Coastal Marine Ecosystems Comprehensive Review

Spatial Classification and Characteristics of Ocean Zones

• Coastal (Neritic) Zone     - This zone is recognized for having the Greatest Biodiversity in the ocean.     - Key ecosystems within this zone include coral reefs, seagrass beds, kelp forests, and oyster reefs.     - The entirety of the coastal zone overlaps with the photic zone, ensuring light availability throughout.     - While it accounts for only $10\%$ of the ocean's total area, it contains $90\%$ of the ocean’s biodiversity.     - It is permanently underwater and extends from the low tide mark out to the edge of the continental shelf.

• Epipelagic (Photic) Zone     - Defined as having enough light for photosynthesis to occur.     - This zone accounts for the greatest overall production of oxygen and glucose globally.     - High productivity is attributed to the large surface area and the presence of phytoplankton.

• Mesopelagic (Twilight) Zone     - This zone receives some light during the day, but the intensity is insufficient for photosynthesis to take place.

• Bathypelagic (Midnight) Zone     - This zone is permanently dark.     - Many organisms residing here utilize bioluminescence to produce their own light.

• Abyssopelagic Zone     - Characterized by the lowest light and highest pressure among the primary vertical zones.     - Note: The Abyssal Zone specifically refers to the benthic (bottom) zone between $4,000$ and $6,000\,m$.     - The majority of the ocean floor consists of the abyssal plain.     - Conditions include extreme darkness, deep depths, cold temperatures, and high pressure.     - There are no primary producers due to the lack of sunlight.     - Organisms depend on "marine snow" (sinking decaying organic material from upper layers) or deep-sea sulfur vent food sources.

• Hadopelagic Zone     - The deepest ocean zone, which includes the world's deep-sea trenches.     - The deepest point on Earth is the Challenger Deep within the Mariana Trench, located in the Hadal zone.

• Intertidal Zone     - The area located between the high tide and low tide marks.     - It is a relatively narrow band that experiences extreme environmental variations throughout a single day, including changes in salinity, sunlight, temperature, water availability, and exposure to air.     - It is sometimes entirely submerged and sometimes exposed to the atmosphere.

• Pelagic Zone     - Defined as the free-swimming zone of the open ocean.     - It is subdivided vertically into the epipelagic, mesopelagic, bathypelagic, abyssopelagic, and hadopelagic zones.

River Mouths, Estuaries, and Coastal Geography

• Classification of River Mouths     - Delta: A fan-shaped landform where sedimentation dominates the landscape.     - Estuary: A funnel-shaped area where tidal forces cause freshwater and saltwater to mix, resultantly creating brackish water.

• Geography of New York City Waterways     - NYC rivers are categorized as Tidal Estuaries and Straits.     - Hudson River: An estuary that extends as far north as Albany.     - East River: Classified as a tidal strait.     - Harlem River: Classified as a tidal strait.     - All three are characterized by brackish water, which is a mixture of freshwater from land-based rivers and saltwater from the ocean.     - These areas represent Ecotones, which are transition areas where two distinct biological communities meet and integrate.

• Oyster Reefs     - Oysters are classified as bivalve mollusks.     - They thrive in brackish estuarine habitats where freshwater river inputs mix with saltwater.     - Oysters function as a Keystone Species because they establish the physical substrate and habitat for numerous other organisms.     - Their role is disproportionate to their abundance in establishing the structure and stability of the ecosystem.

Intertidal and Transitional Ecosystems

• Rocky vs. Sandy Shores     - The type of shore is determined by wave action.     - Wave action dictates the extent of weathering, erosion, and deposition.     - Rocky shores are characterized by stronger wave action than sandy shores.

• Salt Marshes     - Coastal saltwater wetlands that are regularly flooded by the tides.     - Vegetation is dominated by herbs, grasses, and shrubs, but notably contains no trees.     - Cordgrass: A primary producer that performs photosynthesis and serves as food for consumers (herbivores).

• Biological Roles in Coastal Ecosystems     - Primary Producers: Organisms like cordgrass that synthesize their own food.     - Decomposers: Bacteria, which break down the remains of dead organisms into essential nutrients.

