Grazing rates of Elysia tomentosa on native and introduced Caulerpa taxifolia

The marine alga Caulerpa taxifolia Vahl (C. Agardh), recognized globally as one of the most prolific non-native species introductions, has been introduced to several temperate locations from where it has since rapidly expanded. C. taxifolia is protected by a toxin (terpenoid) in its tissues that limits grazing by native herbivores. Sacoglossan molluscs of the genus Elysia are among the few organisms that graze C. taxifolia; however, little is known about their feeding ecology. In the current study, we quantified the grazing rates of Elysia tomentosa on native C. taxifolia (Moreton Bay, Queensland) and introduced C. taxifolia (Botany Bay and Lake Conjola, New South Wales). Grazing rates were similar at Moreton Bay sites and Botany Bay; however, they were significantly lower in Lake Conjola. At the maximum observed grazing rate, slugs ate their body weight in C. taxifolia (dry weight) every 18–24 h. Differences in grazing rates between locations may be explained by differences in C. taxifolia morphology rather than native or introduced origin. Handling editor: J. Padisak     

Spread of Microcosmus squamiger (Ascidiacea: Pyuridae) in the Mediterranean Sea and adjacent waters

The Mediterranean Sea is subject to an ever-increasing arrival of non-indigenous marine organisms. Microcosmus squamiger is a solitary ascidian that inhabits shallow rocky littoral habitats. It probably originated in Australia and it has shown great invasive potential in other parts of the world. In the Mediterranean, M. squamiger has only been reported at a few sites in Spain and Italy. However, the closely related species Microcosmus exasperatus has been reported in several areas of the western Mediterranean. As these species can be easily confused, we re-examined most of the material from previous studies and our personal collections. In addition, sampling was done at several sites along the western Mediterranean and Atlantic coasts. The results showed that the majority of the M. exasperatus reports correspond to M. squamiger, and that M. squamiger is common on the Atlantic shores. This suggests that M. squamiger has entered the Mediterranean through the Gibraltar Strait, while the restricted distribution in the eastern Mediterranean of M. exasperatus suggests that this species is probably a Lessepsian migrant. In the Mediterranean Sea, M. squamiger has the ability to occupy extensive areas of hard substrata and to outcompete native species. Further studies are necessary to assess what impacts this invasive species have on native communities.     

Spread of introduced Caulerpa species in macroalgal habitats

A short-term field experiment was designed to identify layers of Mediterranean macroalgal assemblage conducive to successful spread of two introduced Caulerpa species (Bryopsidales, Chlorophyta). By manipulation of species presence, three experimental assemblages were obtained: (1) encrusting algae, having removed the turf and erect species; (2) encrusting and turfing algae, having removed erect species; (3) encrusting, turfing and erect algae, that is, unmanipulated assemblages, which served as a control. Fragments of the two introduced species Caulerpa taxifolia (Vahl) C. Agardh and Caulerpa racemosa (Forsskål) J. Agardh were transplanted in each of the three assemblages. Width of the colony, blade density and percentage of the substratum covered by the two species were measured.

The susceptibility of the indigenous community to the spread of Caulerpa species was related to type of assemblage. Blade density and amount of substratum covered by the two Caulerpa species were different between species and generally greater for C. taxifolia than for C. racemosa. Overall, the spread of these species was strongly dependent on the type but not directly on the complexity of the assemblage. Turf was more favourable than encrusting species alone, while the least advantageous habitat was where the macroalgal assemblage is composed of encrusting, turf and erect species. In other words, increased number of species in the assemblage reduces invasion of the Caulerpa species but the type of algae in the assemblage is likely to be more important than number of species. The presence of turf promotes the spread of Caulerpa species.     

