A pink water lily at Barton Arboretum and Nature Preserve in Medford, New Jersey. From: Barton Arboretum and Nature Preserve

by Trevor Regan

Summer is (finally) underway, bringing with it an influx of visitors to beaches and all manner of outdoor activities near our waterways. Life is in full swing beneath the water and just at its surface as well. Animals are migrating to or from warmer waters for mating and feeding seasons, and, just as on land, prolonged sunshine is spurring the growth and flourishing of aquatic plants and flowers. 

Marine and aquatic flora create some of the most serene environments on the planet. Picture a lake in golden hour coated by water lilies and hyacinths, with bees buzzing about their blooms and frogs leaping between lily pads. Picture submarine stands of seagrass swaying with the current as fish dart between the stalks. 

As fascinating as they are beautiful, aquatic plants are divided into three main categories: submerged plants, floating plants, and marginal or emergent plants. Submerged plants, as their name indicates, live below the surface of lakes, rivers, seas, and other bodies of water, and are an essential piece in aquatic ecosystems for the oxygen, shelter, and nutrients they produce, provide, and soak up. Most submerged plants propagate through roots and rhizomes, as with many terrestrial plants. A rhizome is an underground stem from which other roots branch off, almost like a major interstate highway that branches off to county and local roads. Some species, like hornwort, lack a root system, relying entirely on absorbed nutrients from the surrounding water to grow and reproduce. This makes them an especially popular choice for home aquariums. 

Floating plants also have two subcategories—floating-leaved and free-floating. Perhaps the most famous aquatic plant, the water-lily, is a floating-leaved plant. With their stems, stalks, blooms, and pads hovering atop the water, the roots of floating-leaved plants descend down the water column and into the floor, anchoring the plant in place on the surface. The water hyacinth is another popular floating plant, though they belong to the free-floating family, with distinctive deep purple roots that wade in the water. Since they are not attached to any soil or sediment, free-floating plants will drift with the wind or current. Enormous rafts of tangled hyacinth are a common sight across its habitat range, which has expanded from the waterways of its native South America to Asia, Europe, and the United States. In Bangladesh, hyacinth rafts are used as fertilizer for the nutrients they release. 

The final major category of aquatic plants is emergent plants. These are your reeds, irises, sedges, and rushes. They begin their lives below shallow waters in marshes and wetlands, rooted to the heavily saturated soil, and then “emerge” up from the surface of the water. Unhindered access to sunlight and relative stability allow emergent species to grow at an accelerated rate compared to their submergent and floating counterparts. Most appear tall and wispy, with light blooms that allow for the wind or insects to carry their seeds for pollination. Emergent plants are among the most resilient flora in the world, as they are uniquely suited to extract terrestrial, aquatic, and aerial nutrients, and have also had to adapt to the erratic, often harsh environments of wetlands, marshes, estuaries, and swamps. Wetland soil, for instance, is thick and holds very little oxygen. To counteract this, emergent plants developed tissues called aerenchyma, which absorb oxygen from the air and funnel it down to their root systems. As they relate to humans and wildlife, emergent plants are critical for erosion control and runoff control, and they create habitats and nesting areas for shoreline organisms. 

There are several threats to aquatic plants. Dredging involves removing sand, silt, and other material from the ocean floor or other bodies of water to prevent flooding, maintain navigation depth, clean contaminated environments, or replenish beaches. While these outcomes are generally beneficial, they exact a severe toll on submerged plant habitats. Rising turbidity, or the haziness of water, limits aquatic plants’ ability to photosynthesize, since less sunlight is able to reach them throughout their growth. Floating and emergent plants stand in the crosshairs of eutrophication, which occurs when a body of water is oversaturated with nutrients such as nitrogen and phosphorus. This creates harmful algal blooms and dead zones, as all of the oxygen that should be fueling the roots, stems, and blooms of water lilies, hyacinths, and reeds is soaked up by toxic green and red algae. All such threats are either man-made or a direct result of pollution. That being said, several organizations are committed to curbing the effects of turbidity and eutrophication and reestablishing aquatic plant habitats, including the Aquatic Gardeners Association, Aquatic Plant Management Society, and independent aquascape hobbyists.



Sources

https://www.1800flowers.com/articles/flower-plant-care/all-about-aquatic-plants

https://www.plantsforallseasons.co.uk/blogs/aquatic-plant-care/creating-a-balanced-aquatic-ecosystem-the-role-of-pond-plants

https://oceanservice.noaa.gov/facts/underwaterplants.html

https://www.biotechniques.com/plant-climate-science/plants-grow-their-own-snorkel-to-breathe-underwater/

A pair of rays gliding over a seagrass meadow. From: Popular Science

by Bethany Woo

Elaborately colorful coral reefs, vast expanses of kelp forests—these marine habitats provide some of the most iconic scenes for scuba divers and web surfers alike. Many travel the globe (or the documentary section on their preferred streaming service) just to get a glimpse at these breathtaking and exotic ecosystems. But what about the mowed-lawn suburban equivalent of the ocean? Seagrass meadows are wide-ranging habitats found along the coasts of almost every continent. Much like meadows you may have seen on land, they consist primarily of rooted grasses that grow with sunlight and produce seeds. These seagrasses, however, are designed for complete submersion in salty water. Physically the seagrasses provide a plethora of ecosystem services such as creating a buffer zone for strong waves, and protecting other sensitive habitats like reefs. They also create stability in the benthic zone, preventing erosion by holding onto sediments within their root system. Similar to emergent plants in marshes, the seagrass in these marine meadows also sequesters carbon. 

