Planet & Ocean Discovery Series: Guam - Open Ocean

Habitats & Adaptations


Characterized by deep waters with varying depths, currents, and temperatures, this ecosystem is home to an array of marine organisms adapted to thrive. Adaptations include streamlined bodies and fins for swimming, large tails, keen senses, sophisticated hunting strategies, and special respiratory systems for oxygen intake.

Key Vocabulary

Atmospheric Pressure


Learning Objectives

  • Students will be able to identify and describe adaptations of marine organisms in deep-water ecosystems that aid in survival.
  • Students will be able to explain how marine organisms adapt to varying depths, currents, and temperatures within deep-water ecosystems and the benefits of these adaptations.
  • Students will be able to compare and contrast the adaptations of different marine organisms, noting similarities and differences.

Body Type

Streamlined bodies and fins are adaptations useful to animals that need to move smoothly with the flow of water. The streamlined body allows the animal to cut through the water with minimal resistance, enabling easier and more efficient swimming. This adaptation is particularly beneficial in the waters around Guam, where ocean currents can be strong and unpredictable.

In the marine ecosystems surrounding Guam, predator species such as reef sharks and certain species of large fish have evolved streamlined bodies and fins to enhance their hunting efficiency. The streamlined shape allows them to achieve greater speeds and agility, making it easier to catch fast-moving prey such as smaller fish and squid. For example, the blacktip reef shark, commonly found around Guam, uses its streamlined body to swiftly navigate through coral reefs and open waters, effectively pursuing its prey. Additionally, their fins provide stability and maneuverability, allowing them to make quick, sharp turns during a chase.

Prey species in Guam’s waters, such as various types of tuna and mackerel, have also developed streamlined bodies to outswim predators and evade capture. These fish exhibit streamlined shapes that allow them to swim at high speeds, crucial for escaping predators like sharks and larger fish. Their fins help maintain balance and stability, aiding them in navigating swiftly through the water to avoid being caught.

The streamlined body shape also increases stability in the turbulent and often unpredictable waters around Guam. This stability is essential for both predator and prey species, as it helps them maintain control and orientation while swimming, conserving energy, and avoiding disorientation. The streamlined design reduces turbulence and drag, allowing marine animals to swim more efficiently over long distances, which is particularly important in the open waters and around the coral reefs of Guam where food sources may be scattered.

Blacktip Reef Shark
The blacktip reef shark, commonly found around Guam, uses its streamlined body to swiftly navigate through coral reefs and open waters, effectively pursuing its prey.

Additionally, their fins provide stability and maneuverability, allowing them to make quick, sharp turns during a chase.
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Haggan - Green Sea Turtle
Green Sea turtles have streamlined shells and large paddle-shaped fins, allowing them to swim and dive swiftly. They can move up to 22 mph when frightened. The species is endangered in Western Pacific waters, including those around Guam. Their streamlined bodies and fins help them navigate strong currents and varying depths effectively. This is essential for their long migratory journeys and for escaping predators. The combination of a streamlined body and powerful fins enables Green Sea turtles to find food, avoid predators, and migrate efficiently. Additionally, their streamlined shape and efficient movement help them conserve energy, crucial for survival, especially in the open ocean where food sources can be scarce.
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Eyesight is crucial for Mahimahi to spot prey near the surface and floating objects. However, their success hinges on more than just visual acuity. Mahi-mahi also possess a keen sense of smell. They can detect the scent of baitfish or other prey from long distances, guiding them to feeding opportunities.
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Shortfin Mako Shark
The Shortfin Mako Shark is a formidable predator thanks to its combined sensory suite. Their excellent vision helps them locate prey in open water, while the lateral line system and electroreception give insight on the prey's location and movement. This allows them to target prey with incredible speed and precision, making them a dominant force in the open ocean.
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Blue Marlin
Eyesight remains key for spotting prey at a distance for Blue Marlin. Additionally, they possess a lateral line system that runs along their bodies. This system detects subtle changes in water pressure, allowing them to track movements of prey even in low-light conditions. Some studies suggest they may also have a weak form of electroreception, enabling them to sense the faint electrical fields emitted by living organisms.
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Senses & Hunting Strategies

In the vast expanse of the open ocean, the hunt for food is a constant dance between predator and prey. Survival depends on sharp senses and clever hunting tactics. Marine life has evolved diverse adaptations to sense their surroundings and find food, even though they may not have the same five senses as humans.

