Biology subjects

Stratmann, T.

Publications and source records attributed to Stratmann, T..

12 recordsLinked to original sources

bioRxiv2026

Taxon-specific differences in C and N cycling and metabolic activity of intertidal organisms: Part B - Long-term processes

Tidal flats cover less than 1% of the surface of our planet, but they provide important ecosystem functions and services, like carbon sequestration and nutrient (re-)mineralization, primary, sec-ondary, and food production, and habitats for a variety of species. Despite their importance, they are threatened by environmental stressors and anthropogenic impacts. Hence, a better under-standing of the interaction between macrozoobenthos, their metabolic activity, and their contri-bution to carbon and nitrogen cycling is important. Therefore, we conducted in-situ pulse-chase tracer experiments at a Pacific oyster (Magallana gigas) reef in the Eastern Scheldt (Southwest Dutch Delta, Netherlands) in summer and autumn 2020. During these experiments, we provided the submerged benthic community with 13C and 15N-enriched bacterioplankton and incubated it in seawater enriched in 1% deuterium oxide (2H2O) for one tidal cycle (~9 h), before the benthic community was kept at in situ conditions for another 14 d. Our aim was (1) to assess seasonal variations in 13C and 15N processing by macrozoobenthos, (2) to evaluate potential life-stage de-pendent differences in 2H uptake - a proxy for metabolic activity, and (3) to identify the macro-zoobenthos taxon which had the highest metabolic turnover rate (MTR). In summer, most bacte-rioplankton-derived 13C- and 15N was taken up by sponges (Halichondria panicea), limpets (Crepidula fornicata), and clams (Ruditapes philippinarum), whereas in autumn, H. panicea, C. fornicata and the sponge Hymeniacidon perlevis dominated 13C and 15N incorporation. Statisti-cally significant differences in 2H uptake between life stages (juvenile/ small vs. adult) was de-tected in Malacostraca (i.e., Rhithropanopeus harrisii), but not in Polychaeta or Bivalvia. There-fore, this difference between taxonomic classes might be linked to mold-intermolt periods. Sea-sonal differences in MTR of H. panicea and M. gigas (i.e., the species with the highest MTRs in summer and autumn) might be linked to seasonal environmental variability, such as temperature and food availability.

ecology↗

bioRxiv2026

Life inside polymetallic nodules

Deep-sea abyssal plains harbour extensive biodiversity, much of which remains undocumented. Polymetallic nodules in the abyssal plains of the Clarion-Clipperton Zone (CCZ), Central Pacific, harbour diverse meiofaunal communities within their crevices, representing an understudied habitat. Given their high concentrations of nickel, copper, and cobalt, nodules are currently one of the primary targets for the extraction of deep-sea mineral resources. Here, we characterise the physical properties of polymetallic nodules, quantify their meiofaunal crevice communities, and compare them to those from the nearby sediments. We show that nodules contain internal cracks and microfossils, that their crevices harbour meiofaunal communities dominated by nematodes and copepods, and that faunal abundance increases significantly with nodule volume. Nodule-crevice nematode and copepod abundances were equivalent to approximately 10% and 25%, respectively, of those recorded in nearby sediments across the two exploration contract areas in the eastern CCZ. Based on 18S rRNA data, nematode and copepod assemblages recovered from nodule crevices differed from those recovered from nearby sediments collected during the same expedition and within the same exploration contract areas. Our findings, therefore, point to the possibility of nodule-associated crevice meiofauna communities and the consequent risk of biodiversity loss associated with nodule removal through potential future commercial mining.

ecology↗

bioRxiv2026

Taxon-specific differences in C and N cycling and metabolic activity of intertidal organisms: Part A - Short-term processes

