Lessepsian invasion without bottleneck: example of two rabbitfish species (Siganus rivulatus and Siganus luridus)

Since the opening of the Suez Canal in the 19th century, a growing number of teleosts species have become permanently established in the eastern Mediterranean. As environmental parameters in the Mediterranean are very different from those in the Red Sea, there is an opportunity to evaluate the gene flow associated with the acclimatisation of these species to their new environment. Initial colonisation may have been restricted to individuals with marginal genotypes compared to populations of the Red Sea, eventually better adapted to the Mediterranean environment. Alternatively, colonisation may have occurred without major genetic differentiation, due to a large flux of immigrants and a continuous gene flow from the populations of origin. Using different molecular genetic techniques (mitochondrial DNA, Exon-Primed Intron-Crossing PCR amplification (EPIC) and Inter-Simple Sequence Repeats (ISSRs), patterns of genetic differentiation on both sides of the Suez isthmus were tested on two Lessepsian rabbitfish species (Siganus rivulatus and Siganus luridus). The absence of genetic differentiation between Mediterranean and Red Sea populations in both species showed that a great number of migrants participated to the colonisation of the Mediterranean, excluding any bottleneck event. This colonisation success suggests large eco-physiological plasticity in S. rivulatus and S. luridus that allowed them to thrive in the new environment.     

Temporal Fluctuations and Settlement Patterns of Native and Lessepsian Herbivorous Fishes on the Lebanese Coast (Eastern Mediterranean)

We provide here the first information on the abundance, settlement patterns and microhabitat use of settlers of two Lessepsian siganid species, Siganus rivulatus and S. luridus, in comparison with the two main native herbivores, Sparisoma cretense (Scaridae) and Sarpa salpa (Sparidae). S. rivulatus was the most abundant species (72%), followed by S. cretense (20%) and S. luridus (8%), whereas S. salpa was rare (<1%). A clear pattern of settlement could be established for S. rivulatus and S. cretense, with similar timing in 1999 and 2000. S. cretense settled in schools late June, while S. rivulatus settled mid-July. A few solitary settlers of S. luridus were observed in July and August, but none of S. salpa. All these herbivorous fish species settled in protected shallow areas offering hard substrates and algal communities. S. rivulatus was the most tolerant and adaptable species, able to settle on a large range of substrates and habitats, including rock pools, muddy harbours and sea grass beds. In the eastern Mediterranean Sea, S. rivulatus might have benefited from a release of competition pressure due to the low diversity and abundance of native herbivores. It has probably replaced S. salpa on the coast of Lebanon, being more competitive than the native sparid.     

Genetics of the early stages of invasion of the Lessepsian rabbitfish Siganus luridus

Information on the initial stages of dispersal and settlement are of great interest in understanding the dynamics of biological invasions and in designing management responses. A newly settled population of the Lessepsian rabbitfish migrant Siganus luridus, that arrived in Linosa Island (Sicily Strait) in 2000, offered a unique opportunity to examine the genetic variability of the early phase of invasion and the starting point to test genetic variation within and between colonist and source populations.Demographics and dynamic aspects of S. luridus in the Mediterranean were evaluated by using phylogeographic and demographic (coalescent) methods based on DNA sequences of the mitochondrial control region. Sequences from 95 S. luridus, 25 Siganus rivulatus, and one of Siganus (Lo) vulpinus and S. doliatus were used. Samples were collected in one locality in the Red Sea (Eilat) and three localities in the Mediterranean (Israel, Greece and Linosa, Italy). Data showed (for the first time in a Lessepsian migrant) a lowering of the genetic diversity of the invading population (Mediterranean) (haplotype diversity 0.879, nucleotide diversity 0.592) compared to the parental one (Red Sea) (haplotype diversity 0.978, nucleotide diversity 0.958).Within the Mediterranean populations, there was no pattern of regional separation and mitochondrial diversity appeared to be preserved during the Linosa colonization, with no traces of founder events. Such evidence agrees with the idea that Lessepsian migration involves many individuals from its earliest stages.     

First record of the Lessepsian fish Siganus rivulatus (Forsskål & Niebuhr, 1775) in the Sea of Marmara (Izmit Bay,Turkey)

The marbled spinefoot, Siganus rivulatus (Forsskål&Niebuhr, 1775) was recorded for the first time in Izmit Bay, Sea of Marmara. One specimen was caught on 30 September 2019 by a small scale fisherman at depth of 25 m. The fish measured 151 mm in total length and weighted of 43.45 g. S. rivulatus is one of the Lessepsian immigrants who entered the Mediterranean more than half a century ago, and has now also easily adapted to the Sea of Marmara, which has a unique two-layered water system.     

