Vermetid Reefs Research Articles

A dynamic subtropical coastal hotspot of benthic foraminifera in the Southeastern Mediterranean indicates early-stage tropicalization

Due to ongoing ocean warming, subtropical environments are becoming accessible to tropical species. Among these environments are the vermetid reefs of the Southeastern Mediterranean (SEM). In the last decades, these valuable coastal habitats witnessed the proliferation of numerous alien species of tropical origin. Among the meiofauna thriving on these reefs are benthic foraminifera, single cell marine organisms that make a significant contribution to global carbonate production. It has been widely recognized that benthic foraminifera, among other invasive species, thrive in the macroalgal cover, and it has been suggested that their populations are becoming a significant new source of sediment substrate. Here, we report on the first systematic assessment of the population size of the benthic foraminifera, allowing a comparison with data from the native tropical habitat of these species. Our study is based on a seasonal sampling of benthic foraminifera from confined sampling areas at four sites along the vermetid reef platforms of the Israeli SEM coast. Our survey reveals a patchy distribution of each species with peak population densities exceeding 100,000 specimens per m2, making the SEM a hotspot of benthic foraminifera, with population densities comparable to tropical coral reef environments. The assemblages of the SEM hotspot are dominated by cosmopolitan foraminiferal taxa and tropical invaders from the Indo-Pacific (e.g., Amphistegina lobifera, Pararotalia calcariformata, soritids, and Hauerina diversa). In contrast to foraminiferal hotspots in the tropics, which are completely dominated by larger symbiont-bearing taxa, the SEM hotspot stands out due to high abundances of non-symbiont-bearing species Textularia agglutinans and small miliolids. An intriguing observation is the significant heterogeneity in composition and density of foraminiferal assemblages between the vermetid reefs' southern and northern areas (Israel), indicating that the productivity of the dominant species are also modulated by local yet unknown environmental factors.

First estimates of Common Sandpiper <i>Actitis hypoleucos</i> and Ruddy Turnstone <i>Arenaria interpres</i> wintering along the coast of Trapani (Sicily, Italy)

A census was carried out using the method of transects along stretches of coast of the Province of Trapani in order to estimate the wintering population of Common Sandpiper and Ruddy Turnstone. Although the International Waterbird Census (IWC) provides accurate estimation of wintering waders in Italy, the number of wintering individuals of Common Sandpiper Actitis hypoleucos and Ruddy Turnstone Arenaria interpres are strongly underestimated. The reason for this underestimation lies in the type of habitat they are used to populate along with the solitary life habits of the Common Sandpiper. To address this issue, we inspected 46.9 km of coastline where we recorded to 92 Ruddy Turnstones and 56 Common Sandpipers. For both species, the sites (coast) where bird-sightings occurred were marked with georeferenced data and classified as harbour area, sandy, rocky (including vermetid reefs) and posidonia banquettes. For each species, the IKA (Index of Abundance per Kilometer) was calculated, both global index and relative to each type of coast. As for the Common Sandpiper we observed 87 individuals, between transects and spot observations in the province of Trapani, which is the 22% of the whole wintering population estimated in Italy. Notably, even greater is the importance of our observations of the Ruddy Turnstone, which accounting for up to 154 individuals corresponds to the 71% of the whole Italian wintering population. Projection of these data to the entire Italian coast allows estimating a wintering population in Italy much larger than that reported so far, especially for the Common Sandpiper, which uses not only the sea cost but also inland wetlands and rivers as suitable wintering habitats for wintering.

Effects of Habitat Fragmentation of a Mediterranean Marine Reef on the Associated Fish Community: Insights from Biological Traits Analysis

