Marine Ecology Midterm

Marine Ecology

the study of the interactions of organisms with physical/biological/geochemical environment; how interactions determine species distribution

The Scientific Method

(1) observation, (2) hypotheses, (3) testing (falsifiable/repeatable), (4) suspend judgment

Scientific theory

broadly accepted explanation for an important phenomenon

Observations

"The chief source of ideas in oceanography comes… from new observations…" (H. Stommel).

The Challenger Expedition (1872-1876)

Covered 70,000 nm; made about 500 deep ocean soundings; recognized relationship between marine sediments and phytoplankton productivity in surface waters

Pelagic zone

water environment

Benthic zone

seafloor environment

Shallow Temperate Ocean Vertical Temperature Gradient

Mixed well (constant temp.) in winter (straight profile); opposite in summer

Open Tropical Ocean Vertical Temperature Gradient

Temp increases as depth decreases until ~1000 m; thermocline layer occurs; then steady at surface

Latitudinal Salinity Gradient

Salinity highest at mid-latitudes; lowest at poles and Equator

Evaporation minus precipitation

Follows salinity trend; highest evaporation at mid-latitude = increased salinity

Latitudinal variation in sea-surface temperatures

Sea-surface temps highest near Equator

Surface ocean currents

Caused by uneven solar heating; create global wind belts and surface current patterns

The Coriolis Effect

Air rises at low latitudes and sinks at high latitudes

Deflection

Speed difference between latitudes causes deflection; N hemisphere → right; S hemisphere → left

Upwelling

Driven by coastal winds + Coriolis effect

Dissolved oxygen

Increases with photosynthesis, wind, ventilation; decreases with bacteria, salinity, temperature

Oceanic carbon

Mostly dissolved inorganic carbon; leads to ocean acidification (H+ lowers pH, less CO3-2 for buffering)

Tides

Important for fishing, hurricanes, sailing, and intertidal organisms

Types of tides

Spring: Earth-Sun-Moon aligned; Neap: not aligned; Flood: low → high; Ebb: high → low

Estuaries

Coastal indentation where fresh & sea water mix; highly productive, nursery grounds, dynamic

Estuarine circulation

Driven by gravity, tides, wind; creates dynamic coastal habitats

Ocean circulation

Function of planetary winds + Earth’s rotation

Diet-breadth model

When food density high → specialize; ignore low-quality food

Time-in-patch model

Time in patch ↑ as travel time between patches ↑ (optimal foraging)

Predator avoidance

Crypsis, deceit, escape responses, mimicry

Fitness

Net production of offspring that survive to breed

Population size

Function of survival, death, immigration, emigration, resources, environment

Reproduction statistics

Low fecundity = 2% daily mortality; high fecundity = 20% daily mortality; seasonal influences

Settlement/recruitment

Controlled by winds, up/downwelling, El Niño, currents, gyres; active larval swimming

Metapopulation

Group of populations in discrete habitats connected by dispersal

Competition

Outcomes: extinction, coexistence via niche shift, or coexistence in variable environments

Speciation

Allopatric = geographic isolation; Sympatric = niche differentiation

Temperature regulation

Homeotherms regulate body temp (warm-blooded); Poikilotherms don’t regulate (cold-blooded)

Temperature stress

Limits growth, reduces enzymatic function, ice damage; polar fish resist freezing

Temperature & floatation

Temp affects density/viscosity → floatation; tropics → more appendages/surface area

Temperature & physiology

Heat gain problem for poikilotherms (tidal pools); heat loss problem for homeotherms (insulation, countercurrent exchange)

Temperature cues

Signal spawning, migration, sex determination (turtles: colder = male; silversides: colder = female)

Influence of oxygen

Needed for ATP synthesis; habitats can be low O2 (sediments, dead zones, oxygen minima)

Oxygen uptake

Diffusion, feathery gills, lungs with high SA, circulatory pigments

Salinity migrations

Anadromous: spawn freshwater (salmon); Catadromous: spawn ocean (eels)

Salinity and osmosis

Fish fluids ~½ ocean salinity; excrete salt with gills; control hydration metabolically

Light zones

Photic = photosynthesis; Aphotic = below photosynthesis

Light adaptations

Too much UV → bleaching; countershading; bioluminescence for ID, defense, mating

Properties of fluids

Density (g/cm³); dynamic viscosity = stickiness; kinematic viscosity = ease of flow

