The potential for mobile demersal fishing to reduce carbon storage and sequestration in seabed sediments

Subtidal marine sediments are one of the planet's primary carbon stores and strongly influence the oceanic sink for atmospheric CO2. By far the most pervasive human activity occurring on the seabed is bottom trawling and dredging for fish and shellfish. A global first-order estimate suggested mobile demersal fishing activities may cause 160-400 Mt of organic carbon (OC) to be remineralised annually from seabed sediment carbon stores. There are, however, many uncertainties in this calculation. Here, we discuss the potential drivers of change in seabed OC stores due to mobile demersal fishing activities and conduct a systematic review, synthesising studies where this interaction has been directly investigated. Mobile demersal fishing would be expected to reduce OC in seabed stores, albeit with site-specific variability. Reductions would occur due to lower production of flora and fauna, the loss of fine flocculent material, increased sediment resuspension, mixing and transport, and increased oxygen exposure. This would be offset to some extent by reduced faunal bioturbation and respiration, increased off-shelf transport and increases in primary production from the resuspension of nutrients. Studies which directly investigated the impact of demersal fishing on OC stocks had mixed results. A finding of no significant effect was reported in 51% of 59 experimental contrasts; 41% reported lower OC due to fishing activities, with 8% reporting higher OC. In relation to remineralisation rates within the seabed, 14 experimental contrasts reported that demersal fishing activities decreased remineralisation, with four reporting higher remineralisation rates. The direction of effects was related to sediment type, impact duration, study design and local hydrography. More evidence is urgently needed to accurately quantify the impact of anthropogenic physical disturbance on seabed carbon in different environmental settings, and incorporate full evidence-based carbon considerations into global seabed management.

Stoma and intestine ultrastructure of the marine free-living nematode Odontophora deconincki (Nematoda: Araeolaimida: Axonolaimidae)

Summary The fine morphology of the buccal capsule and intestine (midgut) of the marine free-living nematode Odontophora deconincki was investigated. The cheilostome is armed with six equal claw-like odontia that can evert radially by opening the mouth. Light-refracting accessory buccal structures within the cheilostomatal cuticle alternate with odontia and consist of two elements: anterior armilloids and posterior granular armilliths. The buccal cavity (pharyngostome) is surrounded by a complex of longitudinal and oblique muscles partially attached to the cheilostome cuticle at the sites of the accessory buccal structures and enabling a wide opening of the mouth. With the described stoma condition, the nematode probably scrapes food particles from the substrate surface. In cross-section, the midgut consists of 5-7 cells that appear uniform throughout its length. An extracellular matrix (glycocalyx) over the microvillar brush varies in thickness and stratification depending on presence or absence of food content in the lumen. Abundant spherocrystals (globular inclusions with concentric striations) were present in all gut cells. No indication of endocytosis or digestive vacuoles was observed in the gut cells and extracellular digestion predominates. Most specimens had a gut content formed from a long cylinder of compressed flocculent material with some barely identifiable components and few spherocrystals expelled from the enterocytes. We assume that the nematode diet comprises a wide range of objects, mainly eukariotic epigrowth organisms, which are shorn off and scraped from the surface of sand grains and then ingested.

Uterine Paramesonephric Cysts in Sprague-Dawley Rats from National Toxicology Program Studies

Congenital uterine wall cysts arising from paramesonephric (Müllerian) and mesonephric (Wolffian) ducts are typically incidental findings in most species. We used immunohistochemistry to characterize and determine the origin of uterine cysts in Sprague-Dawley (SD) rats from multigeneration studies conducted by the National Toxicology Program. Subserosal uterine cysts were observed in 20 of the 2,400 SD rats evaluated in five studies, and 10 cysts were characterized for this study. Single cysts were unilocular, fluid-filled, and occurred throughout the uterus. Microscopically, all cysts had a well-developed smooth muscle wall, lined by flattened to cuboidal, sometimes ciliated, epithelium that stained intensely positive for cytokeratin 18 and paired box protein 8 (PAX8). Most cyst epithelia displayed weak to moderate positivity for progesterone receptor (PR) and/or estrogen receptor α (ER-α), as well as were negative for GATA binding protein 3 (GATA3). Cyst lumens contained basophilic flocculent material. The cysts appeared to be developmental anomalies arising from paramesonephric tissue based on positive PAX8 and ER-α and/or PR staining. Additionally, 70% of the cysts lacked GATA3 expression. Taken together, the subserosal uterine cysts observed in adult rats in these studies most likely arose from the paramesonephric duct.

