Coral Reef Ecology

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Smith Lab at Scripps Institution of Oceanography
Updated: 18 hours 8 min ago

New paper focuses on the small things on a coral reef

Mon, 08/31/2015 - 2:39pm

Jill’s new paper, written with Jen and Levi, came out recently 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. Turf algae are a group of small (~ 1 cm tall) algae that grow like a fuzzy shag carpet. They are a common part of every coral reef in the world, but most people study them as a single homogenous entity. Jill, Levi and Jen argue that we should instead treat turf like a diverse, heterogeneous assemblage. For example, they found that patches turf algae separated by only a few centimeters apart are very different!

 

 Pete Oxford, ILCP)

Just as a forest has more complexity than just its canopy (left), tiny turf algae on coral reefs (right) are diverse, complex, heterogeneous systems (photo credit, forest canopy: Pete Oxford, ILCP)

Think of turf like a forest. Looking down at a forest from above, you could say that it is 100% tree. That might be true, but you would be missing a lot of the interesting ecological detail: What species of trees? How tall are they? Are the different species clumped together or randomly spread out? What kinds of animals live in the forest? We take that same view of turf algae by describing how turf species, height, and density vary across space.

 

Jill had a nice ocean view while working on her turf algae samples Korallionlab's open air lab.

Jill had a nice ocean view while working on her turf algae samples Korallionlab’s open air lab.

Levi and Jill collected the samples for this paper while working at Korallionlab in the Maldives

Levi and Jill collected the samples for this paper while working at Korallionlab in the Maldives

Jill and Levi collected these turf algae samples at the Korallionlab in the Maldives (Read more about their Maldives research in Jill’s previous blog post and an article about their work in the Union-Tribune). This paper is one of the chapters of Jill’s dissertation, which is all about turf algae on coral reefs. Stay tuned to learn more about the ecologically important, but usually overlooked, turf algae!

Jill was really excited to finally collect all 256 samples!

Jill was really excited to finally collect all 256 samples!

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Adventures in Chagos

Mon, 06/01/2015 - 3:28pm

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.

Chagos is located in the middle of the Indian Ocean, just south of the Maldives.

Chagos is located in the middle of the Indian Ocean, just south of the Maldives.

Coconut palms, hermit crabs, and birds dominate the uninhabited islands of Chagos.

Coconut palms, hermit crabs, and birds dominate the uninhabited islands of Chagos.

Coconut palms, hermit crabs, and birds dominate the uninhabited islands of Chagos.

Uninhabited island in Chagos.

Coconut palms, hermit crabs, and birds dominate the uninhabited islands of Chagos.

Coconut palms, hermit crabs, and birds dominate the uninhabited islands of Chagos.

Occasionally, moray eels will come into the tide pools during the day to hunt for crabs.

Occasionally, moray eels will come into the tide pools during the day to hunt for crabs.

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.

A school of bait fish cruises over the reef.

A school of bait fish cruises over the reef.

Large schools of fusiliers often surround divers conducting surveys. Here you can see an aggregation of snappers hovering in the background.

Large schools of fusiliers often surround divers conducting surveys. Here you can see an aggregation of snappers hovering in the background.

Large schools of herbivores, such as these surgeonfish, cruise the reef consuming turf algae.

Large schools of herbivores, such as these surgeonfish, cruise the reef consuming turf algae.

Very small glass fish will school in large numbers and seek refuge beneath ledges on walls or crevices in Porites bommies.

Very small glass fish will school in large numbers and seek refuge beneath ledges on walls or crevices in Porites bommies.

Red snappers (Lutjanus bohar), midnight snappers (Macolor macularis), and black snappers (Macolor niger) often travel in loose groups, searching for food.

Red snappers (Lutjanus bohar), midnight snappers (Macolor macularis), and black snappers (Macolor niger) often travel in loose groups, searching for food.

A school of yellowspot trevally pass through my transect.

A school of yellowspot trevally pass through my transect.

The steephead snapper (Lutjanus gibbus) is often found in large schools near the benthos.

The steephead snapper (Lutjanus gibbus) is often found in large schools near the benthos.

Grey reef sharks patrol the reef during a dusky dive.

Grey reef sharks patrol the reef during a dusky dive.

Tawny nurse sharks are extremely common in Chagos. They have small eyes and poor eyesight and will often come very close to divers to get a better look

Tawny nurse sharks are extremely common in Chagos. They have small eyes and poor eyesight and will often come very close to divers to get a better look

In addition to fish, many invertebrates thrive in this refuge from fishing, including the ever-popular day octopus (Octopus cyanea).

In addition to fish, many invertebrates thrive in this refuge from fishing, including the ever-popular day octopus (Octopus cyanea).

In a rare moment, an painted rock lobster (Panulirus versicolor) comes out of hiding.

In a rare moment, an painted rock lobster (Panulirus versicolor) comes out of hiding.

This hairy yellow hermit crab (Aniculus maximus) was carrying a shell that was about the same size as an American football!

This hairy yellow hermit crab (Aniculus maximus) was carrying a shell that was about the same size as an American football!

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.

Large table Acropora.

Large Acropora table

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/.

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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.

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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.

The reef from above, with a great view of the new corals growing

The reef from above, with a great view of the new corals growing

Baby coral recruits can be seen growing on what used to be an Acropora table; the next generation!

Baby coral recruits can be seen growing on what used to be an Acropora table; the next generation!

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New paper focuses on the small things on a coral reef

Fri, 05/29/2015 - 2:58pm

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.

 

 

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