Marine Biology and Cetaceans Quiz
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Questions and Answers

What type of animal are sperm whales classified as?

  • Reptiles
  • Pinnipeds
  • Fish
  • Cetaceans (correct)

How do seismic survey noise and military sonar negatively affect cetaceans?

  • They enhance their hunting abilities.
  • They interfere with echolocation. (correct)
  • They aid in their migration.
  • They reduce social interactions.

Which whales have shown a slow recovery in populations after commercial hunting was stopped in 1986?

  • Dinosaurs
  • Baleen whales (correct)
  • Pinnipeds
  • Beaked whales

Which whale holds the record for the deepest documented dive?

<p>Cuvier's Beaked Whale (B)</p> Signup and view all the answers

What is a significant adaptation of pinnipeds compared to cetaceans?

<p>Depend on land for breeding. (D)</p> Signup and view all the answers

Which of the following pinniped species is the only living representative of its family?

<p>Walrus (B)</p> Signup and view all the answers

What is a current status of the North Atlantic Right Whale according to conservation status?

<p>Critically endangered (C)</p> Signup and view all the answers

What defines the primary habitat of most pinniped species?

<p>Coastal areas and ice. (D)</p> Signup and view all the answers

What environment do planktonic and nektonic organisms inhabit?

<p>Pelagic realm (D)</p> Signup and view all the answers

Which size category do the smallest nektonic species fall into?

<p>Centimetre nekton (D)</p> Signup and view all the answers

Which zone supports the highest proportion of the world’s pelagic fisheries catch?

<p>Epipelagic zone (D)</p> Signup and view all the answers

What type of fish are among the targeted nektonic species found in the epipelagic zone?

<p>Herring and mackerel (A)</p> Signup and view all the answers

What contributes to the high productivity in the epipelagic zone?

<p>Nutrient-rich waters (C)</p> Signup and view all the answers

How do many nektonic fish and cephalopods disperse their species?

<p>With planktonic larvae (D)</p> Signup and view all the answers

What is the depth range of the epipelagic zone?

<p>0 to 200 m (A)</p> Signup and view all the answers

What is the lifestyle of blanket octopuses?

<p>Both benthic and nektonic (A)</p> Signup and view all the answers

What is a primary survival strategy employed by pelagic ray-finned fishes for their eggs?

<p>Broadcasting large numbers of eggs into the water (B)</p> Signup and view all the answers

How do coastal nektonic fish like Atlantic Herring reduce egg losses?

<p>By forming spawning shoals and depositing eggs on the seabed (B)</p> Signup and view all the answers

What advantage does Sargassum provide for certain fish species regarding egg-laying?

<p>It provides a safe hiding spot for their eggs. (A)</p> Signup and view all the answers

What common strategy do many predatory epipelagic fish use to catch prey?

<p>They are fast swimmers with streamlined body shapes. (B)</p> Signup and view all the answers

Which of the following accurately describes the shape of the John Dory?

<p>Thin and shaped like a dinner plate for ambush (A)</p> Signup and view all the answers

What distinguishes cephalopods from most other molluscs?

<p>They are predominantly nektonic and highly developed. (C)</p> Signup and view all the answers

What role do seabirds play in the pelagic food web?

<p>They are key top predators along with larger nekton. (C)</p> Signup and view all the answers

How do some fish species benefit from laying eggs that become entangled in long trailing filaments of seaweed?

<p>It offers a form of shelter for the eggs. (B)</p> Signup and view all the answers

Which class of fish comprises approximately 1250 marine species of sharks and rays?

<p>Elasmobranchii (D)</p> Signup and view all the answers

Which of the following statements about predatory fish is FALSE?

<p>Counter-illumination is a behavioral adaptation for ambush. (C)</p> Signup and view all the answers

How do deep-diving nekton like whales contribute to nutrient cycling between different marine zones?

<p>By feeding at depth and defaecating at the surface. (C)</p> Signup and view all the answers

What is the predominant nektonic animal in the epipelagic zone?

<p>Fish (D)</p> Signup and view all the answers

Which class of jawless fish includes hagfishes and lampreys?

<p>Myxini and Petromyzonti (A)</p> Signup and view all the answers

What is the significance of Grey Reef Sharks in nutrient cycling?

<p>They transfer nutrients from epipelagic habitats to coral reefs. (D)</p> Signup and view all the answers

What distinguishes the class Actinopterygii among fish classes?

