Halimeda

In 1992, Paul and Van Alstyne reported on the processes that occur after tissue disruption in different species of the calcified green seaweed Halimeda [56]. After wounding, these algae transform their major secondary metabolite, the his-enoylacetate diterpene halimedatetraacetate (48), into halimedatrial (50) and epihalimedatrial (51). The structural relationship between the educt and the reaction products suggests that the transformation occurs by a combination of solvolysis and hydrolysis reactions as indicated in Scheme 14 [108]. 

Scheme 14 The wound-activated transformation of halimedatetraacetate (48) to halimedatrial (50) and the unstable epihalimedatrial (51) increases the defensive potential of Halimeda spp.

Halimeda H. copiosa Widely distributed globally in warm waters Central America, Caribbean Is., South America, Africa, Indian Ocean Is., South-west Asia, South-east Asia, Australia and New Zealand, and Pacific Is. 

On the other hand, association with more palatable seaweeds may have a negative impact on the chemically defended partner. For example, Halimeda specimens from Conch Reef, Florida Keys, with more than 50% of their thalli covered by Dictyota grow significantly slower than unepiphytized thalli (Beach et al. 2003). This study also verified that epiphytic Dictyota negatively affects metabolic rates of Halimeda tuna in part by shading their thalli, but probably also by chemical means, because the exposure to Dictyota-conditioned water elevated respiration rates in a manner similar to when H. tuna is naturally epiphytized by Dictyota. 

Paul VJ, Van Alstyne KL (1992) Activation of chemical defenses in the tropical marine algae Halimeda spp. J Exp Mar Biol Ecol 160 191-203 Reed RH (1983) Measurement and osmotic significance of beta-dimethylsulfoniopiopionate in marine macroalgae. Mar Biol Lett 4 173-181... 

Stark, L. M., Almodovar, L., and Krauss, R. W. Factors affecting the rate of calcification in Halimeda opuntia (L) Lamouroux and Halimeda discoidea Decaisne. J. Phycol. 5, 305-312 (1969). 

Soft corals have been shown to release terpene chemicals into the water column.210 Their interactions with other invertebrates,211 or with algae122-212-213 have been monitored. Some algal species cause localized tissue necrosis, or reduce terpene levels, in adjacent soft corals 122 213 however, stressing soft corals by transplanting them to new sites stimulates terpene synthesis.199 Some species of algae, notably the chemically protected Halimeda spp., grow in abundance at the base of soft coral colonies, but the soft coral chemical defense does not play a role in maintaining this association.214... 

Paul, V. J. and Van Alstyne, K. L., Chemical defense and chemical variation in some tropical Pacific species of Halimeda (Halimedaceae chlorophyta), Coral Reefs, 6, 263, 1988. 

Kerr, J. N. Q. and Paul, V. J., Animal-plant defense association the soft coral Sinularia sp. (Cnidaria, Alcyonacea) protects Halimeda spp. from herbivory,./. Exp. Mar. Biol. Ecol., 186, 183, 1995. 

Koehn, F. E., Gunaserka, S. P., Niel, D. N., and Cross, S. S., Halitunal, an unusual diterpene aldehyde from the marine alga Halimeda tuna, Tetrahedron Lett., 32, 169, 1991. 

Paul, V.J. and Van Alstyne, K.L., Use of ingested algal diterpenoids by Elysia halimedae Macnae (Opisthobranchia Ascoglossa) as anti-predator defenses, J. Exp. Mar. Biol. Ecol., 119, 15, 1988. 

Hillis-Colinvaux, L. Ecology and taxonomy of Halimeda primary producer of coral reefs, Adv. Mar. Biol., 17, 1, 1980. 

Paul, V. J. and Fenical, W., Isolation of halimedatrial chemical defense adaptation in the calcareous reef-building alga Halimeda, Science, 221, 747, 1983. 

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