Habitat fragmentation (HF) is an ecological process, which is potentially also one of the main causes of diversity loss. Many studies have debated the best tools to adopt for assessing the effects of HF. The traditional application of biodiversity metrics might not fully describe the biotic community associated to a particular habitat or the ongoing ecological processes. The community-weighted mean (CWM) seems to be a valid investigation index, since biological traits (BTs) of the associated community are selected by local environmental factors. Furthermore, by combining species with common BTs into Functional Groups (FGs), it is possible to account for ecological functions that are supported by the inclusion of the response of key species within the same context. In our case study, we investigated the possible effect of HF of different Sicilian vermetid reefs on the associated infralittoral fish community based on the (i) vermetid fragmentation level, (ii) nature of the infralittoral substratum and (iii) conservational level of protection. We expected HF to be the main factor in shaping the local fish community; however, the nature of the infralittoral substratum proved to be the principal driver of the ichthyofaunal community. By analysing separately the two infralittoral substrata considered in the study, we observed how HF might affect the associated fish community differently. A pristine vermetid reef seems to sustain a higher number of FGs when established on a rocky substratum. On the other hand, in the presence of a sandy substratum, a fragmented vermetid reef seems to attract a more functionally rich fish community than those accounted for a pristine status. Our results provide some evidence in support of the need to include a broad spectrum of community function descriptors for a more comprehensive characterisation of a habitat and for the assessment of the functioning of its ecosystem.

Seascape characterization of a Mediterranean vermetid reef: a structural complexity assessment

In the Mediterranean Sea, vermetid reefs can modify coastal seascapes forming platforms in the intertidal zone of rocky coasts. With their three-dimensional and seaward-expanding structure, these bioconstructions support high biodiversity levels and provide important ecological functions and ecosystem services. In this study, we perform a first structural characterization of a vermetid reef seascape (hereafter, vermetid reefscape) and quantitatively assess the degree of their contribution to the structural complexity of the coastal seascape. Aerial images of a vermetid reef coast were acquired in the Marine Protected Area of Capo Gallo-Isola delle Femmine (Southern Tyrrhenian Sea) by means of unmanned aerial vehicle technology. In the seascape, the outer reef, platform, and coast classes were identified and digitized in GIS environment. The resulting vermetid reefscape was analysed by means of FRAGSTATS software using metrics belonging to the “area-edge”, “shape”, and “aggregation” categories. To quantitatively assess the structural complexity, the edge density, area-weighted perimeter area ratio, and landscape shape index metrics were applied to the seascapes with and without the vermetid reefs to simulate a sea level rise scenario. In addition, the effect of their presence in terms of coast length (i.e., total edge) was statistically tested using the Wilcoxon signed rank test. The outer reef had the highest total edge value (5,785.6 m) and, at the same time, the lowest class area (1,040 m2). It was also the patchiest, and the most fragmented and geometrically complex class in the seascape. Overall, the bioconstruction positively contributed to the structural complexity of the seascape with higher values of coastal area (12%), edge density (139%), area-weighted perimeter-area ratio (90%), and landscape shape index (66%). The Wilcoxon test revealed a statistically significant effect of the vermetid reefs presence on the coastal total edge (z = 3.9, p < 0.005), with a large effect size (r = 0.74). The results showed an overall higher structural complexity of the vermetid reefscape, indicating that its loss would lead to a significantly less complex seascape, entailing detrimental effects on the supported biodiversity levels and the valuable ecosystem services provided.

New records of introduced species in the Mediterranean Sea (April 2023)

This Collective article reports 17 introduced species and 22 new locations for these species in the Mediterranean Sea. The reports are from three different Marine Strategy Framework Directive (MSFD) subregions (Aegean-Levantine Sea, Adriatic Sea and Western Mediterranean Sea) and the Sea of Marmara and cover ten different countries. The goal of consistent and detailed reporting of introduced species is to complement the existing species inventories and serve as a basis for establishing monitoring strategies and other conservation measures. Some of the reports from this article are the first species records for the Mediterranean Sea, namely the green alga Udotea flabellum from the Aegean Sea (Turkey) and the deepbody boarfish Antigonia capros from the Balearic Sea (Spain). In addition, new records of introduced species are included for different seas, namely the moon crab Matuta victor for the Aegean Sea (Greece), the whale shark Rhincodon typus and the lionfish Pterois miles for the Alboran Sea (Spain), the almaco jack Seriola rivoliana for the Tyrrhenian Sea (Italy), and the hound needlefish Tylosurus crocodilus for the Adriatic Sea (Italy). Furthermore, reports on first country records are included: the red alga Colaconema codicola from Slovenia, the nudibranch Melibe viridis from Bosnia and Herzegovina, the lionfish Pterois miles from Montenegro, and the goldstripe sardinella Sardinella gibbosa from Syria, which also represents a second record for the Mediterranean Sea. Furthermore, the occurrence of the scleractinian coral Oculina patagonica was noted in Gulf of Lion (France). Four polychaete species, namely Leodice antennata, Timarete punctata and Branchiomma bairdi, are reported from the vermetid reef habitat and two of them (L. antennata and B. bairdi) are also recorded for the first time in Lebanon. Evidence for established populations of the Asian date mussel Arcuatula senhousia in the Sea of Marmara (Turkey) and the rayed pearl oyster Pinctada radiata around the island of Sardinia (Italy) is provided.

