In the English Channel, the eastern Bay of Seine is exposed to numerous anthropogenic disturbances, in particular major changes in sediment dynamics, which are expected to greatly impact benthic ...communities. To assess the long-term effects of these stressors on the muddy fine sand benthic community, an original long-term monitoring program has been implemented since 1988. It is based on the sampling of a network of 60 stations during seven surveys over 28 years from 1988 to 2016. We investigate changes of species density, species composition and species diversity at different scales (α-diversity, β-diversity and γ-diversity). Contrary to results obtained in many coastal areas, our results showed a long-term persistence of the community in terms of species composition and structure although a general shift towards muddy sediment has resulted in increased colonisation by species associated with muddy habitats and a decrease in spatial beta diversity.
•The community structure was highly persistent over the last three decades.•Silting-up promoted changes in species composition and a decrease in β-diversity.•Community stability differed according to the scale of observation.•There is a need to implement a sampling strategy combining different scales.
Abstract
Species ranges are shifting globally to track temperature changes in response to climate warming, with substantial variability among taxa. In the English Channel, a biogeographical ...transition zone between the cold temperate and warm temperate provinces of the North-East Atlantic, distribution shifts have been relatively well documented for plankton, fish and intertidal benthic organisms, but little information is available on sublittoral benthos. Following a description of the magnitude of the sea bottom temperature (SBT) rise, the changes in the distribution and occupancy of 65 benthic invertebrate species were analysed by comparing data collected throughout the English Channel at more than 200 stations sampled during a cool period in the 1960s–1970s and at present in 2012–2014. A non-uniform rise in SBT for the last three decades was observed at the regional scale, varying from 0.07 to 0.54°C per decade. This rise differs from that reported for sea surface temperature (SST) in stratified areas suggesting that SBT should be used rather than SST to analyse responses of subtidal organisms to climate change. Despite shifts in both minimum and maximum sea bottom isotherms (2.5 and 3.2 km.year−1, respectively), the distribution centroid shift of most species remained <1.0 km.year−1, regardless of the average temperatures they usually experience. Conversely, decreases were observed in the occurrence of most cold-water species and increases were found in the occurrence of most warm-water species. These results suggest that ongoing climate change could lead to a decrease in benthic biodiversity at range limits, especially where connection routes are lacking for new migrants.
The reproductive cycle of Diopatra marocensis Paxton et al., 1995 has been studied in a population from Ria de Aveiro, Western Portugal with monthly samples, during a two-year period. This species ...presents a direct development with brooding in the parental tube and specimens with gametes inside the coelom and female tubes with eggs and/or larvae were observed in every sampling month. This suggested that the species reproduces during the whole year, with the main reproductive period from April to September. The male:female sex ratio ranged from 1:2 to 1:4, with females always dominating the population. A comparison with other Diopatra Audouin and Milne Edwards, 1833 (Onuphidae) showed that D. marocensis is the largest species with direct development and with the highest number of eggs and larvae inside the parental tube. With the exception of the colour, due to the presence of the gametes in the coelom cavity, no morphological differences between males and females were observed. (c) 2012 Elsevier Ltd. All rights reserved.
Diopatra neapolitana Delle Chiaje, 1841 (Annelida, Onuphidae) is an important economic natural resource in Ria de Aveiro (northwestern coast of Portugal) and throughout Europe. The species is ...intensively harvested for use as fresh bait. However, there is only limited knowledge about its life cycle derived from a previous study in Mediterranean Sea. Reproduction and development patterns are known to vary biogeographically, making it important to base management decisions on locally appropriate information. This work examines reproduction patterns for populations from the Eastern Atlantic, which have not previously been assessed, with an eye towards drawing Atlantic–Mediterranean comparisons and informing local management strategies. The study was conducted from May 2007 to April 2009 in Ria de Aveiro. The reproductive biology of D. neapolitana was described from the proportional variation of worms with gametes in the coelom and from the progression of the oocyte diameter. Individuals with gametes inside the coelom were found all year round, but the peak reproductive period occurred between May and August, when almost all individuals had gametes in the coelom and females contained more oocytes than at any other time of the year. The overall male:female ratio was close to 1:1 and the oocyte diameter ranged from 40 to 240 μm. In vitro fertilization was performed and the results compared to other studies. Based on the present results, some protection measures are suggested to implement a sustainable exploitation of the species.
