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.