Trace element levels in fish from clean and polluted coastal marine sites in the Mediterranean Sea, Red Sea and North Sea

The bioaccumulation of Hg, Cd, Zn, Cu, Mn and Fe was evaluated in the muscle and liver tissue of four fish species (Siganus rivulatus, Diplodus sargus, Lithognatus mormyrus and Plathychtis flesus) from clean and polluted marine coastal sites in the Red Sea, Mediterranean Sea and North Sea within the framework of the MARS 1 program. Representative liver samples were screened for organic contaminants (DDE, PCBs and PAHs) which exhibited very low concentrations. The levels of Cd, Cu, Zn, Fe and Mn found in the muscle tissue in this study were similar among the four species and within the naturally occurring metal ranges. However, differences were found among the sites. In the Red Sea, Cu was higher in the muscle of S. rivulatus at Ardag and Zn at the Observatory (OBS). Cu, Zn and Mn were higher in the Red Sea than in the specimens from the Mediterranean. The differences were attributed to different diets derived from distinctively different natural environments. D. sargus from Haifa Bay (HB) had higher Cd, Cu and Mn values than specimens from Jaffa (JFA), and L. mormyrus higher Cd, Fe and Mn in HB, corresponding to the polluted environmental status of the Bay. No differences in metal levels were found among the North Sea sites, except for Fe that was lower at the Eider station. Hg was low in all the specimens, but the values varied with species and sites. The lowest Hg values were found in S. rivulatus, the herbivorous species, as expected from its trophic level. Hg in P. flesus was higher than in S. rivulatus but still low. Higher Hg values were found in the muscle tissue of L. mormyrus,with the highest values in D. sargus, both carnivorous species from the same family. Hg in D. sargus was higher in HB than in JFA, as expected, but in the larger specimens of L. mormyrus from JFA values were higher, while in the small specimens there were no differences in Hg values. The levels of all metals were higher in the liver than in the muscle, with enrichment factors ranging from 3 to 104, depending on species and sites. The lowest enrichment values were found for Hg. Based on liver values, the specimens of S. rivulatus from the OBS had the highest levels, as well as D. sargus and L. mormyrus from JFA, contrary to the known relative environmental status of the sites. Received: 25 February 1999 / Received in revised form: 5 June 1999 / Accepted: 7 June 1999     

Trait‐based life strategies,ecological niches,and niche overlap in the nekton of the data‐poor Mediterranean Sea

Biological traits can determine species ecological niches and define species responses to environmental variation. Species have a specific functional position in the biological community, resulting in interactions like interspecific competition. In this study, we used biological traits in order to define the life strategies of 205 nektonic species of the Mediterranean Sea. Furthermore, traits related to resource use were analyzed to determine the level of trait and niche overlap and their relationship to life strategies. Focusing on habitats of importance (Posidonia beds, coralligène formations, and lagoons), we investigated strategies and niches of the species present there. Finally, we examined the life strategy of Lessepsian species and investigated the niche overlap between them and indigenous species. Archetypal analysis indicated the existence of three life histories corresponding to strategies already documented for fish (equilibrium, periodic, and opportunistic), with some species also placed in intermediate positions. Niche overlap was evaluated by multiple correspondence analysis and the generation of a single distance metric between all species pairs. This identified species occupying relatively empty (underexploited) ecological niches, like the Lessepsian species Siganus luridus and S. rivulatus, a finding that can also be associated with their establishment in the Mediterranean. Most Lessepsian species were associated with the opportunistic life history strategy, again an important aspect related to their establishment. Also, we documented that most species occurring in important habitats have a relatively high overlap of niches. No significant differences were found in the life strategies across Mediterranean habitats; however, variation in niche overlap and traits related to habitat use was detected. The findings can be useful to determine theoretical competition between species and to identify empty ecological niches. Fisheries science can also benefit from comprehending the dynamics of competing stocks or predict the responses of data‐poor stocks to anthropogenic stressors from known examples of species with shared life strategies.     