European tidal flats that host non-native Magallana gigas reefs contribute to several ecosystem functions. Among others, they provide a habitat for a large variety of associated fauna. However, we often lack detailed information about any trophic interactions of the associated macrozoobenthos species with the oysters, and about their role in the carbon and nutrient cycle. Therefore, we performed ex-situ pulse-chase tracer experiments in the Eastern Scheldt (Southwest Dutch Delta, Netherlands) in summer and autumn 2020, where we fed M. gigas and their associated fauna 13C- and 15N-enriched bacterioplankton while the macrozoobenthos was incubated in water containing deuterium oxide (2H2O; enrichment: 1 - 2.5%). The aim was (1) to assess differences in short-term (<12h) processing of bacterioplankton in summer and autumn, and (2) to study differences in 2H incorporation - a proxy for metabolic activity - of M. gigas and its associated fauna in summer and autumn. In summer, all macrozoobenthos species combined consumed significantly less bacterioplankton-derived 13C and 15N than in autumn, while all macrozoobenthos species combined incorporated comparable amounts of 2H into their tissue in both seasons. Most bacterioplankton-derived 13C and 15N was taken up by sponges (Halichondria panicea, Hymeniacidon perlevis), crabs (Carcinus maenas, Eriocheir sinensis, Rhithropanopeus harrisii), and limpets (Crepidula fornicata). Most 2H was taken up by crabs (C. maenas, E. sinensis), sponges (H. perlevis), and snails (Littorina littorea), implying that these species were the most metabolically active ones. Overall, the metabolic activity was linked to feeding activity in summer 2020, whereas in autumn 2020, the link was weaker and the most metabolically active species were not necessarily the species that had incorporated most 13C and/or 15N.

ecology↗

bioRxiv2025

Ecology of Echinodermata in the Clarion-Clipperton-Fracture Zone (Central Pacific)

Abyssal seascapes between 3,000 and 6000 m water depth represent over 50% of the Planets surface, but the species, functions, and particularly the life history traits that these ecosystems harbour remain poorly understood. Brittle stars (Ophiuroidea) contribute about one third to the invertebrate megabenthos assemblage between 3,800 m and 4,800 m water depth in the Clarion-Clipperton Fracture Zone (CCZ, Northeast Pacific). Starfishes (Asteroidea) are present in lower densities. In the CCZ, Ophiuroidea are often seen near Xenophyophoroidea and attached to glass sponge (Hexactinellida) stalks. We hypothesize that (1) the observed relationship between Ophiuroidea, Xenophyophoroidea, and Hexactinellida is a predator-prey relationship, where Ophiuroidea feed on foraminifera- and sponge-derived organic matter. (2) Ophiuroidea have a reduced dependency on fresh phytodetritus. (3) Brisingida (order of Asteroidea), often clings to stalks to have easier access to particulate organic matter sinking to the seafloor. To test these three hypotheses, we combined bulk and compound-specific stable isotope analyses of fauna (Ophiuroidea, Asteroidea) and sediments with the analyses of seafloor images from the eastern CCZ. Faunal specimens and sediments were collected during three research expeditions between 2019 and 2022, and previously collected seabed images were re-analysed to quantify the major behaviours in which Ophiuroidea and Asteroidea engage. All investigated Echinodermata species had a high trophic level. Phospholipid-derived fatty acids (PLFAs) used as biomarkers suggest that Silax daleus consumes sedimentary detritus that is processed by its gut microbiome. Ophiacantha cosmica is likely a top consumer or scavenger, Ophiosphalma glabrum is an opportunistic omnivore ingesting phytodetritus, bacteria, Crustacea, and Foraminifera, while Ophiuroglypha cf. polyacantha is a more selective omnivore. Freyella benthophila sits mostly on stalks of Hexactinellida and uses this elevated position to catch phytodetritus and zooplankton. Freyastera cf. tuberculata, in comparison, sits mostly on polymetallic nodules from where it preys upon Crustacea moving on the sediment surface. This study confirmed the hypothesis that Ophiuroidea in the CCZ are less dependent on phytodetritus than Holothuroidea in the Peru Basin. It was confirmed that Ophiuroidea consume foraminifera- and sponge-derived organic matter, but Brisingida cling to stalks of Hexactinellida to prey upon Crustacea living in the benthic boundary layer.

ecology↗

bioRxiv2024

Combining 13C, 15N, and 2H to measure feeding and metabolic activity in marine, shallow-water sponges - A pilot study

