Marine Ecosystem Notes

Marine Ecosystem

Overview

• Marine ecosystems are aquatic ecosystems with high salt content.
• They are the most prevalent type of ecosystem on Earth.
• They are teeming with life and provide nearly half of the Earth’s oxygen.
• They provide a home for a wide array of species.

The Ocean's Role

• Seven-tenths of the Earth's surface is covered by ocean.
• The oceans drive our climate system:
  • They absorb approximately half of all solar energy around the equator.
  • This powers currents that extend to the poles.
  • Wind fields follow these currents.
• Oceans provide much of the air we breathe via microscopic phytoplankton:
  • These populations perform half of all photosynthesis.
  • They comprise less than 1% of global biomass.
• Oceans absorb some of the additional $CO_2$ produced by human activity, lessening the impact of global warming.

Marine Zones

Intertidal Zone

• Also known as the foreshore, seashore, or littoral zone.
• The area between high and low tide marks.
• It is above water at low tide and underwater at high tide.

Pelagic Zone

• The water column of the open ocean.
• Divided into regions by depth.
• The word "pelagic" is derived from the Greek word pélagos, meaning 'open sea'.

Abyssal Zone

• A layer of the pelagic zone of the ocean.
• 'Abyss' derives from the Greek word abussos, meaning bottomless.

Benthic Zone

• The ecological region at the very bottom of the sea.
• Includes the sediment surface and some subsurface layers.

Corals

Definition

• Marine invertebrates in the class Anthozoa of phylum Cnidaria.
• They live in compact colonies of identical individual polyps.
• Reef builders inhabit tropical oceans and secrete calcium carbonate ($CaCO_3$) to form a hard skeleton.

Coral Reef Formation

• Coral reefs begin to form when free-swimming coral larvae attach to submerged rocks or other hard surfaces along the edges of islands or continents.
• Fringing Reefs:
  • Most common.
  • Project seaward directly from the shore.
  • Form borders along the shoreline and surrounding islands.
• Barrier Reefs:
  • Differentiated from fringing reefs based on the depth of the lagoon in the back reef (the area near to shore).
• Atoll Reefs:
  • Also called a coral atoll.
  • A ring-shaped coral reef, including a coral rim that encircles a lagoon partially or completely.

Symbiotic Relationship

• Most reef-building corals contain photosynthetic algae called zooxanthellae, which live in their tissues.
• The corals and algae have a mutualistic relationship.

Coral Bleaching

• Occurs when coral polyps expel algae that live inside their tissues.
• Causes:
  • Negative environmental conditions thwart the coral's ability to provide for the zooxanthellae's needs.
• Stressors Implicated in Coral Reef Bleaching:
  • Temperature
  • Solar Irradiance
  • Subaerial Exposure
  • Fresh Water Dilution
  • Inorganic Nutrients
  • Xenobiotics
  • Epizootics

Mangroves

Definition

• Salt-tolerant trees, also called halophytes.
• Adapted to life in harsh coastal conditions.

Types and Descriptions

• Black Mangroves (Avicennia germinans):
  • Easily identified by specialized roots for oxygen uptake.
  • Roots look like tubular bristles sticking out vertically, trapping oxygen for oxygen-starved root systems.
  • These bristles are known as pneumatophores.
• Red Mangrove (Rhizophora mangle):
  • An evergreen tree, growing to about 25 meters in height and 40 centimetres in diameter at breast height.
• White Mangrove (Laguncularia racemosa):
  • The shortest of the three species (reaches 5.6 meters and a diameter of 30 centimetres).
  • Have un-buttressed roots.

Reproductive Strategies

• Mangroves have unique reproductive strategies.
• They disperse propagules via water with varying degrees of vivipary (embryonic development while the propagule is attached to the parent tree).

Adaptations

• To Salinity:
  • Special salt-excreting glands on leaves.
  • Exclusion of salt from entering roots with water uptake.
• To Oxygen Uptake:
  • Special breathing roots to cope with water-saturated soils that limit gaseous exchange.

People and the Ocean

Demographics

• The ocean covers 140 million square miles (363 million square km), approximately 72% of the Earth's surface.
• More than 600 million people (around 10% of the world’s population) live in coastal areas less than 10 meters above sea level.
• Nearly 2.4 billion people (about 40% of the world’s population) live within 100 km (60 miles) of the coast.
• Oceans, coastal, and marine resources are especially important for people in coastal communities, representing 37% of the global population in 2017.

Economic Significance

• About 97% of the world’s fishermen live in developing countries, and fishing is their major source of food and income.
• Women account for most of the workers in secondary marine-related activities such as fish processing and marketing.
• The ocean-economy is estimated at between US3-6 trillion/year.
• Fisheries and aquaculture contribute US100 billion per year and about 260 million jobs to the global economy.
• Shipping is responsible for more than 90% of trade between countries.
• The global oceans-based economy is estimated at US$$3 trillion a year, around 5% of global GDP.
• Approximately 50% of all international tourists travel to coastal areas.

Problems of Marine Ecosystems

Overview

• The oceans are a major resource but are undergoing serious stress.

Specific Problems

• Siltation (Siltification):
  • Pollution of water by particulate terrestrial clastic material.
  • Particle size is dominated by silt or clay.
  • Causes: erosion on land or activities in the water.
• Trawl Fishing:
  • Pulling a fishing net through the water behind boats.
  • Controversial due to environmental impacts.
  • Bottom trawling causes large-scale destruction: coral shattering, habitat damage, seaweed removal.
• Purse Seining:
  • Uses a purse seine, with rings along the bottom, to capture schooling fish near the surface.
  • Effects: Accidental catching of marine mammals (dolphins, seals).
• Red Tide:
  • A common name for algal blooms (large concentrations of aquatic microorganisms).
  • Caused by a few species of dinoflagellates, giving the bloom a red or brown color.
  • May deplete oxygen in the waters and/or release toxins harmful to humans and other animals.
• Other Problems:
  • Climate Change: Coral bleaching, rising sea levels, changing species distributions.
  • Oil & Gas: Prospecting and drilling pose a major threat to sensitive marine habitats and species.
  • Pollution: Untreated sewage, garbage, fertilizers, pesticides, industrial chemicals, plastics harm the entire marine food chain.

Example of Pollution Incident

• A Philippine-flagged vessel the MT Terra Nova carrying 1.4 million litres of industrial fuel sank in rough seas off the Bataan province in the Philippines on 25 July.
• Global emissions of plastic into the ocean - geospatial distribution of plastic entering the ocean through rivers.

Protecting Marine Ecosystems

• United Nations Convention on the Law of the Sea (UNCLOS)
• The Sustainable Development Goals (SDG 14)
• Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES)
• Marine Protected Areas (MPAs)
• National Integrated Protected Areas System (NIPAS) Act
• The Fisheries Code of the Philippines (Republic Act No. 8550)
• Coral Triangle Initiative (CTI)
• The Clean Water Act (Republic Act No. 9275)