Settlement cues

Although many investigators speculate that larvae of some coral reef fishes might use chemical cues to identify suitable settlement sites (Sale 1991), there has been almost no attempt to test this hypothesis. The single available test (Sweatman 1988) is, however, an excellent example of designing assays to achieve ecological 

The following section presents a brief outline of historical and contemporary settlement assay methodologies. 

The above methods can determine if chemical cues are present, but say little about the chemical composition of the cue. Methods facilitating this include the use of organismal washes, homogenates, or extracts, and the fractionation of these chemical mixtures along size or polarity gradients, followed by bioassays of the different fractions. 

Organismal washes have usually been prepared by holding a certain number 

There are two potentially major problems that must be considered when using the types of approaches discussed above. Unfortunately, in several previous studies, these potential problems may have been actual problems. First, investigators often extract all metabolites from a three-dimensional organism and concentrate these on a two-dimensional assay surface. This can produce a grossly inflated 

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Chemically mediated interactions have important direct and indirect effects on communities from both ecological and evolutionary standpoints.22 341 Chemical defense or communication cannot be properly understood unless it is viewed through the lenses of population, community, and ecosystem processes, and this requires consideration of both the biotic and abiotic components of the natural environment.342 For example, chemically mediated foraging is affected by water flow because it relies on water-soluble cues that are carried away from prey.343 345 Similar constraints likewise modify the effectiveness of other waterborne cues, such as alarm signals, sexual pheromones, and settlement cues, in both mobile and sessile organisms.244 345 350... 

Zimmer-Faust, R.K. and Tamburri, M.N., Chemical identity and ecological implications of a waterborne, larval settlement cue, Limnol. Oceanogr., 39, 1075, 1994. 

Krug, RJ. and Manzi, A.E., Waterborne and surface-associated carbohydrates as settlement cues for larvae of the specialists marine herbivore Alderia modesta, Biol. Bull., 197, 94, 1999. 

Several studies now point to the importance of carbohydrates as settlement cues. Many species of coral larvae that settle on crustose coralline algae metamorphose in response to an algal cell wall polysaccharide.17132 The sacoglossan Alderia modesta metamorphoses in response to carbohydrates of different size classes from its algal food Vaucheria longicaulis.144 The sea urchin Holopneustes purpurascens metamorphoses in response to a complex of the sugar floridoside and isethionic acid from the red alga Delisea pule hr a.11 In this case, the combination of compounds was important because neither induced metamorphosis alone. 

The cellular mechanisms underlying the abilities of larvae to detect and respond to both adsorbed and soluble settlement cues are yielding to intense study. It has been shown that larvae of many types have the ability to utilize dissolved cues to settlement, which was thought impossible only 20 to 25 years ago. Understanding the details of larval receptor systems will require the use of most of the modem techniques for studying subcellular biology, but critical breakthroughs have already occurred in this area and more are expected in the next decade. 

Research on larval settlement in MGH s laboratory is currently supported by NSF grant OCE-9907545. VJP received support from NSF grant HRD-9626896 in the Visiting Professorships for Women Program for her research on the chemistry of larval settlement cues. Both authors gratefully acknowledge the assistance and moral support of the students and postdoctoral fellows in their laboratories while their mentors write book chapters. 

Hadfield, M. G., Meleshkevitch, E. A., and Boudko, D. Y., The apical sensory organ of a gastropod veliger is receptor for settlement cues, Biol. Bull., 198, 67, 2000. 

Secondary metabolites are often used as part of an organism s defensive strategy. Secondary metabolites may affect bacterial numbers or promote or deter specific bacteria that provide settlement cues to potential macrofoulers. Secondary metabolites may also deter macrofoulers from settling or kill them once settled. 

Hills JM, Thomason JC, Milligan JL, Richardson M (1998) Do barnacle larvae respond to multiple settlement cues over a range of spatial scales Hydrobiologia 375(376) 101-111... 

Prendergast GS, Zum CM, Bers AV, Head RM, Hansson LJ, Thomason JC (2008) Field-based video observations of wild barnacle cyprid behaviour in response to textural and chemical settlement cues. Biofouling 24 449 159... 

Raimondi PT (1988) Settlement cues and determination of the vertical limit of an intertidal barnacle. Ecology 69 400-407... 

Capturing wild postlarvae Attraction by settlement cues... 

ROBERTS R (2001) A review of settlement cues for larval abalone (Haliotis spp.). Journal of Shellfish Research, 20, 571-586. 

Wethey, D.S. 1986. Ranking of settlement cues by barnacle larvae influence of surface contour. Bull. Mar. Sci. 39 393-400. 

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