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!
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.
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!
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.
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!
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…
By Niko Kaplanis
In a recent collaboration with the Paul Jensen Lab here at Scripps, I travelled to the Northern Channel Islands to assist with collections for their research. The Jensen lab focuses on microbial distributions and interactions with marine plants and invertebrates as well as sequence-based approaches to the discovery of natural products from marine microbes. Our objective for the trip was to collect and identify as many algae and invertebrates as possible. The microbial communities growing in association with these samples were then to be processed and their genes searched for sequences which encode for the production of novel compounds.
My experience with local marine algal species — accrued from field work for my invasive algal project and through serving as a TA for Jen’s phycology lab– earned me the title of seaweed identification expert for the trip, and I was put in charge of collecting and identifying algae. The recent discovery of invasive Sargassum horneri on Santa Cruz Island in 2012 provided a second personal objective for the trip — to add our collection sites to the list of locations where invasive algae had been searched for in the islands. We were specifically looking for this invasive alga also because a recently collected sample of this species from Catalina turned up a genetic sequence which encoded for the production of polybrominated diphenyl ethers or PBDEs. These chemical compounds are typically anthropogenically produced for use in industrial flame retardants, but this discovery suggested that microbial communities potentially growing specifically with this species could be a natural source. These compounds are known to bioaccumulate in both humans and marine mammals and to cause adverse health effects, specifically reducing fertility and having hormone-disrupting effects on estrogen and thyroid hormones. As such, identifying natural sources of these compounds is an active and important area of research.
Our trip began in Santa Barbara Harbor where we loaded our gear onto the Conception, a dive boat operated by the dive charter company Truth Aquatics. Motoring overnight through the rough seas of the Santa Barbara Channel put us at San Miguel Island, the westernmost island in the chain. Through the course of the next four days we would travel east, diving the leeward side of every island in the chain, ending in Anacapa Island.
The diving in the Northern Channel Islands proved to be remarkable, with many marine reserves harboring healthy kelp forests home to a diverse array of invertebrate, fish, and algal species. We were also blessed with abnormally warm water and calm seas, producing a feeling that we were diving an area more akin to the tropics than the California coast. Collections went smoothly, and we were able to collect and identify roughly a dozen unique algae at each site. Interestingly, Sargassum horneri only occurred at Anacapa Island, an area where it had not been previously documented. Whether these samples will produce sequences for novel compounds is not yet known, though the processing of these samples will soon give us an answer. Contributing to this project was a blessing, and I feel very lucky to have been a part of it, and to have been able to nurture a collaboration within our diverse institution.
Jeffery B. Graham Perspectives on Ocean Science Lecture Series presents Dr. Jenner Smith
Check out Dr. Smith’s presentation here! http://www.ucsd.tv/search-details.aspx?showID=28675
Understanding how humans impact marine ecosystems is crucial to developing successful conservation strategies that protect the health of our ocean. Discover how Scripps marine ecologist Jennifer Smith and her team are conducting research relevant to solving human-induced problems in environments ranging from coral reefs to the waters off our shores.
By Adi Khen
As a first-time volunteer at the Smith lab, I got to be involved in one of the most exciting parts of data processing: drying, weighing, acidifying and, basically, slaughtering CAUs!
Let me explain… CAU stands for Calcification Accretion Unit, or in this case a set of two stacked PVC tiles that are used to measure carbonate accretion and successional development on coral reefs. Three years ago, PhD student Levi Lewis, installed 160 CAUs across 8 different reef sites on leeward Maui. Half of the CAUs at each site were “caged,” or enclosed in a stainless steel frame to prevent herbivory, while the rest were “uncaged.” Environmental characteristics at each site, such as temperature, light, pH, salinity, and sedimentation were also measured. By installing and later removing CAUs, researchers are able to sample reef communities without causing extensive damage to the reef.
This past summer, Levi removed all of his CAUs from the reef and brought them back to the lab. The macroalgae that had grown on the tiles, as well as the sediments that had collected on the tiles and the cryptic invertebrates that found shelter among them, were put into separate bags and frozen for future processing. All tiles were photographed for image analysis and then, our slaughterhouse was open for business.
We dried the tiles in a drying oven, weighed them, let them soak in acid until all of their calcified matter dissolved, scraped them, and then dried and weighed them again (the difference between the initial and final tile masses would then represent the amount of carbonate accretion). We also filtered out the remaining fleshy matter from each tile, dried it, and weighed it to find the amount of fleshy biomass on each tile. After several months of the lab reeking of acid, we were left with about 300 clean PVC tiles, and we moved onto our next subjects: the macroalgae and invertebrates.
Macroalgae samples were also collected from the tiles in Maui, and froze for later analysis. Well, we thawed them, sorted each CAU’s algae by type or species, dried them, and then weighed them individually. We could then compare not only the difference in macroalgal cover between sites, but also the density and diversity of the macroalgal communities.
As for the frozen invertebrates, we thawed them, too, sieved them into different size categories, and then identified and quantified the critters from each CAU. This would help us determine the diversity, abundance, and potential importance of cryptic invertebrates in benthic communities.
These days, though our slaughterhouse is no longer in session, we’re getting ready to photoanalyze the surfaces of each of the CAUs to get a better picture of benthic community development on Maui’s reefs.
Clint Edwards, et al. publication, Global assessment of the status of coral reef herbivorous fishes: evidence for fishing effects, has been selected as one of the most influential conservation papers of 2014!! Congratulations Clint & Smith Lab!!!