​Beach ocean science. Algae growing on rocks.

Beach ocean science. Algae growing on rocks. 🌊🌊🌊🌊🌊🔬🔬🔬🔬

Rocks with algae from magic Island lagoon

The How and whyAlgae is not dirt, it is actually a microscopic plant.  Believe it or not,algae is GOOD

Rocks near Waialae

Why is algae beneficial?  Because, it converts the byproducts of fish waste (Nitrogen and CO2) into Oxygen using the energy of light (Photosynthesis).  Fish hate waste, and love oxygen.

Total win/win situation!   In addition, many fish and other ocean life need or benefit from algae in their diets.


All algae require sunlight, water, nutrients, and carbon dioxide for growth. Through the process of photosynthesis, algae convert the carbon dioxide into glucose (sugar). 

The glucose/sugar is then broken down into fatty acids, which under normal conditions, are used to produce membranes for new algal cells. 
Algae blooms most likely the result from a combination of environmental factors including available nutrients, temperature, sunlight, ecosystem disturbance (stable/mixing conditions, turbidity), hydrology (water flow/ water storage levels) and the water chemistry (pH levels, salinity, carbon availability etc).
However the combination of factors that trigger and sustain an algal bloom is not well understood at currently and it is not possible to attribute algal blooms to any one specific reason. 

You can find algae growing on rocks that are in or near bodies of water. We frond ours at various lagoons & by cliffs over oceans

What Algae needs

  • Nutrients

Nutrients promote and support the growth of algae and Cyanobacteria. The eutrophication (nutrient enrichment) of water is considered as a major factor. The main nutrients contributing to eutrophication are phosphorus and nitrogen.
In the landscape, runoff and soil erosion from fertilized agricultural areas and lawns, erosion from water banks, river beds, land clearing (deforestation), and sewage effluent are the major sources of phosphorus and nitrogen entering water ways. All of these are considered as external sources. Internal origin of nutrients comes from the lake/ocean sediments. Phosphate attaches to sediments. When dissolved oxygen concentration is low in the water (anoxic), sediments release phosphate into the water column. This phenomenon encourages the growth of algae.

  • Temperature

Algae usually develop when water temperature is higher and there is increased light. In most places that would be spring time.  However in Hawaii due to more stable weather (it goes from 95° high in summer to 79° high in winter) and being surrounded by ocean water algae can grow most anytime.
The growth is sustained during the warmer months of the year in other areas.  Water temperatures above 77°f are optimal for the growth of Cyanobacteria.

  • Light

Blueish–green algae populations are diminished when they are exposed to long periods of high light intensity (photo-inhibition) but have optimal growth when intermittently exposed to high light intensities. These conditions are met under the water surface where light environment is fluctuating.

  • Stable Conditions

Most algae prefer stable water conditions with low flows, long retention times, light winds and minimal turbulence; other prefer mixing conditions and turbid environments.
Drought, water extraction for irrigation, human and stock consumption and the regulation of rivers by weirs and dams all contribute to decreased flows of water in our river systems. Water moves more slowly or becomes ponded, which encourages the growth of algae.


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