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Mucus Production by Corals Exposed during an Extreme Low Tide

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Abstract

An extreme low tide resulted in the severe exposure of corals on the reef flat surrounding Coconut Island in Kaneohe Bay, Oahu, Hawaii. The exposed corals produced vast quantities of mucus that aggregated as mucous ropes near the shoreline. These mucous ropes were heavily laden with carbonate sediments, amorphous materials, microflora, and microfauna. Compared to the purified liquid mucus of the coral Fungia scutaria, the consolidated mucous ropes were rich in organic material and phosphorus. Pure mucus was relatively low in trophic quality. While the pure mucus may provide corals with some protection against dessication, it is not a particularly rich food source for reef heterotrophs. Perhaps the most important role of coral mucus is the consolidation of microscopic organic particulates into macroscopic aggregates of considerably higher trophic quality than the pure mucus itself.

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... Mucus produced by cnidarians, similarly to other phyla, represents a fundamental aspect of the biology of these organisms and it is essential for several biological functions, including feeding, defending against pathogens, xenobiotics, and a multitude of environmental stressors, warding off aggression, and acting as an attacking weapon (Baier et al., 1985;Rivera-Ortega and Thomè, 2018;Camacho-Pacheco et al., 2022;). Although continuous mucus releasing is physiological, several studies demonstrated that some environmental stressors, such as high particle concentrations or high sediment loads, and exposition to air due to low tide conditions, can increase mucus production (Schuhmacher, 1977;Rublee et al., 1980;Krupp, 1984;Wild et al., 2004;Wild et al., 2005;Liu et al., 2018;). ...
... Briefly, in sessile cnidarians the mucus represents a strong protection against desiccation (Krupp, 1984), as its hydroscopic characteristics allow to keep the coral surface moist during exposure to air due to low tide conditions; however, the mechanisms that control these processes are still unclear. Although the mucous layer is not waterproof, it can greatly reduce the airflow and water exchange rate. ...
... Particulate mucus may also contain varying levels of phosphate or nitrogen, which may for example be influenced by planktonic food availability, colonization by picoplanktonic organisms and nitrogen-fixing bacteria (Hubot et al., 2022). An old view held that coral mucus was a negligible source of nutrients (e.g., Krupp, 1984;Coffroth, 1990). Today, however, it is known that mucus represents an energy substrate, rich in glucose , degradable by microbes and higher organisms (Benson and Muscatine, 1974;Grange, 1991;Rinkevich et al., 1991;Patton, 1994;. ...
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Mucus secretion provides an interface with unique and multifunctional properties between the epithelial cells of many aquatic organisms and their surrounding environment. Indeed, mucus is involved in various essential biological processes including feeding, reproduction, osmoregulation, competition for space, defense against pathogens, xenobiotics, and a multitude of environmental stressors. The ability to produce a functional mucus layer is an important evolutionary step, arising first in Cnidaria that allowed for the development of the mucus-lined digestive cavity seen in higher metazoans. Mucus secretion by cnidarians has been moderately investigated in both corals and jellyfish, which among cnidarians are the ones that have shown the highest secretion rates to date. However, although in corals the production of mucus has received more attention, especially in view of the important ecological role played in coral reefs, in medusozoans the topic is little considered. Although the mucus secreted by corals has innumerable and important immunological, nutritional, and protective responsibilities, it should be remembered that jellyfish too represent a fundamental component of marine trophic web, playing numerous and important roles that are still unclear today. What is certain is that jellyfish are characterized (especially in the era of climate change) by large fluctuations in population density, the ecological implications of which are poorly understood. However, in both cases (Medusozoans and Anthozoans) to date some aspects relating to mucous secretions seem completely obscure, such as the microbiome and its variations as a function of environmental conditions or ontogenetic development, its implications in the field of immunological ecology, the consequent energy costs and finally the role played by the mucus in evolutionary terms. This review summarizes the properties, functions, ecological implications and evolutionary importance of mucus, in cnidarians, mainly focusing its roles in corals and jellyfish. Understanding these aspects relating to the ecological and evolutionary importance played by mucus is of fundamental importance for the ecosystems functioning.
... However, Krupp (1984), Meikle et al. (1988) and Coffroth (1990) have argued that coral mucus is a material of low nutritional value for reef organisms. Coffroth (1990) concluded, in her pilot study on Porites mucus sheets, that their release is not an important nutrient source in coral reefs. ...
... We observed the production of large amounts of coral mucus by many species of corals in response to aerial exposure during low tide at Heron Island, Great Barrier Reef, Australia. Air exposure events have been observed in other reef environments in Australia as well as in New Caledonia, Madagascar, the Red Sea and Hawaii (Daumas et al. 1982, Krupp 1984, Romaine et al. 1997. Exposure of corals to air is, thus, not restricted to the Great Barrier Reef. ...
... It was known from observations that corals release large amounts of mucus during tide-related exposure to air (Krupp 1984). Our experiments quantify this release and highlight the significance of this phenomenon, which causes a strong increase of the normal mucus production rates by Acropora millepora from approximately 0.3 to 3.8 l mucus m -2 coral surface h -1 . ...
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Mucus release by hard corals of the genus Acropora under submersed and naturally occurring air exposure was quantified at Heron Island/Great Barrier Reef. These measurements were conducted with beaker and in situ container incubation techniques. Mucus release rates for A. millepora, normalized to the coral surface area, were 10 +/- 5mg C and 1.3 +/- 0.8 mg N m(-2) h(-1) for submersed corals, and 117 +/- 79 mg C and 13 +/- 8 mg N m-2 h-1 after exposure to air at low tide. This corresponds to increases by factors of 12 for C and 10 for N. The main monosaccharide components of freshly released Acropora mucus were arabinose and glucose, accounting for 14 to 63% and 13 to 41% of the carbohydrates. A protein content of 13 to 26 mg l(-1) caused a low C:N ratio of 8 to 14. The chlorophyll content of 7 to 8 mu g l(-1) in the mucus compared to 0.6 +/- 0.004 mu g l(-1) in the surrounding seawater revealed mucus contamination with zooxanthellae. A low pH value of 7.7 compared to 8.3 in the surrounding seawater indicates the existence of acidic components in fresh coral mucus. Concentrations of most measured inorganic nutrients were highly increased in coral mucus, reaching values of 3 to 4 mu M for silicate, 19 to 22 mu M for phosphate and 20 to 50 mu M for ammonium concentration. Phosphate concentrations were 130-fold higher in coral mucus compared to the surrounding seawater, underlining the role of coral mucus as a carrier of nutrients. Addition of coral mucus to stirred benthic chambers resulted in a shift of phosphate, ammonium and nitrate/nitrite fluxes towards the sediments, confirming the transport of nutrients via coral mucus into permeable reef sands.
... Mass mortalities of corals following extreme low tides and high solar radiation have been reported in Guam (Yamaguchi, 1975), Eastern Pacific (Glynn, 1976;Eakin, 1996;Zapata et al., 2010;Mejıá-Renterıá et al., 2019), the Red Sea (Fishelson, 1973;Loya, 1976), Hawaii (Krupp, 1984), Thailand (Brown et al., 1994) the Central Great Barrier Reef (GBR) in Australia (Anthony and Kerswell, 2007), and Indonesia (Ampou et al., 2017). Armstrong et al. (2007) report a cold weather emersion event for Ningaloo in Western Australia, and Hoegh- Guldberg et al. (2005) describe extensive coral bleaching and subsequent partial mortality following a low water level event at Heron Island in the GBR in which corals were exposed to unusually cold conditions and dry winds. ...
... His results conferred with those of Fishelson (1973) who found that 'brain-like' corals, were more resistant to emersion than the delicate 'bush-like' forms. This may be due to thicker tissue layers being present in some massive genera (Brown et al., 1994;Anthony and Kerswell, 2007) and mucus production which prevents desiccation during emersion (Krupp, 1984). More recently Castrilloń-Cifuentes et al. (2017) found exposure to air simulating naturally occurring tidal exposure did not cause lethal bleaching or reduce growth rates, but that sexual reproduction was negatively affected. ...
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Sea level exerts a fundamental influence on the intertidal zone, where organisms are subject to immersion and emersion at varying timescales and frequencies. While emersed, intertidal organisms are exposed to atmospheric stressors which show marked diurnal and seasonal variability, therefore the daily and seasonal timing of low water is a key determinant of survival and growth in this zone. Using the example of shallow coral reefs, the coincidence of emersion with selected stressors was investigated for eight locations around the Australian coastline. Hourly water levels (1992 – 2016) from a high-resolution sea level hindcast (http://sealevelx.ems.uwa.edu.au), were linked to maximum surface solar radiation data from the Copernicus ERA5 atmospheric model and minimum atmospheric temperature observations from the Australian Bureau of Meteorology to identify seasonal patterns and historical occurrence of coral emersion mortality risk. Local tidal characteristics were found to dictate the time of day when low water, and therefore emersion mortality risk occurs, varying on a seasonal and regional basis. In general, risk was found to be greatest during the Austral spring when mean sea levels are lowest and a phase change in solar tidal constituents occurs. For all Great Barrier Reef sites, low tide occurs close to midday during winter and midnight in the summer, which may be fundamental factor supporting the historical bio-geographical development of the reef. Interannual variability in emersion mortality risk was mostly driven by non-tidal factors, particularly along the West Coast where El Niño events are associated with lower mean sea levels. This paper highlights the importance of considering emersion history when assessing intertidal environments, including shallow coral reef platform habitats, where critical low water events intrinsically influence coral health and cover. The study addresses a fundamental knowledge gap in both the field of water level science and intertidal biology in relation to the daily timing of low tide, which varies predictably on a seasonal and regional basis.
... Furthermore, integration of polyps via streams turned out to be helpful not only in feeding but also as a potential protection against desiccation, as we observed a surface stream-based lift of seawater with mucus to the air-exposed parts of the coral in the lab. This capacity might thus be essential for the survival of corals living in regions experiencing low tides, 24,32 which requires further open-field investigations. Furthermore, the presence of mucus forming a thicker water-retaining layer could enhance the hydration caused by the lifting power of streams. ...
... Furthermore, the presence of mucus forming a thicker water-retaining layer could enhance the hydration caused by the lifting power of streams. 12,13,32 As the water and mucus at the coral surface connect with the internal gastrovascular system via the distributed mouths, we also questioned the dynamics of the liquid flow within the system of internal gastrovascular canals. Previously, a few aspects of the active movement of fluids inside the gastrovascular system of corals were already reported. ...
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Reef-building corals are endangered animals with a complex colonial organization. Physiological mechanisms connecting multiple polyps and integrating them into a coral colony are still enigmatic. Using live imaging, particle tracking, and mathematical modeling, we reveal how corals connect individual polyps and form integrated polyp groups via species-specific, complex, and stable networks of currents at their surface. These currents involve surface mucus of different concentrations, which regulate joint feeding of the colony. Inside the coral, within the gastrovascular system, we expose the complexity of bidirectional branching streams that connect individual polyps. This system of canals extends the surface area by 4-fold and might improve communication, nutrient supply, and symbiont transfer. Thus, individual polyps integrate via complex liquid dynamics on the surface and inside the colony.
... En effet, à l'intérieur du mucus, on trouve par exemple des molécules particulières appelées les acides aminés mycosporine-like (MAAs) qui jouent un rôle de « crème solaire » pour les coraux et les protègent contre le rayonnement ultraviolet du soleil (Drollet et al. 1993(Drollet et al. , 1997. Le mucus est également une protection contre la dessiccation lorsque le corail est exposé à l'air libre lors des marées basses (Daumas and Thomassin 1977;Krupp 1984). Il constitue également une barrière physique qui protège les tissus sous-jacents des dommages causés par les courants et les vagues, le dépôt intempestif de sédiments ou encore la pénétration de polluants (Jaap and Wheaton 1975;Mitchell and Chet 1975;Daumas and Thomassin 1977;Bastidas and Garcia 2004). ...
... Une fois décollée de la surface du corail, la matière organique forme une source de nutrition potentielle pour les autres organismes du récif. La partie dissoute intègre la réserve de DOM de la colonne d'eau, directement utilisable par les organismes benthopélagiques, tandis que la partie particulaire restante forme des agrégats en suspension dans la colonne d'eau qui finissent par couler vers le fond de l'océan et qui viennent alimenter la boucle microbienne des sédiments (Krupp 1984;Wild et al , 2005. La matière organique excrétée par le corail est donc essentielle au fonctionnement du récif car elle favorise la croissance des micro-organismes associés au mucus, soutient la production benthopélagique et participe au recyclage des éléments essentiels (azote, phosphore…) dans l'eau très oligotrophe du récif Bythell and Wild 2011). ...
