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In search of relevant predictors for marine species distribution modelling using the MarineSPEED benchmark dataset
Get PDFAim: Ideally, datasets for species distribution modelling (SDM) contain evenly sampled records covering the entire distribution of the species, confirmed absences and auxiliary ecophysiological data allowing informed decisions on relevant predictors. Unfortunately, these criteria are rarely met for marine organisms for which distributions are too often only scantly characterized and absences generally not recorded. Here, we investigate predictor relevance as a function of modelling algorithms and settings for a global dataset of marine species.Location: Global marine.Methods: We selected well-studied and identifiable species from all major marine taxonomic groups. Distribution records were compiled from public sources (e.g., OBIS, GBIF, Reef Life Survey) and linked to environmental data from Bio-ORACLE and MARSPEC. Using this dataset, predictor relevance was analysed under different variations of modelling algorithms, numbers of predictor variables, cross-validation strategies, sampling bias mitigation methods, evaluation methods and ranking methods. SDMs for all combinations of predictors from eight correlation groups were fitted and ranked, from which the top five predictors were selected as the most relevant. Results: We collected two million distribution records from 514 species across 18 phyla. Mean sea surface temperature and calcite are, respectively, the most relevant and irrelevant predictors. A less clear pattern was derived from the other predictors. The biggest differences in predictor relevance were induced by varying the number of predictors, the modelling algorithm and the sample selection bias correction. The distribution data and associated environmental data are made available through the R package marinespeed and at http://marinespeed.org.Main conclusions: While temperature is a relevant predictor of global marine species distributions, considerable variation in predictor relevance is linked to the SDM set-up. We promote the usage of a standardized benchmark dataset (MarineSPEED) for methodological SDM studies
Kan Vlaanderen het tij nog keren voor de Europese paling? Effecten van tien jaar Europese bescherming op het voortbestaan van de Paling in Vlaanderen
Get PDFDespite the many restoration measures launched to prevent the Eelfrom further decline, glass eel recruitment and yellow eel density remain troublesome. Eel life is challenging in Flemish waters, where migration routes are blocked by barriers, where unnatural banks and toxic substances hamper growth and reproductive capacity and where pumping stations abruptly end many Eels’ lives. In spite of high levels of pollutants in its meat, Eels still end up on anglers plates (ca. 30 tons/year). Urgent actions are needed to increase the amount of easily accessible high-quality watercourses with more natural flow dynamics. As long as the tides are not turned, a more vigorous European policy on the restriction of the Eel fishery (including elvers) seems indispensable
Omschrijving van goede milieutoestand & vaststelling van milieudoelen voor de Belgische mariene wateren. Kaderrichtlijn Mariene Strategie – Art 9 & 10
Get PDFLocal effects of large food-falls on nematode diversity at an arctic deep-sea site: results from an <i>in situ</i> experiment at the deep-sea observatory HAUSGARTEN
Get PDFTo study the response of the smaller benthic biota to larger food-falls and their possible effects on the biodiversity at the deep seafloor, we deployed the halves of a sagittally bisected porpoise (1.3 m in length: each half approximately 18 kg) at 2500 m and 5400 m water depth at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in the eastem Fram Strait. Five weeks after the porpoise deployment, sediments beneath the carcasses and at different distances (0, 20, 40 cm) from these artificial food-falls were sampled with push-corers handled by a Remotely Operated Vehicle. The samples provided empirical evidence for a quick response by sediment-inhabiting bacteria and metazoan meiofauna to the carcasses at both water depths. Compared to control sediments, the substantial pulse of organic matter also led to generally increased meiofauna/nematode densities around the artificial food-falls. The comparison of nematode communities in sediments affected by the carcasses with those in control sediments exhibited shifts in the structural composition and the associated trophic and functional diversity of the nematodes. Our results confirmed that the impact of large food-falls on the deep benthic community largely depend on environmental factors (water depth, alternative food sources) as well as the background species composition, i.e., the structure of the prevailing meiofauna/nematode assemblages and the composition of the necrophagous community present in the wider area
Groundwater overexploitation and seawater intrusion in coastal areas of arid and semi-arid regions
