Exotic Seaweeds Research Articles

Seaweed dispersion under different environmental scenarios based on branches settling velocity and hydrodynamic lagrangian model

We examined the spatial pattern of seaweed branches dispersion based on lagrangian numerical simulation of an experimental cultivation of the seaweed Kappaphycus alvarezii. Sambaqui Beach seaweed cultivation located in the Bay of Santa Catarina Island southern Brazil was used as case study. This work is the first step towards understanding the dispersion and the range of detached branches in the estuarine region. For that, the use of hydrodynamic modeling as tool to support the evaluation of the water dynamics and particles fate was considered. Several environmental datasets are needed as input for hydrodynamic mathematical models, like bathymetry, tide time series, and branches settling velocity. The experiments on branches vertical velocities, in this study, varied from 3.2 until 5.7 cm.s−1, which presented a high correlation with branches volume. These velocities associated with the hydrodynamic model resulted that 90% of the branches will disperse to an area varying from 2 to 6 ha depending on the simulated scenario. Besides, model results shows that particles traveled distances up to 2.5 km, but most of them did not reach the coastline. Although the need for a large amount of data and numerical modeling effort, the results show that this type of approach can reduce the monitoring area around 75% and consequently reduce the need for human resources, time, and inputs in monitoring the dispersion of branches of exotic seaweed in the environment.

Diversity of a bacterial community associated with Cliona lobata Hancock and Gelliodes pumila (Lendenfeld, 1887) sponges on the South-East coast of India

Marine sponges are sources of various bioactive metabolites, including several anticancer drugs, produced mainly by sponge-associated microbes. Palk Bay, on the south-east coast of India, is an understudied, highly disturbed reef environment exposed to various anthropogenic and climatic stresses. In recent years, Palk Bay suffered from pollution due to the dumping of untreated domestic sewage, effluents from coastal aquaculture, tourism, salt pans, cultivation of exotic seaweeds, and geogenic heavy-metal pollution, especially arsenic, mercury, cadmium, and lead. Low microbial-abundant sponge species, such as Gelliodes pumila and Cliona lobata, were found to be ubiquitously present in this reef environment. Triplicate samples of each of these sponge species were subjected to Illumina MiSeq sequencing using V3–V4 region-specific primers. In both C. lobata and G. pumila, there was an overwhelming dominance (98 and 99%) of phylum Candidatus Saccharibacteria and Proteobacteria, respectively. The overall number of operational taxonomic units (OTUs) was 68 (40 and 13 OTUs unique to G. pumila and C. lobata, respectively; 15 shared OTUs). Alphaproteobacteria was the most abundant class in both the sponge species. Unclassified species of phylum Candidatus Saccharibacteria from C. lobata and Chelotivorans composti from G. pumila were the most abundant bacterial species. The predominance of Alphaproteobacteria also revealed the occurrence of various xenobiotic-degrading, surfactant-producing bacterial genera in both the sponge species, indirectly indicating the possible polluted reef status of Palk Bay. Studies on sponge microbiomes at various understudied geographical locations might be helpful in predicting the status of reef environments.

Innovative Benthic Lander for Macroalgae Monitoring in Shallow-Water Environments

The colonization of underwater environments by exotic seaweeds is causing major ecological problems around the world. This project, referred to AMALIA, aims to transform this current ocean threat into an opportunity by adding value to the macroalgae present off the northwest of the Iberian Peninsula. To do so and to observe the presence of seaweeds in situ, an ocean modular submersible platform was developed. This platform was designed to be capable of detecting and surveying surges of invasive seaweeds while withstanding sea conditions. Conceptual designs followed by a screening process were performed, taking into consideration criteria such as operational range and modularity. An open-frame lander was considered and further developed using buckling criteria. In parallel, a state-of-the-art monitoring system was created using spectral imaging, allowing for the future creation of a macroalgae identification system. In addition, sensorial systems for characterizing growth conditions were introduced. Laboratory trials were executed to assess the capability of the system, and sea trials are currently being performed. Numerical simulations and laboratory trials indicate that the structure is fully capable of being deployed for shallow-water environments with a state-of-the-art invasive seaweed monitoring system while maintaining a high degree of modularity.

