Caulerpa taxifolia responses to hyposalinity stress

An investigation into salinity responses of Caulerpa taxifolia was undertaken in a series of laboratory trials to evaluate the use of hyposalinity stress as an eradication strategy. The effect of instantaneous (or shock) exposure to reduced salinity (10 ppt) on the effective quantum yield (EQY) of C. taxifolia for different incubation periods (15, 30, 45, 60, 90, 180, 360, 720 and 1440 min) indicated that 180 min or more at this salinity was required to kill the alga. Average EQY declined by 88.2 ± 4.6% (mean ± S.E.) of the pre-treatment level for the 180 min treatment but were as much as 96.6 ± 2.5% lower than pre-treatment EQY for the 1440 min exposure. Exposure for 90 min or less resulted in an intermediate response, whereas lesser exposures (60, 30 and 15 min) had no lasting effect on C. taxifolia health. The effect of gradual changes in salinity, as might be anticipated in an eradication scenario, on EQY of C. taxifolia was investigated through the dilution of seawater (35 ppt) over different time scales (5 h, 2, 4, 7 and 27 days). In all trials >5 h, the response to hyposalinity was the same regardless of the rate of change in salinity with all treatments resulting in a marked loss in EQY below ∼15 ppt. Declines in the average ratio of EQY after to EQY before for 4, 7 and 27 days treatments (85.2 ± 8.2%, 78.8 ± 9.05% and 77.3 ± 18.2% of pre-treatment levels, respectively), were significantly larger than the 5 h treatment (2.6 ± 4.4% of pre-treatment levels). The 2 days salinity reduction (48.5 ± 17.1%) resulted in an intermediate response. In the 5 h treatment, the exposure to salinities below 15 ppt was less than 3 h, which given the result of the preceding trial explains the lack of substantial EQY response as the minimum exposure period required to kill the alga at 10 ppt is ≥180 min. There is thus no evidence that C. taxifolia is capable of acclimation to gradual reductions in salinity. Consequently, hyposalinity is an effective means of killing the algae and may prove highly effective for populations in relatively small, contained water bodies.     

Spread of the introduced tropical green alga Caulerpa taxifolia in northern Mediterranean waters

The first report of Caulerpa taxifolia in the Mediterranean is from 1984. The alga was found on the rocky shore at Monaco, below the Oceanographic Museum, where it had been on display in tropical aquaria. Within five years, there was an abundance of C. taxifolia on the shores around the first point of observation. In 1987, C. taxifolia appeared on the French coast, 3 km east of Monaco, at Cap Martin. By late 1991, 30 ha of shore in the vicinity of Monaco was covered with the alga. New points of colonization were in Livorno, Italy, 240 km east of Monaco, and to the west at Agay, Le Lavandou, Hyères, Toulon, Les Lecques, Saint Cyprien, 50 to 370 km from Monaco. The westernmost point of colonization, noted in September 1992, was 600 km from Monaco, at Majorca (Balearic island, Spain). Most types of substrata, between 0 and 50 m depth, are susceptible to colonization by C. taxifolia. Seaweed and seagrass populations on the coasts of Monaco and Cap Martin have been significantly reduced or destroyed because of invasion by C. taxifolia.     

Nutrient availability in the sediment and the reciprocal effects between the native seagrass Cymodocea nodosa and the introduced rhizophytic alga Caulerpa taxifolia

Two reciprocal experiments testing for the effects of nutrient addition in the sediment and competitive interactions between the native seagrass Cymodocea nodosa (Ucria) Ascherson and the introduced alga Caulerpa taxifolia (Vahl) C. Agardh were performed. This study was conducted for 13 months (August 1995 until September 1996) in a bay on the south coast of Elba Island (Italy). Each experiment consisted of the manipulation of the level of nutrients (addition vs. control) and the manipulation of the neighbours (presence vs. removal). Response variables were blade density and size for one experiment and shoot density and leaf length of seagrass in the other. Results indicated that the presence of Caulerpa taxifolia did not affect significantly Cymodocea nodosa shoot density and the increased nutrient availability in the sediment did not alter this pattern. Neither the removal of the canopy of the seagrass nor the fertilization of the sediment has influenced significantly the density of the alga. Both species, where co-occurring, show larger size than where the neighbour is removed. Hence, results of this study suggest that the two species on the long term are likely to coexist and that the high nutrient supply of the sediment would not enhance the probability of success neither of the seagrass nor of the alga. Predictions made on the basis of short-term results, that high nutrient loads of the substratum would have represented an even more suitable condition for C. taxifolia to colonize C. nodosa beds and that on the long-term the alga has a high probability of success, did not occur.     

