Clams from the cold province are rounder, flatter and less wedge-shaped than clams from the warm province

How does the shell shape of bivalves from dissipative (high energy) beaches compare to those from reflective (low energy) beaches?

Dissipative species range from blade-shaped to almost spherical, whereas reflective species tend to be wedge-shaped.

Where can mole crabs be found

They occupy unstable sediments within the swash zone

What unique respiratory adaptation is found in mole crabs of the genus Emerita?

The respiratory current of water flows from anterior to posterior, which is different from other decapods.

Their first 4 pairs of walking legs and the uropods are modified for burrowing

The antennae are are adapted for filtering food

Shorter reproductive cycle and recruitment period, and lower abundance of recruits in reflective beaches to dissipative beaches

What is the endogenous rhythm period of the European beach amphipod Talitrus saltator?

$24.5\,\text{hrs}$.

When is the activity of Talitrus saltor limited to

The period during which it would be dark in their natural environment

Where can Philine aperta be found

It occupies the surficial sediment layer of many offshore subtidal molecules where they primarily predate bivalve molluscs

How does Philine aperta bury into sediments

By using hydrostatic adjustments

When does the brittle star Amphiura filiformis exhibit maximal arm emergence for particle capture?

During mid-tides when tidal currents are sufficient to support filter feeding.

What rhythm of swimming does the mud shrimp, Corophium volutator exhibit

An endogenous circa-tidal rhythm of swimming activity which varies seasonally, and also over the spring to neap tide cycle

This semi-lunar variation in phase is not significant during the winter when the rhythm is generally less distinct

What is the reproductive cycle of Corophium volutator

Shows a semi-lunar reproductive cycle in the summer, but the rhythmicity becomes obscure in early spring and autumn, and shifts to a lunar cycle in the cooler season

This change matches changes in the duration of egg development, which is prolonged by lower temperature and reduced food availability.

At what temperature threshold does the reproductive rhythm of Japanese Corophium volutator shift from semi-lunar to lunar?

Below $17.5^\circ\text{C}$.

What is thixotropic sand?

Sand that liquefies when saturated with water, as occurs in the surf zone during an incoming flood tide.

Why are burrows in cohesive sediments typically U-shaped or multi-opening?

Because the small particle size prevents water from penetrating the burrow wall, meaning volume must be actively removed via the burrow lumen to the surface.

What is the common burrow architecture in non-cohesive sandy sediments?

I- or J- shaped burrows, because ventilation flows can penetrate the surrounding porous sediment matrix.

Why do some burrowers construct mucus lined burrows or rubes made either from membranous secretions or calcareous materials, or by cementing sand-grains or selected fragments together

They tubes serve to protect the occupant, act as a lair for catching passing prey, facilitate attachment to various substrata, and/or provide a stable and regulated environment in sandy or muddy substrates

What are the four cyclical behaviours

Diurnal, lunar, tidal and seasonal

When do innate behavioural responses occur

When the modification of behaviour is the result of evolution at the population scale over multiple generations; that is, a predetermined phenotypic trait is produced in response to a predetermined environmental stimulus

When do learning behaviours responses occur

When the modification of behaviour is refined through experience within the lifetime of an individual

What are the three species with flexible feeding strategies

Pseudopolydora kempi (deposit/suspension switch)

Hediste diversicolor (omnivory/scavenging)

Streblospio benedicti (resource tracking)

How does Calianassa subterranea handle the toxicity of rising sulphide levels?

It oxidises toxic sulphide to less toxic thiosulphate.

What is competitive displacement

The removal of a formerly established species from its position or standing as a result of direct or indirect competitive interactions with another species

Which bivalve hosts symbiotic bacteria in its gills to detoxify sulphide?

Solemya reidi.

In the Mugu Lagoon study, which haustoriid amphipod was the competitive dominant?

Acanthohaustorius.

Define character displacement in the context of soft sediment systems.

A phenomenon where differences among similar species are accentuated in regions where they co-occur to reduce resource competition.

How do the body sizes of Hydrobia ulvae and Hydrobia ventrosa change when they co-occur?

H. ulvae becomes larger ($> 3.5\,mm$) and H. ventrosa becomes smaller ($< 3\,mm$) to avoid competing for the same food resource.

How does Macoma balthica alter its behavior in the presence of the predator Crangon crangon?

It buries deeper in the sediment and switches from surficial feeding to deposit feeding.

What agent in the blood of the echiuran worm Urechis caupo is used for sulfide-detoxification?

Haematin.

What specialized defenses does the scale worm Harmothoe imbricata use against predators?

It uses bright green luminescence from its elytra and autotomization (voluntary loss of body parts).