Estimation of Mercury Intake from Selected Fish Species Commercialized in Alexandria,Southeastern Mediterranean Sea,Egypt

Total Hg concentrations were determined in muscle tissue of some fishes with different feeding habits (12 fish species) obtained from the main fishing locations along the Alexandria coast, a region particularly impacted by historic industrial Hg activities. Health risks to human via dietary intake of the edible portion of fish were assessed by the target hazard quotients (THQs). Mercury maximum concentrations corresponding to fish muscle tissue were found in L. mormyrus, S. rivulatus, and S. luridus (3.56, 2.94, and 1.35 μg g^?1 wet weight, respectively). Thence most of these three species bass (75% of L. mormyrus, 76% of S. rivulatus, and 54% of S. luridus) were greater than a 0.47 μg g^?1 threshold corresponding to a 1 meal per month consumption limit. M. cephalus, S. aurita, S. chrysotaenia, B. boops, and A. djedaba bass (100%) were less than a 0.12 μg g^?1 threshold corresponding to a 4 meals per month safe consumption limit. Mercury THQs values, ranging from 0.11–1.76, were of concern. In particular, the health risk was mainly ascribed to consumption of S. rivulatus (1.72) and L. mormyrus (1.76), although also the TEQs values caused by consuming S. luridus (0.64) were rather high, being close to 1.     

Monogenean infestations and mortality in wild and cultured Red Sea fishes

Hyperinfection by the gill-infesting monogeneanAllobivagina sp. (Microcotylea) caused mass mortalities in juveniles ofSiganus luridus cultured in seawater earthen ponds and holding tanks in Eilat (Gulf of Aqaba, Red Sea). Other species ofSiganus and adults ofS. luridus cultured in the same systems acquired a low intensity of infestation. Most hyperinfected fish were emaciated and anaemic with hematocrit values below 10 %. Skin and mouth infestations by the monogeneanBenedenia monticelli (Capsaloidea) caused mass mortalities in grey mullets (Mugilidae). These mortalities occurred in large individuals in wild populations ofLiza carinata from lagoonal habitats in the Gulf of Suez and in most species of grey mullets cultured in Eilat. The intensity of infestation correlated positively with severity of infestation, and the common sites of infestation corresponded with areas of severe pathological alterations. Spontaneous recovery followed the climax of an epizootic, both for infestedS. luridus and infested grey mullets. Decline in infestation coincided with remission of the pathological signs.     

Molecular analysis of the recently described lizardfish Saurida lessepsianus (Synodontidae) from the Red Sea and the Mediterranean,with remarks on its phylogeny and genetic bottleneck effect

The opening of the Suez Canal in 1869 led to a massive influx of Red Sea species that invaded the Mediterranean; this was termed ‘Lessepsian migration'. Among these species was a species of lizardfish, identified by some authors as Saurida undosquamis and by others as S. macrolepis. Recently, the Red Sea and the Mediterranean populations were described according to external characteristics as a unique taxon, Saurida lessepsianus. Our molecular study confirms this finding and determines that all previous records of S. undosquamis and S. macrolepis in the Red Sea and the Mediterranean are misidentifications of S. lessepsianus. The Mediterranean population of S. lessepsianus exhibits a lower genetic variability than that of the Red Sea population, suggesting a bottleneck effect.     

Molecular Evidence for Lessepsian Invasion of Soritids (Larger Symbiont Bearing Benthic Foraminifera)

The Mediterranean Sea is considered as one of the hotspots of marine bioinvasions, largely due to the influx of tropical species migrating through the Suez Canal, so-called Lessepsian migrants. Several cases of Lessepsian migration have been documented recently, however, little is known about the ecological characteristics of the migrating species and their aptitude to colonize the new areas. This study focused on Red Sea soritids, larger symbiont-bearing benthic foraminifera (LBF) that are indicative of tropical and subtropical environments and were recently found in the Israeli coast of the Eastern Mediterranean. We combined molecular phylogenetic analyses of soritids and their algal symbionts as well as network analysis of Sorites orbiculus Forskål to compare populations from the Gulf of Elat (northern Red Sea) and from a known hotspot in Shikmona (northern Israel) that consists of a single population of S. orbiculus. Our phylogenetic analyses show that all specimens found in Shikmona are genetically identical to a population of S. orbiculus living on a similar shallow water pebbles habitat in the Gulf of Elat. Our analyses also show that the symbionts found in Shikmona and Elat soritids belong to the Symbiodinium clade F5, which is common in the Red Sea and also present in the Indian Ocean and Caribbean Sea. Our study therefore provides the first genetic and ecological evidences that indicate that modern population of soritids found on the Mediterranean coast of Israel is probably Lessepsian, and is less likely the descendant of a native ancient Mediterranean species.     

