Beschreibung: Mytilus mussels (Mytilus edulis (ME), M. trossulus (MT), and M. galloprovincialis (MG)) are of interest in many fields of marine science and have been used as model in evolutionary research. For instance, they form mosaic hybrid zones or hybrid swarms in areas of secondary contact and hence are suited to address questions related to the evolution of reproductive barriers, adaptive hybridization or speciation. While existing genomic information mostly focuses on single species (ME, MG), this project generated RNA seq data of all three species from allopatric populations, i.e. samples representing genetically pure specimens. We investigated adult mantle tissue (four specimens per species), which is functionally involved in processes such as reproduction or biomineralization. The project provides three assembled transcriptomes (post filtering total transcript numbers for ME: 353339, MT: 437827, MG: 290267) representing genes annotated to at least 40 level 2 GO-terms (number (percentage) of annotated transcripts for ME: 44434 (12.6%), MT: 43960 (10%), MG: 60064 (20.7%)). Annotation showed that the most abundant 40 GO-terms are equally well covered by contigs of the three Mytilus transcriptomes. Therefore, this project lays a basis for evolutionary research by providing candidate genes representing various molecular functions such as reproduction, cellular processes or immune response. The potential of the new transcriptomes to address evolutionary questions is further exemplified by a pilot study on ME and MT transcriptomes that used reciprocal blast to identify 7652 one-to-one orthologue pairs of transcripts

Beschreibung: The current increase in atmospheric CO2 concentration induces changes in the seawater carbonate system resulting in decreased pH and calcium carbonate saturation state, a phenomenon called ocean acidification (OA). OA has long been considered as a major threat to echinoderms because their extensive endoskeleton is made of high‑magnesium calcite, one of the most soluble forms of calcium carbonate. Numerous studies addressed this question in sea urchins, but very few questioned the impact of OA on the sea star skeleton, although members of this taxon do not compensate their extracellular pH, contrary to most sea urchins. In the present study, adults of the common sea star, Asterias rubens from Kiel Fjord, a site experiencing natural acidification events exceeding pCO2 levels of 2500 μatm, were chronically exposed to different levels of simulated ocean acidification (pHT-SW 8.0, 7.4, 7.2), encompassing present and future conditions, for the duration of 109 days. Corrosion and mechanical properties of skeletal elements were studied using scanning electron microscopy, three-point bending tests as well as nanoindentation. The spines were significantly corroded at pHT-SW 7.4 and below while the ambulacral plates were only affected at pHT-SW 7.2. Nanoindentation of newly formed spines and ambulacral plates did not reveal significant CO2-induced differences in skeleton hardness or elasticity across treatments. Results of three-point bending tests revealed significantly reduced characteristic strength and fracture force of ambulacral plates from the median arm segment at pHT-SW 7.4 and below. These plates are those supporting the tube feet involved in the opening of bivalves during feeding and in the animal attachment to the substrate. Under reduced seawater pH, this might result in fracture of sea star plates during predation on mussel. The present results predict a possible impact of ocean acidification on the skeletal integrity of a marine keystone predator.

Beschreibung: Most molluscs possess shells, constructed from a vast array of microstructures and architectures. The fully formed shell is composed of calcite or aragonite. These CaCO3 crystals form complex biocomposites with proteins, which although typically less than 5% of total shell mass, play significant roles in determining shell microstructure. Despite much research effort, large knowledge gaps remain in how molluscs construct and maintain their shells, and how they produce such a great diversity of forms. Here we synthesize results on how shell shape, microstructure, composition and organic content vary among, and within, species in response to numerous biotic and abiotic factors. At the local level, temperature, food supply and predation cues significantly affect shell morphology, whilst salinity has a much stronger influence across latitudes. Moreover, we emphasize how advances in genomic technologies [e.g. restriction site-associated DNA sequencing (RAD-Seq) and epigenetics] allow detailed examinations of whether morphological changes result from phenotypic plasticity or genetic adaptation, or a combination of these. RAD-Seq has already identified single nucleotide polymorphisms associated with temperature and aquaculture practices, whilst epigenetic processes have been shown significantly to modify shell construction to local conditions in, for example, Antarctica and New Zealand. We also synthesize results on the costs of shell construction and explore how these affect energetic trade-offs in animal metabolism. The cellular costs are still debated, with CaCO3 precipitation estimates ranging from 1–2 J/mg to 17–55 J/mg depending on experimental and environmental conditions. However, organic components are more expensive (~29 J/mg) and recent data indicate transmembrane calcium ion transporters can involve considerable costs. This review emphasizes the role that molecular analyses have played in demonstrating multiple evolutionary origins of biomineralization genes. Although these are characterized by lineage-specific proteins and unique combinations of co-opted genes, a small set of protein domains have been identified as a conserved biomineralization tool box. We further highlight the use of sequence data sets in providing candidate genes for in situ localization and protein function studies. The former has elucidated gene expression modularity in mantle tissue, improving understanding of the diversity of shell morphology synthesis. RNA interference (RNAi) and clustered regularly interspersed short palindromic repeats - CRISPR-associated protein 9 (CRISPR-Cas9) experiments have provided proof of concept for use in the functional investigation of mollusc gene sequences, showing for example that Pif (aragonite-binding) protein plays a significant role in structured nacre crystal growth and that the Lsdia1 gene sets shell chirality in Lymnaea stagnalis. Much research has focused on the impacts of ocean acidification on molluscs. Initial studies were predominantly pessimistic for future molluscan biodiversity. However, more sophisticated experiments incorporating selective breeding and multiple generations are identifying subtle effects and that variability within mollusc genomes has potential for adaption to future conditions. Furthermore, we highlight recent historical studies based on museum collections that demonstrate a greater resilience of molluscs to climate change compared with experimental data. The future of mollusc research lies not solely with ecological investigations into biodiversity, and this review synthesizes knowledge across disciplines to understand biomineralization. It spans research ranging from evolution and development, through predictions of biodiversity prospects and future-proofing of aquaculture to identifying new biomimetic opportunities and societal benefits from recycling shell products.