<p>It is the largest class with about 18,700 marine species. (D)</p> Signup and view all the answers

What is the main habitat distinction for rays within the class Elasmobranchii?

<p>They primarily live a benthic existence with some exceptions. (A)</p> Signup and view all the answers

What adaptation allows sea snakes to swim longer distances?

<p>A sideways flattened tail (B)</p> Signup and view all the answers

Why do sea snakes need to bask in the sun after diving?

<p>To regulate their body temperature (D)</p> Signup and view all the answers

Which feature of coastal waters benefits fish larvae during spawning?

<p>Greater supplies of planktonic food (A)</p> Signup and view all the answers

What primarily drives the migration of nektonic marine animals?

<p>Temperature changes (D)</p> Signup and view all the answers

What is a key characteristic of the Yellow-bellied Sea Snake?

<p>It leads a pelagic existence. (D)</p> Signup and view all the answers

What is a common migration strategy used by pelagic ray-finned fishes?

<p>Moving inshore to spawn (A)</p> Signup and view all the answers

What type of fish do the majority of sea snakes mainly hunt?

<p>Sedentary fish like gobies (D)</p> Signup and view all the answers

Which species is known to utilize Atlantic gyre currents for migration?

<p>North Atlantic Blue Sharks (A)</p> Signup and view all the answers

What occurs after Pacific salmon spawn in rivers?

<p>They die and decompose, providing nutrients to the forest. (D)</p> Signup and view all the answers

Which of the following marine vertebrates is NOT mentioned as engaging in long-distance migration?

<p>Eels (A)</p> Signup and view all the answers

What are the potential risks associated with migration for nektonic marine animals?

<p>Predator exposure and poor conditions (B)</p> Signup and view all the answers

How do mass migrations affect the ecology of marine and terrestrial areas?

<p>They introduce seasonal influxes of prey species. (A)</p> Signup and view all the answers

Which characteristic is true of Atlantic mackerel regarding migration?

<p>Different stocks may migrate to different spawning areas. (B)</p> Signup and view all the answers

In what type of environment do many species prefer to migrate to avoid cold temperatures?

<p>Deep water with stable temperatures (D)</p> Signup and view all the answers

What triggers the largest migration of clupeid fish during the 'sardine run'?

<p>Alterations in water temperature (D)</p> Signup and view all the answers

Which aspect of migration can be significant for conserving energy in fish?

<p>Utilizing ocean currents (C)</p> Signup and view all the answers

What is the typical opening width of a mid-water trawl net used for sampling mesopelagic nekton?

<p>100 m (C)</p> Signup and view all the answers

What is the primary function of the cilia in the neuromast cells?

<p>To sense water-borne vibrations (B)</p> Signup and view all the answers

Which type of vessel is capable of operating larger nets for sampling bathypelagic species?

<p>Research ship of considerable size (D)</p> Signup and view all the answers

How do predators like Sailfish and certain sharks break up fish shoals?

<p>By herding them towards the water surface (B)</p> Signup and view all the answers

What technology enables the opening and closing of the net's mouth during a survey?

<p>Acoustic signal (C)</p> Signup and view all the answers

Which marine mammal characteristic differentiates them from other animals?

<p>Suckling their young on milk (D)</p> Signup and view all the answers

What unique strategy do humpback whales use to catch fish?

<p>Blowing bubble-nets (C)</p> Signup and view all the answers

What advantage does shoaling provide for fish?

<p>Protection from predators (D)</p> Signup and view all the answers

How does the size of nets used for commercial fisheries compare to those used for research?

<p>Commercial nets can be much larger (A)</p> Signup and view all the answers

What happens when fish encounter a predator and panic?

<p>The shoal fractures into smaller groups (D)</p> Signup and view all the answers

What is the primary role of the acoustic signal during net operation?

<p>To open or close the net's mouth (D)</p> Signup and view all the answers

How do flying fishes escape from predators?

<p>By launching out of the water and gliding (C)</p> Signup and view all the answers

What challenges do large nets face when sampling active bathypelagic fish?

<p>These fish often evade capture (D)</p> Signup and view all the answers

What significant advancement in net technology was introduced for the RRS Discovery in 1969?

<p>Remote-controlled opening and closing (D)</p> Signup and view all the answers

What dual role can the swim-bladder and acoustico-lateralis system play for fish?

<p>For sound production and detection of vibrations (C)</p> Signup and view all the answers

What is a significant risk that fish face when shoaling?

