The eastern Mediterranean marine ecosystem is undergoing massive modification due to biological invasions, overfishing, habitat deterioration, and climate warming. Our ability to quantify these ...changes is severely hindered by the lack of an appropriate baseline; most ecological datasets date back a few decades only and show already strong signatures of impact. Surficial death assemblages (DAs) offer an alternative data source that provides baseline information on community structure and composition. In this study, we reconstruct the marine fish fauna of the southern shallow Israeli shelf before the opening of the Suez Canal based on fish otoliths. We quantify the age of the otolith DAs by radiocarbon dating, and describe its taxonomic composition, geographic affinity, and trophic structure. Additionally, we test by radiocarbon dating the hypothesis that Bregmaceros, a presumed Lessepsian invader with continuous presence in the Mediterranean throughout the late Cenozoic, is a relict species. The otolith DA dates back to the mid-Holocene because 75% of the dated otoliths of the native species are older than the opening of the Suez Canal in 1869, suggesting that the DA is a proper baseline for quantifying modern impacts. Consistently, 97% of the otoliths and 88% of the species we collected belong to native Mediterranean species. The native anchovy Engraulis encrasicolus dominates the DAs, although gobiids are the most diverse group (14 species, 28%). The DAs show similar trophic structure to present-day pristine Mediterranean coastal fish assemblages. Two non-indigenous species are recorded here for the first time in the Mediterranean Sea, Amblygobius albimaculatus and Callogobius sp., highlighting the importance of DAs for detecting non-indigenous species. Finally, Bregmaceros otoliths are modern, not supporting the previous hypothesis that the taxon is a Pleistocene relict.
Managing invasive alien species is particularly challenging in the ocean mainly because marine ecosystems are highly connected across broad spatial scales. Eradication of marine invasive species has ...only been achieved when species were detected early, and management responded rapidly. Generalized approaches, transferable across marine regions, for prioritizing actions to control invasive populations are currently lacking. Here, expert knowledge was elicited to prioritize 11 management actions for controlling 12 model species, distinguished by differences in dispersion capacity, distribution in the area to be managed, and taxonomic identity. Each action was assessed using five criteria (effectiveness, feasibility, acceptability, impacts on native communities, and cost), which were combined in an ‘applicability’ metric. Raising public awareness and encouraging the commercial use of invasive species were highly prioritized, whereas biological control actions were considered the least applicable. Our findings can guide rapid decision-making on prioritizing management options for the control of invasive species especially at early stages of invasion, when reducing managers' response time is critical.
Display omitted
•None of the actions was considered ideal for the management of invasive species.•Public awareness and commercial use of invasive species were highly prioritized.•Biological control actions were considered the least applicable.•“Doing nothing” ranked high but should be considered with great caution.
The Mediterranean Sea is a marine biodiversity hotspot already affected by climate-driven biodiversity collapses. Its highly endemic fauna is at further risk if global warming triggers an invasion of ...tropical Atlantic species. Here, we combine modern species occurrences with a unique paleorecord from the Last Interglacial (135 to 116 ka), a conservative analog of future climate, to model the future distribution of an exemplary subset of tropical West African mollusks, currently separated from the Mediterranean by cold upwelling off north-west Africa. We show that, already under an intermediate climate scenario (RCP 4.5) by 2050, climatic connectivity along north-west Africa may allow tropical species to colonize a by then largely environmentally suitable Mediterranean. The worst-case scenario RCP 8.5 leads to a fully tropicalized Mediterranean by 2100. The tropical Atlantic invasion will add to the ongoing Indo-Pacific invasion through the Suez Canal, irreversibly transforming the entire Mediterranean into a novel ecosystem unprecedented in human history.
Native biodiversity collapse in the eastern Mediterranean Albano, Paolo G; Steger, Jan; Bošnjak, Marija ...
Proceedings - Royal Society. Biological sciences/Proceedings - Royal Society. Biological Sciences,
01/2021, Letnik:
288, Številka:
1942
Journal Article
Recenzirano
Odprti dostop
Global warming causes the poleward shift of the trailing edges of marine ectotherm species distributions. In the semi-enclosed Mediterranean Sea, continental masses and oceanographic barriers do not ...allow natural connectivity with thermophilic species pools: as trailing edges retreat, a net diversity loss occurs. We quantify this loss on the Israeli shelf, among the warmest areas in the Mediterranean, by comparing current native molluscan richness with the historical one obtained from surficial death assemblages. We recorded only 12% and 5% of historically present native species on shallow subtidal soft and hard substrates, respectively. This is the largest climate-driven regional-scale diversity loss in the oceans documented to date. By contrast, assemblages in the intertidal, more tolerant to climatic extremes, and in the cooler mesophotic zone show approximately 50% of the historical native richness. Importantly, approximately 60% of the recorded shallow subtidal native species do not reach reproductive size, making the shallow shelf a demographic sink. We predict that, as climate warms, this native biodiversity collapse will intensify and expand geographically, counteracted only by Indo-Pacific species entering from the Suez Canal. These assemblages, shaped by climate warming and biological invasions, give rise to a 'novel ecosystem' whose restoration to historical baselines is not achievable.
