Coral Reef Ecology

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Smith Lab at Scripps Institution of Oceanography
Updated: 7 hours 17 min ago

These Three Reefs Are Not Like Each Other

Thu, 04/09/2015 - 12:33pm

By Maggie Johnson

Representing the Smith coral reef ecology lab in Moorea, French Polynesia.

Representing the Smith coral reef ecology lab in Moorea, French Polynesia.

My field work entails a combination of field and laboratory experiments. Field work is utterly exhausting; working in and on the water for all daylight hours and then in the lab for what remains of the day. But one of the things I love the most about being a marine biologist with field based research is the opportunity to travel and essentially live on the reefs I study. I am back at the Smith lab after an epic 6 months in the field. This last push to collect data for my dissertation involved 3 weeks on Palmyra Atoll, followed by 3 months on Coconut Island at the Hawaii Institute of Marine Biology, and then 1.5 months in Moorea, French Polynesia. My head is still spinning from the travel and long hours in the field, and as the dust settles and I collect my thoughts, I think back to these unique places. With memories of each reef still fresh in mind, I can’t help but think that a coral reef is not a coral reef… is not a coral reef. Spending hours underwater on each reef every day for weeks on end really gave me the chance to realize how different, and yet how similar, coral reefs across the ocean can be.

My research trip started off with the Smith lab research expedition to Palmyra Atoll in the Northern Line Islands (http://www.palmyraresearch.org/). Palmyra Atoll in uninhabited, except for a small research station that maintains not more than 30 staff and researchers at a time. The isolated nature of the atoll, roughly 1,000 miles south of Hawaii, make it the ideal location to study coral reefs in the absence of direct local human impacts. Jumping in the water at Palmyra, you’re likely to see lots of top predators, like sharks and jacks, and the bottom covered by a wide variety of coral species and calcifying algae. These reefs are generally considered among the healthiest coral reefs remaining on the planet.

The fore reef off the northwestern tip of Palmyra Atoll

The fore reef off the northwestern tip of Palmyra Atoll

The shallow reef terrace with many different corals and top predators.

The shallow reef terrace with many different corals and top predators.

The next stop on the tour du tropical Pacific was Coconut Island located in Kaneohe Bay on the island of Oahu. I had the pleasure to work as a visiting research in the lab of Dr. Ruth Gates (http://www2.hawaii.edu/~rgates/Gates_Lab_Website/Gates_Lab.html). The reefs of Kaneohe Bay are in stark contrast to Palmyra, partly due to major differences in the origin and types of reef (Palmyra is an Atoll, Kaneohe consists of fringing, patch and fore reefs off a high volcanic island). Kaneohe Bay has also historically been heavily impact by local human activities, and in the 1970’s there were alarming issues of nutrient pollution from sewage and land runoff into the bay. Additionally, there are differences in reef communities that are typical to reefs of the main Hawaiian islands, such as overall lower coral diversity. On top of these inherent underlying differences, my experience of Kaneohe Bay reefs was marked by a mass bleaching event. My timing was just so that I arrived at the start of a massive bleaching even that wreaked havoc on corals throughout the Hawaiian Islands. Kaneohe Bay experienced temperatures as warm at 31°C for several days in a row. This thermal stress caused many of the corals to expel their symbiotic partners (zooxanthellae) resulting in a process called coral bleaching. Bleaching often results in mortality for many, but not all corals. I had the unique opportunity to assist surveys of bleaching and coral recovery across Kaneohe Bay during my visit. Jumping in the water at Kaneohe Bay, you are likely to see a few dominant species of coral, interesting invertebrates like sea cucumbers and urchins, and lots of macroalgae. And you’re more than likely to run into some sea turtles!

A patch reef in Kaneohe Bay with low coral diversity and its resident sea turtle.

A patch reef in Kaneohe Bay with low coral diversity and its resident sea turtle.

An example of coral bleaching (white).

An example of coral bleaching (white).

