Marine Biology: Marine Reptiles, Birds & Mammals

Overview of Marine Vertebrates and Phylogeny

General Context: The Tree of Life (Vertebrates)
- Vertebrates are distinguished by having a backbone.
- Subgroups include Fish, Amphibians, Reptiles, Birds, and Mammals.
- Phylogenetic traits include the development of the Amniotic Egg and a 4-chambered heart.
Origins and Evolution
- Most marine tetrapods originated on land and in swamps.
- Convergent Evolution: Many different lineages experienced evolution from land and swamps back to the ocean, resulting in similar functional traits across unrelated groups.
Physiological Challenges: Land to Water Transitions
- Oxygen and Breathing: Oxygen availability is significantly lower in water ( $8\,\text{mg/L}$ ) compared to air ( $210\,\text{mg/L}$ ).
- Movements and Constraints:
  - Adaptations include specialized appendages for swimming.
  - Streamlining of body shape to reduce drag.
  - Viscosity: Water is $50\%$ more viscous than air, requiring more energy for movement.
- Internal Body Temperature (Thermoregulation):
  - Endotherms: Face heat loss in water that is approximately $40\times$ larger than in air.
  - Ectotherms: Marine reptiles are ectothermic, which explains their absence from polar regions.
- Hydration and Osmoregulation:
  - Ocean salinity is approximately $34\,\text{ppt}$ ( $1000\,\text{mOsm/l}$ ).
  - In contrast, the blood of land vertebrates is approximately $300\,\text{mOsm/l}$ , and freshwater environments are approximately $1\,\text{mOsm/l}$ .
- Sensory Systems: Evolutionary shifts affect vision, hearing, smelling, tasting, feeling, and communication in an aquatic medium.
- Ecological Shifts: Changes in nutrition/food sources and protection/enemies from terrestrial to marine environments.

Diversity of Marine Tetrapods

Reptiles:
- Total Reptiles: Approximately $7,000$ species.
- Marine Reptiles: Approximately $80$ species.
- New Zealand Context: $0$ marine reptile species.
Birds:
- Total Birds: Approximately $9,700$ species.
- Marine Birds: Approximately $300$ species.
- New Zealand Context: Approximately $80$ marine bird species.
Mammals:
- Total Mammals: Approximately $4,600$ species.
- Marine Mammals: Approximately $131$ species.
- New Zealand Context: Approximately $65$ marine mammal species.

Marine Reptiles: Species Details

Marine Iguana
- There is only $1$ species of marine iguana.
- They grow up to $1\,\text{m}$ long.
- Found in the Galapagos; Charles Darwin described them as "disgusting, clumsy lizards."
- They can dive to depths of $10\,\text{m}$ .
- Diet: Seaweed.
- Natural Predator: The Hawk.
Crocodiles (Saltwater and American)
- Feature saltwater glands for osmoregulation.
- Can grow up to $6\,\text{m}$ and weigh $1000\,\text{kg}$ .
- Conservation history: Hunted extensively until the $1970\text{s}$ ; currently face illegal killing and habitat loss.
- Mobility: In a study of $20$ tagged individuals, $8$ moved into the open ocean, and one traveled $590\,\text{km}$ along the coast.
- Diet: Highly opportunistic, eating fish, sea snakes, turtles, sea birds, dugongs, and rays.
- Human Interaction: Approximately $30$ attacks per year with a $50\%$ mortality rate ( $15$ fatalities/year).
- Comparative Statistics: Sharks were responsible for $439$ fatalities between $1958\text{--}2018$ , averaging $7.5$ fatalities/year.
Sea Snakes
- Approximately $70$ species, typically $1-1.3\,\text{m}$ long.
- Reproduction: Most give birth to live young, though a few are egg-laying. They undergo skin shedding.
- Biology: Carnivores and highly venomous (related to cobras), though generally non-aggressive.
- Human Impact: Hunted for skin and meat.
Sea Turtles
- $7$ total species, mostly with shells (e.g., Green turtles).
- Leatherback Turtle: Weighs up to $900\,\text{kg}$ . Its "shell" is comprised of small bones buried in the skin. They are deep divers, reaching depths of $640\,\text{m}$ .
- Diet: Consume food with low nutrient value.
- Conservation Status: Heavily over-exploited and affected by environmental impacts; $6$ out of $7$ species are endangered.
- Life Cycle: Can live up to $80$ years.