  • Electricity: Sharks and some bony fish can sense the weak electrical fields emitted by living organisms, allowing them to locate prey hidden in murky water or buried in the sand.
  • Gravity: Certain fish and invertebrates use highly sensitive organs (otoliths) to detect minute changes in gravity, aiding in navigation and vertical movement in the water column.
  • Water Pressure: Many marine animals, including dolphins and whales, possess a sophisticated sense of pressure. This allows them to perceive depth, locate underwater features, and even detect approaching predators.
  • Atmospheric Pressure: Fish can sense changes in atmospheric pressure, which can help them predict weather patterns and locate feeding grounds.

These diverse senses work together to paint a detailed picture of the surrounding environment. Olfaction (smell) plays a crucial role for many species. Sharks can detect blood in the water from miles away, while fish and turtles use scent trails to navigate vast distances, like following an invisible map.

Vision is another critical tool, especially for predators that rely on sight to locate prey. Excellent eyesight allows fish like tuna to spot schools of baitfish or bioluminescent flashes at night, while the keen vision of marlin helps them target fast-moving prey near the surface.

Hearing plays a vital role as well. Predators like dolphins use echolocation, emitting sound waves and interpreting the echoes to build a three-dimensional image of their surroundings. This allows them to hunt effectively in low-light conditions or murky water.

The hunting strategies employed in the open ocean are as diverse as the senses themselves. Some predators, like blue marlin, are ambush hunters, relying on their speed and agility to surprise and overpower prey. Others, like yellowfin tuna, utilize their schooling behavior to herd baitfish into a tight ball, making them easier to catch. Opportunistic feeders like mahi-mahi simply snatch prey that comes near the surface or scavenge around floating objects.

By combining their exceptional senses with a variety of hunting tactics, marine predators of the open ocean have become masters of their environment. This ongoing evolutionary arms race, where predators refine their senses and hunting strategies, and prey develop counter-adaptations, ensures a dynamic and ever-changing dance for survival in the vast blue expanse.

The Buoyancy Advantage

Efficient movement and hunting in the open ocean require constant energy conservation. Bony fish, unlike land animals with lungs, rely on gills to extract oxygen dissolved in water. But maintaining position in the water column can be a challenge. Here’s where the swim bladder comes in. This gas-filled internal sac acts like a buoyancy control device. By adjusting the gas content within the bladder, fish can effortlessly stay at their desired depth without expending extra energy on constant swimming motions. This adaptation allows them to focus their energy on hunting and other activities, giving them a significant advantage in the open ocean.

The swim bladder can also be sensitive to pressure changes. As pressure changes, the gas in the swim bladder expands or contracts, which fish can likely detect. 

Yellowfin Tuna
Guam's open ocean teems with Yellowfin Tuna, apex predators with a secret weapon: a swim bladder. This gas-filled organ acts like a silent jetpack, allowing them to effortlessly maintain perfect depth – a crucial advantage in energy conservation. Unlike humans constantly kicking to stay afloat, Yellowfin Tuna can focus their energy on hunting and migration. This translates to pinpoint predation, where they can target prey from surface baitfish to deep-sea krill. The swim bladder also keeps their bodies streamlined, maximizing efficiency during hunts.
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Guam’s deep waters pose a challenge with fluctuating depths, currents, and temperatures. Despite this, a wide variety of marine life thrives here thanks to amazing adaptations.

Both predators and prey share a sleek body and fin design for efficient movement. Sharks use electroreception to sense prey’s electrical fields, while fish navigate with otoliths that detect pressure changes. Dolphins and others use water pressure to perceive depth and even predators. Fish can even sense air pressure, potentially predicting weather and finding food.