Signals of loss: Local collapse of neglected vermetid reefs in the western Mediterranean Sea

During the summer of 2022, an extensive die-off of Dendropoma cristatum and other marine organisms associated with vermetid reefs was observed in the western Mediterranean Sea (northern coast of Sicily). Quantitative data from more than 300 km of coastal stripe indicated that the percentage of dead D. cristatum specimens, showing empty and/or transversely fractured shells, ranged from 64 to 84 % in populations having a density of 2900–4730 ind./m2, suggesting that millions of organisms had recently died along the Sicilian coast. This high mortality range coincided with prolonged desiccation events during which biogenic vermetid reefs were exposed to extreme warm-air conditions for several consecutive days. This warning report about neglected shallow vermetid reefs raises concern regarding the loss of Mediterranean biodiversity, underlining the need to develop and implement monitoring and conservation efforts on a basin-wide scale.

Bridging the knowledge gap on the distribution and typology of vermetid bioconstructions along the Maltese coastline: an updated assessment

In the Maltese Islands, insufficient attention has been paid to vermetid reefs, endemic Mediterranean bioconstructions widely distributed along the southern part of the basin. As a result, this is a largely-overlooked coastal ecosystem despite the multitude ofecosystem services it provides. The perennial urban development in the Maltese Islands calls for the adoption of urgent action to protect coastal habitats, in particular bioconstructions that increase biodiversity and contribute to mitigating the effects of climatechange. The objective of our study was to extensively document the presence and typology of the vermetid reef ecosystems alongthe coast of Malta and Gozo, assessing the occurrence of putative anthropogenic threats on the same ecosystem. Quantitative measurements were additionally taken to morphologically characterize the recorded bioconstructions. Furthermore, we tested thehuman pressure effect on the density of vermetid individuals and associated biodiversity. “True” trottoirs were only documentedalong the south-east coast of Malta, where unfortunately land reclamation projects are expected to be implemented. Although no direct relation between a number of assessed human activities and the density of vermetid individuals was reported in the current study, we suggest the conduction of further studies to investigate the influence of specific disturbances on the conservation status of this ecosystem. This study expands the existing knowledge on the status of vermetid reefs in the Maltese Islands and calls for management and conservation actions to preserve this bioconstruction.

The neglected status of the vermetid reefs in the Mediterranean Sea: A systematic map

• The research on Mediterranean marine habitats is unequally driven by European directives and laws. • A neglected habitat definition is provided. • Bibliometric analyses are used to define the neglected status of habitats. • In the Mediterranean Sea, coralligenous formations are mostly studied. • On the contrary, vermetid reefs can be defined as a neglected habitat. Studied since late 1800, vermetid reefs are marine bioconstructions of well-acknowledged importance in the Mediterranean Sea. Despite their persistence being jeopardized in the whole basin, recent studies have referred to this bioconstruction as a neglected habitat. In this study, we assessed the neglected status of the Mediterranean vermetid reefs in the scientific literature producing a systematic map through a multi-method bibliometric protocol. Scopus and Web of Science databases were jointly used for data collection. Vermetid reefs publication rate (i.e., number of publications per year) was investigated compared to the other Mediterranean bioconstructions using ANOVA analysis and Zero-Inflated Poisson regression. Later, VOSviewer software was used to perform a bibliometric network analysis and for mapping visualization. The analysis aimed at investigating gaps, patterns, and trends of the vermetid reefs together with the other main Mediterranean bioconstructions (i.e., Astroides calycularis , Cladocora caespitosa and coralligenous formations, and sabellariid and Lithophyllum reefs). The ANOVA analysis of the number of publications from 1966 to 2020 found statistically significant differences between coralligenous and vermetid reefs publication rates in the 2006–2010, 2011–2015, and 2016–2020 timeframes and pointed out a clear before/after-2010 pattern in coralligenous publication rate, which was also confirmed by the Zero-Inflated Poisson regression model. The bibliometric network analysis of the bioconstructions literature revealed the same temporal pattern, with the vermetid reefs poorly investigated and weakly connected to newer research lines and conservation topics. Instead, coralligenous showed strong connections with biodiversity conservation and was indicated as a recent research hotspot. Overall, the results of this study confirm previous references of the vermetid reefs as a neglected habitat and, among others, show an increasing research interest in the coralligenous topic.

