Topic 12: Classifying Organisms + Productivity in the Ocean

3 general categories for marine organisms (based on how it moves and where it lives)

1. Plankton (DRIFTERS)

2. Nekton (SWIMMERS)

3. Benthos (BOTTOM DWELLERS)

Plankton

Tiny organisms that drift with ocean currents and represent most of Earth’s biomass (one plankter = individual)

Types of plankton

1. Phytoplankton

2. Zooplankton

3. Holoplankton

4. Meroplankton

Phytoplankton

Autotrophic plankton that produce their own food via photosynthesis

Zooplankton

Heterotrophic plankton that cannot produce their own food – need to ‘eat’ something

Holoplankton

Organisms that spend their entire lives as plankton

Meroplankton

Organisms that spend their juvenile or larval stages as plankton (eg - squid)

Nekton

All animals capable of moving independently of ocean currents by swimming (or other means of propulsion)

Benthos

All animals living near, on or in the ocean floor (at all water depths)

Epifaunal

Organisms living ON the sediment

Infaunal

Organisms living IN the sediment (i.e burrowers)

Nekobenthos

Organisms swimming just ABOVE the bottom

3 Divisions of the marine environment based on sunlight

1. Euphotic zone

2. Disphotic zone

3. Aphotic zone

Euphotic zone

Enough sunlight for photosynthesis, where the bulk of biological productivity in the ocean occurs

Disphotic zone

Enough sunlight for vision but not photosynthesis

Aphotic zone

No sunlig

5 Divisions of the marine environment based on depth (pelagic zones)

1. Epipelagic

2. Mesopelagic

3. Bathypelagic

4. Abyssopelagic

5. Hadopelagic

Epipelagic

Highest zone, light present and high oxygen levels

Mesopelagic

Twilight zone, very little light, low oxygen levels

Bathypelagic + Abyssopelagic

Dark, organisms create their own light (eg –bioluminescence), high pressure, live on detritus

3 Divisions of the benthic (ocean floor) environment based on depth

1. Intertidal

2. Sublittoral

3. Bathyl

Primary Productivity

The rate at which organisms store energy through the formation of organic matter (carbon-based compounds) from inorganic carbon (carbon dioxide); aka rate of biomass formation

Photosynthesis

Chemical reaction where organisms utilize sun’s energy to produce carbohydrates

Units of primary productivity

expressed as gC/m²/yr

• grams of carbon bound into organic material per square metre of ocean surface area per year

• carbon “fixed” in organic matter in the ocean

3 factors affecting primary productivity

1. Solar radiation

2. Nutrient availability

3. Water temperature

Limiting factors

A biotic or abiotic factor that restricts the number or production of an organism (can be too much or too little of that factor)

Why is there very little photosynthesis below 100 m

Phytoplankton like to absorb red light wavelengths, so they stay near the ocean’s surface

Gross primary productivity

Total amount of organic material created by the producers

Net production (gross productivity – respiration)

Since primary producers consume a portion of this organic matter themselves through respiration, the total amount that is left to support the consumers is the net production

Compensation depth for photosynthesis

• Depth where gross photosynthesis is balanced by respiration

• Water depth at which light is limited so that net photosynthesis = zero

Biogeochemical cycle

Cycle by which nutrients are transferred through the land and ocean

Uses of phosphorous (P)

Required for DNA, RNA and energy transfer (ATP)

Uses of nitrogen (N)

• Not used directly, need nitrogen fixation into nitrate (NO3)

• Need to support photosynthesis; supports aquatic plant growth, protein synthesis

Availability of nitrate (NO3) in the open ocean

Increases with depth; upwelling can bring deep water nutrients to surface

Redfield Ratio (of nutrients)

106 carbon: 16 nitrogen: 1 phosphorus

Why the Redfield Ratio exists

Organic processes which tend in some way to control the proportions of these elements in the water

Diazotrophs

Organisms capable of marine N-fixation

Eutrophication

The excessive loading of water with nutrients (N and P) resulting in increased biomass production

5 Consequences of eutrophication

1. Increased oxygen consumption and therefore O2 depletion (anoxia)

2. Algal blooms

3. Effects on biodiversity and food webs

4. Impacts food security and ecosystem health

5. Impacts on humans: disruptions in tourism, fisheries and health industries

HNLC (Fe limitation)

High nutrient, low chlorophyll areas where bioavailable Fe is scarce

Functions of Fe (iron)

Is an essential micronutrient that controls phytoplankton productivity (can be a limiting nutrient)

