Transcriptome and functional analyses of phenotypic plasticity in sea grape Caulerpa okamurae.

Caulerpa is a marine green macroalga distinguished by a large single cell with multiple nuclei. It also exhibits remarkable morphological intraspecies variations, in response to diverse environmental types. However, the molecular mechanisms underlying this phenotypic plasticity remain poorly understood. In this work, we compare the transcriptomes of Caulerpa okamurae Weber Bosse, 1897 displaying altered phenotypes of cultivation and natural phenotypes and investigate significantly regulated genes and their biological functions using differential expression analyses. We observe light-harvesting complex upregulation and cellular framework stability downregulation in altered phenotypes compared to the natural phenotypes. Intertidal macrophytes reduce light capture to avoid photodamage and regulate their morphology to protect against wave damage. In contrast, the lower light conditions and the cultivation environment augment light capture and increase a morphology prioritizing light trapping. Moreover, the addition of simulated wave-sweeping stimuli induces a return to the natural morphology under high-light conditions, showing how mechanical stress affects morphological organization in C. okamurae. We provide detailed gene expression patterns in C. okamurae under varying light intensities and water conditions, suggesting a distinct influence on its morphological traits.

Insights into the bacterial community composition of farmed Caulerpa lentillifera: A comparison between contrasting health states.

The bacterial communities of Caulerpa lentillifera were studied during an outbreak of an unknown disease in a sea grape farm from Vietnam. Clear differences between healthy and diseased cases were observed at the order, genus, and Operational Taxonomic Unit (OTU) level. A richer diversity was detected in the diseased thalli of C. lentillifera, as well as the dominance of the orders Flavobacteriales (phylum Bacteroidetes) and Phycisphaerales (Planctomycetes). Aquibacter, Winogradskyella, and other OTUs of the family Flavobacteriaceae were hypothesized as detrimental bacteria, this family comprises some well-known seaweed pathogens. Phycisphaera together with other Planctomycetes and Woeseia were probably saprophytes of C. lentillifera. The Rhodobacteraceae and Rhodovulum dominated the bacterial community composition of healthy C. lentillifera. The likely beneficial role of Bradyrhizobium, Paracoccus, and Brevundimonas strains on nutrient cycling and phytohormone production was discussed. The bleaching of diseased C. lentillifera might not only be associated with pathogens but also with an oxidative response. This study offers pioneering insights on the co-occurrence of C. lentillifera-attached bacteria, potential detrimental or beneficial microbes, and a baseline for understanding the C. lentillifera holobiont. Further applied and basic research is urgently needed on C. lentillifera microbiome, shotgun metagenomic, metatranscriptomic, and metabolomic studies as well as bioactivity assays are recommended.

Negative effects of warming on seagrass seedlings are not exacerbated by invasive algae.

The observed and projected rise in sea surface temperature challenges marine biodiversity worldwide, and particularly in temperate ecosystems dealing with the arrival of novel species of tropical provenance. When the impacted biota are early life stages of ecosystem engineers, the effects of those impacts are of major concern for ecologists and coastal managers. We experimentally examined the individual and potential additive effects of seawater warming and the presence of the invasive algae on the development of seedlings of the seagrass Posidonia oceanica in a three-month mesocosm experiment. Whereas the presence of the invasive algae (Caulerpa cylindracea and Lophocladia lallemandii) did not result in detrimental effects on seedlings, warming negatively affected seedling development. Interestingly, the presence of both invasive algae may ameliorate the negative effects of warming.

Synergistic reduction of a native key herbivore performance by two non-indigenous invasive algae.

