Understanding Eutrophication

• Eutrophication is a process, not a status of an ecosystem

Definition and Development

• Eutrophication, as a term, was coined by C.H. Weber in 1907 to describe a body of water enriched with nutrients leading to increased primary production.
• The suffix "Eu" signifies beautiful or good, and "trophòs" means nourishment.
• The optimistic intent behind the label has turned negative as the enrichment process has become problematic.

Nutrient Enrichment

• Organic and inorganic inputs to the sea boost phytoplankton production, which sustains the trophic web and fishing industries.
• The Seto Sea in Japan experienced a doubling of primary production and fishing yields between 1951 and 1980.
• Nutrient enrichment must be kept moderate because the quantity of fish harvested is directly proportional to nutrient increase only to a certain level.

Causes and Processes

• Eutrophication was historically a natural phenomenon.
• Nowadays, massive quantities of organic matter and inorganic nutrients from diverse sources promote eutrophication in marine coastal zones.
• These sources include direct discharge, fluvial networks, and sewage systems.
• Increased rainfall can lead to greater nutrient runoff into the sea due to maximum river floods.
• Eutrophication is driven by several definitions, including anomalous enrichment of coastal waters, exponential algae growth, and increased primary production coupled with organic matter accumulation.

Input-Response Model

• An increase in nutrients leads to increased phytoplankton production and algal biomass, which elevates the flow of organic matter to the seabed.

Conceptual Model

• Nutrients from external and internal sources fuel primary production.
• This results in an organic matter pool with labile and refractory components
• This will result in consumption/export and ultimate oxygen depletion leading to mortality and negative ecological consequences.

Environmental and Anthropogenic Factors

• Stratification and phytoplankton blooms are key indicators.
• Temperature increases paired with decreased salinity at the surface.
• Decreasing oxygen levels and the remineralization of organic matter as temperature decreases and salinity increases at the bottom contributes to eutrophication.

Causes of Eutrophication

• Fertilizers and detergents containing high levels of inorganic nutrients stimulate phytoplankton biomass.
• High inputs of allochthonous organic matter drives eutrophication, including sewage treatment plants that add biostimulant compounds such as vitamin B12.
• Enclosed harbors serve as sources of propagation, from which phytoplankton blooms can spread.
• Reduced or inhibited grazing, as well as tropical storms and hurricanes, are also causes, as is sea level rise.

Dystrophic impacts

• Eutrophication can result in dystrophy.
• Dystrophy indicates an environment is severely degraded and recovery timeline is compromised.
• Eutrophic semi-enclosed marine ecosystems can be affected by aging and are impacted by human activities, especially aquaculture.
• Dystrophy has been observed in places facing sewage drains, within harbours, and in areas exploited by mariculture.

Mediterranean Sea

• Eutrophication also occurs here
• Eutrophic and hypoxic hotspots have been identified in the Mediterranean Sea.

Cascading Effects

• Changes in nutrient levels cause cascading effects in coastal ecosystems, including modified primary production, benthic dynamics, and overall biodiversity.

Dead Zones

• Deoxygenation influences life processes from genes to ecosystems, nutrient budgets, biological productivity, and carbon fixation.
• Oxygen minimum zones (OMZs) have expanded extensively since 1950.
• Declining oxygen levels have affected over 500 sites in coastal waters where oxygen is recorded at <2 mg/L.
• Oxygen levels at the bottom of the Baltic Sea have decreased, with low-oxygen areas expanding to 60,000 km².

Species Replacement

• Posidonia beds are being replaced by Cymodocea and Caulerpa meadows in the Mediterranean.
• Water clarity decreases, and sedimentation increases.
• There is a lower presence of C. chromis.
• There will be an increase in mullets.
• Decreased oxygen concentrations in benthic ecosystems results in reduction and replacement of macro-meiobenthic species.
• Anoxic and hypoxic conditions lead to an increase in opportunistic species like Capitella capitata and dominance by polychaetes and bivalves.

Coral Reefs

• Tropical dead zones and mass coral mortalities are occurring on coral reefs.
• A trend from live to dead coral is noted in Bocas del Toro, Panama, due to seasonal anthropogenic hypoxia, low winds, high temperatures, and nutrient increases.
• Eutrophication causes a shift in community structure toward hypoxia-tolerant coral species Oxygenated coral reefs are affected, as well as hypoxic waters.

Global Distribution

• Eutrophication is prevalent worldwide, affecting coastal regions across the globe.

Mitigation Strategies

• Important strategies include reducing greenhouse gas emissions, nutrient runoff, and implementing environmental monitoring.
• Developing mitigation and ecosystem modeling is also important.
• Mitigating eutrophication and deoxygenation involves developing mitigation strategies to lessen their impacts, as well as identifying refuge habitats.

Management Strategies

• Ecosystem-based mitigation and adaption strategies are used to protect marine organisms and fisheries.
• It's important to create and maintain monitoring programs.

Mucilage

Basics

• Mucilage is a separate process from red tides, toxic algae blooms, and dystrophy, but these are related.
• Marine snow is ubiquitous in the world's ocean

Low vs high abundance of nutrients

• Multiple species in low abundance thrive when there isn't competition for nutrients
• High amounts of nutrients leads to few species thriving due to an imbalance of diatoms and an acceleration of dinoflagellates.

Red Tides

• Algal blooms were known as "miracles", not algal blooms, historically.

Examples of species

• Karenia brevis (Florida)
• Gonyaulax (California)
• Thalassiosira (Florida)
• Trichodesmium (Gulf of Mexico)
• N. scintillans (Indian Ocean, 2021)

Composition and formation

• Production is linked to algae response to stress.
• It is known for having polysaccharide exudates with colloidal properties.
• Polysaccharides have colloidal properties.
• Formation involves phytoplankton, bacteria, cyanobacteria, viruses, low nitrogen, and low protein.

Formation

• Key aspects in the creation of the viral infections:
  • Viral contribution
  • Aggregation mechanisms
    • gradual aggregation forms the mucilaginous masses and go through intermediate stages
  • Role of Zeolite A and carboxylic acids

Factors that create Mucilage

• Environmental
• Predatory pressure on phytoplankton
• Prokaryotes contribution
• Overall synergy in these factors

Mucilage Characteristics

• Mucilage appears in structural forms:
  • Flocks
  • Macroflocks
  • Webs
  • Stripes
  • False Bottom

Affects

• It affects sea floors and marine life, in particular sea life that has been negatively affected by a lack of oxygen

Sea Snot Identification

• Remote operated vehicles

Harmful Algal Blooms (HABs)

Basics

• HABs are linked with microalgae
• It causes negative consequences when they damage health and harm ecosystem function
• Can trigger very heterogeneous effects as as new species continue to emerge

Characteristics

• HABs are responsible for human intoxications, sometimes with up to 500,000 cases annually as well as marine animal mortality

Mitigating Algal Blooms

• Techniques ranging from mechanical control and chemical treatments are viable.
• Biological approaches, including using organisms such as pathogens, are viable.

Control strategies

• The Netherlands use filter feeders
• HABs can be affected in multiple stages including the use of Flocculation and clays

Dinophysis

• Dinophysis toxins has an impact of locations globally.

Pfiesteria piscicida

• Alga that caused havoc in North Carolina and Chesapeake Bay, causing damage to local fisheries.