2 Marine life 3 categories: Benthos: bottom dwellers; sponges, crabsNekton: strong swimmers- whales, fish, squidPlankton: animal/plants that drift in water. The have little control over their movement.Includes: diatoms, dinoflagellates, larvae, jellyfish, bacteria.
3 What physical factors are plankton subject to? WavesTidesCurrents
6 Habitat: Holoplankton- spends entire lifecycle as plankton Ex. Jellyfish, diatoms, copepodsMeroplankton- spend part of lifecycle as planktonEx. fish and crab larvae, eggslobstersnailfish
7 Life cycle of a squidSquid experience benthic, planktonic, and nektonic stagesSquid are considered meroplankton (opposite = holoplankton)
8 Habitat: Pleuston- organisms that float passively at the seas surface Ex. Physalia, VelellaNeuston – organisms that inhabit the uppermost few mm of the surface waterEx. bacteria, protozoa, larvae; light intensity too high for phytoplanktonNeuston net
12 Blooms: High nutrients Upwelling Seasonal conditions Phytoplankton- restricted to the euphotic zone where light is available for photosynthesis.Blooms:High nutrientsUpwellingSeasonal conditions
13 Some important types of phytoplankton Diatoms: temperate and polar waters, silica case or shellDinoflagellates: tropical and subtropical waters.... also summer in temperateCoccolithophores: tropical, calcium carbonate shells or "tests"Silicoflagellates: silica internal skeleton... found world wide, particularly in AntarcticCyanobacteria (blue-green algae): not true algae, often in brackish nearshore waters and warm water gyresGreen Algae: not common except in lagoons and estuariesSome important types of phytoplanktonDiatoms: Phylum Chrysophyta Dominant in temperate and polar waters Silica case or shell looks like a "pill box“; Found singly or in chains; Planktonic forms are radially symmetricalCan reproduce very quickly, up to 6x/day via asexual reproduction (also have sexual reproduction)DinoflagellatesDominant in tropical and subtropical waters.... also summer in temperate areas they have two flagella and a shell of cellulose plates (called theca)Asexual reproduction and fast population growth can lead to "red tides"They secrete a neurotoxin called saxitoxin: bioaccumulates in shell fish and other filter feeders... can be fatalCoccolithophoresTropical... often very common Calcium carbonate shells or "tests"Their skeletons make important depositional structures, but "naked" forms are not preservedSilicoflagellates: Biflagellated, silica internal skeleton... found world wide, particularly in Antarctic Cyanobacteria: "Blue-green algae" but not true algae: often in brackish nearshore waters and warm water gyres these bacteria can fix gaseous nitrogen into NH4Green AlgaeNot common except in lagoons and estuaries... often associated with coastal pollution Cryptomonad Flagellates: have chlorophyll a and c... adapted for turbid waters
14 Some important types of zooplankton Crustaceans: CopepodsKrillCladoceraMysidsOstracodsJelliesCniderian (True jellies, Man-of-wars,By-the-wind-sailors)Ctenophores (comb jellies)Urochordates (salps and larvacea)Worms (Arrow worms, polychaetes)Pteropods (planktonic snails)
20 Marine Snow A major component of marine snow is fecal pellets A component of "marine snow" was captured at 55 meters in Monterey Bay, California, by a light scattering optical device that also counts and estimates the size of individual particles contained in a cubic meter of water. The view includes individually settling fecal pellets as well as amorphous aggregates that look like white flakes, which are a half to several millimeters in diameter and often host a large number of fecal pellets. Zooplankton produce the weblike material that helps agglutinate particles to form aggregates.Base of Florida Escarpment covered with marine snow. Octocorals attach to steep sides and under ledges to avoid burial.
