Aquatic pollution: Ecological Dynamics, Phytoplankton Diversity, and Environmental Pollution

Climate Dynamics and the El Niño Phenomenon

El Niño is a climate pattern characterized by the warming of surface waters in the Central and Eastern Pacific Ocean. These events typically recur every $2$ to $7$ years and can persist for approximately one year. The name El Niño, which translates from Spanish as "the boy" or "the Christ child," was coined by Peruvian fishers because the arrival of the western warm pool of water usually occurs around Christmas time.

Key characteristics and current observations include:

Significant ocean temperature anomalies, such as current readings in the Central Pacific reaching $3\,^{\circ}\text{C}$ higher than the historical average.
The emergence of "super El Niño" events, which may represent the largest temperature anomalies in the $80$ years of available scientific records.
Global impacts on weather patterns, including extreme heat (e.g., temperatures reaching $99\,^{\circ}\text{F}$ in Shop Town) and disruptions to the hydrologic cycle.

Environmental and economic consequences of El Niño:

Altered precipitation leads to reduced snowpack in regions like Denver and the Western US. This lack of snowmelt directly impacts the water levels of essential reservoirs, such as Lake Mead and Lake Powell, which have been declining for decades.
Drier ground conditions combined with high air temperatures significantly increase the risk and frequency of wildfires.
Economic losses in the tourism and recreation sectors, such as a drop in ski pass utility when insufficient snow prevents skiing.

Fundamental Ecological Concepts and Autotrophy

Organisms are categorized by their energy sources within an ecosystem. Autotrophs are organisms that produce their own organic compounds from inorganic sources.

Photoautotrophs: These organisms, including land plants and phytoplankton, utilize sunlight as their primary energy source for photosynthesis.
Chemoautotrophs: These organisms use energy derived from inorganic chemical reactions, a process known as chemosynthesis. For example, bacteria in hydrothermal vents oxidize reduced chemicals like hydrogen sulfide ( $H_2S$ ) to manufacture organic molecules.

Nutrient requirements for primary production:

Nitrogen ( $N$ ): Essential for the synthesis of amino acids and proteins.
Phosphorus ( $P$ ): Critical for nucleotides and energy transfer through $ATP$ .
Silicate ( $Si$ ): specifically required by diatoms to construct their cell walls, known as frustules.

Diversity and Adaptations of Phytoplankton

Phytoplankton represent the base of the marine food web and exhibit various shapes, sizes, and pigments.

Diatoms

Diatoms are a major group of phytoplankton characterized by silicate shells (frustules). They categorized by their shape:

Centric Diatoms: Circular or radial symmetry, such as Skeletonema and Chaetoceros.
Pennate Diatoms: Linear or elongated shapes, such as Nitzschia.

Many diatoms form chains or possess spines. These spines serve dual purposes:

Decreasing the sinking rate: Helping the organism stay near the surface to access sunlight for photosynthesis.
Detriment to grazing: Acting as an anti-grazing adaptation by making the diatoms difficult for zooplankton to ingest without irritation.

Dinoflagellates

Dinoflagellates are distinct for their complex genetics, possessing up to $10^{11}$ base pairs in their genetic code—significantly more than humans. While much of this DNA is non-coding, it reflects their ancient evolutionary history.

Dinoflagellates are often associated with Harmful Algal Blooms (HABs):

Red Tides: Discoloration of water (often red) caused by pigments like peridinin. The term "red tide" is considered a misnomer as the blooms are not caused by tides.
Karenia brevis: A specific dinoflagellate common along the Florida coast (Sarasota to Naples). It produces brevotoxins, which can be aerosolized, causing respiratory issues like asthma, or accumulate in the food chain, leading to human illness via fish consumption. These blooms cause billions of dollars in lost tourism revenue.

Trophic Dynamics and the Ecological Pyramid

Energy transfer in an ecosystem is visualized as an ecological pyramid, where each level represents a trophic level. Biomass (often measured as carbon) decreases at higher levels due to energy loss.

Energy loss occurs through three primary mechanisms:

Respiration: The process of burning organic carbon for energy, releasing $CO_2$ .
Heat: Energy lost as a byproduct of metabolic processes.
Excretion: Loss of energy through dissolved organic carbon (DOC) or solid waste (e.g., fecal pellets).

Categories of Zooplankton by size:

Microzooplankton: $10\,\text{to}\,100\,\mu\text{m}$ (e.g., protists, flagellates, ciliates).
Macrozooplankton: $100\,\text{to}\,500\,\mu\text{m}$ (e.g., copepods).
Megazooplankton: $> 1000\,\mu\text{m}$ (e.g., salps, chaetognaths).

The Efficiency of Transfer: Typically, $80\%$ to $90\%$ of energy is lost at each trophic transfer. Direct grazing food chains with fewer levels (e.g., the Peruvian upwelling: Diatom $\rightarrow$ Copepod $\rightarrow$ Sardine) are highly efficient compared to open ocean systems that may have six or more trophic levels.

Food Webs, Detritus, and the Microbial Loop

A food web is more complex than a simple food chain due to larval stages (e.g., barnacle zoea) and varied interactions. Two linked food chains operate simultaneously:

Grazing Food Chain: Based on living primary producers (phytoplankton) being consumed by herbivores (zooplankton).
Detritus Food Chain: Based on non-living organic matter (detritus). Detritivores, including suspension feeders (corals, sponges) and deposit feeders (sea cucumbers, worms on the benthos), consume these particles.

These chains are interconnected:

Waste and sloppy feeding from the grazing chain (DOC and fecal pellets) provide food for the detritus chain.
Recycling of nutrients (nitrogen, phosphorus) from the detritus chain fuels the grazing chain.

The Microbial Loop describes how bacteria utilize dissolved organic carbon (e.g., urea, amino acids). Bacteria have a lower half-saturation constant ( $K_s$ ), meaning they can take up nutrients at much lower concentrations than larger phytoplankton, allowing them to dominate in nutrient-poor environments.

Environmental Pollution and Biological Magnification

Pollutants impact organisms directly or through transfer across trophic levels.

Biological Magnification

This occurs when the ecological transfer efficiency of a pollutant ( $EP$ ) is higher than the ecological transfer efficiency of carbon ( $ET$ ).

Example Calculation: If $ET = 20\%$ and $EP = 60\%$ , the ratio of transfer is $3$ . Over three trophic transfers (e.g., level 2 to level 5): $3 \times 3 \times 3 = 27$ Thus, the pollutant concentration is $27$ times higher at level 5 than at level 2.

Notable Pollutants and Issues

Sewage: Raw sewage contains high levels of E. coli and Enterococcus. Historical dumping in Boston Harbor and Wollaston Beach led to closures lasting $20$ years because pollutants remain trapped in the sediments long after the source is removed.
Toxic Metals: Contaminants like lead ( $Pb$ ), cadmium ( $Cd$ ), and mercury ( $Hg$ ). Recent concerns include cadmium levels in dark chocolate from manufacturing machinery.
Thermal Pollution: Heated water from nuclear power plants reduces the solubility of gases. As temperature increases, the solubility of oxygen ( $O_2$ ) in water decreases, potentially stressing aquatic life.
Pathogens in Seafood: Filter feeders like oysters can concentrate bad bacteria (e.g., Vibrio vulnificus or Vibrio cholerae), especially in warm summer waters.