Thesis
Les coraux Scléractiniaires se développent généralement dans la zone photique peu profonde, exposée au rayonnement ultraviolet (UVs), la composante la plus dangereuse du rayonnement solaire. Le rayonnement UVs augmente avec le réchauffement climatique et s’ajoute à l’ensemble des pressions auxquelles sont soumis les coraux. Les enjeux de cette thèse ont été 1) de mieux comprendre les effets des UVs sur la réponse physiologique des coraux, les flux de matière organique et les bactéries associées au mucus et au corail; et 2) de caractériser l’effet combiné des UVs et d’une augmentation de température, et/ou d’un changement de disponibilité en sels nutritifs. Les résultats obtenus montrent tout d’abord que l’exposition des coraux aux UVs amplifie l’effet négatif de la température sur leur physiologie. Il en est de même pour l’absence en sels nutritifs, essentiels pour la physiologie corallienne. Nos résultats indiquent également que la sensibilité des coraux à un stress UV dépend de l’espèce étudiée et de la densité de symbiontes présents dans les tissus. L’effet négatif des UVs augmente avec la densité de symbiontes, vraisemblablement dû à la formation d’espèces réactives de l’oxygène (ROS) qui provoquent des dommages à l’organisme. Dans cette thèse, nous avons montré que la voie de signalisation JNK (c-Jun N-terminal kinase), hautement conservée au sein des êtres vivants, est impliquée dans la gestion de ces espèces réactives et que son inhibition entraine un blanchissement très rapide des coraux sous UVs et forte température. Finalement, l’excrétion de matière organique ainsi que les bactéries associées sont également impactés par les UVs ce qui pourrait contribuer à d’importants changements biochimiques dans l’eau des récifs coralliens. Les travaux de cette thèse apportent de nouvelles connaissances sur les effets des UVs sur les coraux et soulignent l’importance de les prendre en considération lors de nos prédictions sur le devenir des récifs coralliens face au réchauffement climatique.
... Once formed, mucous sheets can become fouled with algae, protozoa, zooplankton (Mayer and Wild, 2010), bacteria, ciliates, nauplii, crustacea (Coffroth, 1990), fecal pellets, other unidentifiable debris and sediment (Hartnoll, 1974;Johnston and Rohwer, 2007;Krupp, 1984;Lewis, 1973;Mayer and Wild, 2010). The transformation of viscous mucus to a sheet like formation has been linked to fouling by sediment (Ducklow and Mitchell, 1979). ...
... Mucous sheets have been reported in Porites astreoides, P. divaricata, P. furcata, and P. porites in Florida and the Caribbean (Bak and Elgershuizen, 1976;Coffroth, 1985;Ducklow and Mitchell, 1979;Edmunds and Davies, 1986;Glasl et al., 2016;Lewis, 1973;Marcus and Thorhaug, 1981), Porites cylindrica from Japan (Kato, 1987), Porites compressa from Hawaii (Krupp, 1984;Marcus and Thorhaug, 1981), along with P. lutea, P. lobata, P. australiensis and P. murrayensis on the Great Barrier Reef of Australia (Coffroth, 1988;Coffroth, 1990;Stafford-Smith and Ormond, 1992). Similar sheet like structures have also been reported in the corals Diploastrea heliopora, Pachyseris speciosa, Mycedium elephantotus, Pectinia lactuca, P. paeonia, Turbinaria peltata and T. mesenterina (Sofonia and Anthony, 2008;Stafford-Smith and Ormond, 1992), Heliopora coerulea (Lewis, 1973), and in other groups such as gorgonians, alcyonaceans and zoanthids (Coffroth, 1988;Rublee et al., 1980). ...
Article
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Some coral species of the genus Porites can produce thick mucous sheets that partially or completely envelope the colony’s surface. This phenomenon has been reported many times, but the cause and ecological significance remains unclear. In this study, sheet production was examined in response to elevated suspended sediment concentrations associated with a large-scale, extended dredging project on a coral reef. Approximately 400 corals at 16 locations situated from 0.2–33km from the excavation area were examined at fortnightly intervals over the 1.5year dredging campaign. Mucous sheets were observed on 447 occasions (from 10,600 observations), with average mucous prevalence ranging from 0–10%. Overall 74±5% of the colonies <1.5km from the dredging produced one or more sheets. High levels of mucous coverage (≥95% of the colony surface) was observed on 68 occasions, and 82% of these occurred at sites close to the dredging. Approximately 50% of colonies produced ≥3 sheets over the monitoring period, and 90% of these were located close to the dredging. In contrast, at distantly located reference sites (>20km away), mean mucous sheet prevalence was very low (0.2%±0.1), no colonies produced more than 1 sheet, and only 1 colony was observed with high mucous coverage. In a laboratory-based experiment, explants of Porites spp. exposed to fine silt also produced mucous sheets (105 sheets recorded in 1100 observations), with nearly 30% of the fragments exposed to repeated sediment deposition events of 10 and 20mgcm⁻²d⁻¹ producing 2 new sheets over the 28day exposure period. These multiple lines of evidence suggest a close association between mucous sheet formation and sediment load, and that sheet formation and sloughing are an additional mechanism used by massive Porites spp. to clear their surfaces when sediment loads become too high. These results suggest that mucous sheet formation is an effective bioindicator of sediment exposure.
... We noticed that coral re-submersion caused the release of mucus ropes, which typically contain DMS(P) concentrations that are orders of magnitude higher than in seawater 2 . During air exposure, bio-physical mechanisms such as mucus production 53 and/or polyp retraction 54 help to minimise water loss but also limit the cutaneous oxygen supply and potentially cause hypoxia within the tissues 53 . After the first few minutes of air exposure, we did not detect much additional DMS emission so these mechanisms may also restrict the release of DMS when coral is exposed to air, thereby possibly allowing DMS to build up within the mucus. ...
... We noticed that coral re-submersion caused the release of mucus ropes, which typically contain DMS(P) concentrations that are orders of magnitude higher than in seawater 2 . During air exposure, bio-physical mechanisms such as mucus production 53 and/or polyp retraction 54 help to minimise water loss but also limit the cutaneous oxygen supply and potentially cause hypoxia within the tissues 53 . After the first few minutes of air exposure, we did not detect much additional DMS emission so these mechanisms may also restrict the release of DMS when coral is exposed to air, thereby possibly allowing DMS to build up within the mucus. ...
Article
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Corals are prolific producers of dimethylsulfoniopropionate (DMSP). High atmospheric concentrations of the DMSP breakdown product dimethylsulfide (DMS) have been linked to coral reefs during low tides. DMS is a potentially key sulfur source to the tropical atmosphere, but DMS emission from corals during tidal exposure is not well quantified. Here we show that gas phase DMS concentrations (DMSgas) increased by an order of magnitude when three Indo-Pacific corals were exposed to air in laboratory experiments. Upon re-submersion, an additional rapid rise in DMSgas was observed, reflecting increased production by the coral and/or dissolution of DMS-rich mucus formed by the coral during air exposure. Depletion in DMS following re-submersion was likely due to biologically-driven conversion of DMS to dimethylsulfoxide (DMSO). Fast Repetition Rate fluorometry showed downregulated photosynthesis during air exposure but rapid recovery upon re-submersion, suggesting that DMS enhances coral tolerance to oxidative stress during a process that can induce photoinhibition. We estimate that DMS emission from exposed coral reefs may be comparable in magnitude to emissions from other marine DMS hotspots. Coral DMS emission likely comprises a regular and significant source of sulfur to the tropical marine atmosphere, which is currently unrecognised in global DMS emission estimates and Earth System Models.
... Its composition can also be altered by the protocols used for its collection and subsequent analysis. Of consequence, it has been described as both a material of low nutritional value for reef organisms (Krupp 1984, Meikle et al. 1988, Coffroth 1990) and as an important source of nutrients (Ducklow & Mitchell 1979, Coffroth 1990, Sorokin 1993) and dissolved/particulate organic matter (D/POM). While production of particulate or total organic matter in the form of mucus has been relatively well studied (Ducklow & Mitchell 1979, Coffroth 1990, very few data are available on the release of DOC and DON (Crossland 1987, Bythell 1988, Yamamuro & Kayanne 1997, despite DON representing more than 70% of the total dissolved nitrogen in coral reef waters (Crossland & Barnes 1983, Johannes et al. 1983, Smith 1984 and dissolved compounds being more easily absorbed and more directly available to reef organisms. ...
... DOM is therefore a high quality food at that time and may sustain the high bacterial growth and production rates often reported in coral reef waters (Moriarty et al. 1985, Ducklow 1990, Sorokin 1993). The range of C:N ratio obtained in this study (2.5:13) is comparable to those reported for mucous aggregates excreted by other coral colonies (7.4:44;Krupp 1984, Coffroth 1990. The rapid uptake of freshly excreted DOM may explain the low and relatively constant concentrations that have been measured in natural reef environments (Pagès et al. 1997) and the low DOM concentrations measured in reef waters relative to the open ocean (Suzuki et al. 1995). ...
... Vacelet and Thomassin (1991) observed that coral mucus of high molecular weight (more than 6000−8000) was not completely degraded by bacteria and eukaryotes even after 21 d. Krupp (1984) and Coffroth (1990) concluded that coral mucus itself is a material of low nutritional value for reef organisms and that the property to collect organic detritus and to serve as sites of aggregation for microorganisms is a more important trophic role of coral mucus. More recently, Ritchie (2006) and Chen et al. (2007) found antibacterial substance from coral mucus. ...
... Similar results were also reported by Pascal and Vacelet (1981). Krupp (1984) and Coffroth (1990) also suggested that coral mucus is a material of low nutritional value for reef organisms. More recently, Ritchie (2006) observed that mucus from Acropora palmata had antibiotic properties that were likely to play a role in ordering only beneficial microbial communities on the coral surface. ...
Article
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Bacterial decomposition of dissolved organic carbon (DOC) in coral mucus was investigated under dark conditions for 7 months to reveal what percentage of the coral-derived DOC is rapidly utilized by bacteria, and conversely, what percentage remained for a long term as refractory organic matter. During the first week, 38%-47% of DOC released from the hermatypic corals Acropora pulchra and Porites cylindrica were mineralized by bacteria collected from natural reef water. The bacterial abundance dramatically increased from the order of 10 3 to 10 6 cells ml -1 during the 1 week. Some part of the remaining organic C at 1 week was slowly decomposed over 3 months, but further degradation was not observed thereafter. Finally, 32%-44% of the initial DOC was not mineralized over 7 months. These results suggest that, under dark conditions, DOC in coral mucus is not completely degraded by free-living bacteria and contributes to long-term C fixation as refractory organic matter. Introduction It is well known that coral colonies release organic matter to the ambient seawater as dissolved and particulate organic matter (DOM and POM, respectively) (Tanaka et al. 2008). The coral-derived organic matter is often collectively referred to as mucus. The coral mucus has been regarded as ecologically important: bacterial aggregation was found in coral mucus (Ducklow and Mitchell 1979) and coral exudates actually enhanced the growth of pico-and nanoplankton (Ferrier-Pagès et al. 2000). Wild et al. (2004a, b) showed that a part of coral mucus was rapidly mineralized into CO 2 by bacteria in the reef sediment. The organic matter released from corals has been considered to be a good source of energy for microorganisms and to be completely and rapidly mineralized into CO 2 in the coral reef ecosystem. However, some studies proposed negative ideas on the bacterial decomposition of coral mucus. Vacelet and Thomassin (1991) observed that coral mucus of high molecular weight (more than 6000−8000) was not completely degraded by bacteria and eukaryotes even after 21 d. Krupp (1984) and Coffroth (1990) concluded that coral mucus itself is a material of low nutritional value for reef organisms and that the property to collect organic detritus and to serve as sites of aggregation for microorganisms is a more important trophic role of coral mucus. More recently, Ritchie (2006) and Chen et al. (2007) found antibacterial substance from coral mucus. These studies suggest that some part of the organic matter released from corals is not rapidly mineralized by bacteria but remain as relatively refractory organic matter. Therefore, no previous studies have revealed what % of the coral-devied organic matter is rapidly decomposed by bacteria and what % is not. The purpose of this study is to quantitatively investigate bacterial degradability of coral mucus for a long term. Dissolved organic matter in pure coral mucus was put under dark and the change in organic C concentration due to bacterial mineralization was observed over 7 months.
... The coral surface is constantly exposed to a variety of physical, chemical and microbial insults and therefore needs an extensive protective system for survival. Copious mucus release has been reported on exposure to air (low tide) (Krupp 1984), heavy sedimentation (Hubbard & Pocock 1972) and pollutants (Mitchell and Chet 1975;Neff and Anderson 1981;Peters 1981). The physical barrier function of the surface mucus layer (SML) depends on the thickness of the SML (Chapter 4). ...
