Impacts on Marine Life
Traditionally, impacts from wastewater pollution have been associated with human health, but the detrimental effects of wastewater pollution on marine life—and the indirect impacts they have on people—cannot be overlooked. Wastewater transports pathogens, nutrients, contaminants, and solids into the ocean that can cause coral bleaching and disease and mortality for coral, fish, and shellfish. Wastewater pollution can also alter ocean temperature, pH, salinity, and oxygen levels, disrupting biological processes and physical environments essential to marine life.
Wastewater pollution increases corals’ exposure to disease-causing viruses, bacteria, or other microorganisms, collectively known as pathogens. Outbreaks of two of the most common coral diseases, white pox and black band disease, have been linked to wastewater pollution. White pox is directly caused by the human gut pathogen Serratia marcescens, while black band disease is strongly associated with macroalgal cover that increases in polluted waters.
Nutrients are essential building blocks for marine life. However, excess nutrients from land-based sources of pollution—like agricultural runoff and wastewater—in the marine environment cause coral bleaching and disease, decreased coral reproductivity, decreased coral skeletal integrity, decreased coral cover and biodiversity, increased phytoplankton shading, and algal overgrowth. As shellfish filter nutrients from the water for shell and tissue formation, they also take in pathogens and other pollutants. Excess contamination can lead to declines in shellfish health. Ongoing nutrient loading and the resulting algal blooms can devastate coral reefs and coastal ecosystems and are predicted to increase in frequency and scale as a result of climate change.
Algal blooms consume oxygen and block sunlight that underwater plants need to produce oxygen, resulting in an environment with low levels of dissolved oxygen called hypoxia. As oxygen is depleted, fish and crabs will move away. Hypoxic environments can trigger coral bleaching events, leading to increased damage and decreased recovery capacity of corals. These oxygen-depleted environments are projected to increase in frequency and severity with climate change.
Nutrients in wastewater stimulate algal growth. The resulting algal blooms on the ocean surface block sunlight from reaching the zooxanthellae that photosynthesize to provide corals with food and oxygen. Without enough oxygen, corals cannot respire or produce the calcium carbonate needed to build their skeletons.
Algal blooms contribute to ocean warming and acidification, and can produce toxins that can kill fish, mammals, and birds, and may cause human illness or even death in extreme cases.
Solids and Other Contaminants
Wastewater also contains suspended solid materials—like decomposing plant matter, algae, minerals, and silt—that float in the water. In the ocean, these solids can:
- Block light. These solids float in the water, blocking sunlight. Depending on the amount and length of time the solids remain, this can result in decreased photosynthesis and coral growth.
- Distress corals. When these solids settle on corals, it causes physical stress including smothering, decreased food production, and reduced reproduction.
- Clog filters. Suspended particles are ingested by shellfish, clogging their filters.
- Decrease water clarity. The reduced water clarity also makes it harder for fish to find food and can disrupt reproduction.
Endocrine disruptors—compounds which impact the endocrine system—are a particularly concerning type of CEC. These include naturally occurring or synthetic hormones as well as chemicals produced for textile, plastic, household, or agricultural uses. Research has begun to show the ways that these pollutants cause harm to marine life:
- In low concentrations, antidepressants have been shown to impact fish behavior and cause mortality.
- Synthetic hormones and endocrine disruptors—like estrogen from birth control pills or parabens found in soaps—can impair reproductivity and contribute to aggressive tendencies in fish.
- Recent studies have identified endocrine disruptors that bioaccumulate in fish tissue.
- In corals, endocrine disruptors decrease the number of egg-sperm bundles and reduce growth rates.