Beschreibung: Shell formation and repair occurs under the control of mantle epithelial cells in bivalve molluscs. However, limited information is available on the precise acid–base regulatory machinery present within these cells, which are fundamental to calcification. Here, we isolate mantle epithelial cells from the Pacific oyster, Crassostrea gigas and utilise live cell imaging in combination with the fluorescent dye, BCECF-AM to study intracellular pH (pHi) regulation. To elucidate the involvement of various ion transport mechanisms, modified seawater solutions (low sodium, low bicarbonate) and specific inhibitors for acid–base proteins were used. Diminished pH recovery in the absence of Na+ and under inhibition of sodium/hydrogen exchangers (NHEs) implicate the involvement of a sodium dependent cellular proton extrusion mechanism. In addition, pH recovery was reduced under inhibition of carbonic anhydrases. These data provide the foundation for a better understanding of acid–base regulation underlying the physiology of calcification in bivalves.

Beschreibung: Ocean warming impacts the fitness of marine ectothermic species, leading to poleward range shifts, re-shuffling of communities, and changes in ecosystem services. While the detrimental effects of summer heat waves have been widely studied, little is known about the impacts of winter warming on marine species in temperate regions. Many species benefit from low winter temperature-induced reductions in metabolism, as these permit conservation of energy reserves that are needed to support reproduction in spring. Here, we used a unique outdoor mesocosm system to expose a coastal predator-prey system, the sea star Asterias and the blue mussel Mytilus, to different winter warming scenarios under near-natural conditions. We found that the body condition of mussels decreased in a linear fashion with increasing temperature. Sea star growth also decreased with increasing temperature, which was a function of unaltered predation rates and decreased mussel body condition. Asterias relative digestive gland mass strongly declined over the studied temperature interval (ca twofold). This could have severe implications for reproductive capacity in the following spring, as digestive glands provide reserve compounds to maturing gonads. Thus, both predator and prey suffered from a mismatch of energy acquisition versus consumption in warmer winter scenarios, with pronounced consequences for food web energy transfer in future oceans.

Beschreibung: In the last few decades, numerous studies have investigated the impacts of simulated ocean acidification on marine species and communities, particularly those inhabiting dynamic coastal systems. Despite these research efforts, there are many gaps in our understanding, particularly with respect to physiological mechanisms that lead to pathologies. In this review, we trace how carbonate system disturbances propagate from the coastal environment into marine invertebrates and highlight mechanistic links between these disturbances and organism function. We also point toward several processes related to basic invertebrate biology that are severely understudied and prevent an accurate understanding of how carbonate system dynamics influence organismic homeostasis and fitness-related traits. We recommend that significant research effort be directed to studying cellular phenotypes of invertebrates acclimated or adapted to elevated seawater pCO2 using biochemical and physiological methods.

Beschreibung: Data sets are outputs of two experiments (each experiment includes two or more temporally replicated trials - named by date) that were conducted using a newly developed Fluorometer and Oximeter equipped Flow-through Setup (FOFS). The corresponding method paper is titled 'Simultaneous recording of filtration and respiration in marine organisms in response to short-term environmental variability'. The paper is under review by Limnology and Oceanography: Methods. The main directory of experimental data (e.g., FOFS_test/blank_trials) contain subdirectories termed raw_data_temperature (including °C-temperature .xlsx files), raw_data_Chl, and raw_data_Oxygen, the two latter contains folders named after the starting dates of the trials (e.g., 04_nov). Each of these folders has three subfolders named after the three stages of the trial (i.e., pre, main, and post). Each subfolder includes data sheets of mV-Chl (.CSV) or %air-saturation (.xlxs, which are outputs of the DO calulator.py) that were collected in the corresponding stage and trial. The data can be processed through the Python scripts accompanying the method paper, providing time-series of filtration, respiration, and scope for growth along daily thermal cycles for the studied blue mussel Mytilus spp. specimens (see the paper for details).

Beschreibung: We used the Kiel Outdoor Benthocosm (KOB) facility for our winter-warming experiment. We used 10 of the 12 available replicate tanks and exposed communities in each of the 10 tanks to a different thermal regime. The experiment was run between 24 November 2017 and 12 April 2018. Experimental tanks were stocked with 500 mytilid mussels and 5 sea stars (A. rubens) each.

Beschreibung: Laboratory experiments were performed measuring calcification rates in Baltic Sea mussel at various salintiies, bicarbonate and calcium ion concentrations. Predictors of calcification were calculated and correlated with calcification rates. Field monitoring of carbonate chemistry, salinity and temperature was conducted and correlated with field calcification rates in southwest Baltic Sea mussel reefs.