6.4 Marine Ecosystems and Biodiversity
8 min read•august 14, 2024
Marine ecosystems are diverse and complex, ranging from to deep-sea vents. These environments support a wide array of life, each adapted to unique conditions. Understanding marine biodiversity is crucial for appreciating the ocean's role in Earth's systems.
Marine organisms have evolved fascinating adaptations to thrive in challenging environments. From osmoregulation to bioluminescence, these traits enable survival in extreme conditions. Species interactions and play vital roles in shaping marine communities and maintaining ecosystem balance.
Major Marine Ecosystems
Coral Reefs and Kelp Forests
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- Coral reefs are shallow, warm-water ecosystems dominated by reef-building corals that create complex habitats supporting high biodiversity
- Found in tropical and subtropical regions with clear, nutrient-poor waters (Caribbean Sea, Great Barrier Reef)
- Corals secrete calcium carbonate skeletons that form the foundation of the reef structure
- Provide shelter, food, and nursery grounds for a wide variety of fish, invertebrates, and other marine life
- are temperate, coastal ecosystems characterized by dense stands of large, brown algae (kelp) that provide shelter and food for diverse marine life
- Occur in cool, nutrient-rich waters along rocky coastlines (California, Australia, South Africa)
- Giant kelp (Macrocystis pyrifera) can grow up to 2 feet per day and reach heights of 100 feet or more
- Support a complex food web, including sea otters, sea urchins, fish, and invertebrates
Deep-Sea Communities and Other Marine Ecosystems
- , such as and , exist in the aphotic zone and rely on chemosynthetic primary production by microorganisms
- Hydrothermal vents occur along mid-ocean ridges where superheated, mineral-rich water escapes from the seafloor
- Cold seeps are found on continental margins where methane and other hydrocarbons seep from the sediment
- Chemosynthetic bacteria form the base of the food web, supporting unique assemblages of organisms (giant tube worms, clams, crabs)
- Other major marine ecosystems include , , , , and the open ocean ()
- Estuaries are transitional zones where rivers meet the sea, characterized by varying salinity and high productivity (Chesapeake Bay, Amazon River estuary)
- Salt marshes and mangrove forests are coastal wetlands that provide critical habitat for juvenile fish and protect shorelines from erosion and storms
- Seagrass beds are submerged meadows that stabilize sediments, store carbon, and serve as nurseries for many marine species
- Each marine ecosystem has unique physical and chemical characteristics, such as temperature, light availability, and nutrient levels, that shape its community structure and function
- Temperature influences metabolic rates, species distributions, and ecosystem productivity
- Light availability determines the depth of the photic zone and the vertical distribution of photosynthetic organisms
- Nutrient levels (nitrogen, phosphorus, iron) control and the abundance of and macroalgae
Adaptations of Marine Organisms
Morphological and Physiological Adaptations
- Marine organisms have evolved adaptations to cope with the challenges of their environments, such as high salinity, pressure, and limited light
- Osmoregulation mechanisms help maintain water balance in cells and tissues (salt glands in seabirds, specialized kidneys in marine mammals)
- Pressure-resistant proteins and membranes allow deep-sea organisms to function under extreme hydrostatic pressure
- Bioluminescence, the production of light by living organisms, is common in deep-sea species for communication, camouflage, and attracting prey (anglerfish, vampire squid)
- Adaptations can be morphological (e.g., streamlined body shapes for efficient swimming), physiological (e.g., osmoregulation to maintain water balance), or behavioral (e.g., vertical migration to follow food sources)
- Streamlined body shapes reduce drag and improve swimming efficiency in fast-moving predators (sharks, dolphins, tuna)
- Countershading, a color pattern with a dark back and light belly, helps fish blend in with the background when viewed from above or below
- Vertical migration allows zooplankton to feed near the surface at night and avoid predators by descending to darker depths during the day
Species Interactions and Keystone Species
- Species interactions, such as predation, competition, and symbiosis, play crucial roles in shaping marine communities and ecosystem dynamics
- Predation can control the abundance and distribution of prey species, leading to trophic cascades that affect the entire ecosystem
- Competition for limited resources, such as food and space, can drive niche partitioning and species coexistence
- Symbiotic relationships, including mutualism, commensalism, and parasitism, involve close associations between two or more species
- Examples of symbiotic relationships include the mutualism between coral polyps and zooxanthellae, and the commensalism between clownfish and sea anemones
- Coral polyps provide shelter and nutrients for zooxanthellae, while the algae supply the coral with oxygen and remove waste products
- Clownfish gain protection from predators by living among the stinging tentacles of sea anemones, while the anemones benefit from the clownfish's nitrogen-rich waste
- Keystone species, such as sea otters in kelp forests and parrotfish in coral reefs, have disproportionately large impacts on their ecosystems through trophic cascades and habitat modification
- Sea otters prey on sea urchins, which can overgraze kelp forests if left unchecked, leading to the formation of urchin barrens
- Parrotfish consume algae that compete with coral for space, helping to maintain the balance between coral and algal cover on reefs
Marine Biodiversity and Threats
Importance and Value of Marine Biodiversity
- Marine biodiversity encompasses the variety of life in the ocean, including genetic diversity, species diversity, and ecosystem diversity
- Genetic diversity refers to the variation in genes within a species, which enables adaptation to changing environmental conditions
- Species diversity is the number and relative abundance of different species in an ecosystem
- Ecosystem diversity describes the variety of habitats, communities, and ecological processes in the marine environment