Anchors aweigh: Fragment generation of invasive Caulerpa taxifolia by boat anchors and its resistance to desiccation

We use two experiments to assess the role of anthropogenic activities in disseminating the invasive alga, Caulerpa taxifolia. First, we tested the hypothesis that the removal of fragments of C. taxifolia from an estuary would be dependent on anchor type (sand versus rock) and anchor attachment (chain versus rope). Second, we hypothesised that the viability of different sized clumps (1, 5 and 10 g dry weight) of C. taxifolia would be dependent on aerial exposure (1 h, 1 day and 3 days) and environmental conditions (sun versus shade, damp rope versus no rope). Fragments of C. taxifolia were consistently removed by anchors regardless of the anchor type; overall, 82% of anchors lowered into C. taxifolia beds removed fragments. Rock and sand anchors removed similar sized clumps of C. taxifolia (up to 15 g dry weight), while chain attachments removed significantly larger clumps compared to ropes (up to 0.5 g dry weight). Once removed from the water, fragment survivorship increased with clump size, protection from desiccation (i.e. greatest under damp shaded ropes) and decreased with length of aerial exposure. Most shaded clumps survived 1 h of aerial exposure, while none, irrespective of their size, survived 3 days. Our study confirms that the anchoring of vessels removes fragments of C. taxifolia from estuaries and that conditions inside anchor lockers may enhance fragment survivorship. Thus, vessels may be an important vector for dispersal of C. taxifolia within and between estuaries.     

Genetic polymorphism in Caulerpa taxifolia (Ulvophyceae) chloroplast DNA revealed by a PCR‐based assay of the invasive Mediterranean strain

Abstract An invasive, cold‐tolerant strain of the tropical green alga Caulerpa taxifolia was introduced recently in the Mediterranean Sea and along the Californian coast. We screened 50 aquarium and open‐sea C. taxifolia specimens for the presence/absence of an intron located in the rbcL gene of chloroplast DNA. We also reanalysed a total of 229 sequences of the Internal Transcribed Spacer (ITS) of ribosomal DNA, combining previously published sequences from different studies with 68 new sequences to complement rbcL data. The introduced Mediterranean strain was found to be characterized by the absence of the rbcL intron and by the occurrence of a particular monomorphic ITS type. A PCR assay based on rbcL gene was developed to detect new introductions of the invasive strain of C. taxifolia. This rapid and inexpensive test could be useful to assist environment managers in the preservation of coastal marine ecosystems.     

Modeling the Increase and Control of Caulerpa taxifolia, an Invasive Marine Macroalga

Population modeling based on species’ demography makes it possible to predict the pace of an invasion and evaluate the likelihood of success of different control strategies. We modeled the initial (density-independent) rate of increase of Caulerpa taxifolia (Vahl) C. Agardh (aquarium strain), a green alga that has markedly altered marine communities where it has invaded in the Mediterranean Sea. Parameter values for patch growth (from stolon extension) and reproduction (by asexual fragmentation and reattachment) were gleaned from published studies. Only the most conservative model, invoking field growth rates and low levels of fragment reattachment (2.5 m⁻² of existing patch each summer), closely matched observed increases (4–14 × annually). The most effective times for control (greatest reduction in rate of increase) were removal of established patches before summer and removal of fragments after summer. These times correspond to just before maximum growth and just after maximum reproduction, respectively. Only a combined strategy, incorporating 99% removal of all fragments and annual removal of 99% of established patches, was predicted to eliminate C. taxifolia entirely (λ < 1). This level of effort is only likely to be possible during the first few years of an invasion, arguing strongly for careful monitoring and rapid response to potential high-impact invaders.     