Seabirds: Adaptations and Diversity

Physical Adaptations
- Thermoregulation: Endotherms that utilize fats and dense feathers for insulation.
- Physiology: Possess light bones and oil glands for waterproofing.
- Camouflage: Countershading (darker on top, lighter on bottom).
- Behavior: Most are capable of flight and many species mate for life. They must nest on land.
Penguins
- $18$ total species.
- Flightless: Wings have evolved into flippers.
- Found exclusively in the Southern Hemisphere.
- Largest Species: Emperor Penguin ( $1.3\,\text{m}$ ).
- Colonies: Can consist of up to $1.5$ million individuals.
- New Zealand Penguins: $13$ species recorded, $9$ breed in the region, and $3$ breed on the mainland (Little Blue, Yellow-eyed, and Fjordland crested).
Divergent Evolution and Resource Partitioning
- Morphological adaptations in beaks allow for niche diversification (similar to Darwin's finches):
  - Petrel: Heavy beak for holding and tearing prey.
  - Razorbill: Heavy, streamlined beak for deeper prey.
  - Tern: Straight, narrow beak for swallowing shallow fish whole.
  - Skimmer: Large lower beak; feeds while flying along the water's surface.

Marine Mammals: Carnivora and Sirenia

Order Carnivora
- Sea Otters: Existed for approximately $5$ million years. They are the largest mustelids ( $2$ species), weighing approximately $30\,\text{kg}$ . They have dense fur and high metabolic needs, eating $25\%$ of their body weight per day. Intelligent tool-users and a Keystone species. Hunted to near-extinction.
- Polar Bears: Considered a subspecies of the brown bear, appearing $0.1-1$ million years ago. Weigh approximately $700\,\text{kg}$ and are found only in the Northern Hemisphere. They eat seals on ice and are threatened by hunting and global warming.
Order Sirenia
- Appeared approximately $60$ million years ago from ancient "Tethytheria" (relatives of elephants).
- Includes $3$ species of Manatees (found in fresh and salt water) and $1$ species of Dugong (strictly marine).
- Characteristics: Tropical/Subtropical, slow-moving, up to $500\,\text{kg}$ , herbivores.
- Reproduction: $1$ calf every $3$ years.
- Historical note: Steller's Sea Cow ( $1741\text{--}1768$ ).

Marine Mammals: Pinnipedia and Cetacea

Order Pinnipedia (Sea Lions, Seals, Walruses)
- Appeared approximately $30$ million years ago (evolved from arctoid carnivores like ursids or musteloids).
- Characteristics: Endotherms, possess hair, blubber, large brains.
- Reproduction: Viviparous with a placenta, live birth, provision of milk, and few offspring.
- Diversity: $33$ species globally. New Zealand has $4$ : NZ fur seal, NZ sea lion, leopard seal, and elephant seal.
Order Cetacea (Whales, Dolphins)
- Appeared approximately $50$ million years ago from artiodactyl ungulates (relatives of hippos).
- Exhibit dramatic convergent evolution; the entire life cycle occurs in the ocean (umbilical cord, tail, and reduced rear limbs in embryos).
- Diversity: $91$ species total (including $5$ river dolphins).
Suborder Mysticeti (Baleen Whales)
- Approximately $12$ species ( $9$ observed in NZ).
- Large and slow; possess $2$ blowholes.
- Feed via baleen (made of keratin) for filter-feeding.
- Furrow Whales / Rorquals: Family Balaenopteridae.
- Migration: Generally feed near poles during the summer.
Suborder Odontoceti (Toothed Whales)
- Approximately $78$ species ( $34$ observed in NZ).
- Generally smaller and faster than baleen whales; possess $1$ blowhole.
- Possess teeth and act as predators.

Comparative Diving Depths

Hector’s Dolphin: $10\,\text{m}$
Pearl-diver: $40\,\text{m}$
Emperor Penguin: $200\,\text{m}$
"Crazy diver": $318\,\text{m}$
Bottlenose Dolphin: $536\,\text{m}$
Beluga Whale: $647\,\text{m}$
Elephant Seal: $2385\,\text{m}$
Cuvier’s Beaked Whale: $2992\,\text{m}$
Sperm Whale: <3000\,\text{m}