不同温度下杉叶蕨藻对风信子鹿角珊瑚附生微生物群落的影响

全球变暖引发珊瑚礁区向大型海藻场生态演替现象与日俱增,大型海藻对珊瑚的影响主要包括抑制生长、发育与繁殖,但不同的海藻对不同的珊瑚具有不同的影响,二者之间的关系仍未有定论。为探究热压力所引起二者竞争关系的变化,以枝状风信子鹿角珊瑚(Acroproa hyacinthus)和大型底栖海藻杉叶蕨藻(Caulerpa taxifolia)为研究对象,设置了环境温度(27℃)与热压力温度(30℃),比较藻类间接接触和直接接触珊瑚对珊瑚附生微生物群落结构的影响,并从培养水环境及海藻表面微生物中寻找影响珊瑚表面微生物的原因。结果表明,去除嵌合体后共获得3369713条优化序列,并且大部分细菌得到注释。环境温度下,间接接触与直接接触组微生物表达模式接近,海藻的处理使得珊瑚表面附生微生物种类、丰度、PcoA区分度最高。门水平上,微生物群落主要由变形菌门、拟杆菌门、蓝细菌门、厚壁菌门、放线菌门组成。目水平上,微生物群落主要由红细菌目、黄杆菌目、肠杆菌目、蓝细菌目、假单胞菌目、噬几丁质菌目组成。这些细菌表型主要包括革兰氏阴性、好氧细菌、移动元件含量和胁迫耐受四大类,生态功能主要包括化能异养和需氧化能异养。对12个处理组的36个样本进行核心ASV分析(amplicon sequence variants),共获得139个核心ASVs。以假单胞菌目、黄杆菌目、噬几丁质菌目、红细菌目为主,还包括立克次氏体菌目、伯克霍尔德氏菌目、肠杆菌目、疣微菌目等。通过线性判别分析(linear discriminant analysis)可比较各组中相对丰度具有显著差异的细菌类群。环境温度下,群落中弧菌(Vibrio)、邻单胞菌(Plesiomonas)、奈瑟氏菌(Neisseria)以及螺旋体菌(Brevinema)相对丰度显著升高;温度升高后,珊瑚白化且胞内寄生病原微生物丰度显著升高,如米卡弧菌(Micavibrionales)与立克次氏体菌(Rickettsiales);热压力下,海藻的加入缓解了珊瑚白化、减少了胞内寄生性微生物丰度、显著提高了益生菌海命菌(Marivita)以及Halioxenophilus丰度。因此,在不同温度下杉叶蕨藻既作为压力源转移病原菌,又协助珊瑚抵抗胞内寄生菌,结果有助于理解大型海藻-珊瑚的竞争关系,解释海藻对珊瑚的潜在生态影响。     

MEDITERRANEAN CAULERPA TAXIFOLIA AND C. MEXICANA (CHLOROPHYTA) ARE NOT CONSPECIFIC

In 1984, Caulerpa taxifolia (Vahl) C. Agardh was reported along the coast of Monaco. Over the past decade it has spread along 60 km of the Mediterranean coastline and presently represents a potential risk to biodiversity. Several explanations have been advanced regarding the presence of C. taxifolia in the Mediterranean. One hypothesis maintains that the alga was introduced accidentally into the sea at Monaco, where it has been used as a decorative alga in aquaria. Caulerpa taxifolia has not been reported in earlier marine floras of the Mediterranean, and its sudden appearance has suggested that it may be a recent introduction. Another hypothesis proposes that C. taxifolia and Caulerpa mexicana Sonder ex Kützing are morphological variants of one another and hence conspecific taxa. Caulerpa mexicana has been found in the eastern Mediterranean since at least 1941. In order to establish the taxonomic identities of these taxa, individuals from five populations of C. taxifolia and four populations of C. mexicana were collected from within and outside of the Mediterranean. Comparative DNA sequence analysis of the nuclear ribosomal cistron, including the 3′-end of the 18S, ITS1, 5.8S, and ITS2 regions, show clear phylogenetic separation of the two taxa using parsimony and maximum likelihood analyses. Separation is maintained whether the analyses are based on just the more conserved 18S data or just the fast- evolving spacers. The two species are thus not conspecific. For specimens of uncertain identity (i.e. taxifolia–mexicana intermediates), a PCR diagnostic amplification can easily be performed because the ITS1 in C. taxifolia is 36 nucleotides shorter than the ITS1 in C. mexicana. Whether or not C. taxifolia has been present for a longer period of time in the marine flora, either as a cryptic endemic species or as the result of one or more introductions, represents an additional hypothesis that will require identification of biogeographic populations from throughout the world, as well as a population-level study of the Mediterranean region.     

