Marine Zoology & Ecosystems: Marine Ecology

4 ocean depth zones

Epipelagic, Mesopelagic, Bathypelagic, Abyssopelagic

Depth as a driver

drives distribution & diversity of marine species

Depth as a driver: light

decreases

Depth as a driver: temp

decreases

Depth as a driver: pressure

increases

Depth as a driver: nutrient availability

decreases

Why photosynthesis is key

photosynthetic organisms= fundamental food source

explains why o2 levels change with depth

light energy is...

trapped & used to produce organic matter through photosynthesis

Primary production

conversion of energy to organic substances by photosynthetic producers

Photosynthesis ranges from

large seaweed (macro) to microscopic phytoplankton

Light is...

fundamental limiting factor controlling ocean productivity

Autotroph

an organism that can form nutritional organic substances from simple inorganic substances such a CO2

Photoautotroph

an organism that uses light energy to drive the synthesis or organic substances from inorganic CO2

Metabolism

the chemical & physical processes by which a living thing uses food for energy & growth

Epipelagic zone depth

0-200m

Mesopelagic zone depth

200-1000m

Bathypelagic depth

1000-4000m

Abyssopelagic depth

4000-6000m

Epipelagic zone is also known as

photic zone

Epipelagic zone: what % of ocean metabolism occurs

90%

Epipelagic zone

home to some of the most productive ecosystems on earth

Phytoplankton

important photosynthesisers in our oceans

Drifting plants= phyto (plants) plankton (drifters)

Zooplankton: important pathway of...

energy transfers between producers & higher trophic levels

Zooplankton: population control

bottom-up

limited by food availability

Zooplankton blooms only able to develop...

once phytoplankton biomass has become sufficient to sustain zooplankton grazing rates

Antarctic Krill

dominant zooplankton species

Does climate influence phytoplankton & zooplankton blooms?

yes

Zooxanthellae:

unicellular microalgae of yellow or brown colour

photosynthetic symbionts found in animals or protists

Coral symbiotic relationship with

zooxanthellae- basis of reef construction

Coral reefs: species richness of animals

high

Coral reefs: how many multicellular species

at least 830,000

Coral reefs: how many species of marine fish

4000- almost 1/3 of global total

Coral reefs:

biodiversity hotspot

Coral reefs limited to

tropical & subtropical regions

Coral reefs: occupy approx

3% of total area of tropical continent shelf

Coral reef: driven by

climate & climate related factors- e.g. sea surface temps

Coral reef: act as

ecosystem engineers by secreting complex calcium carbonate skeletons

Coral reef: structure

3D structures create favourable conditions for wide range of marine organisms

Coral reef: Influences

ecosystem functioning- reef dynamics differ markedly from surrounding benthic & pelagic systems

Ecosystem engineer:

organism that modifies its environment to create optimal conditions for itself & associated organisms

Importance of light in coral reef ecosystem (light)

light energy from the sun

Importance of light in coral reef ecosystem (phytoplankton)

photosynthesise- base of pelagic food web

Importance of light in coral reef ecosystem (zooplankton & fish)

zooplankton feed on phytoplankton

fish feed on zooplankton

Importance of light in coral reef ecosystem (nutrient water)

coral reefs- typically occur in low nutrient waters- low productivity

Importance of light in coral reef ecosystem (coral-algae)

Algae-Use light energy to photosynthesise

Produce sugars and energy

coral- Provides shelter and nutrients (e.g. waste products)

Importance of light in coral reef ecosystem (ammonia)

ammonia= waste

taken up by coral algae, phytoplankton

Importance of light in coral reef ecosystem (detritus)

upwelling of detritus (organic matter)

provides extra nutrient input to reef

Trophic structure

position an organism occupies in food chain

Trophic structure: levels

Producers, primary consumers, secondary consumers, tertiary consumers & apex predators

Trophic structure: energy

energy transfer between trophic levels is inefficient

only 10-60% of energy passed from 1 level to another

Trophic structure: biomass & energy

Bottom of structure- high biomass & energy

top of structure- low biomass & energy

Energy flow: biological carbon pump

process by which carbon fixed by phytoplankton is transferred through the food web and exported to the deep ocean.