... The SML thickness has been reported by combining above data with the estimated surface area of coral head (Wild et al. 2005, Koren & Rosenberg 2006. In another approach, cell biologists have used rate of production term to mean either the rate of synthesis of mucus inside cell or the rate of production of mucus on the surface (Crossland et al. 1980, Krupp 1984. Thus there remains a need to define these terms clearly. ...
... Although one might expect a coral being exposed to air to result in stress or mortality (and thus an erratic δ 18 O signal), corals that are regularly exposed to air have been observed to have a high stress tolerance (West and Salm, 2003). The stress-response mechanism of mucus release during exposure to air (and in response to other adverse environmental factors such as extreme temperatures, altered salinity, pollution and sedimentation [Marcus and Thornhaug, 1982;Mitchell and Chet, 1975;Loya and Rinkevich, 1980;Wild et al., 2006]) protects corals from desiccation and bleaching during low-tide events (Krupp, 1984). This mucus is extremely hydroscopic and serves to maintain moisture in surface tissues of corals during exposure to air (Krupp, 1984), which may explain HR-316's perseverance, albeit its intermittent exposure at low tide. ...
... The stress-response mechanism of mucus release during exposure to air (and in response to other adverse environmental factors such as extreme temperatures, altered salinity, pollution and sedimentation [Marcus and Thornhaug, 1982;Mitchell and Chet, 1975;Loya and Rinkevich, 1980;Wild et al., 2006]) protects corals from desiccation and bleaching during low-tide events (Krupp, 1984). This mucus is extremely hydroscopic and serves to maintain moisture in surface tissues of corals during exposure to air (Krupp, 1984), which may explain HR-316's perseverance, albeit its intermittent exposure at low tide. ...
Article
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Paleoclimate reconstructions often utilize coral reefs with very long time spans such as the genus Porites and Diploastrea , because of their potential to provide centuries of continuous climate records via geochemical signatures. Smaller corals, such as the genus Isopora, have been essentially unexplored as climate archives because their small skeletons (<1 m) and short lifespans (years to decades) do not provide such continuous geochemical records. There has not been a practical application for such corals until recently. In early 2010, the Integrated Ocean Drilling Program Leg 325 (IODP-325) cored drowned fossil reefs off the Great Barrier Reef (GBR) with the objectives of reconstructing sea level and surface ocean conditions since the Last Glacial Maximum. Out of 213 massive fossil corals that were recovered, most were massive Isopora colonies. A 30-specimen subset of these fossils range in age from ˜32,000 to ˜11,500 years before present with even temporal spacing, based on preliminary U/Th dating of core catcher samples. This age distribution is excellent for meeting IODP-325 objectives, but the suitability of Isopora for paleoclimate analyses remains unknown. This study presents an important preliminary step for the analysis of this fossil collection---a geochemical assessment of modern Isoporan specimens grown under known conditions. Millimeters-scale delta 18O analyses of eight Isoporan corals from three locations in the Indo-Pacific region (Heron Reef, Myrmidon Reef, and Madang, Papua New Guinea) were performed. delta18O analysis results reflect relative regional differences in seasonal sea surface temperature (SST) cycle amplitude and mean annual SST. A delta18O-SST calibration using seasonal amplitudes yields a relationship of -0.15‰/°C, while a calibration using mean annual values yields -0.1‰6/°C. These values suggest a low delta18O-SST sensitivity in comparison to what has been determined for many other coral genera. In addition to serving as a preliminary study for analysis of these fossil specimens, this assessment will help pave the way for utilizing similarly small coral types for paleoclimate applications.
... Desiccation and ultraviolet radiation are threats when corals become exposed to air at low tide. At Heron Island (our study area in the Australian Great Barrier reef), exposure of corals to air at low tide is a common phenomenon, as is also observed at other reef environments in Australia, New Caledonia, Madagascar , the Red Sea and Hawaii (Daumas et al. 1982, Krupp 1984, Romaine et al. 1997). When exposed to air, as well as under other stress conditions (e.g. ...
... (6) Sedimentation of the aggregates, energy transfer to the heterotrophic food chain and benthic system. Several authors have suggested that coral mucus and mucus-particle aggregates may be a source for nutrients and energy for the microbial food chain and heterotrophic organisms in the reef (Johannes 1967, Coles & Strathma 1973, Benson & Muscatine 1974, Ducklow & Mitchell 1979b ), while others argued that mucus particles instead represent a nutrient-poor material with little value for reef organisms (Krupp 1984, Meikle et al. 1988, Coffroth 1990). Krupp (1984) suggested that it was the particles attached to mucus, rather than mucus itself, that converted coral mucus into a valuable food source. ...
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Corals exude large volumes of nutrient-containing mucus when exposed to air during low spring tides, as a protective mechanism against desiccation and UV radiation. Currents and waves of the incoming flood detach the mucus from the corals, thereby increasing organic carbon and nutrient concentrations in the reef water. During transport into the reef lagoon, a large fraction of the mucus dissolves. Roller-table experiments demonstrated that this dissolved mucus leads to the formation of marine snow. The non-dissolving gel-like fraction of the mucus rapidly accumulates suspended particles from the flood water and forms in temporal sequence mucus strings, flocs, surface films, surface layers and thick mucus floats. In a platform reef in the Great Barrier Reef, Australia, we characterized each of these mucus phases and observed the exponential increase of algal and bacterial cells in the ageing mucus. aggregates. Within 3 hours, the dry weight of the aggregates increased 35-fold, chlorophyll it 192-fold, bacteria cell density 546-fold, C 26-fold, and N 79-fold. After waves destroy the buoyant mucus floats, the mucus aggregates release enclosed gas bubbles and quickly sink to the lagoon sediments, where they are consumed by the benthic community. This releases aggregate-bound nutrients, which fuel benthic and planktonic production in the lagoon. During ebb tide, corals filter the lagoon water and close the recycling loop. We conclude that coral mucus enhances the filtration capacity of coral reefs and fuels reef benthos, thereby increasing the import of oceanic particles and enhancing recycling in the reef ecosystem.
... While it is widely recognised that corals produce mucus on exposure to air and that such secretions will act as protection against desiccation (Daumas & Thomassin 1977, Krupp 1984, the mechanisms by which this is achieved are less certain. Krupp (1984) argued that since mucus is extremely hydroscopic it would act to maintain moisture on the surfaces of corals during exposure to air. ...
... While it is widely recognised that corals produce mucus on exposure to air and that such secretions will act as protection against desiccation (Daumas & Thomassin 1977, Krupp 1984, the mechanisms by which this is achieved are less certain. Krupp (1984) argued that since mucus is extremely hydroscopic it would act to maintain moisture on the surfaces of corals during exposure to air. Denny (1989) noted that the secretion of mucus in gastropod molluscs exposed to air dried quickly, forming a stiff thin wall that sealed off the underlying soft tissues from the air above. ...
Article
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The coral surface mucus layer provides a vital interface between the coral epithelium and the seawater environment and mucus acts in defence against a wide range of environmental stresses, in ciliary-mucus feeding and in sediment cleansing, amongst other roles. However, we know surprisingly little about the in situ physical and chemical properties of the layer, or its dynamics of formation. We review the nature of coral mucus and its derivation and outline the wide array of roles that are proposed for mucus secretion in corals. Finally, we review models of the surface mucus layer formation. We argue that at any one time, different types of mucus secretions may be produced at different sites within the coral colony and that mucus layers secreted by the coral may not be single homogeneous layers but consist of separate layers with different properties. This requires a much more dynamic view of mucus than has been considered before and has important implications, not least for bacterial colonisation. Understanding the formation and dynamics of the surface mucus layer under different environmental conditions is critical to understanding a wide range of associated ecological processes.
... Its composition can also be altered by the protocols used for its collection and subsequent analysis. Consequently, it has been described both as a material of low nutritional value for reef organisms (Krupp 1984, Meikle et al. 1988, Coffroth 1990) and as a n important source of nutrients (Ducklow & Mitchell 1979, Coffroth 1990, Sorokin 1993) and dissolved and particulate organic matter (DOM and POM). ...
... DOM is therefore a high quality food at that time and may sustain the high bacterial growth and production rates often reported in coral reef waters (Moriarty et al. 1985, Ducklow 1990, Sorokin 1993). The range of C:N ratios obtained in this study (2.5 to 13) is close to that reported for mucous aggregates excreted by other coral colonies (7.4 to 44; Krupp 1984, Coffroth 1990. The rapid uptake of freshly excreted DOM may explain the low and relatively constant concentrations that have been measured in natural reef environments (Pages et al. 1997) and the low DOM concentrations measured in reef waters relative to the open ocean (Suzuki et al. 1995). ...
Article
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Corals are known to release large amounts of particulate and dissolved organic carbon (POC and DOG) and nitrogen (PON and DON). Production of POC and PON in the form of mucus has been relatively well studied, but very few data are available on the release of DOC and DON by corals. In order to investigate several aspects of carbon and nutrient cycling in corals, release of DOC and DON by fed and unfed colonies of the zooxanthellate coral Galaxea fascicularis (Linnaeus 1767) was measured in the laboratory under controlled conditions. Colonies were either fed with artemia or supplied with nitrogen- and phosphorus-enriched seawater. We measured DOC and DON fluxes from corals using the high temperature catalytic oxidation method and DOC release as C-14-photosynthate using a radioisotope technique. Corals released significant amounts of dissolved organic matter (DOM). Two large release peaks were observed in mid-morning and mid-afternoon. DOC concentrations increased from ca 100 mu M (background level) to 300-1700 mu M, depending on the size of the colony and the trophic status. DON concentrations also increased from 15 to 120 mu M Release rates varied from 2-3 mu mol DOC and 0.5-0.6 mu mol DON (mg protein)(-1) d(-1) for the unfed colonies to 13-25 mu mol DOC and 1-3 mu mol DON (mg protein)(-1) d(-1) for the artemia-fed colonies to 4-6 mu mol DOC and 0.2-1.3 mu mol DON (mg protein)(-1) d(-1) for the nutrient-enriched colonies. Fed corals therefore released more DOC than unfed colonies, but tended to conserve organic nitrogen, suggesting that heterotrophic nutrition may serve corals as a source of new nutrients. Calculations of the carbon balance for the unfed colonies showed that DOC release represents ca 14% of the net daily photosynthetically fixed carbon. Following each peak in release, concentrations of DOM fell back to routine background levels. The role of free-living, epibiotic and/or intracellular bacteria in the uptake of DOM was therefore investigated. Colonies were labelled with C-14-bicarbonate and the subsequent release of C-14-DOM was followed in filtered seawater treated with and without prokaryotic inhibitors. No subsequent uptake of C-14-DOM was observed in the presence of inhibitors, suggesting that bacteria may play an important role in DOM uptake. This process may lead to tight nutrient recycling within coral colonies and may enable corals to thrive in oligotrophic waters.
... Mucus production by corals is a physiological response to multiple stress factors, such as exposure to low tide (Krupp, 1984), invertebrate larval settlement (Fearon and Cameron, 1996), and sediment deposition (Bythell and Wild, 2011). In addition, an increase in suspended particles in the surrounding water may also promote mucus production (Erftemeijer et al., 2012), and corals exposed to increasing amounts of MPs show a higher rate of mucus production (Corinaldesi et al., 2021). ...
Article
Microplastic (MP) pollution has been detected in coral reefs, raising concerns regarding its global impact. Although they cover a small portion (<1%) of the total area of the world's oceans, coral reefs are geological and biological structures that trap MPs and disproportionately enhance their accumulation. In this review, we attempted to understand how coral reefs act as short- and long-term sinks for MPs. We describe five characteristics that lead to the enrichment of microplastics in coral reefs: 1) adhesion on reef-building corals at distinct depths; 2) ingestion by reef organisms (e.g., suspension feeders, such as sponges, ascidians, and corals), bioconcentration, and formation of short-term (i.e., years to decades) biological sinks for MPs; 3) formation of long-term (i.e., centuries) MP sinks in coral skeletons and unconsolidated subsurface sediments; 4) reduction of sediment resuspension and seafloor turbulent kinetic energy by complex marine forest architecture that reduces bottom shear stress, facilitates the retention, and deposition of small (<0.5 mm) and high-density floating MPs; and 5) diagenesis of Anthropocene sedimentary rocks containing MPs. We estimate that reef processes may remove more than 10% of floating MPs in shallow tropical waters yearly. Statistical results show that microplastic abundance for reef-building corals are higher than values found in reef sediments and especially in seawater. Moreover, pellets, films, foams and mainly fragments and fibers have been found. These field-based data support our hypothesis of sinks in the reef sediments and organisms. We highlight the role of these seascapes in the interception of MPs as traps and sinks in reef sediments, biota, and carbonate frameworks. As coral reefs are prone to MP accumulation and can become pollution hotspots, global initiatives are necessary to conserve these rich ecosystems and prevent rapidly increasing plastic pollution.