The effects of light and nutrients on Caulerpa taxifolia and growth

Caulerpa taxifolia, an invasive species elsewhere in the world, is native to Moreton Bay where its distribution has been increasing in recent years. In Australia, dense beds of C. taxifolia are predominantly found in areas of low light and high nutrients (low water quality). Monitoring data from Moreton Bay suggests that native C. taxifolia is not directly replacing seagrass, but that there is a successional trend of seagrass loss and subsequent C. taxifolia colonization. The current study examined responses of C. taxifolia in relation to changes in environmental conditions using ambient water quality and a light/nutrient manipulative experiment. In the ambient water quality experiment we found that C. taxifolia grew significantly faster in areas with higher light (lower turbidity). The manipulative experiment demonstrated that nutrients stimulate C. taxifolia growth, however, light availability and seasonality appear to influence the response of C. taxifolia growth to nutrients in Moreton Bay. These findings suggest that C. taxifolia is unlikely to colonize seagrass beds in areas with high light and low nutrients; however, in areas with moderate light and moderate to high nutrients C. taxifolia and seagrass are likely to coexist.     

Hydromedusae of the Mediterranean Sea

Mediterranean hydromedusae can be classified in several categories: common species, widely distributed throughout the Mediterranean and rare species reported from the Pacific, Indian or Atlantic Oceans; seasonal species comprising cold-season species with a boreal affinity and warm-season species with a hot to temperate affinity; neritic and mid-ocean species; surface species and meso-, infra-, and bathypelagic species. Holoplanktonic species are known to be associated with stable hydrological conditions (offshore waters, deep waters, summer and winter homothermy), whereas meroplanktonic species are more likely to be found in more disturbed hydrological conditions (coastal waters, surface waters, spring and autumn periods of temperature fluctuation). A general pattern of medusa distribution is established based upon comparative study throughout the Mediterranean.     

Alexandrium catenella and Alexandrium minutum blooms in the Mediterranean Sea: Toward the identification of ecological niches

Annual recurrent blooms of the toxic dinoflagellates Alexandrium catenella and Alexandrium minutum were detected from 2000 to 2003 in harbours along the Catalan coast. The interrelation study between the occurrence of the blooms and specific external conditions at the study sites demonstrated that different factors are required for the bloom of each Alexandrium species. Concentrations higher than 10⁵ cells l⁻¹ of A. catenella were only detected in Tarragona harbour. These blooms were associated with water surface temperature between 21 and 25 °C and salinities of around 34 psu or higher than 37 psu. A. minutum appeared widely spread along the Catalan coast, though the most intensive and recurrent blooms of this species were observed in Arenys de Mar harbour. Concentrations of millions of cells per litre of A. minutum were associated with water temperatures below 14 °C and salinities of around 34–36 psu. A. minutum cell densities showed a positive significant correlation with NO₃ but a negative correlation with NH₄. On the other hand, A. catenella blooms dominated when both NO₃ and NH₄ levels were high. The prevailing inorganic nitrogen form (NO₃ vs. NH₄) could explain why these two species rarely coincide in the same harbours. Accumulation of cysts in the sediment was found to be an important potential factor for the recurrence of these species. The 4.3 × 10³ A. catenella cysts cm⁻³ of wet sediment in Tarragona harbour and the 3.02 × 10³ A. minutum cysts cm⁻³ of wet sediment in Vilanova harbour were the highest concentrations observed from the cyst study. Confined waters such as harbours play an important role as reservoirs for the accumulation of cysts and vegetative cells, which contributes to the expansion of these dinoflagellates in the region. However, the particular environmental conditions are also decisive factors of bloom intensity.     