21 Marine SnowParticles sinking from sunlit surface waters through the ocean’s dimly lit twilight zone are swept sideways by currents. Conventional moored or tethered traps designed to catch the particles are like “rain gauges in hurricanes,” said WHOI biogeochemist Ken Buesseler. He and engineer Jim Valdes are designing a new-generation neutrally buoyant untethered vehicle called the Twilight Zone Explorer, which will be swept along with the currents. It will surface periodically to relay data via satellite. (Illustration by Jack Cook, Woods Hole Oceanographic Institution)
22 Nutritional modes of zooplankton: Herbivores: feed primarily on phytoplanktonCarnivores: feed primarily on other zooplankton (animals)Detrivores: feed primarily on dead organic matter (detritus) Omnivores: feed on mixed diet of plants and animals and detritus
23 Vertical Zonation of Zooplankton Epipelagic: upper m water column; high diversity, mostly small and transparent organisms; many herbivoresMesopelagic = 300 – 1000 m; larger than epipelagic relatives; large forms of gelatinous zooplankton (jellyfish, appendicularians) due to lack of wave action; some larger species (krill) partly herbivorous with nightly migration into epipelagic regimes; many species with black or red color and big eyes (why?); Oxygen Minimum Zone: 400 – 800 m depth, accumulation of fecal material due to density gradient, attract high bacterial growth, which in turn attracts many bacterial and larger grazers; strong respiration reduces O2 content from 4-6 mg l-1 to < 2 mg l-1Bathypelagic: 1000 – 3000 m depth, many dark red colored, smaller eyesAbyssopelagic: > 3000 m depth, low diversity and low abundanceDemersal or epibenthic: live near or temporarily on the seafloor; mostly crustaceans (shrimp and mysids) and fish
24 Diurnal vertical migration Organisms within the deep scattering layer undertake a daily migration to hide in deep, darker waters during daytime. Vertical MigrationDefinition: Migration pattern over 24 hrs, typically upwards at night and downwards during the day; known since Challenger-expedition (1872) but still poorly understood, several hypotheses:Avoid visual predators during daylight at greater depths and return to shallow zones with abundant food during nightSave energy during non-feeding daylight time in deeper, colder waterExploit different currents at different depths to remain in general area or to ascent to fresh, ungrazed food resources the next dayRange: up to 200 m (copepods) to 800 m (krill); speed 10 – 200 m h-1Migration patterns: Nocturnal migration: single daily ascent (sunset) and descent (sunrise); most common patternTwilight migration: two ascents and two descents every 24 hrs; sunset rise to minimum midnight depth followed by midnight sink; at sunrise, animals ascent again, followed by sink to daytime depthReverse migration: surface rise during the day, descent at night; seldomConsequences:Increased and expedited vertical transport of organic matter: animals capture prey at shallower depths and transport it downwards either as their body mass or fecal products; both are faster than sedimentationNot all individuals migrate the same range at the same time; population will loose some and gain others, enhances genetic mixingSamples from same depths taken during day and night will differ in species composition and total biomassDeep Scattering Layers: False echosound signals by larger zooplankton (krill, shrimp) and fish, but sometimes also copepods; track migration patterns
25 Diurnal Vertical Migration Each species has its own preferred day and night depth range, which may vary with lifecycle.Nocturnal Migrationsingle daily ascent near sunsetTwilight migration (crepuscular period)two ascents and two descentsReverse migrationrise during day and descend at night
26 Advantages for Diurnal vertical migration An antipredator strategy; less visual to predatorsZooplankton migrate to the surface at night and below during the day to the mesopelagic zone. Copepods avoid euphasiids which avoid chaetognaths.
27 Advantages for DVM Energy conservation Encounter new feeding areas Get genetic mixing of populationsHastens transfer of organic material produced in the euphotic zone to the deep sea
28 Plankton Patchiness Zooplankton not distributed uniformly or randomly Aggregated into patches of variable sizeDifficult to detect with plankton nets- Nets “average” the catch over the length of the towMay explain enormous variability in catches from net tows at close distances apartPlankton PatchinessIn the ocean, zooplankton do not occur evenly or randomly. The are aggregated into patches that occur in both the horizontal and vertical.These patches may be a few centimeters in scale or s of kilometers.Traditional sampling tools do a poor job of detecting this patchiness because they average the catch over the length of the tow.This patchiness may explain why there is so much variability in repeated net tows taken in close proximity to each other.