... investigating their potential sensitivity to nSLA disturbances, as coral species show contrasted responses to environmental disturbances (Carpenter et al., 2008;Darling et al., 2012;Hughes et al., 2018). For instance, massive corals are likely more resistant to long emersion than branching and digitate corals (Fishelson, 1973) which may be related to more efficient mechanisms to resist dehydration and UVs in massive coral forms (Krupp, 1984;Brown et al., 1994) through for example mucus secretion (Brown and Bythell, 2005). ...
Article
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Among induced mass-mortality events on coral reef, extreme low tides may ultimately lead to considerable reef community deaths on intertidal reef flats due to unusually long and significant aerial exposure. Here, we report an extensive coral mortality event induced by a negative sea level anomaly (nSLA) that occurred across Reunion Island during the austral winter season between June and October 2015 preceding the 2015–2016 El Niño Southern Oscillation (ENSO) event. The nSLA was strong and long in duration with a rapid drop of 35 cm in the mean sea level over a one-month period. Surveys conducted over seven reef flat sites before and after the nSLA revealed that mean coral cover drastically decreased from 54.5 ± 12.7% in early 2015, to 27.4 ± 6.9% in November 2015, which is an equivalent cover loss of 50% following the 2015 nSLA event. The shallowest sites showed a greater decrease in coral cover while the deepest parts of the reef flat remained unaffected. We found a significant correlation between the bathymetry and the relative coral cover variation. Using this relationship between depth and coral cover changes, high-resolution hyperspectral imagery and Lidar bathymetric airborne data, we mapped the impacts of this event at the scale of the whole reef. Overall the modeled loss reached 13.0 ha, which represents a decrease of 45.5% of all live coral cover in this area during the 2015 nSLA event. The impact of a nSLA on emersion times is much greater than the regular variation in tide amplitude between neap and spring tides, reaching new bathymetric ranges that are usually stable in terms of water submersion. Temporal variation of coral cover on Reunion Island reef flat revealed regular decreases to be compared with mean low-water-level events among other sea and climatic related disturbances and stressors.
... While coral reef literature describes the effects of aerial exposure for minutes to several hours per day (e.g., Rosser and Veron 2011, Castrillón-Cifuentes et al. 2017, Sweet et al. 2017, to our knowledge, this is the longest period described in the literature of a reef coral that has survived out of water conditions. We hypothesize that this remarkable ability to regenerate may be due to the depth to which the coral retracted its polyps within the skeleton (Kitano et al. 2013), potentially linked to production of persistent mucus that efficiently protected the retracted coral tissue against desiccation (Krupp 1984), and to the regrowth of possible tissue remnants (DeFilippo et al. 2016). The remaining retracted tissue may have been in a state of quiescence (dormancy), a survival mechanism often demonstrated by temperate scleractinian corals as a response to cold water stress (Grace 2017). ...
Article
Prolonged aerial exposure can be detrimental for coral health. Here, we present an observation of a scleractinian corals' outstanding regeneration after exposure to air for several months. This observation may lead to new ways to investigate the regenerative capacity of reef-building corals.
... The coral surface mucus layer provides a vital interface between the surfaces of the coral polyp and the seawater environment and mucus can act in defense against a wide range of environmental stresses including sediment removal (Ducklow and Mitchell, 1979;Kato, 1987;Veron, 2000;Brown and Bythell, 2005;Huettel et al., 2006;Banaszak, 2007;Johnston and Rohwer, 2007;Jatkar, 2009;Wooldridge, 2009;Jatkar et al., 2010;Bythell and Wild, 2011;Glasl et al., 2016). The production of mucous sheets on corals has led some workers to propose that mucus production is solely a response to stressful conditions (Bak and Elgershuizen, 1976;Thompson, 1980;Krupp, 1984;Kato, 1987;Bessell-Browne et al., 2017). ...
Article
Bessell-Browne et al. (2017) published a paper where they proposed using mounding Porites spp. corals from Western Australia as a bio-indicator of sediment stress on coral reefs. They based their interpretations on results obtained during the monitoring of a capital dredging program coupled with laboratory sediment dousing experiments. They stated that because these Porites species generate mucous sheets in response to sediment loading, they could be used as an early warning indicator of sediment stress adjacent to sensitive coral resources. While their results are compelling, there are several confounding issues that arise questioning the wide-scale application and use of Porites spp. corals as bio-indicators. Using examples of Porites species from both the Indo-Pacific and Caribbean, I detail a number of contrary results that reveal that mucous sheet development is most likely attributed to mucus production and subsequent mucus sloughing that are cued to an endogenous lunar cycle (approximately 28 days in duration) and not necessarily as a direct strategy to protect the coral tissue from harm due to sediment stress. While the mucous sheet becomes fouled with sediment during the cycle, the amount of sediment observed may not be a response to the level of sediment stress, but where in the 28-day cycle the mucous sheet is observed. Thus, depending on when you observe the colony (early, middle or late in the 28-day cycle) the level of purported sediment impact would be highly variable. This variability leads to an unacceptably high rate of both Type-I and Type-II statistical errors. Because of the cyclical, endogenous nature of mucus production in many Porites spp., extreme caution should be employed before using these species to infer the level of sediment impact associated with dredging projects or their use as a predictive tool of sediment stress on coral reefs.
... The initial response of corals to pollution is at the levei of the individual, either througb behavioural (Lasker, 1980;Dallmeyer et al., 1982;Rogers, 1983) or physiologieal responses (Dallmeyer et al., 1982;Krupp, 1984;Glynn et al., 1985). Beyond this, changes in the comaunity may occur through coast (Murray et al., 1977), and mOlt likely to the nature and quantity of domestie and industrial effluents entering the coastal waters (Tomascik and ~ander, 1985;Lewis, 1985). ...
Thesis
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Fourteen environmental variables were monitored at seven locations along the leeward coast of Barbados on a weekly basis over a one year period, 1981 to 1982. The physicochemical and biological data indicate that the environmental gradient detected along the leeward coast of the island is associated with eutrophication of the inshore water masses. The response of scleractinian coral communities to various environmental conditions was determined by community structure and function analyses. The structure of scleractinian coral communities was studied along the environmental gradient with a quantitative sampling method (line transect) in terms of species composition, abundance, cover, trophic position, zonation and diversity patterns. The functional response of scleractinian corals to the various environmental conditions was analysed through coral growth rates and reproductive potential. Statistically discernible and biologically significant differences in coral growth rates, reproductive potential, community structure, benthic algal cover, and Diadema antillarum Philippi densities were recorded among the seven fringing reefs. High correlations between environmental variables and biotic patterns indicate that eutrophication processes were directly and/or indirectly affecting both the community structure and function of the scleractinian coral assemblages.
... Mucus can be released as particulate organic matter (POM), or as dissolved organic matter (DOM), and is defined as a mixture of organic compounds containing glycoproteins such as mucins, carbohydrate and lipids (Mitchell & Chet, 1975;Wild et al., 2010;Bythell & Wild, 2011). Several functions of mucus have been proposed for corals and have been reviewed in detail by Brown & Bythell (2005); the functions include defenses against desiccation (Krupp, 1984), sedimentation (Schuhmacher, 1977;Rogers, 1990), UV damage (Drollet et al., 1997), pathogenesis (Ritchle, 2006) other pollutants such as oil and heavy metals (Mitchell & Chet, 1975) and physical damage (Meesters, Moordeloos & Bak, 1994). The mucus released into the water is also known to serve as an important organic carbon source for coral reef organisms (Marshall, 1965). ...
Article
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Release rates of particulate organic carbon and nitrogen (POC and PON) and dissolved organic carbon (DOC) from the scleractinian coral Acropora tenuis were measured during the day and night in summer and winter seasons. Physiological parameters including calcification, photosynthesis and respiration rates were also measured simultaneously. The release rate of both POC and DOC was significantly higher in summer compared to winter and higher during the day compared to the night. The daily release rate of total organic carbon (POC + DOC) was 1,094 and 219 μmol C cm ⁻² d ⁻¹ for summer and winter, respectively, being 4.9 times higher in summer. The POC:PON ratios of the particulate organic matter released during daytime in both seasons (summer: 12.8 ± 5.7, winter: 12.0 ± 4.1) were significantly higher than those during nighttime (summer: 6.1 ± 2.5, winter: 2.2 ± 1.8). The DOC:POC ratio was 0.5 ± 0.03 during summer and 0.32 ± 0.98 during winter, suggesting higher mucus release in particulate form. Daily net production was estimated to be 199 and 158 μg C cm ⁻² d ⁻¹ for summer and winter, respectively, with the amount of carbon released as mucus accounting for 6.5% and 1.6% of the net carbon fixation, respectively. The study reveals diurnal and seasonal changes in the quantity and quality of mucus released from this coral species. Since coral mucus is used as a food source by reef macro-organisms, and can also serve as an energy source for micro-organisms, the observed changes in mucus release rates are expected to influence the seasonal dynamics of organic carbon and nitrogen cycling over coral reefs.
... At one time, coral mucus was thought to be a negligible source of nutrients (e.g., Krupp 1984;Coffroth 1990). However, it is now widely accepted that strand or weblike mucus acts as a particle trap for sediment and microorganisms in which pico-and nanoplankton have been shown to increase fiveto sixfold (Ferrier-Pagès et al. 2000;Wild et al. 2004a;Allers et al. 2008;Naumann et al. 2009). ...
Chapter
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Tropical scleractinian corals are dependent to varying degrees on their photosymbiotic partners. Under normal levels of temperature and irradiance, they can provide most, but not all, of the host’s nutritional requirements. Heterotrophy is required to adequately supply critical nutrients, especially nitrogen and phosphorus. Scleractinian corals are known as mesozooplankton predators, and most employ tentacle capture. The ability to trap nano- and picoplankton has been demonstrated by several coral species and appears to fulfill a substantial proportion of their daily metabolic requirements. The mechanism of capture likely involves mucociliary activity or extracoelenteric digestion, but the relative contribution of these avenues have not been evaluated. Many corals employ mesenterial filaments to procure food in various forms, but the functional morphology and chemical activities of these structures have been poorly documented. Corals are capable of acquiring nutrition from particulate and dissolved organic matter, although the degree of reliance on these sources generally has not been established. Corals, including tropical, deep- and cold-water species, are known as a major source of carbon and other nutrients for benthic communities through the secretion of mucus, despite wide variation in chemical composition. Mucus is cycled through the planktonic microbial loop, the benthos, and the microbial community within the sediments. The consensus indicates that the dissolved organic fraction of mucus usually exceeds the insoluble portion, and both serve as sources for the growth of nano- and picoplankton. As many corals employ mucus to trap food, a portion is taken back during feeding. The net gain or loss has not been evaluated, although production is generally thought to exceed consumption. The same is true for the net uptake and loss of dissolved organic matter by mucus secretion. Octocorals are thought not to employ mucus capture or mesenterial filaments during feeding and generally rely on tentacular filtration of weakly swimming mesozooplankton, particulates, dissolved organic matter, and picoplankton. Nonsymbiotic species in the tropics favor phytoplankton and weakly swimming zooplankton. Azooxanthellate soft corals are opportunistic feeders and shift their diet according to the season from phyto- and nanoplankton in summer to primarily particulate organic matter (POM) in winter. Cold-water species favor POM, phytodetritus, microplankton, and larger zooplankton when available. Antipatharians apparently feed on mesozooplankton but also use mucus nets, possibly for capture of POM. Feeding modes in this group are poorly known.
... Much of the photosynthates produced by the algal partner are passed to the coral host which is then processed into mucus production (up to 45% of the fixed carbon; Brown and Bythell, 2005;Davies, 1984;Edmunds and Davies, 1989;Grottoli et al., 2006;Palardy et al., 2008). This surface mucus layer protects corals from sediment and other pollutant loads, UV radiation and desiccation, and enables competition for space (Chadwick, 1988;Drollet et al., 1997;Krupp, 1984;Sleigh, 1989). However, some of the important services that mucus plays in coral health are yet to be clarified, including its specific role in defence against pathogens and disease development (reviewed in Brown and Bythell, 2005). ...