Native generalist grazers can control the populations of non-indigenous invasive algae (NIIA). Here, it was found that the simultaneous consumption of two co-occurring NIIA, Caulerpa cylindracea and C. taxifolia var. distichophylla, hinders the grazing ability of the main Mediterranean herbivorous, the native sea urchin Paracentrotus lividus. The ingestion of any of the two NIIA alone did not produce any difference in sea urchin righting time with respect to usual algal diet. In contrast, the simultaneous consumption of both NIIA, which grow intermingled in nature and are consumed by P. lividus, retarded its righting behavior. Such result reveals substantial physiological stress in the sea urchin, which resulted in reduced motility and coordination. The reported findings reveal the potential of NIIA co-occurrence to escape the supposed control exerted by the main native generalist grazer in Mediterranean sublittoral communities, which in turn can be locked in an "invaded" state.

Marine macroalga Caulerpa: role of its metabolites in modulating cancer signaling.

Cancer, the leading causes of death worldwide, causes multiple metabolic and physiological alterations, leading to an unregulated proliferation of cells. The existing anticancer therapies are usually nonspecific with side effects and or are extremely expensive, thus hunt for better therapeutics is still on, specially efforts are made to look for naturally occurring molecules. Sea harbors several organisms which are unexplored for their biological potentials. Green macroalga genus, Caulerpa, is one such invaluable repository of bioactive metabolites like alkaloids, terpenoids, flavonoids, steroids and tannins with reported bioactivities against many diseases including cancer. Anti-cancerous metabolites of Caulerpa like caulerpenyne (Cyn), caulerpin, caulersin, and racemosin C, possess unique structural moieties and are known to exhibit distinct effects on cancer cells. Theses metabolites are reported to affect microtubule dynamics, unfolded protein response, mitochondrial health, cell cycle progression, metabolic and stress pathways by their cross-talk with signalling proteins like AMPK, GRP78, GADD153, Bid, Bax, AIF, Bcl2, P21, cyclin D, cyclin E, caspase 9, and PTP1B. Targeting of multiple cancer hallmarks by Caulerpa metabolites, with concomitant modulations of multiple signalling cascades, displays its multifactorial approach against cancer. Evaluation of anti-cancer properties of this genus is particularly important as Caulerpa species are widely edible and utilized in several delicacies in the coastal countries. This is the first review article providing a consolidated information about the role of Caulerpa in cancer with major contributing metabolites and plausible modulations in cancer signaling and prospects.

Biotic resistance and vegetative propagule pressure co-regulate the invasion success of a marine clonal macrophyte.

Propagule pressure is considered a major driver of plant invasion success. Great propagule pressure would enable invasive species to colonize new areas overcoming the resistance of native species. Many highly invasive aquatic macrophytes regenerate from vegetative propagules, but few studies have experimentally investigated the importance of propagule pressure and biotic resistance, and their interaction, in determining invasion success. By manipulating both recipient habitat and the input of vegetative propagules of the invasive seaweed Caulerpa cylindracea in mesocosm, we examined whether higher propagule pressure would overcome the resistance of a native congeneric (Caulerpa prolifera) and influence its performance. With the native, C. cylindracea population frond number decreased irrespectively of pressure level. High propagule pressure did not increase stolon length and single plant size decreased due to the effects of intra- and interspecific competition. Native biomass decreased with increasing C. cylindracea propagule pressure. These results indicate that higher propagule pressure may fail in enhancing C. cylindracea invasion success in habitats colonized by the native species, and they suggest that biotic resistance and propagule pressure co-regulate the invasion process. These findings emphasize the need to preserve/restore native seaweed populations and may help to design effective management actions to prevent further C. cylindracea spread.

Under the canopy: Community-wide effects of invasive algae in Marine Protected Areas revealed by metabarcoding.

We analysed with multigene (18S and COI) metabarcoding the effects of the proliferation of invasive seaweeds on rocky littoral communities in two Spanish Marine Protected Areas. The invasive algae studied were Caulerpa cylindracea, Lophocladia lallemandii and Asparagopsis armata. They are canopy-forming, landscape-dominant seaweeds, and we were interested in their effects on the underlying communities of meiobenthos and macrobenthos, separated in two size fractions through sieving. A new semiquantitative treatment of metabarcoding data is introduced. The results for both markers showed that the presence of the invasive seaweed had a significant effect on the understory communities for Lophocladia lallemandii and Asparagopsis armata but not for Caulerpa cylindracea. Likewise, changes in MOTU richness and diversity with invasion status varied in magnitude and direction depending on the alga considered. Our results showed that metabarcoding allows monitoring of the less conspicuous, but not least important, effects of the presence of dominant invasive seaweeds.

