Microbial to reef scale interactions between the reef-building coral
            Montastraea annularis
            and benthic algae

Competition between reef-building corals and benthic algae is of key importance for reef dynamics. These interactions occur on many spatial scales, ranging from chemical to regional. Using microprobes, 16S rDNA pyrosequencing and underwater surveys, we examined the interactions between the reef-building coral Montastraea annularis and four types of benthic algae. The macroalgae Dictyota bartayresiana and Halimeda opuntia , as well as a mixed consortium of turf algae, caused hypoxia on the adjacent coral tissue. Turf algae were also associated with major shifts in the bacterial communities at the interaction zones, including more pathogens and virulence genes. In contrast to turf algae, interactions with crustose coralline algae (CCA) and M. annularis did not appear to be antagonistic at any scale. These zones were not hypoxic, the microbes were not pathogen-like and the abundance of coral–CCA interactions was positively correlated with per cent coral cover. We propose a model in which fleshy algae (i.e. some species of turf and fleshy macroalgae) alter benthic competition dynamics by stimulating bacterial respiration and promoting invasion of virulent bacteria on corals. This gives fleshy algae a competitive advantage over corals when human activities, such as overfishing and eutrophication, remove controls on algal abundance. Together, these results demonstrate the intricate connections and mechanisms that structure coral reefs.

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Rapid relative increase of crustose coralline algae following herbivore exclusion in a reef of El Salvador

PeerJ ◽

10.7717/peerj.10696 ◽

2021 ◽

Vol 9 ◽

pp. e10696

Author(s):

Xochitl E. Elías Ilosvay ◽

Johanna Segovia ◽

Sebastian Ferse ◽

Walter Ernesto Elias ◽

Christian Wild

Keyword(s):

El Salvador ◽

Benthic Community ◽

Anthropogenic Impacts ◽

Coral Cover ◽

Benthic Algae ◽

Coralline Algae ◽

Crustose Coralline Algae ◽

Night Time ◽

Herbivore Exclusion ◽

Turf Algae

The Eastern Tropical Pacific (ETP) is one of the most isolated and least studied regions in the world. This particularly applies to the coast of El Salvador, where the only reef between Guatemala and Nicaragua, called Los Cóbanos reef, is located. There is very little published information about the reef’s biodiversity, and to our knowledge, no research on its ecology and responses to anthropogenic impacts, such as overfishing, has been conducted. The present study, therefore, described the benthic community of Los Cóbanos reef, El Salvador, using the Line-Point-Intercept-Transect method and investigated changes in the benthic community following the exclusion of piscine macroherbivores over a period of seven weeks. Results showed high benthic algae cover (up to 98%), dominated by turf and green algae, and low coral cover (0–4%). Porites lobata was the only hermatypic coral species found during the surveys. Surprisingly, crustose coralline algae (CCA) showed a remarkable total cover increase by 58%, while turf algae cover decreased by 82%, in experimental plots after seven weeks of piscine macroherbivore exclusion. These findings apparently contradict the results of most previous similar studies. While it was not possible to ascertain the exact mechanisms leading to these drastic community changes, the most likely explanation is grazing on turf by small grazing macroherbivores that had access to the cages during the experiment and clearing of CCA initially covered by epiphytes and sediments. A higher CCA cover would promote the succesful settlement by corals and prevent further erosion of the reef framework. Therefore it is crucial to better understand algal dynamics, herbivory, and implications of overfishing at Los Cóbanos to avoid further reef deterioration. This could be achieved through video surveys of the fish community, night-time observations of the macroinvertebrate community, exclusion experiments that also keep out herbivorous macroinvertebrates, and/or experimental assessments of turf algae/CCA interactions.

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Associations between Benthic Cover and Habitat Complexity Metrics Obtained from 3D Reconstruction of Coral Reefs at Different Resolutions

Remote Sensing ◽

10.3390/rs12061011 ◽

2020 ◽

Vol 12 (6) ◽

pp. 1011 ◽

Cited By ~ 2

Author(s):

Atsuko Fukunaga ◽

John H. R. Burns ◽

Kailey H. Pascoe ◽

Randall K. Kosaki

Keyword(s):