<p>Easier detection by sonar from fishermen (C)</p> Signup and view all the answers

What lifestyle do most octopuses tend to lead?

<p>Benthic lifestyle (C)</p> Signup and view all the answers

Which category of organisms overlaps in size with the smallest nekton?

<p>Macroplankton (C)</p> Signup and view all the answers

What is the primary zone where the majority of pelagic fisheries catch is sourced?

<p>Epipelagic zone (A)</p> Signup and view all the answers

What primarily contributes to the high productivity in the epipelagic zone?

<p>High nutrient availability from phytoplankton (C)</p> Signup and view all the answers

What is a characteristic feature of planktonic organisms?

<p>They drift on ocean currents (B)</p> Signup and view all the answers

Which nektonic species are specifically noted for their commercial importance?

<p>Small to medium-sized fishes and squid (A)</p> Signup and view all the answers

What is the approximate depth range of the epipelagic zone?

<p>0 to 200 m (B)</p> Signup and view all the answers

Which of the following categories represents the largest planktonic organisms?

<p>Megaplankton (C)</p> Signup and view all the answers

What role do brown bears play in the Great Bear Rainforest ecosystem?

<p>They recycle nutrients through their feeding habits. (C)</p> Signup and view all the answers

Which factor poses a significant threat to Pacific salmon stocks?

<p>Escapees from salmon farms. (A)</p> Signup and view all the answers

What environmental conditions do Pacific Sardines prefer for spawning?

<p>Cold water between 10 and 20°C. (A)</p> Signup and view all the answers

How does climate change affect fish migration patterns?

<p>By altering current flows and water temperatures. (A)</p> Signup and view all the answers

What is a primary source of nutrients for the Great Bear Rainforest's biodiversity?

<p>Spawning salmon and their decomposition. (D)</p> Signup and view all the answers

What do animals need to navigate effectively over long distances during migration?

<p>Both a map and compass. (D)</p> Signup and view all the answers

Which marine animal is NOT listed as a predator of fish in the coastal ecosystem of South Africa?

<p>Hummingbird (B)</p> Signup and view all the answers

What is a consequence of bears being messy while feeding on fish?

<p>It enriches the forest with nutrients. (D)</p> Signup and view all the answers

What is the primary purpose of the Grey Whales' long migration south?

<p>To access warmer waters for breeding (C)</p> Signup and view all the answers

What factor significantly influences the Northern Elephant Seals' migration patterns?

<p>Breeding and molting cycles (D)</p> Signup and view all the answers

How do Northern Elephant Seals feed during their migration?

<p>By hunting in the Gulf of Alaska and North Pacific (A)</p> Signup and view all the answers

What is a potential impact of climate change on Grey Whales' migration?

<p>Altered timings or extent of their migration patterns (C)</p> Signup and view all the answers

What characterizes the migratory behaviors of large oceanic sharks?

<p>Their migrations often depend on feeding opportunities (B)</p> Signup and view all the answers

What distinguishes a double migration in the case of Northern Elephant Seals?

<p>Migration to southern areas for breeding and again for moulting (B)</p> Signup and view all the answers

What primarily drives the migration of whale sharks?

<p>Seasonal food availability (C)</p> Signup and view all the answers

What threat do Grey Whale calves face during their return journey?

<p>Predation by pods of Orca (D)</p> Signup and view all the answers

What is the primary reason Caribbean Spiny Lobsters migrate into deeper water during autumn?

<p>To avoid rough waters and stabilize in warmer conditions (A)</p> Signup and view all the answers

What triggers the mass migration of Christmas Island Red Crabs to the coast?

<p>The first rains of the rainy season (D)</p> Signup and view all the answers

How do the planktonic larval stages of certain crabs relate to their terrestrial existence?

<p>They require returning to water for egg release (B)</p> Signup and view all the answers

What is a characteristic behavior of Caribbean Spiny Lobsters during migration?

<p>They migrate in a single file, ‘nose-to-tail’ fashion (B)</p> Signup and view all the answers

Which of the following best describes the seasonal migration patterns of benthic fish?

<p>They undertake migrations between feeding and spawning grounds (C)</p> Signup and view all the answers

Why do Loggerhead Turtles return to their hatching areas?

<p>To reproduce and lay eggs in familiar environments (C)</p> Signup and view all the answers

What aspect of the migration of Christmas Island Red Crabs is timed precisely with lunar cycles?