The polychaete Pectinaria koreni exhibits a complex life cycle characterized by non-overlapping generations and widespread larval dispersal. To explore how “local” metapopulation genetic structure ...varies spatially and temporally during population turnover, we combined observations on demography, larval dispersal through hydrodynamic modelling and population genetics of successive age cohorts in the Baie de Seine (eastern English Channel, France). Mature adults (March), newly settled (July) and later-stage juveniles (September) were sampled in 2003 on the edge and in the main demes of the metapopulation. Demes displayed an asynchronous dynamics due to variations in habitat quality affecting reproductive timing (e.g. three distinct spawning events observed) and in local larval supply linked to temporal fluctuations of hydrodynamism. Two-source populations were identified among dense areas with the greatest larval retention and self-recruitment rates: one with a single recruitment event, stable temporal genetic variation and a strong spatial genetic re-homogenization during turnover, and the other with two recruitment events and significant allele frequency changes over time. Sink habitats displayed single recruitment event and experienced strong inter-generational (juveniles vs adults) genetic changes due to genetic drift associated with strong winter mortalities. Altogether, results suggested that adult spawning asynchrony and sweepstakes reproductive success, together with genetic drift, played a greater role than hydrodynamics itself in determining effective recruitment rates at some sites and generating genetic patchiness.
Calcification, a process common to numerous marine taxa, has traditionally been considered to be a significant source of CO₂ in tropical waters only. A number of relatively recent studies, however, ...have shown that significant amounts of CO₂ are also produced in temperate waters, although none of these studies was carried out on rocky shores, which are considered to be very productive systems. We compared the CO₂ fluxes due to respiration and calcification in two temperate species, the cirripedes Chthamalus montagui and Elminius modestus. The population dynamics of both species were estimated at two sites during a 1-year experimental period in order to establish mean organic (ash-free dry weight) and CaCO₃ (dry shell weight) production. Based on these parameters, we estimated the CO₂ fluxes due to respiration and calcification. CaCO ₃ production was estimated to be 481.0 and$1,803.9 g_{CaCO3} m^{ - 2} year^{ - 1} $at each site, representing 3.4 and$12.7mol_{CO2} m^{ - 2} year^{ - 1} $respectively, of released CO₂. These fluxes represent each 47% of the CO₂ released as a result of respiration and calcification. The production of CaCO₃ at the high-density site was: (1) among the highest values obtained for temperate organisms, and (2) comparable to the estimated CO₂ fluxes for coral reefs. As calcifying organisms are well represented in temperate ecosystems in terms of both density and biomass, our results provide clear evidence that calcification of temperate organisms should not be underestimated. Additional studies on other rocky shore taxa are needed before the relative importance of calcification in rocky intertidal carbon budgets can be generalized.
This study uses enzymatic and mitochondrial genes to infer the relative importance of historical processes and contemporary hydrodynamic features on the observed patterns of genetic structure in ...subdivided populations of Pectinaria koreni (Polychaeta: Pectinariidae) along the coasts of Brittany and the English Channel. Nucleotide sequence variation of a 603-bp fragment of the mtDNA cytochrome oxidase subunit I gene revealed a surprisingly deep phylogeographic break of about 16% divergence separating the Brittany and Channel populations, which coincides with a biogeographic boundary along the western coast of Brittany. Deep sequence divergence with fixed haplotype differences and the inversion of allele frequencies at two enzyme loci suggests the occurrence of potential cryptic or sibling species of P. koreni. The two clades showed opposite features. Channel populations exhibited bimodal match-mismatch curves due to two highly divergent haplotypes occurring at high frequencies and no overall heterozygote deficiencies at enzyme loci, suggesting respectively, a historic secondary contact between two differentiated populations followed by contemporary panmixia. On the contrary, Brittany populations displayed unimodal curves with low nucleotide diversity and highly significant heterozygote deficiencies, probably reminiscent of a recent population expansion and recolonisation of Brittany with contemporary admixture of divergent populations.