Niche Complementarity and Resistance to Grazing Promote the Invasion Success of Sargassum horneri in North America

Invasive species are a growing threat to conservation in marine ecosystems, yet we lack a predictive understanding of ecological factors that influence the invasiveness of exotic marine species. We used surveys and manipulative experiments to investigate how an exotic seaweed, Sargassum horneri, interacts with native macroalgae and herbivores off the coast of California. We asked whether the invasion (i.e., the process by which an exotic species exhibits rapid population growth and spread in the novel environment) of S. horneri is influenced by three mechanisms known to affect the invasion of exotic plants on land: competition, niche complementarity and herbivory. We found that the removal of S. horneri over 3.5 years from experimental plots had little effect on the biomass or taxonomic richness of the native algal community. Differences between removal treatments were apparent only in spring at the end of the experiment when S. horneri biomass was substantially higher than in previous sampling periods. Surveys across a depth range of 0–30 m revealed inverse patterns in the biomass of S. horneri and native subcanopy-forming macroalgae, with S. horneri peaking at intermediate depths (5–20 m) while the aggregated biomass of native species was greatest at shallow (<5 m) and deeper (>20 m) depths. The biomass of S. horneri and native algae also displayed different seasonal trends, and removal of S. horneri from experimental plots indicated the seasonality of native algae was largely unaffected by fluctuations in S. horneri. Results from grazing assays and surveys showed that native herbivores favor native kelp over Sargassum as a food source, suggesting that reduced palatability may help promote the invasion of S. horneri. The complementary life histories of S. horneri and native algae suggest that competition between them is generally weak, and that niche complementarity and resistance to grazing are more important in promoting the invasion success of S. horneri.

From exotic to invasive in record time: The extreme impact of Rugulopteryx okamurae (Dictyotales, Ochrophyta) in the strait of Gibraltar

In 2015, the exotic seaweed Rugulopteryx okamurae was detected for the first time on the south side of the Strait of Gibraltar, in Ceuta (northern Africa). This highly sensitive area is ideal for monitoring local environmental impacts arising from global warming, as well as the intrusion of alien species. Within one year, R. okamurae became an invasive species with an overflowing competitive capacity and growth. In 2015, more than 5000 tons of upstream biomass was extracted from beaches in Ceuta, and it has since spread irrepressibly on rocky illuminated bottoms of the subtidal zone to a maximum observed depth of 40 m. The highest coverage (80–90%) of R. okamurae in Ceuta was observed between 10 and 20 m depth in illuminated habitats, where it was having a severe impact on local benthic communities which were displaced. Between 5 and 30 m depth, coverage of R. okamurae exceeded 70% over a wide variety of substrate types. A submarine sentinel sessile bioindicators permanent quadrats (SBPQ) station installed in 2013 on poorly lit, vertical, and shady substrate in the El Estrecho Natural Park, on the north side of the Strait of Gibraltar (Tarifa), detected the presence of R. okamurae in July 2016 and recorded the subsequent increase in coverage. These findings reveal the useful role of this type of monitoring SBPQ sentinel station for the detection of impacts and exotic species in marine protected areas, and for the monitoring of global warming based on indicator species. We conclude that the catastrophic bloom of R. okamurae exhibited an initial geographical expansion (2015–2017) to the northern coastal area of the Strait of Gibraltar (Tarifa-Gibraltar) and subsequent extension in the south of the Iberian Peninsula, towards the Atlantic coast (2018) and the Mediterranean coast (2019). This bloom could have been associated with the temperature peak in July 2015 and was thus possibly linked to global warming.

Macroalgas exoticas en la costa de Chile: patrones espaciales y temporales en el proceso de invasion

In this paper we propose a checklist of 14 species of exotic seaweeds on the Chilean coast, and three species which, being native to the Chilean coast, have been introduced in areas outside their natural range. This list was compiled from previously published checklist, debugged the misidentified records, and incorporating new ones. The distribution of exotic seaweeds is not homogeneous along the coast, but it is concentrated in areas near ports and aquaculture centers. Most species display a fairly bounded distribution, and only four tend to invade ( i.e ., increase its range of distribution over time). However, considering that most introductions are recent (the last 60 years) and the positive relationship between amplitude of the distribution range and residence time of species on the Chilean coast, we suggest that some of these species may be in an expansion phase, which would explain its restricted distribution. This work not only updates the information related to exotic seaweed on the Chilean coast, but also allows us to understand the invasion process, through the analysis of the patterns described in these systems.

