Temporal and spatial variability in shallow- and deep-water populations of the invasive Caulerpa racemosa var. cylindracea in the Western Mediterranean

The invasive green alga Caulerpa racemosa var. cylindracea represents an important threat to the diversity of Mediterranean benthic coastal ecosystems by interfering with native species and modifying benthic assemblages. The present study deals, for the first time, with the temporal and spatial variability of the biomass and phenology of C. racemosa considering both deep- and shallow-water populations. Two sampling depths (30 and 10 m) were sampled at three different rocky bottom sites every 3 months in the Archipelago of Cabrera National Park (Western Mediterranean). All morphometric variables analysed showed a spatial variation and temporal patterns depending on depth. Between depths, C. racemosa biomass, stolon length, number of fronds and frond length were usually significantly higher at deep-water populations, suggesting that C. racemosa grows better in deep-waters. Deep- and shallow-water populations displayed a high temporal variation although no evidence of seasonal patterns was found, in contrast with what has been reported by other authors. The sources of this variability are still unknown but probably both physical factors and differential herbivory pressures display a key role.     

Comparative Analysis of Nutrient Composition of Caulerpa lentillifera from Different Regions

This study investigated the difference of nutrient composition in Caulerpa lentillifera collected from different regions.The nutrient compositions of C.lentillifera from China's Hainan and Shandong provinces were determined and compared with those from Semporna(Malaysia),Sabah(Malaysia),Petchburi(Thailand),and two other species of seaweeds(Malaysia).The results showed that the polysaccharide and protein contents of C.lentillifera from Hainan(44.82%±0.98%and 12.5%±0.70%),Shandong(43.22%±1.42%and 14.7%±0.72%),Petchburi(59.27%±2.31%and 12.49%±0.30%),and Sabah(44.02%±2.01%and 19.38%±1.48%)were higher than those of Eucheuma cottonii(26.49%±3.01%and 9.76%±1.33%)and Sargassum polycystum(33.49%±1.70%and 5.40%±0.07%),respectively.The polyunsaturated fatty acid contents in C.lentillifera from Hainan(29.98%)and Shandong(22.11%)were higher than that in Semporna(16.76%±0.27%),Sabah(9.49%),and S.polycystum(20.34%±0.43%),but lower than that in E.cottonii(51.55%±0.57%).In Caulerpa lentillifera of Hainan and Shandong provinces,the essential amino acid(EAA)/total amino acid(TAA)ratios were 35.22%and 38.78%,respectively;and the EAA/ETAA ratios were 54.36%and 63.35%,respectively.The EAA composition of C.lentillifera was close to the ideal model of Food and Agriculture Organization/World Health Organization.C.lentillifera was rich in mineral elements,including calcium((3315.85±127.55)mg(100 g)^-1 and(3728.35±92.38)mg(100 g)^-1),magnesium((6715.74±82.58)mg(100 g)^-1 and(8128.59±242.72)mg(100 g)^-1),and trace elements,including iron((510.65±5.47)mg(100 g)^-1 and(1972.97±183.35)mg(100 g)^-1),selenium((1.04±0.08)mg(100 g)^-1 and(0.83±0.15)mg(100 g)^-1),and zinc((33.90±0.13)mg(100 g)^-1 and(11.75±2.05)mg(100 g)^-1).These results showed that C.lentillifera was more nutritious than S.polycystum or E.cottonii in terms of polysaccharide,protein,and fatty acid contents.Furthermore,both C.lentillifera species collected from Hainan and Shandong provinces show more basic nutrients.Therefore,C.lentillifera has important development and application prospects.     

Differential herbivory of invasive algae by native fish in the Mediterranean Sea

The potential role of generalist herbivores to serve as a source of biotic resistance against algal invasion in marine ecosystems has been poorly examined. The present study investigates the capacity of Mediterranean herbivorous fishes to consume three of the most invasive seaweeds of the Western Mediterranean (Caulerpa racemosa, Lophocladia lallemandii and Womersleyella setacea) and examines vertical and temporal variations of such consumption. Our results show that although fish feed throughout the depth gradient examined (5–35 m), they concentrate in shallow waters, and can consume high amounts of C. racemosa. Such high ingestion of C. racemosa does not appear to be random, since this alga is consistently chosen when offered in pairs with several native species. Conversely, L. lallemandii and W. setacea are barely eaten by fish even though they can be very abundant in the field throughout the year. Our results suggest that fish could be an important controlling agent that has been overlooked in temperate marine invasions, and they may be able to provide certain resistance to C. racemosa invasion. In contrast, they are unlikely to exert any important control effects on L. lallemandii or W. setacea.     