<p>The release of larvae into the water (B)</p> Signup and view all the answers

What type of habitat do adult Christmas Island Red Crabs prefer to inhabit?

<p>Inland forested areas for nesting (B)</p> Signup and view all the answers

Flashcards

Nekton

Animals that swim actively in the water column.

Plankton

Organisms that drift with ocean currents.

Pelagic environment

The water column from the surface to a short distance above the seabed.

Epipelagic zone

The top layer of the pelagic environment, from the surface to about 200 meters.

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Macroplankton

Plankton between 2 and 20 cm in size.

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Megaplankton

Plankton 20 to 200 cm in size.

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Benthic lifestyle

A way of life on the seabed.

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Pelagic fisheries

Fish caught in the pelagic environment.

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Pelagic Food Web

The network of interactions between organisms in the open ocean, from producers to top predators.

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Sharks (elasmobranchs)

Top predators in the marine pelagic environment, especially in the epipelagic zone.

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Fish Biodiversity

A variety of different types of fish in a place.

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Fish Classes

Seven groups of fish that are not closely related but have evolved separately.

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Ray-finned fishes (Actinopterygii)

The largest class of fish, with about 18,700 marine species.

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Jawless Fish

A class of fish that lack jaws, including hagfish and lampreys.

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Cetacean echolocation

Cetaceans use sound waves to navigate and hunt. They emit clicks and whistles, which bounce off objects and return to them, allowing them to build a sonic map of their surroundings.

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Seismic survey noise impact

Seismic surveys use loud air guns to map the ocean floor. These loud noises disrupt cetacean echolocation, making it harder for them to navigate and hunt.

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Sperm whale's deep diving

Sperm whales can dive to incredible depths, reaching over 1 km, to hunt for squid and fish.

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Beaked whales' deep diving

Beaked whales, particularly Cuvier's beaked whale, are also known for their deep diving abilities, with recorded dives exceeding 3000 meters.

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Commercial whaling impact

Commercial whaling has significantly impacted certain whale populations, leading to a decline in numbers for species like Blue, Sei, Fin, and North Atlantic Right whales.

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Pinniped lifestyle

Pinnipeds (seals, sea lions, fur seals, and walrus) are adapted for both aquatic and terrestrial life. They return to land to breed, molt, and rest.

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Pinniped distribution

Most pinnipeds are found in cold polar and cold-temperate regions, often near coastal areas.

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Pinniped families

Pinnipeds are divided into three families: eared seals (Otaridae), true seals (Phocidae), and walrus (Odobenidae).

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Egg survival strategy for pelagic fish

Pelagic fish lay large numbers of eggs into the water, relying on sheer quantity for survival. These eggs become a food source for zooplankton and other fish.

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Atlantic Herring spawning strategy

Atlantic Herring gather in large groups, called spawning shoals, and deposit eggs on the seabed. This provides protection and overwhelms potential predators.

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Seaweed and debris for egg protection

Some fish use floating seaweed or debris, like palm fronds, as safe hiding places for their eggs. This strategy is used by fish that live near the surface, like flying fish.

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Epipelagic predator challenge

Epipelagic predators, like tuna and sharks, face the challenge of getting close to their fast-moving prey in open water.

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Epipelagic predator adaptations

Many epipelagic predators are streamlined for speed, with efficient body shapes for quick swimming. They also use counter-illumination to camouflage themselves.

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Ambush predator

This type of predator relies on stealth and surprise to catch prey, rather than speed. They often have unusual body shapes to blend in with their surroundings.

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John Dory ambush strategy

The John Dory, a flat fish shaped like a plate, uses its unique shape to become nearly invisible to prey when approaching from directly above.

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Cephalopod lifestyles

While the vast majority of mollusks are benthic, cephalopods, including squid, octopus, and cuttlefish, are mainly nektonic, with squid being fully nektonic.

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Sea Snake Adaptations

Sea snakes have a flattened tail for swimming, but most are restricted to coastal areas due to their limited swimming speed. They primarily rely on taste and smell to hunt.

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Exception: Yellow-bellied Sea Snake

The Yellow-bellied Sea Snake is an exception to the typical sea snake lifestyle. It's pelagic, meaning it swims in open ocean waters, and forms large groups that drift on the surface.

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Nekton Migration: Why?

Nektonic animals migrate for food and breeding. They move to find the best resources and safe breeding areas. Temperature changes also influence their movements.