Rapid adaptation to controlling new microbial epibionts in the invaded range promotes invasiveness of an exotic seaweed

Summary Rapid adaptation to novel biotic interactions and abiotic factors in introduced ranges can be critical to invasion success of both exotic terrestrial and aquatic plants. Seaweeds are extremely successful biological invaders in marine environments. Along with herbivores, foulers − ubiquitous enemies in the marine environment − have the potential to determine the success or failure of invasive seaweeds. However, research on the topic of rapid adaptation of seaweeds to biotic challenges is still in its nascent stages and rapid adaptation of seaweeds to fouling is unexplored. We tested whether the impressive invasion success of the red macroalga Gracilaria vermiculophylla may be enhanced by the rapid adaptation of chemical control (defence) of new bacterial epibionts in the invaded range. The native and invasive G. vermiculophylla populations investigated were equally well defended against currently co‐occurring bacterial epibionts isolated from their respective ranges. In contrast, the native populations were weakly defended against bacterial epibionts from the invaded range, whereas the invasive populations were weakly defended against bacterial epibionts from their native range. Apparently during the invasion process, invasive populations have adapted their control capacity to cope with the new epibionts but have lost the capacity to fend off old epibionts. Synthesis. These results provide the first evidence that a change in habitat and, thus, confrontation by new enemies, may trigger rapid defence adaptation of seaweeds, which could be necessary for invasiveness. Such adaptation dynamics as found in the current study could be also applicable to other types of host plant – enemy interaction e.g. plant root – microbe interactions, freshwater plant – fouler interactions in general and for cases of shifting plant – enemy interactions in course of climate change.

The role of overgrazing and anthropogenic disturbance in shaping spatial patterns of distribution of an invasive seaweed

Summary Natural and human‐generated disturbances are widely acknowledged as key drivers of biological invasions. Understanding the role of spatial patterns of compounded disturbances in determining invader establishment and spread can enhance the effectiveness of control strategies. Using the framework of 1/f noise models and by means of a field experiment, we evaluated how the simultaneous exposure of Posidonia oceanica meadows to disturbances (namely overgrazing and rhizome uprooting from vessel anchoring) differing in spatial extent and degree of autocorrelation influenced the establishment and spread of the invasive seaweed, Caulerpa racemosa. Effects on invader establishment and spread were evaluated by means of mixed‐effect models relating spatial patterns of disturbance and presence or abundance of C. racemosa, quantified through spectral coefficients. The spatial distribution of C. racemosa mimicked that of overgrazing, both variables showing positive autocorrelation. Yet, C. racemosa was unable to disperse from disturbed patches into adjacent intact areas. The uprooting of rhizomes did not promote the establishment of C. racemosa, but magnified (≃18 times) the proliferation of the exotic seaweed when coupled with overgrazing. Synthesis and applications. Fish overgrazing of Posidonia oceanica lessens the resistance of seagrass beds to invasion by Caulerpa racemosa. Thus, conservation strategies (e.g. marine protected areas) aiming to restore over‐exploited fish populations may indirectly enhance the susceptibility of P. oceanica meadows to invasion by C. racemosa. Uprooting of P. oceanica rhizomes, such as that caused by boat anchoring, exacerbates the effects of overgrazing. The anchoring of recreational vessels should be, therefore, strictly regulated in areas characterized by intense grazing of P. oceanica leaves. More generally, our study shows that native herbivores may indirectly facilitate invasion by reducing the resistance of resident plant communities and suggests that sounded strategies for controlling the establishment and spread of invasive species require taking into account the interactive effects of natural and anthropogenic disturbances.

