Plankton Part I – Plankton Basics, Larval Ecology, and Plankton Diversity
Tuesday (31 January 2006) and Thursday (2 February 2006)

Plankton Diversity
I. Definitions
    A. Functional groups of plankton --
           1. plankton -- limited locomotion
               a. phytoplankton
               b. zooplankton
               c. bacterioplankton
               d. viroplankton
            2. nekton -- strong swimming animals in the pelagic

    B. Sizes of plankton (Table 2.1, Nybakken)
    C. Life history of plankton
        1. holoplankton -- spend their entire life cycle in the plankton
        2. meroplankton -- spend a part of their lives in the plankton

Meroplankton -- Larvae and Larval Ecology
I. Many marine organisms produce larvae in their life cycles
    A. Larvae - independent, morphologically different stages that develop from fertilized eggs and undergo a metamorphosis before becoming adults.
    B. Recruitment
    C. Difficult to study
    D. Widely dispersing

II. Larval types and strategies – Vance (1973)
    A. Assumptions often made by scientists studying larval strategies:
        1. mortality in the plankton is constant over time
        2. mortality in plankton not related to the size of the larvae
        3. egg size is inversely related to time spent in the plankton
    B. Larval strategies
        1. Planktotrophic larvae
            a. little yolk
            b. feed while swimming
            c. animals that produce this type of larva usually produce many eggs
            d. Advantages:
                (1) large number of young produced for a given amount of energy
                (2) wide dispersal

            e. Disadvantages
                (1) larvae depend on plankton for food (unreliable -- patchy)
                (2) long time in the plankton increases chances of being eaten
            f. Favored when:
                (1) planktonic food is predictable
                (2) mortality is low
                (3) dispersal necessary
                (4) development time is short

            g. Often seen in
                (1) larger animals
                (2) organisms inhabiting rare patches of habitat -- longer time to find appropriate habitat

        2. Lecithotrophic larvae
            a. fewer, energy-rich eggs (eggs with lots of yolk).
            b. larvae do not feed while swimming.
            c. less time in the water column before settling or metamorphosizing
            d. Advantages
                (1) spend less time in plankton -- less likely to be eaten
                (2) not dependent on plankton for food -- will not starve

            e. Disadvantages
                (1) fewer eggs and larvae can be produced per available energy (larger)
                (2) less dispersal (shorter time in plankton)
                (3) larger target for predators

            f. Favored when:
                (1) dispersal is necessary
                (2) planktonic mortality is high

        3. Nonpelagic or direct development
            a. Adult produces few eggs, each with a very large amount of yolk
            b. Long development without additional energy sources
            c. No free-swimming larvae
            d. Advantages - planktonic mortality is zero (not in plankton); don't starve

            e. Disadvantages
                (1) only a very few eggs can be produced per available energy
                (2) no dispersal
            f. Favored when (common in polar regions)
                (1) less reliable food source for planktonic larvae
                (2) perhaps greater selective pressure for survival of those eggs that are produced

        4. Factors affecting relative success of different types of larvae:
            a. energy allocation
            b. dispersal
            c. relative abundance of microhabitat space
            d. longevity of adults
            e. Some species can alter their reproductive strategy

III. Larval ecology and community establishment
       A. Variation in recruitment:
        1. Production of larvae (energy; fertilization)
        2. Dispersal of these larvae in the plankton
            a. Physical currents
            b. Seasonality of larval production
        3. Risk of mortality during dispersal            

        4. Settlement of larvae and metamorphosis

            a. Mechanisms by which larvae settle in habitats -- preferences
                (1) larvae can 'test' the substrate
                (2) many preferentially settle where there are conspecifics
                (3) can delay metamorphosis if haven't found preferred habitat
            b. Stimuli
                (1) light -- + phototactic as early larvae; then switch to - phototactic at end of larval period

                (2) pressure
                (3) salinity
                (4) gravity
                (5) fluid movement (tides, currents)
                (6) chemical cues from organisms -- pheromones
                    from food species, conspecifics, predators

        5. Growth and survival after settlement

IV. Stereotypical life-history strategies
A. Opportunistic species (r-selected; intrinsic rate of growth) 
    1. rapid development
    2. short life spans 
    3. reproduce frequently
    4. high death rates
    5. often small; sometimes sessile
    6. often early colonizers on disturbed habitat
    7. examples: single-celled algae, protozoans, copepods and rotifers
B. Equilibrium species (K-selected; carrying capacity) 
    1. slow development
    2. longer life spans
    3. reproduce less often
    4. low death rates
    5. often larger and mobile
    6. often are better competitors
    7. examples: marine mammals

C. Really this is oversimplified and these are two ends of a continuum


I. Phytoplankton
    A. Role in the marine system and interesting facts
        1. great phylogenetic diversity
        2. photosynthetic – chlorophyll a is common to all
        3. some secondarily colorless
        4. some partially heterotrophic
        5. can be unicellular or have colonies; simple in structure
        6. small size and rapid reproduction
        7. can grow rapidly, forming blooms     

