A comparison of spatially explicit and classic regression modelling of live coral cover using hyperspectral remote-sensing data in the Al Wajh lagoon, Red Sea

Live coral is a key component of the Al Wajh marine reserve in the Red Sea. The management of this reserve is dependent on a sound understanding of the existing spatial distribution of live coral cover and the environmental factors influencing live coral at the landscape scale. This study uses remote-sensing techniques to develop ordinary least squares and spatially lagged autoregressive explanatory models of the distribution of live coral cover inside the Al Wajh lagoon, Saudi Arabia. Live coral was modelled as a response to environmental controls such as water depth, the concentration of suspended sediment in the water column and exposure to incident waves. Airborne hyperspectral data were used to derive information on live coral cover as a response (dependent) variable at the landscape scale using linear spectral unmixing. Environmental controls (explanatory variables) were derived from a physics-based inversion of the remote-sensing dataset and validated against field-collected data. For spatial regression, cases referred to geographical locations that were explicitly drawn on in the modelling process to make use of the spatially dependent nature of coral cover controls. The transition from the ordinary least squares model to the spatially lagged model was accompanied by a marked growth in explanatory power (R 2 = 0.26 to 0.76). The theoretical implication that follows is that neighbourhood context interactions play an important role in determining live coral cover. This provides a persuasive case for building geographical considerations into studies of coral distribution

Abrupt transitions between macrobenthic faunal assemblages across seagrass bed margins

The nature of the transition from one contrasting macrobenthic assemblage to another across interfaces between intertidal seagrass and unvegetated sand was investigated in the subtropical Moreton Bay Marine Park, eastern Australia, via six two-dimensional core lattices. The same pattern of transition was manifested in each lattice. Macrofaunal abundance, species density (both observed and estimated total) and assemblage composition did not vary with distance away from the interface within the 0.75 m wide marginal bands of each habitat type. Neither were there significant differences in assemblage metrics or composition between the marginal and non-edge regions of either habitat. There were, however, very marked differences in assemblage composition, abundance and species density across the 25 cm wide strip on either side of the actual interface, the interacting assemblages reacting symmetrically. All these differences therefore took place over an ecotone distance of only 0.5 m at most. Spatial trends in assemblage metrics across the boundary zone were captured accurately by second and third order polynomial regression models. It also appeared that edge effects on individual species within the seagrass were a variable local response not a consistent effect of closeness to the bare sand

Comparing the information content of coral reef geomorphological and biological habitat maps, Amirantes Archipelago (Seychelles), Western Indian Ocean

Increasing the use of geomorphological map products in marine spatial planning has the potential to greatly enhance return on mapping investment as they are commonly two orders of magnitude cheaper to produce than biologically-focussed maps of benthic communities and shallow substrates. The efficacy of geomorphological maps derived from remotely sensed imagery as surrogates for habitat diversity is explored by comparing two map sets of the platform reefs and atolls of the Amirantes Archipelago (Seychelles), Western Indian Ocean. One mapping campaign utilised Compact Airborne Spectrographic Imagery (19 wavebands, 1 m spatial resolution) to classify 11 islands and associated reefs into 25 biological habitat classes while the other campaign used Landsat 7 þ ETM imagery (7 bands, 30 m spatial resolution) to generate maps of 14 geomorphic classes. The maps were compared across a range of characteristics, including habitat richness (number of classes mapped), diversity (ShannoneWeiner statistic) and thematic content (Cramer’s V statistic). Between maps, a strong relationship was revealed for habitat richness (R2 ¼ 0.76), a moderate relationship for class diversity and evenness (R2 ¼ 0.63) and a variable relationship for thematic content, dependent on site complexity (V range 0.43 e0.93). Geomorphic maps emerged as robust predictors of the habitat richness in the Amirantes. Such maps therefore demonstrate high potential value for informing coastal management activities and conservation planning by drawing on information beyond their own thematic content and thus maximizing the return on mapping investment

Reef-scale assessment of intertidal large benthic foraminifera populations on one tree Island, great barrier reef and their future carbonate production potential in a warming ocean

Populations of large benthic foraminiferans (LBFs) that inhabit coral reef platforms are major producers of calcium carbonate (CaCO3) in reef ecosystems. This study documented the population density of living intertidal LBF populations at One Tree Reef (OTR), southern Great Barrier Reef, in a community dominated by Marginopora vertebralis and Baculogypsina sphaerulata. Densities of 7.7 × 103 M. vertebralis individuals (ind.)/m2 and 4.5 × 105 B. sphaerulata ind./m2 were estimated for these populations in May 2011. We applied remote-sensing technology to determine reef-scale estimates of suitable Foraminifera habitats and used these to estimate overall stocks of LBF populations on the intertidal algal flat at OTR of ca. 2800 metric tons. The growth rate of M. vertebralis was determined in a laboratory study, and the data were used to calculate the annual CaCO3 production of the reef flat by the LBF population. The response of M. vertebralis to ocean warming was investigated using 3-week incubations at temperatures ranging from ambient sea surface temperature to +6°C. There were significant decreases in growth and concomitant CaCO3 production in 6°C warmer water, which resulted in shell dissolution of M. vertebralis. These results indicate that climate-driven ocean warming projected for the region will result in significant decreases in CaCO3 production in overall foraminiferan populations, although species-specific effects should be further investigated

