Large-area imaging reveals biologically driven non-random spatial patterns of corals at a remote reef

For sessile organisms such as reef-building corals, differences in the degree of dispersion of individuals across a landscape may result from important differences in life-history strategies or may reflect patterns of habitat availability. Descriptions of spatial patterns can thus be useful not only for the identification of key biological and physical mechanisms structuring an ecosystem, but also by providing the data necessary to generate and test ecological theory. Here, we used an in situ imaging technique to create large-area photomosaics of 16 plots at Palmyra Atoll, central Pacific, each covering 100 m2 of benthic habitat. We mapped the location of 44,007 coral colonies and identified each to the lowest taxonomic level possible. Using metrics of spatial dispersion, we tested for departures from spatial randomness. We also used targeted model fitting to explore candidate processes leading to differences in spatial patterns among taxa. Most taxa were clustered and the degree of clustering varied by taxon. A small number of taxa did not significantly depart from randomness and none revealed evidence of spatial uniformity. Importantly, taxa that readily fragment or tolerate stress through partial mortality were more clustered. With little exception, clustering patterns were consistent with models of fragmentation and dispersal limitation. In some taxa, dispersion was linearly related to abundance, suggesting density dependence of spatial patterning. The spatial patterns of stony corals are non-random and reflect fundamental life-history characteristics of the taxa, suggesting that the reef landscape may, in many cases, have important elements of spatial predictability.

Clinton B. Edwards, Yoan Eynaud, Gareth J. Williams, Nicole E. Pedersen, Brian J. Zgliczynski, Arthur C.R. Gleason, Jennifer E. Smith, Stuart A. Sandin. 2017. Coral Reefs

Full Article Here

Re-evaluating the health of coral reef communities: baselines and evidence for human impacts across the central Pacific

Jennifer E. Smith, Rusty Brainard, Amanda Carter, Saray Grillo, Clinton Edwards, Jill Harris, Levi Lewis, David Obura, Forest Rohwer, Enric Sala, Peter S. Vroom, Stuart Sandin. 2016. Proceedings of the Royal Society B.

Numerous studies have documented declines in the abundance of reef-building corals over the last several decades and in some but not all cases, phase shifts to dominance by macroalgae have occurred. These assessments, however, often ignore the remainder of the benthos and thus provide limited information on the present-day structure and function of coral reef communities. Here, using an unprecedentedly large dataset collected within the last 10 years across 56 islands spanning five archipelagos in the central Pacific, we examine how benthic reef communities differ in the presence and absence of human populations. Using islands as replicates, we examine whether benthic community structure is associated with human habitation within and among archipelagos and across latitude. While there was no evidence for coral to macroalgal phase shifts across our dataset we did find that the majority of reefs on inhabited islands were dominated by fleshy non-reef-building organisms (turf algae, fleshy macroalgae and non-calcifying invertebrates). By contrast, benthic communities from uninhabited islands were more variable but in general supported more calcifiers and active reef builders (stony corals and crustose coralline algae). Our results suggest that cumulative human impacts across the central Pacific may be causing a reduction in the abundance of reef builders resulting in island scale phase shifts to dominance by fleshy organisms.

Full Article Here

Herbivore space use influences coral reef recovery

Yoan Eynaud, Dylan E. McNamara, Stuart A. Sandin. 2016. Royal Society Open Science.

Herbivores play an important role in marine communities. On coral reefs, the diversity and unique feeding behaviours found within this functional group can have a comparably diverse set of impacts in structuring the benthic community. Here, using a spatially explicit model of herbivore foraging, we explore how the spatial pattern of grazing behaviours impacts the recovery of a reef ecosystem, considering movements at two temporal scales—short term (e.g. daily foraging patterns) and longer
term (e.g. monthly movements across the landscape). Model simulations suggest that more spatially constrained herbivores are more effective at conferring recovery capability by providing a favourable environment to coral recruitment and growth. Results also show that the composition of food available to the herbivore community is linked directly to the pattern of space use by herbivores. To date, most studies of variability among the impacts of herbivore species have considered the diversity of feedingmodes andmouthparts. Our work provides a complementary view of spatial patterns of foraging, revealing that variation in movement behaviours alone can affect patterns of benthic change, and thus broadens our view of realized links between herbivore diversity and reef recovery.

Full Article Here

Scaling the Annotation of Subtidal Marine Habitats

Perry Naughton, Clinton Edwards, Vid Petrovic, Ryan Kastner, Falko Kuester and Stuart Sandin. 2015. Proceedings of the 10th International Conference on Underwater Networks & Systems

Visually documenting sea floor habitats has the potential to answer challenging questions in several maritime disciplines including: ecology, geology, and archaeology. Unfortunately, the attenuation of visible light underwater limits the imaging footprint of a single image to square meters. This limitation makes representing large habitats, on the order of hundreds of square meters and beyond, an intensive process requiring the collection, storage, processing and annotation of thousands of high resolution images per hundred square meters of sea floor. This paper describes a pipeline for dealing with these challenges efficiently and effectively using visual data of coral reef communities processed into a three dimensional model. We evaluate the resources and technological advancements required to scale this problem to orders of magnitude larger than the current state of the art and motivate the need for networked underwater data collection platforms to push the scalability of this method.

Full Article Here

Shift from coral to macroalgae dominance on a volcanically acidified reef

I. C. Enochs, D. P. Manzello, E. M. Donham, G. Kolodziej, R. Okano, L. Johnston, C. Young, J. Iguel, C. B. Edwards, M. D. Fox, L. Valentino, S. Johnson, D. Benavente, S. J. Clark, R. Carlton, T. Burton, Y. Eynaud & N. N. Price. 2015. Nature Climate Change.

Rising anthropogenic CO2 in the atmosphere is accompanied by an increase in oceanic CO2 and a concomitant decline in seawater pH (ref. 1). This phenomenon, known as ocean acidification (OA), has been experimentally shown to impact the biology and ecology of numerous animals and plants2, most notably those that precipitate calcium carbonate skeletons, such as reef-building corals3. Volcanically acidified water at Maug, Commonwealth of the Northern Mariana Islands (CNMI) is equivalent to near-future predictions for what coral reef ecosystems will experience worldwide due to OA. We provide the first chemical and ecological assessment of this unique site and show that acidification-related stress significantly influences the abundance and diversity of coral reef taxa, leading to the often-predicted shift from a coral to an algae-dominated state4, 5. This study provides field evidence that acidification can lead to macroalgae dominance on reefs.

Full Article Here