- High biodiversity enhances ecosystem resilience, productivity, and the provision of ecosystem services, such as fisheries, coastal protection, and carbon sequestration
- Greater species diversity can buffer ecosystems against environmental perturbations and species loss
- Diverse ecosystems are often more productive due to niche complementarity and the efficient use of resources
- Marine ecosystems provide valuable services, such as food production, shoreline stabilization, and the regulation of climate and biogeochemical cycles
Major Threats to Marine Biodiversity
- Major threats to marine biodiversity include , habitat destruction, pollution, climate change, and invasive species
- Overfishing can lead to the collapse of fish stocks, trophic cascades, and shifts in community structure
- Excessive removal of top predators can release prey populations from predation pressure, leading to ecosystem imbalances
- Bycatch, the unintentional capture of non-target species, can threaten vulnerable populations such as sea turtles, sharks, and seabirds
- Habitat destruction, such as the degradation of coral reefs and coastal development, reduces the availability of critical habitats for marine organisms
- Coral reefs are threatened by , rising sea temperatures, pollution, and physical damage from fishing gear and anchors
- Coastal development, such as dredging, land reclamation, and the construction of seawalls, can destroy wetlands, mangroves, and other important habitats
- Pollution, including plastic debris, oil spills, and nutrient runoff, can have toxic effects on marine life and cause eutrophication and hypoxia
- Plastic debris can entangle or be ingested by marine animals, leading to injury, starvation, and death
- Nutrient runoff from agricultural and urban areas can stimulate harmful algal blooms and create oxygen-depleted "dead zones"
- Climate change impacts, such as ocean acidification and rising sea temperatures, can disrupt the physiology and behavior of marine organisms and alter ecosystem functioning
- Ocean acidification, caused by the absorption of atmospheric carbon dioxide, can impair the ability of calcifying organisms (corals, mollusks) to build their shells and skeletons
- Rising sea temperatures can cause coral bleaching, the expulsion of symbiotic algae from coral tissues, leading to coral mortality and reef degradation
- Invasive species, introduced through shipping, aquaculture, and the aquarium trade, can outcompete native species and disrupt ecosystem balance
- The lionfish, native to the Indo-Pacific, has become a major threat to coral reef ecosystems in the Caribbean and western Atlantic
- The European green crab has altered coastal habitats and displaced native species in North America, Australia, and South Africa
- Overfishing can lead to the collapse of fish stocks, trophic cascades, and shifts in community structure
Primary Productivity in Marine Food Webs
Primary Productivity and Energy Transfer
- Primary productivity in marine ecosystems is driven by photosynthesis by phytoplankton and macroalgae in the photic zone, and chemosynthesis by microorganisms in deep-sea environments
- Phytoplankton, microscopic algae that drift with currents, are responsible for approximately 50% of global primary production
- Macroalgae, such as kelp and seaweeds, are important primary producers in coastal ecosystems
- Chemosynthetic bacteria use chemical energy from hydrogen sulfide or methane to fix carbon dioxide into organic compounds
- The rate of primary productivity varies across marine ecosystems, depending on factors such as nutrient availability, light penetration, and water column stability
- Upwelling zones, where deep, nutrient-rich waters are brought to the surface, support high primary productivity (Peruvian upwelling, California Current)
- Oligotrophic regions, such as the open ocean gyres, have low nutrient concentrations and lower primary productivity
- Energy is transferred through marine food webs via trophic levels, from primary producers to primary consumers (herbivores), secondary consumers (carnivores), and higher-level predators
- Phytoplankton are consumed by zooplankton, small crustaceans, and filter-feeding organisms (copepods, krill, bivalves)
- Zooplankton and other primary consumers are eaten by small fish, jellyfish, and larger invertebrates
- Small fish and invertebrates are preyed upon by larger fish, seabirds, and marine mammals
- The efficiency of energy transfer between trophic levels is typically low (around 10%), limiting the number of trophic levels in marine food webs
- Much of the energy consumed by organisms is lost through respiration, heat, and undigested materials
- The low efficiency of energy transfer constrains the biomass and abundance of organisms at higher trophic levels
Trophic Cascades and the Microbial Loop
- The concept of trophic cascades illustrates how changes in the abundance of predators can indirectly affect the abundance and distribution of organisms at lower trophic levels
- In the North Pacific, the removal of sea otters by fur traders in the 18th and 19th centuries led to an increase in sea urchin populations and the destruction of kelp forests
- The reintroduction of sea otters has helped to restore kelp forests by controlling sea urchin numbers and allowing kelp to regrow
- The microbial loop, involving the cycling of dissolved organic matter by bacteria and their consumption by protists and zooplankton, plays a significant role in marine food web dynamics and nutrient recycling
- Bacteria consume dissolved organic matter released by phytoplankton, zooplankton, and other organisms
- Protists, such as ciliates and flagellates, graze on bacteria and are in turn consumed by larger zooplankton
- The microbial loop transfers energy and nutrients from the dissolved organic pool back into the classical food chain, increasing the efficiency of nutrient recycling and energy flow in marine ecosystems
Key Terms to Review (26)
Benthic invertebrates: Benthic invertebrates are animals without a backbone that live on or in the sediment at the bottom of aquatic environments, such as oceans, rivers, and lakes. These organisms play crucial roles in marine ecosystems by participating in nutrient cycling, providing food for various marine species, and contributing to the overall biodiversity of their habitats.