Fathom

[Extract] Terrestrial, bipedal, air breathing, and poorly waterproofed, how can humans fathom the bottom of the sea? This article was composed by an anthropologist, a cultural theorist, a philosopher, a coastal geographer, a cultural geographer, a feminist studies scholar, an artist, a spatial scientist, an ecocritic, a free diver, an STS scholar, a spear fisher, a biologist, a marine ecologist, a poet, a dancer, and a swimmer. (If the math does not add up, we remind you that we are always more than one.) Our insights emerged from a one-day workshop at Clovelly Beach in Sydney, Australia, on land and in the water, where we shared our perspectives and practices in researching ocean environments. Our collaboration is an experiment in multidisciplinary practice-based inquiry, where differences and tensions need not preclude collaborative understanding. In this article we combine emerging critical ocean studies and blue humanities perspectives to propose fathoming as a vital, embodied practice that gathers technoscientific acts of measurement together with practices of immersion, imagination, and speculation. Through collaborative multi-situated inquiry1 we learn new things not only about the sea but also about the limits of epistemological mastery and the rewards of knowing with

A comparison of spatially explicit and classic regression modelling of live coral cover using hyperspectral remote-sensing data in the Al Wajh lagoon, Red Sea

Live coral is a key component of the Al Wajh marine reserve in the Red Sea. The management of this reserve is dependent on a sound understanding of the existing spatial distribution of live coral cover and the environmental factors influencing live coral at the landscape scale. This study uses remote-sensing techniques to develop ordinary least squares and spatially lagged autoregressive explanatory models of the distribution of live coral cover inside the Al Wajh lagoon, Saudi Arabia. Live coral was modelled as a response to environmental controls such as water depth, the concentration of suspended sediment in the water column and exposure to incident waves. Airborne hyperspectral data were used to derive information on live coral cover as a response (dependent) variable at the landscape scale using linear spectral unmixing. Environmental controls (explanatory variables) were derived from a physics-based inversion of the remote-sensing dataset and validated against field-collected data. For spatial regression, cases referred to geographical locations that were explicitly drawn on in the modelling process to make use of the spatially dependent nature of coral cover controls. The transition from the ordinary least squares model to the spatially lagged model was accompanied by a marked growth in explanatory power (R 2 = 0.26 to 0.76). The theoretical implication that follows is that neighbourhood context interactions play an important role in determining live coral cover. This provides a persuasive case for building geographical considerations into studies of coral distribution

Community calcification in Lizard Island, Great Barrier Reef: a 33 year perspective

Measurements of community calcification (G) were made during September 2008 and October 2009 on a reef flat in Lizard Island, Great Barrier Reef, Australia, 33years after the first measurements were made there by the LIMER expedition in 1975. In 2008 and 2009 we measured G=61±12 and 54±13mmolCaCOm·day, respectively. These rates are 27-49% lower than those measured during the same season in 1975-76. These rates agree well with those estimated from the measured temperature and degree of aragonite saturation using a reef calcification rate equation developed from observations in a Red Sea coral reef. Community structure surveys across the Lizard Island reef flat during our study using the same methods employed in 1978 showed that live coral coverage had not changed significantly (~8%). However, it should be noted that the uncertainty in the live coral coverage estimates in this study and in 1978 were fairly large and inherent to this methodology. Using the reef calcification rate equation while assuming that seawater above the reef was at equilibrium with atmospheric PCO and given that live coral cover had not changed G should have declined by 30±8% since the LIMER study as indeed observed. We note, however, that the error in estimated G decrease relative to the 1970's could be much larger due to the uncertainties in the coral coverage measurements. Nonetheless, the similarity between the predicted and the measured decrease in G suggests that ocean acidification may be the primary cause for the lower CaCO precipitation rate on the Lizard Island reef flat

Five practical uses of spatial autocorrelation for studies of coral reef ecology

The organisation of benthic communities across coral reefs is underpinned by spatially structured ecological processes and neighbourhood interactions such as larval dispersal, migration, competition and the spread of disease. These give rise to spatial autocorrelation in reef communities. This paper demonstrates how the measurement of spatial autocorrelation can profitably be incorporated into studies of coral reef ecology through a series of 5 simple statistical exercises: for the generation of maps depicting the strength of spatial relationships between ecological communities, as an indicator of optimal dimensions for sampling ecological communities on coral reefs, as a diagnostic tool for model misspecification, as an indicator of a spatial process underpinning the distribution of an observed community pattern and as a surrogate for missing variables in a model. The benefits of incorporating spatial autocorrelation include (1) quantifying the extent and pattern of autocorrelation across reefs, (2) signifying the presence of redundant information in field datasets, (3) indexing the nature and degree to which fundamental assumptions of classic (i.e. non-spatial) statistical techniques are violated, (4) indicating the nature (spatial versus non-spatial) of an observable pattern to be modelled, and (5) offering an opportunity to partition out and utilise the spatially structured component of model error as a surrogate for a missing variable. Collectively, the statistical exercises presented here provide a persuasive case for the measurement and interrogation of spatial autocorrelation in studies of coral reef ecology

An investigation of seagrass patterns at Alphonse Atoll, Seychelles: linking structure to function in marine landscapes

The idea of landscapes as shifting patch mosaics, structured by a range of biological and physical stochastic forces, is well suited to shallow tropical environments, where seagrass patches lie within a matrix of soft sediments or rocky substrates. The interaction of wave fields and tidal currents with carbonate sediment transport can result in linear morphologies of reef flat material with alternating sand tongues and seagrass beds. Patch-level metrics capture phenomena such as linearity in one variable, which can be evaluated over a gradient of predictable environmental change. Interrogating the statistical properties of patch ensembles enables the links between observed structures and the processes that govern them to be empirically investigated. This study demonstrates how habitat maps derived from remotely sensed Compact Airborne Spectrographic Imager (CASI) data can be used to investigate critical controls of landscape mosaics through the application of geostatistical techniques to Alphonse Atoll, Seychelles