Reynold's Number

Ratio of inertia to viscosity (dimensionless)

Moving water

Laminar = smooth, low Re; Turbulent = chaotic, high Re

Principle of Continuity

Velocity inversely ∝ cross-sectional area; applies to pipes and branches

Bernoulli's Principle

High velocity → low pressure; creates lift

Drag

Pressure difference up/downstream; Disk drag > sphere drag > teardrop drag

Sessile drag adaptations

Flexibility, grow into current, strengthen body

Reynold's Number & flow

High Re = turbulent wake; Low Re = smooth flow

Plankton

Phytoplankton = plants; Zooplankton = animals; Mixoplankton = mixed

Plankton vertical position

Controlled by density, swimming, turbulence, size

Picoplankton/cyanobacteria

Autotrophic; N fixation; regulate CO2; 30–80% of primary productivity

Diatoms

Silica shells, reproduce by fission, abundant in cold nutrient-rich waters

Dinoflagellates

Two flagella, mixotrophic, cysts, cause red tides

Coccolithophorids

Autotrophic; CaCO3 plates; change water color

Phytoplankton diversity

Different groups → different needs & properties

Harmful algal blooms

Excess phytoplankton → O2 depletion, toxicity, dead zones

Types of HABs

Red tides = dinoflagellates; Brown = diatoms; Green = Euglena; Mahogany = dinoflagellates

Paralytic Shellfish Poisoning

Dinoflagellate saxitoxin; can cause respiratory arrest in 24h

Brevetoxins

Dominant fish-killer in Gulf of Mexico

Types of zooplankton

Herbivores, carnivores, omnivores

Meroplankton

Mollusks, worms, crustaceans, echinoderms, fish larvae; few survive

Zooplankton facts

Vertical migration; short lifespan; patchy density; holoplankton vs meroplankton

Crustacean zooplankton

Chitin skeleton, segmented, jointed appendages (copepods, krill)

Copepods

Use antennae to sense; feeding currents trap particles

Krill

10k eggs/female; support baleen whales; feed on phytoplankton & zooplankton

Cnidarian plankton

Jellyfish; colonial forms with specialized tasks

Other zooplankton

Ctenophores, pteropods

Nekton

Strong swimmers; high Re; thin boundary layer; minimize drag

Types of nekton

Cephalopods, fish, mammals, birds, sea turtles

Buoyancy control

Nautilus chambers, cuttlebone, osmotic pump

Fish

Dominant nekton; cartilaginous vs bony; abundant in upwelling/coastal/estuarine areas

Fish feeding

Suction, ram, teeth, suspension feeding

Fish forms

Rovers, surface-oriented, bottom fish, deep-bodied, eel-like

Sharks & Rays

Cartilaginous, sensory systems, live birth, rays filter feed

Bony fish

Small, bioluminescent, poorly muscled

Locomotion types

Swimming, cruising, maneuvering

Fish oxygen use

Countercurrent exchange in gills

Fish buoyancy

Swim bladder (bony fish); lipids (sharks)

Marine mammals

Homeotherms, live births, nurse young, communication

Types of marine mammals

Cetaceans, pinnipeds, mustelids, sirenians

Cetaceans

Baleen/toothed; migrate N in summer (feed), S in winter (reproduce)

Mammal diving

Adaptations: blood storage, slow heart rate, restrict circulation

The Bends

Gas bubbles avoided by small lungs, restricted circulation

Mammals tied to land

Walrus, seals, otters, manatees/dugongs

Sea turtles

Marine reptiles; nest on land; migration; diet varies; leatherbacks regulate temp

Patchiness of plankton

Form patches; controlled by turbulence vs growth

Light loss

Absorption + scattering; compensation depth = photosynthesis = respiration

Compensation light intensity

Light level at compensation depth

Light intensity

Decreases with depth; compensation depth = O2 consumed = O2 produced

Spring bloom

Occurs when mixing depth < critical depth

Primary production

Top-down = grazing; bottom-up = temp, light, nutrients

Nutrients

Substances plants need; limited supply

Nitrogen forms

NO3 most abundant; NO2; NH4 recycled fastest

Nitrogen cycling

Nitrifiers: NH4→NO2→NO3; Denitrifiers: NO3→NH4→N2

Other limiting elements

P for ATP, Si for diatoms, Fe as cofactor (HNLP regions)

Phytoplankton succession

Driven by nutrient uptake shifts, stratification, chromatic adaptation