🐠Marine Biology Unit 10 – Marine Ecology and Ecosystems

Key Concepts and Definitions

• Marine ecology studies the interactions between marine organisms and their environment, including both biotic (living) and abiotic (non-living) factors
• Ecosystems are complex networks of interactions among organisms and their physical surroundings (coral reefs, kelp forests)
• Biodiversity refers to the variety of life at all levels, from genes to ecosystems, and is essential for ecosystem stability and resilience
• Trophic levels describe the position of an organism in a food chain or food web, with primary producers at the bottom and apex predators at the top
  • Primary producers (phytoplankton, seagrasses) convert sunlight into organic matter through photosynthesis
  • Consumers (zooplankton, fish, marine mammals) feed on other organisms to obtain energy and nutrients
• Ecosystem services are the benefits that humans derive from ecosystems (food production, coastal protection, nutrient cycling)
• Anthropogenic impacts are the effects of human activities on the environment (overfishing, pollution, climate change)

Marine Ecosystem Types

• Coastal ecosystems are found in the shallow waters near the shore and include estuaries, salt marshes, mangroves, and seagrass beds
  • Estuaries are semi-enclosed bodies of water where freshwater from rivers mixes with saltwater from the ocean (Chesapeake Bay)
  • Salt marshes are coastal wetlands dominated by salt-tolerant plants (cordgrass) that provide habitat for many species
• Coral reefs are underwater structures built by coral polyps that support high levels of biodiversity and provide essential ecosystem services
• Open ocean ecosystems are vast and deep, with distinct zones based on depth and light penetration (epipelagic, mesopelagic, bathypelagic)
• Hydrothermal vents are deep-sea ecosystems that support unique communities of organisms adapted to extreme conditions (high temperatures, toxic chemicals)
• Polar ecosystems are found in the Arctic and Antarctic regions and are characterized by cold temperatures, seasonal ice cover, and specialized adaptations of marine life

Physical and Chemical Factors

• Temperature affects the distribution, metabolism, and behavior of marine organisms, with many species adapted to specific temperature ranges
• Salinity is the concentration of dissolved salts in seawater and varies depending on factors such as evaporation, precipitation, and freshwater input
• Light penetration decreases with depth, limiting photosynthesis and primary production to the upper layers of the ocean (photic zone)
• Nutrients (nitrogen, phosphorus, iron) are essential for the growth and reproduction of marine organisms and can be limiting factors in some ecosystems
  • Upwelling is the process by which deep, nutrient-rich waters are brought to the surface, stimulating primary production (Humboldt Current)
• Ocean currents transport heat, nutrients, and organisms across vast distances and influence global climate patterns (Gulf Stream)
• Tides are the regular rise and fall of sea levels caused by the gravitational pull of the moon and sun, creating intertidal zones with unique adaptations

Biodiversity in Marine Ecosystems

• Marine biodiversity is estimated to be higher than terrestrial biodiversity, with many species yet to be discovered
• Biodiversity is not evenly distributed, with hotspots of diversity found in tropical regions (coral reefs) and areas of high productivity (upwelling zones)
  • The Indo-Pacific region is home to the highest diversity of coral reef species, with over 600 species of coral and 2,000 species of fish
• Endemism refers to species that are found nowhere else on Earth and is common in isolated ecosystems (Hawaiian Islands)
• Genetic diversity within species is important for adaptation to changing environmental conditions and resilience to disturbances
• Functional diversity describes the variety of ecological roles played by different species in an ecosystem (herbivores, predators, decomposers)
• Biodiversity loss is a major concern, with many marine species threatened by human activities such as overfishing, habitat destruction, and climate change

Trophic Interactions and Food Webs

• Food chains are linear sequences of organisms, each feeding on the one below it and being eaten by the one above it
  • A typical marine food chain might include phytoplankton, zooplankton, small fish, larger fish, and apex predators (sharks, seabirds)
• Food webs are more complex networks of feeding relationships that include multiple food chains and account for omnivory and detritivory
• Trophic cascades occur when changes in the abundance of one species (sea otters) have ripple effects throughout the food web (kelp forests)
• Bottom-up control refers to the influence of primary producers on the abundance and diversity of higher trophic levels
• Top-down control refers to the influence of predators on the abundance and behavior of their prey
• Energy transfer between trophic levels is inefficient, with only about 10% of the energy from one level being passed on to the next (trophic pyramid)

Ecosystem Functions and Services

• Primary production is the process by which autotrophs (phytoplankton, seagrasses) convert sunlight into organic matter, forming the base of marine food webs
• Nutrient cycling is the movement of essential nutrients (nitrogen, phosphorus) through ecosystems, mediated by biological and physical processes
  • Nitrogen fixation is the process by which atmospheric nitrogen is converted into a form that can be used by organisms (cyanobacteria)
• Carbon sequestration is the removal of carbon dioxide from the atmosphere and its storage in marine sediments and biomass (blue carbon)
• Coastal protection is provided by natural barriers such as coral reefs, mangroves, and seagrass beds that absorb wave energy and reduce erosion
• Fisheries are an important source of food and livelihood for millions of people worldwide, with many communities dependent on healthy marine ecosystems
• Tourism and recreation are major economic activities in coastal areas, with coral reefs and other marine ecosystems attracting millions of visitors each year

Human Impacts and Conservation

• Overfishing has led to the depletion of many fish stocks and the collapse of some fisheries (Atlantic cod)
  • Bycatch is the unintended capture of non-target species (sea turtles, dolphins) in fishing gear and is a major threat to marine biodiversity
• Habitat destruction, such as the clearing of mangroves for aquaculture or the dredging of seagrass beds for coastal development, reduces the availability of critical habitats for marine life
• Pollution, including nutrient runoff, plastic debris, and oil spills, can have devastating effects on marine ecosystems and the organisms that depend on them
  • Eutrophication is the excessive growth of algae due to nutrient pollution, leading to oxygen depletion and dead zones (Gulf of Mexico)
• Climate change is causing ocean warming, acidification, and sea level rise, with far-reaching consequences for marine ecosystems and human communities
• Marine protected areas (MPAs) are a key conservation tool, providing refuge for marine life and allowing for the recovery of degraded ecosystems
• Ecosystem-based management is an approach that considers the entire ecosystem, including humans, in the management of marine resources and the mitigation of threats

Research Methods and Tools

• Remote sensing techniques, such as satellite imagery and underwater acoustics, allow for the monitoring of marine ecosystems at large scales
• Oceanographic instruments, such as CTDs (conductivity, temperature, depth) and ADCPs (acoustic Doppler current profilers), measure physical and chemical properties of seawater
• Biological sampling methods, such as trawls, nets, and underwater visual censuses, are used to study the distribution, abundance, and diversity of marine organisms
  • Environmental DNA (eDNA) is a novel approach that uses genetic material in water samples to detect the presence of marine species
• Tagging and tracking technologies, such as satellite tags and acoustic telemetry, provide insights into the movements, behavior, and habitat use of marine animals
• Ecosystem modeling is used to simulate the complex interactions and dynamics of marine ecosystems and to predict their responses to environmental changes and human impacts
  • Ecopath with Ecosim (EwE) is a widely used ecosystem modeling software that integrates food web dynamics, fisheries, and environmental factors
• Citizen science initiatives engage the public in data collection and monitoring efforts, increasing awareness and participation in marine conservation (iNaturalist, Reef Check)