Field transplantation of seagrass (Posidonia oceanica) seedlings: Effects of invasive algae and nutrients.

Seedlings are a key life stage in seagrasses, providing genetic diversity and being a useful tool for restoration. We examined the influence of increased sediment nutrients and the presence of the invasive macroalga Caulerpa cylindracea on the success of in situ transplanting Posidonia oceanica seedlings in a six-month experiment. Our results indicate that one-year old seedlings successfully survive in the field and their survival and growth are positively affected by the presence of C. cylindracea. Furthermore, nutrient addition in the sediment had positive effects on both C. cylindracea (increasing its cover) and seedlings (increasing leaf development), and the increased C. cylindracea cover did not result in detrimental effects on seedlings. Therefore, biological invasions and nutrient addition do not reinforce each other in the short term to negatively impact transplanted seedlings, which highlights facilitative interactions between invasive algae and native seagrass and provides useful information for successful strategies of seagrass restoration.

Habitat associations of an expanding native alga.

There are many examples of native macrophytes becoming locally dominant and spreading outside their traditional distributions, but the causes and impacts are often not understood. In New South Wales, Australia, the green alga Caulerpa filiformis is undergoing a range expansion and has transitioned from a subdominant to a dominant alga on several rocky shores around the Sydney coastline. Here we investigated relationships between established patches of C. filiformis, the habitat it occupies and associated algal communities at multiple subtidal sites over the green alga's 700 km range. We tested the following predictions: 1) C. filiformis cover differs among substrata, being greatest on turf-forming algae; 2) C. filiformis cover is positively related to environmental variables linked to increased sedimentation (e.g. reduced reef width, surface slope, increased rugosity and distance from shore); 3) occurrence of C. filiformis is associated with a change in macrophyte community structure and a reduction of macrophyte richness; 4) intact native algal canopies inhibit C. filiformis spread, but turf-forming algae and bare sand are susceptible to invasion. Substratum associations were highly consistent among sites, but contrary to our prediction, C. filiformis was most commonly associated with rock or rock + sand substratum and less frequently associated with turf-forming algae substratum. C. filiformis cover was negatively correlated with reef width, which explained most of the variation observed, although local scale variables distance from shore, reef slope, and water depth were also correlated with C. filiformis cover. Algal diversity and community composition typically differed in the presence of C. filiformis, often with a reduction of algal abundances, in particular Sargassum spp., although results varied among substrata and sites. However, monitoring of borders suggested that C. filiformis does not invade and outcompete undisturbed adjacent canopy-forming algae over a 12 month period. Our results suggest that disturbance processes (possibly linked to sedimentation) acting at the site and quadrat scale are likely important determinants of C. filiformis cover and spread, and hence its potential ecological impacts.

Potential effects of an invasive seaweed (Caulerpa cylindracea, Sonder) on sedimentary organic matter and microbial metabolic activities.

Caulerpa cylindracea (Sonder), among the most successful marine bio-invaders on a global scale, poses severe threats to biodiversity. However, the effects of this seaweed on the quantity and the biochemical composition of sedimentary organic matter are still poorly known. Since the whole set of sedimentary features affects the availability of substrates for benthic microbial communities, we: i) investigated the biochemical composition of sediments colonized and not-colonized by C. cylindracea, and ii) compared the metabolic patterns of the microbial communities associated with C. cylindracea and in the sediments colonized and not-colonized by the seaweed. Our results show that C. cylindracea can influence the quantity and biochemical composition of sedimentary organic matter (OM), and that microbial populations associated with colonized sediments do have specific metabolic patterns and degradation capacities. Caulerpa cylindracea can also influence the metabolic patterns of the microbial community specifically adapted to degrade compounds released by the seaweed itself, with possible consequences on C cycling.