Article
Rapidly changing climate regimes combined with other anthropogenic pressures are implicated in increased disease epizootics among reef building corals, resulting in changing habitat structure. These accumulated stressors directly contribute to disease outbreaks by compromising the coral host immune system, modulating virulence of microbial pathogens, and/or disrupting the balance within the microbiome of the holobiont. Disentangling coral disease causation has been challenging, and while progress has been made for certain diseases in terms of the roles the associated microorganisms play, it is evident that like in other marine or terrestrial systems, compromised host health cannot always be attributed to a single causative agent. Here, we summarise the current state in knowledge of microbial induced coral diseases, and discuss challenges and strategies to further disentangle disease causation. With the major environmental pressures coral reefs face over the next century, understanding interactions between host, environmental and microbial causative agent(s) that lead to disease, is still a priority to enable development of effective strategies for building resilience into coral populations. This article is protected by copyright. All rights reserved.
... Another possible explanation for different FA content between immerged and exposed to the air corals is the mucus that is commonly reported in exposed corals as a mechanism to protect the organisms against desiccation, radiation and predation (Krupp 1984;Huettel et al. 2006;Santos et al. 2016). The production of this mucus is closely related with higher density of zooxanthellae (Santos et al. 2016). ...
Article
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The colonization of intertidal habitats is a challenging process. During low tide, many photosynthetic organisms, including symbiotic zoanthids, can be partially exposed to air eliciting significant physiological impairments, which may ultimately dictate the rate of colonization in such environments. Within this context, the present study aims to investigate, for the first time, the effects of air exposure on the fatty acid (FA) content and photobiological parameters of Palythoa caribaeorum, by comparing emerged and immersed polyps, within the same colony, during low tide. Tidal environment did not significantly affect FA percentages, but polyps that were emerged showed lower FA content than the immersed ones. Saturated FA fraction contributed the most to those dissimilarities, followed by the highly unsaturated and polyunsaturated FA fractions. Concomitantly, polyps that were permanently immersed displayed significantly higher values of the maximum quantum yield of photosystem II (F
... Functionally speaking, coral mucus protects corals by filtering out intruding foreign matter and serves as an exchange interface between coral tissues and seawater that allows organic and inorganic materials to enter and leave (Wild et al. 2004(Wild et al. 2008. Because of the functional characteristics of the mucus which contribute to its own small food chain (Johannes 1967, Coles and Strathma 1973, Benson and Muscatine 1974, Ducklow and Mitchell 1979, Krupp 1984, many organisms were discovered in the mucus including animals (mollusks, crustaceans, cnidarians, and nematodes), protozoa (ciliates and foraminifera), diatoms, microbes, and carbonate particles (Huettel et al. 2006). ...
Article
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The distribution of bacteria in coral mucus has long been poorly understood, although most coral-associated bacteria were suggested to dwell in the mucus and epidermis of corals. We hypothesized that different bacterial groups have different distribution patterns in the mucus and epidermis. To test this hypothesis, we overcame technical difficulties of mucus preservation during sample preparation and inspected the distributions of 2 dominant coralassociated bacterial groups, the alphaproteobacteria and gammaproteobacteria, in the mucus and epidermis of the coral, Euphyllia glabrescens, collected from Kenting and Ludao (also known as Green I.) in southern Taiwan. We used catalyzed reporter deposition-fluorescence in situ hybridization to detect the location of the bacteria in the mucus and epidermis, and results showed that the 2 bacterial groups had different distribution patterns in the coral. Alphaproteobacteria were frequently distributed at the interface between the mucus and epidermis, while gammaproteobacteria were only detected in the gastrodermis and rarely observed in the mucus or epidermis. This study provides the 1st direct evidence that different bacterial groups have habitat specificity in coral mucus.
... Le mucus au sens large, c'est-à-dire comprenant toutes les substances excrétées par les polypes (Crossland, 1987), est composé de glucides, d'aminoglucides, de protéines, de phospholipides, de triglycérides, de stérols et d'esters gras, en proportion variable (Daumas & Thomassin, 1977 ;Ducklow & Mitchell, 1979a ;Crossland, 1987 ;Meikle et al., 1988 ;Coffroth, 1990). Le C/N varie habituellement entre 5 et 7 (Krupp, 1984 ;Vacelet & Thomassin, 1991), bien que pouvant atteindre 14 chez certains Porites (Coffroth, 1990). Ducklow & Mitchell (1979a) ont montré que le mucus comprend un peuplement bactérien inféodé (dénombré par unités formant colonie) et permet la croissance de certains isolats bactériens. ...
Article
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Detrital fluxes are considered important in coral reef ecosystems and the production of heterotrophic bacterial biomass is a key process integrating the various pathways of detritus decomposition. This review examines the importance of the biomass, production and activity of heterotrophic bacteria, the linkage between possible sources and bacterial growth, and the fate of the bacterial biomass produced. Microbiological studies in coral reef environments have up until now been rather limited, making it still impossible to produce a quantitative assessment of the role of heterotrophic bacteria in organic matter cycles within coral reef environments. Nonetheless, a number of common elements can be identified. The bacterioplankton constitutes the dominant biomass in terms of carbon in reef waters, as it does in other oligotrophic to mesotrophic marine environments. This dominance is even stronger for nitrogen and phosphorus because of the low ratios of bacterial C/N and C/P. The bacterioplankton therefore represents an important stock which could overcome the nutritional limitations of benthic communities in coral reef environments characterized by limited mineral resources. This trophic potential has been confirmed by in situ studies. Thus, over reefs, the bacterial growth rates and exoenzymatic activities are greater than in lagoons and a fortiori in surrounding oceanic waters. Bacterioplankton production above reefs reaches values comparable to that of phytoplankton production. These characteristics suggest that bacterioplankton use organic matter produced by benthic organisms. Reef bacterioplankton is in contrast less abundant than in the surrounding waters. This small population size and high growth rate, associated with a considerable renewal of water, indicates that the bacterioplankton is very actively consumed by attached organisms. This trophic link has furthermore been demonstrated experimentally in controlled environments. In order to establish more quantitatively this trophic role of bacterioplankton in coral reef functioning, considerable research effort will be required. To characterize and quantify in situ the link between bacterioplankton and other organisms, both planktonic and benthic, the study of spatial and temporal fluctuations of bacterial parameters in relation to hydrodynamics will require the use of instrumentation with a high data acquisition rate, in order to obtain sufficient resolution.
... The SML has a range of roles: (i) desiccation resistance (Krupp 1984); (ii) protection against UV radiation and oxygen radicals (Drollett et al. 1997); (iii) mucociliary transport of microbes for ingestion (Goldberg 2002;Ritchie 2006); (iv) a medium for secreted allelochemicals with antimicrobial properties (Ritchie 2006; Shnit-Orland and ...
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Viruses are a ubiquitous component of coral reef ecosystems, with several viral types, from at least seven prokaryotic and 20 eukaryotic virus families currently characterised from the surface mucopolysaccharide layer (SML), coral tissue and the water column. However, little is known about the ecology and function of these viruses. For example, what are the environmental drivers of viral abundance and diversity on coral reefs? In this study, the abundance and distribution of virus-like particles (VLPs) associated with the SML and reef water of the coral Montipora capitata were determined using epifluorescence microscopy, while transmission electron microscopy was employed to determine the morphological diversity of VLPs. Sampling was conducted across the Coconut Island Marine Reserve (CIMR) reef system, Kane’ohe Bay, O’ahu, Hawai’i. Viral abundance was correlated with select environmental drivers and prokaryote abundance, while non-metric multidimensional scaling was used to determine the key environmental drivers of the viral community assemblage. The water column contained high concentrations of VLPs (5.98 × 107 ml-1 ) and prokaryotes (3.11 × 106 ml-1 ), consistent with the considerable anthropogenic impacts at this location. In comparison, the SML contained lower concentrations of VLPs (2.61 × 107 ml-1 ) and prokaryotes (2.08 × 106 ml-1 ); of note, the densities of viruses and prokaryotes in the SML were strongly coupled while those in the reef water were not. VLP density in the water column varied spatially across the reef, with the most sheltered site and the only one not situated on the reef crest having a greater VLP density than the other sites. Temporal variations in the density of microbes (i.e. viruses and prokaryotes) in the reef water were pronounced, while in the SML microbial densities remained constant. However, no specific environmental drivers of this variability could be identified. In contrast, temperature and water quality were correlated with shifts in the morphological diversity of VLPs across the reef. Small (< 50 nm) polyhedral/spherical VLPs were dominant, and were positively correlated to chlorophyll-a concentration when in the SML. In this same habitat, Fuselloviridae-like VLPs, filamentous VLPs and bead-shaped VLPs were positively correlated to temperature. In the reef water a different pattern was apparent: large (> 100 nm) Podoviridae-like VLPs and elongate Myoviridae-like VLPs, as well as lemon-shaped VLPs of both size classes showed positive associations with turbidity, while large filamentous VLPs, Geminiviridae-like VLPs and rod-shaped VLPs were positively associated with temperature. These results demonstrate that the viral community of Coconut Island’s reef is highly diverse, and subject to spatial and temporal change, especially in the water column. However, while the environmental drivers of viral diversity were partly elucidated, we are still a long way from understanding the drivers of viral abundance. More detailed study, both spatially and temporally, of the CIMR environment is required, as is comprehensive molecular analysis of the viral community of Kane’ohe Bay. Only then can we begin to understand the importance of viruses to the health and function of this, and other reef sites.
... Mild or moderate bleaching is commonly followed by recovery, but the long-term effects of high temperature of seawater will end in an irreversible bleaching and massive death of corals. As an adverse effect of rising up seawater temperature, coral animal undergo stress, response to this stress, corals release high amounts of organic matters as mucus and ammonia (Krupp 1984). The composition of coral mucus contains variable of macromolecular compounds (Ducklow and Mitchell 1979). ...
Article
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Coral Reefs are declining worldwide due to bleaching and diseases. Biogeochemical role and mechanisms of behavior of dissolved organic matter remain unexplained on this context. Here we discuss the changes of dissolved organic nitrogen by composition of amino acids as a model study, to demonstrate linkage of coral stress to elevated temperature and behavior of chemical substances in the coral biological system. Results suggest that high concentrations of nutrients and organic matters are due to the materials release by coral organism under the elevation of water temperature. This indicates observed organic nitrogen such as amino acids, peptides, proteins released as response to coral thermal stress. C: N and N: P ratio of coral mucus of thermal stressed and initial shows that thermal stress increases production of organic nitrogen and connected to increase of total amino acid could be peptides or proteins. This is shown by total hydrolyzed amino acids released from coral under the heat stress contains mix of peptides or proteins. However, to determine and confirmed source of organic nitrogen within this context need further experiments integrating microbial sources and processes. We propose to include chemical perspective in the coral biological system by the concept of chemical symbiosis.
... Mild or moderate bleaching is commonly followed by recovery, but the long-term effects of high temperature of seawater will end in an irreversible bleaching and massive death of corals. As an adverse effect of rising up seawater temperature, coral animal undergo stress, response to this stress, corals release high amounts of organic matters as mucus and ammonia (Krupp 1984). The composition of coral mucus contains variable of macromolecular compounds (Ducklow and Mitchell 1979). ...
Conference Paper
Coral Reefs are declining worldwide due to bleaching and diseases. Biogeochemical role and mechanisms of behavior of dissolved organic matter remain unexplained on this context. Here we discuss the changes of dissolved organic nitrogen by composition of amino acids as a model study, to demonstrate linkage of coral stress to elevated temperature and behavior of chemical substances in the coral biological system. Results suggest that high concentrations of nutrients and organic matters are due to the materials release by coral organism under the elevation of water temperature. This indicates observed organic nitrogen such as amino acids, peptides, proteins released as response to coral thermal stress. C: N and N: P ratio of coral mucus of thermal stressed and initial shows that thermal stress increases production of organic nitrogen and connected to increase of total amino acid could be peptides or proteins. This is shown by total hydrolyzed amino acids released from coral under the heat stress contains mix of peptides or proteins. However, to determine and confirmed source of organic nitrogen within this context need further experiments integrating microbial sources and processes. We propose to include chemical perspective in the coral biological system by the concept of chemical symbiosis.
... Unlike endolithic molluscs Kleemann and Hoeksema, 2002;Mas-sin, 1989Mas-sin, , 2000Massin and Dupont, 2003;Owada and Hoeksema, 2011) ectoparasitic epitoniids do not inflict serious visible damage to their host corals, as for instance seen in infestations by flatworms (Hoeksema and Farenzena, 2012). The mucus layer secreted by mushroom corals may be a means to protect their soft tissue against damage and is believed to be nutritious for other animals (Krupp, 1982(Krupp, , 1984(Krupp, , 1985Drollet et al., 1993). Mushroom corals are successful in regenerating and repairing their tissue (Chadwick and Loya, 1990;Kramarsky-Winter and Loya, 1996;Chadwick-Furman et al., 2000). ...