Implementation of artificial substrates for Dendropoma cristatum (Biondi 1859) reef restoration: Testing different materials and topographic designs.

Vermetid reefs are intertidal key habitats that strongly increase the biological and ecological value of the coastal ecosystems, providing ecological goods and services. In some parts of the Mediterranean Sea, this habitat is experiencing an increasing decline, due to environmental and anthropogenic pressures and the lack of officially coordinated strategies promoting its conservation at the basin scale.Moreover, experimental data testing for vermetid reef restoration is presently scant. Here we tested the potential to achieve new vermetid colonies on engineered substrates, aiming for their further transplantation to depleted reefs for restoration purposes. We investigated in the field the settlement rate of the central-Mediterranean vermetid species Dendropoma cristatum on artificial tiles made of different concrete mixtures (geopolymer concrete, pozzolanic concrete mixed with fine sand, magnesian concrete, pozzolanic concrete mixed with magnesium and coarse sand) and one plastic material (expanded polyvinyl chloride), engineered with a range of interstice shapes and sizes (i.e., holes and crevices of 1 and 2 mm), obtaining on each tile four different topographic designs. Also, the benthic fauna colonization on these engineered tiles has been monitored.While the material typology had a relative effect on the settlement of D. cristatum, the presence of specific topographic designs played an important role, not only for the reef-builder species but also for the benthic fauna. A significantly higher vermetid density and invertebrate taxonomic richness and individual abundance were associated with the hole presence on the tiles, confirming to be the preferred interstice type among those texted. Furthermore, geopolymer concrete was the material that showed higher resistance to the intertidal conditions and durability after the experiment.The production of geopolymer tiles engineered with hole interstices may be a valid option for future studies aiming at the restoration of this intertidal key habitat. However, while our achievements correspond to a higher vermetid and benthic invertebrate settlement within a few weeks of field experiment, post-settlement processes need to be considered in the perspective to restore the functionality of a degraded reef.

The buffer effect of canopy-forming algae on vermetid reefs' functioning: A multiple stressor case study

Biodiversity plays a key role for our planet by buffering ongoing and future changes in environmental conditions. We tested if canopy-forming algae enhancing biodiversity (CEB) in a Mediterranean intertidal reef ecological community could alleviate the effect of stressors (heat waves and pollution from sewage) on community metabolic rates (as expressed by oxygen consumption) used as a proxy of community functioning. CEB exerted a buffering effect related to the properties of stressor: physical-pulsing (heat wave) and chronic-trophic (sewage). After a simulated heat wave, CEB was effective in buffering the impacts of detrimental temperatures on the functioning of the community. In reefs exposed to chronic sewage effluents, benefits derived from CEB were less evident, which is likely due to the stressor's contextual action. The results support the hypothesis that ecological responses depend on stressor typology acting at local level and provide insights for improving management measures to mitigate anthropogenic disturbance.

The Microbiome Associated with the Reef Builder Neogoniolithon sp. in the Eastern Mediterranean.

The development of coastal vermetid reefs and rocky shores depends on the activity of several reef builders, including red crustose coralline algae (CCA) such as Neogoniolithon sp. To initiate studies on the interaction between Neogoniolithon sp. and its associated bacteria, and their impact on the algae physiological performance, we characterized the bacterial community by 16S rRNA gene sequencing. These were extracted from the algal tissue and adjacent waters along two sampling campaigns (during winter and spring), in three study regions along a reef in the east Mediterranean Israeli coast and from laboratory-grown algae. The analysis revealed that aquaria and field communities differ substantially, suggesting that future research on Neogoniolithon sp. interaction with its microbiome must rest on aquaria that closely simulate coastal conditions. Some prokaryote classes found associated with the alga tissue were hardly detected or absent from surrounding water. Further, bacterial populations differed between sampling campaigns. One example is the presence of anaerobic bacteria and archaea families in one of the campaigns, correlating with the weaker turbulence in the spring season, probably leading to the development of local anoxic conditions. A better understanding of reef-building activity of CCA and their associated bacteria is necessary for assessment of their resilience to climate change and may support coastal preservation efforts.