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Migration: Energy Use and Risks

Migration requires a lot of energy. Animals face predators and harsh conditions, but the benefits must outweigh these risks.

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Temperate Species Movements

Many temperate species move seasonally to avoid cold winters. They may shift between shallow coastal waters in summer and deeper, warmer waters in winter.

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Onshore/Offshore Movements

Animals may move between shallow coastal waters and deeper waters based on temperature. Shallow waters are good in summer but too cold in winter.

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Basking in Sea Snakes

Sea snakes, after diving into cold water, need to bask in the sun to warm up. This is a form of behavioral thermal regulation.

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Sea Snake Diet

Most sea snakes eat sedentary fish found at the bottom. This is different from pelagic fish, which are found in open water.

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Long-distance migrations

Migrations covering extensive distances, often thousands of kilometers, similar to those undertaken by terrestrial mammals.

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Inshore spawning

A strategy where pelagic fish move closer to coastlines to reproduce, utilizing nutrient-rich waters and sheltered areas for their young.

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Atlantic Mackerel migration

Different populations of Atlantic Mackerel may migrate to separate spawning grounds, showcasing varied migration patterns within a species.

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Energy conservation in migration

Fish utilize ocean currents to minimize energy expenditure during their migrations, riding the flow for greater efficiency.

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North Atlantic Blue Shark migration

Female North Atlantic Blue Sharks employ Atlantic gyre currents to navigate between mating and feeding grounds, showcasing the significance of currents in long-distance migrations.

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Mass migrations and ecosystem impact

Large-scale migrations, often involving millions of individuals, introduce a temporal aspect to the ecology of an area by bringing in large amounts of prey species seasonally.

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Sardine run

A massive migration of sardines, sometimes numbering millions, triggered by temperature changes, demonstrating the ecological significance of seasonal events.

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Pacific Salmon and forest ecology

Pacific Salmon, returning to freshwater rivers for spawning, contribute nutrients to terrestrial ecosystems after death, influencing forest health by providing essential resources to trees.

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Nektonic Lifestyle

A way of life where animals actively swim in the water column, not drifting with currents like plankton.

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Why do many pelagic organisms have planktonic larvae?

Planktonic larvae drift with ocean currents, helping to disperse the species, allowing them to reach new areas and colonize vast distances.

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What is the overlap between nekton and plankton?

The size range of some smaller nekton (centimeter nekton) overlaps with the size range of macroplankton (2-20 cm).

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Why is the epipelagic zone crucial for fisheries?

This zone is nutrient-rich, leading to high productivity of phytoplankton, which supports diverse nektonic animals, many of which are commercially fished.

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What is the relationship between nutrient levels and fish populations?

Areas with high nutrient levels, such as those with upwelling, support abundant fish populations, as they provide a fertile environment for phytoplankton and the entire food web.

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What are some examples of epipelagic predators?

Tuna, sharks, and some squid are important predators in the epipelagic zone. These predator-prey relationships are crucial for the balance of the ecosystem.

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Lateral Line System

A sensory system in fish that detects vibrations and water pressure changes, allowing them to sense prey, predators, and navigate their environment.

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Acoustico-Lateralis System

A combined system in fish that includes the lateral line system and the inner ear, responsible for both hearing and detecting vibrations in water.

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Shoaling

A behavior where fish gather in large groups for protection from predators, increased foraging efficiency, and other benefits.

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Predator Strategies for Breaking Shoals

Predators use tactics like herding, trapping, and splitting shoals to isolate and catch individual fish.

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Bubble-Net Feeding

A hunting technique used by Humpback whales, where they blow a ring of bubbles to encircle fish and then lunge upwards to catch them.

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Gliding Fish

Flying fishes (Exocoetidae) launch themselves out of the water using their strong tails and large fins to glide for a distance before re-entering the water to escape predators.

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Counter-Illumination Camouflage

A strategy used by epipelagic predators where they produce light from their underside that matches the light coming from above, making them harder to see.

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Mid-water Trawl Net

A net designed to collect organisms from the mid-water depths, with a mouth that opens and closes by remote control using acoustic signals.

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Multinet Trawl

A system using multiple nets at different depths, hauled up sequentially to efficiently collect organisms from various depth layers.

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Why are mid-water trawls usually large?

Nektonic animals become less numerous as depth increases, requiring larger nets to capture enough samples for analysis.

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What are the specific adaptations of marine mammals?