Aim
The Mediterranean Sea is a hotspot of endemism and it is warming at two to three times the rate of the global ocean. The continental masses that surround it constrain species range shifts. ...Therefore, as seawater temperature increases, distributions of marine species may contract into few small cooler refugia, with consequent risk of extinction from range contraction and fragmentation, particularly for endemics. We assess this risk for 15 molluscs of conservation concern occurring in the Mediterranean Sea. Invertebrates have been rarely assessed so far, despite their diversity and their importance for ecosystem functioning.
Location
The Mediterranean Sea and Eastern Atlantic Ocean.
Methods
We used ensemble species distribution models to project the future range of our target species and assess their IUCN Red List status.
Results
As hypothesized, our models predicted major range shifts, contractions and fragmentation in the Mediterranean Sea for all species. Under moderate emission scenarios such as RCP4.5, up to 12 of the 15 target species will be eradicated from the eastern and southern warmer sectors. Under severe emission scenarios such as RCP8.5 and by the end of the century, we predict the global extinction of the endemic Patella ferruginea and Pinna nobilis. Non‐endemic species may buffer range loss in the Mediterranean with range gains in the Atlantic Ocean. Still, we predict that only a single species, Zonaria pyrum, will have marginal total range gains in future climate warming scenarios.
Main conclusions
Eight species will become threatened and the fate of Patella ferruginea and Pinna nobilis contrasts the belief that marine species are less prone to extinction than continental species under a warming climate.
Native biodiversity loss and invasions by nonindigenous species (NIS) have massively altered ecosystems worldwide, but trajectories of taxonomic and functional reorganization remain poorly understood ...due to the scarcity of long‐term data. Where ecological time series are available, their temporal coverage is often shorter than the history of anthropogenic changes, posing the risk of drawing misleading conclusions on systems' current states and future development. Focusing on the Eastern Mediterranean Sea, a region affected by massive biological invasions and the largest climate change‐driven collapse of native marine biodiversity ever documented, we followed the taxonomic and functional evolution of an emerging “novel ecosystem”, using a unique dataset on shelled mollusks sampled in 2005–2022 on the Israeli shelf. To quantify the alteration of observed assemblages relative to historical times, we also analyzed decades‐ to centuries‐old ecological baselines reconstructed from radiometrically dated death assemblages, time‐averaged accumulations of shells on the seafloor that constitute natural archives of past community states. Against expectations, we found no major loss of native biodiversity in the past two decades, suggesting that its collapse had occurred even earlier than 2005. Instead, assemblage taxonomic and functional richness increased, reflecting the diversification of NIS whose trait structure was, and has remained, different from the native one. The comparison with the death assemblage, however, revealed that modern assemblages are taxonomically and functionally much impoverished compared to historical communities. This implies that NIS did not compensate for the functional loss of native taxa, and that even the most complete observational dataset available for the region represents a shifted baseline that does not reflect the actual magnitude of anthropogenic changes. While highlighting the great value of observational time series, our results call for the integration of multiple information sources on past ecosystem states to better understand patterns of biodiversity loss in the Anthropocene.
Human‐driven extinctions of native species and introductions of nonindigenous ones have significantly modified the world's biota, often already before the onset of scientific monitoring. Focusing on the Eastern Mediterranean Sea, we analyzed an 18‐year‐long dataset on live‐collected mollusks and compared it to historical biodiversity information reconstructed from decades‐ to centuries‐old accumulations of empty shells preserved on the seafloor. We found that the living species assemblage, even at the beginning of monitoring, was already very different from what lived in the region historically. Our results highlight that scientists must combine different sources of information to accurately describe and understand biodiversity changes.
The Eastern Mediterranean Sea hosts more non-indigenous species than any other marine region, yet their impacts on the native biota remain poorly understood. Focusing on mollusks from the Israeli ...rocky intertidal, we explored the hypothesis that this abiotically harsh habitat supports a limited trait diversity, and thus may promote niche overlap and competition between native and non-indigenous species. Indeed, native and non-indigenous assemblage components often had a highly similar trait composition, caused by functionally similar native (Patella caerulea) and non-indigenous (Cellana rota) limpets. Body size of P. caerulea decreased with increasing C. rota prevalence, but not vice versa, indicating potential asymmetric competition. Although both species have coexisted in Israel for >15 years, a rapid ‘replacement’ of native limpets by C. rota has been reported for a thermally polluted site, suggesting that competition and regionally rapid climate-related seawater warming might interact to progressively erode native limpet performance along the Israeli coast.