Get PDFThe exploitation of groundwater resources is of high importance and has become very crucial in the last decades, especially in coastal areas of arid and semi-arid regions. The coastal aquifers in these regions are particularly at risk due to intrusion of salty marine water. One example is the case of Tripoli city at the Mediterranean coast of Jifarah Plain, North West Libya. Libya has experienced progressive seawater intrusion in the coastal aquifers since the 1930s because of its ever increasing water demand from underground water resources. Tripoli city is a typical area where the contamination of the aquifer in the form of saltwater intrusion is very developed. Sixty-four groundwater samples were collected from the study area and analyzed for certain parameters that indicate salinization and pollution of the aquifer. The results demonstrate high values of the parameters Electrical Conductivity, Na+, K+, Mg2+, Cl− and SO42−, which can be attributed to seawater intrusion, where Cl− is the major pollutant of the aquifer. The water types according to the Stuyfzand groundwater classification are mostly CaCl, NaCl and Ca/MgMix. These water types indicate that groundwater chemistry is changed by cation exchange reactions during the mixing process between freshwater and seawater. The intensive extraction of groundwater from the aquifer reduces freshwater outflow to the sea, creates drawdown cones and lowering of the water table to as much as 25 m below mean sea level. Irrigation with nitrogen fertilizers and domestic sewage and movement of contaminants in areas of high hydraulic gradients within the drawdown cones probably are responsible for the high NO3− concentration in the region
Understanding processes at the origin of species flocks with a focus on the marine Antarctic fauna
Get PDFSpecies flocks (SFs) fascinate evolutionary biologists who wonder whether such striking diversification can be driven by normal evolutionary processes. Multiple definitions of SFs have hindered the study of their origins. Previous studies identified a monophyletic taxon as a SF if it displays high speciosity in an area in which it is endemic (criterion 1), high ecological diversity among species (criterion 2), and if it dominates the habitat in terms of biomass (criterion 3); we used these criteria in our analyses. Our starting hypothesis is that normal evolutionary processes may provide a sufficient explanation for most SFs. We thus clearly separate each criterion and identify which biological (intrinsic) and environmental (extrinsic) traits are most favourable to their realization. The first part focuses on evolutionary processes. We highlight that some popular putative causes of SFs, such as key innovations or ecological speciation, are neither necessary nor sufficient to fulfill some or all of the three criteria. Initial differentiation mechanisms are diverse and difficult to identify a posteriori because a primary differentiation of one type (genetic, ecological or geographical) often promotes other types of differentiation. Furthermore, the criteria are not independent: positive feedbacks between speciosity and ecological diversity among species are expected whatever the initial cause of differentiation, and ecological diversity should enhance habitat dominance at the clade level. We then identify intrinsic and extrinsic factors that favour each criterion. Low dispersal emerges as a convincing driver of speciosity. Except for a genomic architecture favouring ecological speciation, for which assessment is difficult, high effective population sizes are the single intrinsic factor that directly enhances speciosity, ecological diversity and habitat dominance. No extrinsic factor appeared to enhance all criteria simultaneously but a combination of factors (insularity, fragmentation and environmental stability) may favour the three criteria, although the effect is indirect for habitat dominance. We then apply this analytical framework to Antarctic marine environments by analysing data from 18 speciose clades belonging to echinoderms (five unrelated clades), notothenioid fishes (five clades) and peracarid crustaceans (eight clades). Antarctic shelf environments and history appear favourable to endemicity and speciosity, but not to ecological specialization. Two main patterns are distinguished among taxa. (i) In echinoderms, many brooding, species-rich and endemic clades are reported, but without remarkable ecological diversity or habitat dominance. In these taxa, loss of the larval stage is probably a consequence of past Antarctic environmental factors, and brooding is suggested to be responsible for enhanced allopatric speciation (via dispersal limitation). (ii) In notothenioids and peracarids, many clades fulfill all three SF criteria. This could result from unusual features in fish and crustaceans: chromosome instability and key innovations (antifreeze proteins) in notothenioids, ecological opportunity in peracarids, and a genomic architecture favouring ecological speciation in both groups. Therefore, the data do not support our starting point that normal evolutionary factors or processes drive SFs because in these two groups uncommon intrinsic features or ecological opportunity provide the best explanation. The utility of the three-criterion SF concept is therefore questioned and guidelines are given for future studies