Article
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Examination of about 60,000 scleractinian corals of the fami-lies Dendrophylliidae, Euphylliidae and Fungiidae for the pres-ence of associated wentletrap snails (Gastropoda: Epitoniidae) revealed various ectoparasitic life history strategies. Twenty Indo-Pacific wentletrap species were found, which were either host-specific or generalist. Most species were associated with mushroom corals, especially free-living species belonging to the Fungiidae. Snails showed different preferences with regard to their position relative to mushroom corals, the host's size and its substrate. No preferences for depth were found. Infestation rates of mushroom corals in multi-species assemblages were negatively correlated with coral densities, which indicates that epitoniid veliger larvae may actively look for preferential hosts. Indirect proof was found that burrowing shrimps remove any epitoniid that is on or underneath the mushroom coral under which they have their burrow. Fishes like wrasses and damsel-fishes were seen to eat the snails the moment their host corals were overturned, which suggests that the host corals may pro-vide the snails with protection against predators.
... Unlike endoparasitic molluscs of the families Coralliophilidae and Mytilidae (Bouillon et al., 1980;Massin, 1989Massin, , 1992Hoeksema and Achituv, 1993;Hoeksema and Kleemann, 2002;Kleemann and Hoeksema, 2002;Massin and Dupont, 2003), the ectoparasitic epitoniids do not appear to infl ict serious visible damage to their coral hosts. The thick layer of mucus secreted by most mushroom corals may be defensive and in itself is believed to have high food quality (Krupp, 1982(Krupp, , 1984(Krupp, , 1985Chadwick, 1988). Mushroom corals are very successful in regenerating and repairing their tissue (Chadwick and Loya, 1990;Kramarsky-Winter and Loya, 1996;Chadwick-Furman et al., 2000). ...
... The release of mucus by corals may help to conserve essential nutrients in oligotrophic reef ecosystems by counteracting the export of nutrients offshore (Wild et al. 2004a). This organic material is produced and released in varying quantities and quality by corals, which serves the functions of surface-cleaning from sedimentation (Schuhmacher 1977), protection against desiccation during air exposure (Krupp 1984), discouraging fouling organisms (Ducklow and Mitchell 1979a) and also as a stress reaction to changes in temperature, salinity, turbidity (Rublee et al. 1980;Telesnicki and Goldberg 1995) and pollution (Loya and Rinkevich 1980). Coral mucus appears as a transparent, moderately viscous liquid (Ducklow and Mitchell 1979b) and comprises particulate and dissolved fractions (Brown and Bythell 2005). ...
Article
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Mucus released by corals can function as an important energy carrier and particle trap in reef ecosystems with strong tidal currents. In fringing reefs with calm conditions, these processes may occur on smaller spatial scales. Observations of coral mucus dynamics in the Northern Red Sea revealed highly particle-enriched and negatively buoyant mucus strings attached to ∼27% of coral colonies for up to 79 min. Mucus strings of the scleractinian coral genus Acropora exhibited three orders of magnitude higher particulate organic carbon and nitrogen concentrations when compared with freshly released coral mucus, which confirms efficient particle trapping. After detachment from the coral surface, more than 95% of mucus strings rapidly descended to the reef sea floor within less than 1 m. Such mucus-induced transport may account for 21–25% of the total sedimentary particulate organic matter supply. In situ and laboratory analyses of planktonic and benthic microbial degradation of mucus strings showed high rates of up to 16 and 26% particulate organic carbon h–1, respectively. These findings suggest a newly discovered, tight sediment–water coupling mechanism via coral mucus that may contribute to rapid nutrient recycling in oligotrophic fringing coral reefs.
... Mucoid organic exudates continuously released by corals (Meikle et al. 1988) play an important role in heterotrophic feeding (Duerden 1906, Yonge 1930, Lewis and Price 1975, Lewis 1977, Sleigh et al. 1988, Goldberg 2002) as a defence against smothering by sediment (Schumacher 1977), desiccation (Daumas and Thomassin 1977, Krupp 1984), physical (Brown and Bythell 2005) and UVR related (Drollet et al. 1997) damage, pathogens (Ducklow and Mitchell 1979, Rublee et al. 1980, Cooney et al. 2002) or pollutants (Mitchell and Chet 1975, Neff and Anderson 1981, Bastidas and Garcia 2004). However, as mucoid organic exudates can dominate the suspended particulate matter (Johannes 1967, Marshall 1968) in reef waters, they are obviously also major components of the coral reef ecosystem's nutrient cycles. ...
... One aspect of coral mucus production that has received only limited consideration is its strong relationship to the breakdown of the coral-algae association, in which the zooxanthellae are released en masse ('coral bleaching') (Fig. 2;Kato 1987). Indeed, enhanced mucus release is associated with many known bleaching risk factors, including heat stress (Neudecker 1983, Kato 1987, cold stress (Steen & Muscatine 1987, Saxby et al. 2003, aerial exposure (Krupp 1984, Kato 1987, Romaine et al. 1997, low flow (Coffroth 1985(Coffroth , 1988, salinity stress (Coffroth 1985, Kato 1987, van Woesik et al. 1995, excess solar radiation (Drollet et al. 1993(Drollet et al. , 1997, excessive sedimentation (Coffroth 1985), cyanide exposure (Cervino et al. 2003), or herbicide exposure (Jones & Kerswell 2003). ...
Article
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Symbiotic reef corals exude large volumes of mucus when exposed to environmental conditions that challenge the integrity of the coral-algae endosymbiosis. Here, the physiological consequences of CO2-limitation within the 'dark' photosynthetic reactions of the algal endosymbionts ('zooxanthellae') are investigated as the possible cause of the release of 2 different forms of mucus: mucus-polysaccharide and mucus-lipid. This mechanism may explain why the experimental addition of specific host-derived free amino acids (commonly referred to as 'host factors') enhances photosynthate release and carbon fixation rates from in vitro zooxanthellae. Furthermore, it reinforces the often-ignored importance of the coral host in maintaining the stability and functioning of the intact symbiosis in the face of environmental stress, even supporting the possibility that disruption to hostcontrolled processes ultimately triggers the breakdown of the symbiosis leading to the mass expulsion of zooxanthellae ('coral bleaching').
... A wide range of studies has shown that mucus is produced by corals as a feeding aid (Yonge 1930;Abe 1938;Lewis and Price 1976;Lewis 1977) as well as in response to a variety of stresses including desiccation (Krupp 1984; Stafford-Smith, personal observation), chemical pollutants (Jaap and Wheaton 1975;Mitchell and Chet 1975), temperature (Neudecker 1979), physical damage (Stafford-Smith, personal observation), and sediment (Hubbard and Pocock 1972;Bak and Elgershuizen 1976;present study). The form and volume of mucus production in response to the various stimuli may vary greatly. ...
Article
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Mechanisms of sediment rejection by 42 species of Scleractinia from 31 genera, all with wide Indo-Pacific distributions, were investigated in situ and in the laboratory at Lizard Island, northern Great Barrier Reef. Rejection mechanisms of flat tissues (generally six replicates plus controls) were studied in response to a single rapid influx of 50 mg cm⁻² of 70/30% calcium carbonate/quartz sediment of each of four particle sizes: silt (<63 pm), fine sand (63-250 μm), coarse sand (500 μrn to 1 mm), and granules (1-3 mm). Additional observations were made of responses to variations in sediment loads (to a maximum of 1000 mg cm⁻²) , to individual sediment particles, and to less-dense organic sediment and food, as well as of the effects of tissue angles, colony morphology, and in situ environmental conditions. Ciliary currents, tissue expansion, and mucus entanglement occur in all of the species studied. Direct tentacle manipulation and pulsed partial contraction of the polyp or coenosarc also occur but were not observed in all species. Mesenteries may play a subsidiary or incidental role. Active-rejection mechanisms are consistent within species and, with the principal exception of some Faviidae species, are similar for the congeneric species studied. Species are categorized according to their observed active-rejection capability. This capability is positively correlated with calice size: all species with large calices (> 10 mm in diameter) are capable of rejecting influxes of up to at least 50 mg cm⁻² of the tested sediment sizes with comparative ease; those species with small calices (<2.5 mm in diameter), particularly the two Porites species and the three Montipora species, are poor active rejectors; and other species, notably Acropora hyacinthus and Pocillopora darnicornis, though having some active-rejection capability, exhibit morphologies that make active rejection mostly redundant. Species with calices between 2.5 and 10 mm in diameter show more variation, but all very active rejectors in this size class have strong ciliary mechanisms. There are differences in the area of a colony involved in the rejection of sediment influxes, depending on sediment size and density. Rejection of heavy influxes of all sediment sizes is principally restricted to flat or concave surfaces, whereas individual particles of silt and fine sand as well as light influxes of silt and almost neutrally buoyant particles of larger sizes frequently require active rejection from strongly inclined, and even near-vertical, surfaces. The significance of these findings in terms of energy budgets is discussed.
... Corals that are broken, diseased or undergoing partial mortality are under considerable stress. A common stress response by corals is to increase mucous production (Loya & Rinkevich, 1980;Krupp, 1984;Telesnicki & Goldberg, 1995;Wild et al., 2004Wild et al., , 2005. Therefore, by targeting these damaged areas, L. unilineatus is most probably focusing on areas that have the highest availability of mucus. ...
Article
This paper describes a 2 month study of the patterns of abundance, feeding pressure, diet and feeding selectivity in corallivorous tubelip wrasses (Labridae), rarely studied, yet widespread and abundant group of corallivores on Indo-Pacific coral reefs. The relative abundance and feeding pressure of corallivorous wrasses and butterflyfishes (Chaetodontidae) in Kimbe Bay, Papua New Guinea, were compared. Overall, tubelip wrasses were more than twice as abundant as corallivorous butterflyfishes and accounted for three times as many feeding bites on corals. The three most abundant tubelip wrasses (yellowtail tubelip Diproctacanthus xanthurus, Allen's tubelip Labropsis alleni and the tubelip wrasse Labrichthys unilineatus) were all obligate corallivores taking > 97% of bites from the surface of live corals. Labropsis alleni and D. xanthurus were highly selective, consuming preferred prey species in proportions significantly higher than expected given their availability. In contrast, L. unilineatus was fairly non-selective and consumed most corals in direct accordance with their availability. As coral predators, tubelip wrasses are highly comparable to coral-feeding butterflyfishes in the coral species consumed, range of dietary specialization and their reliance on live coral. Tubelip wrasses, however, may supersede butterflyfishes as the predominant corallivorous family in some Indo-Pacific locations, and coral-feeding tubelip wrasses are likely to be severely affected by coral decline.
... high contribution of coral mucus to the bulk POM is also suggested from the observation of low C to nitrogen (N) ratios of the POM (hata et al., 2002). Although a number of previous studies have focused on the chemical composition (i.e., proteins, carbohydrates, and lipids) of the released organic matter (Krupp, 1984;Meikle et al., 1988;vacelet and Thomassin, 1991), sizes of the organic matter have rarely been investigated, thus there are few comparisons of the production rates between dOM and POM. ...
Article
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Coral colonies are one of the major producers of dissolved and particulate organic matter (DOM and POM, respectively) in coral reefs. To investigate the net release rates of DOM and POM and the production ratios (DOM:POM), the reef-building corals Porites cylindrica (Dana, 1846) and Acropora pulchra (Brook, 1891) were incubated separately and accumulation rates of DOM and POM in the overlaying seawater were simultaneously measured over 4 d. Release rates of the newly synthesized organic matter by symbiotic algal photosynthesis were also measured using a 13C-labeling technique. Dissolved organic carbon (DOC) was produced at rates of 340 and 380 nmol C cm-2 d-1 for P. cylindrica and A. pulchra, respectively, and particulate organic carbon (POC) was produced at 590 and 740 nmol C cm-2 d-1, respectively. POC was produced at a significantly higher rate than DOC for both coral species: the average ratios were 0.6 and 0.5 for P. cylindrica and A. pulchra, respectively. Particulate organic nitrogen was also produced at a significantly higher rate than dissolved organic nitrogen. These results indicate that reef-building corals produce more POM than DOM at least over the time scale of a few days. Newly-synthesized organic carbon accounted for < 10% of the accumulated bulk DOC, suggesting that most of the released DOC was derived from previously-synthesized organic carbon.
... revealed that mucus is continuously released by 328 all investigated corals, but in increased quantities when environmen-329 tal stress factors such as high loads of sediments(Schuhmacher, 1977) 330 or particle concentrations in the water column(Rublee et al., 1980) 331 occur. Mucus release by corals is also highly increased when corals are 332 exposed to air at extreme low tides(Krupp, 1984; Wild et al., 2004a, 333 2005b). A recent seasonal study in the Red Sea further indicates 334 that light availability and water temperature positively affect mucus 335 release by corals (Naumann et al., 2010a, 2010b). ...