Fractal Dimension ◽

Coral Reefs ◽

Habitat Structure ◽

Coral Cover ◽

Three Dimensional ◽

Structural Complexity ◽

Coralline Algae ◽

Crustose Coralline Algae ◽

Surface Areas ◽

Abundance And Diversity

Quantifying the three-dimensional (3D) habitat structure of coral reefs is an important aspect of coral reef monitoring, as habitat architecture affects the abundance and diversity of reef organisms. Here, we used photogrammetric techniques to generate 3D reconstructions of coral reefs and examined relationships between benthic cover and various habitat metrics obtained at six different resolutions of raster cells, ranging from 1 to 32 cm. For metrics of 3D structural complexity, fractal dimension, which utilizes information on 3D surface areas obtained at different resolutions, and vector ruggedness measure (VRM) obtained at 1-, 2- or 4-cm resolution correlated well with benthic cover, with a relatively large amount of variability in these metrics being explained by the proportions of corals and crustose coralline algae. Curvature measures were, on the other hand, correlated with branching and mounding coral cover when obtained at 1-cm resolution, but the amount of variability explained by benthic cover was generally very low when obtained at all other resolutions. These results show that either fractal dimension or VRM obtained at 1-, 2- or 4-cm resolution, along with curvature obtained at 1-cm resolution, can effectively capture the 3D habitat structure provided by specific benthic organisms.

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Indicators of coral reef ecosystem recovery following reduction in logging and implementation of community-based management schemes in the Solomon Islands.

Pacific Conservation Biology ◽

10.1071/pc140075 ◽

2014 ◽

Vol 20 (1) ◽

pp. 75 ◽

Cited By ~ 5

Author(s):

S Albert ◽

A Grinham ◽

B Gibbes ◽

I Tibbetts ◽

J udy

Keyword(s):

Water Quality ◽

Management Practices ◽

Pacific Islands ◽

Coral Cover ◽

Solomon Islands ◽

Coralline Algae ◽

Herbivorous Fish ◽

Crustose Coralline Algae ◽

Ecosystem Recovery ◽

Community Based

The livelihood of many coastal communities in the Pacific Islands is directly dependent on the health of adjacent coral reefs. Reduction in water quality and over-harvesting of herbivorous fish are known to drive reef ecosystems towards a more degraded state. Community-based resource management practices have the potential to improve damaged reefs but quantitative data on their effectiveness remains largely unreported. This study investigated how land use changes and implementation of marine management influenced water quality, herbivorous fish biomass and reef condition of Marovo Lagoon in the Solomon Islands. Four study sites were located along a gradient of water quality, with two of the sites located inside marine protected areas (MPAs) designated in 2006. The results suggest that water quality in coastal areas adjacent to catchments modified by logging was negatively impacted. However, following natural revegetation of bare soil in the catchment between 2000 and 2010, water quality improved at all sites. The biomass of herbivorous fish was significantly greater in the MPAs compared to other sites and, importantly, we detected an increase in herbivore biomass between 2005 and 2008. Inshore reefs adjacent to logging operations had significantly lower coral cover and higher macroalgal cover than those offshore. Between 2005 and 2008 all sites showed an increase in crustose coralline algae cover and a decrease in turf algae colonising rocks, with the changes indicative of improving reef health. Collectively, these results indicate that reduction in logging and implementation of community-based management can have a positive influence on reefs in Marovo Lagoon.

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Fine Scale Temporal and Spatial Dynamics of the Stony Coral Tissue Loss Disease Outbreak Within the Lower Florida Keys

Frontiers in Marine Science ◽

10.3389/fmars.2021.631776 ◽

2021 ◽

Vol 8 ◽

Author(s):

Sara D. Williams ◽

Cory S. Walter ◽

Erinn M. Muller

Keyword(s):

Spatial Clustering ◽

Coral Cover ◽

Spatial Scales ◽

Florida Keys ◽

Incidence Rates ◽

Tissue Loss ◽

Coral Tissue ◽

Maximum Temperature ◽

Small Scale ◽

Stony Coral

One of the latest threats to Florida’s Coral Reef is the stony coral tissue loss disease (SCTLD) outbreak which affects all but a few Caribbean scleractinian species and has spread throughout the Caribbean since 2014. Without a known pathogen, ecological studies of disease dynamics are essential for understanding SCTLD susceptibility at the individual colony and reef level. We investigated the epizootiology of the SCTLD outbreak in the lower Florida Keys at two spatial scales (among reefs ∼1 km and within reefs <10 m) over a 19 month period. In May 2018, three sites absent of SCTLD were established to characterize coral demographics (i.e., live tissue cover and colony diameter) along an offshore to nearshore gradient, and were subsequently surveyed for disease every 2–3 weeks until December 2019. SCTLD was first noted within the offshore and mid-channel reef sites in early October 2018 and later appeared at the nearshore site in early February 2019. SCTLD was negatively correlated with thermal stress, showing reduced progression and incidence rates after 2–3 weeks of water temperatures above the mean monthly maximum temperature for the region (i.e., 2–3 degree heating weeks). Although Pseudodiploria strigosa, Dichocoenia stokesii, Colpophyllia natans, and Diploria labyrinthiformis were the most susceptible species at our sites, areas with more Montastraea cavernosa and Orbicella faveolata colonies had higher prevalence and greater tissue loss associated with disease. The disease was more severe within quadrats with high species diversity, high coral cover, and disproportionately affected larger colonies. Our spatial analyses suggest that (1) SCTLD followed a contagious disease model within small (<10 m) spatial scales, (2) colonies within 1.5–3 m of a diseased coral were at higher risk for subsequently showing disease signs compared with those farther away, and (3) high incidence rates coincided with the loss of small scale (<10 m radius) spatial clustering, suggesting pulses of contagious spread on large spatial scales.

