AICE Marine Unit 4

4.1 Classification of Marine Organisms

Organisms are placed in hierarchical groups based on what?
Shared characteristics and evolutionary relationships.

Scientific naming system? Example?
Binomial nomenclature (Genus + species).
Example: Homo sapiens (Genus capitalized, species lowercase, both italicized).

Levels of classification (least → most specific):
Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species
Acronym example: Dumb Kids Play Catch On Freeway Get Smashed

Dichotomous keys:
You must recognize anatomical features to choose between paired statements.

4.2 Key Groups of Marine Organisms

Plankton

Key features:

  • Plankton: drift with currents, weak swimmers.

  • Phytoplankton: photosynthetic, base of food web.

  • Zooplankton: animals that drift; can be larvae or adults.

Two main phytoplankton groups:

  • Diatoms

  • Dinoflagellates

HABs:
Harmful algal blooms → overgrowth of certain phytoplankton (often dinoflagellates) producing toxins that kill fish and harm humans.

Zooplankton characteristics + examples:

  • Heterotrophic

  • Often transparent

  • Many are larvae
    Examples: copepods, krill, jellyfish larvae.

Echinoderms

Key characteristics:
Radial symmetry (adults), water vascular system, tube feet, endoskeleton of calcium plates.

Ecological importance:

  • COTS: coral predators → outbreaks damage reefs.

  • Sea urchins: graze algae → prevent overgrowth.

  • Sea cucumbers: recycle nutrients by processing sediment.

  • Antarctic krill: key food source for whales, seals, penguins.

Economic importance:
Fisheries (sea cucumbers, sea urchins), tourism, reef health supports economies.

Crustaceans

Key characteristics:
Exoskeleton of chitin, jointed legs, segmented bodies, mandibles, 2 pairs of antennae.

Label/adaptations:

  • Cephalothorax: protection + holds major organs

  • Abdomen: movement

  • Carapace: armor protection

  • Long antennae: sensing environment

  • Chela (claws): catching food/defense

  • Swimming legs: mobility

  • Walking legs: bottom-walking

  • Tail: rapid escape (tail flip)

Ecological importance:
Food source for many species; detritivores; recyclers.

Economic importance:
Fisheries (shrimp, lobster, crab).

Bony Fish

Class: Osteichthyes

Key characteristics:
Bony skeleton, operculum, swim bladder, scales, lateral line.

Label/adaptations:

  • Lateral line: detects vibrations

  • Operculum: protects gills & pumps water

  • Gills: gas exchange

  • Scales: protection and reduce drag

  • Swim bladder: buoyancy control

Ecological importance:
Major mid-trophic consumers; maintain food webs.

Economic importance:
Fishing industry, food security.

Importance of Peruvian anchoveta:
World’s largest single-species fishery; key for fishmeal and global food chains.

Cartilaginous Fish

Class: Chondrichthyes
Includes sharks, rays, skates.

Key characteristics:
Cartilage skeleton, denticles, exposed gill slits, oily liver for buoyancy.

Label/adaptations:

  • Gill slits: efficient gas exchange

  • Denticles: reduce drag

  • Caudal fin: propulsion

  • Dorsal fins: stability

  • Pelvic fins: steering

  • Pectoral fins: lift

  • Anal fin: stability

  • Spiracle: allows breathing while resting

Ecological importance:
Apex predators maintain balance.

Economic importance:
Tourism, fisheries (though declining).

Importance of blue shark:
Widespread, significant predator; heavily fished.

Chordates

Shared features of bony & cartilaginous fish:
Notochord (in embryos), dorsal nerve cord, gill slits, post-anal tail.

Compare bony vs cartilaginous fish:

  • Skeleton: bone vs cartilage

  • Buoyancy: swim bladder vs oily liver

  • Gills: covered operculum vs exposed slits

  • Scales: smooth scales vs denticles

  • Reproduction: more variety in sharks (live birth common)

Macroalgae

Definition:
Large seaweeds (green, red, brown algae).

Label/adaptations:

  • Holdfast: anchors

  • Stipe: support

  • Blades: photosynthesis

  • Gas bladder: flotation

  • Thallus: whole body structure

Ecological importance:
Habitat, oxygen production.

Economic importance:
Food, fertilizers, products (agar, alginate).

Marine Plants

Three variants:

  • Floating plants: free-floating (Sargassum)

  • Emergent plants: roots underwater, leaves above (mangroves)

  • Submergent plants: fully underwater (seagrass)

Seagrass:
Flowering plant with rhizomes; anchors in sediment, tolerant to salinity & low light.

Label/adaptations:

  • Rhizome: anchors & spreads

  • Leaf: photosynthesis

  • Flower: reproduction

  • Roots: absorb nutrients

Ecological importance:
Nursery habitats, stabilize sediment, carbon storage.

Economic importance:
Supports fisheries, protects coastlines.

4.3 Biodiversity

Definition:
Variety of life in an area.

Three types:

  • Species diversity: number of species

  • Genetic diversity: variation within species

  • Ecological diversity: variety of habitats & roles

Importance:
Resilience, food webs, ecosystem services.

Low biodiversity environments:

  • Hydrothermal vents: extreme heat/toxins → only specialists survive.

  • Reef slopes: strong currents, less stable environment.

High biodiversity environments:

  • Coral reefs: stable, warm, nutrient cycling.

  • Rocky shores: many microhabitats.

4.4 Population & Sampling

Definitions:

  • Habitat: where organisms live

  • Niche: role in ecosystem

  • Species: organisms that can interbreed

  • Population: group of same species

  • Community: all organisms in area

  • Ecosystem: community + abiotic factors

  • Biotic factors: living influences

  • Abiotic factors: non-living environmental factors

Biotic factors:
Competition, predation, symbiosis, disease.

Abiotic factors:
Salinity, temp, pH, DO, sunlight, turbidity, nutrients, air exposure, wave action, desiccation.

Sampling strategies:

  • Random: unbiased; may miss rare species

  • Systematic: regular intervals; good for gradients

  • Line transect: records organisms touching the line

  • Belt transect: wider area; more detailed but slower

Mark-release-recapture:
Used for mobile populations.
Capture → mark harmlessly → release → recapture.
Population = (marked × total captured second time) / recaptured marked.

Limitations:
Animals may avoid traps, marking may fade, migration.

Simpson’s Index (D):
Measures biodiversity.
High D = diverse.
Low D = few species dominate.

Spearman’s Rank (rs):
Correlation test using ranked data.
Tells you if two variables increase together (+), one increases while other decreases (–), or have no relationship (0).