Crocosphaera is a genus of cyanobacteria, single-celled organisms that get energy through photosynthesis. They are abundant in the world’s oceans and have a significant collective impact on marine chemistry despite their small size.
Unveiling Crocosphaera’s Cellular Identity
Crocosphaera belongs to a group of bacteria known as cyanobacteria, sometimes referred to as blue-green algae. The most well-studied species, Crocosphaera watsonii, measures between 2.5 and 6 micrometers in diameter, making it a member of the ocean’s picoplankton community. These spherical cells are rich in pigments like phycocyanin or phycoerythrin, which harvest light energy. Phycoerythrin-rich strains are adept at capturing the blue light that penetrates the clear waters of the open ocean.
A defining characteristic of Crocosphaera is its temporal separation of photosynthesis and nitrogen fixation. During the day, it performs photosynthesis, producing oxygen. At night, it switches to nitrogen fixation, a process inhibited by oxygen, by pausing its photosynthetic machinery.
Where Crocosphaera Thrives
Crocosphaera is found in warm, sunlit, and nutrient-poor regions of the open ocean, known as oligotrophic gyres. These areas are considered the deserts of the sea because they have low concentrations of nutrients like nitrogen and phosphorus. These cyanobacteria thrive in waters above 24 degrees Celsius, a condition met in tropical and subtropical oceans. Their distribution spans vast stretches of the Pacific, Atlantic, and Indian Oceans.
Light availability is a primary requirement, so they are concentrated in the euphotic zone, the upper layer of the ocean where sunlight penetrates. While adapted to low-nutrient conditions, their growth can be limited by the availability of phosphorus.
Crocosphaera’s Contributions to Ocean Ecosystems
Crocosphaera’s ability to perform nitrogen fixation is a major contribution to marine ecosystems. This is the process of converting atmospheric nitrogen gas (N₂), which is unusable by most organisms, into ammonia and other usable nitrogen compounds. This process provides a new source of nitrogen for the microbial community, fueling primary production by other phytoplankton and forming the base of the marine food web.
Through photosynthesis, Crocosphaera also contributes to the oceanic carbon cycle. Like plants, these cyanobacteria take up carbon dioxide from the atmosphere and convert it into organic carbon. This process removes a greenhouse gas and provides the building blocks for marine life, supporting everything from other microbes to larger fish.
Scientific Exploration of Crocosphaera
Scientists study Crocosphaera using field and laboratory methods. Researchers collect water samples from the open ocean to analyze the abundance and distribution of the cells. Cultivating these organisms in a lab setting is challenging because it is difficult to replicate the low-nutrient conditions of their natural environment.
Molecular techniques are also used to study Crocosphaera. Scientists can identify and quantify these cyanobacteria by detecting specific genes, such as the nifH gene involved in nitrogen fixation. This genetic information allows researchers to track different populations. On a larger scale, satellite imagery and oceanographic models help estimate their global distribution and activity, providing insights into their impact on ocean biogeochemistry. Ongoing research aims to understand how these microbes will respond to climate change and ocean acidification.