Michael J Sweet | University of Derby (original) (raw)

Papers by Michael J Sweet

For many corals, the timing of broadcast spawning correlates strongly with a number of environmen... more For many corals, the timing of broadcast spawning correlates strongly with a number of environmental signals (seasonal temperature, lunar, and diel cycles). Robust experimental studies examining the role of these putative cues in triggering spawning have been lacking until recently because it has not been possible to predictably induce spawning in fully closed artificial mesocosms. Here, we present a closed system meso-cosm aquarium design that utilizes microprocessor technology to accurately replicate environmental conditions, including photoperiod, seasonal insolation, lunar cycles, and seasonal temperature from Singapore and the Great Barrier Reef (GBR), Australia.

Invertebrates account for more than 89% of all extant organisms in the marine environment, repres... more Invertebrates account for more than 89% of all extant organisms in the marine environment, represented by over 174,600 species (recorded to date). Such diversity is mirrored in (or more likely increased by) the microbial symbionts associated with this group and in the marine natural products (or MNPs) that they produce. Since the early 1950s over 20,000 MNPs have been discovered, including compounds produced by symbiotic bacteria, and the chemical diversity of compounds produced from marine sources has led to them being referred to as "blue gold" in the search for new drugs. For example, 80% of novel antibiotics stemming from the marine environment have come from Actinomycetes, many of which can be found associated with marine sponges, and compounds with anti-tumorigenic and anti-diabetic potential have also been isolated from marine symbionts. In fact, it has been estimated that marine sources formed the basis of over 50% of FDA-approved drugs between 1981 and 2002. In this review, we explore the diversity of marine microbial symbionts by examining their use as the producers of novel pharmaceutical actives, together with a discussion of the opportunities and constraints offered by " blue gold " drug discovery.

This study aimed to assess how the size-frequency distributions of coral genera varied between re... more This study aimed to assess how the size-frequency distributions of coral genera varied between reefs under different fishing pressures in two contrasting Indian Ocean locations (the Maldives and East Africa). Using generalized linear mixed models, we were able to demonstrate that complex interactions occurred between coral genera, coral size class and fishing pressure. In both locations, we found Acropora coral species to be more abundant in non-fished compared to fished sites (a pattern which was consistent for nearly all the assessed size classes). Coral genera classified as ‘stress tolerant’ showed a contrasting pattern i.e. were higher in abundance in fished compared to non-fished sites. Site specific variations were also observed. For example, Maldivian reefs exhibited a significantly higher abundance in all size classes of ‘competitive’ corals compared to East Africa. This possibly indicates that East African reefs have already been subjected to higher levels of stress and are therefore less suitable environments for ‘competitive’ corals. This study also highlights the potential structure and composition of reefs under future degradation scenarios, for example with a loss of Acropora corals and an increase in dominance of ‘stress tolerant’ and ‘generalist’ coral genera.

Coral disease surveys were conducted in Bintan, Kepulauan Riau Province. The purpose was to ident... more Coral disease surveys were conducted in Bintan, Kepulauan Riau Province. The purpose was to identify the abundance of corals showing signs of Yellow Syndrome (YS) disease and to describe similar pathological signs to that of AYBD throughout Bintan District. Three belt transects (2 m x 50 m in size) were set up to determine the abundance of coral reef attacked by YS disease. Line intercept transects were used to determine the percentage of live corals in the surveyed areas. The survey showed that the YS disease syndrome attacked 8 different genera i.e. Acropora, Montipora, Porites, Pavona, Turbinaria, Favia, Platygyra, and Favites. The highest attack happened at Mapur Island (0.06 kol/m 2) on Porites lutea, Turbinaria peltata, T. mesenterina, Acropora bruggemanni, and Pavona frondifera. The survey also indicated that there may have been at least two types of YS i.e. the first type caused by a boring and/or over-growing sponge species and the second type caused by a kind of pathogenic microbe. Regardless the causal agent of YS, the severity of YS attack on coral urged immediate action to be undertaken and should include initial microscopic and histology examinations. Based on this initial microscopic and histology examinations it was found out that YS bears a close resemblance to the Arabian Yellow Band Disease. This study, however, argued that the word " disease " may have been incorrectly used without identifying a specific causal agent.

