Monthly Archives: February 2015

The Faces and Functions of Algae on the Reef

By Samantha Clements

Algae, often referred to as “seaweed,” are underwater “plants” that, unlike land plants, lack a vascular system. Algae live underwater and obtain water, nutrients, and sunlight directly from the environment. Because algae don’t need a vascular system, they come in many shapes and sizes and may look very different from land plants. Some algae, such as Ventricaria (“Sailor’s Eyeball”), can exist as a single cell that can grow to be larger than 10 cm in diameter!

A large Ventricaria cell (~10cm) sits nested within a Pachyseris colony

A large Ventricaria cell (~10cm) sits nested within a Pachyseris colony

A large Ventricaria cell (~10cm)

Benthic scientist, Samantha Clements, takes a selfie in the reflective surface of a large Ventricaria specimen (~8cm)

For many people, algae on coral reefs are synonymous with environmental decline. Often the presence of algae is associated with terms such as “harmful algal bloom” and “eutrophication,” which imply the negative effects of too much algae in an environment. It’s true that under some conditions algae can grow uncontrolled and become a problem for reef-building corals, as they compete for both space and sunlight on the reef. One thing that can lead to an overgrowth of algae is an excess of nutrients in the water, either naturally from upwelling of nearby nutrient-rich waters, or from anthropogenic sources, such as agricultural runoff from land. These nutrients act as fertilizers for plants on the reef, allowing them to grow very quickly. Another thing that can cause algae to grow uncontrolled on a reef is release from the pressure of herbivory. This is often caused by overfishing in communities where reef fish and other herbivores, such as sea urchins, are consumed as an important source of dietary protein.
Algae, however, are very important to a healthy coral reef ecosystem under natural conditions. They provide important habitat for many small creatures and act as the base of the food chain that fuels the community of coral reef critters. Algae come in all shapes, sizes, colors, and textures and have about as many functions as faces! Halimeda, a bright green, segmented alga, has branches that contain calcium carbonate—these calcified segments become sand on the reef when they fall off and crumble. Crustose coralline algae (CCA) is a type of red, calcified algae that grows as a pink crust on the reef and is often referred to as the “cement of the reef” because it grows over loose bits of reef and essentially glues them together. It also provides a very important substrate for coral larvae to settle on. Turf is an assemblage of small, primarily filamentous, algae that grow as a dense mat. Turf is an important food source for herbivorous fishes and sea urchins, and fills most of the space on the reef where corals aren’t already growing. Many algae add to the natural beauty of the reef, such as the bright red blades of Peyssonnelia growing in shady overhangs, and the curly-cues of Padina growing between corals wherever there’s space.

This Phyllidia nudibranch makes its way through a dense bed of Halimeda

This Phyllidia nudibranch makes its way through a dense bed of Halimeda

Padina grows in beautiful curls that fill in the space between fingers of branching Porites

Padina grows in beautiful curls that fill in the space between fingers of branching Porites

Cyanobacteria is a type of algae that occurs naturally on reefs, but can become problematic (and often scary looking!) in large quantities

Cyanobacteria is a type of algae that occurs naturally on reefs, but can become problematic (and often scary looking!) in large quantities

In the Smith Lab, we often collect algae to make algal pressings for our herbarium, a collection of pressed and dried algae with information about the date and location each specimen is found. Algal pressings can be very beautiful, often resembling intricate watercolor paintings. They provide important information about which algae grow in various environments and act as a catalog of diversity for the places we’ve been.
While algae have the potential to become a nuisance, they are always part of a healthy reef community. There are natural fluctuations in the abundance of algae found on a reef, but the most important things we can do to ensure algae don’t get out of control are to protect our reefs from overfishing and pollution. The rest is up to nature!

Benthic scientist, Samantha Clements, photographs an algal specimen for collection

Benthic scientist, Samantha Clements, photographs an algal specimen for collection

A gelatinous red alga collected for identification

A gelatinous red alga collected for identification

Samantha organizes algal pressings from the Global Reef Expedition’s Herbarium

Samantha organizes algal pressings from the Global Reef Expedition’s Herbarium

Herbarium pressing of Caulerpa

Herbarium pressing of Caulerpa

Herbarium pressing of Padina

Herbarium pressing of Padina

Herbarium pressing of Portieria

Herbarium pressing of Portieria

Adventure in Puerto Morelos, Mexico

By Mike Fox

 

Last week I traveled south to Puerto Morelos, Mexico to participate in an intensive 3-week course about Light and Photosynthesis on Coral Reefs. Hosted by Dr. Roberto Iglesias-Prieto and the National Autonomous University of Mexico (UNAM), this class provides an incredible opportunity to study the photosynthetic physiology of corals, algae, and seagrasses. Our course is taught at the UNAM Institute of Marine Science and Limnology, located on the shores of the second largest barrier reef system in the world, the Mesoamerican reef.

The UNAM campus. Puerto Morelos, Mexico.

The UNAM campus. Puerto Morelos, Mexico.

I first learned about coral reefs while completing my undergraduate degree. During that time I spent almost two years living and working in the Caribbean. The turquoise waters and white sandy beaches were easy to fall in love with but it was the corals and the algae I learned about there that inspired my career as a marine scientist. I still think about those reefs and their familiar species of coral so I was very excited to return to the Caribbean after five years away.

Imagine my surprise when I first went out to the beach and found that it was practically buried in seaweed!! There are plenty of stories about the coral reefs in the Caribbean being completely overgrown by algae but even the worst reports hadn’t prepared me for this. However, after a bit of research, I am happy to report that this seaweed is not coming from the local reef. The brown alga that is covering the beaches is known as Sargassum natans, and shockingly it has traveled from hundreds of miles away!

The amount of Sargassum that has washed ashore over the past week is truly amazing. It also makes our walk to school a little more difficult on the narrow sections of the beach!

The amount of Sargassum that has washed ashore over the past week is truly amazing. It also makes our walk to school a little more difficult on the narrow sections of the beach!

Globally, 2014 was the hottest year on record. Unfortunately, in the Florida Keys these warm temperatures caused considerable coral bleaching. Although warm water temperatures can be harmful to corals, they are not necessarily bad for other organisms. While the corals in the Keys were bleaching, the Sargassum in the nearby Sargasso Sea was thriving. It turns out that the extreme productivity of the Sargassum population in the Sargasso Sea this year has caused far more algal biomass to wash ashore on beaches in the Caribbean than usual. During the summer months, wind and current patterns typically deposit some of this floating forest along the beaches of the northern Caribbean Islands. This year, however, extensive deposits of Sargassum have been reported as far south as Trinidad and as far east as Africa! So far, no one that I have spoken to here in Puerto Morelos can ever remember Sargassum deposits of this magnitude along the Mesoamerican reef.

With more Sargassum coming in each day, the beaches here look more like our beaches at home in California where we sometimes find them buried under kelp after big swell events. Although one thing is for sure, with themassive amount of Sargassum that has been washing ashore across the entire Caribbean region, the primary productivity of the Sargasso Sea is nothing short of awe-inspiring. Most of the resorts here are frantically trying to remove the seaweed from the beaches but from my point of view it serves as an impressive reminder of the wonders of nature. Thinking about how connected our marine ecosystems are, I can’t help but wonder if there will be any lasting impacts on the seagrass and reef systems just offshore. I guess we will just have to wait and see…

beach_removal

Many tourists come to the Mexican Yucatan to enjoy the miles of white sand beaches so the resorts are fighting a losing battle to keep their beaches clear of the seaweed.

boats

Pangas in the local harbor floating on a huge mass of Sargassum that washed ashore after a small storm.

scripps oceanography uc san diego