Host-Microbiome Interactions in a Changing Sea: The Gill Microbiome of an Invasive Oyster under Drastic Temperature Changes

The gill tissue of bivalve mollusks hosts rich symbiotic microbial communities that may contribute to host health. Spondylus spinosus is an invasive Lessepsian oyster in the Eastern Mediterranean Sea that has become highly abundant while constantly expanding its range northwestward. Using 16S rRNA gene amplicon sequencing, we examined how temperature affects S. spinosus oysters and their gill microbiota in a series of experiments: exposing them to the current annual seawater temperature range, to the colder temperature of the Western Mediterranean Sea, and to the elevated temperature as predicted under global warming scenarios. The bacterial genus Endozoicomonas dominated the communities of the S. spinosus, mainly upon exposure to winter-like (16 °C) temperatures. Exposure to the elevated seawater temperature resulted in a significant change in the bacterial communities, while the oysters maintained normal functioning, suggesting that the oyster may survive a seawater warming scenario. Exposure to 11 °C led to the health deterioration of the oysters, the emergence of opportunistic pathogens, such as Arcobacter, Vibrio, Colwelliaceae, and Pseudoalteromonas, and a decline in the relative abundance of Endozoicomonas, suggesting that S. spinosus might not survive Western Mediterranean Sea winters. Both the host and its gill bacteria are thus greatly affected by temperature, which could consequently restrict the range of expansion of this and other invasive oysters.

New Record of Dendronephthya sp. (Family: Nephtheidae) from Mediterranean Israel: Evidence for Tropicalization?

Bio-invasions have the potential to provoke cascade effects that can disrupt natural ecosystems and cause ecological regime shifts. The Mediterranean Sea is particularly prone to bio-invasions as the changing water conditions, evoked by climate change, are creating advantageous conditions for Lessepsian migrants from the Red Sea. Recently, in May 2023, a new alien species was documented in the Mediterranean Sea-a soft coral of the genus Dendronephthya. This discovery was made by divers conducting 'Long-Term Ecological Research' surveys, along the coast of Israel, at a depth of 42 m. Genetic and morphological testing suggest that the species identity may be Dendronepthya hemprichi, an Indo-Pacific coral, common in the Red Sea. According to life history traits of this species, such as accelerated attachment to available surfaces and fast growth, we expect it to rapidly expand its distribution and abundance across the Mediterranean Sea.

Invading bivalves replaced native Mediterranean bivalves, with little effect on the local benthic community

The construction of the Suez Canal connected the Red Sea and the Mediterranean Sea, which allowed rapid marine bio-invasion. Over the last century, several bivalve species have invaded the Levantine basin, yet their distribution and impact on the benthic community have not been thoroughly studied. Large-scale benthic surveys along the rocky substrate of the Israeli Mediterranean coastline indicate that invading bivalves, such as Spondylus spinosus, Brachidontes pharaonis, and Pinctada radiata, now dominate the rocky environment, with densities of tens to hundreds of individuals per m². No native bivalve specimens were found in any of the transects surveyed. The small-scale ecological effects of the established invading populations on the benthic community were examined over a year using an in-situ exclusion experiment where all invading bivalves were either physically removed or poisoned and kept in place to maintain the physical effect of the shells. Surprisingly, the experimental exclusion showed a little measurable effect of bivalve presence on the invertebrate community in close vicinity (~ 1 m). Bivalve presence had a small, but statistically significant, effect only on the community composition of macroalgae, increasing the abundance of some filamentous macroalgae and reducing the cover of turf. The generally low impact of bivalves removal could be due to (1) wave activity and local currents dispersing the bivalve excreta, (2) high grazing pressure, possibly by invading herbivorous fish, reducing the bottom-up effect of increased nutrient input by the bivalves, or (3) the natural complexity of the rocky habitat masking the contribution of the increased complexity associated with the bivalve's shell. We found that established invading bivalves have replaced native bivalve species, yet their exclusion has a negligible small-scale effect on the local benthic community.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10530-022-02986-1.