BackgroundShallow-water sponges can reach high densities and have several functions in the ecosystem, such as, providing microhabitats for other species or being involved in benthic-pelagic coupling. They also have a fast cell turnover so they can serve as test animals for the development of new methods to measure the metabolic activity of individual organisms. Here, we measured the feeding and metabolic activity of the common intertidal sponge Halichondria panicea using a triple stable isotope labeling experiment with a 13C and 15N-enriched bacteria as substrate and 2H from deuterated water. We also constrained pathways of phospholipid-derived fatty acid (PLFA) biosynthesis in the sponge and its microbiome. MethodsSponges were collected in the Eastern Scheldt (North Sea) and incubated in 1% 2H-enriched seawater in the presence of 13C- and 15N-enriched substrate of inactivated bacteria for 12 h. Water samples for the analysis of dissolved inorganic carbon (DIC), 13C-DIC, and inorganic nutrients were taken at the begin and the end of the incubations, while oxygen concentration in the water was recorded continuously. Seawater incubations with the addition of substrate bacteria served as blanks and dead sponges incubated in 1% 2H-enriched seawater served as controls for the incorporation of 2H into inactive tissue. At the end of the experiment, sponges were sampled for bulk analyses of 13C, 15N, and 2H in sponge tissue, and for 13C and 2H incorporation into phospholipid-derived fatty acids (PLFAs). ResultsSponges consumed oxygen, nitrite, nitrate, and silicon, while they excreted ammonia and released 13C-DIC. They incorporated 4.82 mol 13C mmol C-1 d-1, 2.46 mol 15N mmol C-1 d-1, and 0.49 mol 2H mmol C-1 d-1 into bulk sponge tissue. The PLFAs extracted from the sponges contained on average 5.61 g 13C g-1 dry mass (DM) sponge and 5.43 ng 2H g-1 DM sponge. Most 13C was incorporated into bacteria-specific PLFAs derived from the substrate bacteria; 2H, in comparison, was mostly built in sponge-specific PLFAs. ConclusionH. panicea from the Eastern Scheldt were in a similar condition as starving specimens from the Baltic Sea which suggests that the large bivalve stocks in the Eastern Scheldt outcompete this sponge for food. During the incubation experiment, however, the sponges were well fed as indicated by the silicon and oxygen uptake rates. The significantly higher uptake rates of 2H by living sponges compared to dead sponges proved that deuterated water can be used to measure the metabolic activity of individual filter-feeding specimens, but more test with species of diverse biological traits and growth stages are recommended. Additionally, we suggest to focus on compound-specific 2H uptake, as these data were less affected by 1H exchange of non-covalently bound 1H. Assessing 13C- and 2H-enriched PLFAs of the incubated H. panicea also revealed that the sponge microbiome produced the bacteria-specific PLFAs i-C14:0, ai-C15:0, i-C17:0, and ai-C17:0 using C from the substrate bacteria. The ai-C15:0 was subsequently elongated and desaturated to build the sponge-specific PLFA ai-C25:2. Other sponge-specific PLFAs were formed using C14:0 and C16:0 from the sub-strate bacteria as precursors.

ecology↗

bioRxiv2024

Dissolved organic matter fluxes and fatty acid composition from shallow-water and deep-water demo- and hexactinellid sponges from New Zealand

