New Ecological Role of Seaweed Secondary Metabolites as Autotoxic and Allelopathic

Abstract

Allelopathy and autotoxicity are well-known biological processes in angiosperms but are very little explored or even unknown in seaweeds. In this study, extract and major pure compounds from two distinct populations of the red seaweed Laurencia dendroidea were investigated to evaluate the effect of autotoxicity through auto-and crossed experiments under laboratory conditions, using chlorophyll fluorescence imaging to measure inhibition of photosynthesis (PSII) as a variable response. Individuals of L. dendroidea from Azeda beach were inhibited by their own extract (IC 50 = 219 µg/ml) and the major compound elatol (IC 50 = 87 µg/ml); both chemicals also inhibited this seaweed species from Forno beach (IC 50 = 194 µg/ml for the extract and IC 50 = 277 µg/ml for elatol). By contrast, the extract of L. dendroidea from Forno and its major compound obtusol showed no inhibitory effect in individuals of both populations; but obtusol was insoluble to be tested at higher concentrations, which could be active as observed for elatol. The Azeda population displayed higher susceptibility to the Azeda extract and to elatol, manifested on the first day, unlike Forno individuals, in which the effect was only detected on the second day; and inhibition of PSII was more pronounced at apical than basal portions of the thalli of L. dendroidea. This first finding of seaweed autotoxicity and allelopathic effects revealed the potential of the chemistry of secondary metabolites for intra-and inter-populational interactions, and for structuring seaweed populations.

Marine natural products

“…These results indicate the geographic importance of intraspecies chemical communication and the ability of algae to help structure benthic communities in local marine ecosystems. 420…”

Variability in Seaweed Chemical Defense and Growth Under Common Garden Conditions

“…Therefore, we can hypothesize that even in the absence of herbivory pressure and competition, but under optimal or non-stressful laboratory conditions (e.g., such as sufficient nutrient provision and light), there was an allocation of energy to produce elatol at the expense of other aspects such as growth itself. This small terpenoid seems to act as a constitutive defense, able to be induced by external signals, whose efficiency depends on dose and kind of ecological interaction (Sudatti et al, 2018;Sudattti et al, 2020).…”

Warming may increase the vulnerability of calcareous algae to bioinvasions

“…stictiforme specimens under thermal stress treatments, the higher percentage of specimens affected by the invasive alga W. setacea than by the artificial treatment points to an allelopathic effect of algae overgrowth. It is well known that many benthic algae species produce toxic secondary metabolites, which act as agents against herbivory and antifouling (Paul et al, 2001;Sudatti et al, 2020). Although the secondary metabolites of W. setacea have not been studied to date, chemical interactions should not be disregarded.…”