6. Coastal and Marine Systems Exhaustive Study Guide
Overview of the Global Marine Environment
General Statistics and Surface Coverage: * Approximately of the Earth’s surface is covered by sea water. * The average depth of the world's oceans is approximately . * Marine environments comprise of the available living space on the planet.
Biological Diversity: * Oceans are inhabited by representatives from almost every major taxonomic group of organisms.
Scientific Knowledge Gaps: * Human knowledge of the marine environment is extremely poor in comparison to our understanding of terrestrial environments.
Human Impact: * Soaring human populations have created unprecedented demands on global marine resources, as highlighted in the "BLUE PLANET 2" context.
Adapting to Life in the Sea: Oxygen and Respiration
Oxygen Availability and Saturation: * Atmospheric Oxygen: Air contains approximately oxygen. * Oceanic Oxygen: Concentration in the ocean depends on ocean-atmosphere gaseous exchange.
Solubility Factors: * At a temperature of and a pressure of , there is approximately of oxygen per liter of water.
Biological Influence: * Oxygen levels are further influenced by biological activity (e.g., photosynthesis and respiration).
Specialized Adaptations: * Due to the low concentration of dissolved oxygen compared to air, all marine organisms possess specialized organs, such as gills, to extract oxygen from the water.
Adapting to Life in the Sea: Light and Primary Production
Light Penetration: * Light diminishes progressively with depth and is completely extinguished at approximately .
Vertical Zonation of Light: * Euphotic Surface Layer: Extends from to . * Twilight Zone: Extends from to . * Aphotic Zone: Below , there is absolutely no light.
Biological Consequences: * Primary production is strictly restricted by light availability. * Consequently, the majority of marine life is found within the Euphotic zone. * Organisms living in deep-sea environments depend on food that sinks from the upper layers.
Sub-Saharan Sea Currents: Benguela and Agulhas
Current Characteristics: * Agulhas Current: Characterized by high biodiversity but relatively low abundance of individual organisms. * Benguela Current: Characterized by relatively low biodiversity but very high abundance of organisms.
Broad Environmental Effects: * These currents significantly affect rainfall patterns, the climate of the interior, human settlement patterns, and the distribution of marine resources.
Species Richness Gradient: * The richness of marine life (the number of different species) increases progressively from the Cunene River in Namibia, around the coast, and up toward Mozambique.
The Mechanics and Dynamics of Tides
Primary Causes of Tides: * Gravitational Attraction: Exerted by both the sun and the moon. * Centrifugal Force: Generated by the rotation of the Earth-Moon system.
Equilibrium of Forces: * Opposite forces maintain the position of the Earth and the Moon system. * Side Nearest the Moon: Gravitational Force (GF) is greater than Centrifugal Force (CF), pulling water toward the moon and creating a bulge. * Side Opposite the Moon: Centrifugal Force (CF) is greater than Gravitational Force (GF), pulling water away from the moon and creating a second bulge.
Tidal Cycle: * This dynamic results in two areas with water bulges and two areas with less water, leading to two high tides and two low tides daily.
Standard Tidal Benchmarks: * M.H.W.S.: Mean High Water of Spring tides. * M.H.W.N.: Mean High Water of Neap tides. * M.T.L.: Mean Tide Level. * M.L.W.N.: Mean Low Water of Neap tides. * M.L.W.S.: Mean Low Water of Spring tides.
Intertidal Stress Factors: * Immersion Gradient: Increasing stress for terrestrial species as they move toward the level of lowest tides. * Emersion Gradient: Increasing stress for marine species as they move toward the level of highest tides. * Biological Performance and Exposure: A graph indicates that individual survival, individual growth, and reproduction performance drop as the percentage exposure to air increases from to .
Sandy Beaches: Characteristics and Threats
Environmental Challenges: * Sandy beaches are mobile and dynamic environments. * Wave Energy and Sediment: Strong waves result in coarse sand; low-energy waves result in fine or muddy sediments. * Water Retention: Grain size determines the ability of the substrate to retain water, which is critical (NB) for burrowing organisms. * Substrate Stability: There is no stable or hard substrate, meaning there are no primary producers.
Trophic Roles: * Organisms are primarily filter feeders or detritivores. * Organisms must adapt by burrowing deep or moving up and down the beach with the tide.
Primary Threats: * Urban development. * Mining. * Off-road vehicles (banned in South Africa in 2007). * Pollution, specifically oil spills.
Rocky Shores: Adaptations and Pressures
Tidal Fluctuations: * The intertidal zone constantly fluctuates between immersion and emersion.
Physical Challenges: * Upper Shore: Primary challenge is exposure to air and potential desiccation (drying out). * Lower Shore: Primary challenge is exposure to powerful, high-energy waves.
Biological Factors: * Increased predation pressure is higher lower down the shore. * Competition for space is intense in the less physically demanding areas.
Specific Threats: * Global climate change. * Formal and informal human settlement. * Invasion by alien species. * Resource exploitation, particularly of Pyura stolonifera (red bait) and mussels. * Mining activities leading to sedimentation or diamond dredging.
