11 Soft-bottom Habitats Flashcards
how much of the earth surface is covered by seawater?
70%
on the seafloor you will mostly find ___ ?
- soft-sediments
- not just sand and mud –> hugely diverse habitats
- especially estuaries-continental shelves
- diverse in species, habitats, physical and chemical conditions
soft-bottom environments harbor many different biogenic ecosystems, like __ ?
ecologies between soft and rocky shores are very different. How are soft shores?
- 3D
- potentially lower competition
- more buffered from variations in water column conditions
- availability of food is good
- environment very unstable –> need for flexible behaviors (movements, feeding habits, patterns of recruitment)
are there many habitat specific- rare species in soft shore habitats?
yes, there is a high number of them
what do marine sediments differ in ?
- size
- origin
- composition
how do marine sediments differ in size?
- Size classification divides sediment by grain size into boulder,cobble, pebble, sand, silt and clay
– Mud is a mixture of silt and clay
how do marine sediments differ in origin?
Origin classification divides sediment into five categories
1) terrigenous sediments
2) biogenic sediments (biogenic ooze, any pelagic sediment that contains more than 30 percent skeletal material)
3) authigenic sediments (chemical and biochemical precipitates that has been formed in place – e.g. hydrothermal activities - on the sea floor and include metalrich sediments and ferromanganese nodules)
4) volcanogenic sediments and
5) cosmogenic sediments
how do marine sediments differ in composition?
- organic content
- inorganic content
- mineralogy
terrigenous sediments
strongly reflect their source and are transported to the sea by wind, rivers and glaciers
authigenic sediment
chemical and biochemical precipitates that form on the sea floor and include e.g. ferromanganese nodules
particle size
- the size range is enormous (<1 micrometer up to > 20cm)
what is the Wentworth Scale?
- scale of particle size in sediments
- particle size expressed as phi (Ø)
- (Ø) is the negative log to the base of 2 diameters in mm
- mud = all particles < 63 micrometers, they have cohesive properties
table of sediment sizes
from largest to smallest size:
- boulder
- cobble
- pebbles
- sand
- silt
- clay
- measurable in phi: sizes from Ø = - 8 (largest, boulder) to Ø = 10 (smallest, clay)
- also measurable in mm - nm or inches
particle sorting - distribution of grain size of sediments
- there is a classification of sediment by degree of sorting
- considered well-sorted if most particles appear in the same size classification (low variance)
- poorly sorted sediments comprised of multiple sizes (large variance)
relationship between high/low energy environments and sediment size
- High energy environments characteristically yield sediments larger in size
- Small particles (silts, clays) indicate low energy environment
- deeper usually means muddier but most of the shelf is sandy
Do different sediment types provide habitat to diverse species of organisms?
yes :)
parameters of sediments
(what is measureable?)
what is the Hjulstrom’s Diagram?
- illustrate the relationship between water velocity, energy for erosion, transportation and deposition, and sediment particle size
- the grain size indicates the condition under which sediment is deposited AND resuspended.
- the average grain size reflects the energy of the depositional environment
The Hjulström’s diagram typically includes zones that represent different sedimentary processes based on the combination of water velocity and sediment particle size. These zones are:
1) Deposition Zone: At low water velocities, fine particles settle out of the water column due to gravity, leading to deposition.
2) Erosion Zone: At higher water velocities, the energy of the flowing water is sufficient to transport and erode particles. In this zone, coarser particles can be entrained and transported.
3) Transport Zone: This is the range of water velocities where sediment transport is most effective. Particles of varying sizes can be transported and sorted by the flowing water.
- The diagram helps to understand how different sediment sizes respond to varying water velocities.
- It’s a useful tool for predicting whether sediment particles will be eroded, transported, or deposited under different flow conditions.
- The relationship depicted in the diagram is influenced by factors such as particle size, water velocity, and the nature of the fluid (e.g., water or air).
mobile benthos
It is comprised of all organisms that live on the surface of the sediment (epifauna) and within the sediment (infauna).
what is interstitial fauna?
Animals that inhabit the spaces between individual sand grains. The term is often used synonymously with meiofauna, mesofauna, and microfauna
what are important ecosystem engineers in soft-sediments?
burrowing organisms
what do organisms influence in terms of sediments?
organismshave an influence of the composition and mobility of sediments
what are the biogeochemical gradients in sediments modified by?
- they are modified by plants and animals
what does a life in sediments require?
organisms have a need for specific adaptations to live in the sediments
what is bioturbation?
- sediment destabilizing
- by mixing and disturbing sediments and soils
key physical and chemical parameters in soft bottoms?
surficial sediment distribution
- is variable
there is different functional groups that dominate along what gradients?
- hydrodynamic gradient
- grain-size gradients
low energy, fine sediment: deposit feeders
high energy, coarse sediment: suspension feeders
relationship of particle size and the distribution of the biota
size of organisms equals size of grains/particles
vertical zonation on sandy shores
- absence of well-defined zonation
- distribution along a land-sea gradient
1) supralittoral zone (crabs+arthropods)
2) intertidal zone (shellfish+polychaets)
3) subtidal zone(shellfish,echinoderms, fish)
distribution of species varies along sediment vertical profile
(in sediment)
the food supply to the benthos is controlled how?
- oceanographic controls
- Primary production on the continental shelf fuels about 90% of the world’s fisheries
Variations in the benthic community and sediment structure along what gradient?
- gradient of organic enrichment
- another type of vertical zonation related to the amount of oxygen availability –> more anoxic tolerant but less competitive species will be distributed deeper in the substratum, while less tolerant but more competitive species will be found in the firsts layers
- diagram of changes in fauna and sediment structure (by Pearson and Rosenberg, 1978)
what did Pearson & Rosenberg (1978) and Rhoads et al. (1978) generate?
- general successional models that predict opportunistic responses in soft-sediment communities
- they were developed for muddy and subtotal habitats
there is a lack of generality - especially in experimental studies
- Habitat-, species- and life stage- dependent colonization
- Variable presence of ‘climax’ communities
- Mixed community types
- Variable opportunistic responses
name human impacts in sedimentary environments
- aquaculture
- exploitation of non-living resources and engineering
- elevated rates of sediment loading
- urbanizing the coasts
- invasive species
- fishing + trawling
- eutrophication
- …
eutrophication (as human impact on sedimentary environments)
soft-bottoms are very valuable ecosystems
aquaculture (as human impact on sedimentary environments)
exploitation of non-living resources and engineering (as human impact on sedimentary environments)
- sand mining
- oil and gas
- minerals
- cable-laying
- shoreline modification
elevated rates of sediment loading
our coasts are being urbanized (as human impact on sedimentary environments)
-e.g. solar panels on water or wind turbines
anoxia in sedimentary environmnets
- Oxygen minimum zones (OMZs) are regions of the ocean with hypoxic waters, where oxygen concentrations typically are < 0.5 ml L-1 (or about < 20mM).
- Large areas of the bathyal seafloor within oxygen minimum zones and some fjords and basins experience permanent severe hypoxia (<0.5 ml O2 per l).
what does homogenization lead to?
- loss of ecological function and natural heritage values (in marine ecosystems)
- if losses reduce resilience –> can lead to sudden and dramatic change of the system
what are the factors driving deep sea systems?
facts about deep sea biota