Sea level rise can severely reduce biodiversity and community net production on rocky shores

Sea level rise (SLR), driven by anthropogenic climate change, can be a major threat to coastal ecosystems. Among the most biologically diverse but SLR-threatened coastal ecosystems are rocky shores, especially in regions with a small tidal range. Nonetheless, the impacts of SLR on rocky shore biodiversity, community structure and ecosystem functions have rarely been studied. Here, we use the biogenic intertidal ecosystem, Mediterranean vermetid reefs on the Israeli coast, as case study for testing the potential impact of SLR on reef communities, with surveys, 3D topographic mapping plus SLR simulations, and a manipulative community translocation experiment. We show that: (1) biodiversity is much lower on very shallow, permanently submerged, horizontal rocky surfaces compared to that on intertidal reef platforms, (2) the extensive intertidal platforms will permanently drown under even modest SLR scenarios, (3) the rich intertidal community will transform, when permanently submerged, either to a very different but still rich community when protected from grazing by highly abundant invasive fish (rabbitfish), or to a much poorer turf community when exposed to such fish grazing, and (4) the reef community net production will drastically drop under permanent submersion. Because the main ecosystem engineer of the vermetid reefs, Dendropoma anguliferum (Monterosato, 1878), is nearly extinct in the southeast Levant, it is unlikely that new reefs will be formed higher on the shore in the future, presumably resulting in extensive coastal ecological shifts. Considerable coastal community shifts are forecasted for many regions globally due to SLR, as many shorelines are predicted to suffer from “coastal squeeze”. Hence, similar manipulative experiments are encouraged in other regions to test for generality vs. context dependency in SLR ecological impacts. We suggest that in cases where essential/unique intertidal habitats like vermetid reefs are expected to vanish by SLR, constructing carefully-planned, ecologically friendly, artificial alternatives should be considered.

An investigation of vermetid reefs from the Miocene of Peru, with the description of a new species

Exquisitely preserved fossils of a new reef-building vermetid species from shallow-marine lower Miocene (Burdigalian) deposits of the Chilcatay Formation and upper Miocene (Tortonian) sediments of the Pisco Formation of Peru are here reported and described in detail for the first time. These finds are assigned to the living genus Thylacodes and recognized as representatives of a new species, Thylacodes devriesi sp. nov. This new taxon is known by long, almost straight tube-like shells that display peculiar ornamentations in form of striated lamellae and are arranged in an organ-pipe fashion. This discovery represents an important addition to the knowledge of the systematics and distribution of Thylacodes in South America in the geological past. Paleoenvironmental and taphonomic inferences drawn by the fossil remains of this reef-forming species are herein discussed for both the Chilcatay and Pisco Formations in the broader framework of the South American fossil record of Vermetidae.

Invasive alien species in Mediterranean Marine Protected Areas: the Egadi Islands (Italy) case study

ABSTRACT Invasive alien species (IAS) are one of the most severe threats to Mediterranean Sea biodiversity. Currently, the effectiveness of Marine Protected Areas (MPAs) in providing protection for marine biodiversity from IAS is still not fully understood. Here, we analysed eight Mediterranean MPAs located in a strategic geographic position within the Mediterranean basin. All the analysed MPAs were affected by the presence of IAS - evidence of the vulnerability of MPAs to biological invasion. Valuable habitats such as vermetid reef and coralligenous formations have become victim to numerous alien species. Alien species populations are likely to continue increasing in the Mediterranean Sea, so implementing appropriate and effective policies and management action is urgently required within MPAs for the effective control of biological invasions. A collaboration between researchers, policy makers and citizens is essential in order to ensure management strategies are effective and long-lasting.