• High reactivity of Fe2+ with O

• Low solubility of Fe3+

Sources of Fe

• Dust is a major external source

• Riverine sources and glacial sources at continental margins

Carbon Dioxide Removal (CDR) technique

Can artificially add Fe to the ocean’s surface to stimulate growth of phytoplankton

3 categories of organisms in an ecosystem

1. producers (autotrophic)

2. consumers (heterotrophic; herbivores, carnivores, and omnivores)

3. decomposers (break down organic compounds – dead, dying, and waste products)

Energy flow in marine ecosystems

Is unidirectional, flows from autotrophs (primary producers) upwards— energy is transferred up to higher trophic levels (energy lost as you move up)

5 Trophic levels

1. Primary producer

2. Primary consumer

3. Secondary consumer

4. Tertiary consumer

5. Apex predator

4 reasons why phytoplankton are important

1. Their huge population comprises 90 to 96% of surface ocean’s carbohydrates

2. Make huge contributions to food webs

3. Very important for productivity

4. Producers of atmospheric oxygen

3 Types of phytoplankton

1. Coccolithophores

2. Diatoms

3. Dinoflagellates

Coccolithophores

• Phytoplankton covered with small plates (coccoliths) made of CaCO3

• Live in moderate to low nutrient conditions

• Tend to live in waters that are brightly lit and temperate to warmer

Causes of phytoplankton blooms (exponential growth)

1. Favourable winds and currents

2. ‘Overfeeding’

3. High water conditions

4. Seasonal

5. Latitude dependent

Dinoflagellates

• Single-celled phytoplankton, typically microscopic

• Internal skeleton made of cellulose and siliceous (SiO2)

• Variety of shapes and sizes

• Have flagella that allows the organism to adjust its orientation and vertical position in the water – best use of light available, obtain nutrients

• Can be bioluminescent

Red tides and harmful algal blooms (HAB)

• Dinoflagellate explosion

• Red because dinoflagellates contain a red pigment

• Can be toxic or non-toxic

• Deplete water of oxygen

Diatoms

• Some of the most productive photosynthesizers

• Their presence indicates high nutrient conditions

• Component of siliceous ooze

• Tests (shells) made of silica

Phytoplankton global distribution

• Abundance varies with location

• Phytoplankton distribution corresponds to nutrient distribution in the water (upwelling areas)

Marine cyanobacteria (type of phytoplankton)

• Smallest photosynthesizers

• Live in nutrient-poor (oligotrophic) water between 40N and 40S

• A major primary producer as 1 ml of surface seawater has 100,000 cells or more

Macroscopic algae (i.e seaweed)

• Looks plant-like, but NOT a plant

• Has no vascular tissue

Thallus

Entire body of macroscopic algae

Holdfast

Specialized structure at base that attaches macroscopic algae to a surface

Gas bladders

Hollow, gas-filled structure on frond

Stipe

Stem-like structure (not present in all types of macroscopic algae)

Frond

Flattened structure resembling a leaf

What is “Seaweed”

• Unicellular / multicellular algae – not plants (non-vascular)!

• Can photosynthesize

• Great diversity in size and shape

3 main classes of seaweed based on colour

1. Green (chlorophyta)

2. Red (rhodophyta)

3. Brown (kelp)

Where is seaweed found

Can only live in the euphotic zone and able to thrive in shallow water

• Some limiting factors of temperature, nutrient supply, and substrate

Where is green seaweed (chlorophyta) found

Intertidal zones and shallow water

Where is red seaweed (rhodophyta) found

The most abundant type, found attached to substrate or encrusting

Where is brown seaweed (kelp) found

Kelp forests!

What are marine angiosperms

Marine plants that reproduce with flowers & seeds (such as sea grasses and mangroves)

• These are autotrophic, vascular plants – hydrophytes or macrophytes

Mangroves

• Grow in intertidal zone

• Only found in lower latitudes

• Can expel salt

• Their unique prop root system helps maintain position in moving sediment (able to withstand rising and falling tides)

• Kelp forests dominate where mangroves don’t grow

Chemosynthesis

The conversion of one or more C- containing molecules (CO2 or CH4) into organic matter using oxidation of inorganic compounds (H2, H2S or ferrous ions) as a source of energy

• Occurs in aphotic zone near hydrothermal vents

• May have been habitat for very first life

Riftia pachyptila

Gutless giant tube worms that have an organ containing chemosynthetic bacteria; form a symbiotic relationship