Eutrophication affects the resistance of fucoids to an introduced alga spread.

This study investigates whether eutrophication can affect the capacity of the canopy alga Cystoseira brachycarpa to impede or limit the spread of the introduced species Caulerpa cylindracea. By means of a manipulative field study (16 months long), the effects of nutrient enrichment and C. cylindracea removal were tested on the canopy-alga and the associated macroalgal community. Results highlighted deep changes through time due to nutrient enrichment, as C. brachycarpa decreased and Halopteris scoparia increased in cover. Furthermore, C. brachycarpa was also affected by the presence of the introduced species Caulerpa cylindracea which, in turn, was found significantly advantaged by nutrient enrichment. Overall, our findings suggest that eutrophication can drive the substitution of Cystoseira with H. scoparia, leading to the shift from canopy to opportunistic species, which are unable to avoid the spread of C. cylindracea.

Carry over effects of nutrient addition on the recovery of an invasive seaweed from the winter die-back.

Nutrient enrichment of coastal waters can enhance the invasibility and regrowth of non-native species. The invasive alga Caulerpa cylindracea has two distinct phases: a well-studied fast-growing summer phase, and a winter latent phase. To investigate the effects of nutrient enrichment on the regrowth of the seaweed after the winter resting-phase, a manipulative experiment was carried out in intertidal rockpools in the North-western Mediterranean. Nutrients were supplied under different temporal regimes: press (constant release from January to May), winter pulse (January to March) and spring pulse (March to May). Independently from the temporal characteristics of their addition, nutrients accelerated the re-growth of C. cylindracea after the winter die-back, resulting in increased percentage covers at the peak of the growing season. Nutrient addition did not influence the number and length of fronds and the biomass. Native components of the algal community did not respond to nutrient additions. Our results show that nutrient supply can favour the spread of C. cylindracea even when occurring at a time of the year at which the seaweed is not actively growing.

Differential response of coral communities to Caulerpa spp. bloom in the reefs of Indian Ocean.

Coral reef ecosystems are disturbed in tandem by climatic and anthropogenic stressors. A number of factors act synergistically to reduce the live coral cover and threaten the existence of reefs. Continuous monitoring of the coral communities during 2012-2014 captured an unprecedented growth of macroalgae as a bloom at Gulf of Mannar (GoM) and Palk Bay (PB) which are protected and unprotected reefs, respectively. The two reefs varying in their protection level enabled to conduct an assessment on the response of coral communities and their recovery potential during and after the macroalgal bloom. Surveys in 2012 revealed a live coral cover of 36.8 and 14.6% in GoM and PB, respectively. Live coral cover was lost at an annual rate of 4% in PB due to the Caulerpa racemosa blooms that occurred in 2013 and 2014. In GoM, the loss of live coral cover was estimated to be 16.5% due to C. taxifolia bloom in 2013. Tissue regeneration by the foliose and branching coral morphotypes aided the recovery of live coral cover in GoM, whereas the chances for the recovery of live coral cover in PB reef were low, primarily due to frequent algal blooms, and the existing live coral cover was mainly due to the abundance of slow-growing massive corals. In combination, results of this study suggested that the recovery of a coral reef after a macroalgal bloom largely depends on coral species composition and the frequency of stress events. A further study linking macroalgal bloom to its specific cause is essential for the successful intervention and management.

Caulerpa cylindracea Sonder invasion modifies trophic niche in infralittoral rocky benthic community.