Unmanned aerial vehicle technology to assess the state of threatened biogenic formations: The vermetid reefs of mediterranean intertidal rocky coasts

Vermetid bioconstructions are biogenic formations, built by sessile gastropod molluscs belonging to the family Vermetidae worldwide distributed, occurring in the intertidal and upper subtidal in the rocky shores. In the Mediterranean basin, they occur in complex and tridimensional structures that enhance the local biodiversity, allowing to qualify the structuring species as ecosystem engineers. Due to their ecological relevance and considerable extension along the coasts, we assessed their structural complexity using unmanned aerial vehicle (UAV) technology, as tool of littoral cartography analysis of these bioconstructions, and plaster hemispheres dissolution as a descriptor index of the water movement on them. We adopted an UAV to produce a very high spatial resolution map along 830m of rocky coast where these vermetid gastropods occur. Through an orthophoto with a GSD (Ground Sample Distance) of 1 cm, different complexity values of indentation degree (or roughness profiles) of the reef boundaries were detected, corroborating literature data carried out with traditional measurement techniques (e.g., tape measure). Our results indicate that the most complex zone of reef is the outer edge, facing the open sea, with a decreasing trend toward the inner edge. Concerning the experimental approach conducted using plaster hemispheres placed along the platform, it reveals that water movement is a structuring factor of the vermetid reef complexity along the rocky coast. Overall, the application of UAV technique allows an appropriate approach to analyze different zones of the vermetid reefs with a high-accuracy on a large spatial scale, greatly reducing sampling effort, and generating important implications for future monitoring and conservation programs.

Assessing vermetid reefs as indicators of past sea levels in the Mediterranean

The endemic Mediterranean reef building vermetid gastropods Dendropoma petraeum complex (Dendropoma spp) and Vermetus triquetrus develop bio-constructions (rims) on rocky shorelines at about Mean Sea Level (MSL) and are therefore commonly used as relative sea-level (RSL) markers. In this study, we use elevations and age data of vermetid reefs to (1) re-assess the vertical uncertainties of these biological RSL indicators, and (2) evaluate the vertical growth rates along a Mediterranean east-west transect, in attempt to explain the differences found in both growth rates and uncertainties. In Israel, Differential Global Positioning System (DGPS) and laser measurements relative to the local datum show that the reef surfaces mainly occupy the upper intertidal zone with variations in elevation from +0.51 ± 0.07 m to +0.13 ± 0.05 m along the coast. However, in specific sites the vertical uncertainty exceeds the tidal range. In some places the local vermetid species D. anguliferum and V. triquetrus appear to alternate along the vertical rim profiles. This study documents a spatial variability of vertical growth rates, ranging from ~1 mm yr−1 in Israel and Crete, to ~0.1–0.2 mm yr−1 in NW Sicily and Spain. The order of magnitude of the difference in growth rates correlates with the east-west spatial thermal gradient of Sea-Surface Temperature (SST). Preferential skeleton deposition of D. petraeum and V. triquetrus measured by growth axis δ18O analysis shows that most calcification occurs at SST above the mean annual value. These findings indicate that vermetid reefs are a site-specific RSL indicator, displaying various vertical uncertainties and inner-structure complexities. Local data on the indicative range of vermetids are required when reconstructing relative sea-level changes using fossil vermetids.

Community dynamics and ecological shifts on Mediterranean vermetid reefs

Mediterranean coastal ecosystems experience many local and global stressors and require long-term monitoring to detect and follow trends in community structure. Between 2009 and 2017, we seasonally and annually monitored the spatiotemporal community dynamics at 11 sites on the rocky shores of the southeastern Mediterranean, focusing on the understudied intertidal vermetid reef ecosystem. Marked seasonal trends were found in biodiversity, with the highest diversity in winter and spring. Canopy-forming brown algae, dominating the northwestern Mediterranean intertidal reefs, were generally scarce on the reef platform and almost only found in tidepools. Interannual shifts in community structure were driven mostly by sharp fluctuations in a few dominant native and alien species and the regional mass mortality of an Indo-Pacific mussel in summer 2016. Compared to an older macroalgae dataset, dating back to 1973–1995, we found that some warm-affinity (summer) taxa became more dominant and cold-affinity (winter) species less dominant, while one once conspicuous species, Halimeda tuna, completely disappeared. The observed community shifts are probably driven mostly by stressors related to climate change. We encourage forming a network of long-term, multi-site ecological monitoring programs in the Mediterranean to improve our understanding of ecosystem change and to enable making better predictions at the basin scale.

Ocean acidification and elevated temperature negatively affect recruitment, oxygen consumption and calcification of the reef-building Dendropoma cristatum early life stages: Evidence from a manipulative field study.

