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Chapter 2

BIOL 3450 Chapter Notes - Chapter 2: Sodium Chloride, Lunar Phase, Echinoderm

Course Code
BIOL 3450
Beren Robinson

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Water as a medium for life
Sea water versus fresh water
sea was the cradle of multicellular development
marine forms were much advanced than in land or freshwater
all water provides buoyancy and protection from desiccation and extreme temps
sea water ( unlike freshwater) provides a ready supply of dissolved salts essential for aquatic
orgs which need to maintain high ionic concentration in tissues and internal fluids . Due to high
conc of salts in the sea, marine organisms have an internal salt concentration equal to that of the
sea ( NaCl is similar to that of the water but calcium and mg are lower internally)
need effective osmoregulatory abilities to survive in freshwater or will lose all salts through
excretion or excess water may be absorbed leading to cell damage
To colonize freshwater must 1) remove excess water 2) actively maintain internal salt
concentrations 3) can reduce internal salt concentrations ( lower than marine animals but higher
than the freshwater)
Osmoregulators and osmoconformers
Osmoconformers-organisms whose body fluids follow external osmotic conditions
Osmoregulators – maintain constant internal concentrations
For osmoregulation need 1) impermeable external membrane 2)ability to remove excess
water or salt
Oregulators are freshwater animals, produce more urine, up to 40% of body weight per day
( 10 % in marine), have higher metabolic rates ( acidification makes this more difficult)
Diversity of aquatic life
Diversity of marine life
38/40 phyla in the animal kingdom occur in sea, 20 confined to marine env
Marine diversity is less extensive
Major groups of marine animals include : Echinodermata ( starfish, sea urchins,) which are
confined to sea water, porifera and cnidarian (jeelyfish, coral, sea anemones) are almost
exclusively marine, mollsca and nematode are the most diverse in the sea
Arthopoda are respresented almost exclusively by crustaceans
In the intertidal zone ( where light penetrates the sea bed) macrophytes (multi cellular
photosynthesizers) are dominated by algea
Diactoms are the only abundant algae common in both marine and fresh water diatoms
Ecological groupings of aquatic organisms
Classification tends to happen according to habitat or according to functional feeding
Classification by habitat
Organisms can be categorized by 4 main groups: pelagic, benthic, neutson and fringing-
which the part of the water the organism lives in
Pelagic organisms
Live in the water column and are futher subdivided into plankton and nekton
Plankton include algea, bacteria and a variety of animals, either completely passive or with
powers of locomotion too weak to swim against horizontal current and therefore drift in the water
column. Typically divided into phytoplankton and zooplankton reflective of ecological function
Nekton are active swimmers with independent motion- all are animals including fish but also
whales, tutles, squids and aquatic birds
Plankton can be further subdivided
Holoplankton are permanent members, represented by many taxa in the sea but dominated
in lakes by branchiopod crustaceans including cladocerans and copepods
Meroplankton are temporary members spending only have their life cycle in the plankton
they include larvae of anemones, barnacles, crabs and even fish which end up as nektons. They
are a feature of the sea especially coastal water often as sedentary adult forms of coastal species
using their planktonic stage for dispersal. Less diverse in FW but individually can be very
Benthic organisms
Sit in the bed of the water body
Animals living or attached to the bottom are known as epifauna
Those who burrow in soft sediments or live in spaces between the sediment are known as
Hyporheos are those species which inhabit sediments where surface water and ground
waters interact ( the hyphorpheic zone)
Macrophytes are attached multicellular plant and algae
Peiphyton are filamentous algae called periphyton , benthic microphytes or
Epiphytic algae grown on microphytes
Benthic consumers can be divided by size- macro fauna ( >0.5 mm or >500 microm),
meiofauna (10-500 microm) and microorganisms ( <10 microm)
Associated with water surface supported by surface tension
Acar ( mites) and Collembola ( springtails) along with larger insects
Often require still water so restricted in rivers and sea. Include cnidarian
Fringing communities
Floral communities that occur where the water is shallow enough for light to reach the bottom
allowing growth for attached photosynthesizers, which may be submerged or emergent to the air
Tend to have higher plants like water lilies with a high biomass of algae
Wetlands have this vegetation
Classification by functional group-benthos
Five groups of benthic invertabrates classified by trophic role in freshwater
Grazer-scrapers feed upon attached algae
Shredder eat CPOM
Collectors feed on FPOM
Collector-filterers removing them from the water column
Collector-gatherers pick them off the river bed
Predators consume other living animals
Common system in M enviro, diff names: carnivores, filter feeder, herbivores, surface deposit
feeders and subsurface deposit feeders
Distinction is not always in clear cut groups ie Periphytonbut useful for when the taxonomy of
the organism sampled is poorly resolved and is valuable in attempts to use aspects of the
organism’s biology, its biological traits as a means of assessing ecological function
Classification by functional groups- pelagic
Hard to classify based off food eaten bc eat anything that fits mouth
The pelagic food web
Traditionally: small phytoplankton (dominated by algae) carried out p.p and energy was
consumed by progressively larger organisms
In addition to this phytoplankton, there is a range of very small phytop consisting of
photosynthetic bacteria and microflaggelates for more of the p.p than the net phytoplankton
Large pelagic species act as almost exclusively predators but in smaller species there is
overlap in size between the photosynthetic groups and zooplankters so the consumers are both
predators and grazers
Phagocytic protists act as grazers and predators. Plankton are therefore classified by size
which will change as many species grow bigger into adulthood
The microbial loop
Many bacteria in the pelagic are photosynthetic but other specialize in feeding upon DOC,
derived from much larger algal cells
15% of algae synthesized sugar diffuse into surrounding waters which is added upon by the
messy feeding of zooplankton which shred algal cell apart and add more DOC into the water
The loss of DOC vary from 20-60% during p.p
DOC is consumed by bacteria which in turn is eaten by microflagellates
Ciliates eat the microf which are then eaten by traditional zooplankton
The microbial activity allows DOC which would be lost to re-enter the loop
Aquatic Life cycles
General features of life cycles
Simple and complex lifecycles
Simple= shown by mammals and birds where the offspring is morphologically similar to the
adult and develops by gradual modification over time
Complex= two or more morphologically dissimilar stages with abrupt change ie a
metamorphosis, found in most invertebrates
Asexual and sexual repro
protists reproduce through conjugation where two cells merge and genetic material is
exchanged before separating once more
multicellular have two haploid cells come together to create a diploid cell which develops into
an individual
higher plants and algae alternate between haploid and diploid multicellular phase
asexual reproduction: 1) fission which is the physical separation of part of the individual to
create a new one- common in unicellular protists like corals, tunicates and hydroids 2)
parthenogenesis is dev from an unfertilized egg
asexual pros: population growth rates can be very high con: genetic adaptations to changing
conditions is not possible, so high extinction probability
some animals can reproduce sexually when conditions deteriorate, producing a dormant
form which reproduce asexually once conditions improve (common in FW not M, where
conditions are more stable)
for emergent macrophytes growth for rhizomes is the main form of repro for established beds
Ensuring fertilization
con in sexual repro is that gametes need to come into contact which each other
some species are hermaphrodites, producing both male and female gametes in an
organism and can self fertilize
genetic exchange is the pro of sexual repro
External Fertilization
take advantage of buoyancy and mobility of fluid medium to disperse gametes
fertilization occurs in water, hard for single pair of gametes to come into contact so need to
produce a large amount and eggs/sperm need to be released at the same time so need some
kind of environmental cue ex) occurs in coral reefs follow day length changes and lunar cycle as