Biodiversity hotspots: Biodiversity hotspots are regions that are both rich in unique species and experiencing significant habitat loss. These areas are vital for conservation efforts because they support a large number of endemic species—organisms that are not found anywhere else on the planet—while facing threats from human activities such as deforestation, pollution, and climate change. Protecting these hotspots is crucial for maintaining global biodiversity and ecosystem health.
Catch Limits: Catch limits are regulatory measures that set the maximum amount of fish or marine species that can be harvested within a specific time frame, usually to ensure sustainable fishing practices. These limits are crucial for maintaining fish populations and protecting marine ecosystems from overfishing, which can lead to biodiversity loss and the collapse of fisheries. By controlling how much is taken from the ocean, catch limits help balance the needs of fishing communities with the health of marine ecosystems.
Cold seeps: Cold seeps are areas on the ocean floor where hydrocarbons, such as natural gas and oil, seep out slowly from the Earth's crust into the surrounding seawater. These unique ecosystems support a variety of specialized organisms that thrive in nutrient-rich conditions, contributing to marine biodiversity. Cold seeps play a critical role in nutrient cycling and are often associated with unique biological communities, making them important for understanding marine ecosystems.
Coral reefs: Coral reefs are underwater structures formed by the accumulation of coral polyps, tiny marine animals that secrete calcium carbonate to create a hard skeleton. These vibrant ecosystems are among the most diverse habitats on Earth, providing essential services to marine life and coastal communities while also being highly sensitive to environmental changes.
Deep-sea communities: Deep-sea communities refer to the unique ecosystems found in the dark, cold, and high-pressure environments of the ocean's depths, typically below 200 meters. These communities are characterized by a diverse array of organisms, many of which have adapted to extreme conditions, and they play a crucial role in marine biodiversity. Understanding these communities helps in comprehending the overall health and function of marine ecosystems and their response to environmental changes.
Ecosystem-based management: Ecosystem-based management is an approach to managing natural resources that considers entire ecosystems, including humans, rather than focusing on individual species or resources in isolation. This method emphasizes the interconnectedness of various components within an ecosystem and aims to balance ecological health with social and economic needs, especially in marine environments where biodiversity is crucial for resilience and productivity.
Estuaries: Estuaries are coastal areas where freshwater from rivers meets and mixes with saltwater from the ocean, creating a unique and highly productive ecosystem. These regions serve as vital habitats for a diverse range of species and act as nurseries for many marine organisms. The mixing of different water types in estuaries supports high levels of biodiversity and plays an essential role in nutrient cycling and filtering pollutants.
Hydrothermal vents: Hydrothermal vents are fissures on the ocean floor that emit heated water enriched with minerals, often supporting unique ecosystems. These vents play a crucial role in the Earth's geochemical cycles and offer insights into early life forms, suggesting that similar environments may have existed during Earth's formation and early history.
Kelp forests: Kelp forests are underwater ecosystems formed by dense growths of kelp, a type of large brown algae that thrives in nutrient-rich, cold coastal waters. These forests provide essential habitats for numerous marine species, playing a significant role in the overall biodiversity of marine ecosystems, and serving as a vital resource for coastal communities.
Keystone Species: A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. These species play a crucial role in maintaining the structure of an ecological community, influencing the population dynamics of other species and the overall biodiversity within that community.
