Category: Publications

Coral reef resilience differs among islands within the Gulf of Mannar, southeast India, following successive coral bleaching events

K. Diraviya Raj, Greta S. Aeby, G. Mathews, Gareth J. Williams, Jamie M. Caldwell, R. L. Laju, M. Selva Bharath, P. Dinesh Kumar, A. Arasamuthu, N. Gladwin Gnana Asir, Lisa M. Wedding, Andrew J. Davies, Monica M. Moritsch, J. K. Patterson Edward

Abstract

We used a 12-yr data set of benthic cover (2005–2017), spanning two bleaching events, to assess changes in benthic cover and coral community composition along 21 islands within Gulf of Mannar (GoM), southeast India. Overall, between 2005 and 2017 reefs had a simultaneous decrease in relative coral cover (avg. =  − 36%) and increase in algal cover (avg. =  + 45%). Changes in benthic cover were not consistent among islands, ranging from − 34 to + 5% for coral cover and from − 0.3 to + 50% for algae. There was a spatial gradient in coral mortality, which increased among islands from west to east. However, there was a disconnect between coral loss and subsequent increases in algae. Algal cover increased more on islands in west GoM where coral loss was minimal. Environmental co-factors (coral cover, percent bleaching, degree heating weeks, fish densities, Chl-a, pollution) explained > 50% of the benthic cover responses to successive bleaching. Coral survival was favored on islands with higher fish densities and chlorophyll-a levels, and increases in algal cover were associated with higher measures of pollution from terrestrial runoff. Coral morphotypes differed in their response following successive bleaching resulting in changes in the relative abundance of different coral morphotypes. Existing climate projections (RCP8.5) indicate a 22-yr gap in the onset of annual severe bleaching (ASB) for reefs in the east versus west GoM, and ASB was ameliorated for all reefs under the RCP4.5 projections. There is limited knowledge of the resilience of GoM reefs, and this study identifies coral morphotypes and reefs that are most likely to recover or decline from successive bleaching, in the context of forecasts of the frequency of future bleaching events in GoM.

[sendpaper paperurl=”raj_2021.pdf”]

Full Citation

Raj KD, Aeby GS, Mathews G, Williams GJ, Caldwell JM, Laju RL, Bharath MS, Kumar PD, Arasamuthu A, Asir NGG, Wedding LM, Davies AJ, Moritsch MM, Edward JKP (2021) Coral reef resilience differs among islands within the Gulf of Mannar, southeast India, following successive coral bleaching events. Coral Reefs 40: 1029-1044

Manuscript DOI

https://doi.org/10.1007/s00338-021-02102-0

Three‐dimensional mapping reveals scale‐dependent dynamics in biogenic reef habitat structure

Tim Jackson‐Bué, Gareth J. Williams, Guy Walker‐Springett, Steven J. Rowlands, Andrew J. Davies

Abstract

Habitat structure influences a broad range of ecological interactions and ecosystem functions across biomes. To understand and effectively manage dynamic ecosystems, we need detailed information about habitat properties and how they vary across spatial and temporal scales. Measuring and monitoring variation in three‐dimensional (3D) habitat structure has traditionally been challenging, despite recognition of its importance to ecological processes. Modern 3D mapping technologies present opportunities to characterize spatial and temporal variation in habitat structure at a range of ecologically relevant scales. Biogenic reefs are structurally complex and dynamic habitats, in which structure has a pivotal influence on ecosystem biodiversity, function and resilience. For the first time, we characterized spatial and temporal dynamics in the 3D structure of intertidal Sabellaria alveolata biogenic reef across scales. We used drone‐derived structure‐from‐motion photogrammetry and terrestrial laser scanning to characterize reef structural variation at mm‐to‐cm resolutions at a habitat scale (~35 000 m²) over 1 year, and at a plot scale (2500 m²) over 5 years (2014–2019, 6‐month intervals). We found that most of the variation in reef emergence above the substrate, accretion rate and erosion rate was explained by a combination of systematic trends with shore height and positive spatial autocorrelation up to the scale of colonies (1.5 m) or small patches (up to 4 m). We identified previously undocumented temporal patterns in intertidal S. alveolata reef accretion and erosion, specifically groups of rapidly accreting, short‐lived colonies and slow‐accreting, long‐lived colonies. We showed that these highly dynamic colony‐scale structural changes compensate for each other, resulting in seemingly stable reef habitat structure over larger spatial and temporal scales. These patterns could only be detected with the use of modern 3D mapping technologies, demonstrating their potential to enhance our understanding of ecosystem dynamics across scales.

