Marine Ecology Flashcards
Describe and explain the seasonal cycle of biological activity (e.g., phytoplankton, zooplankton and fish biomass and production) in the pelagic.
Other factors influence phytoplankton growth rates, including water temperature and salinity, water depth, wind, and what kinds of predators are grazing on them. Phytoplankton can grow explosively over a few days or weeks. Basically, the seasonal cycle is driven by sea-surface temperature and the onset of the thermocline leading to phytoplankton blooms during spring, the prevalence of thermal stratification leading to exhaustion of nutrients and subsequent demise of phytoplankton during summer-autumn, and remixing and regeneration of nutrients during winter.
Plankton predominantly comprises short-lived organisms. As a rule, these reproduce so rapidly that several generations may be produced within a single year. The development of planktonic organisms generally follows a regular annual cycle that begins with a spring bloom of the phytoplankton.
Fish biomass:
LOOK AT SLIDES
Explain how environmental factors and the species diversity and biomass of benthic communities vary from the continental shelf to the deep sea.
There are a lot of factors that can affect benthic biodiversity along a depth gradient like water temperature, light availability, oxygen (and other elements) concentration and pressure.
Interactions between pelagic and benthic environments are related to a variety of abiotic and biotic processes that have a major influence on the structure and dynamics of marine ecosystems. Transport of particulate and dissolved materials, gases, as well as living organisms, and also sedimentation and erosion are subsumed under these processes that induce a shifting of materials between benthic and pelagic material pools and vice versa. Imbalances in these transactions result in a change of biotic structures and have far-reaching consequences for the development of the communities. Exchange processes are either directed from water to the bottom sediment (termed as pelagic–benthic) or reversed (termed as benthic–pelagic), and impact on abiotic material pools as well as on the biota, such as producers and consumers, or can be related to the exchange between abiotic and biotic material components.
Describe and explain intertidal zonation on rocky shores
Intertidal zonation refers to the frequently observed pattern by which species replace one another along a gradient from the low to high tide lines along many of the world’s coastlines.
variation in the distribution of organisms caused by differences in both biotic and abiotic conditions along an environmental gradient. Organisms living on the rocky shore have different adaptations to these factors and therefore will be able to survive at different heights on the shore accordingly.
The intertidal zone or littoral zone is the shoreward fringe of the seabed between the highest and lowest limit of the tides. The upper limit is often controlled by physiological limits on species tolerance of temperature and drying. The lower limit is often determined by the presence of predators or competing species.
The rocky intertidal ecosystem can be divided into four zones: the splash zone, high intertidal, middle intertidal, and low intertidal
What is the Coriolis effect (force)?
Apparent deflection of a moving object when viewed from a rotating frame of reference.
Freely moving objects on the surface of the Earth experience the ‘Coriolis force’.
On a non-rotating planet, ocean currents (and winds) would flow directly from areas of high pressure to low pressure.
Because Earth rotates, currents (and winds) flow to the right of this direction north of the equator, and to the left of this direction south of the equator.
What is Ekman Transport?
Friction between wind and water surface causes water to move in direction of wind.
The Coriolis effect deflects this current.
The surface layer drags the layer beneath, which is also deflected.
The net movement of the ocean’s surface layer is perpendicular to the right of the wind in the Northern Hemisphere and to the left in the Southern Hemisphere.
Deep Ocean Circulation and Thermohaline Circulation
Thermohaline circulation is due to differences in the density that arise from variations of temperature and salinity.
thermo = heat
haline = salt (halide ions)
Solar radiation warms waters in the tropics, causing them to expand (become less dense) and float.
The ocean loses heat to the atmosphere at high latitudes (air colder than water), causing the surface waters to cool and contract (become denser) and sink.
What affects the density of sea water?
Density = mass/volume
Units kg m-3
Density increases as temperature decreases
Density increases as salinity increases
Density increases during ice formation because salt is excluded from the ice
Density decreases following rain due to dilution of salt
Mechanisms of Deep Water Formation
The mechanisms of deep-water formation are different in North & South Atlantic.
In the North Atlantic, high salinity water (brought north by the Gulf Stream) is cooled in winter leading to deep convective mixing.
On the Antarctic continental shelf, ice formation increases salinity and upon further cooling, the dense water flows off the shelf and down the continental slope.
Thermohaline Conveyor Belt
North Atlantic Deep Water flows south along the western side of the N. Atlantic.
Antarctic Bottom Water is the densest water and flows north along the western side of the S Atlantic.
