All About Algae

text and photos by Peter Vroom


Despite the nonflattering images of “pond scum” many people often associate with algae, marine algae (or macrophytes) have proven themselves to be among the most diverse, most ecologically important, most prevalent, and most beautiful organisms present in tropical reef systems. Their importance to the ecosystem is staggering: algae form the base of the food chain, occupy much of the available substrate, and help to oxygenate the water, allowing animal life to thrive. Additionally, without microscopic symbiotic algae living in healthy coral tissue, most corals would be unable to survive – a scenario that is becoming all too real as coral bleaching events (processes where stressed corals expel their algal symbionts) become more common.


Although large, fleshy algal forms are often the most recognizable floral components on reefs, tiny turf algae and crustose coralline red algae are also extremely prevalent and play significant roles in the ecosystem. Turf algae are the first to colonize vacant substrate and cover essentially every nonliving hard surface on the reef. Turf algae are also among the most important food source for herbivorous fish and invertebrates. Relatively fast growing crustose coralline red algae act as a glue that cements together loose components of the reef system, and serve as a settling surface for larval invertebrates and other algae. Without crustose algae holding everything together, much of the reef would be washed into deep water or onto shore during heavy winter storms.

Clearly, without algae there would be no tropical reef ecosystem, yet marine algae are among the least studied and least understood organisms on the reef. More research is sorely needed to catalog and quantify the species that are present on reef systems around the Pacific, and ecological studies are necessary to examine the role of these critical plants in reef ecosystems.

To accomplish these objectives, CRED is studying tropical reef algae to address the following questions:

•  What is the best way to quantify algal functional groups (macroalgae, crustose coralline algae, turf algae) in tropical reef settings? 
•  What species are present in each island ecosystem and in what quantity? 
•  Do changes in algal populations serve as a good environmental indicator of reef heath? 
•  How do algal diversity and abundance change over time? 
•  Can biogeographical hypotheses be formulated about algal dispersal and evolution using qualitative and quantitative data from island groups around the Pacific? 

A modified Rapid Ecological Assessment technique that incorporates the use of digital cameras and photoquadrats is our primary field method, which we will be employing on this cruise.