Kelp Forests and Estuaries
Kelp Forests: * Location: Found only on the west coasts of Namibia and South Africa within the Benguela Large Marine Ecosystem. * Biodiversity: Comparable to rainforests; they support species such as abalone (Haliotis midae) and rock lobsters (Jasus lalandii). * Main Threat: Over-exploitation of economically valuable resources (abalone and lobster), making conservation non-negotiable.
Estuaries: * Definition: The meeting place of river and sea where fresh river water and salty sea water interplay. * Characteristics: Unique, highly productive, and rich in biodiversity. * Indicators: Physical nature is determined by Salinity and Temperature. * Case Example: The burrowing estuarine mudprawn Upogebia africana regulates its local environment's temperature by pumping water through its burrow. * Threats: Pollution, habitat loss/degradation, freshwater abstraction, upstream dams (reducing episodic flushing), shoreline development, introduced species, and unrestrained fishing.
Coral Reefs
Definition: Underwater ecosystems characterized by reef-building corals that provide habitats for diverse marine life.
Anatomy of a Coral Polyp: * Components include: Tentacles, Mouth, Mesenterial filaments, Gastrovascular cavity, Gonad, Gastrodermal tube (solenia), and a Calcium carbonate skeleton.
African Reef Locations and Types: * Tanzania: Outer fringing reefs, Inner fringing reefs, and Patch reefs. * Madagascar: Emergent fringing reefs, Emergent barrier reefs, Patch reefs, and standard Fringing reefs. * Reef Category Definitions: * Fringing Reefs: Grow near the coastline, separated by shallow lagoons. * Barrier Reefs: Parallel to the coastline, separated by deep/wide lagoons. * Patch Reefs: Grow up from the open bottom of the island, often small. * Atolls: Located in the middle of the sea.
Threat Levels on Africa's East Coast: * Threats vary by region (Eritrea, Ethiopia, Kenya, Tanzania, Mozambique, Djibouti, Somalia, Comoros, Madagascar, Seychelles, Mauritius). * Specific Threats: Tourism, climate change, ocean acidification, aquarium trade, resource exploitation, and plastic waste (micro and macro).
Marine Management and Protected Areas (MPAs)
IUCN Definition of an MPA: A clearly defined geographical space, recognized, dedicated, and managed, through legal or other effective means, to achieve the long-term conservation of nature with associated ecosystem services and cultural values.
South African MPA Context: * Prior to 2019: 25 declared MPAs (23 permanent coastal, 1 seasonal, 1 large Prince Edward Islands MPA). * Coverage: Mainland MPAs covered of the ocean area ( no-take). * Expansion (2019): 20 new MPAs gazetted on 23 May 2019, expanding total protection of mainland ocean territory to .
Benefits of MPAs: * of marine ecosystem types are represented. * Total area: . * They safeguard marine animals and habitats, acting as an "insurance policy" for the ocean economy. * Protect spawning and nursery areas for fish. * "No-take" zones allow populations to restock adjacent areas.
Case Studies in Marine Threats
Seismic Blasting for Oil and Gas: * Event: 2020 Shell application for blasting off the Wild Coast. * Method: High-powered air guns firing every seconds at . * Impacts: Noise affects sea life for kilometers. Mammals suffer hearing loss, masking of communications, and behavioral disturbances (feeding/breeding). It reduces commercial catch rates. * Conservation Concerns: The survey timing coincided with peak spawning and the migration of Southern Right, Humpback, and Bryde’s whales (often with calves). * Legal Ruling: A judge ruled against the blasting because affected communities with traditional fishing rights were not properly consulted, and potential "irreversible harm" was a reasonable concern.
Poaching in South Africa: * Target Species: Abalone (Haliotis midae) and West Coast rock lobster (Jasus lalandii). * Drivers of Poaching: Community marginalization (apartheid legacy), state failure, parallel authority structures, corruption, poor management, greed, drug dependency, and exclusion of traditional fishers from formal reform.
Over-exploitation and Resource Management: * Upwelling affects temperature, nitrates, and carbon content, influencing biodiversity. * Key commercial species: Pilchards, Anchovies, Hake, and Horse Mackerel.
Plastic Pollution
Global and Local Scale: * Global plastic production reached approximately million tonnes by 2015. * South Africa is among the top 20 countries mismanaging waste.
The Great Pacific Garbage Patch: * Weight: million tons. * Size: Twice the size of Texas ( feet deep). * Contains times more plastic than plankton.
Microplastics (KZN Study - Naidoo 2018 PhD): * High concentrations found on the urban coastline and coastal shelf of KwaZulu Natal. * Sites south of the harbor have highest concentrations. * Scientific Findings: Juvenile fish fed microplastics showed lower growth and survival rates, threatening future stocks in urban estuaries. * Trophic Transfer: Microplastics are ingested by seabirds, mammals, fish, and invertebrates. Abundance in SA anchovy and sardine is above median global values. * Human Health Gap: There is potential for microplastic transfer from fish to humans, but specific data on health impacts is currently lacking in the South African context.