How does predation affect carbon flow?

Moves carbon to higher trophic levels.

What is excretion in zooplankton?

Release of dissolved waste products.

What is egestion?

Release of faecal pellets containing organic carbon.

What are aggregates (marine snow)?

Clumps of dead cells, faecal pellets, and organic debris.

What is carbon export?

The sinking of organic carbon from surface waters to the deep ocean.

Why are sinking particles important?

They transport carbon to depth for long-term storage.

What is remineralisation?

Breakdown of organic matter into inorganic nutrients and CO₂ by bacteria.

What role do bacteria play in the carbon cycle?

Recycle organic carbon and nutrients.

What is vertical migration?

Daily movement of zooplankton between surface and deep waters.

How does vertical migration contribute to carbon transport?

Zooplankton respire and excrete carbon at depth (active carbon pump).

Why is deep remineralisation important?

Carbon stays out of the atmosphere for longer.

What determines how long carbon is stored in the ocean?

The depth at which it is remineralised.

Ecosystem Functional Groups:

coral reef fishes exhibit a wide range of important ecosystem functions

Functional groups:

group of organisms that perform similar ecological roles

Functional groups: 3 types

Herbivory, Grazers, Excavators, Scrapers & Browsers:

Regime shift

large, abrupt & persistent changes in structure & function of ecosystems

What is herbivory?

Feeding on autotrophs (e.g. algae)

Why is herbivory a key process on coral reefs?

It controls algal growth and maintains coral dominance

Describe the herbivore community on coral reefs.

Large and diverse guild of herbivores

Give an example of a coral reef herbivore.

Sea urchin (e.g. Diadema) that consumes algae

What do corals and algae compete for on reefs?

Space

Why is herbivore control of algae critical?

It prevents algae from outcompeting corals

When is herbivory especially important?

After disturbances (e.g. storms, bleaching)

What happens when grazing pressure is removed?

Turf algae and macroalgae dominate the benthos

Which benthic group dominates without herbivores?

Macroalgae (and turf algae)

What happened to coral cover after Hurricane Allen?

Coral cover was reduced

What caused reduced coral cover after the Diadema die-off?

Loss of grazing allowed algae to dominate

How did herbivore loss affect reef resilience to Hurricane Gilbert?

Reduced resilience and recovery

What is an ecosystem regime shift on coral reefs?

A long-term change in dominant benthic organisms

What regime shift is described here?

Coral-dominated → macroalgae-dominated reef

functional grouping in ecosystems

Grouping species by the ecological roles they perform rather than by taxonomy

Why does the importance of functional grouping become clear after mass die-offs

Loss of one species reveals whether others can perform the same ecological role

Which mass die-off highlighted the role of grazers on coral reefs?

The die-off of Diadema sea urchins

What happens when a key grazer is lost?

Reduced grazing pressure and increased algal dominance unless replaced by other grazers

What happens when one grazer species is lost?

Other species with similar functions may fill the niche

Which fish are the most significant grazers on Caribbean reefs?

Parrotfish

Why are parrotfish important for reef ecosystems?

They control algal growth and help maintain coral dominance

Which fish are termed grazers on coral reefs?

Fish that constantly nibble turf algae on reefs

What type of algae do most grazers feed on?

Turf algae

What is the difference between scrapers/excavators and other grazers?

They remove turf algae and also scrape away underlying calcium carbonate

What substrate do scrapers and excavators expose

Bare limestone

Which reef component is removed during scraping/excavation?

Some calcium carbonate (CaCO₃)

Why are scrapers and excavators important to coral reefs?

They clear space for settlement of benthic organisms

Which key organisms benefit from scraping and excavation?

Corals (larval settlement)

How do scrapers and excavators help maintain reef resilience?

By preventing algal overgrowth and promoting coral recruitment

Mesopelagic Zone: photosynthesis

not beyond ~200, lack sunlight

Mesopelagic Zone: metabolism

supported by transport of organic material (POM) from euphotic zones

POM stands for

particulate organic matter