Full Citation

Jackson‐Bué T, Williams GJ, Walker‐Springett G, Rowlands SJ, Davies AJ (2021) Three‐dimensional mapping reveals scale‐dependent dynamics in biogenic reef habitat structure. Remote Sensing in Ecology and Conservation 

Manuscript DOI

http://doi.org/10.1002/rse2.213

Habitat modification by Ascophyllum canopy negatively impacts macrofaunal communities on soft-sediment shores

Gilson, AR & Davies AJ

Canopy-forming macroalgae are known to act as ecosystem engineers, altering the physical parameters of the local environment, and as a result, driving changes in local biodiversity. Although a large body of evidence exists regarding macroalgal canopies on intertidal rocky shores, little is known regarding attached perennial species in soft sediment environments. The aim of this study was to assess whether the presence of an Ascophyllum nodosum canopy altered physical parameters, leading to the formation of different environmental conditions in the areas around the canopy and whether this led to changes in the local community. Sediment cores were taken in canopy-present and canopy-absent treatments at four sites over four sampling periods covering winter (November and January) through to spring (March and May) to assess modification of seven physical parameters: particle size, sand/silt/clay content, chlorophyll a, organic carbon, pore water content and temperature, as well as for macrofaunal diversity. Results revealed significant differences between treatments for all variables with the exception of clay content. Areas below the canopy were dominated by a high abundance of opportunistic species indicating a more disturbed environment, with increased levels of organic enrichment, anoxia and scouring found to be the principal sources of physical disturbance. In conclusion, differences in abiotic parameters between canopy and non-canopy areas in soft-sediment environments were driven both directly and indirectly by the presence of the algal canopy. This facilitated an alternative community composition that enhanced biodiversity within algal-sediment shores.
[sendpaper paperurl=”2020_Gilson.pdf”]

Full Citation

Gilson AR, Davies AJ (2020) Habitat modification by Ascophyllum canopy negatively impacts macrofaunal communities on soft-sediment shores. Marine Environmental Research 162: 105193

DOI

https://doi.org/10.1016/j.marenvres.2020.105193

Drivers of sex-specific trade-offs in the macroalga Ascophyllum nodosum

Kurr M, Davies AJ

Little is known about reproductive trade-offs in seaweeds, but sex-specific differences in mortality, production of metabolites, threshold size for reproduction, and susceptibility to herbivory have been reported. The macroalga Ascophyllum nodosum exhibits sex-specific trade-offs at sites where wave-action and herbivory are stronger, because females increase their investment into reproduction at the expense of chemical defences. Females may do this at stressed sites because of high germling and juvenile mortality, or to compensate for lower fecundity due smaller adult sizes at these sites. This study aimed to determine which is the case by comparing A. nodosum in an area where stressors (wave-action and herbivory) impacted upon both adult performance and juvenile mortality, to one where only adult performance was impacted (by ice-damage). Seven populations of the algae were compared at both the regional (> 1000 km) and local scales (< 50 km), to assess the presence of sex-specific differences in algal size, sex-ratio, and the chemical defences and tissue condition of both vegetative and reproductive structures. Taking a multi-scale approach is a useful way to determine which abiotic variables are driving biological patterns, because variability in the latter mirrors variability in the former. Sex-specific trade-offs were more common at both the regional and local scale when herbivory and wave-exposure were high. Other factors caused differences in physiology at both scales, but did not drive sex-specific differences. Furthermore, sex-specific differences were consistent in the defence of reproductive tissues at all sites, suggesting that this was not driven by stress at all. Therefore, sex-specific differences in A. nodosum are caused by some stressors, not caused by others, and are present in some fashion regardless of stress. This is the first study to directly quantify sex-specific trade-offs at different spatial scales in populations of either plants or algae, and as such it reveals novel insights into the driving forces behind them.
[sendpaper paperurl=”2020_Kurr.pdf”]

Full Citation

Kurr M, Davies AJ (2020) Drivers of sex-specific trade-offs in the macroalga Ascophyllum nodosum. Plant 8 (3): 54-63.