Smell is another key sense. Sharks detect blood from afar, while fish and turtles navigate by scent trails. Vision is crucial for predators like tuna and marlin, with some fish seeing bioluminescence. Dolphins use echolocation, sound waves to “see” in the dark.

Hunting strategies are diverse. Blue marlin ambush prey with speed, while yellowfin tuna herd baitfish for easier capture. Opportunistic feeders like mahi-mahi snatch surface prey.

These adaptations make Guam’s deep-sea creatures masters of their ever-changing environment.

Environmental Importance


The open ocean plays a critical role in supporting biodiversity and sustaining marine food webs by providing a habitat for a wide range of species, including fish, migratory species, and pelagic organisms. These species influence the distribution and abundance of species throughout the region. Additionally, the open ocean acts as a carbon sink, absorbing atmosphere carbon dioxide, which helps regulate global climate.

Key Vocabulary

Carbon cycle
Carbon sink

Food web

Learning Objectives

  • Students will be able to explain how producers, herbivores, carnivores, and omnivores in the ocean interact through feed relationships.
  • Students will be able to analyze how changes in one population can cascade through the food web.
  • Students will be able to identify the role of phytoplankton in the carbon cycle and its importance for a healthy environment.
  • Students will be able to explain how the ocean acts as a carbon sink, absorbing carbon dioxide from the atmosphere. 

Next Generation Science Standards Alignment

LS2.A: Interdependent Relationships in Ecosystems –The intricate web of the marine food web exemplifies interdependent relationships within an ecosystem. Primary producers, like phytoplankton, capture energy from the sun and form the base of this food chain. These producers are consumed by primary consumers, such as zooplankton, who transfer energy to the next level. Secondary consumers, including fish and smaller shrimp, then feed on the primary consumers. Finally, tertiary consumers, like larger fish and sharks, occupy the top of the food chain by preying on secondary consumers. This interconnected web demonstrates how all organisms in the marine ecosystem rely on each other for survival and the flow of energy.

LS2-5: Ecosystem Dynamics, Function, and Biodiversity – Within a marine food web, changes in one population can have cascading effects on other populations. Imagine a scenario where overfishing significantly reduces the population of a specific type of fish (primary consumer) that feeds on plankton (primary producer). This decrease in fish would lead to an increase in plankton populations as there are fewer predators to consume them. However, an unchecked rise in plankton could deplete the nutrients available for other organisms, ultimately affecting the entire food web. This example demonstrates how a seemingly isolated change in one population can have rippling effects throughout the interconnected web of marine life.

Marine Food Web

Guam hosts a unique and intricate marine food web. This ecosystem is characterized by a complex network of interactions among various species, all driven by the need to obtain energy and matter to sustain life. The marine food web in the open ocean around Guam involves producers, consumers, and decomposers, each playing a crucial role in maintaining ecological balance.

Marine Producers
In the open ocean around Guam, the primary producers are predominantly phytoplankton. These microscopic, photosynthetic organisms are the foundation of the marine food web, converting sunlight, carbon dioxide, and nutrients into organic matter through photosynthesis. Phytoplankton productivity is critical in supporting the entire marine ecosystem, as they are the primary source of energy for a wide range of organisms.

Primary Consumers
Primary consumers in Guam’s open ocean include various species of zooplankton, small pelagic fish, and other invertebrates that feed on phytoplankton. Copepods, krill, and other zooplankton are vital links in the food web, transferring energy from the primary producers to higher trophic levels. Small fish such as sardines and anchovies also play a significant role as primary consumers, feeding on zooplankton and smaller phytoplankton.

Secondary and Tertiary Consumers
Secondary consumers in the open ocean around Guam consist of larger fish, cephalopods, and some marine mammals. These organisms prey on the primary consumers. For example, tuna, mackerel, and dolphinfish are significant secondary consumers that feed on smaller fish and zooplankton. Cephalopods like squid are also important secondary consumers, preying on smaller fish and crustaceans.

Tertiary consumers include larger predatory fish, marine mammals, and seabirds. Apex predators such as sharks, billfish (like marlins and swordfish), and certain species of dolphins prey on secondary consumers, maintaining the balance of marine populations and contributing to the health of the ecosystem.

