Frank Melzner

• Group Leader at GEOMAR Helmholtz Centre for Ocean Research Kiel

Mussels from the genus Mytilus, key inhabitants of the benthos, are important for the aquaculture industry and one of the most sustainable sources of animal protein available. Species within the Mytilus edulis complex ( M. edulis, M. galloprovincialis and M. trossulus ) are commonly found in temperate regions globally and can easily hybridise whene...

The simulation of deep‐sea conditions in laboratories is technically challenging but necessary for experiments that aim at a deeper understanding of physiological mechanisms or host‐symbiont interactions of deep‐sea organisms. In a proof‐of‐concept study, we designed a recirculating system for long‐term culture (>2 yr) of deep‐sea mussels Gigantida...

Low-salinity stress can severely affect the fitness of marine organisms. As desalination has been predicted for many coastal areas with ongoing climate change, it is crucial to gain more insight in mechanisms that constrain salinity acclimation ability. Low-salinity induced depletion of the organic osmolyte pool has been suggested to set a critical...

Baltic blue mussels can colonise and dominate habitats with far lower salinity (<10 psu) than other Mytilus congeners. Pervasive gene flow was observed between Western Baltic Mytilus edulis living at high salinity conditions and Eastern Baltic M. trossulus living at lower salinites, with highest admixture proportions within a genetic transition zon...

Background Biomineralization by molluscs involves regulated deposition of calcium carbonate crystals within a protein framework to produce complex biocomposite structures. Effective biomineralization is a key trait for aquaculture, and animal resilience under future climate change. While many enzymes and structural proteins have been identified fro...

The Baltic Sea has a salinity gradient decreasing from fully marine (> 25) in the west to below 7 in the central Baltic Proper. Habitat-forming and ecologically dominant mytilid mussels exhibit decreasing growth when salinity < 11; however, the mechanisms underlying reduced calcification rates in dilute seawater are not fully understood. Both [HCO3...

The Baltic Sea has a salinity gradient decreasing from fully marine (> 25) in the West to below 7 in the Central Baltic Proper. Reef forming mytilid mussels exhibit decreasing growth when salinity

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 utilis...

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 mu...

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 benef...

The current increase in atmospheric CO 2 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, o...

Shell matrix proteins (SMPs) are occluded within molluscan shells and are fundamental to the biological control over mineralization. While many studies have been performed on adult SMPs, those of larval stages remain largely undescribed. Therefore, this study aimed to characterize the larval shell proteome of the blue mussel for the first time and...

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 o...

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. I...

The physiological processes driving the rapid rates of calcification in larval bivalves are poorly understood. Here, we use a calcification substrate‐limited approach (low dissolved inorganic carbon, CT) and mRNA sequencing to identify proteins involved in bicarbonate acquisition during shell formation. As a secondary approach, we examined expressi...

In coastal temperate regions such as the Baltic Sea, calcifying bivalves dominate benthic communities playing a vital ecological role in maintaining biodiversity and nutrient recycling. At low salinities, bivalves exhibit reduced growth and calcification rates which is thought to result from physiological constraints associated with osmotic stress....

Coastal global oceans are expected to undergo drastic changes driven by climate change and increasing anthropogenic pressures in coming decades. Predicting specific future conditions and assessing the best management strategies to maintain ecosystem integrity and sustainable resource use are difficult, because of multiple interacting pressures, unc...

In vivo confocal Raman microscopy (CRM), polarized light microscopy and Fourier transform infrared spectroscopy (FTIR) were used to determine if a significant amount of amorphous calcium carbonate (ACC) exists within larval shells of Baltic mytilid mussels (Mytilus edulis-like) and whether the amount of ACC varies during larval development. No evid...

Aim Experimental simulation of near‐future ocean acidification (OA) has been demonstrated to affect growth and development of echinoderm larval stages through energy allocation towards ion and pH compensatory processes. To date, it remains largely unknown how major pH regulatory systems and their energetics are affected by trans‐generational exposu...

In estuarine coastal systems such as the Baltic Sea, mussels suffer from low salinity which limits their distribution. Anthropogenic climate change is expected to cause further desalination which will lead to local extinctions of mussels in the low saline areas. It is commonly accepted that mussel distribution is limited by osmotic stress. However,...