The third stop in my travels was Moorea, French Polynesia. I did research for my MS degree at Cal State Northridge (http://www.csun.edu/~mbgsclub/) in Moorea, so this was much like returning to my ‘home’ reef. Moorea is similar to Hawaii in that it is also a high volcanic island. The reefs of Moorea, however, are characterized by a much higher diversity of coral species and overall less macroalgae. Jumping into the water on Moorea you’re likely to see many species of colorful corals, lots of colorful parrotfishes, and a variety of both fleshy and calcified macroalgae. My first trip to Moorea was in 2006, as part of the Three Seas Program with Northeastern University (http://www.northeastern.edu/cos/mes/experiential-education/three-seas/). Interestingly, I noticed that 9 years later there are some major differences in the coral reef community… but that is a story for another time.

The fore reef on the north shore in Moorea, French Polynesia.

The fore reef on the north shore in Moorea, French Polynesia.

A coral outcropping on the back reef of the north shore in Moorea, French Polynesia.

A coral outcropping on the back reef of the north shore in Moorea, French Polynesia.

While I sift through the data I collected during my epic journey, I think back to these three interesting and unique locations. Palmyra, Kaneohe and Moorea are all very different from each other. I wonder how we can ever really understand a coral reef when they vary so widely in composition and structure within even one geographic region of the ocean? This is a question that many coral reef scientists often think of when trying to make broad generalizations from relatively focused experiments at one or a few locations, and one that I am still trying to find the answer to. A reef is not a reef, and I am grateful I had the opportunity to spend time at each of these reefs in order to fully understand how different, yet similar, coral reefs can be.

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The Sargassum horneri Invasion at Catalina Island

Mon, 03/16/2015 - 3:54pm

By Niko Kaplanis

In April of 2006, during a survey for the Channel Islands Research Program (CIRP), renowned scientists Kathy Ann Miller and John Engle discovered an established population of the invasive alga Sargassum horneri near the Wrigley Marine Science Center at Santa Catalina Island. This was the first instance of the species being documented at one of California’s offshore islands. Reconnaissance surveys spurred by this initial discovery then revealed established populations at San Clemente Island in May of 2007, and subsequently, populations have been discovered throughout the rest of the Channel Island chain. S. horneri has now become very well established at Catalina, expanding its range to occupy the entire leeward (north) side of the island, as well as some locations on the more exposed and native-algal dominated south shore, and flourishing through multiple generations.

A thick wall of Sargassum horneri, some plants reaching more than 2 m in length

A thick wall of Sargassum horneri, some plants reaching more than 2 m in length

In the past month I visited Catalina to assist with ongoing research on the S. horneri invasion at Catalina lead by Lindsay Marks, a PhD student at UC Santa Barbara. Lindsay has undertaken a heroic effort — conducting monthly surveys at sites throughout the leeward side of the island and running multiple removal experiments—with the goal of tracking the invasion and providing detailed information on the ecology, life history, reproductive capacity, and impacts of this species.

 Sampling a quadrat.

Sampling a quadrat.

The visit provided mind-blowing insight into how dominant S. horneri can become at invasion locations. Each of the nine sites we dove was entirely dominated by thickets of the invasive alga growing in incredible densities extending from the shallow sub-tidal down to depths of 60 or 80 ft. Both the densities and abundances observed at Catalina far exceed those of San Diego, which may be a result of the longer invasion history at the island, a difference in the invasion environment, or some other as-of-yet unknown factor. The island is also starkly devoid of native Macrocystis pyrifera, the giant kelp that typically forms kelp forests along the island’s coast. While this phenomenon can’t be directly attributed to the Sargassum invasion – other factors such as persistently warm water ocean temperatures in the area are also likely in play—it is reasonable to assume that the invasion is contributing to it.

The thicket from above.

The thicket from above.

The thicket from below.

The thicket from below.

The island provides an exciting opportunity to study the invasion, and I am grateful to Lindsay Marks for inviting me to assist with her research. Whether the population will remain persistent in the current densities and spatial abundances, and whether an invasion on the scale observed at Catalina will occur elsewhere is unclear, but her work is sure to provide some insight into these questions.

One of the few sites still dominate by native macroalgae.

One of the few sites still dominate by native macroalgae.

 

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The Faces and Functions of Algae on the Reef

Fri, 02/27/2015 - 12:30pm

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

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Adventure in Puerto Morelos, Mexico

Mon, 02/09/2015 - 10:53am
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.

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