    B. A bit of phytoplankton diversity
        1. Cyanobacteria
            a. ancient – first PS organisms on earth – fossil stromatolites from 3 billion years ago;             

            b. prokaryotes
            c. in addition to chlorophyll they have a blue accessory pigment, phycocyanin, and a red pigment, phycoerythrin
            d. abundant in the tropics
            e. Red Sea may have been named for the red color of the cyanobacterium Trichodesmium erythraeum
            f. Some can fix atmospheric nitrogen into useable forms
        2. Diatoms (Bacillariophyceae)
            a. siliceous frustule
            b. resembles a Petri dish with a top and bottom
            c. each half is a valve or theca

            d. no flagellae or cilia
            e. diatomaceous earth (used in filters and abrasives)
            f. reproduction mode is unique
                i. each half makes a new smaller half to fit inside of it
                ii. the size of the diatom population (average size) decreases with each successive generation
                        -- some keep getting smaller; few of the original size
                iii. size is restored when the diatoms undergo sexual reproduction and form an auxospore

                iv. a few marine diatoms don’t reduce size when reproducing
            e. many diatoms produce vital fatty acids that are needed by marine animals
            f. some diatoms also produce a toxin -- domoic acid (natural amino acid); can kill organisms (causes amnesic shellfish poisoning; ASP)
        3. Dinoflagellates (Dinophyceae, Pyrrophyta)
            a. some are armored -- have cellulose plates
            b. are flagellated -- have two unequal flagella in grooves
            c. some have long spines (antipredator devices; influence sinking)
            d. many are photosynthetic
            e. some are not photosynthetic; graze small cells or are parasites
            f. some produce toxins
                i. also responsible for red tides
                ii. toxins
                    a) saxitoxins paralytic shellfish poisoning (PSP)
                    b) brevitoxins neurotoxic shellfish poisoning (NSP).
                    c) okadaic acid
                    d) ciguatoxins ciguatera fish poisoning
                    e) Pfiesteria toxin
            g. some species bioluminesce
            h. some dinoflagellates have a non-motile zooxanthellae stage that is an endosymbiont in the tissues of some invertebrates (like coral)
        4. Haptophytes (Coccolithophoridae, Haptophyceae)
            a. small flagellates (<20 mm)
            b. unique appendage -- haptonema
            c. marked calcareous or organic plates
            d. coccolithophores
        5. Prochlorophytes --
            a. primitive bacteria
            b. 0.6 -0.8 mm
            c. most numerically abundant phytoplankters in the open ocean; productive

        6. Other
            a. silicoflagellates (Chrysophyceae)
            b. cryptomonads (Cryptophyceae)
            c. motile green algae (Chlorophyceae)
            d. alpha proteobacteria

III. Diversity of Zooplankton
    A. Phylum Arthropoda
        1. Copepods (Phylum Arthropoda, subphylum Crustacea, subclass Copepoda)
            a. holoplanktonic
            b. often the most abundant members of the zooplankton – main herbivores in the ocean – 70-90% of the zooplankton biomass
            c. small – a few mm in length
            d. Life cycle
                (1) nauplius larva (6 naupliar stages)
                (2) metamorphosis
                (3) copepodid (6 stages- CI to CVI)
                (4) adult stage is the last copepodid stage
                (5) males and females
                (6) female carries eggs attached to her body in an egg sac until they hatch as nauplii
            e. feeding
                (1) mostly herbivores
                (2) some copepods are carnivorous or omnivorous
                (3) can actively select particles using both ‘smell’ and sight

        2. Order Euphausiaceakrill; can form dense swarms; eat phytoplankton and detritus; up to 6 cm; eaten by fish, seabirds and even many whales

        3. Other arthropods: Cladocera, Ostracoda, Mysidacea, Amphipoda
    B. Protozoans – heterotrophic; eukaryotic, "microzooplankton"
        1. Sarcomastigophora (amoeboid forms)
            a. Foraminiferans (forams)
                (1) skeletons made of CaCO3
                (2) most live on the bottom; a few planktonic species are abundant
                (3) pseudopodia
            b. Radiolarians
                (1) skeletons made of SiO2
                (2) exclusively marine
                (3) also feed with pseudopodia
        2. Ciliophora – ciliates; tintinnids – build cases
        3. flagellates
    C. Cnidarians – radially symmetrical
        1. Life cycle alternates between polyps (benthic) and medusas (‘jellyfish’)
        2. Have tentacles and stinging cells (nematocysts)
        3. Hydrozoa
            Siphonophores – hydrozoan colonies
        5. Scyphozoa – the jellyfish stage is dominant; carnivorous

    D. Ctenophores – comb jellies
        1. carnivorous – catch prey with sticky cells (colloblasts)
        2. locomotion with rows of fused cilia – ctenes
    E. Phylum Annelida
        polychaete worms; mostly benthic, but some pelagic
    F. Phylum Mollusca
            1. pteropods – small snails with a modified foot that forms a pair of ‘wings’ that they flap to stay afloat -
                have a mucous net or eat other pteropods
            2. heteropods - large carnivores; jellylike bodies

            3. pelagic shelled snail, Janthina, stays at the surface by clinging under a bubble raft; eat Portuguese men-of-war!
            4. squid – most are nekton, but some small ones are plankton
    G. Phylum Chaetognatha, “arrow worms”
        1. nearly transparent; streamlined; fish-like fins
        2. voracious predators of copepods and other plankton
    H. Chordata -- salps/tunicates
        1. salps – can be colonial and reach several meters in length; filter feed
        2. larvaceans – filter feeders; live inside a mucus house -- can capture really small pico and nanophytoplankton

IV. New technology -- tracking with electronic systems
        towed video microscopy; acoustics

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