Understanding mollusk calcification sensitivity to ocean acidification (OA) requires a better knowledge of calcification mechanisms. Especially in rapidly calcifying larval stages, mechanisms of shell formation are largely unexplored—yet these are the most vulnerable life stages. Here we find rapid generation of crystalline shell material in mussel...

In estuarine coastal systems such as the Baltic Sea, mussels suffer from low salinity which limits their distribution. Anthropogenic climate change is expected to cause further desalination which will lead to local extinctions of mussels in the low saline areas. It is commonly accepted that mussel distribution is limited by osmotic stress. However,...

Increased maintenance costs at cellular, and consequently organism level, are thought to be involved in shaping the sensitivity of marine calcifiers to ocean acidification (OA). Yet, knowledge of the capacity of marine calcifiers to undergo metabolic adaptation is sparse. In Kiel Fjord, blue mussels thrive despite periodically high seawater PCO2, m...

Ocean acidification severely affects bivalves, especially their larval stages. Consequently, the fate of this ecologically and economically important group depends on the capacity and rate of evolutionary adaptation to altered ocean carbonate chemistry. We document successful settlement of wild mussel larvae (Mytilus edulis) in a periodically CO2-e...

While secondary contact between Mytilus edulis and M. trossulus in North America results in mosaic hybrid zone formation, both species form a hybrid swarm in the Baltic. Despite pervasive gene flow, Baltic Mytilus species maintain substantial genetic and phenotypic differentiation. Exploring mechanisms underlying the contrasting genetic composition...

It is widely assumed that the ability of an introduced species to acclimate to local environmental conditions determines its invasion success. The sea anemone Diadumene lineata is a cosmopolitan invader and shows extreme physiological tolerances. It was recently discovered in Kiel Fjord (Western Baltic Sea), although the brackish conditions in this...

Carbon capture and storage is promoted as a mitigation method counteracting the increase of atmospheric CO2 levels. However, at this stage, environmental consequences of potential CO2 leakage from sub-seabed storage sites are still largely unknown. In a 3-month-long mesocosm experiment, this study assessed the impact of elevated pCO2 levels (1,500...

Deep-sea hydrothermal vents are patchily distributed ecosystems inhabited by specialized animal populations that are textbook meta-populations. Many vent-associated species have free-swimming, dispersive larvae that can establish connections between remote populations. However, connectivity patterns among hydrothermal vents are still poorly underst...

Recent modeling results suggest that oceanic oxygen levels will decrease significantly over the next decades to centuries in response to climate change and altered ocean circulation. Hence, the future ocean may experience major shifts in nutrient cycling triggered by the expansion and intensification of tropical oxygen minimum zones (OMZs), which a...

Calanoid copepods and euphausiids are key components of marine zooplankton communities worldwide. Most euphausiids and several copepod species perform diel vertical migrations (DVMs) that contribute to the export of particulate and dissolved matter to midwater depths. In vast areas of the global ocean, and in particular in the eastern tropical Atla...

Calanoid copepods and euphausiids are key components of marine zooplankton communities worldwide. Most euphausiids and several copepod species perform diel vertical migrations (DVMs) that contribute to the export of particulate and dissolved matter to midwater depths. In vast areas of the global ocean, and in particular in the eastern tropical Atla...

The HydroC® CO2 sensor was deployed from a pontoon at the waterfront of the GEOMAR west shore building into Kiel Fjord, Western Baltic Sea (Kiel, Germany; 54°19'48.78"N, 010° 8'59.44"E). Since the pontoon is floating the deployment depth of the sensor was constant at 1m. Data of three deployment intervals are published here: 1) July 2012 - December...

Biomineralization processes in bivalve molluscs are still poorly understood. Here we provide an analysis of specifically expressed sequences from a mantle transcriptome of the blue mussel, Mytilus edulis. We then developed a novel, integrative shell injury assay to test, whether biomineralization candidate genes highly expressed in marginal and pal...

Shell growth of oysters requires calcium uptake from the environment and transport to the area of shell formation. A shell regeneration assay in combination with radiolabelled calcium was used to investigate uptake and distribution of calcium to different tissues and hemolymph fractions in Pacific oysters, Crassostrea gigas (Bivalvia, Ostreoida). O...