The Mediterranean basin is one of the most invaded seas of the world. Invasive species have affected coastal benthic communities inducing structural changes. Since first reports, in the early 90s, Caulerpa cylindracea is considered one of the most important invasive event in the Mediterranean Sea where it has invaded large areas of soft bottoms, seagrass meadows and rocky shores. To assess effects of C. cylindracea in rocky ecosystems, benthic food webs have been compared between invaded and non-invaded coastal conditions through stable isotopes analyses. In addition, the convex hull area of the two types of conditions has been calculated as a proxy for the total extent of trophic diversity within each food web. Results have shown that the trophic niche width is at least 1.4 times wider in invaded conditions than in non-invaded conditions. In addition, this study gives further evidence of similar feeding analogies between the invasive herbivore fish, Siganus luridus and native herbivore fish Sparisoma cretense as both are feeding at the same isotopic level. This investigation provides with new scientific data to assess bionvasions in invaded and non-invaded conditions at assemblage level in coastal systems.

Ecophysiological responses of three Mediterranean invasive seaweeds (Acrothamnion preissii, Lophocladia lallemandii and Caulerpa cylindracea) to experimental warming.

The Mediterranean Sea is a hotspot for invasive species and projected Mediterranean warming might affect their future spreading. We experimentally examined ecophysiological responses to the temperature range 23-31 °C in three invasive seaweeds commonly found in the Mediterranean: Acrothamnion preissii, Caulerpa cylindracea and Lophocladia lallemandii. The warming range tested encompassed current and projected (for the end of 21st Century) maximum temperatures for the Mediterranean Sea. Optimal ecophysiological temperatures for A. preissii, C. cylindracea and L. lallemandii were 25 °C, 27 °C and 29 °C, respectively. Warming below the optimal temperatures enhanced RGR of all studied invasive seaweeds. Although sensitive, seaweed photosynthetic yield was less temperature-dependent than growth. Our results demonstrate that temperature is a key environmental parameter in regulating the ecophysiological performance of these invasive seaweeds and that Mediterranean warming conditions may affect their invasion trajectory.

High tolerance to simulated herbivory in the clonal seaweed, Caulerpa cylindracea.

Tolerance can enable introduced plants to establish in the face of intense consumption by native herbivores. The siphonacous seaweed, Caulerpa cylindracea, despite being heavily grazed by native herbivores, is one of the most successful invaders in the Mediterranean. By means of a field experiment simulating herbivore grazing, we tested whether regeneration from damaged creeping stolons may allow C. cylindracea to compensate or overcompensate for biomass loss. In order to simulate different grazing intensities, the cover of C. cylindracea was either left untouched or clipped to 25%, 50% or 75% of the original value. After 2 months, C. cylindracea cover increased by ∼ 450% in 75% removal plots, ∼ 200% in 50% removals and ∼ 70% in 25% removals, whilst the increment in controls was just ∼ 6%. Such differential growth rates resulted in no difference in the cover of C. cylindracea between clipped (irrespective of clipping intensity) and control plots. Thus, regeneration from remnant clipped stolons could compensate for biomass loss, suggesting that non-native siphonaceous seaweeds can withstand intense mechanical damage and, possibly, grazing by herbivores. This compensatory mechanism may underpin the success of some of the most invasive clonal plants.

Spreading patterns of the invasive Caulerpa cylindracea Sonder along the west Istrian Coast (northern Adriatic Sea, Croatia).

The northern Adriatic Sea represents the northernmost and thus the coldest biogeographic sector of the Mediterranean Sea. In 2004, the invasive green alga Caulerpa cylindracea was recorded for the first time in the northern Adriatic at a site of the west Istrian Coast. Until 2010, additional C. cylindracea mats have only formed up to 7 km northward from the first colonisation site. Subsequently, the alga was also recorded at sites widespread along the entire coast. Both the first 2004 colonisation event and the 2011-2014 colonisation of distant sites occurred during periods of winter seawater temperatures higher than 9 °C. In general, algal spreading was markedly slow. Approximately 10 years after the first record, C. cylindracea has affected less than 1% of the entire west Istrian coastline. The colonisation predominantly occurred in ports and urbanised bays (seaside resorts) suggesting that anthropogenic activities might enhance algal diffusion.

Beyond the border: effects of an expanding algal habitat on the fauna of neighbouring habitats.