Aim: There is global consensus that marine protected areas offer a plethora of benefits to the bi... more Aim: There is global consensus that marine protected areas offer a plethora of benefits to the biodiversity within and around them. Nevertheless, many organisms threatened by human impacts also find shelter in unexpected or informally protected places. For coral reef organisms, refuges can be tourist resorts implementing local environment-friendly bottom-up management strategies. We used the coral reef ecosystem as a model to test whether such practices have positive effects on the biodiversity associated with de facto protected areas. Location: North Ari Atoll, Maldives. Methods: We modelled the effects of the environment and three human management regimes (tourist resorts, uninhabited and local community islands) on the abundance and diversity of echinoderms and commercially important fish species, the per cent cover of reef benthic organisms (corals, calcareous coralline algae, turf and macroal-gae) and the proportion of coral disease. We used multivariate techniques to assess the differences between reef components among the management regimes. Results: Reefs varied between the management regimes. A positive " resort effect " was found on sessile benthic organisms, with good coral cover and significantly less algae at resort islands. Corals were larger and had fewer diseases in uninhabited islands. Minor " resort effect " was detected on motile species represented by commercial fish and echinoderms. Main conclusions: In countries where natural biodiversity strongly sustains the tourist sector and where local populations rely on natural resources, a balance between tourism development, local extraction practices and biodiversity conservation is necessary. The presence of eco-friendly managed resorts, which practices would need to be certified on the long term, is beneficial to protect certain organisms. House reefs around resorts could therefore provide areas adding to existing marine protected areas, while marine protection efforts in local community islands should focus on improving fishing management. K E Y W O R D S coral reefs, echinoderms, generalized linear mixed-effect models, human impact, Maldives, management, reef fish, refuge, tourist resort

The user has requested enhancement of the downloaded file. All in-text references underlined in b... more The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately.

Shifts in the microbiome of the intertidal coral Coelastrea aspera (formally known as Goniastrea ... more Shifts in the microbiome of the intertidal coral Coelastrea aspera (formally known as Goniastrea aspera) from Phuket, Thailand, were noted over the course of a 4-d period of spring tides. During this time, corals were naturally exposed to high temperatures, intense solar radiation, sub-aerial exposure and tidally induced water fluxes. Analysis of the 16S microbiome highlighted that the corals harbored both 'core or stable' communities and those which appeared to be more 'transient or sporadic.' Only relatively few microbial associates were classified as core microbes; the majority were transient or sporadic. Such transient associates were likely to have been governed by tidally induced variations in mucus thickness and water fluxes. Here we report strong shifts in the bacterial community of C. aspera over a short temporal scale. However, we also show significant differences in the timing of shifts between the two age groups of corals studied. More rapid changes (within 2 d of sub-aerial exposure) occurred within the 4-yr-old colonies, but a slightly delayed response was observed in the 10-yr-old colonies, whereby the microbial associates only changed after 4 d. We hypothesize that these shifts are age related and could be influenced by the observed baseline differences in the microbiome of the 4-and 10-yr-old corals, bacteria–bac-teria interactions, and/or host energetics.

Metagenomic and electron microscopy studies confirm that the coral microbiome contains a rich div... more Metagenomic and electron microscopy studies confirm that the coral microbiome contains a rich diversity and abundance of viruses. While there have been no definitive tests of disease causation by viruses in corals, viruses have been implicated as coral pathogens in a number of studies. Growing evidence also indicates that latent viral infections can compromise the algal symbionts under environmental stress and may be involved in the coral bleaching response. Conversely, bacteriophages and archaeal phage viruses are abundant in the microbiome of healthy corals and are likely to be involved in complex ecological networks, genetic material transfer and selective co-evolution within the surface mucus layers and tissues. The relative importance of viral control of bacterial and archaeal populations is unknown, but they are almost certain to be exerting some level of control on the composition and maintenance of the coral microbiome. While rapid leaps in the capability to detect viruses have been made due to advances in metagenomics and bioinformatics, these approaches need now to be integrated with in vitro culture and challenge experiments to assess the functional roles of viruses in health and disease, and it is imperative that interactions with other members of the coral microbiome are taken into account when assessing disease causation.