Bivalve calcification, particularly of the early larval stages, is highly sensitive to the change in ocean carbonate chemistry resulting from atmospheric CO2 uptake. Earlier studies suggested that declining seawater [CO32-] and thereby lowered carbonate saturation affect shell production. However, disturbances of physiological processes such as aci...

Elevated pCO2 drives lower growth and yet increased calcification in the early life history of the cuttlefish Sepia officinalis Ocean acidification is an escalating environmental issue and associated changes in the ocean carbonate system have implications for many calcifying organisms. The present study followed the growth of Sepia officinalis from...

Bivalve calcification, particularly of the early larval stages, is highly sensitive to the change in ocean carbonate chemistry resulting from atmospheric CO2 uptake. Earlier studies suggested that declining seawater [CO32−] and thereby lowered carbonate saturation affect shell production. However, disturbances of physiological processes such as aci...

Impact of seawater carbonate chemistry on the calcification of marine bivalves

The squat lobster Pleuroncodes monodon is a key species of the highly productive, but oxygen-poor upwelling system of the Eastern Tropical South Pacific. Observations of P. monodon in the water column off Peru have led to the hypothesis that anoxic conditions force this otherwise primarily benthic species to adopt a pelagic lifestyle. Here we show...

Bivalve calcification, particularly of the early larval stages, is highly sensitive to the change in ocean carbonate chemistry resulting from atmospheric CO2 uptake. Earlier studies suggested that declining seawater [CO32−] and thereby lowered carbonate saturation affect shell production. However, disturbances of physiological processes such as aci...

Salinity strongly influences development and distribution of the sea star Asterias rubens. In Kiel Fjord, located in the western Baltic Sea, A. rubens is the only echinoderm species and one of the main benthic predators controlling blue mussel (Mytilus edulis) abundance. However, Kiel Fjord with an average salinity of about 15 is located close to t...

The cellular mechanisms of calcification in sea urchin larvae are still not well understood. Primary mesenchyme cells within the larval body cavity form a syncytium to secrete CaCO3 spicules from intracellular amorphous CaCO3 (ACC) stores. We studied the role of Na(+)K(+)2Cl(-) cotransporter (NKCC) in intracellular ACC accumulation and larval spicu...

Recent modeling results suggest that oceanic oxygen levels will decrease significantly over the next decades to centuries in response to climate change and altered ocean circulation. Hence the future ocean may experience major shifts in nutrient cycling triggered by the expansion and intensification of tropical oxygen minimum zones (OMZs). There ar...

Changes in seawater carbonate chemistry that accompany ongoing ocean acidification have been found to affect calcification processes in many marine invertebrates. In contrast to the response of most invertebrates, calcification rates increase in the cephalopod Sepia officials during long-term exposure to elevated seawater pCO2. The present trial in...

The tissue distribution and ontogeny of Na+/K+-ATPase has been examined as an indicator for ion-regulatory epithelia in whole animal sections of embryos and hatchlings of two cephalopod species: the squid Loligo vulgaris and the cuttlefish Sepia officinalis. This is the first report of the immunohistochemical localization of cephalopod Na+/K+-ATPas...

Experimental ocean acidification leads to a shift in resource allocation and to an increased [HCO3-] within the perivisceral coelomic fluid (PCF) in the Baltic green sea urchin Strongylocentrotus droebachiensis. We investigated putative mechanisms of this pH compensation reaction by evaluating epithelial barrier function and the magnitude of skelet...

Sampling was conducted during RV Meteor cruise M93 in austral summer 2013 in an area from 11ºS to 14ºS and approximately 120 km offshore to within 10 km of the Peruvian coast. Specimens were collected using a Hydrobios Multinet Maxi (0.5 m2 mouth opening, 330 µm mesh size, 9 nets) and a WP-2 net (Hydrobios, 0.26 m2 mouth opening, 200 µm mesh size)....

Respiration and ammonium excretion rates at different oxygen partial pressure were measured for calanoid copepods and euphausiids from the Eastern Tropical South Pacific and the Eastern Tropical North Atlantic. All specimens used for experiments were caught in the upper 400 m of the water column and only animals appearing unharmed and fit were used...