Pyropia suborbiculata (Bangiales, Rhodophyta): first records from the northeastern Atlantic and Mediterranean of this North Pacific species

Vergés A., Sánchez N., Peteiro C., Polo L. and Brodie J. 2013. Pyropia suborbiculata (Bangiales, Rhodophyta): first records from the northeastern Atlantic and Mediterranean of this North Pacific species. Phycologia 52: 121–129. DOI: 10.2216/12-003.1Pyropia suborbiculata is a bladed Bangiales that was originally reported from Asia but was also recorded as an introduced species in the Atlantic United States, New Zealand, Canary Islands and Brazil. Here we report for the first time the expansion of its distribution to Europe (northeastern Atlantic and Mediterranean coasts) on the basis of collections from the Iberian Peninsula (Spain and Portugal). Comparison of morphological and molecular data of our specimens with those of P. suborbiculata confirmed conspecificity and allowed us to differentiate it from other similar species traditionally reported in this area. The species' extensive distribution in the Iberian Peninsula and identical rbcL sequences obtained from native and introduced strains suggested a recent introduction, probably from the northwestern Pacific, the source of numerous exotic seaweeds introduced to Europe. Although this is the first report in Europe of this taxon, it could have been easily overlooked until now because of its small thalli.

Habitat heterogeneity promotes the coexistence of exotic seaweeds

Despite the progressive accumulation of exotic species in natural communities, little effort has been devoted to elucidating the mechanisms underpinning the coexistence of invaders in environmentally and biologically heterogeneous systems. The exotic seaweeds, Asparagopsis taxiformis and Caulerpa racemosa, exhibit a segregated distribution on Mediterranean rocky reefs. A. taxiformis dominates assemblages in topographically complex habitats, but is virtually absent on homogenous platforms. In contrast, C. racemosa achieves extensive cover in both types of habitat. We assessed whether differences in their distribution were generated by biotic interactions (between invaders and/or between invaders and natives) or by environmental constraints. Three models were proposed to explain seaweed distribution patterns: (1) invaders inhibit one another; (2) native assemblages, differing between complex and simple habitats, prevent the establishment/spread of one invader, but not that of the other; and (3) environmental conditions regulate the establishment/persistence of the seaweeds in different habitats. We removed the dominant invader and resident assemblages in each type of habitat. Moreover, A. taxiformis thalli were transplanted into the habitat dominated by C. racemosa to establish whether its failure to colonize the simple habitat was due to the lack of propagules or post-recruitment mortality. C. racemosa spread in the complex habitat was not influenced by the removal of resident assemblages, but it was slightly enhanced by A. taxiformis removal. Neither C. racemosa removal nor that of resident assemblages promoted A. taxiformis colonization and survival in simple habitats. Our results suggest that heterogeneity in environmental conditions can promote invader coexistence by mitigating the effects of negative biotic interactions. Therefore, the accumulation of introduced species in native communities does not necessarily imply established invaders fostering further invasion.

The effects of exotic seaweeds on native benthic assemblages: variability between trophic levels and influence of background environmental and biological conditions

Background Biological invasions are among the most severe threats to marine biodiversity. The impacts of introduced seaweeds on native macroalgal assemblages have been thoroughly reviewed. In contrast, no attempt has been made to synthesize the available information on the effects of exotic seaweeds on other trophic levels. In addition, it has not been clarified whether the effects of introduced seaweeds on native assemblages vary according to background physical and biological conditions.

The seaweed Caulerpa racemosa on Mediterranean rocky reefs: from passenger to driver of ecological change

Disentangling the ecological effects of biological invasions from those of other human disturbances is crucial to understanding the mechanisms underlying ongoing biotic homogenization. We evaluated whether the exotic seaweed, Caulerpa racemosa, is the primary cause of degradation (i.e., responsible for the loss of canopy-formers and dominance by algal turfs) on Mediterranean rocky reefs, by experimentally removing the invader alone or the entire invaded assemblage. In addition, we assessed the effects of enhanced sedimentation on the survival and recovery of canopy-forming macroalgae at a relatively pristine location and how their loss affects the ability of C. racemosa to conquer space. C. racemosa did not invade dense canopy stands or influence their recovery in cleared plots. Competition with C. racemosa could not explain the rarity of canopy-forming species at degraded sites. Removing the assemblages invaded by C. racemosa and preventing reinvasion did not trigger the transition from algal turfs to canopies, but it enhanced the cover of morphologically complex erect macroalgae under some circumstances. Once established, C. racemosa, enhancing sediment accumulation, favors algal turfs over erect algal forms and enables them to monopolize space. Our results show that introduced species that rely on disturbance to establish can subsequently become the main drivers of ecological change.

