Lecture 9.1 – Nekton, Benthos

Reading: Chapter 14 and 15 but the textbook is much more detailed than our lecture – read this for interest rather than trying to memorize all the information! Learning Outcomes

After today’s lecture you should be able to... • Explain the methods that nekton use to stay afloat in the water column and how different organisms swim • Describe how nekton obtain prey and the difference between cold-blooded and warm-blooded fish • Describe/explain/identify strategies that nekton use to avoid becoming prey • Identify examples of marine reptiles, seabirds, and marine mammals and describe/explain their special adaptions • Explain the patterns in abundance of benthic life and identify primary producers • Explain the challenges and adaptions of benthic organisms which live in the intertidal zone on rocky and sediment-covered shores • Explain the differences between benthos that populate kelp forests vs coral reefs • Describe the benthos we find on the abyssal plain, near hydrothermal vents, at cold seeps, and really, really deep in the ocean and how they are adapted to these environments How nekton stay afloat

• Unlike plankton, nekton are larger and often contain hard, dense body parts e.g. bones/organs • They stay afloat using: – Internal gas chambers (called swim bladders in fish) which the animal can inflate and deflate

How nekton stay afloat

How nekton swim

• Huge variety of methods: – Squid take in water and expel it through their siphon

How nekton swim

• Huge variety of methods: – Squid take in water and expel it through their siphon – Fish contract and relax muscles along their sides so that their body moves in a wave from front to back and they move forwards. Their fins contribute to movement but also are used for braking, turning and balance.

How nekton obtain prey

• Nekton can be lungers or cruisers: – Lungers wait for prey to come close – Cruisers actively seek prey • The faster fish swim the more energy they use • Cold-blooded fish have same temperature as their environment – known as poikilothermic – and tend to be slower • Warm-blooded fish maintain their body temperatures higher than their environment – known as homeothermic – and tend to be faster. May help their muscles work better. How nekton avoid predation: Schooling

• Individuals group together in numbers from 10 to 100,000s • Move together and fish maintain position and direction by detecting vibrations of their neighbors as they move • Advantages include: – Occupy a small volume so predators less likely to find them – A predator won’t eat all of the school – School can appear threatening to single predators – Constant shifting positions and directions of school can be confusing for predators

https://www.youtube.com/watch?v=xYl4m0xFcCU How nekton avoid predation: Symbiosis

• Individuals can form relationship with other organisms to help them survive – Commensalism: less dominant organism benefits without harming the dominant organism e.g. remoras (suckerfish)

How nekton avoid predation: Symbiosis

• Individuals can form relationship with other organisms to help them survive – Mutualism: both organisms benefit e.g. clownfish and anenome

How nekton avoid predation: Symbiosis

• Individuals can form relationship with other organisms to help them survive – Parasitism: one organism benefits at the expense of the other e.g. isopods and fish

How nekton avoid predation: Others?

• Other strategies to avoid becoming prey? – Transparency, countershading and camouflage – Speed – Secreting poisons or sticky substances – Mimicry (pretending to be a different organism)

https://www.youtube.com/watch?v=t-LTWFnGmeg Seabirds

• Some birds have developed extremely close links to the ocean • Examples include: – Albatross – Penguins – Gulls and terns – Pelicans and cormorants – Puffins

Seabirds

• Some birds have developed extremely close links to the ocean • Examples include: – Albatross – Penguins – Gulls and terns – Pelicans and cormorants – Puffins • Reproduce on land but spend much of their time in ocean • Often migrate very large distances following food sources • Many are adapted to dive or swim

Marine Mammals

• Some of the most charismatic ocean organisms • Mammals are animals that: – Are warm-blooded – Breathe air – Have hair or fur for at least part of their life – Bear live young and produce milk for those young

Marine Mammals: Sea otters Marine Mammals: Sea otters Marine Mammals: Polar bears

Marine Mammals: Polar bears

Marine Mammals: Cetacea Marine Mammals: Cetacea

• Common adaptions include: – Streamlined shape – Insulating layer of blubber – Limbs modified to flippers – Blowholes on top of skull – Few hairs – Horizontal tail fin for propulsion and powerful muscles – Hugely efficient oxygen usage Marine Mammals: Toothed whales

• Include all dolphins, porpoises, killer whales, sperm whales • Have teeth • Form complex and long-lived social groups • Best able to use sound for echo location and communication Marine Mammals: Baleen whales

• Include larger whales such as blue whales, humpback whales, gray whales • Feed on low trophic level organisms such as krill using plates of baleen – made of keratin Marine Mammals: Baleen whales

• Include larger whales such as blue whales, humpback whales, gray whales • Feed on low trophic level organisms such as krill using plates of baleen – made of keratin What do these organisms have in common? How many marine species are there?

• About 1.8 million known species in the world • 2000 new terrestrial or marine species discovered each year • Total number of species on Earth likely to be ~ 6-12 million

Benthic = live on sea floor Pelagic = live in open ocean Where is the benthic life in the ocean?

Review: Distribution of primary productivity Benthic primary producers

Plants – few species include grass-like plants in bays and estuaries e.g. turtle grass, and mangroves

Seaweeds – macroscopic algae Red - found in warm and cold waters Green – not common in seawater, mostly intertidal Brown – can be large (including kelp) http://www.eeb.ucsc.edu/pacificrockyintertidal/data-products/sea-star-wasting/ Intertidal benthos: Rocky shores

Challenges?

Intertidal benthos: Rocky shores

Intertidal benthos: Sediment-covered shores

Sediment-covered shores include beaches, marshes and mud-flats

Challenges?

Adaptations? Animals: Infaunal vs Epifaunal

Epifaunal = live on top of seafloor Infaunal = live within sediment on seafloor Shallow offshore benthos: Rocky bottoms

• Rocky bottoms usually covered by seaweeds e.g. kelp forests of California

• Provide food and shelter for:

mollusks, starfish, sea urchins, sea slugs, fish, octopi, lobsters, mammals e.g. sea otters and seals