Marine plants

• Categories: Algae; microorganisms; pollution; water-related life

Water is essential to life. The earliest plants, primarily algae, formed in bodies of saline water covering prehistoric Earth. During the Silurian period, approximately 441 million to 410 million years ago, some aquatic plants began to grow on land, but many plants remained solely water-based. These marine plants have provided fundamental nourishment in the food chain. No marine animals would have evolved or been able to survive if marine plants had not existed. Marine plants support all higher saltwater life-forms. Marine sediments formed by algae often contain fossils that reveal aspects of marine plants’ evolutionary history. The distribution of marine plants was affected by plate tectonics as continents moved and ocean shapes changed.

Oceans cover most of the earth’s surface. About 2.2 million species live in oceans, about 90 percent of which remain undescribed or yet to be categorized. As a result, oceans are significant to the well-being of life and economies. Marine plants consist of two major types: the sea grasses and the algae and seaweeds. Seagrasses represent members of some of the more complex plants, while algae and seaweeds display simple forms and are often microscopic.

Marine plants range from tiny single-celled organisms to large, intricate forms. Because all marine plants require sunlight to manufacture food, they mostly develop near water surfaces. Nutrients are also gathered from particles that currents wash up from sea floors. Marine plants can adapt to specific conditions, such as limited light and underwater caves. Some are phosphorescent, generating chemical lights.

Types

The smallest marine plants are phytoplankton, which are single-celled and form the basis of the marine food chain. Diatoms (Bacillariophyta) are glassy microscopic cells that frequently link together in chains. Few marine plants are angiosperms, although along tropical coasts, flowering marine plants often accumulate. Green algae (Chlorophyta) is the most common marine plant. Chlorophyll causes these algae to have bright green coloring. When algae leaves calcify, they add layers to ocean sediments. Botanists believe that 200,000 algae species exist, even though only 36,000 have been identified.

Red algae (Rhodophyta), tinted by the pigment phycoerythrin, are the largest type of marine plants and the most diverse. Some red algae adhere to corals, thus creating reefs. Both green and red algae species prefer warm water to cold water. In contrast, brown algae (Phaeophyta), colored with fucoxanthin pigment, are usually found in cold or temperate water, and few species live in the tropics. On reefs, brown algae frequently are the dominant organisms. Blue-green bacteria, or cyanobacteria (formerly called blue-green algae), are photosynthetic bacteria and can be microscopic, converting nitrogen from the atmosphere into forms that most marine plants can use.

Habitats

Marine plants live in diverse habitats near shores or in salt marshes and open seas worldwide. Giant kelp, a seaweed found in the South Pacific, grows in groups in warm coastal waters. In contrast, sea ice algae live on floating ice sheets. Migrating marine plants drift in a variety of water conditions.

On reefs, marine plants have several roles. Primarily, marine plants, including macroalgae and sea grasses, provide nourishment and shelter for animals. Marine plants assist corals in constructing reefs; then some plants, such as coralline algae, hold the reefs intact.

Algae live inside marine animals. Coral tissues host several million algae per square inch, and these marine plants provide 90 percent of the nutrients needed by the coral. The symbiotic relationship is based on a cycle of coral enzymes that cause algae to release carbohydrates and algae to receive nitrogen from coral waste. Algae are shaded from intense sunlight by coral pigments. Algae also live in panels inside giant clams and in sponges and flatworms. In kelp bed forests, marine plants serve as food and habitats for such diverse animals as seals, eels, and octopuses. Marine plants also benefit from animals; for example, some can secure nitrogen from seabird guano.

Marine plants are vulnerable to pollution. Seagrass beds and reefs have been damaged by toxins or destroyed by industrial development projects. Dredging and harvesting coral injures marine plants. Fertilizers, pesticides, oils, radioactive material, sewage, and hazardous wastes are drained into oceans. Often tropical commercial fishers use explosives to stun fish, inadvertently destroying marine plant habitats. Sea grasses have died in Maryland’s polluted Chesapeake Bay.