Apex Predators
In Guam’s open ocean, apex predators such as oceanic whitetip sharks, mako sharks, blue sharks, large tuna species, marlins, and bottlenose dolphins play crucial roles in maintaining the balance of the marine ecosystem. They regulate prey populations, ensuring healthy species diversity and preventing overpopulation of certain species. These top predators are essential for the overall stability and resilience of the oceanic food web around Guam.

Decomposers in the open ocean, including bacteria and fungi, break down dead organic matter, recycling nutrients back into the ecosystem. This decomposition process is essential for maintaining the productivity of the open ocean, supporting the growth of phytoplankton and other primary producers.

Primary Producer - Phytoplankton
Phytoplankton are microscopic, photosynthetic organisms that form the foundation of the marine food web in Guam's open ocean. Utilizing sunlight, carbon dioxide, and nutrients from the water, they perform photosynthesis, producing organic matter that serves as the primary source of energy for a wide range of marine organisms. Phytoplankton are crucial for the ecosystem, supporting the growth of zooplankton, small fish, and ultimately the larger predators, and they play a significant role in the global carbon cycle by sequestering carbon dioxide from the atmosphere.
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Secondary Consumer - Flying Fish
In Guam's open ocean, flying fish function as secondary consumers, utilizing specialized brush-like teeth to filter plankton from the water column. Additionally, flying fish possess well-developed pectoral fins that facilitate aerial gliding as an escape mechanism, enhancing their survival against predators like tuna and marlin.
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Apex Predator - Oceanic Whitetip Shark
Oceanic whitetip sharks rule Guam's open ocean as apex predators. They keep prey populations like fish and squid in check, preventing any one species from dominating. This promotes biodiversity and ensures a healthy mix of marine life. As they feed, they release nutrients back into the system, fueling plankton growth at the base of the food chain. These sharks are vital for a balanced and functioning open ocean ecosystem.
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Carbon Sequestration
Phytoplankton and other organisms in the sunlight zone also play an important role in carbon sequestration, which is the process of storing carbon in the ocean. Phytoplankton takes up carbon dioxide from the atmosphere through photosynthesis and stores it in the form of organic matter. When phytoplankton and other marine organisms die, their carbon-rich bodies sink to the ocean floor, where it can be stored for thousands of years.
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Carbon Cycle

The carbon cycle is the process by which carbon is exchanged between the atmosphere, ocean, and land. It plays a critical role in regulating the Earth’s climate and maintaining biodiversity.

The carbon cycle is mainly driven by photosynthesis, which is the process by which plants, algae, and some bacteria convert sunlight and carbon dioxide into oxygen and organic compounds. This process is performed by phytoplankton, which is the base of the marine food web and responsible for a large part of the Earth’s oxygen production.

Variations in the availability of nutrients and light can significantly impact the carbon cycle. Changes in nutrient availability, such as nitrogen and phosphorus, can affect the growth and productivity of phytoplankton. Similarly, fluctuations in light intensity and duration due to factors like seasonal changes or water turbidity can influence the rate of productivity of phytoplankton and overall carbon fixation in the ecosystem.


The open ocean surrounding Guam serves as a vital ecosystem supporting diverse marine life and playing a crucial role in global environmental processes. It provides habitat for a wide array of species, including migratory fish and pelagic organisms, which contribute to the region’s biodiversity and sustain complex food webs. Additionally, the open ocean acts as a significant carbon sink, absorbing atmospheric carbon dioxide through processes like photosynthesis by phytoplankton. This carbon sequestration helps regulate global climate patterns, highlighting the ecosystem’s essential role in maintaining ecological balance and supporting human well-being.

The Changing Climate


The open ocean waters around Guam are heavily impacted by climate change, with rising temperatures and ocean acidification threatening marine biodiversity and ecosystem stability. These changes affect nutrient availability, disrupt food webs, and alter fish populations, crucial for local fisheries. Effective management and adaptive strategies are essential to sustain marine life and coastal communities reliant on fishing.