Urban seagrass: status of Posidonia oceanica facing the Genoa city waterfront (Italy) and implications for management

A system of five adjacent Posidonia oceanica meadows facing the waterfront of Genoa city (Ligurian Sea, NW Mediterranean) was investigated over different spatial scales (meters-kilometers) using three environmental indices: conservation index (CI), substitution index (SI) and phase-shift index (PSI). CI revealed differences mostly at large spatial scale, distinguishing the poor condition of the meadows closest to Genoa centre and harbour from the comparatively healthy condition of the farthest meadows. SI showed differences mostly at small spatial scale (i.e., within meadows), suggesting the influence of local factors in the re-colonisation of regressed meadows by the seagrass Cymodocea nodosa and/or the invasive alga Caulerpa racemosa. Mapping of PSI showed that the meadows closest to Genoa centre and harbour have undergone a nearly total phase shift and have no real potential for recovery: attempts to re-establish P. oceanica there might be a waste of time and money. On the contrary, the meadows farthest from Genoa centre and harbour showed a comparatively low level of phase shift and could still fully recover given specific management actions.     

温度、照度和氮磷营养盐对长茎葡萄蕨藻富硒的影响

【目的】探索富硒长茎葡萄蕨藻(Caulerpalentillifera)的培养条件。【方法】以亚硒酸钠(Na_2SeO_3)为硒源,采用单因素实验,研究不同硒浓度对长茎葡萄蕨藻的生长、光合色素和硒富集量的影响,通过正交实验,找出适宜长茎葡萄蕨藻富硒的最佳温度、照度和氮磷比组合条件。【结果】在亚硒酸钠0、0.5、1.0、2.0、4.0、8.0mg/L条件下,随亚硒酸钠添加量增加,藻体硒质量分数(干基)从1.70μg/g增加至50.10μg/g,且各组间差异均有统计学意义(P<0.05);亚硒酸钠添加量2.0 mg/L时,藻体硒质量分数达到11.7μg/g;添加量大于2.0 mg/L时,显著抑制藻体的生长(P<0.05),藻体叶绿素a和叶绿素b含量显著性降低(P<0.05);添加量低于2.0 mg/L时,藻体的生长、叶绿素a和叶绿素b含量均无显著性差异;类胡萝卜素含量各组间无明显变化。在培养液亚硒酸钠质量浓度为2.0 mg/L的条件下,藻体最适的生长条件组合是温度28℃、照度2 000 lx、氮磷比10∶1,藻体的最优富硒条件是温度24℃、照度2 000 lx、氮磷比8∶1。【结论】长茎葡萄蕨藻在开发含硒安全性功能海藻食品方面有较大应用潜力。     

不同温度下长茎葡萄蕨藻无机碳利用

【目的】阐明长茎葡萄蕨藻对无机碳的利用方式。【方法】运用pH漂移技术,探索藻体质量、藻体部位、照度和海水体积对长茎葡萄蕨藻(Caulerpa lentillifera)的pH补偿点的影响,并研究在3种不同温度(20、25、30℃)下,乙酰唑胺(AZ)、乙氧苯丙噻唑磺胺(EZ)、4,4′-二异硫氰基芪2,2′-二磺酸(DIDS)、钒酸盐(Van)4种抑制剂对长茎葡萄蕨藻无机碳的利用影响。【结果】藻体质量、藻体部位、照度和海水体积对长茎葡萄蕨藻的pH补偿点均无显著性影响(P>0.05),在一定范围内藻体质量或照度越大,达到pH补偿点时间越短,且pH补偿点均大于9。20℃下各抑制剂的抑制作用最大,其次为30℃,25℃最小,但3种温度下各抑制剂的抑制率无显著差别(P> 0.05)。4种抑制剂中DIDS对长茎葡萄蕨藻pH补偿点和无机碳利用均无显著影响(P> 0.05),剩余3种抑制剂的抑制作用依次为EZ>AZ>Van。【结论】藻体质量、藻体部位、照度和海水体积对长茎葡萄蕨藻pH补偿点无影响。温度对长茎葡萄蕨藻吸收利用无机碳没有明显影响。长茎葡萄蕨藻能利用HCO_3^-作为无机碳源进行光合作用。     

Functional changes due to invasive species: Food web shifts at shallow Posidonia oceanica seagrass beds colonized by the alien macroalga Caulerpa racemosa