Marine mammals evolved from land animals but adapted with features like suckling young on milk and having hair (though reduced in cetaceans) for a marine life.

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What is the benefit of a multinet trawl?

It saves time compared to using a single net and making separate tows at various depths, improving sampling efficiency.

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How does a mid-water trawl net operate?

It's lowered with its mouth closed, then opened at the target depth by an acoustic signal from the ship, and closed again before hauling to capture organisms at that depth.

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What kind of fish are bathypelagic trawls used for?

Large, commercial trawls are designed for catching species like redfish that live in deep, open ocean waters.

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Why are some mid-water trawls exceptionally large?

They are designed to capture large, active fish and cephalopods, which are often difficult to catch in deep ocean environments.

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Salmon Run

A large-scale migration of salmon, often millions of individuals, moving from the ocean to freshwater rivers for spawning.

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Nutrient Input

The influx of nutrients, like nitrogen, from the ocean into terrestrial ecosystems, often through the decomposition of salmon.

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Temperate Rainforest

A large, moist forest with diverse plant life, found in moderate climates, like the Great Bear Rainforest.

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Sardine Migration

A massive movement of sardines, called a sardine run, driven by temperature changes, often attracting large predators.

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Predator Attraction

Large-scale migrations, like the sardine run, attract numerous predators, resulting in a dense concentration of both prey and predators.

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Map and Compass

During migration, animals need both a spatial map (knowing their location) and directional compass (knowing which way to go).

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Currents and Migrations

Ocean currents can influence the direction and timing of migrations, providing pathways for animals and affecting their distribution.

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Climate Change Impact

Changing ocean currents due to climate change can disrupt migration patterns and have significant effects on marine ecosystems.

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Grey Whale Migration

Grey Whales undertake a long annual migration of 15,000-20,000 km between their feeding grounds in the Arctic and warmer breeding waters in Mexico and Baja California.

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Why do Grey Whales Migrate?

Grey Whales need to migrate because their summer feeding grounds in the Arctic freeze over in winter, making food unavailable.

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Climate Change Impact on Grey Whales

Climate change has reduced Arctic ice coverage and will potentially affect the timing and extent of Grey Whale migrations.

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Northern Elephant Seal Migration

Northern Elephant Seals make exceptionally long migrations, up to 21,000 km, for breeding and moulting, traveling from Alaska to breeding grounds in Mexico and California.

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Why do Northern Elephant Seals Migrate?

Northern Elephant Seals migrate to warmer areas for breeding and moulting as the northern waters become too cold.

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Whale Shark Migration

While Whale Sharks have a global distribution, they don't follow specific migration routes. Instead, they travel long distances for seasonal food bonanzas.

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What is the difference between Grey Whale and Northern Elephant Seal migration?

While Grey Whales migrate for food driven by seasonal changes in their feeding grounds, Northern Elephant Seals migrate for breeding and moulting, which happens in warmer areas.

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What are some key factors influencing migrations in marine animals?

Temperature changes, food availability, breeding, and moulting are all key factors that influence migratory patterns in marine animals.

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Loggerhead Turtle Migration

Loggerhead turtles, especially in the Mediterranean, return to the same beaches where they hatched to reproduce.

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Benthic Species Migrations

Animals living on the seabed can also migrate, but over shorter distances, often for food or to avoid harsh conditions.

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Caribbean Spiny Lobster Queuing

These lobsters migrate in single file lines, saving energy and protecting themselves from predators.

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Red Crab Mass Migration

Millions of Christmas Island Red Crabs migrate to the coast to mate and release their larvae.

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Flatfish Spawning Migrations

Some flatfish migrate between feeding and spawning grounds, even though they are not strong swimmers.

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Why do pelagic fish lay lots of eggs?

They lay many eggs since they are vulnerable to predators and a high number increases the chances of some offspring surviving.

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Atlantic Mackerel migration patterns

Different populations of Atlantic Mackerel migrate to separate spawning grounds, showing how migrations can vary within a species.