29 Problems Detecting Patches with Nets Nets are poor tools for looking at the fine-scale (meters-km) patchiness of plankton.Consider this example. We tow a plankton net with a diameter of 1 m along a 400 m distance. We will filter about 400 cubic meters of water.In the first example, all the copepods in the water are in one place about half way along the tow. In the bottom example, all the copepods are distributed fairly evenly along the tow.In both cases we wind up with 11 copepods/400 cubic meters or copepods/cubic meter.Can we determine where the copepods were concentrated along the tow path? Unfortunately not. To do that we need to use other tools such as towed video camera systems and pumps.
30 Causes of Patchiness Aggregations around phytoplankton - If phytoplankton occurs in patches, grazers will be drawn to food- Similar process that led to phytoplankton patches will form zooplankton patchesGrazing “holes”Physical process- Langmuir Cells- Internal wavesCauses of PatchinessWe saw a number of mechanisms that led to patches of phytoplankton.Feeding on patches of phytoplankton will also lead to formation of patches of zooplankton.Other mechanisms that we’ll take a look at include grazing holes created by predators and physical processes such as Langmuir cells and Internal Waves.
31 Grazing HolesWhen predators swim through a patch of plankton, they will remove animals along their path. These holes create patches.This image is another example of how vertical migration and predation interact to create patches.Fieberling Guyot is a seamount in the Pacific. The rocks on the seamount are covered with benthic organisms that feed on plankton.At night the zooplankton migrate to the surface to feed. At dawn they migrate down; however, many of those that migrate down over the seamount are lost to predators on the seamount. When they rise the next evening, there is a hole over the seamount where animals were consumed.This image shows patches of plankton after several nights on the seamount. Note the hole near the top of the seamount and higher amounts of plankton away from the seamount. The holes are not exactly over the seamounts because of horizontal currents.
32 Accumulation of Plankton in Langmuir Cells Buoyant particles and upward-swimming zooplankton will accumulate over downwelling zonesAccumulation of Plankton in Langmuir CellsAnimals that can swim upwards against the downward water flow will concentrate in the slick. Similarly, buoyant particles such as bubbles, floating seaweed and debris will also accumulate in the slicks.
33 Langmuir Cells Langmuir Cells First noted by Irving Langmuir when crossing the Atlanice. He saw long bands of floating Sargassum seaweed aligned in the direction of the wind. These observations prompted him to carry out a series of experiments in a lake to find the process which had produced these bands.The stress of the wind blowing across the surface of the water gives rise to vertically circulating Langmuir Cells in the water.
34 Langmuir Cells Langmuir Cells At the boundary of two cells, the water will either flow upwards towards the surface or downwards.Downward flows will appear as slicks (shiny smooth water) while upward flows will appear as rough, rippled areas.Zooplankton and flotsam can accumulate in the downward convergences.
35 Internal Waves Underwater waves propagated along the thermocline Generated by overflow over rough topographyMuch greater amplitude than surface wavesInternal Waves- ht 300 m or greater, surface wave 20 m htInternal waves are underwater waves that propagate along the pycnocline.If youÕve ever seen those wave toys that have bluewater and clear oil in them inside of a plexiglas box, youÕve seen something like an internal wave.They form when tidal currents flow over jumps in the bathymetry (for example over the edge of the continental shelf or a submarine bank).Their height can be much greater than surface waves because the effects of gravity are less pronounced.From the surface on a calm day, you can often see internal waves as a series of slicks on the water surface
36 Satellite image of internal wave Internal WavesThese internal wave slicks were photographed during the summer off Mississippi sound.Notice the roughly parallel slicks on the surface. These slicks represent zones of downwelling and the rough areas between them are zones up upwelling.Zooplankton can be concentrated in these slicks in much the same way that they are concentrated over downwelling zones in Langmuir cells.These examples are just a few of the ways that physical processes can interact with biology to generate patches of plankton. Your textbook contains several other examples.
37 Deep sea scattering layer: Composite echogram of hydroacoustic data showing a distinct krill scattering layer.Black line represents surface tracking of a blue whale feedingpatchiness
38 Inquiry Where do plankton aggregate? What is the difference between holoplankton and meroplankton?What is marine snow composed of?What is the connection between the deep sea scattering layer and DVM?Why aren’t phytoplankton found in neuston?