Physiological ecology
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  Mycosporine-like amino acids
 

Mycosporine-like amino acids (MAAs) strongly absorb UV radiation in the 310-360nm range and are widely believed to act as sunscreens against biologically damaging UVB and UVA wavelengths. Support for this notion comes from observations that shallow water-inhabiting organisms have greater concentrations of MAAs than deeper water-inhabiting ones.

Topics on the physiological ecology of sea anemones include mycosporine-like amino acids considered here, and METABOLISM and TEMPERATURE, DESICCATION, & OTHER STRESSES located elsewhere.

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Research study 1
 

photograph of clones of sea-anemones Anthopleura elegantissima on a rockAnother physiological challenge for intertidal anemones is the potentially damaging effects of ultraviolet wavelengths.  UV-absorbing mycosporine-like amino acids (MAAs) have been found in several cnidarian species, including corals, and studies on Anthopleura elegantissima collected from Bodega Bay and Santa Barbara, California disclose the presence of 4 major MAAs.  These are found mainly in the tissues of the anemones, with only a small proportion (12%) being found in the zooxanthellae.  However, contrary to expectation based on what is known from studies on other invertebrates, controlled experiments show that A. elegantissima exposed for 28d to UV radiation do not regulate their concentrations of MAAs.  Stochaj et al 1994 Mar Biol 118: 149.

NOTE  these include the previously known shinorine and porphyra-334, and 2 new compounds mycosporine-taurine, and mycosporine-2 glycine

 

 

 

 

 

 

 

Two or more large clones of aggregating anemones Anthopleura elegantissima.
Few west-coast researchers have taken experimental advantage of the
presence of genetically identical individuals in such aggregations. The present
assemblage, for example, has clonemates separated vertically by at least 1.5m

 

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Research study 2

 

histogram showing UV effects on mycosporine-like amino acids in sea anemones Anthopleura elegantissimaIn another study of UV effects on MAA concentrations in Anthopleura elegantissima, researchers compare production of MAAs in both symbiotic (with symbionts) and aposymbiotic (without symbionts) individuals.  The symbiotic specimens are collected from a single aggregation in a rocky intertidal region around Santa Barbara, California, while the aposymbiotic ones are collected from seawater outlet pipes at the UC, Santa Barbara marine laboratory.  After 8wk exposure to UV (280-400nm) the researchers record no significant effects of UV on MAA concentrations in symbiotic individuals (see histogram). However, in aposymbiotic individuals exposed to UV, MAA concentrations are significantly elevated over concentrations in ones not exposed to UV. MAAs are not present in the symbiont itself, Symbiodinium californium, in culture or in the culture medium, nor in symbionts freshly isolated from anemones, suggesting that the anemones are obtaining these MAAs from an exogenous source. Banaszak & Trench 1995 J Exp Mar Biol Ecol 194: 233.

NOTE  the researchers find the same 4 MAAs in A. elegantissima as noted in Research Study 1 above, as well as palythine and mycosporine-glycine as minor components, and asterina-330 in trace amounts

 

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Research study 3
 

If UV irradiation is not important in regulating amounts and types of MAAs in sea anemones, then what is?  Some old and some new ideas are investigated in a comprehensive study of 4 species of Anthopleura collected at various locations from northern Washington to southern California.  graph showing concentrations of mycosporine-like amino acids (MAAs) in sea anemone Anthopleura elegantissima in relation to concentration of symbiontsSpecifically, the researchers compare patterns of MAAs in A. elegantissima with: 1) mostly zooxanthellae, 2) mostly zoochlorellae, 3) mixed populations of symbionts, and 4) no symbionts (aposymbiotic). Additionally, they also examine MAA patterns in the other 3 species.  With a few exceptions, results show that the complements of 4 major MAAs in all species reflect phylogenetic differences among them rather than type of symbiont, presence or absence of symbionts, or environmental factors such as type of food. One exception occurs in A. elegantissima where the concentration of  mycosporine-2 glycine increases with density of zooxanthellae (see graph). The authors, however, discuss this relationship and conclude that it is not so clear-cut as it seems.  Other factors may be involved.

Major findings in the study, then, are that MAA complements in Anthopleura reflect the taxonomic and phylogenetic differences among the species, and that MAAs are possibly synthesised rather than being derived dietarily or from their symbionts.  Although UV-screening has in the past been foremost in the minds of MAA investigators, in view of these results and the results of other studies, the present authors discuss alternative possible functions, including other physiological or even predator-defensive roles.  Shick et al. 2002 Biol Bull 203: 315.

NOTE  these are A. elegantissima, A. xanthogrammica, A. sola, and A. Artemisia. The last species is thought by these authors to lack symbionts

NOTE mycosporine-taurine, shinorine, porphyra-334, and mycosporine-2 glycine

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