Age and growth of Lessepsian rabbitfish from the eastern Mediterranean

Rabbitfish are currently an important component of the eastern Mediterranean inshore fishery. This study estimates age and calculates growth of Siganus rivulatus and S. luridus from the Lebanese coastal waters based on otolith analysis and compares results with available data from different geographical locations. Annual periodicity of alternating zones was confirmed for S. rivulatus, in which one opaque and one translucent zone were observed to deposit each year, but not for S. luridus. Both species appear to have a maximum lifespan of 6 years. The von Bertalanffy growth functions were L_t = 318.9(1 ? e^{?0.225(t+1.307)}) for S. rivulatus and L_t = 274.9(1 ? e^{?0.330(t+1.039)}) for S. luridus and length–weight relationships were estimated as for S. rivulatus and for S. luridus. The rabbitfish catches of the Lebanese fishery consist mainly of individuals which have not reached their first maturity. Rabbitfish from the eastern Mediterranean coastal waters appear to grow rapidly most of the year and are thus able to maintain relatively important population size despite intensive fishing pressure.     

Marine molluscs from the Iztuzu beach near Dalyan (Mediterranean coast of Turkey)

Abstract

A total of l84 species of marine molluscs has been identified from shells collected on the beach of Iztuzu near Dalyan (Mu?la province, Turkey). Of these, 16 species of gastropod and 4 species of bivalvia are new For the extreme Eastern Mediterranean. Only three species of Lessepsian migrants (from the Red Sea via the Suez canal) have been found.     

Habitat niche breadth predicts invasiveness in solitary ascidians

A major focus of invasion biology is understanding the traits associated with introduction success. Most studies assess these traits in the invaded region, while only few compare nonindigenous species to the pool of potential invaders in their native region. We focused on the niche breadth hypothesis, commonly evoked but seldom tested, which states that generalist species are more likely to become introduced as they are capable of thriving under a wide set of conditions. Based on the massive introduction of tropical species into the Mediterranean via the Suez Canal (Lessepsian migration), we defined ascidians in the Red Sea as the pool of potential invaders. We constructed unique settlement plates, each representing six different niches, to assess ascidian niche breadth, and deployed them in similar habitats in the native and invaded regions. For each species found on plates, we evaluated its abundance, relative abundance across successional stages, and niche breadth, and then compared (1) species in the Red Sea known to have been introduced into the Mediterranean (Lessepsian species) and those not known from the Mediterranean (non‐Lessepsian); and (2) nonindigenous and indigenous species in the Mediterranean. Lessepsian species identified on plates in the Red Sea demonstrated wider niche breadth than non‐Lessepsian species, supporting the niche breadth hypothesis within the native region. No differences were found between Lessepsian and non‐Lessepsian species in species abundance and successional stages. In the Mediterranean, nonindigenous species numerically dominated the settlement plates. This precluded robust comparisons of niche breadth between nonindigenous and indigenous species in the invaded region. In conclusion, using Red Sea ascidians as the pool of potential invaders, we found clear evidence supporting the niche breadth hypothesis in the native region. We suggest that such patterns may often be obscured when conducting trait‐based studies in the invaded regions alone. Our findings indicate that quantifying the niche breadth of species in their native regions will improve estimates of invasiveness potential.     

First record of Boulenger's anthias Sacura boulengeri (Heemstra 1973) in the Red Sea

In November 2020, we observed several individuals and collected one juvenile of an unidentified anthiadine fish (Serranidae) between depths of 250 and 307 m near vertical walls of rocky reefs in the northern Red Sea. Further morphological and molecular analyses revealed that the collected specimen matches Sacura boulengeri, a species previously reported only from the Gulf of Oman to India.     

Multi-annual changes in the parasite communities of rabbitfish Siganus rivulatus (Siganidae) in the Gulf of Aqaba, Red Sea