DOI

http://dx.doi.org/10.11648/j.plant.20200803.12

Beyond the tip of the seamount: Distinct megabenthic communities found beyond the charismatic summit sponge ground on an arctic seamount (Schulz Bank, Arctic Mid-Ocean Ridge)

H.K. Meyer, A.J.Davies, E.M.Roberts, J.R. Xavier, P.A. Ribeiro, H.Glenner, S.-R. Birkely, H.T.Rapp

Abstract

Our understanding of the benthic communities on arctic seamounts and descriptions of such communities in habitat classification systems are limited. In recent years, Schulz Bank (73°52′N 7°30′E), a seamount on the Arctic Mid-Ocean Ridge (AMOR), has become well studied but the work has primarily focused on an arctic sponge ground at the summit. This has compounded a general assumption that the most biologically interesting community is on the summit alone. With the potential threat of deep-sea mining on nearby sites on AMOR, it is crucial to form a baseline understanding of the benthic megafaunal communities not only on the summit, but on the slopes and base of the seamount as well. Using video footage collected by a remotely operated vehicle in 2017 and 2018 to survey the seamount from 2700 to 580 m depth, several distinct megafauna communities on Schulz Bank were identified. Specifically, five biotopes, two of which were dominated by large structure-forming sponges, appeared to follow a depth gradient and change with the type of substrata present. The sponge-dominated communities on the summit and lower slope had the highest average community densities and number of morphotaxa per image compared to the upper slope and seamount base communities. Most notably, sponge-dominated bedrock walls on the lower slopes challenge the assumption that the summit is the most dense and diverse community on Schulz Bank. The results from this study lay the foundation for future research and conservation efforts of arctic sponge grounds by looking beyond the seamount summit to bring a full view of enigmatic sponge dominated ecosystems.

[sendpaper paperurl=”2022_Meyer.pdf”]

Full Citation

Meyer HK, Davies AJ, Roberts EM, Xavier JR, Ribeiro PA, Glenner H, Birkely S_R, Rapp HT (2022) Beyond the tip of the seamount: Distinct megabenthic communities found beyond the charismatic summit sponge ground on an arctic seamount (Schulz Bank, Arctic Mid-Ocean Ridge). Deep-sea Research Vol 1

Manuscript DOI

https://doi.org/10.1016/j.dsr.2022.103920

Distribution modelling of the Eurasian Otter (Lutra lutra) on the Isle of Anglesey, Wales

Riley TG, Waggit JJ, Davies AJ

The Eurasian otter (Lutra lutra) remains a high priority conservation species despite recent increases in UK populations. Specifically, a marked increase in surveyed site occupancy (50%) was observed on the Isle of Anglesey (North Wales) between 2002 and 2009. Understanding the drivers that act upon the distribution of L. lutra will allow for more targeted conservation efforts. In this study, species distribution modelling (MaxEnt) was applied to predict the potential distribution of L. lutra across Anglesey. Elevation and, distance to roads and water (m) were found to be the most influential factors in determining the distribution of individuals across all models. The generated models performed better than random and were capable of identifying areas where L. lutra could potentially occur across Anglesey (AUC = 0.818). Locations for concentrating future research efforts are suggested through analysis of spatial variation, human disturbance effects and population analysis across the study region. This study provides a baseline of L. lutra habitation possibility across Anglesey and exposes areas for future conservation in habitat management and research efforts.
[sendpaper paperurl=”2020_Riley.pdf”]

Full Citation

Riley TG, Waggit JJ, Davies AJ (2020) Distribution modelling of the Eurasian Otter (Lutra lutra) on the Isle of Anglesey, Wales. Otter, Journal of the International Otter Survival Fund 6: 30-39

Helen’s paper made the cover of Ecography

Spatial scaling properties of coral reef benthic communities

Ford HV, Gove JM, Davies AJ, Graham NAJ, Healey JR, Conklin EJ, Williams GJ

The spatial structure of ecological communities on tropical coral reefs across seascapes and geographies have historically been poorly understood. Here we addressed this for the first time using spatially expansive and thematically resolved benthic community data collected around five uninhabited central Pacific oceanic islands, spanning 6° latitude and 17° longitude. Using towed-diver digital image surveys over ~140 linear km of shallow (8–20 m depth) tropical reef, we highlight the autocorrelated nature of coral reef seascapes. Benthic functional groups and hard coral morphologies displayed significant spatial clustering (positive autocorrelation) up to kilometre-scales around all islands, in some instances dominating entire sections of coastline. The scale and strength of these autocorrelation patterns showed differences across geographies, but patterns were more similar between islands in closer proximity and of a similar size. For example, crustose coralline algae (CCA) were clustered up to scales of 0.3 km at neighbouring Howland and Baker Islands and macroalgae were spatially clustered at scales up to ~3 km at both neighbouring Kingman Reef and Palmyra Atoll. Of all the functional groups, macroalgae had the highest levels of spatial clustering across geog- raphies at the finest resolution of our data (100 m). There were several cases where the upper scale at which benthic community members showed evidence of spatial cluster- ing correlated highly with the upper scales at which concurrent gradients in physical environmental drivers were spatially clustered. These correlations were stronger for surface wave energy than subsurface temperature (regardless of benthic group) and turf algae and CCA had the closest alignments in scale with wave energy across functional groups and geographies. Our findings suggest such physical drivers not only limit or promote the abundance of various benthic competitors on coral reefs, but also play a key role in governing their spatial scaling properties across seascapes.