These two deep currents meet in the S. Atlantic and flow eastward into the Indian and S. Pacific Oceans
The deep water flows from the Atlantic to the Pacific, are balanced by a return flow of warm surface waters from the Pacific to the Indian and back to the Atlantic Ocean.
The combination of these slow deep and surface water flows is referred to as a conveyor belt.
The thermohaline circulation is sluggish compared with the wind-driven circulation.
The entire circulation and replacement of the deep waters takes about 1000 years
750 years for the Atlantic
1500 years for the Pacific
What is an ion?
an ion is a charged atom or charged molecule
ions form by adding or removing one or more electrons from an atom or molecule
a cation is a positively charged ion
e.g., sodium ion: Na+
an anion is a negatively charged ion
e.g., chloride: Cl-
sulfate: SO42-
ionic bonds hold crystals together
e.g., sodium chloride (= table salt): NaCl
Why is water sometimes described as a universal solvent?
Water (H2O) can dissolve more things than any other natural substance.
It is a polar molecule, that can form hydrogen bonds.
Water is good at dissolving salts
which consist of positively (+) and negatively (-) charged ions
NaCl → Na+ + Cl-
What are the sources of the ions in seawater?
Runoff from the continents (weathering of rocks) Na+ , K+, Ca2+ , Mg2+ Volcanic activity (hydrothermal vents) HS- , Cl-
How does the rule of constant proportions make measuring salinity easier?
The rule of constant proportions states that the relative amounts of the various ions in seawater are always the same (e.g., independent of salinity)
e.g.
Chloride = 55.03% of salinity everywhere in the sea
Sodium = 30.59% of salinity everywhere in the sea
the rule holds for other major ions
This allows chloride, which is easy to measure, to be used to calculate salinity
Chlorinity = mass of chloride in a kg of seawater
Conductivity is now commonly used to measure salinity in practical salinity units (psu)
1 psu = 1 ‰ or 1 ppt
Limiting Nutrients
The two main limiting nutrient elements for biological production in sea are nitrogen (N) and phosphorus (P).
These are present as dissolved inorganic ions
phosphate: PO43-
nitrate : NO3-
Concentrations of these ions are often very low in surface waters.
Productivity of the oceans often depends on the regeneration (recycling) of inorganic N and P from organic matter.
Vertical profiles of dissolved O2
Feature: oxygen minimum zone
located in thermocline
high respiration rate
limited exchange of water
What are Biogeochemical cycles?
Pathways by which a chemical element moves through different compartments (called reservoirs).
Examples Carbon cycle Nitrogen cycle Sulphur cycle Phosphorus cycle
The Carbon cycle
CO2 moves between ocean and atmosphere due to physical-chemical processes (Solubility pump).
C is exchanged between the ocean and the biota via:
Photosynthesis removes CO2 from the atmosphere and ocean.
CO2 + H2O + light → CH2O + O2
Respiration releases CO2 to the atmosphere and ocean:
CH2O + O2 → CO2 + H2O
Carbon enters the foodweb via grazing
Carbon is returned to the ocean as CO2 via respiration
Some primary produces will sink when they die, sequestering (storing) carbon in sediments
Dead stuff becomes detritus/POM (Particulate organic matter) which can be:
Decomposed by bacteria, producing CO2, POM, and DOM (Dissolved organic matter)
Feed on by animals, returning carbon to the foodweb
detritus/POM that is not decomposed sinks, sequestering carbon in sediments
The biological pump
Phytoplankton and macro-algae (seaweed) fix carbon
Incorporating C into the food chain (grazing) - or releasing it as DOC/POC
Feacal pellets, marine snow, and dead marine organisms sink to the deeper layers
Where they decay consuming dissolved oxygen and giving off CO2.
Upwelling returns this CO2 to the epipelagic.
The biological pump requires the input of nutrients (N, P) to sustain plankton blooms.
Microbes and the carbon cycle
Play a critical role in all nutrient cycles
Fixing carbon
Link to the food chain
Also a source of CO2
Microbial action can make carbon inaccessible recalcitrant – RDOM
This sinks and can be stored for 1000s of years
Microbes decompose POM and DOM, producing dissolved CO2
Microbes degrade the most assessable carbon first.
Carbon that is harder to degrade, called recalcitrant carbon (RDOM), sinks before is can be degraded and is stored in sediments.
The balance between how much carbon sinks and how much is releases is critical in global carbon budgets.
The Nitrogen cycle
Nitrogen is fixed by bacteria and cyanobacteria
Key players: Trichodesmium spp.