Biomarker assessment of spatial and temporal changes in the composition of flocculent material (floc) in the subtropical wetland of the Florida Coastal Everglades

Environmental context Flocculent material (floc) in freshwater and coastal areas of the Florida Everglades plays an important role in food web dynamics and nutrient cycling. Using biomarkers and pigment chemotaxonomy, we determined the organic matter composition of floc from different environments in the Everglades, and found that it is dominated by local biomass inputs and influenced by hydrological regimes. With the on-going restoration of the Florida Everglades, it is important to gain a better understanding of the biogeochemical dynamics of floc, including its sources, transformations and reactivity. Abstract Flocculent material (floc) is an important energy source in wetlands. In the Florida Everglades, floc is present in both freshwater marshes and coastal environments and plays a key role in food webs and nutrient cycling. However, not much is known about its environmental dynamics, in particular its biological sources and bio-reactivity. We analysed floc samples collected from different environments in the Florida Everglades and applied biomarkers and pigment chemotaxonomy to identify spatial and seasonal differences in organic matter sources. An attempt was made to link floc composition with algal and plant productivity. Spatial differences were observed between freshwater marsh and estuarine floc. Freshwater floc receives organic matter inputs from local periphyton mats, as indicated by microbial biomarkers and chlorophyll-a estimates. At the estuarine sites, the floc is dominated by mangrove as well as diatom inputs from the marine end-member. The hydroperiod (duration and depth of inundation) at the freshwater sites influences floc organic matter preservation, where the floc at the short-hydroperiod site is more oxidised likely due to periodic dry-down conditions. Seasonal differences in floc composition were not consistent and the few that were observed are likely linked to the primary productivity of the dominant biomass (periphyton in the freshwater marshes and mangroves in the estuarine zone). Molecular evidence for hydrological transport of floc material from the freshwater marshes to the coastal fringe was also observed. With the on-going restoration of the Florida Everglades, it is important to gain a better understanding of the biogeochemical dynamics of floc, including its sources, transformations and reactivity.

Evidence of lasting impact of the Deepwater Horizon oil spill on a deep Gulf of Mexico coral community

A coral community 11 km southwest of the site of the Deepwater Horizon blowout at 1,370 m water depth was discovered 3.5 months after the well was capped on 3 November 2010. Gorgonian corals at the site were partially covered by a brown flocculent material (floc) that contained hydrocarbons fingerprinted to the oil spill. Here we quantify the visible changes to the corals at this site during five visits over 17 months by digitizing images of individual branches of each colony and categorizing their condition. Most of the floc visible in November 2010 was absent from the corals by the third visit in March 2011, and there was a decrease in the median proportions of the colonies showing obvious signs of impact after the first visit. During our second visit in 2010, about six weeks after the first, we documented the onset of hydroid colonization (a sign of coral deterioration) on impacted coral branches that increased over the remainder of the study. Hydroid colonization of impacted portions of coral colonies by the last visit in March 2012 correlated positively with the proportion of the colony covered by floc during the first two visits in late 2010. Similarly, apparent recovery of impacted portions of the coral by March 2012 correlated negatively with the proportion of the coral covered with floc in late 2010. A notable feature of the impact was its patchy nature, both within and among colonies, suggesting that the impacting agent was not homogeneously dispersed during initial contact with the corals. While the median level of obvious visible impact decreased over time, the onset of hydroid colonization and the probability of impacts that were not visually obvious suggest that future visits may reveal additional deterioration in the condition of these normally long-lived corals.

Utrastructural observations on Goussia metchnikovi (Laveran, 1897) in the spleen of gudgeon, Gobio gobio L.

The ultrastructure of gamonts and sporulated oocysts of Goussia metchnikovi in the spleen of gudgeon, Gobio gobio from the river Lee, England is described. In developing microgamonts, small amylopectin granules were grouped centrally and nuclei were often arranged peripherally, close to the surface membrane. Nuclear chromatin condensed into peripheral dense portions that became the nuclei of flagellated microgametes, released to the parasitophorous vacuole. The cytoplasm of macrogametes had larger, scattered amylopectin granules, lipid globules and small electron-dense bodies, but no obvious wall forming bodies; peripheral vesicular structures with the appearance of mitochondria were also present and the parasitophorous vacuole contained flocculent material, but was otherwise free of structures. Sporulated oocysts contained four sporocysts and oocyst walls appeared to consist of a single membrane. Sporocyst walls showed a dehiscence suture, characteristic of the genus Goussia, which had filamentous extensions in places. The sporocyst wall comprised a dense inner layer and a thin outer layer with a fuzzy coat, separated by an electron lucent layer. Groups of oocysts were encapsulated by fibrous layers and inflammatory cells, and many sporocysts and their contained sporozoites showed evidence of elimination by the host.

