By Samantha Clements.
This year, during the months of March and April, I conducted coral reef benthic surveys for the Khaled bin Sultan Living Oceans Foundation (KSLOF) in Chagos. Chagos is the largest archipelago in the world and lies within the British Indian Ocean Territory. The islands of the archipelago are very far from any continents and have been uninhabited and protected since the 1970’s, and therefore provide a unique environment, free of local human impacts, to study coral reefs and the faunal communities they support.
Since Chagos is protected from fishing, fish from all trophic levels, from herbivores to planktivores and predators, are able to thrive in large numbers. Additionally, they often grow to be much larger than similar species in areas where fishing is allowed.
Since Chagos is uninhabited, the corals that build the reefs are free from local anthropogenic stressors, such as pollution, sedimentation, and other direct interaction. The coral cover is relatively high on most reefs and often dominated by large tables of the genus Acropora.
Despite being free from local anthropogenic stressors, these corals are still susceptible to global stressors, such as ocean acidification and global warming. During our time in Chagos, our science team witnessed a coral bleaching event, the first reported in the Indian Ocean this year. For more information about the bleaching event, check out an interview with KSLOF’s chief scientist, Dr. Andrew Bruckner: http://www.cbsnews.com/news/indian-ocean-reefs-hit-by-coral-bleaching/.
Though bleaching can be detrimental to coral reefs if the event lasts for a long period of time, there is hope for recovery in Chagos, as recruitment of new corals is high in many places where past episodes of bleaching or disease have wiped out coral in the recent past.
Overall, the KSLOF Chagos expedition was an incredible adventure and a wonderful chance to see how a coral reef lives and functions without the direct interference of local human populations.
By Jill Harris
Jill’s new paper, written with Jen and Levi, was recently accepted for publication in the Marine Ecology Progress Series. Their paper, Quantifying scales of spatial variability in algal turf assemblages on coral reefs, describes how turf algae on a coral reef are variable over very small scales. Stay tuned for the official publication of the paper, but in the mean time here is the abstract to quench your curiosity!
Quantifying variability over multiple spatial scales is a fundamental goal in ecology, providing insight into which scale-dependent processes most strongly influence community structure. On coral reefs, the ubiquitous turf algae are the primary food source for herbivores and competitors for space with corals. Turf algae will likely increase in the future, because they thrive under conditions that reduce coral cover. Turfs are typically treated as a single homogenous functional group, but analyzing them as a variable assemblage is more informative. We used a hierarchical sampling design to quantify four scales of variability in turf assemblages from centimeters (within single dead coral heads) to kilometers (across islands) on the rarely studied Lhaviyani Atoll, Maldives. We used four metrics, each reflecting different ecological processes: percent cover, canopy height, richness, and assemblage composition. For most of these metrics, variability was significant at multiple spatial scales. However, for all metrics, the smallest scale (centimeters) explained the greatest proportion of overall variability. The least variability in cover, canopy height, and richness occurred among sites (100’s meters), suggesting that processes such as competition, predation, and vegetative growth are heterogeneous at small scales. In contrast, assemblage composition was least variable at the largest scale (kilometers), suggesting that oceanographic processes or a well-mixed propagule supply reduce variability. With declining coral and increasing cover of turf on reefs worldwide, it will become increasingly important to understand the dynamics of coral-turf competitive interactions. However, because turf assemblages are highly variable at small spatial scales, these interactions require more detailed consideration.
By Maggie Johnson
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 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!
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.
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.
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.
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.
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 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.