The term " microbiome " was first coined in 1988 and given the definition of a characteristic mic... more The term " microbiome " was first coined in 1988 and given the definition of a characteristic microbial community occupying a reasonably well defined habitat which has distinct physio-chemical properties. A more recent term has also emerged, taking this one step further and focusing on diseases in host organisms. The " pathobiome " breaks down the concept of " one pathogen = one disease " and highlights the role of the microbiome, more specifically certain members within the microbiome, in causing pathogenesis. The development of next generation sequencing has allowed large data sets to be amassed describing the microbial communities of many organisms and the field of coral biology is no exception. However, the choices made in the analytical process and the interpretation of these data can significantly affect the outcome and the overall conclusions drawn. In this review we explore the implications of these difficulties, as well as highlighting analytical tools developed in other research fields (such as network analysis) which hold substantial potential in helping to develop a deeper understanding of the role of the microbiome in disease in corals. We also make the case that standardization of methods will substantially improve the collective gain in knowledge across research groups.

HAYATI Journal of Biosciences, 2015

Coral diseases that have emerged since the early 1970s have caused significant regional ecologica... more Coral diseases that have emerged since the early 1970s have caused significant regional ecological impacts. However, there has been a paucity of research into coral disease in South-East Asia, including Indonesia. This study provides baseline coral disease data in the Kepulauan Seribu Marine National Park. Previously only one type of disease (White Syndrome, WS) has been detected at this site. In this study we show a positive correlation between overall coral cover and the dominant reef building coral Montipora spp. on research sites and found that two main diseases, Black Band Disease (BBD) and WS, were highly prevalent throughout all reefs. Based on spatial location, the highest abundance of BBD (0.08 col. m−2) was found at sites nearer (zone 1) to the mainland, whilst for WS (0.05 col. m−2) highest abundance was found at middle sites (zone 2). According to the temporal data, the highest abundance of BBD (0.77 col. m−2) was found during the transition period (between wet and dry seasons) whilst for WS higher abundance occurred within the dry season (0.07 col. m−2). There was a significant difference in disease abundance among seasons which was correlated with increasing temperature and light intensity along with variations in total organic matters, nitrite and phosphate levels. Moreover, the middle sites experienced additional stress from the waste material originating from the mainland, transported via currents flowing in this direction (the currents flow in reverse during the rainy season).

The number of ecophysiological studies involving reef corals has increased markedly over the last... more The number of ecophysiological studies involving reef corals has increased markedly over the last 20 years, driven primarily by the concern over the potential effects of anthropogenic change on coral communities. In particular, the evaluation of the effects of global climate change has prompted major research efforts into understanding the consequences of both rising seawater temperatures and ocean acidification on the physiology of corals. In recent years the recognition that corals harbour not only symbiotic algae but also a diverse microbial consortium, which may both influence and be influenced by the physiology of the animal host, has added an extra layer of complexity to this biological system known collectively as the 'coral holobiont'. The present review draws together an extensive literature on ecophysiological responses of the coral holobiont to anthropo-genic change, with specific references to the latest molecular and genetic developments in the field. It also highlights gaps in our basic understanding of coral physiology and draws attention to the value of extreme physical habitats in elucidating the acclimatory and adaptive scope of reef corals to climate change.