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A cross-ocean comparison of responses to settlement cues in reef-building corals

10.7287/peerj.preprints.264v1 ◽

2014 ◽

Author(s):

Sarah W Davies ◽

Eli Meyer ◽

Sarah M Guermond ◽

Mikhail V Matz

Keyword(s):

Climate Change ◽

Coral Species ◽

Coral Cover ◽

Coralline Algae ◽

Crustose Coralline Algae ◽

Coral Recruitment ◽

Coral Larvae ◽

Settlement Cues ◽

The Pacific ◽

Caribbean Coral

Caribbean coral reefs have deteriorated substantially over the past 30 years, which is broadly attributable to the effects of global climate change. In the same time, Indo-Pacific reefs maintain higher coral cover and typically recover rapidly after disturbances. This difference in reef resilience is largely due to much higher coral recruitment rates in the Pacific. We hypothesized that the lack of Caribbean coral recruitment might be explained by diminishing quality of settlement cues and/or impaired sensitivity of Caribbean coral larvae to those cues, relative to the Pacific. To evaluate this hypothesis, we assembled a collection of bulk samples of reef encrusting communities, mostly consisting of crustose coralline algae (CCA), from various reefs around the world and tested them as settlement cues for several coral species originating from different ocean provinces. Cue samples were meta-barcoded to evaluate their taxonomic diversity. We observed no systematic differences either in cue potency or in strength of larval responses depending on the ocean province, and no preference of coral larvae towards cues from the same ocean. Instead, we detected significant differences in cue preferences among coral species, even for corals originating from the same reef. We conclude that the region-wide disruption of the settlement process is unlikely to be the major cause of Caribbean reef loss. However, due to their high sensitivity to the effects of climate change, shifts in the composition of CCA-associated communities, combined with pronounced differences in cue preferences among coral species, could substantially influence future coral community structure.

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Evidence for water-mediated mechanisms in coral–algal interactions

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2016.1137 ◽

2016 ◽

Vol 283 (1836) ◽

pp. 20161137 ◽

Cited By ~ 28

Author(s):

Hendrikje Jorissen ◽

Christina Skinner ◽

Ronald Osinga ◽

Dirk de Beer ◽

Maggy M. Nugues

Keyword(s):

Flow Chamber ◽

Flow Speed ◽

Coralline Algae ◽

Field Observations ◽

Surface Oxygen ◽

Transport Mechanisms ◽

Crustose Coralline Algae ◽

Turf Algae ◽

Diffusive Boundary ◽

Underlying Mechanisms

Although many coral reefs have shifted from coral-to-algal dominance, the consequence of such a transition for coral–algal interactions and their underlying mechanisms remain poorly understood. At the microscale, it is unclear how diffusive boundary layers (DBLs) and surface oxygen concentrations at the coral–algal interface vary with algal competitors and competitiveness. Using field observations and microsensor measurements in a flow chamber, we show that coral (massive Porites ) interfaces with thick turf algae, macroalgae, and cyanobacteria, which are successful competitors against coral in the field, are characterized by a thick DBL and hypoxia at night. In contrast, coral interfaces with crustose coralline algae, conspecifics, and thin turf algae, which are poorer competitors, have a thin DBL and low hypoxia at night. Furthermore, DBL thickness and hypoxia at the interface with turf decreased with increasing flow speed, but not when thick turf was upstream. Our results support the importance of water-mediated transport mechanisms in coral–algal interactions. Shifts towards algal dominance, particularly dense assemblages, may lead to thicker DBLs, higher hypoxia, and higher concentrations of harmful metabolites and pathogens along coral borders, which in turn may facilitate algal overgrowth of live corals. These effects may be mediated by flow speed and orientation.

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