Multiple stable isotope analyses were used to examine the trophic shifts at faunal assemblages within the invading macroalga Caulerpa racemosa in comparison to established communities of Posidonia oceanica seagrass meadows. Sampling of macrobenthic invertebrates and their potential food sources of algal mats and seagrass meadows in Mallorca (NW Mediterranean) showed differences in species composition of faunal and primary producers among seagrass and C. racemosa. Accordingly, changes in food web structure and trophic guilds were observed, not only at species level but also at community level. The carbon and nitrogen isotope signatures of herbivores, detritivores and deposit feeders confirmed that the seagrass provided a small contribution to the macrofaunal organisms. δ¹³C at the P. oceanica seagrass and at the C. racemosa assemblages differed, ranging from −6.19 to −21.20‰ and −2.67 to −31.41‰, respectively. δ¹⁵N at the Caulerpa mats was lower (ranging from 2.64 to 10.45‰) than that at the seagrass meadows (3.51–12. 94‰). Significant differences in isotopic signatures and trophic level among trophic guilds at P. oceanica and C. racemosa were found. N fractionation at trophic guild level considerable differed between seagrass and macroalgae mats, especially for detritivores, deposit feeders, and herbivores. Filter feeders slightly differed with a relatively lower N signal at the seagrass and CR values at community level and at trophic guild level were higher in the C. racemosa invaded habitats indicating an increase in diversity of basal resource pools. C. racemosa did seem to broaden the niche diversity of the P. oceanica meadows it colonised at the base of the food web, may be due to the establishment of a new basal resource. The extent of the effects of invasive species on ecosystem functioning is a fundamental issue in conservation ecology. The observed changes in invertebrate and macrophytic composition, stable isotope signatures of concomitant species and consequent trophic guild and niche breadth shifts at invaded Caulerpa beds increase our understanding of the seagrass systems.     

Persistence of biological invasion effects: Recovery of macroalgal assemblages after removal of Caulerpa racemosa var. cylindracea

The present study evaluated the capability of recovery of Mediterranean macroalgal assemblages on rocky bottom invaded by Caulerpa racemosa. A manipulative experiment was performed to compare the structure of native assemblages that: (a) were invaded by the alga, (b) were invaded, but where the invasive alga was removed, and (c) had never been invaded. Macroalgal assemblages differed significantly between areas invaded by C. racemosa and control areas. Moreover, one year after removal of the invader, the recovery of community was minimal. Overall, recovery consisted of a significant increase in species richness and cover of macroalgae, but cover of each vegetation layer (encrusting, turf and erect) did not vary significantly between cleared and Invaded plots through time. Results showed that the effects of the colonization persist after the removal of the alga and the process of recovery of the assemblages appears to be quite slow. This finding might be an important contribution to evaluate invasion costs and thus potentially useful for an effective addressing of control strategies.     

Fragmentation as a Strategy for Caulerpa Species: Fates of Fragments and Implications for Management of an Invasive Weed

Abstract. The successful growth of fragments to full size macroalgal clones is well known for many taxa in mariculture. From an ecological context, however, few studies relate success by invasive species to the ability to fragment readily, disperse widely or re-attach rapidly - obvious hallmarks of weedy species. This study compares morphologically and ecologically distinct species of the green alga Caulerpa : in the Mediterranean, Caulerpa taxifolia is well known as an invasive weed; Caulerpa prolifera grows around or inside seagrass beds and is not apparently invasive; Caulerpa verticillata is among the most diminutive species, with potentially the most restricted reef distribution. We tested three hypotheses: (i) fragment success is independent of size, (ii) fragment success is independent of position within the plant and (iii) fragments from all species will be equally successful in establishing rhizoids, the first step to re-attachment. The success of small fragments (5–40 mm lengths) cut from distinct locations within replicate plants was scored for survival and establishment of rhizoids in bioassays. Additionally, for C. taxifolia , estimates were made of the force needed to puncture upright and prostrate axes, thereby estimating forces required to generate fragments from these two sources. Among the three species, only upright axes of C. taxifolia readily recovered from fragmentation stress for fragment sizes > 10 mm. The forces required to fragment upright axes were substantially less than for comparable rhizome portions. Fragments of C. prolifera were viable only for rhizome portions; fragments of C. verticillata were not viable at any size examined in this study. Estimates of viable fragment size, origin and force required to fragment axes for C. taxifolia support existing field data suggesting that fragmentation is the effective propagation mechanism underlying the spread of this invasive weed.     

Effects of the spread of the alga Caulerpa racemosa var. cylindracea on the sponge assemblage from coralligenous concretions of the Apulian coast (Ionian Sea, Italy)

The present work investigated the modifications induced by the spread of the green macroalga Caulerpa racemosa var. cylindracea (Bryopsidales, Chlorophyta) on the sponge assemblage of Apulian coralligenous concretions (Ionian Sea – Torre Ovo, Italy). The study of qualitative and quantitative sponge composition was carried out before (2004) and after (2006) the spread of this invasive alga by means of traditional (quadrat scraping) and photographic sampling methods. Results indicate that the spread of the green alga is concomitant with a significant decrease in percentage sponge cover both on horizontal- and on vertical-oriented substrates. In addition, strong modifications to the structure of the community in terms of repartition of the available substrate have been observed since the algal spread. Conversely, no major changes have affected the specific composition of the sponge assemblage, suggesting that at this stage of colonization the algal spread has not produced a loss of sponge biodiversity. However, there is a clear need to monitor closely the C. racemosa invasion to verify its long-term impact on the sponge assemblage.