Reduced performance of native infauna following recruitment to a habitat-forming invasive marine alga

Despite well-documented negative impacts of invasive species on native biota, evidence for the facilitation of native organisms, particularly by habitat-forming invasive species, is increasing. However, most of these studies are conducted at the population or community level, and we know little about the individual fitness consequences of recruitment to habitat-forming invasive species and, consequently, whether recruitment to these habitats is adaptive. We determined the consequences of recruitment to the invasive green alga Caulerpa taxifolia on the native soft-sediment bivalve Anadara trapezia and nearby unvegetated sediment. Initially, we documented the growth and survivorship of A. trapezia following a natural recruitment event, to which recruitment to C. taxifolia was very high. After 12 months, few clams remained in either habitat, and those that remained showed little growth. Experimental manipulations of recruits demonstrated that all performance measures (survivorship, growth and condition) were significantly reduced in C. taxifolia sediments compared to unvegetated sediments. Exploration of potential mechanisms responsible for the reduced performance in C. taxifolia sediments showed that water flow and water column dissolved oxygen (DO) were significantly reduced under the canopy of C. taxifolia and that sediment anoxia was significantly higher and sediment sulphides greater in C. taxifolia sediments. However, phytoplankton abundance (an indicator of food supply) was significantly higher in C. taxifolia sediments than in unvegetated ones. Our results demonstrate that recruitment of native species to habitat-forming invasive species can reduce growth, condition and survivorship and that studies conducted at the community level may lead to erroneous conclusions about the impacts of invaders and should include studies on life-history traits, particularly juveniles.     

Impact of Caulerpa taxifolia colonization on the littoral ichthyofauna of North-Western Mediterranean sea: preliminary results

After its accidental introduction in the French waters of the Mediterranean, the green seaweed Caulerpa taxifolia is now spreading along the coast of the Alpes-Maritimes, invading various biotopes (rock, sand and Posidonia oceanica seagrass beds). During the spring and fall of 1992, we evaluated the impact of C. taxifolia on the infralittoral ichthyofauna of Cap Martin (Menton) and compared invaded and reference sites, in shallow (3–8 m) and deep (11–25 m) stations. Caulerpa taxifolia apparently does not have any effect on the composition and global species richness of the ichthyofauna. Therefore, no exclusion phenomenon has been observed and fish behavior has remained normal (feeding habits, reproduction, recruitment). However, fish density and biomass are slightly lower in the colonized sites. Negative regression was observed, in shallow sites during the spring season, between the percentage of substrate invaded by C. taxifolia and the average density of fish assemblages (slope= –0.13, r=0.26, p<0.01). Despite these observations, C. taxifolia meadows seem to be a favorable environment for the recruitment of some species of Labridae (Coris julis, Symphodus ocellatus), Sparidae (Diplodus annularis) and Serranidae (Serranus cabrilla) in the fall.The relative importance of C. taxifolia as environmental parameter and of other habitat characteristics (structural complexity, substrate slope, hydrodynamism, depth, fishing pressure) is discussed to explain these differences. The results of this first study indicate that there exists no simple relation between the presence of C. taxifolia and fish assemblages.     

Phylogenetic analyses of Caulerpa taxifolia (Chlorophyta) and of its associated bacterial microflora provide clues to the origin of the Mediterranean introduction

The accidental introduction of Caulerpa taxifolia into the Mediterranean is no longer under dispute. What has eluded researchers until now, is definitive evidence for the original, biogeographical source population. Here we present two independent lines of evidence that support an Australian origin for the Mediterranean populations of C. taxifolia. First, we reanalysed algal rDNA-internal transcribed spacer (rDNA-ITS) sequences, combining previously published sequences from different studies with 22 new sequences. The ITS sequence comparison showed that the Australian sample is the sister group of the Mediterranean-aquarium clade. Second, cloned bacterial 16S rDNA gene sequences were analysed from the associated microflora of C. taxifolia collected from Australia, Tahiti, the Philippines and the Mediterranean. Five bacterial lineages were identified, of which three were dominant. Alpha Proteobacteria were the most abundant and were found in all samples. In contrast, members of the beta Proteobacterial line and Cytophaga-Flexibacter-Bacteroides line (CFB) were mainly associated with Mediterranean and Australian samples. Frequency distributions of the five bacterial lineages were significantly different among biogeographical locations. Phylogenetic analyses of the 54 bacterial sequences derived from the four C. taxifolia individuals resulted in a well-resolved tree with high bootstrap support. The topologies of the beta Proteobacteria and CFB mirror the geographical sources of their algal hosts. Bacterial-algal associations provide an identification tool that may have wide application for the detection of marine invasions.     