The production of organic matter and calcium carbonate by a dense population of the brittle star Acrocnida brachiata (Echinodermata) was calculated using demographic structure, population density, ...and relations between the size (disk diameter) and the ash-free dry weight (AFDW) or the calcimass. During a 2-year survey in the Bay of Seine (Eastern English Channel, France), organic production varied from 29 to 50 g AFDW m⁻² year⁻¹ and production from 69 to 104 gcaco3 m⁻² year⁻¹. Respiration was estimated between 1.7 and 2.0 mol CO2 m⁻² year⁻¹. Using the molar ratio (Ψ) of CO₂ released: CaCO₃ precipitated, this biogenic precipitation of calcium carbonate would result in an additional release between 0.5 and 0.7 mol CO2 m⁻² year⁻¹ that represented 23% and 26% of total CO₂ fluxes (sum of calcification and respiration). The results of the present study suggest that calcification in temperate shallow environments should be considered as a significant source of CO₂ to seawater and thus a potential source of CO₂ to the atmosphere, emphasizing the important role of the biomineralization (estimated here) and dissolution (endoskeletons of dead individuals) in the carbon budget of temperate coastal ecosystems.
The production of organic matter and calcium carbonate by a dense population of the brittle star Acrocnida brachiata (Echinodermata) was calculated using demographic structure, population density, ...and relations between the size (disk diameter) and the ash-free dry weight (AFDW) or the calcimass. During a 2-year survey in the Bay of Seine (Eastern English Channel, France), organic production varied from 29 to 50g sub(AFDW) m super(-2)year super(-1) and CaCO sub(3) production from 69 to 104g sub(CaCO3)m super(-2)year super(-1). Respiration was estimated between 1.7 and 2.0mol sub(CO2)m super(-2)uear super(-1). Using the molar ratio (q) of CO sub(2) released: CaCO sub(3) precipitated, this biogenic precipitation of calcium carbonate would result in an additional release between 0.5 and 0.7mol sub(CO2)m super(-2)year super(-1) that represented 23% and 26% of total CO sub(2) fluxes (sum of calcification and respiration). The results of the present study suggest that calcification in temperate shallow environments should be considered as a significant source of CO sub(2) to seawater and thus a potential source of CO sub(2) to the atmosphere, emphasizing the important role of the biomineralization (estimated here) and dissolution (endoskeletons of dead individuals) in the carbon budget of temperate coastal ecosystems.
Calcification, a process common to numerous marine taxa, has traditionally been considered to be a significant source of CO sub(2) in tropical waters only. A number of relatively recent studies, ...however, have shown that significant amounts of CO sub(2) are also produced in temperate waters, although none of these studies was carried out on rocky shores, which are considered to be very productive systems. We compared the CO sub(2) fluxes due to respiration and calcification in two temperate species, the cirripedes Chthamalus montagui and Elminius modestus. The population dynamics of both species were estimated at two sites during a 1-year experimental period in order to establish mean organic (ash-free dry weight) and CaCO sub(3) (dry shell weight) production. Based on these parameters, we estimated the CO sub(2) fluxes due to respiration and calcification. CaCO sub(3) production was estimated to be 481.0 and Equation at each site, representing 3.4 and Equation respectively, of released CO sub(2). These fluxes represent each 47% of the CO sub(2) released as a result of respiration and calcification. The production of CaCO sub(3) at the high-density site was: (1) among the highest values obtained for temperate organisms, and (2) comparable to the estimated CO sub(2) fluxes for coral reefs. As calcifying organisms are well represented in temperate ecosystems in terms of both density and biomass, our results provide clear evidence that calcification of temperate organisms should not be underestimated. Additional studies on other rocky shore taxa are needed before the relative importance of calcification in rocky intertidal carbon budgets can be generalized.
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