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.     

Antioxidant response and caulerpenyne production of the alien Caulerpa taxifolia (Vahl) epiphytized by the invasive algae Lophocladia lallemandii (Montagne)

Invasive algae alter the structure and function of ecosystems. The red algae Lophocladia lallemandii grows in the West Mediterranean epiphyting the green algae Caulerpa taxifolia, another invasive alga. Our aim was to determine whether the invasive algae Lophocladia, recently introduced in the West Mediterranean, induces oxidative stress and an antioxidant response in Caulerpa taxifolia. We measured the caulerpenyne production, the activities of antioxidant enzymes and the levels of markers of lipid peroxidation in Caulerpa taxifolia. Caulerpenyne concentration was significantly higher in Caulerpa taxifolia epiphytized by Lophocladia. End-products of lipid peroxidation -malondialdehyde (MDA) and 4-hydroxinonenal (4-HNE)- were significantly increased in Caulerpa taxifolia samples from the station with Lophocladia. Antioxidant enzyme activities -catalase and superoxide dismutase (SOD)-, as well as H₂O₂ production significantly increased in the Lophocladia station compared to the control station. The activities of catalase and SOD determined in Lophocladia lallemandii showed no significant differences between Lophocladia living alone and Lophocladia epiphytating Caulerpa taxifolia. Caulerpa taxifolia epiphytized by Lophocladia lallemandii responded by increasing the caulerpenyne and H₂O₂ production and the antioxidant enzymes activities as a defensive mechanism against the new invasive algae.     

The Introduced Green Alga Caulerpa Taxifolia Continues to Spread in the Mediterranean

The tropical green alga Caulerpa taxifolia in the Mediterranean has spread steadily since its introduction in 1984. At the end of 2000, approximately 131km² of benthos had been colonized in 103 independent areas along 191km of coastline in six countries (Spain, France, Monaco, Italy, Croatia and Tunisia). Large regions neighboring the invaded areas appear favorable to further colonization, and there is thus no reason to believe that spreading will slow down in the years to come.     

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.     

Comparative genetics of scyphozoan species reveals the geological history and contemporary processes of the Mediterranean Sea

Jellyfish are useful genetic indicators for aquatic ecosystems as they have limited mobility and are highly exposed to the water column. By using comparative genomics and the molecular clock (timetree) of Rhizostoma pulmo, we revealed a divergence point between the East and West Mediterranean Sea (MS) populations that occurred 4.59 million years ago (mya). It is suggested that the two distinct ecological environments we know today were formed at this time. We propose that before this divergence, the highly mixed Atlantic and Mediterranean waters led to the wide dispersal of different species including R. pulmo. At 4.59 mya, the Western and Eastern MS were formed, indicating the possibility of a dramatic environmental event. For the first time, we find that for the jellyfish we examined, the division of the MS in east and west is not at the Straits of Sicily as generally thought, but significantly to the east. Using genomics of the Aurelia species, we examined contemporary anthropogenic impacts with a focus on migration of scyphozoa across the Suez Canal (Lessepsian migration). Aurelia sp. is among the few scyphozoa we find in both the MS and the Red Sea, but our DNA analysis revealed that the Red Sea Aurelia sp. did not migrate or mix with MS species. Phyllorhiza punctata results showed that this species was only recently introduced to the MS as a result of anthropogenic transportation activity, such as ballast water discharge, and revealed a migration vector from Australia to the MS. Our findings demonstrate that jellyfish genomes can be used as a phylogeographic molecular tool to trace past events across large temporal scales and reveal invasive species introduction due to human activity.     