Cryptocentrus steinhardti (Actinopterygii; Gobiidae): a new species of shrimp-goby, and a new invasive to the Mediterranean Sea

A new species of shrimp-goby was collected at depths of 60–80 m off the southern Israeli Mediterranean coast. A unique ‘DNA barcoding’ signature (mtDNA COI and Cytb) revealed that it differs from any other previously bar-coded goby species clustered phylogenetically with the shrimp-gobies group, in which Cryptocentrus is the most speciose genus. A morphological study supported the assignment of the fish to Cryptocentrus and differentiated the new species from its congeners. The species is described here as Cryptocentrus steinhardti n. sp. However, the present phylogenetic analysis demonstrates a paraphyly of Cryptocentrus and emphasizes the need for revision of the genus based on integrating morphological and genetic characteristics. This finding constitutes the third record of an invasive shrimp goby in the Mediterranean Sea. An intriguing ecological issue arises regarding the possible formation of a fish-shrimp symbiosis in a newly invaded territory. Describing an alien tropical species in the Mediterranean prior to its discovery in native distribution is an unusual event, although not the first such case. Several similar examples are provided in the present article.

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.

Genetic diversity and phylogenetic relationships of threadfin breams (Nemipterus spp.) from the Red Sea and eastern Mediterranean Sea

The present work utilized partial sequences of cytochrome c oxidase subunit I (COI) to study Red Sea populations of threadfin breams (Nemipteridae), and compare their genetic diversity to that of Mediterranean Sea (Nemipterus randalli only) and Indo-Pacific populations. A Maximum Likelihood tree separated four fish species - N. randalli, N. japonicus, N. bipunctatus, and N. zysron - into four clades. Haplotype analyses revealed a strong case of the founder effect for the Lessepsian migrant N. randalli: Three haplotypes represented all sampled geographical ranges in the Mediterranean Sea and only one haplotype was shared with a Red Sea individual, presenting evidence that the colonizing population was founded by a small number of migrants. The Red Sea population of N. japonicus shared haplotypes with Persian Gulf and Indian Ocean populations, but South China Sea populations remained fully isolated. The haplotype networks of N. randalli and N. bipunctatus also revealed haplotype sharing between Red Sea and Indian Ocean populations. For N. zysron, one haplotype was shared between Indonesia and the Persian Gulf. We discuss the impact of continued usage of public database sequences of initially misidentified organisms and provide recommendations for avoiding distribution of sequences with incorrect scientific names.

Ocean warming is the key filter for successful colonization of the migrant octocoral Melithaea erythraea (Ehrenberg, 1834) in the Eastern Mediterranean Sea

Climate, which sets broad limits for migrating species, is considered a key filter to species migration between contrasting marine environments. The Southeast Mediterranean Sea (SEMS) is one of the regions where ocean temperatures are rising the fastest under recent climate change. Also, it is the most vulnerable marine region to species introductions. Here, we explore the factors which enabled the colonization of the endemic Red Sea octocoral Melithaea erythraea (Ehrenberg, 1834) along the SEMS coast, using sclerite oxygen and carbon stable isotope composition (δ ¹⁸O_SC and δ ¹³C_SC), morphology, and crystallography. The unique conditions presented by the SEMS include a greater temperature range (∼15 °C) and ultra-oligotrophy, and these are reflected by the lower δ ¹³C_SCvalues. This is indicative of a larger metabolic carbon intake during calcification, as well as an increase in crystal size, a decrease of octocoral wart density and thickness of the migrating octocoral sclerites compared to the Red Sea samples. This suggests increased stress conditions, affecting sclerite deposition of the SEMS migrating octocoral. The δ ¹⁸Osc range of the migrating M. erythraea indicates a preference for warm water sclerite deposition, similar to the native depositional temperature range of 21-28 °C. These findings are associated with the observed increase of minimum temperatures in winter for this region, at a rate of 0.35 ± 0.27 °C decade^-1 over the last 30 years, and thus the region is becoming more hospitable to the Indo-Pacific M. erythraea. This study shows a clear case study of "tropicalization" of the Mediterranean Sea due to recent warming.

They are here to stay: the biology and ecology of lionfish (Pterois miles) in the Mediterranean Sea

The lionfish, Pterois miles, is one of the most recent Lessepsian immigrants into the Mediterranean Sea, and it poses a serious threat to marine ecosystems in the region. This study assesses the basic biology and ecology of lionfish in the Mediterranean, examining morphometrics, reproduction and diet as well as population structure and distribution. The population density of lionfish has increased dramatically in Cyprus since the first sighting in late 2012; by 2018 aggregations of up to 70 lionfish were found on rocky grounds with complex reefs and artificial reefs in depths of 0-50 m. Lionfish in Cyprus become mature within a year, and adults are capable of spawning year-round, with peak spawning in summer when the sea-surface temperature reaches 28.4°C. The Cypriot lionfish grow faster and bigger than in their native range, and females are more common than males. Lionfish are generalist predators in these waters, as also found in their native range, consuming a range of teleost and crustacean prey, some of which are of high economic value (e.g., Spicara smaris and Sparisoma cretense) or have an important role in local trophic webs (e.g., Chromis chromis). Overall, the reproductive patterns, the presence of juveniles and adults throughout the year, the rapid growth rates and the generalist diet indicate that lionfish are thriving and are now already well established in the region and could potentially become the serious nuisance that they are in their temperate and tropical western Atlantic-invasive range.

