Transcript Plankton
Plankton Marine life 3 categories: 1. Benthos: bottom dwellers; sponges, crabs 2. Nekton: strong swimmers- whales, fish, squid 3. Plankton: animal/plants that drift in water. The have little control over their movement. Includes: diatoms, dinoflagellates, larvae, jellyfish, bacteria. What physical factors are plankton subject to? 1. Waves 2. Tides 3. Currents Plankton classified by: • Size • Habitat • Taxonomy Size: • Picoplankton (.2-2 µm) bacterioplankton • Nanoplankton (2 - 20 µm) protozoans • Microplankton (20-200 µm) diatoms, eggs, larvae • Macroplankton (200-2,000 µm) some eggs, juvenile fish • Megaplankton (> 2,000 µm) includes jellyfish, ctenophores, Mola mola Habitat: • Holoplankton- spends entire lifecycle as plankton Ex. Jellyfish, diatoms, copepods • Meroplankton- spend part of lifecycle as plankton Ex. fish and crab larvae, eggs snail lobster fish Habitat: • Pleuston- organisms that float passively at the seas surface Ex. Physalia, Velella • Neuston – organisms that inhabit the uppermost few mm of the surface water Ex. bacteria, protozoa, larvae; light intensity too high for phytoplankton From The World Book (TM) Multimedia Encyclopedia (c) 1999 World Book, Inc., 525 W. Monroe, Chicago, IL 60661. All rights reserved. Maira & Rod Borland, Bruce Coleman, Inc. Taxonomy Phytoplankton- restricted to the euphotic zone where light is available for photosynthesis. Blooms: • High nutrients • Upwelling • Seasonal conditions Some important types of phytoplankton • • • • • • Diatoms: temperate and polar waters, silica case or shell Dinoflagellates: tropical and subtropical waters.... also summer in temperate Coccolithophores: tropical, calcium carbonate shells or "tests" Silicoflagellates: silica internal skeleton... found world wide, particularly in Antarctic Cyanobacteria (blue-green algae): not true algae, often in brackish nearshore waters and warm water gyres Green Algae: not common except in lagoons and estuaries Some important types of zooplankton • Crustaceans: Copepods Krill Cladocera Mysids Ostracods • Jellies • Coelenterates (True jellies, Man-of-wars, By-thewind-sailors) • Ctenophores (comb jellies) • Urochordates (salps and larvacea) • Worms (Arrow worms, polychaetes) • Pteropods (planktonic snails) Chaetognath Copepod Fish larvae Jelly-like house Okiopleura Marine snow Marine snow Zooplankton: larvae, copepods. Some produce oil to help them float. Smaller population size than the phytoplanktoton. Zooplankton population size increases after phytoplankton size increases. zooplankton phytoplankton Winter Spring Summer Fall Nutritional modes of zooplankton: • Herbivores: feed primarily on phytoplankton • Carnivores: 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 Diurnal vertical migration Vertical Migration Diel vertical Migration Each species has its own preferred day and night depth range, which may vary with lifecycle. 1. Nocturnal Migration • single daily ascent near sunset 2. Twilight migration (crepuscular period) • two ascents and two descents 3. Reverse migration • rise during day and descend at night Advantages for Diurnal vertical migration 1. An antipredator strategy; less visual to predators Zooplankton migrate to the surface at night and below during the day to the mesopelagic zone. Copepods avoid euphasiids which avoid chaetognaths. Advantages for DVM 1. Energy conservation • Encounter new feeding areas • Get genetic mixing of populations • Hastens transfer of organic material produced in the euphotic zone to the deep sea Plankton Patchiness • Zooplankton not distributed uniformly or randomly • Aggregated into patches of variable size • Difficult to detect with plankton nets - Nets “average” the catch over the length of the tow • May explain enormous variability in catches from net tows at close distances apart 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 patches • Grazing “holes” • Physical process - Langmuir Cells - Internal waves Accumulation of Plankton in Langmuir Cells • Buoyant particles and upwardswimming zooplankton will accumulate over downwelling zones Deep sea scattering layer: Composite echogram of hydroacoustic data showing a distinct krill scattering layer. Black line represents surface tracking of a blue whale feeding patchiness