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Study Notes

Open Water Lifestyles: Marine Nekton

  • Marine nekton are actively swimming animals in the water column
  • Unlike plankton, nekton have the strength to control their movement
  • Most nekton are vertebrates, particularly fish
  • Cetaceans (whales and dolphins) and pinnipeds (seals) are nekton
  • Marine snakes and turtles are also nekton
  • Squid, a prominent invertebrate, are predominantly nektonic
  • Pelagic fisheries are largely based on shoaling fish and squid.
  • Some birds, such as penguins, spend most of their time in the water, and could arguably be considered nekton.
  • Marine mammals are also considered nekton
  • Whale sharks (Rhincodon typus) utilize migration, but lack predictable routes

Nekton and Plankton

  • Nekton and plankton overlap in size
  • Macroplankton and centimetre nekton overlap in size (2–20cm)
  • Megaplankton can overlap in size (20–200cm) with nektonic species
  • Pelagic realm encompasses the water column from the surface to a short distance above the seabed

Epipelagic Nekton

  • The epipelagic zone (0-200m) is highly biodiverse
  • Pelagic fisheries catch mostly comes from this zone
  • Coastal upwelling areas are nutrient-rich, supporting high productivity
  • Important commercial species include herring, anchovies, mackerel, and squid
  • Pelagic fish often form large shoals
  • Shoals provide a strategy for predator avoidance

Fish

  • Fish are the dominant nektonic animals in the epipelagic zone
  • 7 classes of chordates: Elasmobranchs (sharks and rays), Chimaeras, Ray-finned fishes, Jawless fishes (hagfish and lampreys), Coelacanths, Lungfishes
  • Ray-finned fishes (Actinopterygii) are the largest class of fish, with approximately 18,700 marine species.
  • Some fish species are anadromous and migrate from ocean to freshwater for spawning

Predator Avoidance

  • Shoaling is a major survival strategy for many small epipelagic fish species.
  • Predators find it more difficult to target individual fish within large shoals
  • The lateral line system plays a crucial role in maintaining a standard nearest neighbour distance.
  • Cilia and cupula in the lateral line system detect water-borne vibrations to help fish navigate effectively
  • Some predator strategies involve breaking up shoals and trapping fish.

Cephalopods

  • Squid are numerous and important ocean predators
  • Squid have no external shell
  • They have a lightweight internal shell for buoyancy control in cuttlefish
  • Sepia, squid & Nautilus are examples

Other Invertebrates

  • Crustaceans such as squat lobsters may be nektonic
  • Shrimp-like mysids (Mysidacea) and euphausiids (Euphausiacea) are often found in large swarms
  • Cnidarians, like jellyfish, can have weak swimming abilities.
  • Some crustaceans, such as squat lobsters, form large swarms.
  • Some molluscs, such as squid, are entirely nektonic.

Mesopelagic Nekton

  • The mesopelagic zone (200-1000m) has many apex predators (e.g. sharks, cetaceans), which have feeding forays into this zone.
  • Important groups include lanternfishes, gonostomatids, hatchetfishes, and viperfishes -Mesopelagic fishes are important part of the oceanic ecosystem.
  • Fish in mesopelagic layer migrate vertically

Bathypelagic Nekton

  • The bathypelagic zone (1000–4000m), characterized by lack of light, has adapted nektonic species to this darkness.
  • Examples of species are chimaeras (deeper than 200m) and anglerfishes
  • Some species have adapted body forms, and bioluminescence for survival.
  • Some bottom-dwelling fish also live in the bathypelagic zone.
  • Some species like chimaeras, are adapted for deep-water life
  • Some species have developed bioluminescence-based adaptations

Whale Migration

  • Whales migrate extensively between cold feeding areas (e.g. Arctic, Antarctica) and warmer, less productive breeding areas (e.g. tropics).
  • This is driven by food availability.
  • Important for species such as humpback whales.
  • Some whales migrate extensively, covering great distances

Pinniped Migration

  • Pinnipeds have a connection to land. They return to land for breeding, molting, and resting
  • Pinnipeds have strong swimming abilities, but constrained by dependence on land
  • Species like the elephant seals exhibit unusually extensive migrations of up to 21,000km.
  • Some pinnipeds migrate long distances for breeding and feeding

Fish Migration

  • Fish use migration for feeding and breeding, and for seasonal changes
  • Some species utilize currents for migration

Marine Reptile Migration

  • Marine reptiles exhibit varied migration patterns
  • Reptiles exhibit strong swimming abilities to cover distances
  • Migration is important for feeding, breeding, and avoiding extreme weather.

Marine mammal Migration

  • Migration is essential for food sources and breeding grounds
  • Species like Grey Whales make a lengthy migration in response to favorable food and habitat conditions
  • Migratory animals are highly sensitive to climate change.
  • Some whales and dolphins migrate to different areas based on food resources
  • Migration can encompass long distances

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