Worldwide coral reef decline appears to be accompanied by an increase in the spread of hard coral... more Worldwide coral reef decline appears to be accompanied by an increase in the spread of hard coral diseases. However, whether this is the result of increased direct and indirect human disturbances and/or an increase in natural stresses remains poorly understood. The provision of baseline surveys for monitoring coral health status lays the foundations to assess the effects of any such anthropogenic and/or natural effects on reefs. Therefore, the objectives of this present study were to provide a coral health baseline in a poorly studied area, and to investigate possible correlations between coral health and the level of anthropogenic and natural disturbances. During the survey period, we recorded 20 different types of coral diseases and other compromised health statuses. The most abundant were cases of coral bleaching, followed by skeletal deformations caused by pyrgomatid barnacles, damage caused by fish bites, general pigmentation response and galls caused by cryptochirid crabs. Instances of colonies affected by skeletal eroding bands, and sedimentation damage increased in correlation to the level of biochemical disturbance and/or proximity to villages. Moreover, galls caused by cryptochirid crabs appeared more abundant at sites affected by blast fishing and close to a newly opened metal mine. Interestingly, in the investigated area the percentage of corals showing signs of 'common' diseases such as black band disease, brown band disease, white syndrome and skeletal eroding band disease were relatively low. Nevertheless, the relatively high occurrence of less common signs of compromised coral-related reef health, including the aggressive overgrowth by sponges, deserves further investigation. Although diseases appear relatively low at the current time, this area may be at the tipping point and an increase in activities such as mining may irredeemably compromise reef health.

A high prevalence of skin pigmented lesions of 15% was recently reported in coral trout Plectropo... more A high prevalence of skin pigmented lesions of 15% was recently reported in coral trout Plectropomus leopardus, a commercially important marine fish, inhabiting the Great Barrier Reef. Herein, fish were sampled at two offshore sites, characterised by high and low lesion prevalence. A transcriptomic approach using the suppressive subtractive hybridisation (SSH) method was used to analyse the differentially expressed genes between lesion and normal skin samples. Transcriptional changes of 14 genes were observed in lesion samples relative to normal skin samples. These targeted genes encoded for specific proteins which are involved in general cell function but also in different stages disrupted during the tumourigenesis process of other organisms, such as cell cycling, cell proliferation, skeletal organisation and cell migration. The results highlight transcripts that are associated with the lesion occurrence, contributing to a better understanding of the molecular aetiology of this coral trout skin disease.

Microbial photoautotrophs on glaciers engineer the formation of granular microbial-mineral aggreg... more Microbial photoautotrophs on glaciers engineer the formation of granular microbial-mineral aggregates termed cryoconite which accelerate ice melt, creating quasi-cylindrical pits called 'cryoconite holes'. These act as biogeochemical reactors on the ice surface and provide habitats for remarkably active and diverse microbiota. Evolution of cryoconite holes towards an equilibrium depth is well known, yet interactions between microbial activity and hole morphology are currently weakly addressed. Here, we experimentally perturbed the depths and diameters of cryoconite holes on the Greenland Ice Sheet. Cryoconite holes responded by sensitively adjusting their shapes in three dimensions ('biocryomorphic evolution') thus maintaining favourable conditions for net autotrophy at the hole floors. Non-targeted metabolomics reveals concomitant shifts in cyclic AMP and fucose metabolism consistent with photo-taxis and extracellular polymer synthesis indicating metabolomic-level granular changes in response to perturbation. We present a conceptual model explaining this process and suggest that it results in remarkably robust net autotrophy on the Greenland Ice Sheet. We also describe observations of cryocon-ite migrating away from shade, implying a degree of self-regulation of carbon budgets over mesoscales. Since cryoconite is a microbe-mineral aggregate, it appears that microbial processes themselves form and maintain stable autotrophic habitats on the surface of the Greenland ice sheet.