Mangrove forests: Mangrove forests are coastal ecosystems characterized by salt-tolerant trees and shrubs that thrive in intertidal zones where saltwater and freshwater meet. These unique ecosystems provide vital habitats for a variety of marine and terrestrial species, playing a crucial role in biodiversity and coastal protection.
Marine protected areas: Marine protected areas (MPAs) are designated regions of the ocean where human activities are restricted or managed to conserve marine ecosystems and biodiversity. These areas are critical for protecting vulnerable species, habitats, and the overall health of marine environments, while also serving as a tool for sustainable resource management and ecological restoration.
Nutrient Cycling: Nutrient cycling refers to the movement and exchange of organic and inorganic matter back into the production of living matter. This process is essential for ecosystems as it ensures that vital nutrients like carbon, nitrogen, and phosphorus are continuously recycled through various biogeochemical cycles, sustaining life. The cycling of nutrients connects the various components of ecosystems, including living organisms, soil, water, and the atmosphere, maintaining their productivity and health.
Ocean acidification: Ocean acidification is the process by which the ocean becomes more acidic due to increased carbon dioxide (CO2) absorption from the atmosphere. This change in pH levels disrupts marine ecosystems and has significant implications for biodiversity, marine resources, and the global carbon cycle.
Ocean warming: Ocean warming refers to the increase in ocean temperatures due to climate change and the absorption of excess heat from greenhouse gases in the atmosphere. This phenomenon is closely linked to changes in marine ecosystems, affecting biodiversity, species distribution, and the health of ocean habitats. Ocean warming can disrupt the delicate balance of marine food webs and has significant implications for the overall health of the oceans.
Overfishing: Overfishing refers to the practice of catching fish from the ocean at rates faster than they can reproduce, leading to a depletion of fish stocks and threatening marine biodiversity. This practice disrupts the balance of marine ecosystems and can result in the collapse of fish populations, which impacts not only the environment but also the livelihoods of communities that rely on fishing for food and income.
Pelagic zone: The pelagic zone refers to the open ocean environment that extends from the surface down to the ocean floor, excluding coastal and benthic regions. This vast area is crucial for understanding ocean water properties, including temperature, salinity, and currents, as well as supporting a diverse range of marine ecosystems and organisms that contribute to overall ocean biodiversity.
Phytoplankton: Phytoplankton are microscopic, photosynthetic organisms found in aquatic environments, serving as the foundational producers in marine food webs. These organisms play a critical role in generating oxygen and absorbing carbon dioxide, contributing significantly to the overall health of marine ecosystems and biodiversity. As primary producers, phytoplankton are essential for supporting diverse marine life, making them a key component in understanding ecological dynamics.
Primary productivity: Primary productivity refers to the rate at which primary producers, like plants and phytoplankton, convert sunlight and nutrients into organic matter through photosynthesis. This process forms the foundation of the food web in marine ecosystems, supporting a diverse range of organisms and maintaining overall biodiversity. Understanding primary productivity is essential for grasping how energy flows through marine environments and impacts various ecological interactions.
Rachel Carson: Rachel Carson was an American marine biologist, conservationist, and author who is credited with advancing the global environmental movement through her groundbreaking book 'Silent Spring'. Her work highlighted the dangers of pesticide use and its detrimental impact on ecosystems, particularly marine life, influencing policies and raising awareness about biodiversity conservation, environmental regulations, and public health issues related to environmental degradation.
Salt marshes: Salt marshes are coastal wetlands that are flooded and drained by salt water brought in by the tides. These areas are characterized by the presence of salt-tolerant vegetation and play a crucial role in marine ecosystems by providing habitat, filtering pollutants, and protecting shorelines from erosion.
Sea level rise: Sea level rise refers to the increasing height of the ocean's surface, primarily caused by two main factors: the melting of glaciers and polar ice, and the thermal expansion of seawater as it warms. This phenomenon has significant implications for coastal regions, marine ecosystems, and global climate patterns, affecting everything from habitat loss to increased flooding in vulnerable areas.
Seagrass Beds: Seagrass beds are underwater ecosystems formed by flowering plants that grow in shallow marine waters. These habitats play a crucial role in maintaining marine biodiversity, providing food and shelter for various marine organisms, and contributing to the overall health of coastal environments.
Sustainable fisheries: Sustainable fisheries refer to fishing practices that maintain fish populations and their ecosystems at healthy levels, ensuring that fish stocks can replenish themselves over time. This approach balances the needs of the fishing industry with environmental health, promoting biodiversity and the resilience of marine ecosystems.
Sylvia Earle: Sylvia Earle is a renowned marine biologist, oceanographer, and conservationist known for her pioneering research and advocacy for marine ecosystems. Her work emphasizes the importance of ocean health and biodiversity, as well as the need for sustainable practices to protect these vital resources. Earle's efforts have significantly raised awareness about the threats facing marine environments, including overfishing, pollution, and climate change.