... Furthermore, grazing (like other stressors) may also induce corals to produce higher amounts of carbon-rich mucous (e.g. Krupp, 1984;Riegl and Branch, 1995). Intact colonies, in contrast, have no need for active regeneration. ...
Article
A detailed understanding of the dual role of parrotfish as both key herbivores and potentially important corallivores is essential to the study of coral health and reef trophodynamics. Some Caribbean parrotfish regularly consume live coral, and discriminate both among coral species and among colonies within a particular species. While they prefer Montastraea spp. corals, which are dominant Caribbean reef builders, causes of selective and persistent grazing of certain colonies remain unknown. We manipulated coral exposure to parrotfish grazing through a long-term cage exclusion experiment in Belize, comparing initially grazed vs. intact (non-grazed) Montastraea spp. colonies. We measured nutrition-related characteristics (C:N ratio, %C, and %N) as well as defensive characteristics (nematocyst density and skeletal hardness) to determine if any of these variables accurately predicted parrotfish grazing. There were substantial reductions in coral nutritional quality (C:N) associated with parrotfish grazing, although these changes appear to be a consequence rather than a cause of parrotfish selectivity. Likewise, nematocyst densities were suppressed in grazed corals, also likely a result of chronic grazing stress. We found no intraspecific differences in skeletal hardness related to grazing. These results provide further demonstration of the physiological consequences of grazing, but the cause of preferential grazing by parrotfishes on certain Montastraea spp. colonies still requires further investigation.
... Mucus secretion onto the epidermal tissue surface by mucus gland cells (i.e. mucocytes) forms a protective surface mucus layer, which supports heterotrophic ciliary feeding ability, protects the coral against desiccation (Krupp, 1984), sedimentation (Riegl and Branch, 1995) and pathogens (Ritchie, 2006), as well as physical and ultraviolet-radiation-related damage (reviewed in Brown and Bythell, 2005;Drollet et al., 1993), and enhances coral resistance to changes in temperature and salinity (Marcus and Thorhaug, 1982). The protective surface mucus layer of scleractinian corals is continuously replaced, and thus large amounts of particulate (POM) and dissolved organic matter (DOM) are released into the water column (Ferrier-Pagès et al., 1998;Naumann et al., 2010;Wild et al., 2008). ...
Article
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The release of organic matter (OM) by scleractinian corals represents a key physiological process that importantly contributes to coral reef ecosystem functioning, and is affected by inorganic nutrient availability. Although OM fluxes have been studied for several dominant reef taxa, no information is available for soft corals, one of the major benthic groups in tropical reef environments. Thus, this study investigates OM fluxes along with other key physiological parameters (i.e. photosynthesis, respiration and chlorophyll a tissue content) in the common soft coral genus Xenia after a 4-week exposure period to elevated ammonium (N; 20.0 μmol l(-1)), phosphate (P; 2.0 μmol l(-1)) and combined inorganic nutrient enrichment treatment (N+P). Corals maintained without nutrient enrichment served as non-treated controls and revealed constant uptake rates for particulate organic carbon (POC) (-0.315±0.161 mg POC m(-2) coral surface area h(-1)), particulate nitrogen (PN) (-0.053±0.018 mg PN m(-2) h(-1)) and dissolved organic carbon (DOC) (-4.8±2.1 mg DOC m(-2) h(-1)). Although DOC uptake significantly increased in the N treatment, POC flux was not affected. The P treatment significantly enhanced PN release as well as photosynthesis and respiration rates, suggesting that autotrophic carbon acquisition of zooxanthellae endosymbionts influences OM fluxes by the coral host. Our physiological findings confirm the significant effect of inorganic nutrient availability on OM fluxes and key metabolic processes for the soft coral Xenia, and provide the first clues on OM cycles initiated by soft corals in reef environments exposed to ambient and elevated inorganic nutrient concentrations.
Chapter
The phylum Cnidaria contains an estimated 11 000+ living species and is almost exclusively an aquatic group, primarily marine but with some freshwater species and a few terrestrial parasitic species. Cnidarians reproduce both sexually and asexually, most species incorporating both methods. They produce gametes (eggs and sperm), can be monoecious, producing both eggs and sperm, or dioecious, with individuals of separate sexes (gonochoric). Cnidarians are soft‐bodied, diploblastic (two cell layers) metazoans (animal kingdom), with primary radial symmetry (although with some variations). Threats to cnidarians include climate change, infectious diseases, development of shorelines, increase in surface runoff, land‐based sources of pollution, ship groundings, and damaging fishing techniques (dynamite, nets, etc.). As a possible indicator of some of these detrimental changes, there has been an increase in the frequency of jelly blooms.
Article
Scleractinian corals play important roles in the biogeochemical cycles of the coral reef ecosystem through coral metabolic activities. In particular, the cycling of dissolved organic matter (DOM) in coral reefs has often been focused on in recent years because of the improvement of the DOM analytical technique. This article summarizes recent findings on DOM in coral reefs and compares the chemical characteristics between DOM released from coral colonies and DOM produced on ecosystem scales. The present review shows that the carbon to nitrogen ratios (C:N ratios) of DOM are in a similar range between coral- and ecosystem-scales in Shiraho Reef, Japan, indicating that the coral colonies might be one of the major DOM producers. The efficient nitrogen recycling in coral-algal symbiotic colonies has also been demonstrated in recent years and this explains why corals can release nitrogen-rich DOM, even though the ecosystem is filled with oligotrophic seawater. A series of these biogeochemical and ecophysiological studies would provide a better understanding of the mechanisms which have been maintaining coral reef ecosystems.
Chapter
Coral reef “bleaching”, has long been considered a pathological response to a variety of environmental stresses. Given the threat of climate change, and the documented mass mortalities of corals as a result of episodic bleaching caused by high temperatures, environmental triggers have become the focus for the vast majority of contemporary bleaching studies. This chapter outlines and reviews the various factors, other than high temperature, high light and infectious agents, which have been reported to cause coral bleaching. It compares and contrasts these factors in terms of the critical thresholds which trigger bleaching, the mechanisms underlying the bleaching response, and the associated disease signs (in addition to loss of symbionts and/or photosynthetic pigments) which can accompany bleaching in each case. The chapter also highlights responses which might reflect an “animal stress response” rather than an “algal stress response” and identifies common targets of stress in each partner, wherever possible.
Article
Around intertidal coral reefs, viscous layers, flocs, and bubbles can form on the water surface, and these are collectively referred to as mucus aggregates. To assess effects of substances contained in mucus aggregates on population growth rates of autotrophic and heterotrophic organisms, aqueous materials extracted from mucus aggregates and polysaccharides collected from cultured microalgae were added to rocky intertidal reef sediments in a controlled laboratory experiment. Temporal changes in autofluorescence cell density and nonautoflorescence cell density in reef sediments were examined. Results suggested that microorganism population growth in subtropical rocky intertidal reefs is limited by low concentrations of organic carbon and nutrients in the environment, and that components of mucus aggregates can supplement these materials, leading to increased microbial population growth rates. In particular, aqueous extracts of mucus aggregates contained nutrients that likely promoted growth of autotrophic bacteria, whereas extracellular polymeric substances (EPS) contained polysaccharides that likely promoted growth of heterotrophic bacteria.
Article
The purpose of this study was to assess degradation and utilization of the mucus produced by 3 coral reef Anthozoa (Sarcophyton, Fungia and Acropora) by microorganisms. This was achieved by carrying out long term in situ incubations at Nouméa lagoon (New Caledonia). The microbial population including bacterial and eukaryotic cells was monitored by cell counts, cultures of mucus degraders, and by estimation of microbial activity from the pool of adenylates and enzymatic activity. In addition the chemical composition (C and N) of the mucus was monitored and its morphological features were observed by scanning electron microscope (SEM). Only slight differences were found between the 3 types of mucus studied. On the whole, they follow the same pattern of change. After a short bacterial growth phase (4 days), a bloom of eukaryotes (Flagellates, Ciliates and Diatoms) was observed. This eukaryote population remained constant for at least 10 days. A similar pattern has been described in the breakdown of detritus of plant origin. Several observations suggest that bacteria utilize only certain components of mucus, the most widely used being proteins, triglycerides and wax esters; these latter two compounds are known to be the dissolved photosynthetic products released by zooxanthellae during mucus secretion. Neither bacteria nor eukaryotes completely degrade the mucus web even after 21 days of incubation. The likelihood that mucus excretion is a defensive reaction against physical and chemical stresses might explain why mucus is a poor, or even inhibiting medium for the bacterial degraders isolated from the mucus itself.
Article
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It is well known that corals release transparent and mucoid organic matter (coral mucus) to the ambient seawater. This mucus release is important for various physiological functions of corals such as defense against stress, particle trap and cellular metabolic regulation. Coral mucus is mainly composed of carbohydrates, proteins and lipids, of which most are dissolved organic matter and thus utilized by heterotrophic bacteria and incorporated into the microbial loop. A fraction of the mucus, with its high molecular weight and sticky properties, captures large amounts of particulate organic matter in the seawater, forming large organic aggregates which are efficiently assimilated into higher trophic levels. Thus, coral mucus is incorporated into reef organisms in a variety of processes and functions as an important organic energy source in reef systems. This article reviews some types of mucus forms, chemical composition and production rates of mucus, and the contribution of mucus to heterotrophs from biogeochemical and ecological perspectives and suggests some future works for coral mucus studies.
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Seven fringing reef complexes were chosen along the leeward coast (west) of Barbados to study the effects of eutrophication processes upon the scleractinian coral assemblages. The structure of scleractinian coral communities was studied along an eutrophication gradient with a quantitative sampling method (line transect) in terms of species composition, zonation and diversity patterns. On the basis of these data the fringing reefs were divided into three ecological zones: back reef, reef flat, and spur and groove. Statistically discernible and biologically significant differences in scleractinian coral community structure, benthic algal cover and Diadema antillarum Philippi densities were recorded among the seven fringing reefs. High correlations between environmental variables and biotic patterns indicate that the effects of eutrophication processes (nutrient enrichment, sedimentation, turbidity, toxicity and bacterial activity) were directly and/or indirectly affecting the community structure of scleractinian coral assemblages. In general, species diversity was most sensitive in delineating among-reef, and among-zone, differences, which were attributed to intensification of eutrophication processes. Porites astreoides Lamarck, P. porites (Pallas), Siderastrea radians (Pallas), and Agaricia agaricites (Linnaeus) were the most abundant coral species in the polluted southern reefs. The absence and/or low abundance of coral species previously characterized as well adapted to high turbidity and sedimentation [i.e. Montastrea cavernosa Linnaeus, Meandrina meandrites (Linnaeus)] indicate that eutrophication processes may adversely affect these species. It is suggested that sediment rejection abilities, combined with feeding and reproductive strategies, are the primary biological processes of scleractinian corals through which eutrophication processes directly and/or indirectly affect the structure of coral communities.
Article
Mucus films, flocs or foams consisting of fine sand, algae and detritus frequently occur in the surface waters of rocky intertidal reef flats during incoming tide. These masses are referred to as mucus aggregates. We examined the developmental process of mucus aggregates and their abundance, distribution, migration and trophic composition. The trophic composition of mucus aggregates was then compared to those of sediments to evaluate their potential nutritional value for benthic animals. The organic matter content, chlorophyll a concentration, microalgal density and bacteria-derived fatty acid contents of mucus aggregates were higher than those observed in sediment, suggesting that mucus aggregates contain not only high levels of organic matter but also dense concentrations of microalgae and bacteria; therefore, mucus aggregates may serve as a qualitatively more energetic food source for benthic fauna compared to sediments. Benthic diatoms were the most abundant organisms in mucus aggregates. Large numbers of diatoms were trapped in fine mineral particles and mucilage-like strings, suggesting that a portion of the mucus is secreted by these benthic microalgae.Mucus aggregate accounted for only 0.01–3.9% of the daily feeding requirements of the dominant detritivore, Ophiocoma scolopendrina (Echinodermata: Ophiuroidea) over the entire sampling area. In contrast, for the species population on the back reef, where mucus aggregates ultimately accumulate, mucus aggregates provided from 0.4 to 113.3% of food for this species. These results suggest that mucus aggregate availability varies spatiotemporally and that they do not always provide adequate food sources for O. scolopendrina populations.