The impacts of novel habitat-forming organisms on associated fauna have been difficult to predict, and may affect the fauna of neighbouring habitats due to changes in the spatial configuration of habitat patches of differing quality. Here, we test whether the localised expansion of a native habitat-forming macroalga, Caulerpa filiformis, on subtidal reefs can affect the abundance of fauna associated with a neighbouring macroalgal habitat. C. filiformis was a functionally distinct habitat for fauna, and the total abundance of epifauna associated with the resident alga, Sargassum linearifolium, was reduced at some sites when in close proximity to or surrounded by C. filiformis. Experimental manipulation of habitat configuration demonstrated that the low abundance of gastropods on S. linearifolium when surrounded by C. filiformis was likely explained by C. filiformis acting as a physical dispersal barrier for mobile fauna. Changes to the spatial configuration of novel and resident habitats can thus affect the abundance of fauna in addition to the direct replacement of habitats by species undergoing range expansions or increasing in abundance.

Ecological structure and function differs between habitats dominated by seagrasses and green seaweeds.

Marine vegetated habitats, e.g. seagrass meadows, deliver essential functions and services to coastal ecosystems and human welfare. Impacts induced by humans, however, have facilitated the replacement of seagrasses by alternative vegetation, e.g. green rhizophytic seaweeds. The implications of habitat shifts for ecosystem attributes and processes and the services they deliver remain poorly known. In this study, we compared ecosystem structure and function between Cymodocea nodosa seagrass meadows and bottoms dominated by Caulerpa prolifera, a green, native, rhizophytic seaweed, through 5 ecological proxies: (i) primary production (via community metabolism), (ii) composition and abundance of epifauna (a proxy for provision of habitat for epifauna), composition and abundance of (iii) small-sized (juvenile) and (iv) large-sized (adult) fishes (proxies for provision of habitat for fishes), and (v) sediment retention (a proxy for sediment stabilization). Four of these proxies were greater in C. nodosa seagrass meadows than in C. prolifera beds: gross primary productivity (∼1.4 times), the total abundance, species density and biomass of small-sized fishes (∼2.1, 1.3 and 1.3 times, respectively), the total abundance and species density of large-sized fishes (∼3.6 and 1.5 times, respectively), and sediment stabilization (∼1.4 times). In contrast, the total abundance and species density of epifauna was larger (∼3.1 and 1.7 times, respectively) in C. prolifera than in C. nodosa seagrass beds. These results suggest that ecosystem structure and function may differ if seagrasses are replaced by green rhizophytic seaweeds. Importantly, ecosystem functions may not be appropriate surrogates for one another. As a result, assessments of ecosystem services associated with ecosystem functions cannot be based on exclusively one service that is expected to benefit other services.

Potential use of Caulerpa fastigiata biomass for removal of lead: kinetics, isotherms, thermodynamic, and characterization studies.

The present study attempts to analyze the biosorption trend of biosorbent Caulerpa fastigiata (macroalgae) biomass for removal of toxic heavy metal ion Pb (II) from solution as a function of initial metal ion concentration, pH, temperature, sorbent dosage, and biomass particle size. The sorption data fitted with various isotherm models and Freundlich model was the best one with correlation coefficient of 0.999. Kinetic study results revealed that the sorption data on Pb (II) with correlation coefficient of 0.999 can best be represented by pseudo-second-order. The biosorption capacity (q e ) of Pb (II) is 16.11 ± 0.32 mg g(-1) on C. fastigiata biomass. Thermodynamic studies showed that the process is exothermic (ΔH° negative). Free energy change (ΔG°) with negative sign reflected the feasibility and spontaneous nature of the process. The SEM studies showed Pb (II) biosorption on selective grains of the biosorbent. The FTIR spectra indicated bands corresponding to -OH, COO(-), -CH, C = C, C = S, and -C-C- groups were involved in the biosorption process. The XRD pattern of the C. fastigiata was found to be mostly amorphous in nature.