Sponges are an important component of shallow- and deep-water ecosystems enhancing eukaryotic biodiversity via diverse endo- and epibiota and by providing three dimensional habitats for benthic invertebrates and fishes. Sponge biodiversity is particularly high in the waters around New Zealand (Southwest Pacific), where we collected two shallow- and two deep-water sponge species (Tedania sp., Suberea meandrina, Farrea raoulensis, Artemisina sp.) for ex-situ incubation experiments to detect whether these sponges may process dissolved organic matter. We assessed the biochemical and phospholipid-derived fatty acids (PLFAs) and measured dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) fluxes. Changes in fluorescent dissolved organic matter (FDOM) over time were analyzed and the results were linked to the bacterial communities of the sponge holobiont. Dried sponge tissue consisted of 17.5 {+/-} 3.75% organic (org.) C and of 4.34 {+/-} 1.02% total nitrogen (TN) with a natural stable isotope composition of -19.0 {+/-}0.25{per thousand} for {delta}13org. C and of 10.2 {+/-}2.43{per thousand} for {delta}15TN. None of the DOC fluxes was significant and only the release of TDN by Tedania sp. was significantly different from 0 mol TDN g org. C-1 d-1. We detected the presence of four fluorophores in the FDOM pool: 2 tryptophan- and protein-like fluorophores (C1, C2), 1 humic-like fluorophore (C3), and 1 tyrosine-like fluorophore (C4). The maximum fluorescence intensity Fmax of C1 decreased significantly in S. meandrina incubations, whereas Fmax of C2 grew in the same incubations. Fmax of C3 increased in Tedania sp. incubations, in which Fmax of C4 decreased. In comparison, Fmax of C4 in S. meandrina rose. The PLFA composition of sponge tissue was dominated by long-chain fatty acids, saturated fatty acids, and monosaturated fatty acids and most PLFAs were sponge- and bacteria-specific. The bacterial community of the demosponges Artemisina sp., S. meandrina and Tedania sp. consisted mostly of Proteobacteria and Chloroflexota, whereas the dominating bacteria phylum of the hexactinellid F. raoulensis was Proteobacteria. We proposed that the holobionts of S. meandrina and Tedania sp. contain bacteria that are involved in the transformation and degradation of DOM. In S. meandrina, Chloroflexota and Poribacteria may degrade tryptophan-like fluorophores to a chemically modified tryptophan-like and protein-like fluorophore, while producing a tyrosine-like fluorophore. In Tedania sp., Chloroflexota may contribute to the release of significant amounts of TDN by producing humic-like fluorophores, while degrading tyrosine-like fluorophores. Farrea raoulensis may not take up DOM due to a lack of Poribacteria and Chloroflexota or may use colloidal instead of truly dissolved DOC.

ecology↗

bioRxiv2024

Nutrient fluxes, oxygen consumption and fatty acid composition from deep-water demo- and hexactinellid sponges from New Zealand

Sponges are an important component of deep-water ecosystems enhancing eukaryotic biodiversity by hosting diverse endo- and epibiota and providing three dimensional habitats for benthic invertebrates and fishes. As holobionts they are important hosts of microorganisms which are involved in carbon and nitrogen cycling. While increasing exploration of deep-water habitats results in new sponge species being discovered, little is known about their physiology and role in nutrient fluxes. Around New Zealand (Southwest Pacific), the sponge biodiversity is particularly high, and we selected six deep-sea sponge clusters (Saccocalyx, Suberites, Tedania, Halichondria/ Dendoricella, Sceptrulophora, Lissodendoryx) for in-situ and ex-situ experiments. We investigated the biochemical composition of the sponges, measured oxygen consumption and inorganic nutrient fluxes, as well as bacterial and phospholipid-derived fatty acid (PLFA) compositions. Our aim was to assess differences in fluxes and fatty acid composition among sponge clusters and linking their bacterial communities to nitrogen cycling processes. All sponges excreted nitrite and ammonia. Nitrate and phosphate excretion were independent of phylum affiliation (Demospongiae, Hexactinellida). Nitrate was excreted by the Halichondria/ Dendoricella and Lissodendoryx clusters, whereas the Suberites, Tedania, and Sceptrulophora clusters consumed it. Phosphate was excreted by Sceptrulophora and Halichondria/ Dendoricella clusters and consumed by all other clusters. Silicon was consumed by all sponge clusters, except for Saccocalyx and Halichondria/ Dendoricella clusters. Oxygen consumption rates ranged from 0.17 to 3.56{+/-}0.60 mmol O2 g C d-1. The PLFA composition was very sponge-cluster dependent and consisted mostly of long-chain fatty acids. Most PLFAs were sponge-specific, followed by bacteria-specific PLFAs, and others. All sponge clusters, except for Suberites, were low-microbial abundance (LMA) sponges whose bacterial community composition was dominated by Proteobacteria, Bacteroidota, Planctomycetota, and Nitrospinota. The Suberites cluster consisted of high-microbial abundance (HMA) sponges with Proteobacteria, Chloroflexota, Acidobacteriota, and Actinobacteriota as dominant bacteria. Based on the inorganic nitrogen flux measurements, we identified three types of nitrogen cycling in the sponges: In type 1, sponges (Dendoricella spp. indet., Lissodendoryx cluster) respired aerobically and ammonificated organic matter (OM) to ammonium, fixed N2 to ammonium, and nitrified aerobically heterotrophically produced ammonium to nitrate and nitrite. In type 2, sponges (Halichondria sp., Sceptrulophora, Suberites, Tedania clusters) respired OM aerobically and ammonificated it to ammonium. They also reduced nitrate anaerobically to ammonium via dissimilatory nitrate reduction to ammonium. In type 3, ammonium was microbially nitrified to nitrite and afterwards to nitrate presumably by ammonium-oxidizing Bacteria and/ or Archaea.