Marine and coastal biodiversity – ecosystems, species and genetic material – provide enormous benefits for human well-being. Hundreds of millions of people rely directly on marine biodiversity for their livelihoods. Oceans are critical to many important global geo-chemical processes, such as climate regulation and carbon cycling. Ocean ecosystems p...

Ocean acidification has the potential to affect growth and calcification of benthic marine invertebrates, particularly during their early life history. We exposed field-collected juveniles of Asterias rubens from Kiel Fjord (western Baltic Sea) to 3 seawater CO2 partial pressure (pCO(2)) levels (ranging from around 650 to 3500 mu atm) in a long-ter...

Ocean acidification is expected to decrease calcification rates of bivalves. Nevertheless in many coastal areas high pCO2 variability is encountered already today. Kiel Fjord (Western Baltic Sea) is a brackish (12-20 g kg-1) and CO2 enriched habitat, but the blue mussel Mytilus edulis dominates the benthic community. In a coupled field and laborato...

Ocean acidification has the potential to affect growth and calcification of benthic marine invertebrates, particularly during their early life history. We exposed field-collected juveniles of Asterias rubens from Kiel Fjord (western Baltic Sea) to 3 seawater CO2 partial pressure (pCO2) levels (ranging from around 650 to 3500 µatm) in a long-term (3...

Larval stages are considered as the weakest link when a species is exposed to challenging environmental changes. Reduced rates of growth and development in larval stages of calcifying invertebrates in response to ocean acidification might be caused by energetic limitations. So far no information exists on how ocean acidification affects digestive p...

This study investigated the effects of seawater pH (i.e., 8.10, 7.85 and 7.60) and temperature (16 and 19 �C) on (a) the abiotic conditions in the fluid surrounding the embryo (viz. the perivitelline fluid), (b) growth, development and (c) cuttlebone calcification of embryonic and juvenile stages of the cephalopod Sepia officinalis. Egg swelling in...

Experimental ocean acidification leads to a shift in resource allocation and to an increased [HCO3 −] within the perivisceral coelomic fluid (PCF) in the Baltic green sea urchin Strongylocentrotus droebachiensis. We investigated putative mechanisms of this pH compensation reaction by evaluating epithelial barrier function and the magnitude of skele...

Ocean acidification is expected to decrease calcification rates of bivalves. Nevertheless, in many coastal areas high pCO2 variability is encountered already today. Kiel Fjord (Western Baltic Sea) is a brackish (12-20 g kg(-1) ) and CO2 enriched habitat, but the blue mussel Mytilus edulis dominates the benthic community. In a coupled field and labo...

The cuttlefish Sepia officinalis expresses several hemocyanin isoforms with potentially different pH optima, indicating their reliance on efficient pH regulation in the blood. Ongoing ocean warming and acidification could influence the oxygen-binding properties of respiratory pigments in ectothermic marine invertebrates. This study examined whether...

Calcifying echinoid larvae respond to changes in seawater carbonate chemistry with reduced growth and developmental delay. To date, no information exists on how ocean acidification acts on pH homeostasis in echinoderm larvae. Understanding acid-base regulatory capacities is important because intracellular formation and maintenance of the calcium ca...

Anthropogenic CO2 emissions are acidifying the world’s oceans. A growing body of evidence demonstrates that ocean acidification can impact survival, growth, development and physiology of marine invertebrates. Here, we tested the impact of long-term (up to 16 months) and trans-life-cycle (adult, embryo/larvae and juvenile) exposure to elevated pCO2...

Marine organisms have to cope with increasing CO2 partial pressures and decreasing pH in the oceans. We elucidated the impacts of an 8-week acclimation period to four seawater pCO2 treatments (39, 113, 243 and 405 Pa/385, 1,120, 2,400 and 4,000 μatm) on mantle gene expression patterns in the blue mussel Mytilus edulis from the Baltic Sea. Based on...

Ocean acidification is elicited by anthropogenic carbon dioxide emissions and resulting oceanic uptake of excess CO2 and might constitute an abiotic stressor powerful enough to alter marine ecosystem structures. For surface waters in gas-exchange equilibrium with the atmosphere, models suggest increases in CO2 partial pressure (pCO2) from current v...