On the occurrence of Cheilopogon furcatus in the Mediterranean Sea

The spotfin flyingfish Cheilopogon furcatus is recorded for the first time in the Mediterranean Sea, near Zarzis, in the Gulf of Gabès, southern Tunisia. This record is probably due to migration from the eastern Atlantic through the Strait of Gibraltar.     

The Sperm Whale,Physeter macrocephalus,in the Eastern Mediterranean Sea

Abstract

After the successful establishment of free–living populations of Rose–ringed Parakeets (Psittacula krameri) and Common Mynas (Acridotheres tristis) in Jeddah, an overview of all exotic birds imported into Jeddah in the first three months of 1990 is given.     

First record of the bluespotted cornetfish from the Mediterranean Sea

Three specimens of the Indo-Pacific Bluespotted cornetfish Fistularia commersonii are recorded for the first time from the Mediterranean. The presence of this species in the Mediterranean is due to migration from the Red Sea via the Suez Canal.     

The littoral fish community of the Lebanese rocky coast (eastern Mediterranean Sea) with emphasis on Red Sea immigrants

The organisation of the coastal rocky fish community of Lebanon was investigated for the first time, using visual censuses. A total of 62 fish species were recorded between the surface and 32 m depth, 8 species being Red Sea migrants. Species richness and fish abundance were positively correlated first with substrate complexity and second with depth. The trophic structure of the community was dominated by diurnal zooplanktivores (Chromis chromis, Oblada melanura and Spicara smaris) and mesocarnivores 1 (Coris julis and Thalassoma pavo), and did not vary significantly with depth. The Lessepsian migrants represented 13% of the species richness and 19% of the total abundance of individuals. They dominated among herbivores, nocturnal zooplanktivores and macrocarnivores. The Lessepsian Siganus luridus and S. rivulatus (Siganidae), Pempheris vanicolensis (Pempheridae) and Sargocentron rubrum (Holocentridae) were now among the most common fish species on the Lebanese rocky coast. Lessepsian fish species displayed either similar ecological niches in the Red Sea and in the Levantine basin (P. vanicolensis, S. rubrum) or an enlargement of their depth distribution towards deeper waters in their new environment (S. luridus, S. rivulatus). This study will serve as a baseline for future studies as eastern Mediterranean communities are subjected to a steady increase in Red Sea migrant species.     

Adaptive colouration of Mediterranean labrid fishes to the new habitat provided by the introduced tropical alga Caulerpa taxifolia

Since the introduction of the invasive tropical alga Caulerpa taxifolia in the Mediterranean Sea. a new, uniformly green habitat has been available to local fish assemblages. Underwater visual censuses of three species, Symphodus ocellatus, Symphodus roissali and Coris julis , revealed a higher proportion of green morphs in the C. taxifolia meadows compared to those inhabiting their usual indigenous habitats. In a fourth species, Symphodus rostratus , the distribution of the different colour morphs did not differ between the two habitats investigated. Experiments in aquaria proved that S. ocellatus and S. roissali were homochromic species able to adapt their colouration to the environment. In contrast, no colour change was observed in S. rostratus during the experiments.     

First record of Risso's Dolphin,Grampidelphis griseus,in the Eastern Mediterranean Sea

Abstract

The present distribution of the Black Francolin (Francolinus francolinus) in Cyprus is concentrated in two restricted areas: the Karpasia peninsula in the north-east of the island, where about 200 birds live; and the lowlands of Paphos district in the west of Cyprus, where about 150 birds occur mainly on Akamas peninsula and around the villages of Paphos and Polis. As the decline of the population is correlated with the level of hunting, protection is urgently needed.     

Allozyme differentiation of bonito in the Mediterranean Sea

Bonito Sarda sarda samples collected in three areas from the Mediterranean Sea exhibited considerable genetic heterogeneity over all locations. This provided preliminary evidence for two different groups of bonito, one for the Ligurian and the Ionian Seas and the other for the Aegean Sea.