•Intertidal hard substrate molluscan assemblages had low trait diversity.•Native and non-indigenous assemblage components often were functionally similar.•Limpets were numerically dominant at all sampling sites and drove this similarity.•Native limpet size decreased with increasing prevalence of non-indigenous limpets.•Climate warming and competition may interact to erode native limpet fitness.
Aim
A large body of ecological theory predicts that non‐indigenous species (NIS) are successful invaders if their niches overlap little with native taxa. Native–non‐indigenous trait dissimilarity, ...however, may also be observed if NIS have outcompeted ecologically similar native species. Discriminating these scenarios is essential for assessing invasion impacts but requires baseline assemblage data that are frequently unavailable. We overcome this impediment by analysing death assemblages – identifiable organism remains in the seafloor – which are natural community archives. Focusing on molluscs from the heavily invaded Eastern Mediterranean, we gain insights into the contentious role of competitive displacement by NIS as the primary driver of the massive regional declines of native populations, and their potential to alter ecosystem functioning.
Location
Israel/Eastern Mediterranean.
Time period
Pre‐Lessepsian invasion (pre‐1869) to contemporary.
Major taxa studied
Mollusca.
Methods
We sampled molluscan living and death assemblages from various substrates on the Israeli shelf and compiled trait information on all constituent species. We then compared the abundance‐weighted trait composition and functional diversity of native and non‐indigenous assemblage components. Death assemblage time‐coverage was quantified radiometrically.
Results
Native and non‐indigenous assemblage components consistently differed in trait composition, both in present‐day (i.e., living) and historical (i.e., death) assemblages, irrespective of habitat conditions. Furthermore, present‐day non‐indigenous assemblage components had a different trait composition than historical native assemblages. These findings suggest that the increasing NIS dominance has considerably altered the functional properties of shallow‐water molluscan assemblages.
Main conclusions
By utilizing death assemblages, we show that native and non‐indigenous assemblage components have differed in trait composition since the onset of the invasion, suggesting that competition was unlikely the primary driver of the regional‐scale native biodiversity loss. Our findings, however, also imply that NIS cannot functionally compensate for native species disappearance. Instead, the transition towards increasingly NIS‐dominated assemblages has profoundly altered ecosystem functioning, with unknown consequences.
Marine ecosystems are increasingly threatened by the cumulative effects of multiple human pressures. Cumulative effect assessments (CEAs) are needed to inform environmental policy and guide ...ecosystem-based management. Yet, CEAs are inherently complex and seldom linked to real-world management processes. Therefore we propose entrenching CEAs in a risk management process, comprising the steps of risk identification, risk analysis and risk evaluation. We provide guidance to operationalize a risk-based approach to CEAs by describing for each step guiding principles and desired outcomes, scientific challenges and practical solutions. We reviewed the treatment of uncertainty in CEAs and the contribution of different tools and data sources to the implementation of a risk based approach to CEAs. We show that a risk-based approach to CEAs decreases complexity, allows for the transparent treatment of uncertainty and streamlines the uptake of scientific outcomes into the science-policy interface. Hence, its adoption can help bridging the gap between science and decision-making in ecosystem-based management.
Display omitted
•Cumulative effects assessments (CEAs) are inherently complex and seldom linked to real-world management processes•A risk-based CEA contains risk identification, risk analysis and risk evaluation, revealing the risk of exceeding thresholds•Embedding CEAs in a risk management process reduces complexity, streamlines scientific products, and increases transparency•CEAs can be supported in practice by standardized terminology, procedures and the recent development of integrative methods
Human disturbance modifies selection regimes, depressing native species fitness and enabling the establishment of non-indigenous species with suitable traits. A major impediment to test the effect of ...disturbance on invasion success is the lack of long-term data on the history of invasions. Here, we overcome this problem and reconstruct the effect of disturbance on the invasion of the bivalve
Anadara transversa
from sediment cores in the Adriatic Sea. We show that (1) the onset of major eutrophication in the 1970s shifted communities towards species tolerating hypoxia, and (2)
A. transversa
was introduced in the 1970s but failed to reach reproductive size until the late 1990s because of metal contamination, resulting in an establishment and detection lag of ~25 years. Subfossil assemblages enabled us to (1) disentangle the distinct stages of invasion, (2) quantify time-lags and (3) finely reconstruct the interaction between environmental factors and the invasion process, showing that while disturbance does promote invasions, a synergism of multiple disturbances can shift selection regimes beyond tolerance limits and induce significant time lags in establishment. The quantification of these time lags enabled us to reject the hypothesis that aquaculture was an initial vector of introduction, making shipping the most probable source.
PDF