Atelocyanobacterium spp.
(cyanobacteria)
Bacteria and archaea cycle nitrogen between ammonia, nitrites, and nitrates via nitrification (aerobic)
Fixed nitrogen and nitrates are taken into the biota and cycle through the food web
This nitrogen can be excreted as DON, or sink when taxa die (POM).
Bacteria and archaea recycle POM and DON in decomposition (ammonification)
Nitrogen is returned to the atmosphere via bacterial Denitrification (anaerobic)
The phosphorus cycle
Not found as a gas (Contrast to Carbon and Nitrogen)
Normally as part of a phosphate ion: PO43-
Found as salts in ocean sediments or in rocks.
Uplift brings ocean sediments to land.
Phosphate becomes available by chemical weathering.
Input to oceans is via rivers.
Enters the foodweb through uptake by plants, algae and bacteria.
Dissolved phosphate is precipitated and sinks into sediments
More on Limiting nutrients
Nutrients, particularly N and P, limit the fertility of many undisturbed ecosystems.
P is typically the main limiting nutrient in freshwaters, followed by N.
N is usually most limiting in marine systems, followed by P.
Although CO2 may limit photosynthesis in terrestrial plants, inorganic C is rarely limiting in aquatic systems.
The micronutrient Fe, has recently been found to be the main limiting nutrient over about 1/3 of the ocean surface – Iron fertilisation hypothesis.
Jawless Fish (Agnatha)
cylindrical, elongated body cartilaginous skull lack vertebrae lack jaws lack scales feed by suction using a round muscular mouth and sharp teeth
Hagfishes
Marine Jawless elongate fish Lack fins No vertebra (sort of) Burrow in muddy bottoms at moderate depths in cold waters Feed mainly on dead or dying fish Produce slime!
Lampreys
Mainly freshwater or costal
- Some migrate to the ocean to mature and bread
in freshwater
Have unpaired fins
Redemptory vertebra
Most species are not parasitic!
- sea and river lamprey attach to fish, rasp a hole
into the victim, and feed on fluids and tissues
Cartilaginous Fishes
Class Chondrichthyes
Cartilage skeleton - lighter and more
flexible than bone
Placoid scales - tough sandpaper like skin
Moveable hinged jaws
Ventral mouth with well developed teeth
Maintain buoyancy through a oil-rich
liver
Can detect weak electric field to locate
prey - ampullae of Lorenzini
Sharks
Fusiform shape (tapered at both ends) - aids
movement through water
Strong caudal (tail) fin for propulsion
Two dorsal fins and paired pectoral fins
5-7 gill slits on each side of body behind the
head
Most are carnivorous
Largest sharks are filter feeders (whale
shark - Rhincodon typus)
Ampullae of Lorenzin
Sensing organ that uses electroreceptors to
detect the weak electrical currents emitted by
living organisms.
• For example fish hiding under sand.
• Consists of pores connected to gel filled
tubes.
• Also found in other chondrichthyes (e.g. rays)
Bony Fishes
Class Osteichtyes
Dominant vertebrates in the sea More taxonomically diverse than rays & sharks Wide range of shape, size, color, swimming ability, feeding habits, reproduction and behavior
Skeleton made of bone
Anterior, midline mouth
Swim bladder to provide buoyancy
Scales made of bone, covered by skin and mucus
Gills protected by a flap of bony plates
(operculum)
Swim bladder
Swim bladder (5% of animal’s volume). Two gas filled sacs – fish achieve neutral buoyancy by changing the volume/pressure of the bladder.
Only in bony fish - so what about sharks?
Altered salt content of cellular fluids (low salt) relative
to seawater.
High lipid content
- liver may occupy up to 25% of volume of a shark
Also “flying” using fins for lift
Lateral Line System
Gelatin-filled tunnel
- runs beneath skin along each side from tail to head
- contains clusters of nerve cells for detecting vibration
- detects reflections of bow waves off nearby objects, including other fishes
Allows rapid movement near solid surfaces and tight schooling
Body form in relation to feeding and habitat in bony fishes
Rover predators (tuna, marlin, blue shark) long torpedo
shaped = efficient swimmers
Lie-in-wait (ambush) predators (barracuda) – Body
does not taper. Acceleration from strong powerful tail,
(caudle peduncle is wide).