Expected temperature rise and seawater pH decrease may affect marine organism fitness. By a transplant experiment involving air-temperature manipulation along a natural CO2 gradient, we investigated the effects of high pCO2 (~1100 μatm) and elevated temperature (up to +2 °C than ambient conditions) on the reproductive success, recruitment, growth, shell chemical composition and oxygen consumption of the early life stages of the intertidal reef-building vermetid Dendropoma cristatum. Reproductive success was predominantly affected by temperature increase, with encapsulated embryos exhibiting higher survival in control than elevated temperature conditions, which were in turn unaffected by altered seawater pH levels. Decreasing pH (alone or in combination with temperature) significantly affected the shell growth and shell chemical composition of both embryos and recruits. Elevated temperatures along with lower pH led to decreases of ~30% oxygen consumption and ~60% recruitment. Our results suggest that the early life stages of the reef-builder D. cristatum are highly sensitive to expected environmental change, with major consequences on the intertidal vermetid reefs they build and indirectly on the high biodiversity levels they support.

Biogenic habitat shifts under long-term ocean acidification show nonlinear community responses and unbalanced functions of associated invertebrates

Experiments have shown that increasing dissolved CO2 concentrations (i.e. Ocean Acidification, OA) in marine ecosystems may act as nutrient for primary producers (e.g. fleshy algae) or a stressor for calcifying species (e.g., coralline algae, corals, molluscs). For the first time, rapid habitat dominance shifts and altered competitive replacement from a reef-forming to a non-reef-forming biogenic habitat were documented over one-year exposure to low pH/high CO2 through a transplant experiment off Vulcano Island CO2 seeps (NE Sicily, Italy). Ocean acidification decreased vermetid reefs complexity via a reduction in the reef-building species density, boosted canopy macroalgae and led to changes in composition, structure and functional diversity of the associated benthic assemblages. OA effects on invertebrate richness and abundance were nonlinear, being maximal at intermediate complexity levels of vermetid reefs and canopy forming algae. Abundance of higher order consumers (e.g. carnivores, suspension feeders) decreased under elevated CO2 levels. Herbivores were non-linearly related to OA conditions, with increasing competitive release only of minor intertidal grazers (e.g. amphipods) under elevated CO2 levels.Our results support the dual role of CO2 (as a stressor and as a resource) in disrupting the state of rocky shore communities, and raise specific concerns about the future of intertidal reef ecosystem under increasing CO2 emissions. We contribute to inform predictions of the complex and nonlinear community effects of OA on biogenic habitats, but at the same time encourage the use of multiple natural CO2 gradients in providing quantitative data on changing community responses to long-term CO2 exposure.

Threatened biogenic formations of the Mediterranean: Current status and assessment of the vermetid reefs along the Lebanese coastline (Levant basin)

Vermetid reefs are a key intertidal habitat in the warm-temperate part of the Mediterranean Sea and in some subtropical and tropical regions in the Atlantic and Pacific oceans. This unique and highly diverse ecosystems is under siege due to both the high anthropogenic pressure and the global climate change, with documented local population declines in the Eastern Mediterranean. This study aims at evaluating the conservation state of vermetid reefs along the Lebanese coast (Eastern Mediterranean), where seawater warming, habitat degradation and coastal urbanization likely threaten their presence. In order to assess the conservation status of vermetid reefs in Lebanon, five sites were randomly selected among those belonging to three impact classes: i) not impacted (i.e. protected), ii) moderately impacted, and iii) impacted. Two different non-destructive methods were applied to assess the presence of living vermetids Dendropoma anguliferum (Monterosato, 1878) and Vermetus triquetrus (Bivona-Bernardi, 1832) which shape the reef, and the associated communities. Our results highlight that no living vermetid reefs were recorded in the impacted sites where evident signs of bio-physical erosion of the reef are already underway. Living individuals of Vermetus triquetrus were found in some not impacted and moderately impacted sites, while living individuals of the endemic reef-builder Dendropoma anguliferum were found only at very low densities at the not impacted (protected) site. Such findings corroborate preliminary observations of population decline in the Eastern Mediterranean, and of vermetid reefs vulnerability to human disturbances. This raises concerns about the near future persistence of vermetid reefs in the region, and represents a call for management and conservation actions to preserve this reef-building species in the Mediterranean Sea.