Key Vocabulary


Learning Objectives


Next Generation Science Standards Alignment


Rising Temperatures

As sea temperatures rise, marine species in the open ocean around Guam are forced to adapt by migrating to cooler waters. This migration can lead to shifts in species distribution, potentially introducing new species to the region while causing local extinctions of those unable to adapt or move. For example, tropical fish species may extend their range, while species adapted to cooler temperatures may retreat or face decline.

Influence on Metabolism and Reproduction
Increased temperatures can accelerate the metabolism of marine organisms, leading to higher energy requirements. For some species, this can enhance growth rates and reproduction, while for others, it may cause stress and reduce reproductive success. Species with narrow temperature tolerance ranges are particularly vulnerable, potentially leading to decreased biodiversity in the region.

Impacting Marine Food Webs
Temperature changes can disrupt the timing of biological events, such as phytoplankton blooms and the breeding cycles of zooplankton and fish. These mismatches can have cascading effects throughout the food web, impacting predator-prey relationships and the availability of food for higher trophic levels, including commercially valuable fish species.

Pilot Whales and Feeding
Pilot whales in the open waters around Guam primarily feed on squid. If rising temperatures alter squid distribution or abundance, pilot whales might need to expend more energy searching for food, impacting their health and reproduction.
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Calcium Carbonate Shells
Acidic waters pose a severe threat to calcifying organisms, such as shellfish and planktonic species like pteropods, which rely on calcium carbonate to form their shells and skeletons. Lower pH levels reduce the availability of carbonate ions, essential for shell formation, leading to weaker and more brittle shells. This vulnerability can reduce survival rates and impact species at the base of the marine food web.
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Ocean Acidification

Ocean acidification is caused by the absorption of excess atmospheric carbon dioxide (CO2) by seawater, forming carbonic acid. This process decreases the pH of the water, making it more acidic. The open ocean around Guam, being directly exposed to atmospheric changes, is particularly susceptible to these chemical shifts.

When atmospheric CO2 dissolves in seawater, it reacts with water molecules to form carbonic acid (H2CO3). Carbonic acid is unstable and quickly dissociates into bicarbonate ions (HCO3-) and hydrogen ions (H+). The increase in hydrogen ions lowers the pH of seawater, resulting in a more acidic environment. Additionally, these hydrogen ions can combine with carbonate ions (CO32-) to form more bicarbonate ions.

The reduction in available carbonate ions is critical because many marine organisms, such as shellfish and certain types of plankton, rely on carbonate ions to form their calcium carbonate (CaCO3) shells and skeletons.

Nutrient Cycling and Productivity

As the surface waters around Guam warm due to rising temperatures, the density difference between warmer surface waters and cooler, deeper waters increases. This creates a more stratified water column, where layers of water with different temperatures (and therefore different densities) form distinct strata that do not mix easily.

In a stratified water column, the lack of vertical mixing means that nutrient-rich waters from the deep cannot easily rise to the surface. Deep waters are typically rich in nutrients such as nitrates, phosphates, and silicates, which are essential for the growth of phytoplankton (the primary producers in the ocean).

This can lead to reduced upwelling. Upwelling is a process where deep, nutrient-rich waters are brought to the surface, typically driven by wind and ocean currents. Warmer surface temperatures can weaken these upwelling processes, further limiting the supply of nutrients to the surface waters.

Some phytoplankton, such as cyanobacteria (blue-green algae), can fix atmospheric nitrogen into forms usable by other organisms. Ocean acidification can inhibit this nitrogen fixation process, reducing the overall availability of nitrogen in the ocean, which is a critical nutrient for marine life.
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Next Generation Science Standards Alignment

LS1.A: Structure and Function – Organisms have structures that serve different functions, such as streamlined bodies and fins for efficient movement
LS1.D: Information Processing – Marine organisms demonstrate a variety of senses beyond the typical 5, and their hunting strategies involve information processing.
LS1.C: Organization for Matter and Energy Flow in Organisms – Adaptations in respiratory systems, such as gills and swim bladders, allow marine organisms to efficiently intake oxygen.
LS4.C: Adaptation – Organisms have specific adaptations that allow them to thrive in different environments, such as low oxygen or anaerobic conditions.

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