The impact of seawater acidification on calcifying organisms varies at the species level. If the impact differs between predator and prey in strength and/or sign, trophic interactions may be altered. In the present study, we investigated the impact of 3 different seawater pCO(2) levels (650, 1250 and 3500 mu atm) on the acid-base status or the grow...

Anthropogenic CO2 emission will lead to an increase in seawater pCO2 of up to 80–100 Pa (800–1000 μatm) within this century and to an acidification of the oceans. Green sea urchins (Strongylocentrotus droebachiensis) occurring in Kattegat experience seasonal hypercapnic and hypoxic conditions already today. Thus, anthropogenic CO2 emissions will ad...

The present study provides a first finding of the acid‐base regulating machinery (ion‐transporters relevant for acid‐base regulation) in cephalopod, and series of studies showed that they exhibit specialized ion regulatory cells (ionocytes) on their skin and yolk epithelium. A feature that was so far only reported for fish. In addition, several ion...

The marine mussel Mytilus edulis and its closely related sister species are distributed world-wide and play an important role in coastal ecology and economy. The diversification in different species and their hybrids, broad ecological distribution, as well as the filter feeding mode of life has made this genus an attractive model to investigate phy...

Information of sample composition within the different transcriptome runs as well as of sequence data generated with *FLX or Titanium chemistry before and after quality control. Data after quality control were used for the assembly (see table S2). (DOC)

Information about genome sources of the different species used for phylogenetic analysis. (DOC)

Putative M. edulis immune relevant genes identified via BLAST analysis. A) Sequence and domain information. Domain information of M. edulis contigs was deduced by amino-acid sequence investigation using SMART [27] and NCBI dart [28] with default thresholds. B) Comparison with selected species. Putative M. edulis immune genes were compared via tBLAS...

TNF related M. edulis transcripts with conserved TNF or TNFR domains identified by PROSITE. (DOC)

M. edulis contigs with high similarity to LPS induced TNF-alpha factor (LITAF) - like proteins of other organisms. (DOC)

Caspase-like contigs of M. edulis . (DOC)

Conserved motifs in M. edulis big defensin transcripts identified in Mytilus edulis. The amino acid sequence of 5 Mytilus edulis big defensins are compared with big defensin amino acid sequences from Argopecten irradians (AiBD, GenBank accession no. DQ334340) and Venerupis philippinarum (VpBD, GenBank accession no. HM562672). Further the conserved...

Assembly strategy of the Mytilus edulis transcriptome. Cleaned and quality controlled reads were initially assembled with either Celera (1. Assembly) or NEWBLER (2. Assembly). Resulting Contigs (C) and singletons (S) were subsequently further assembled in multiple rounds (R) using TGICL (Cap3) assembler and AMOS. For Run numbers 115–284 see table S...

Antimicrobial peptides identified in M. edulis . (DOC)

Alignment (aln format) used for phylogenetic analysis. (ALN)

Deduced amino acid sequence of NF-κB-like contigs of the blue mussel Mytilus edulis. In mammals the five proteins of the NF-κB transcription factor family (p65 (RelA), RelB, c-Rel, p105/p50 (NF-κB1), p100/52 (NF-κB2)) form distinct transcriptionally active homo- and heterodimeric complexes. The p50/p65 dimer is the most prominent heterodimer in mos...

19 MACPF domain bearing contigs of M. edulis. 5 of these fragments showed similarity to macrophage expressed gene-1, and 3 to apextrin, while 11 fragments could not be annotated. Proteins containing the MACPF domain but lacking other domains of the MAC complex members were reported in several other lower invertebrates (for review see, [108]). Some...

Alignment (phy format) used for phylogenetic analysis. (PHY)

Local reservoir ages are often estimated from the difference between the radiocarbon ages of aquatic material and associated terrestrial samples for which no reservoir effect is expected. Frequently, the selected aquatic material consists of bivalve shells that are typically well preserved in the archaeological record. For instance, large shell mid...

Anthropogenic CO2 emission will lead to an increase in seawater pCO2 of up to 80-100 Pa (800-1000 µatm) within this century and to an acidification of the oceans. Green sea urchins (Strongylocentrotus droebachiensis) occurring in Kattegat experience seasonal hypercapnic and hypoxic conditions already today. Thus, anthropogenic CO2 emissions will ad...