The sea-hare Aplysia brasiliana promotes induction in chemical defense in the seaweed Laurencia dendroidea and in their congeneric neighbors.

Inducible chemical defenses are more common in temperate seaweeds than tropical ones, and are directly detected by increase of chemical contents, or indirectly by differential consumption of live seaweed tissues or artificial food with algal extracts by herbivores. In general, seaweed-induced chemical defense occur between 11 and 20 days after both simulated/artificial or direct herbivory. Here, we used experimental procedures to assess induced chemical defense in the tropical red seaweed Laurencia dendroidea as response to direct grazing, chemical cues from grazed conspecific neighbors and only presence of herbivores. Chemical defenses were analyzed by detecting the palatability of artificial food containing L. dendroidea extracts offered to Aplysia brasiliana and by comparative analyses of extracts from this seaweed by Gas Chromatography/Mass Spectroscopy, as well as metabolomic data analysis by Principal Component Analysis. Our results revealed that direct grazing by A. brasiliana induced a rapid (after 48 h) response among individuals of L. dendroidea, as did waterborne chemical cues from grazed conspecifics, but the presence of sea hare alone did not elicit a response. Increased resistance to grazing was accompanied by significative changes in sesquiterpene metabolomic chemical profile, revealing that induced defense: may be more widespread among seaweeds, independent of latitude; can involve changes in other classes of substances besides phlorotannins or not only the increase in the content of a single compound; and may be a rapid and ecologically coherent response to consumers. In addition, the importance of incorporating the metabolomic approach when examining inducible chemical defense in seaweeds is also emphasized.

Effects of elevated nutrients and CO2 emission scenarios on three coral reef macroalgae.

Coral reef macroalgae are expected to thrive in the future under conditions that are deleterious to the health of reef-building corals. Here we examined how macroalgae would be affected by exposure to future CO2 emission scenarios (pCO2 and temperature), enriched nutrients and combinations of both. The species tested, Laurencia intricata (Rhodophyta), Turbinaria ornata and Chnoospora implexa (both Phaeophyceae), have active carbon-concentrating mechanisms but responded differently to the treatments. L. intricata showed high mortality under nutrient enriched RCP4.5 ("reduced" CO2 emission) and RCP8.5 ("business-as-usual" CO2 emission) and grew best under pre-industrial (PI) conditions, where it could take up carbon using external carbonic anhydrase combined, potentially, with proton extrusion. T. ornata's growth rate showed a trend for reduction under RCP8.5 but was unaffected by nutrient enrichment. In C. implexa, highest growth was observed under PI conditions, but highest net photosynthesis occurred under RCP8.5, suggesting that under RCP8.5, carbon is stored and respired at greater rates while it is directed to growth under PI conditions. None of the species showed growth enhancement under future scenarios, nutrient enrichment or combinations of both. This leads to the conclusion that under such conditions these species are unlikely to pose an increasing threat to coral reefs.

Induction of halogenated vesicle transport in cells of the red seaweed Laurencia obtusa.

In clones of the red alga Laurencia obtusa, the frequency of vesicle transport from corps en cerise (CC) to the cell wall region was evaluated in response to differences in temperature, irradiance, desiccation, bacterial fouling, and bromine (Br) availability. In addition, the morphology of the corps en cerise was analyzed. Traffic of vesicles was induced by exposing L. obtusa to low temperatures and variations in irradiance. It was also verified that bacterial fouling induced vesicle traffic. Under high temperatures and desiccation, the membranous tubular connections were lost and transport of vesicles was not seen. The morphology of the corps en cerise varied according to the availability of Br in seawater. Exocytosis of secondary metabolites by L. obtusa was shown to vary in relation to temperature, irradiance, desiccation and bacterial fouling. The data suggest that the transport of vesicles in L. obtusa may be related to the inhibition of the microfouling community on the algal surface.

Intra-cellular storage, transport and exocytosis of halogenated compounds in marine red alga Laurencia obtusa.

The production of secondary metabolites in seaweed have been related to a capability to partition compounds into cellular specialized storage structures, like gland cells and the corps en cerise (CC) or cherry bodies. The possible mechanisms that bring these compounds to the thallus surface remain poorly understood. Therefore, the aim of this work is perform a characterization of the CC and determine the intra-cellular dynamics of halogenated compounds in Laurencia obtusa. The dynamics of CC and the mechanisms related to the intra-cellular transport of halogenated compounds were evaluated by using optical tweezers and time-lapse video microscopy. The CC were isolated and its elemental composition was characterized using X-ray microanalysis. The cellular distribution of halogenated compounds was also demonstrated by fluorescence microscopy. Three-dimensional reconstruction technique was used to provide a visualization of the structures that connect CC to cell periphery. As main findings, we confirmed that the halogenated compounds are mainly found in CC and also in vesicles distributed along the cytoplasm and within the chloroplasts. We demonstrated that CC is mechanically fixed to cell periphery by a stalk-like connection. A vesicle transport though membranous tubular connections was seen occurring from CC to cell wall region. We also demonstrated a process of cortical cell death event, resulting in degradation of CC. We suggested that the vesicle transportation along membranous tubular connections and cell death events are related to the mechanisms of halogenated compounds exudation to the thallus surface and consequently with defensive role against herbivores and fouling.

Stable isotope analysis of production and trophic relationships in a tropical marine hard-bottom community.

Seagrasses produce much of the organic carbon in the shallow waters of the Caribbean and it has long been assumed that a substantial portion of this carbon is exported to nearby habitats, contributing substantially to their food webs. In the shallow coastal waters of the Florida Keys (USA), seagrass intersperses with hard-bottom habitat where bushy, red macroalgae are the most prominent primary producers. However, the relative importance of seagrass-derived carbon versus autochthonous algal production or phytoplankton in supporting higher trophic levels within hard-bottom communities has never been investigated. We compared the carbon and nitrogen isotopic values of potential primary producers and representative higher trophic level taxa from hard-bottom sites on the bay-side and ocean-side of the Florida Keys. We also included in our study a set of bay-side sites that experienced significant ecological disturbances over the past decade (e.g., cyanobacteria blooms, seagrass die-off, and sponge die-offs) that may have altered trophic relationships in those regions. We did not detect any differences among regions in the trophic status of hard-bottom taxa that might be associated with ecosystem disturbance. However, our results suggest that autochthonous production of algal detritus is an important source of secondary production in these hard-bottom communities, with seagrass and phytoplankton contributing smaller fractions.

Extracts and sesquiterpene derivatives from the red alga Laurencia chondrioides with antibacterial activity against fish and human pathogenic bacteria.

During screening of seaweeds from different places in Europe for antimicrobial activities against human and fish pathogenic bacteria, Laurencia chondrioides was identified as a promising species. By bioassay-guided isolation, followed by structure elucidation by mass spectrometry and 1H- and 13C-NMR spectrometry, two sesquiterpenoides of the chamigrene-type from the selected red seaweed Laurencia chondrioides were identified. Both compounds inhibit the growth of some fish and human pathogenic bacteria.