ecology↗

bioRxiv2023

Role of Astrophorina sponges (Demospongiae) in food-web interactions at the Flemish Cap (NW Atlantic)

Deep-sea sponges are important contributors to carbon and nitrogen cycling due to their large filtration capacity. Species of the suborder Astrophorina form dense sponge grounds in the North Atlantic, where they serve as prey for spongivores, but also have non-trophic interactions with commensal epi- and endobionts. At the Flemish Cap (NW Atlantic) Astrophorina sponges are present in four previously described deep-sea epifaunal assemblages: the deep-sea coral assemblage, the lower slope assemblages 1 and 2, and the deep-sea sponge assemblage. To investigate their role in trophic and non-trophic interactions at the Flemish Cap, we developed trophic-/ non-trophic interaction web models for each of the four faunal assemblages using the published literature. By excluding the sponges from the models, we estimated how many trophic, facultative and obligatory non-trophic links would be lost, and how this removal affected food-web properties (number of compartments, links, link density, and connectance). Astrophorina sponges were mostly linked via facultative non-trophic links to 60, 59, 86, and 92 compartments in the deep-sea coral, the lower slope 1 and 2, and the deep-sea sponge assemblages, respectively. Direct trophic links only existed to Echinasteridae and Pterasteridae. As removing Astrophorina sponges from the interaction webs of the different assemblages had the highest impact on food-web properties compared to removing any other fauna present, these sponges were considered "highest impact taxa". They were also identified, along with sea pens, as "structural species"/ "habitat formers" and "foundation species" based on non-trophic interactions in the deep-sea coral and deep-sea sponge assemblages.

ecology↗

bioRxiv2023

Deconvolving feeding niches and strategies of abyssal holothurians from their stable isotope, amino acid, and fatty acid composition

Holothurians are the dominant megabenthic deposit feeders in the Peru Basin (South-East Pacific) and feed to various degrees of selectively on the heterogenous pool of sedimentary detritus, but diet preferences for most holothurian species are unknown. This study reconstructs the diets of 13 holothurian species of the orders Elasipodida, Holothuriida, and Synallactida, from bulk stable isotope analyses ({delta}13C, {delta}15N) of holothurian body walls and guts, gut contents, and feces that were combined with compound-specific stable isotope analyses of amino acids, phospholipid-derived fatty acids, and neutral lipid-derived fatty acids in the body wall. Fatty acid concentrations showed high levels of storage lipids, an likely adaption to limited food supply to abyssal plains. Amino acid {delta}15N isotope values allowed estimating trophic levels of holothurian species and calculating heterotrophic re-synthesis of amino acids. Fatty acids served as trophic markers for feeding on diatom- and dinoflagellate derived phytodetritus, bacteria, Foraminifera, and detritus containing the PUFA C22:1{omega}9-cis. Several holothurian species seemed to be secondary consumers of detritus, while bacteria in their guts were primary consumers of this detritus. A Sorensen-Dice coefficient based cluster analysis using data of trophic levels, levels of heterotrophic re-synthesis of amino acids, feeding selectivity, and food sources/ diet suggested three trophic groups, characterized by different trophic levels. We show that this multi-biomarker driven approach allows to deconvolve trophic niches and feeding selectivity in one of the most challenging environments on earth and to identify dependence of deep-sea species to organic matter inputs that vary with season and/or climate.

zoology↗

bioRxiv2022

Habitat types and megabenthos composition from three sponge-dominated high-Arctic seamounts