Description of the skeleton of the fossil beaked whale <i>Messapicetus gregarius</i>: searching potential proxies for deep-diving abilities
Get PDFZiphiidae (beaked whales) are a successful family of medium- to large-sized toothed whales. Their extant members perform regular deep dives beyond the photic zone to forage for cephalopods and fish. Conversely, extinct long-snouted stem ziphiids are interpreted as epipelagic predators. However, some aspects of this hypothesis remain unclear due to the lack of clear morphological proxies for recognizing regular deep divers. We compared the forelimb, neck, and pterygoid sinus system of the fossil ziphiid Messapicetus gregarius with those of other odontocetes to evaluate the potential of these body regions as proxies to assess deep-diving specialization. The reconstructed musculature of the neck and forelimb of M. gregarius was also compared with that of other odontocetes. We also quantified variation in the proportions of the forelimb and the hamular fossa of the pterygoid sinus (HF) using 16 linear measurements. The degree of association between diving behaviour in extant odontocetes and these measurements was evaluated with and without phylogenetic correction. Reconstruction of the neck musculature suggests that M. gregarius possessed a neck more flexible than most extant ziphiids due to the lower degree of fusion of the cervical vertebrae and the large insertions for the M. longus colli and Mm. intertransversarii ventrales cervicis. While neck rigidity might be related to deep diving, differences in neck flexibility among extant ziphiids indicate a more complex functional interpretation. The relationship between forelimb morphology and diving behaviour was not significant, both with and without phylogenetic correction, suggesting that it cannot be used to assess deep-diving abilities with the parameters considered here. Measurements of the HF revealed successful to evaluate deep-diving abilities in odontocetes, with an enlargement of this structure in deep divers. Considering other evidence that suggests an epipelagic behaviour, we propose different scenarios to explain the observation of an enlarged HF in M. gregarius: (1) this species may have fed at different depths; (2) it performed deep dives to avoid potential predators; or (3) the enlarged HF and deep-diving habitat correspond to an ancestral condition, with M. gregarius returning to a more epipelagic habitat
Quantifying climate feedbacks in polar regions
Get PDFThe concept of feedback is key in assessing whether a perturbation to a system is amplified or damped by mechanisms internal to the system. In polar regions, climate dynamics are controlled by both radiative and non-radiative interactions between the atmosphere, ocean, sea ice, ice sheets and land surfaces. Precisely quantifying polar feedbacks is required for a process-oriented evaluation of climate models, a clear understanding of the processes responsible for polar climate changes, and a reduction in uncertainty associated with model projections. This quantification can be performed using a simple and consistent approach that is valid for a wide range of feedbacks, offering the opportunity for more systematic feedback analyses and a better understanding of polar climate changes
Impact of farming non-indigenous scallop <i>Argopecten irradians</i> on benthic ecosystem functioning: a case-study in Laizhou Bay, China
Get PDFThe farming of the non-indigenous bay scallop Argopecten irradians in coastal waters generates large amounts of biodeposits that potentially change the trophic pathways and quality of the benthic food web at lower trophic levels such as meiobenthos. To understand the trophic link between faecal pellets of bay scallop and meiobenthos in the aquaculture area, we investigated the resource use of harpacticoid copepods and nematodes inside and outside of 3 bay scallop farms in Laizhou Bay (Bohai Sea, China) using natural abundance of stable carbon and nitrogen isotopes together with fatty acid profiling. Faeces were found to be enriched in δ15N compared to all other food sources, which made faecal matter traceable. The enriched δ15N in several meiobenthos at the farms, together with the mixing model results, indicated that faeces could be a new food source for most of harpacticoid copepods and some nematodes. The quantities and the pathways of assimilation differed between the copepod families, depending on their feeding behaviors and the receiving environment. Furthermore, due to the presence of higher levels of polyunsaturated fatty acids, in particular docosahexaenoic acid, the dominant copepod family Canuellidae that abundantly consumed scallop faeces showed enhanced nutritional quality compared with those in the control sites. Thus, aquaculture of non-indigenous bay scallops provided a food source that was directly and indirectly consumed by meiobenthos underneath the scallop farms and improved the quality of lower level consumers as a food item in the benthic food web