The ecological roles of algae in the ocean are critical to the sustainability of all life on earth. The single-celled microscopic group of algae called phytoplankton produces at least half of the earth’s oxygen. These tiny organisms are also a major food source for many animal species. They transfer vital energy manufactured during photosynthesis to an extensive food web that stretches across diverse marine habitats. Any change in the ocean’s chemistry or physical structure could have a profound effect on these important organisms.
In effect many of these species function as environmental indicators. A sudden change in population could suggest the presence of an environmental stressor in its early stages. Scientists became aware of the effects of climate change when coral reefs showed acute signs of bleaching. Instead of the bright colors associated with coral animals they turned a skeletal white. This was an indication that they had lost their symbiotic algae called zooxanthellae. A slight change in water temperature can initiate this bleaching phenomenon. The algae provide essential nutrients to the coral so if they don’t recover their symbionts, the coral can die. Once that happens the complex coral reef ecosystem can collapse and many dependent species will perish. Unfortunately as world temperatures increase due to climate change, bleaching incidents have also increased.
Algae can act as local indicators as well. A population bloom of sea lettuce (Ulva lactuca) is indicative of increased nutrient runoff. The water surface is covered with this microscopic species and can create an unhealthy situation when it begins to decompose. The bacteria responsible for decomposition consume the dissolved oxygen in the water resulting in respiratory challenges for benthic species including mollusks and crabs. And unless they can swim to more oxygenated waters fish kills can result as well.
Algae are also habitats for a wide array of tiny invertebrates including bryozoans, worms and hydroids. They can shelter small animals at low tide and prevent desiccation. They are sources of food via direct herbivory or secondarily as a source of detritus. The presence of a diverse population of algae is often seen in a stable ecosystem.
Algae evolved millions of years ago and today colonize most habitats on earth. They are the dominant plant-like organisms in the ocean and play a significant role in the ecology of the marine environment.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.