Article
The production, release, and subsequent consumption of coral mucus on reefs has been portrayed as a potential pathway for the transfer of coral and zooxanthellae production to other reef organisms. However, reported mucus production rates and analyses of nutritional value vary widely. Poritid corals provide a test system to measure mucus production because they produce mucous sheets which can be collected quantitatively. Fluid mucus and mucous sheets were collected fromPorites astreoides, P. furcata, P. divaricata during 1986 and 1987 on reefs in the San Blas Islands, Panama, La Parguera, Puerto Rico and the Florida Keys, USA. Mucus samples were collected from Indo-pacific poritids (P. australiensis, P. lutea, P. lobata, andP. murrayensis) on the Great Barrier Reef during 1985. Biochemical analyses of the fluid mucous secretions, and the derivative mucous sheet, indicate that the mucus is primarily a carbohydrateprotein complex.Porites fluid mucus had a mean caloric content of 4.7 cal mg–1 ash-free dry weight (AFDW), while mucous sheets contained 3.5 cal mg–1 AFDW. Sixty-eight percent of the mucous sheet was ash, while fluid mucus was 22% ash. The high ash and low organic contents suggest that mucous sheets have a low nutritional value. C:N ratios varied (range 6.9 to 13.7 for fluid mucus, and 4.8 to 5.9 for mucous sheets), but were similar to typical C:N ratios for marine organisms. Bacterial numbers and chlorophyll a concentrations were higher on mucous sheets than in the surrounding water. Although bacteria aggregate on mucous sheets, bacteria accounted for less than 0.1% of the carbon and nitrogen content of the mucous sheet. Lower C:N ratios in aged mucus, i.e. mucous sheets versus fluid mucus, were attributed to a loss of carbon rather than an increase in nitrogen. Mucous sheet production accounts for a small proportion (< 2%="" gross="" photosynthesis)="" of="" published="" values="" for="" coral="" production.="" in="" the="" san="" blas="" islands,="">P. astreoides produced mucous sheets at a rate of 1.5 g C m–2 y–1 and 0.3 g N m–2 y–1.P. astreoides andP. furcata produced mucous sheets with a lunar periodicity and may provide approximately monthly pulses of carbon and nitrogen to the reef food-web. However, the low annual production rates suggest that mucous sheets make a small contribution to overall energy flow on coral reefs.
Article
The amount of mucus released by the Mediterranean coral Cladocora cespitosa (L.) was determined in laboratory experiments and the incorporation of mucus into bacterial biomass was investigated by means of incubation experiments in 1984. Mean mucus release was 8.5 g (mucus dry wt) pclyp-1 h-1 and amounted to 44% of the respiratory carbon losses of the coral since mean organic carbon content of freshly collected mucus was 102.2g C mg (mucus dry wt)-1. Due to the abundance of C. cespitosa in the shallow littoral of the Bight of Piran, the energy content of mucus released is estimated to correspond to about 20% of the phytoplankton primary production in this area. Furthermore, the carbon conversion efficiency of 20% obtained from the bacterial population during decomposition of mucus indicates the high nutritional value of C. cespitosa mucus, although bacterial carbon onto mucus particles contributes less than 0.1% to the total organic carbon pool of the mucus.
Article
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Field populations of the gorganian Briariurn asbestinum produced and lost a mucus sheath in 5-10 days. C to N ratio (by weight) of the mucus was 8.9. An extensive bacterial community was evident, but makes only a small contribution to carbon and nitrogen pools. Laboratory studies suggested that mucus production and bacterial populations increase with increasing turbidity.
Article
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This study investigates the community structure of reefbulding corals in terms of species composition, zonation and diversity patterns, as well as possible factors affecting the observed distributions. The study was carried out by a series of line transects run underwater with SCUBA apparatus from the reef flat to a depth of 30 m. The reefs of Eilat are of the fringing type, with seleractinian corals as the most important hermatypic organisms. The different zones of the reef are analyzed on the basis of topographical characteristics of the reef, as well as from the numerical data on abundance and living coverage, using cluster analysis of all transects surveyed. The present knowledge concerning species diversity is reviewed and analyzed in the context of hermatypic coral data. Three different diversity indices (the species count, Simpson's index and Shannon and Weaver's index) were calculated for estimating the diversity obtained on different zones of the reef. It was found that there is a successive increase in diversity of hermatypic corals from shallow water to a depth of 30 m. Species diversity and living voverage of corals were significantly greater in steeper zones as compared to flatter zones of the reef. A possible explanation for this phenomenon is the accumulation of sediments in the flat zones. It is proposed that the severe and umpredictable nature of the reef flat may account for low abundance and living coverage of corals. It is also proposed that deep-water species which do not invade shallow water are species which have developed high specialization to their local environment. The idea that light intensity is a significant factor in calcium-carbonate deposition by scleractinian corals is supported by field measurements of individual colonies at different depths.
Article
Mucus from a variety of reef corals has been found to contain wax ester (cetyl palmitatc) and triglycerides. Observation revealed extensive mucus feeding by many species of reef fishes. When coral mucus is artificially dispersed fish assemble and avidly ingest it. Coral mucus could be an energy source linking the coral producer and small fish consumers in reef communities. Reef-building corals are dominant and highly productive life forms in tropical coral reef communities. Their symbiotic dinoflagellate algae (zooxanthellae), which, for example, constitute from 45-60% of the protein biomass of Pocillopora damicornis, provide the coral animal with products of their photosynthesis, notably glycerol, ala- nine, and glucose (Muscatine and Cerni- chiari 1969; Lewis and Smith 1971). The animal, in turn, provides the algae with ammonia for production of amino acids and protein (Kawaguti 1953; Muscatine and D'Elia unpublished). This symbiotic exchange of reduced carbon and nitrogen occurs within the coral tissues, thereby minimizing dilution with the ocean and ensuring the survival of corals in an envi- ronment relatively poor in dissolved and particulate nitrogen compounds. Since the zooxanthellae in corals are among the major primary producers in reef communities, questions arise as how and to what extent their energy-rich products are made available to other members of the reef community. Feeding on coral polyps by reef fishes has been reported as one type of predation on corals (IIiatt and Strasburg 1960). Perhaps more novel is the observation by Johannes ( 1967) of substan- tial mucus release by corals on windward reefs in Eniwetok and the subsequent for-
Article
The secretion of mucus by eight species of scleractinian corals was measured in situ at the Red Sea reef in Eilat, Israel. Selected coral heads were covered with plastic bags and the total organic matter collected after 24 h was determined. The rate of mucus production by massive forms was significantly greater than that by hemispherical or branched species, supporting the suggestion that the massive species use mucus secretion as a mechanism to prevent burial in heavy sedimentation areas on this reef. Overall mucus production results in about 51 mg of particulate organic production m ⁻³ day ⁻¹ . Laboratory feeding experiments and assimilation measurements with Acartia negligens feeding on radioactive mucus indicate that the zooplankters can assimilate up to 50% of the organic matter of the mucus. Calorific determinations show this material to contain 5.2 ± 0.13 cal mg ⁻¹ ash‐free dry weight.
Article
The mucus of reef corals may be an important component of coral reef trophic structure. However, difficulties in the collection, purification and analyses of coral mucus have resulted in inconsistencies among compositional studies, making interpretations about the trophic importance of coral mucus uncertain. Thus, immunochemical studies were undertaken to understand the biochemistry of the mucus of the solitary scleractinian coral Fungia scutaria. Double-diffusion and solid-phase radioimmunoassay studies corroborated electrophoretic evidence in elucidating some aspects about the composition of the mucus. One component of the mucus may be a sulfated acid polysaccharide (MAP) strongly associated with protein or peptide. This MAP component may occur in the mucus of other scleractinians since the antiserum prepared against Fungia mucus reacted with the mucus of the scleractinian Montipora verrucosa. Most of this cross-reactivity appeared to reside in the MAP component. Immunochemical techniques may be valuable in elucidating the composition of coral mucus, its structure, and its importance in the biology and ecology of corals and coral reefs.
Article
Sublethal exposures to pollutants can increase mucus secretion by corals and this in turn can lead to elevated bacterial levels and consequent damage to the coral. A basic model describing the salient features of the bacteria-coral mucus interaction is constructed. Estimation of the many parameters involved provides an opportunity to make a semi-quantitative comparison with experimental data. Qualitative analysis of an extended model shows how entrapment of bacteria in a mucus filament matrix might lead to an explosive increase in the bacterial population when stress exceeds a critical value. A succession of models is presented, from the simplest to more complex and inclusive models. This succession chronicles our thinking concerning the biology and microbial ecology of the coral surface and shows how model building can lead to a better understanding of the systems under consideration.
Article
The copepod Acartia tonsa and the reef mysid Mysidium integrum ingest stained coral mucus. Ingestion rates determined with radioisotope-labeled mucus ranged from 4 to 81% body carbon 24 h-1 for the copepods and I to 70% body carbon 24 h-1 for the mysids. Incorporation was measured by comparing the organic composition of fecal material and by the incorporation of isotope-labeled mucus. A. tonsa incorporated 47% of ingested ash-free material, 68% of carbon and 36% of nitrogen. M. integrum incorporated 44% of ingested ash-free matter, 57% of carbon and 55% of nitrogen. Incorporation estimates using 14C-labeled mucus were 65% and 39% for incorporation by A. tonsa and M. integrum respectively. A. tonsa and M. integrum incorporated both the mucus substrate and the epiphytic bacteria of the mucus-detritus.
Article
1. Cutaneous mucus glands of Rana catesbeiana discharge lumenal fluid onto the surface of the integument synchronously and periodically. Each discharge of fluid is a rapid and discrete event and can be viewed with magnification in the living animal. Discharge occurs in response to sympathetic nervous stimulation. 2. The frequency of mucus discharge depends upon central nervous impulses and increases over the approximate range of body temperature 20–28 C. Discharge frequencies during heating exceed steady state values at identical temperatures, and may be as high as 17/minute. Local heating of the thigh does not elicit changes in discharge frequency in that region, whereas local heating of the head does. Transections and lesions of the brain suggest that the anterior hypothalamus is involved in controlling mucus gland activity. Peripheral afferents appear to modify central impulses determining the frequency of mucus discharge. 3. Direct measurements of cutaneous evaporative water loss were made by recording humidity changes of air as it passed over an area of skin beneath a ventilated capsule. Frogs which frequently discharged mucus maintained steady states of evaporative water loss comparable to that of a free water surface. Frogs in which mucus gland activity was inhibited by sympathetic blockade demonstrated drying of the integument and declining rates of evaporative water loss. 4. It is suggested that thermal modulation of mucus discharge possibly functions to maintain a moist and viable integument during terrestrial basking.
Article
The occurrence of marine invertebrates in the branches of living and dead corals has long been recognized. Two crab genera, Trapezia and Tetralia, of the family Xanthidae are determined by Garth (1964) as being obligate commensals of the coral families Pocilloporidae and Acroporidae, respectively. Crane (1947) lists species of the genus Trapezia as being found only in pocilloporid corals along the west coast of tropical America. Miyake (1939), in listing the Brachyura of Micronesia, records Trapezia cymodoce as collected from Stylophora, a pocilloporid coral. Garth 's original collecting techniques used at Eniwetok Atoll, Marshall Islands, were refined in his later collecting in July 1959, at which time he segregated each collection of coral by species to avoid mixing coral commensals found therein.
Article
Current concepts of the structure of mucus have suggested to many investigators that an unidentified cross linking agent must be present to form the mucin network. It is proposed that the mucus globule membrane is the unidentified component and that the relative amount of the membrane, and hence the size of the mucus globule, is the factor that determines the viscosity of mucus. The presence of this membrane in mucus has been established by several studies, but it appears to have been excluded from most of the compositional studies by purification prior to analysis. Supporting data are cited.
Article
THE surface of the stomach is covered by a layer of mucous gel which protects the underlying mucosa from the harmful, acidic stomach contents. The principal component of the gel has been isolated from pig gastric mucus, purified, and shown to be a glycoprotein of molecular weight 2×106 (Table 1)1,2. This glycoprotein consists of four equal sized subunits (molecular weight 5 × 105) joined by disulphide bridges3,4. Each glycoprotein subunit consists of a protein core, 14% by weight of the glycoprotein, with carbohydrate side chains attached. The protein core consists of two regions, one rich in serine, threonine and proline and bearing all the carbohydrate, the other having an amino acid composition characteristic of a globular protein. The latter contains cystine residues which bridge the four subunits. Mild reducing agents and proteolytic enzymes each split the glycoprotein into four subunits4,5. The carbohydrate chains, approximately 15 residues in a branched structure, account for 82% by weight of the glygoprotein and carry ester sulphate residues. The problem therefore is to explain how such a glycoprotein molecule can associate to form a gel which in vivo is essentially impermeable to proteolytic enzymes and which can act as a barrier to protons probably by supporting a pH gradient.
Article
Vitamin A was found in human and bovine mucus, principally as retinyl esters, and was traced to a fraction containing the mucus globule membrane, which was obtained by differential centrifugation of dissolved mucus. This fraction has not been isolated before.
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