ABSTRACT: Diseases of sea urchins have been implicated in dramatic transitions of marine ecosyste... more ABSTRACT: Diseases of sea urchins have been implicated in dramatic transitions of marine
ecosystems. Although no definitive causal agent has been found for many of these outbreaks, most
are hypothesised to be waterborne and bacterial. Here we show the first report of a novel disease
affecting at least 2 species of urchins off the south-eastern coast of Australia. The aetiological
agent, identified via a range of molecular techniques, immuno-histology and inoculation experiments,
was found to be the opportunistic pathogen Vibrio anguillarum. The disease appears to be
temperature-dependent, with a faster transmission rate and increase in prevalence during ex -
perimental trials conducted at higher temperatures. Furthermore, analysis of long-term field data
suggests that it may have already reached epidemic proportions. With the increases in ocean
temperatures brought about by climate change, this novel urchin disease may pose a severe
problem for the organisms associated with the temperate reefs off Australia and/or the ecosystem
as a whole.

Black band disease (BBD) is the oldest recognised disease associated with scleractinian corals. H... more Black band disease (BBD) is the oldest recognised disease associated with scleractinian corals. However, despite this, few BBD surveys have been conducted in the Indonesian archipelago, one of the world's hot spots for coral diversity. In this study, we show that BBD was recorded in the reefs of Kepulauan Seribu, Indonesia, at the time of surveying. The disease was found to mainly infect corals of the genus Montipora. In some instances, upwards of 177 colonies (31.64%) were found to be infected at specific sites. Prevalence of the disease ranged from 0.31% to 31.64% of Montipora sp. colonies throughout the archipelago. Although BBD was found at all sites, lower frequencies were associated with sites closest to the mainland (17.99 km), as well as those that were furthest away (63.65 km). Despite there being no linear relationship between distance from major population centers and BBD incidence, high incidences of this disease were associated with sites characterized by higher levels of light intensity. Furthermore, surveys revealed that outbreaks peaked during the transitional period between the dry and rainy seasons. Therefore, we suggest that future surveys for disease prevalence in this region of Indonesia should focus on these transitory periods.

Bacterial and ciliate assemblages associated with aquarium corals displaying white syndrome (WS) ... more Bacterial and ciliate assemblages associated with aquarium corals displaying white syndrome (WS) and brown jelly syndrome (BJS) were investigated. Healthy (n = 10) and diseased corals (WS n = 18; BJS n = 3) were analysed for 16S rRNA gene bacterial diversity, total bacterial abundance and vibrio-specific 16S rRNA gene abundance. This was conducted alongside analysis of 18S rRNA gene sequenc-ing targeting ciliates, a group of organisms largely overlooked for their potential as causal agents of coral disease. Despite significant differences between healthy and diseased corals in their 16S rRNA gene bacterial diversity, total bacterial abundance and vibrio-specific rRNA gene abundance, no domi-nant bacterial ribotypes were found consistently within the diseased samples. In contrast, one ciliate morphotype, named Morph 3 in this study (GenBank Accession Numbers JF831358 for the ciliate isolated from WS and JF831359 for the ciliate isolated from BJS) was observed to burrow into and under...

PloS one, 2015

Prokaryotic and ciliate communities of healthy and aquarium White Syndrome (WS)-affected coral fr... more Prokaryotic and ciliate communities of healthy and aquarium White Syndrome (WS)-affected coral fragments were screened using denaturing gradient gel electrophoresis (DGGE). A significant difference (R = 0.907, p < 0.001) in 16S rRNA prokaryotic diversity was found between healthy (H), sloughed tissue (ST), WS-affected (WSU) and antibiotic treated (WST) samples. Although 3 Vibrio spp were found in WS-affected samples, two of these species were eliminated following ampicillin treatment, yet lesions continued to advance, suggesting they play a minor or secondary role in the pathogenesis. The third Vibrio sp increased slightly in relative abundance in diseased samples and was abundant in non-diseased samples. Interestingly, a Tenacibaculum sp showed the greatest increase in relative abundance between healthy and WS-affected samples, demonstrating consistently high abundance across all WS-affected and treated samples, suggesting Tenacibaculum sp could be a more likely candidate for pa...

HAYATI Journal of Biosciences, 2015

PloS one, 2015