Preparation of tubulin from Caulerpa, a marine green alga, using casein as a protective agent against proteolytic degradation

Bidirectional organelle movements taking place in the cytoplasm of the rhizomes of Caulerpa, a coenocytic marine green alga, have been indicated to be dependent on microtubules (Kuroda, K. & Manabe, E. (1983) Proc. Jpn. Acad. 59B, 131-134; Manabe, E. & Kuroda, K. (1984) Proc. Jpn. Acad. 60B, 118-121). However, when a crude extract of Caulerpa rhizomes was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and subjected to immunoblotting with monoclonal anti-tubulin antibody, no reacting band could be detected. This apparent absence of tubulin in the extract was found to be a result of the complete degradation of tubulin by potent intrinsic proteolytic activity. All of the commercially available protease inhibitors so far tested (p-chloromercuriphenylsulfonic acid, phenyl methylsulfonyl fluoride, 1-chloro-4-phenyl-3-tosylamido-2-butanone, 7-amino-1-chloro-3-tosylamido-2-heptanone, p-tosyl-L-arginine methyl ester, soybean trypsin inhibitor, antipain, chymostatin, leupeptin, and pepstatin) failed to inhibit the activity completely. But addition of casein at the concentration of 1% (weight per volume) to the solutions used for preparation was effective in protecting tubulin from proteolytic degradation, thus making it possible to prepare tubulin from the crude extract of Caulerpa. On SDS-PAGE, the Caulerpa alpha-tubulin thus prepared was a little smaller in molecular weight than that of rabbit brain.     

Caulerpenyne from Caulerpa taxifolia has an antiproliferative activity on tumor cell line SK-N-SH and modifies the microtubule network.

Caulerpenyne, the major secondary metabolite synthesized by the green marine alga Caulerpa taxifolia, is cytotoxic against several cell lines. To identify possible targets of this toxin, we investigated the effect of caulerpenyne on the neuroblastoma SK-N-SH cell line. Caulerpenyne induced an inhibition of SK-N-SH cell proliferation with an IC50 of 10 +/- 2 microM after 2 hr of incubation.We observed no blockage in G2/M phase and an increase in cell death. On immunofluorescence microscopy, caulerpenyne affected the microtubule network in SK-N-SH cell line; we observed a loss of neurites and a compaction of the microtubule network at the cell periphery. In vitro, after 35 min of incubation, caulerpenyne inhibited the polymerization of pig brain purified tubulin or microtubule proteins, with an IC50 of 21 +/- 2 microM and 51 +/- 6 microM respectively. Analysis by electron microscopy indicated that caulerpenyne induced aggregation of tubulin, which may be responsible for inhibition of microtubule polymerization and bundling of residual microtubules.     

Tolerance of two invasive thistles to repeated disturbance

Many invasive species have short life cycles, high reproduction, and easily dispersed offspring that make them good ruderal species under disturbance. However, the tolerance of such ruderal species to disturbance is often overlooked. In a 2-year mowing study, we applied frequent intense disturbances to examine the tolerance of two congeneric invasive thistles, Carduus acanthoides and Carduus nutans, and potential differences in their responses. Our results show that both species can survive multiple mowing events, with C. acanthoides surviving repeated intense mowing through a whole season. Furthermore, C. acanthoides was found to adjust its growth form to the disturbance regime, and successfully overwintered and reproduced in the subsequent growing season if the disturbance was terminated. Our results support the idea that tolerance to disturbance should be considered when examining invasions by short-lived monocarpic species, since avoidance of disturbance via rapid life cycle completion and seed production, and tolerance of disturbance via regrowth can co-occur in these species. Consequently, management of short-lived invasives should take both life history strategies into account.     