Because seagrasses efficiently trap sediments, along with decomposing fish, plankton, algae, and whatever else happens to drift between thin blades of green, microbes go to town eating up everything they can find in a process called aerobic remineralization. Microbes effectively sap all oxygen from the sediment in order to break down organic material. This lack of oxygen slows the rate of decomposition exponentially, meaning carbon normally released when organic material breaks down is trapped, then layered beneath more and more sediment. All plants require oxygen to flourish, so how does seagrass cope in an anoxic environment? The answer is aerenchyma! Aerenchyma are porous air spaces that can store and transport oxygen to the root tips, creating what some have called an oxygen “shield.” A deeply intricate process that works to create refuge for juvenile fish, invertebrates, turtles, manatees, and more.

So what is the status of these rolling (underwater) meadows? Truth be told, they have seen their fair share of anthropogenic horrors. Bottom trawling is a commercial fishing practice that utilizes a large net dragged on the ocean floor, which can decimate entire ecosystems, and seagrass meadows are no different. Human waste and runoff commonly accumulate in these habitats and essentially bury the seagrass, inhibiting growth. Sometimes eutrophication from this nutrient runoff causes algal blooms that suffocate seagrass by blocking sunlight and reducing the little available oxygen. Luckily, the economic benefits of seagrass meadows have not been lost on us humans. Our favorite commercial fish need nursery space to grow, and our most beloved marine ecotourism attraction, the sea turtle, needs seagrass fields to graze upon. Dollar signs aside, these meadows, according to Woods Hole Oceanographic Institute, harbor more than 40,000 fish in just one acre. Many seagrass meadows are already marine protected areas, and efforts are ongoing to propagate more meadows with seeds and seagrass sprigs. Seagrass meadows may not be as flashy as a fan coral, but they are truly beautiful ecosystems that may one day help to mitigate climate change if given the opportunity to thrive.

Sources

https://www.whoi.edu/ocean-learning-hub/ocean-topics/ocean-life/ocean-plants/seagrass-meadows/

https://ui.adsabs.harvard.edu/abs/2025EGUGA..2715655F/abstract

https://www.sciencedirect.com/science/article/pii/S0025326X24010907

The process of sequestering carbon. From: World Ocean Review

by Bethany Woo

Carbon dioxide (CO₂) is the main “greenhouse gas” that contributes to climate change and global warming by trapping heat in the Earth’s atmosphere causing temperature increases both in the ocean and on land. Although CO₂ is naturally released by living creatures (including humans) during exhalation, the rapid increase in unnatural releases of CO₂ due to humans burning coal, oil, and natural gas have exponentially boosted atmospheric CO₂ levels. In efforts to combat / counteract CO₂ increases and climate change, scientists are studying and exploring carbon sequestration.

Carbon sequestration is the process by which CO₂ in the atmosphere is captured and converted or stored in another form, preventing it from contributing to global warming. One of the largest natural carbon sequestration “sinks” (or absorbers) is actually the ocean! The ocean is able to capture, convert, and store carbon through a biological pump and a physical pump. The biological pump refers to when oceanic organisms, like phytoplankton and seaweed, photosynthesize, taking in carbon dioxide, before dying and sinking. This sinking carries carbon trapped in the tissues of these organisms to the bottom of the ocean, where they are then stored via sedimentation (buried by sediments). The physical pump refers to when gas exchange occurs between the ocean surface and atmosphere that dissolves CO₂ out of the atmosphere and into the ocean. The ocean does an amazing job of carbon sequestration, and is estimated to hold 40x more carbon than the atmosphere!

Unfortunately, humans have disrupted the ocean’s biological pump. Due to adding more CO₂ into the atmosphere, we have forced the ocean to absorb more CO₂, leading to ocean acidification which damages/degrades ecosystems like coral reefs and also decreases the ocean’s ability to absorb more CO₂. To help combat climate change, scientists are exploring ways to promote ocean carbon sequestration and artificially store more CO₂ in the ocean. These include abiotic approaches that rely on the physical or chemical processes and properties of ocean (i.e. artificially influencing ocean currents to cause downwelling and upwelling), as well as biotic approaches that rely on oceanic organisms in ocean to convert, capture, and sink carbon (i.e. restoring coastal wetlands, cultivating seaweed).

https://www.usgs.gov/faqs/what-carbon-sequestration

https://ocean-climate.org/en/awareness/the-ocean-a-carbon-sink/

https://www.wri.org/insights/ocean-based-carbon-dioxide-removal