The parasite communities of the rabbitfish, Siganus rivulatus, were used to track multi-annual changes in the northern Gulf of Aqaba, Red Sea, in an environment subjected to ongoing anthropogenic impact. Parasitological data from these fish were collected from 1998 to 2000, with spring and fall samplings at three locations: at a coral reef (OBS), at a sandy beach area (NB) and at a mariculture cage farm (FF). These data were compared with data from 1995–1997 as well as data collected during 1981–1985 at the coral reef sampling site. The data analyses indicate that the ratio between heteroxenous and monoxenous parasite species declined significantly at all sites between 1995–1997 and 1998–2000. During the same period, the species richness of monoxenous parasites increased significantly at all sites. The species richness of heteroxenous parasites decreased significantly at the coral reef site, but remained steady at the other two sites. This coincided with a significant increase in the prevalence of monogeneans at the OBS and FF sites and a significant decrease in the prevalence of digeneans at the FF and NB sites. The decline in the abundance of the latter, specifically of Opisthogonoporoides sp. and Gyliauchen sp., was even more significant when compared with the 1981–1985 data. The prevalence of other gut helminths, namely the digenean Hexangium sigani and the nematodes Cucullanus sigani and Procamallanus elatensis, however, showed a significant increase over the same period. Analysis of the species richness and diversity indices of the parasite communities did not reveal conspicuous differences. These, however, did become apparent when heteroxenous and monoxenous members of particular taxa were analyzed separately. Therefore, when using parasite assemblages to detect ecological changes, it is essential to analyze not only at the community level, but also to consider separate components of particular parasitic groups. Communicated by H. von Westernhagen, A. Diamant     

Spatial Relationships Between an Introduced Snapper and Native Goatfishes on Hawaiian Reefs*

It has been suggested that the introduced blueline snapper (Lutjanus kasmira, Family: Lutjanidae) may adversely affect populations of native fishery species in Hawai’i through competition for spatial or dietary resources, or through predation on young fish. We studied the habitat use patterns of L. kasmira and several native reef fish species using direct observation by SCUBA divers. Habitat use patterns of the yellowtail goatfish (Mulloidichthys vanicolensis, Family: Mullidae) were most similar to those of L. kasmira. Both species were primarily found low in the water column and were closely associated with areas of vertical relief. Individual M. vanicolensis were found higher in the water column when L. kasmirawere present, but L. kasmira were not similarly affected by M. vanicolensis. This finding suggests asymmetrical competition for shelter, in which the dominant L. kasmira displaces M. vanicolensis farther into the water column. This displacement from the protection of the reef could increase the vulnerability of M. vanicolensisto predators and fishers. *The US Government’s right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.     

Trematodes of Red Sea fishes: <Emphasis Type="Italic">Hexangium brayi</Emphasis> n. sp. (Angiodictyidae Looss, 1902) and <Emphasis Type="Italic">Siphodera aegyptensis </Emphasis>n. sp. (Cryptogonimidae Ward, 1917), with a review of their genera

Specimens of the marine fishes Siganus luridus (Siganidae) and Caesio suevica (Lutjanidae) were caught in the Red Sea off the coast of Sharm El-Sheikh, South Sinai, Egypt. Twelve (30%) and eight (17%) fish, respectively, were found to harbour intestinal trematodes. S. luridus was parasitised by Hexangium brayi n.␣sp. (Angiodictyidae) and C. suevica by Siphodera aegyptensis n. sp. (Cryptogonimidae). H. brayi n. sp. is differentiated from the other two species of the genus by the vitelline follicles which are confined to the inter-caecal field, its body shape which is distinctly pyriform, the terminations of the intestinal caeca which are distinctly saccular, the eggs which are few in number, and by the excretory vesicle which gives off a lateral arm on each side that divides into two long collecting ducts. S. aegyptensis n. sp. is most similar to S.␣cirrhiti Yamaguti, 1970, but differs in having a definite number of testes (nine), seven arranged in a ring and the other two situated symmetrically or diagonally within this ring, and vitelline follicles extending posteriorly to the level of the anterior lobes of the ovary. Both genera Hexangium Goto & Ozaki, 1929 and Siphodera Linton, 1910 are reviewed in detail and redefined.     

The fish assemblage on a coralligenous shallow shelf off the Mediterranean coast of northern Israel

The fish assemblage on the shallow coralligenous shelf (16-30m depth) off Haifa, Israel was sampled using trammel nets throughout a period of 1 year. Complementary data were obtained via underwater censuses of fish on an artificial reef established later in the sampling area. Fortythree species of fish were sampled by trammel nets, 79% of which were observed also during the underwater censuses. Although fish of Red Sea origin constituted only 11.6% of the species composition in the net samples, they contributed 46.2% of the fish abundance and 40.6% of the biomass in these samples. This was supported by the finding that species of Red Sea origin contributed 64% of the abundance of large fish counted on the artificial reef. Siganus luridas, S. rivulatus and Sargocentron rubrum are the main contributors in number and biomass among fish of Red Sea origin. It is suggested that the biogenic rocky bottom of this area contains several components which are similar to biogenic habitats favoured by these benthic species in the Red Sea; this may explain the high abundance of these species in the studied area.