Production and properties of agar from the invasive marine alga, Gracilaria vermiculophylla (Gracilariales, Rhodophyta)

The utilization potential, in terms of agar production, of the invasive alga, Gracilaria vermiculophylla, collected at Ria de Aveiro, northwestern Portugal was investigated. The agar yield ranged from 15% to 33%, with pre-extraction treatment with alkali generally increasing the yield. The gel quality (gel strength and apparent Young’s modulus) was best (>600 g cm^?2 and >1,000 kPa, respectively) when alkali treatment with 6% NaOH for 3.5 h was performed. At these pretreatment conditions, the effect of extraction time was also investigated and highest yield and best gel quality were obtained with a 2 h extraction time. By employing these extraction conditions, G. vermiculophylla can be a source of industrial food-grade agar. The structure of agar from G. vermiculophylla was determined through chemical techniques and FTIR and NMR spectrometry. It is mainly composed of alternating 3-linked d-galactose and 4-linked 3,6-anhydro-l-galactose, with methyl substitution occurring at 16–19 mol% of C-6 in 3-linked units and 2–3 mol% of C-2 in 4-linked units. A minor sulfation on C-4 of 3-linked units was also detected; while precursor units (6-sulfated 4-linked galactosyl moieties) were found in the native extract.     

Tolerance of the invasive tunicate Styela clava to air exposure

Styela clava is a subtidal invasive marine species in Northern Europe, Atlantic Canada, Australia and New Zealand. It grows attached to solid substrata, including boat hulls, ropes, moorings, piers and aquaculture equipment, all of which can aid its spread to new locations. It interferes with feeding of mussels and oysters, and increases their harvesting costs. Being subtidal, it could be assumed that tunicates would rapidly die in air and thus exposure to air would be a practical method to prevent their spread on boats and equipment. This study tested their survival when exposed to air for up to (1) 120?h at a constant temperature of 10?°C, (2) shade ambient 15–27?°C, and (3) full sun ambient 15–29?°C. Humidity was consistently high (78–100%). The results indicated that survival was longer when the air temperature was cooler. Larger individuals of S. clava generally survived for longer out of seawater than smaller individuals. The results predict that two weeks of exposure to air for two weeks could be an effective management method to eradicate S. clava from marine equipment when the air temperature is 10?°C. However, drying time would be less under conditions of low humidity and under direct sunlight.     

Phycoerythrin of the marine blue-green alga Trichodesmium thiebautii

Spectroscopic characteristics of the phycoerythrin obtainedfrom the marine blue-green alga Trichodesmium thiebautii wereinvestigated. The algal sample was collected at its naturalhabitat, the East China Sea. The phycoerythrin showed an absorptionspectrum and a fluorescence excitation spectrum with three peaksin the visible wave-length region at 500, 547 and 565 nm. Thisproperty is very different from that of the cyanophycean phycoerythrin,which has a single peak at 565 nm, but it is similar to thatof the rhodophycean phycoerythrin with three peaks at 500, 550and 565 nm. (Received April 20, 1974; )     

Spatial refuges and associational defenses promote harmful blooms of the alga Caulerpa sertularioides onto coral reefs

Extreme population fluctuations, or outbreaks, are driven by interacting processes that are often more complex than isolated changes in consumer or resource control. Blooms of the macroalga Caulerpa sertularioides in the eastern tropical Pacific overgrew and killed reef-building corals, with blooms onto reefs corresponding to cool La Niña phases of inter-decadal fluctuations of the El Niño–Southern Oscillation. We quantified factors responsible for the maintenance of C. sertularioides patches in off-reef areas, namely an associational mutualism with an epiphytic cyanobacteria (Lyngbya majuscula), coupled with spatial refuges at the scales of individual thalli and habitat. Maintenance of near reef algal populations with a strong response to nutrient addition showed that these populations were primed to bloom onto reefs in response to enhanced nutrient delivery, such as those potentially associated with La Niña conditions. However, our experiments demonstrated that no single factor related to consumer or resource control was likely to stimulate bloom formation in isolation. Rather, we propose a novel model of reef bloom formation where off-reef blooms are sustained by processes reducing consumer control, and then bloom onto reefs through an interaction between increased allochthonous nutrient input and an uncoupling of consumer control by an association with epiphytic cyanobacteria.