Perspectives on mucus secretion in reef corals

Abstract

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. KEY WORDS:Mucin · Mucopolysaccharide · Coral surface microlayer · CSM · Surface mucopolysaccharide layer · SML Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 296: [291][292][293][294][295][296][297][298][299][300][301][302][303][304][305][306][307][308][309] 2005 We feel that it is time that the study of mucus was revisited for at least 3 reasons. Firstly, mucus plays an important part in coral disease which has been responsible for significant coral mortality, particularly in the Caribbean (Porter et al. 2001) and more recently in the Indo-Pacific provinces (Sutherland et al. 2004). In this context mucus may function both as a protective physicochemical barrier (Peters 1997, Santavy & Peters 1997, Hayes & Goreau 1998, Sutherland et al. 2004) and as a growth medium for bacteria, including potential pathogens (Ducklow & Mitchell 1979b, Rublee et al. 1980, Toren et al. 1998, Banin et al. 2001, Lipp et al. 2002. But what do we actually know about the dynamics of the in situ mucus layer or its physico-chemical properties that might influence bacterial entrainment, growth or inhibition? Apparently we know very little. Even the most fundamental measure, the rate of mucus production, is extremely difficult to assess and is poorly defined in the literature. When, for example, authors report increased mucus production rates due to environmental stress, is this actually an increase in synthesis or merely an increase in the release of stored mucus?Secondly, coral algal symbionts play an important role in governing the composition of mucus, with 20 to 45% of daily net photosynthate being released as mucus and dissolved organic carbon (Davies 1984, Crossland 1987, Bythell 1988, Edmunds & Davies 1989. It follows then that during bleaching, when densities of algal symbionts are significant...

Nutritional status and metabolism of the coral Stylophora subseriata along a eutrophication gradient in Spermonde Archipelago (Indonesia)

“…The host respires a large portion of photosynthates, and the acquired ATP is used inter alia for G (Al-Horani et al 2003;Allemand et al 2004) and mucus production (Brown and Bythell 2005), while the other portion provides compounds for the synthesis of cellular proteins, lipids (Muscatine and Cernichiari 1969;Dubinsky and Jokiel 1994), and mucus (Crossland 1987). The latter can account for 20-45% of the net photosynthate production (Brown and Bythell 2005).…”

“…This is often reflected in increased respiration rates (Abdel-Salam et al 1988), decreased P/R ratios (Riegl and Branch 1995;Anthony and Fabricius 2000), decreased photophysiological performance (Philipp and Fabricius 2003), and/or decreased calcification rates (Cortes and Risk 1985;Rogers 1990). Increased particle loads may also enhance coral mucus production in response to particles settling on the coral surface (Stafford-Smith 1993;Riegl and Branch 1995;Brown and Bythell 2005). In spite of significant inputs of riverine nutrients, the associated changes in inorganic nutrient concentrations are often insignificant due to their rapid incorporation by nutrientstarved plankton in reefs (Furnas et al 2005).…”

Bioindicators of changes in water quality on coral reefs: review and recommendations for monitoring programmes

“…Mucus is produced by some corals to clean the colony surface of sediments, or as a response to emersion during low tides, turbidity, pollutant exposure, changes in salinity and water temperatures and injury (Stafford-Smith and Coral Reefs (2009) 28:589-606 597 Ormond 1992; Stafford-Smith 1993;Brown and Bythell 2005). Some corals, however, will not produce mucus when stressed, or will stop producing mucus after prolonged stress.…”

A bacterial pathogen uses dimethylsulfoniopropionate as a cue to target heat-stressed corals

“…This mucus contains a broad range of chemicals, including water-soluble glycoproteins, amino acids and metabolites (Brown and Bythell, 2005). In the mucus of many coral species, the sulfur compound dimethylsulfoniopropionate (DMSP) reaches concentrations (1-62 mM) orders of a magnitude higher than in the surrounding seawater (6-11 nM) (Broadbent and Jones, 2004;Van Alstyne et al, 2006).…”

“…The surface of a coral is lined with mucus of variable viscosity, which is continuously excreted for cleansing, feeding and defense (Brown and Bythell, 2005). This mucus contains a broad range of chemicals, including water-soluble glycoproteins, amino acids and metabolites (Brown and Bythell, 2005).…”