The trophic significance of the invasive seaweed Sargassum muticum in sandy beaches

Native and exotic seaweeds frequently lie on the beach and sustain part of the benthic food web. However, the role of exotic seaweeds as food sources for beach consumers has been poorly studied. We studied the temporal and spatial variability in the trophic significance of the invasive brown seaweed Sargassum muticum on sandy beaches. We measured the stable isotopes ( δ 13C and δ 15N) in the tissues of S. muticum and of invertebrate consumers and estimated the dietary biomass proportion of S. muticum during four sampling dates at two beaches and heights on the shore. Samples were collected from eight pitfall traps placed at a distance of 2 m from each other. Detrital macroalgae and seagrasses were also collected by hand within an area of 30 cm around each pitfall trap. We measured the spatial and temporal variability in the isotope composition of the beach consumers and of S. muticum using different models of analyses of variance. We then calculated the biomass proportion of S. muticum to the animal diet with a two-isotopic mixing model. The invasive alga S. muticum seemed to be one of the main food sources for the amphipod Talitrus saltator and, to a less extent, for the isopod Tylos europaeus. The importance of S. muticum was however temporally variable and decreased during spring (in March and May), probably due to the availability of native macrophytes. The supply of invasive wrack to beach food webs thus deserves more attention if we want to understand their role in influencing food web dynamics.

Mechanisms of invasion: establishment, spread and persistence of introduced seaweed populations

Abstract Understanding the mechanisms that facilitate or inhibit invasion of exotic seaweeds is crucial in assessing the threat posed by their incursion and to define control options. In this paper, we consider how life history characteristics of the invading species and properties of the recipient environment influence the likelihood of invasion, giving particular emphasis to how disturbance influences the establishment, spread and persistence of introduced seaweed populations. Very few commonalities in key life history traits emerge since each species possesses a unique set of traits that confers a high capacity for invasiveness. Consequently, for seaweeds at least, predictions of invasibility based on life history characters alone are unlikely to be useful. In contrast, it is clear that disturbance is an important process in the establishment of these invasive species. With the possible exception of Caulerpa taxifolia, disturbance appears to be a critical factor that is either a key requirement (e.g., Codium fragile ssp. tomentosoides, Sargassum muticum and Undaria pinnatifida), or which accelerates (e.g., Fucus serratus) establishment and spread. The role of disturbance in the persistence of the invaders is more complex and depends on the species concerned. In several cases there is substantial evidence for positive feedback mechanisms that enable introduced species to persist in the absence of the disturbance factor that facilitated establishment in the first place. These circumstances define examples of ecological hystereses that pose particular challenges for management and control. The evidence suggests that, in several cases, preventing anthropogenically mediated disturbance to canopies of native seaweeds should be considered as a potential control option to minimise the risk of establishment of exotic species at high densities. However, for these kinds of introduced species, once they are established, control options that primarily target the disturbance are unlikely to represent viable management options.

The Diversity and Availability of Caulerpa Species Found in Retail Aquarium Outlets in Southern California, USA

AbstractBiological invasions are recognized as a serious threat to marine biodiversity. Within the last 2 years, invasive populations of Caulerpa taxifolia were found in southern California's coastal waters as well as in New South Wales, Australia. In addition, two other seaweeds (Undaria pinnatifida and Caulacanthus ustulatus) also appear to have recently invaded southern California's warm temperate waters. The introduction of C. taxifolia has attracted much attention because this exotic seaweed is thought to have significantly altered the structure of Mediterranean marine ecosystems following its 1984 invasion. The southern California inoculation of C. taxifolia is believed to have resulted from the release of aquarium specimens. Besides C. taxifolia, other species of Caulerpa being sold for aquarium use also may have the potential to invade temperate waters. As a first step towards making this determination, the availability (% frequency) of Caulerpa species being sold in southern California for aquarium use was ascertained. Fifty retail saltwater aquarium stores were visited in three southern California counties between November 2000 and August 2001. Sixteen Caulerpa taxa were identified from the retail aquarium outlets. Caulerpa species were sold in 52% of these stores. C. taxifolia, ‘Mediterranean form’, was offered for sale in 10% of the visited stores; C. serrulata var. hummii (18%), C. racemosa (14%), and C. racemosa var. lamourouxii (14%) were the most commonly sold species. These data indicate that the aquarium industry is bringing into the region other species of Caulerpa besides C. taxifolia. Some of these species may also have the potential to invade temperate waters.