• Mangroves     - Salt-tolerant trees and shrubs categorizable into three main species:         - Red Mangroves: Found furthest into the water; they utilize rhizophores (prop roots) for stability.         - White and Black Mangroves: Utilize pneumatophores (aerial roots) for gas exchange, allowing them to survive in sediment with low oxygen conditions.     - Ecosystem Services provided by Mangroves:         - Flood protection (including protection against Tsunamis, also known as ‘harbor waves’).         - Providing fish nurseries.         - Preservation of biodiversity.

The Neritic Zone: Specialized Habitats and Biology

• Spatial Definition     - Extends from the low tide boundary of the intertidal zone to the edge of the continental shelf.

• Seagrass Beds     - Contain the only true angiosperms (flowering plants) that live entirely underwater.     - They provide a food source for many organisms, specifically including green sea turtles, which possess specialized beaks for consumption.

• Coral Reefs     - Extremely biodiverse habitats built upon corals.     - Corals: Animals in the Kingdom Cnidaria.     - Symbiosis: Corals host symbiotic algae called Zooxanthellae.     - Anatomy: Corals have stinging cells called cnidocytes which contain organelles called nematocysts used to sting prey.     - Nutritional Exchange: Corals provide safe internal conditions for the Zooxanthellae; in return, Zooxanthellae provide the corals with the majority of their food via photosynthesis.     - Nutrition Types: Corals exhibit both autotrophic nutrition (via Zooxanthellae) and heterotrophic nutrition (using stinging tentacles to catch food).     - Corals are typically found in shallow water because Zooxanthellae require light for photosynthesis.     - Ecosystem Services: Coral reefs support tourism, recreation, and food production.

• Calcium Carbonate ($CaCO_3$)     - Corals, bivalve mollusks (clams, oysters), and many plankton use $CaCO_3$ to construct their tough, rigid shells or exoskeletons.     - Building these structures becomes difficult as ocean pH drops due to ocean acidification.

Trophic Levels and Energy Flow

• Primary Producers (Autotrophs): Perform photosynthesis to make food/glucose available to the rest of the ecosystem.
• Primary Consumers (Herbivores): Organisms that consume primary producers.
• Secondary Consumers (Primary Carnivores): Organisms that consume primary consumers.
• Tertiary Consumers (Secondary Carnivores): Organisms that consume secondary consumers.
• Energy Flow: In food webs, arrows indicate the direction of energy flow and nutrient transfer (from the eaten to the eater).

Global Threats: Warming and Acidification

• Ocean Warming and Coral Bleaching     - Caused by increasing ocean temperatures resulting from the greenhouse effect and global warming.     - Corals have a narrow range of temperature tolerance.     - Mechanics of Bleaching: Prolonged temperature increases cause corals to expel their Zooxanthellae.     - The symbionts (Zooxanthellae) release Reactive Oxidative Species (ROS), which are damaging to the host coral cells.     - To protect themselves from ROS, corals release the algae from their cells.     - Without Zooxanthellae, corals lose their primary food source, leading to death and the loss of biodiversity.

• Ocean Acidification     - Caused by the ocean's absorption of $CO_2$.     - Chemical Process:         - $CO_2 + H_2O \rightarrow H_2CO_3$ (Carbonic acid)         - $H_2CO_3$ dissociates into $H^+$ (protons) and $HCO_3^-$ (bicarbonate).     - As the concentration of $H^+$ increase, the pH of the ocean decreases.     - Effect on Shell Building: Protons ($H^+$) released by carbonic acid consume carbonate ions ($CO_3^{2-}$). This leads to a decreased availability of carbonate, making it difficult for organisms to build or incorporate calcium carbonate ($CaCO_3$).     - Primary Cause: The combustion of fossil fuels, which releases $CO_2$ into the atmosphere, which is then absorbed by the ocean.

Keystone Species and Essential Vocabulary

• Sea Otters     - Considered a keystone species in kelp forests.     - They are vital for maintaining ecosystem structure and stability because they eat sea urchins.     - Without sea otters, sea urchins would overpopulate and destroy the ecosystem by eating and detaching the kelp.

• Acidity and pH Scale     - Measured on a scale of $0$ to $14$.     - $7$ is neutral; values below $7$ are acidic; values above $7$ are basic (alkaline).     - Ocean acidification is currently lowering the pH and making the ocean less alkaline, though it is not yet technically "acidic" (below $7$).

• Salinity     - A measure of the salt ($NaCl$) concentration.     - Saltwater (Ocean): Approximately $3\%$ salt.     - Freshwater: $0.1\%$ salt or less.