Coastal ecology Study Guide

📖 Core Concepts Marine coastal ecosystems: Highly productive, biodiverse zones extending to the outer continental shelf. Habitat types: Intertidal zones, estuaries, lagoons, coral reefs, seagrass meadows, mangrove forests, salt marshes, kelp forests. Ecosystem services: Nutrient cycling, water purification, carbon sequestration (blue‑carbon), coastal protection, fisheries nursery grounds, recreation. Key drivers of change: Pollution (eutrophication), overfishing, coastal development, climate change (sea‑level rise, warming, acidification), invasive species. Food‑web dynamics: Top‑down (predators) vs. bottom‑up (primary productivity) forces; trophic cascades alter habitat structure and carbon storage. Seascape connectivity: Movement of organisms, nutrients, and sediments among mangroves, seagrasses, and coral reefs; essential for nursery‑to‑adult life‑stage transitions. Regime shift: Abrupt, large‑scale change in ecosystem structure/function, often triggered by combined climate and fishing pressures. --- 📌 Must Remember Productivity gradient: Intertidal → estuary → lagoon → reef/seagrass/mangrove → open ocean (decreases). Blue‑carbon hotspots: Mangroves, salt marshes, seagrass meadows store > 50 % of coastal carbon in sediments. Eutrophication pathway: Nutrient excess → algal blooms → reduced light → loss of macrophytes → hypoxia. Trophic cascade rule: Remove apex predator → herbivore boom → habitat loss (e.g., urchins overgraze kelp). Key nutrients: Nitrogen (N) & phosphorus (P) drive primary production in coastal waters. TURFs (Chile): Exclusive seafloor rights → aim to reduce overharvest; success limited by enforcement. Seascape principle: Protecting habitat corridors (e.g., mangrove‑seagrass‑reef) boosts fish abundance inside MPAs. --- 🔄 Key Processes Carbon sequestration in vegetated habitats Photosynthesis → biomass → burial in anoxic sediments → long‑term storage. Eutrophication cycle Runoff (N, P) → phytoplankton bloom → respiration → O₂ depletion → benthic mortality. Trophic cascade Predator removal → mesopredator increase → primary producer decline → habitat degradation. Seascape connectivity flow Nursery (mangrove/seagrass) → juvenile migration → adult habitat (reef) → spawning → larval dispersal → settlement back to nurseries. Regime shift trigger Persistent stress (e.g., overfishing + warming) → crossing threshold → new stable state (e.g., kelp forest → algal barren). --- 🔍 Key Comparisons Mangroves vs. Salt Marshes Location: Tropical/subtropical intertidal vs. temperate low‑energy shorelines. Dominant plants: Aerial‑root trees vs. herbaceous cordgrass. Coral Reefs vs. Kelp Forests Water chemistry: Warm, nutrient‑poor vs. cold, nutrient‑rich. Primary producers: Symbiotic zooxanthellae vs. large brown algae. Estuaries vs. Lagoons Water exchange: Strong tidal mixing (estuaries) vs. limited exchange, often barrier‑separated (lagoons). Top‑down vs. Bottom‑up control Driver: Predator pressure vs. nutrient/primary productivity. --- ⚠️ Common Misunderstandings “All coastal habitats sequester the same amount of carbon.” – Sequestration rates vary; mangrove soils are far deeper and store more carbon than kelp can. “Eutrophication only harms algae.” – It cascades to loss of seagrass/kelp, hypoxia, and fish kills. “Marine Protected Areas automatically restore fish stocks.” – Without connectivity to nurseries and enforcement, benefits are limited. “TURFs guarantee sustainability.” – Success hinges on compliance, monitoring, and adaptive governance. --- 🧠 Mental Models / Intuition “Habitat pyramid”: Think of coastal habitats as stacked layers of protection—each lower layer (e.g., mangroves) buffers the next (seagrass, reef). Removing a lower layer destabilizes the whole pyramid. “Fishing as a top‑down lever”: Visualize a lever where pulling (overfishing) lifts the predator side, causing a chain reaction down the food web. “Eutrophication as a feedback loop”: More nutrients → more algae → less light → fewer macrophytes → more nutrients released from sediments → loop intensifies. --- 🚩 Exceptions & Edge Cases Cold‑water coral reefs: Exist in nutrient‑rich, deeper waters—different from typical warm, oligotrophic reefs. Mangrove survival in high salinity: Some species tolerate near‑pure seawater; not all mangroves need freshwater input. TURFs in mixed‑use fisheries: May coexist with open‑access zones, creating “spill‑over” benefits or conflicts. Upwelling‑driven productivity: In some coastal upwelling zones, eutrophication risk is lower because rapid water exchange flushes nutrients. --- 📍 When to Use Which Assessing carbon storage → prioritize mangrove, salt‑marsh, and seagrass surveys; ignore coral reefs (low sediment carbon). Designing MPAs → use seascape connectivity maps to include nursery habitats and larval corridors. Diagnosing fishery declines → first check top‑down (predator loss) then bottom‑up (nutrient/primary productivity) indicators. Mitigating eutrophication → target land‑based nutrient sources (agricultural runoff) before marine interventions. --- 👀 Patterns to Recognize “Three‑zone intertidal pattern”: High → middle → low zones correspond to increasing submersion time and biodiversity. “Tri‑system interaction”: Presence of all three habitats (mangrove, seagrass, reef) usually signals high fish nursery productivity. “Shift from kelp to algal barren”: Look for simultaneous urchin surge and predator decline. “Hypoxia hotspots”: Occur near eutrophic estuaries with limited water exchange (lagoons, sheltered bays). --- 🗂️ Exam Traps Distractor: “Coral reefs are major carbon sinks.” → True carbon fixation occurs, but long‑term storage is minimal compared to vegetated habitats. Misleading choice: “Overfishing only reduces fish biomass.” → It also triggers trophic cascades affecting habitat structure and carbon storage. Near‑miss: “All seagrass loss is caused by direct trampling.” → Nutrient overload and reduced light are primary drivers. Confusing statement: “TURFs eliminate all illegal fishing.” → Enforcement gaps can still allow poaching. ---