First evidence of establishment of the rayed pearl oyster, Pinctada imbricata radiata (Leach, 1814), in the eastern Adriatic Sea

The Mediterranean Sea is increasingly under threat from invasive species that may negatively affect biodiversity and/or modify ecosystem structure and function. The bivalve mollusc Pinctada imbricata radiata is listed among the 100 most invasive species in the Mediterranean. A first finding of an established population of P. imbricata radiata in the coastal waters of the eastern Adriatic Sea, is presented in this paper. Six and then 30 live specimens were collected in 2015 and in 2017, respectively, at depths of 5 to 15m from the island of Mljet, Croatia. DNA sequencing of the mitochondrial cytochrome c oxidase I gene (COI) revealed three different haplotypes. All samples showed greatest similarity (98 to >99%) to P. radiata COI sequence records in GenBank (=P. imbricata radiata as used in this paper). A Neighbour Joining tree placed all Croatian samples within the 100% bootstrap supported clade for P. imbricata radiata.

Remarkable size-spectra stability in a marine system undergoing massive invasion

The Mediterranean Sea is an invasion hotspot, with non-indigenous species suspected to be a major driver behind community changes. We used size spectra, a reliable index of food web structure, to examine how the influx of Red Sea fishes into the Mediterranean Sea has impacted the indigenous species community. This is the first attempt to use changes in the size spectra to reveal the effect of biological invasions. We used data from trawl catches along Israel's shoreline spanning 20 years to estimate changes in the community size spectra of both indigenous and non-indigenous species. We found that the relative biomass of non-indigenous species increased over the 20 years, especially for small and large species, leading to a convergence with the indigenous species size spectra. Hence, the biomass of indigenous and non-indigenous species has become identical for all size classes, suggesting similar energetic constraints and sensitivities to fishing. However, over this time period the size spectrum of indigenous species has remained remarkably constant. This suggests that the wide-scale invasion of non-indigenous species into the Mediterranean may have had little impact on the community structure of indigenous species.

The clinical effects of the venomous Lessepsian migrant fish Plotosus lineatus (Thunberg, 1787) in the Southeastern Mediterranean Sea

CONTEXT

Plotosus lineatus is a venomous fish that has migrated from the Indo-Pacific region to the Mediterranean Sea (Lessepsian migrant). Its presence in the Mediterranean Sea was first recorded in 2002 and was observed in growing schools. Its spines contain toxins with lytic, hemolytic and edematous activities.

OBJECTIVE

To characterize the injuries caused by Plotosus lineatus in the Southeastern Mediterranean Sea.

METHODS

A prospective observational case series of consultations provided by a national Poison Center pertaining to Plotosus lineatus from 2007 to 2016. Demographic and clinical data and method of fish identification were retrieved from the medical toxicological records, and described.

RESULTS

Eighty four cases were included; the main findings are: median age 35 (range 3-80) years, 91.7% males, 51.2% fishermen, 78.6% palm injuries, 94% and 4.8% were mildly and moderately injured, respectively. Main local manifestations included pain, puncture wound, swelling, and erythema (90.5%, 70.2%, 33.3%, and 16.7%, respectively). Systemic signs were minor and infrequent (≤7.1%), including hypertension, tachycardia, vomiting, chills, and weakness. Management included wound disinfection, immersion in hot water, tetanus prophylaxis, and analgesics. No patient required hospital admission. The fish was identified mostly by the victim with the aid of the Poison Center (mainly by typical description, and a picture), and some by marine biologists.

CONCLUSIONS

Plotosus lineatus is a new fish in the Southeastern Mediterranean Sea. It affects fishermen handling fishing nets, and beach hikers stepping on or holding it. Injuries caused by its spines usually result in minor effects; pain may be intense. Treatment includes disinfection, analgesics, and antitetanus and antibiotics as needed. No lethal cases were recorded, unlike exposure of animals to the venom of the Indo-Pacific species; reason is unclear. Our series illustrates the consequences of manmade disruption of ecosystem resulting in invasion of toxic species to a new environment, affecting human health.