Flatfish (flounder and plaice - bottom dwelling
Deep-bodied (butterfly fish) – lots of contact with water
= manoeuvrable, tight turns
Eel-like (moray eel) fishes are adapted for moving
through crevices
Anadromous and catadromous fish
Anadromous: Feed and grow at sea - Reproduce in freshwaters
• Salmon
Catadromous: Feed and grow in freshwaters
Reproduce at sea
European and American Eels
The Epipelagic
Topmost zone, light is abundant ▪ This is where photosynthesis takes place = lots of food ▪ You need to see your lunch before it sees you – or you become lunch! ▪ Speed is king – escape or catch Adaptations: - Large eyes - Strong muscles, fast swimming - Counter shading - Streamlined
Mesopelagic environment
Sufficient sunlight for vision, but not photosynthesis ▪ Energy comes from sinking organic material - ≈20% of primary production sinks out of the epipelagic - <5% of primary production reaches 1000 m Depends on the surface layers for O2 Natural thermocline
Short on food: Most adaptations are
concerned with finding food, or conserving
energy
They also have to stay afloat, within these
constraints
Vision is still a key sense: Seeing in the dark,
and not being seen is key.
Despite the lack of food, as much as 95% of
fish biomass may be in the mesopelagic!
Mesopelagic Fishes
Adaptions to lack of food
Common adaptations:
▪ Small size – don’t waste energy Make the most of every meal ▪ Large mouths ▪ Hinged extendible jaws ▪ Needle-like teeth ▪ Unspecialised diets
Mesopelagic Fishes
Adaptions to lack of food
Common adaptations:
▪ Small size – don’t waste energy Make the most of every meal ▪ Large mouths ▪ Hinged extendible jaws ▪ Needle-like teeth ▪ Unspecialised diets
Carnivores have:
▪ large mouth
▪ extendible jaws & needle-like teeth (e.g.
viperfish & rattrap fish)
Zooplanktivores have:
▪ smaller mouths to rapidly ingest small prey
▪ upward facing eyes to spot zooplankton in
the downwelling light (e.g. lanten fish)
The two strategies of
mesopelagic fish
Stay put, sit and wait
2. Go find food
Many mesopelagic fish undergo a diel vertical migration,
moving up to the surface at night (when they are safer from
predators) to find food.
This is the biggest migration on earth.
Vertical migration
Following food source (e.g. zooplankton)
‘Safer’ from predators at night
Vertical migrators possess
- well developed muscles
- swim bladder (often filled with lipid rather than gas)
Migrators contribute to the deep-scattering layer
Migrators bring surface production down with them
- enriching food in the mesopelagic
- non-migratory predators feed on them
Characteristics of non migrators
non-migrators cope with the reduced food supply (relative to migrators) by reducing energy demand ▪ near neutral buoyancy ▪ lack swim bladders ▪ less muscle ▪ watery flesh ▪ soft weak bones Sit and wait predators - lurk in the dark and wait for a meal (use of lures)
Mesopelagic Fishes
Adaptions to low light
Look up ▪ Large, often tubular, eyes ▪ Upward orientation ▪ Main retina for upward field ▪ Secondary retina for lateral vision
Vision is still important in the mesopelagic, but
counter shading is less effective with less light.
Most fish are looking up at you so common
adaptations are:
• Transparency
• Lateral compression of body to reduce
silhouette
Counter illumination
Counter illumination -
- photophores (light emitting organs) on underside
(ventral)
- bioluminescence - blue light to match spectrum of
downwelling light
Countershading - using coloration (silver
sides and black backs) to blend in.
Bathy & abyssopelagic
Adaptations to Very Low food Supply
We see many adaptations that we saw in the
mesopelagic to deal with lack of food:
▪ Week flabby muscles (don’t waste energy)
▪ Large mouth/teeth
▪ Generally slow metabolisms
▪ Reduced or no swim bladder
▪ Bioluminescence
Adaptations seen in mesopelagic fish to low food are generally exaggerated. Don’t miss a meal: ▪ large mouth ▪ hinged extendible jaws ▪ long sharp teeth ▪ bioluminescent lure Don’t waste energy: ▪ sluggish ▪ flabby watery muscles ▪ weak skeletons ▪ poorly developed respiratory and circulatory systems ▪ poorly developed nervous system ▪ lack swim bladders
Sex in the deep sea
Hard to find a mate in a sparsely populated
sea. Especially when you don’t move much.
▪ Some species are simultaneous
hermaphrodites
▪ Some use pheromones to find each other
▪ Angler fish have dwarf males that attach to
females (can’t waste an opportunity to mate)
Deep sea benthic fish
No natural light here and very little food.