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Full Citation

Ford HV, Gove JM, Davies AJ, Graham NAJ, Healey JR, Conklin EJ, Williams GJ (2021) Spatial scaling properties of coral reef benthic communities. Ecography 44(2): 188-198

DOI

http://dx.doi.org/10.1111/ecog.05331

Submarine canyons influence macrofaunal diversity and density patterns in the deep-sea benthos

Robertson CM, Demopoulos AWJ, Bourque JR, Mienis F, Duineveld GCA, Lavaleye MSS, Koivisto RKK, Brooke SD, Ross SW, Rhode M, Davies AJ

Submarine canyons are often morphologically complex features in the deep sea contributing to habitat heterogeneity. In addition, they act as major conduits of organic matter from the shallow productive shelf to the food deprived deep-sea, promoting gradients in food resources and areas of sediment resuspension and deposition. This study focuses on the Baltimore and Norfolk canyons, in the western North Atlantic Ocean, and investigates how different biogeochemical drivers influence canyon and slope macrofaunal communities. Replicated sediment cores were collected along the main axes (~180–1200 m) of Baltimore and Norfolk canyons and at comparable depths on the adjacent slopes. Cores were sorted, assessing whole community macrofaunal (>300 μm) abundance, diversity and standing stocks. Canyon communities were significantly different from slope communities in terms of diversity, abundance patterns and community assemblages, which were attributed to high levels of organic matter enrichment within canyons. There was a significant departure from the expected density-depth relationship in both canyons, driven by enhanced abundances between 800 and 900 m canyon depths, which was characterised as a deposition zone for organic matter. Bathymetric zonation, sediment dynamics, organic enrichment, and disturbance events were clear factors that structured the benthic communities in both Baltimore and Norfolk canyons. Coupling family-level community data, with sediment grain-size and biogeochemistry data explained community dynamics across depth and biogeochemical gradients, providing further evidence that canyons disrupt macrofaunal diversity and density patterns in the deep-sea benthos.
[sendpaper paperurl=”2020_Robertson.pdf”]

Full Citation

Robertson CM, Demopoulos AWJ, Bourque JR, Mienis F, Duineveld GCA, Lavaleye MSS, Koivisto RKK, Brooke SD, Ross SW, Rhode M, Davies AJ (2020) Submarine canyons influence macrofaunal diversity and density patterns in the deep-sea benthos. Deep Sea Research Part I: Oceanographic Research Papers.

DOI

https://doi.org/10.1016/j.dsr.2020.103249

Scale-dependent spatial patterns in benthic communities around a tropical island seascape

E. Aston, G. Williams, M. Green, A.J. Davies, L. Wedding, J. Gove, J-B. Jouffray, T. Jones, J. Clark

Understanding and predicting patterns of spatial organization across ecological communities is central to the field of landscape ecology, and a similar line of inquiry has begun to evolve sub-tidally among seascape ecologists. Much of our current understanding of the processes driving marine community patterns, particularly in the tropics, has come from small-scale, spatially-discrete data that are often not representative of the broader seascape. Here we expand the spatial extent of seascape ecology studies and combine spatially-expansive in situ digital imagery, oceanographic measurements, spatial statistics, and predictive modeling to test whether predictable patterns emerge between coral reef benthic competitors across scales in response to intra-island gradients in physical drivers. We do this around the entire circumference of a remote, uninhabited island in the central Pacific that lacks the confounding effects of direct human impacts. We show, for the first time, that competing benthic groups demonstrate predictable scaling patterns of organization, with positive autocorrelation in the cover of each group at scales.

Full Citation

E. Aston, G. Williams, M. Green, A.J. Davies, L. Wedding, J. Gove, J-B. Jouffray, T. Jones, J. Clark (Accepted) Scale-dependent spatial patterns in benthic communities around a tropical island seascape, Ecography, 10.1111/ecog.04097

Accepted MS

Download the Authors Accepted Manuscript here.