Some scientists speculate that the growing ozone hole might place Antarctic marine plants at risk. Changing tides affect marine plant distribution because they alter water levels. Overfishing and acid spills intensify toxic sites. Toxins sicken fish, which develop cancerous tumors, and people who consume this diseased fish are often poisoned. Fungi and bacteria transported in freighters’ ballast water from other regions can harm marine plants; for example, slime molds kill turtle grass. Algae frequently develop fungi because excessive nitrogen causes them to produce amino acids and deplete carbon supplies. Marine plants can be relocated by shipping vessels and can overtake native plants in distant areas.

An overabundance of algae can smother coral reefs if the supply of nitrogen is not balanced. If coral becomes too warm and expels algae, the coral appears bleached white because the algae remove the coral’s energy and color source. When too much nitrogen floods an area, sometimes an algal bloom or toxic red tide occurs and can have devastating results. As algae multiply because of excessive nutrients, creating algal blooms, they usurp oxygen from other marine plants and organisms, which starve. In 1996 many Florida manatees were killed by a red algal tide. The next year, the US National Aeronautical and Space Administration’s Sea-Viewing Wide Field-of-View Sensor satellite began to detect concentrations of marine plants by using light wavelengths. From late 2017 to early 2019, a prolonged red tide bloom along Florida’s Gulf Coast severely harmed marine ecosystems, killing large numbers of fish and other ocean life, while also causing respiratory issues and $2.7 billion in economic losses.

Uses

The oceans represent 95 percent of the earth’s biosphere and affect planetary climatic conditions. Roughly half of the oxygen on Earth comes from the oceans, and oceanic phytoplankton plays a major role in this oxygen production process. Phytoplankton alone produces up to 20 percent of oxygen in the entire biosphere. The status of marine organisms’ health indicates environmental problems that humans and land organisms might encounter.

Humans have historically appropriated marine plants for medicinal uses. Because many marine plants have biotoxins, they are valuable for the development of pharmaceuticals. Using submersible technologies, oceanographers gather samples and cooperate with pharmaceutical manufacturers to seek new chemical compounds to combat disease. Because of the diversity and novelty of marine plants, scientists hope to offer new treatments for diseases resistant to existing nonmarine-plant-derived drugs. Future marine sanctuaries are envisioned to protect such potentially potent natural resources.

Marine plants have also been used as a source of nutrients. Algae with docosahexaenoic acid (DHA), a chemical usually found in human milk and vital to infants’ brain development, are commercially processed. Approximately 40 percent of baby formula is made from these algae. The algae Dunaliella bardawil contains the orange pigment beta-carotene, which the human body converts into vitamin A. Commercial production of this algae manufactures carotene. Red algae are the chief ingredient of some seaweed drinks and are also useful as thickeners for cooking.

Other commercialization of marine plants includes harvesting seaweed for a variety of products, including foods and fertilizer. Researchers aspire to transfer proteins identified in Dunaliella bardawil, which resist extreme saltiness and sun exposure, to land plants that are cultivated in places with high salinity and sunlight conditions.

In an attempt to reduce crop losses, scientists study the physiological relationship of algae and water for optimum cell growth and photosynthesis to understand how such terrestrial plants as corn can manage moisture better, thereby withstanding droughts. Researchers conduct molecular examinations of marine and land plants to comprehend how water supply influences growth rate and metabolism. The cells of the alga Chara corallina are large enough that scientists can easily observe how dehydration affects them over a short time period.

Marine plants have a direct relationship to Earth’s climate. Iron deficiencies can be detrimental when marine plants become anemic. Oceanic iron and plant absorption of carbon dioxide is connected to ice age cycles and global warming. Paleoceanographers investigated sediment samples to study the impact of a 150,000-year period of global warming that occurred fifty-five million years ago. They hypothesize that marine plants increased in number to remove atmospheric carbon dioxide and reduce temperatures but warn that modern emissions would be too great for similar resolution.

Bibliography

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