Seamounts are isolated underwater mountains often stretching >1,000 m above the seafloor. They are usually identified as biodiversity hotspots of marine life, and host benthos assemblages that may vary on regional (among seamounts) and local (within seamounts) scales. Here, we collected seafloor imagery of three seamounts at the Langseth Ridge in the central Arctic Ocean to assess habitats and megabenthos community composition at the Central Mount (CM), the Karasik Seamount (KS), and the Northern Mount (NM). The majority of seafloor across these seamounts comprised bare rock, covered with a mixed layer consisting of sponge spicule mat intermixed with detrital debris composed primarily of polychaete tubes as well as sand, gravel, and/ or rocks. The megabenthos assemblages consisted of in total 15 invertebrate epibenthos taxa and four fish taxa, contributing to mean megabenthos densities of 55,745 ind. ha-1 at CM, 110,442 ind. ha-1 at KS, and 65,849 ind. ha-1 at NM. The faunal assemblages at all three seamounts were dominated by demosponges of the order Tetractinellida that contributed between 66% (KS) and 85% (CM) to all megabenthos. Megabenthos assemblages living on bare rock or on mixed substrate differed among seamounts and across individual seamounts.

ecology↗

bioRxiv2022

Role of polymetallic-nodule dependent fauna on carbon cycling in the eastern Clarion-Clipperton Fracture Zone (Pacific)

The abyssal seafloor in the Clarion-Clipperton Fracture Zone (CCZ) in the central Pacific is covered with large densities of polymetallic nodules, i.e., metal concretions containing iron, manganese, nickel, cobalt, and copper. These nodules are of economic interested and considered potential future resources for said metals, but they also host a variety of deep-sea fauna. In a recent study it was estimated that the removal of these nodules would lead to a loss of up to 18% of all taxa in the CCZ. Here, I assess the impact of removing these nodule-dependent taxa on carbon cycling at two sites (B4S03, B6S02) of the Belgian exploration license area in the eastern CCZ. For this purpose, I developed two highly-resolved carbon-based food web models with 72 (B6S02) to 77 (B4S03) food-web compartments consisting of different detritus pools, bacteria, metazoan meiobenthos, macrobenthic isopods, polychaetes and other macrobenthos, megabenthic cnidarians, crustaceans, poriferans, holothurians and other invertebrate megabenthos, and fish. These compartments were connected with 304 (B6S02) to 338 (B4S03) links which were reduced by 5-6% when nodule-dependent faunal compartments were removed. The models estimated the total system throughput T.., i.e., the sum of all carbon flows in the food webs, in intact food webs as 1.24 mmol C m-2 d-1 and 1.20 mmol C m-2 d-1 at B4S03 and B6S02, respectively, whereupon 67.7% (B4S03) to 69.8% (B6S02) of T.. flowed through the microbial loop. A removal of the nodule-dependent fauna did not affect this microbial loop, but reduced the scavenger loop by 54.6% (B6S02) to 84.1% (B4S03). Overall, nodule-dependent fauna is responsible for only a small fraction of total carbon cycling at the eastern CCZ. Therefore, when the effect of prospective deep-seabed mining on carbon cycling is investigated, its impact on benthic prokaryotes and the microbial loop should be addressed specifically.

ecology↗

bioRxiv2021

Polymetallic nodules are essential for food-web integrity of a prospective deep-seabed mining area in Pacific abyssal plains

Polymetallic nodule fields provide hard substrate for sessile organisms on the abyssal seafloor between 3,000 and 6,000 m water depth. Deep-seabed mining targets these mineral-rich nodules and will likely modify the consumer-resource (trophic) and substrate-providing (non-trophic) interactions within the abyssal food web. However, the importance of nodules and their associated sessile fauna in supporting food-web integrity remains unclear. Here, we use seafloor imagery and published literature to develop highly-resolved trophic and non-trophic interaction webs for the Clarion-Clipperton Fracture Zone (CCZ, central Pacific Ocean) and the Peru Basin (PB, south-east Pacific Ocean) and to assess how nodule removal will modify these networks. The CCZ interaction web included 1,028 compartments connected with 59,793 links and the PB interaction web consisted of 342 compartments and 8,044 links. We show that knock-down effects of nodule removal resulted in a 17.9% (CCZ) to 20.8% (PB) loss of all compartments and 22.8% (PB) to 30.6% (CCZ) loss of network links. Subsequent analysis identified stalked glass sponges living attached to the nodules as key structural species that supported a high diversity of associated fauna. We conclude that polymetallic nodules are critical for food-web integrity and that their absence will likely result in reduced local benthic biodiversity.

ecology↗