Molecular Comparison of Bacterial Communities within Iron-Containing Flocculent Mats Associated with Submarine Volcanoes along the Kermadec Arc

ABSTRACT Iron oxide sheaths and filaments are commonly found in hydrothermal environments and have been shown to have a biogenic origin. These structures were seen in the flocculent material associated with two submarine volcanoes along the Kermadec Arc north of New Zealand. Molecular characterization of the bacterial communities associated with the flocculent samples indicated that no known Fe-oxidizing bacteria dominated the recovered clone libraries. However, clones related to the recently described Fe-oxidizing bacterium Mariprofundus ferrooxydans were obtained from both the iron-containing flocculent (Fe-floc) and sediment samples, and peaks corresponding to Mariprofundus ferrooxydans, as well as the related clones, were observed in several of our terminal restriction fragment length polymorphism profiles. A large group of epsilonproteobacterial sequences, for which there is no cultured representative, dominated clones from the Fe-floc libraries and were less prevalent in the sediment sample. Phylogenetic analyses indicated that several operational taxonomic units appeared to be site specific, and statistical analyses of the clone libraries found that all samples were significantly different from each other. Thus, the bacterial communities in the Fe-floc samples were not more closely related to each other than to the sediment communities.

Ultrastructural and cytochemical studies on vitellogenesis in trypanorhynch cestode Dollfusiella spinulifera Beveridge, Neifar et Euzet, 2004 (Eutetrarhynchidae)

The first description of vitellogenesis in the Trypanorhyncha is presented in this paper. Though the type of vitellogenesis and mature vitellocyte in Dollfusiella spinulifera appear to be unique among the Eucestoda, to some extent they resemble that observed in the lower cestodes, namely the Tetraphyllidea and Pseudophyllidea. Maturation is characterized by: (1) an increase in cell volume; (2) extensive development of large, parallel, frequently concentric cisternae of GER that produce proteinaceous granules; (3) development of Golgi complexes engaged in packaging this material; (4) continuous enlargement of proteinaceous granules within vesicles and their transformation into shell globule clusters; and (5) progressive fusion of all vesicles, with flocculent material containing the proteinaceous granules and shell globule clusters, into a single very large vesicle that characterises mature vitellocytes of this tapeworm. Cell inclusions in and around the large vesicle consist of flocculent material of a very low density, a few shell globule clusters, moderately dense proteinaceous granules and numerous large droplets of unsaturated lipids. A new previously unreported mode of transformation of proteinaceous granules into shell globule clusters, that evidently differs from that of pseudophyllideans and tetraphyllideans, is described. Cytochemical staining with periodic acid-thiosemicarbazide-silver proteinate for polysaccharides indicates a strongly positive reaction for membrane-bound glycoproteins in all membranous structures such as GER, mitochondria, Golgi complexes, nuclear and cell plasma membranes. Similar staining revealed β-glycogen particles scattered in the cytoplasm of maturing vitellocytes. Typical cytoplasmic β-glycogen particles appear mainly during early vitellocyte maturation but it is characteristic for this species that they are only seldom visible in mature cells. Some working hypotheses concerning the interrelationship between this particular pattern of vitellogensis, possible mode of egg formation in D. spinulifera, its embryonic development and trypanorhynchean life cycle, are drawn and discussed.

Does fertilization in the filarial nematode Dirofilaria immitis occur through endocytosis of spermatozoa?

Information on the ultrastructural details of fertilization in filarial nematodes are still unavailable. Here we report new data on this process in Dirofilaria immits, the heartworm of dogs and cats. Electron microscopy allowed us to observe oocytes engulfing spermatozoa through an endocytosis-like process. We also observed spermatozoa inside the oocytes which still possessed their plasma membrane and which were clearly enveloped by a further membrane, likely derived from the endocytosis process. At this stage, at the interface between the sperm membrane and the endocytotic membrane (vacuolar space), we observed flocculent material in the proximity of the membranous organelles (MOs) of the sperm. In the proximity of the MOs, we also observed the enlargement of the vacuolar space. Other images showed the dissolution of the sperm membrane, and the release of nuclear masses and organelles in the egg cytoplasm. We did not observe the fusion of lysosomes to the endocytotic vacuoles. In addition, the lysis of the sperm organelles has never been observed inside the vacuoles containing the whole sperm. Thus we suggest that the degradation of the endocytotic and sperm plasma membranes is determined by material released by the MOs. Since we did not observe the entry of sperm into the oocytes by other mechanisms, we also suggest that endocytosis is the normal process used by the spermatozoon to get into the egg cytoplasm in D. immitis. Finally, during our observations of the seminal receptacle we did not observe any structure in the spermatozoa which could be interpreted as an intracellular bacterium. This is consistent with previous results indicating that the bacterium Wolbachia in filarial nematodes is not transmitted through the sperm.