Very little food reaches the bottom
- Food falls (whale carcasses etc)
- Marine snow and fecal pellets (POM)
Covered in a fine muddy sediment.
- bacteria and meiofaunna degrade POM/DOM and make
it available to the food chain
- Fish also scavenge larger food fall directly
Characteristics of deep sea benthic fish
Scavengers with strong muscles to move to
food falls
▪ Relatively large and slow growing
▪ Often elongated (eel-like)
▪ Strong muscles (will swim a long way to find
food).
▪ Small or no eyes (few are bioluminescent)
▪ Black/brown in color
phytoplankton: Diatoms
unicellular protist
about 40-50% of marine primary productivity
silica cell wall called a frustule
single cells or long chains
capable of rapid growth tolerant of low light temperate and polar regions bloom forming (spring bloom, upwelling) adequate light high nutrient concentrations subject to intense grazing pressure from zooplankton cysts (dormant stage) survive for years (e.g. in sediments) seed for new population growth
Coccolithophores
Coccosphere
Cell wall composed of calcium carbonate (CaCO3) plates
Complex, and still poorly understood, life cycle
Often important in tropical waters
Capable of forming large blooms, usually following the diatom bloom
Major source of CaCO3 to the sea floor.
Responsible for extensive CaCO3 rock formations (e.g. White Cliffs of Dover).
Upon dying, coccolithophores produce large amounts of dimethyl sulfide (DMS), a gas that escapes to the atmosphere.
DMS may aid cloud formation and allows sulfur to be transported from the ocean to the land.
Dinoflagellates
Dinoflagellates motile using two flagella longitudinal (trailing behind the cell) transverse (around the cell's middle) cell wall (theca) consists of cellulose
Capable of vertical migration in stratified waters
Slow growing, requiring high light
Form cysts that can persist in sediments for years
seed for new population growth when environmental conditions are favourable
Red tides, not due to rapid growth, but rather due to
persistence and
accumulation of toxins associated with defences against grazers
Small contribution to marine primary productivity
None-the-less, ecologically and economically important
Includes about 100 toxic species, producing a variety of effects in man and fish.
Cyanobacteria
prokaryotic
blue-green to pink in colour
phycobiliproteins (phycocyanin, phycoerythrin) are major light-harvesting pigments
includes the smallest and some of the largest phytoplankton
Trichodesmium is capable nitrogen fixation - transforming N2 gas into ammonium
Synechococcus accounts for about 20-30% of total ocean primary productivity
Prochlorococcus is the smallest photosynthetic cell (<1 µm diameter)
What are the characteristics of the zooplankton?
heterotrophic protists and animals
rely directly, or indirectly, on phytoplankton for food
largest biomass in surface waters (epipelagic)
metazoan zooplankton Crustacean zooplankton Chaetognaths (arrow worms) Pteropods (molluscs) Gelantinuos zooplankton (coelenterates, ctenophores, salps)
protozooplankton
ciliates, flagellates, amoeboids
Single-celled animals that are grouped based on motility into flagellates ciliates amoeboids: foraminifera radiolaria
consume bacteria, phytoplankton and other protozooplankton
fed upon by larger zooplankton
mixotrophic protists are both photosynthetic and phagotrophic
Protozooplankton
Radiolaria
silicate test
feed using long, thin, retractable pseudopodia
planktonic species may contain symbiotic algae (zooxanthellae)
many benthic species
BACTERIO- and VirioPlankton
The term bacterioplankton refers only to heterotrophic prokaryotic organisms in the plankton.
excludes cyanobacteria, which are autotrophic.
includes archaea, which are not bacteria.
Bacterioplankton consume organic matter consuming O2 and releasing CO2.
Bacterioplankton also play important roles in the nitrogen cycle.
Virioplankton are viruses that infect bacteria, phytoplankton, protozoa and other organisms.
Plankton DEFINITIONS
Meroplankton = zooplankton that spend part of their life in the plankton and the remainder in the benthos Holoplankton = planktonic organisms that spend their entire life in the plankton Ichtyoplankton = planktonic developmental stages of fish Neuston = organisms associated with the sea surface Pleuston = organisms that protrude into the air (Portuguese man-of-war)
Primary production
Autotroph = an organism that manufactures its own organic carbon using energy from the sun or other sources.
photosynthesis uses light energy (photoautotrophy)
chemosynthesis uses chemical energy (chemoautotrophy)
Primary production = the conversion of inorganic carbon into organic compounds by autotrophs.
