Marine Zoology & Ecosystems: Pelagic Communities

Epipelagic environment depth

0-200m

Epipelagic enviornment: primary site for

photosynthesis- it is sunlit

Epipelagic environment: driven by

currents & mixing

mixed surface layer

varies in temp

Thermocline definition

transition layer between warmer mixed water at surface & cooler deep water below

Thermocline: acts as

significant barrier to vertical mixing of nutrients, o2 & heat

Thermocline: during different times of year

depth and strength varies by season & year

semi-permanent in tropics

variable in temp regions

shallow/ non-existent in polar regions

Why is the open ocean a desert

lack nutrients

no substates from land

phytoplankton photosynthesising- zooplankton creates desert by eating phytoplankton

no nutrient mixing between cold waters & upper layers

Upwelling

wind-driven motion of dense, cooler, nutrient rich water from deep replaces warmer nutrient-depleted surface water

Adaptations: movement & swimming

propel by- producing thrust in opposition to resistive drag force

minimise drag, max thrust

Frictional drag

cause by friction between skin and boundary layer (thin layer fluid)

stickiness of fluid adheres to skin

fish creates mucus, long lipid and protein chains- act as surfactants

Pressure drag

dependent of shape of body in flow

drag minimised when fluid moving along body surface remains attached

streamline- flow minimised

Bernoulli principle

pressure increases= velocity decreases

or vice versa

Rough Skin

effective in controlling flow over body & reduces drag

texture generates turbulence in boundary layer near body surface

Adaptations: Colour

countershading

adjust in response to changes in light to match background

orienting to the sun improves camouflage

Adaptations: buoyancy

lungs, air sacs, blubber, oil rich tissues

Adaptations: Senses (Salt)

Salt management

Reptiles- salt glands

birds- supraorbital salt glands

mammals- kidneys, hormones, metabolic seawater

Adaptations: Senses (Magnetoreception)

long distance navigation

detect and respond to Earth's magnetic field

Marine turtles: species and IUCN list

Vulnerable: Olive Ridley, Leatherback, Loggerhead

Critically endangered: Kemp's Ridley, Hawksbill

Least concern: Green

Data deficient: Flatback

Marine turtles: breathing

air breathing: aerobic dives

inhale before dive

Marine turtles: Salt

lachrymal gland in orbital cavity

Leatherback turtles

no hard shell

2.7 in length

over 500kg

eat jellyfish- back of throat has back facing spine so stops them floating back out

Leatherback turtles: Osmoregulation

large lachrymal gland

Leatherback turtles: Thermoregulation

endothermic tendencies

small body to weight ration

constant movement maintain body temp

Leatherback turtles: Buoyancy

Retain lung air, adjust posture, alternate swimming and gliding

Pelagic marine birds: species

Procellariiformes (~120 species)- albatross

Suliformes (~20 spp)- boobies, gannets

Phaethontiformes (3 spp) tropic birds

Pelagic marine birds: Challenges: Osmoregulation

Ingest seawater & saline prey

supraorbital glands behind eyes

2-3x more concentrated than seawater

kidneys handle nitrogenous waste= minim water loss

Pelagic marine birds: Challenges: Thermoregulation

homeotherm

plumage insulation

counter-current heat exchange

basking

wing-spreading

gular fluttering (cooling)

Pelagic marine birds: Challenges: Foraging

patchy prey- flexible foraging strategies & large scale movements

Pelagic marine birds: Challenges: Migration & navigation

extreme distance- wind corridor reliance

take regular stops- mostly nocturnal migrators

Marine Mammals: Thermoregulation

blubber: thick fat layer- insulation & energy store

otter- air trapping pelage

large body size- low SA:V

Counter-current heat exchange

Counter-current heat exchange

dorsal fin made of cartilage- used as cc

when dolphin stressed= shunt heat inwards so they overheat

Marine Mammals: Diving

Collapsible lungs & flexible rib cage- replace 95% air in lungs

High O2 stores- redistributed into muscles instead of lungs

Bradycardia & peripheral vasoconstriction

Marine Mammals: Osmoregulation

reniculate kidneys

hormones- angiotensin- help stop salt building up in body

water balance- metabolic & dietary water

Thermoregulation: Turtles, Birds & Mammals

Turtles- ectothermic

Birds & mammals- endothermic

Salt balance: Turtles, Birds & Mammals

Turtles & Birds- salt glands

Mammals- Hormones

Locomotion: Turtles, Birds & Mammals

Turtles- flippers for swimming

Birds- wings for flight and diving

Mammals- flukes & streamlined bodies

Reproduction: Turtles, Birds & Mammals

Turtles & birds- Oviparous (eggs)

Mammals- viviparous (live young)

Sensory: Turtles, Birds & Mammals

Turtles- magnetoreception, good vision

Birds- visions & magneto & olfactory cues

Mammals- hearing & echolocation

Why does nutrient recycling dominate

Stratification blocks new nutrient input

External nutrient supple is extremely low

phytoplankton use nutrients faster than they are replaced

microbial loop retains nutrients in surface

recycling prevents nutrients from being lost to the deep

organisms are adapted to conserve nutrients

Human pressures

Over fishing, climate change, plastics, ship noise, bycatch

Case study: Marine mammal entanglement issue

300,000 mm die per year

ghost gear- long lasting hazard

energy loss from dragging gear

reduces reproduction & survival

Case study: Marine mammal entanglement solutions

gear modification- breakaway lines

dynamic management zones

ghost gear recovery programs