Comments On The Pseudo-Microfossil Linotolypen

Hollow, black reticulate ‘microfossils’ of unknown affinity found in Ordovician to late Cretaceous sediments from North America, Europe and Australia were given the name Linotolypa by Eisenack in 1962. In 1978, he recognised that they were pseudo-microfossils consisting of asphalt, and noted that their structure resembled that of soap bubbles formed in agitated suspensions. These objects are well known as a component of the particles caught from the air by pollen and spore traps at the present day. They are correctly termed ‘cenospheres’ and are formed from coal and possibly pitch and fuel oil by incomplete combustion. If their presence were to be confirmed in Palaeozoic sediments, this would provide important new evidence for the occurrence of fire in the geological record and of the history of levels of O2 in the atmosphere.

Radiolaria: Major exporters of organic carbon to the deep ocean

Very large pulses of particulate organic matter intermittently sink to the deep waters of the open ocean in the Northeast Atlantic. These pulses, measured by moored sediment traps since 1989, can contribute up to 60% of the organic flux to 3000 m in a particular year and are thus a major cause of the variability in carbon sequestration from the atmosphere in the region. Pulses occur in the late summer and are characterized by material that is very rich in organic carbon but with low concentrations of the biominerals opal and calcite. A number of independent lines of evidence have been examined to determine the causes of these pulses: (1) Data from the Continuous Plankton Recorder (CPR) survey show that in this region, radiolarian protozoans intermittently reach high abundances in the late summer just preceding organic pulses to depth. (2) CPR data also show that the interannual variability in radiolarian abundance since 1997 mirrors very closely the variability of deep ocean organic deposition. (3) The settling material collected in the traps displays a strong correlation between fecal pellets produced by radiolaria and the measured organic carbon flux. These all suggest that the pulses are mediated by radiolarians, a group of protozoans found throughout the world’s oceans and which are widely used by paleontologists to determine past climate conditions. Changes in the upper ocean community structure (between years and on longer timescales) may have profound effects on the ability of the oceans to sequester carbon dioxide from the atmosphere.

Sedimentation of acantharian cysts in the Iceland Basin: Strontium as a ballast for deep ocean particle flux, and implications for acantharian reproductive strategies

Acantharian cysts were discovered in sediment trap samples from spring 2007 at 2000 m in the Iceland Basin. Although these single-celled organisms contribute to particulate organic matter flux in the upper mesopelagic, their contribution to bathypelagic particle flux has previously been found negligible. Four time-series sediment traps were deployed and all collected acantharian cysts, which are reproductive structures. Across all traps, cysts contributed on average 3-22%, and 4―24% of particulate organic carbon and nitrogen (POC and PON) flux, respectively, during three separate collection intervals (the maximum contribution in any one trap was 48% for POC and 59% for PON). Strontium (Sr) flux during these 6 weeks reached 3 mg m―2 d―1. The acantharian celestite (SrSO4) skeleton clearly does not always dissolve in the mesopelagic as often thought, and their cysts can contribute significantly to particle flux at bathypelagic depths during specific flux events. Their large size (∼ I mm) and mineral ballast result in a sinking rate of ∼ 500 m d―1; hence, they reach the bathypelagic before dissolving. Our findings are consistent with a vertical profile of salinity-normalized Sr concentration in the Iceland Basin, which shows a maximum at 1700 m. Profiles of salinity-normalized Sr concentration in the subarctic Pacific reach maxima at ≤ 1500 m, suggesting that Acantharia might contribute to the bathypelagic particle flux there as well. We hypothesize that Acantharia at high latitudes use rapid, deep sedimentation of reproductive cysts during phytoplankton blooms so that juveniles can exploit the large quantity of organic matter that sinks rapidly to the deep sea following a bloom.

Marine snow studies in the Northeast Atlantic Ocean: distribution, composition and role as a food source for migrating plankton

During a 25 d Lagrangian study in May and June 1990 in the Northeast Atlantic Ocean, marine snow aggregates were collected using a novel water bottle, and the composition was determined microscopically. The aggregates contained a characteristic signature of a matrix of bacteria, cyanobacteria and autotrophic picoplankton with inter alia inclusions of the tintiniid Dictyocysta elegans and large pennate diatoms. The concentration of bacteria and cyanobacteria was much greater on the aggregates than when free-living by factors of 100 to 6000 and 3000 to 2 500 000, respectively, depending on depth. Various species of crustacean plankton and micronekton were collected, and the faecal pellets produced after capture were examined. These often contained the marine snow signature, indicating that these organisms had been consuming marine snow. In some cases, marine snow material appeared to dominate the diet. This implies a food-chain short cut wherby material, normally too small to be consumed by the mesozooplankton, and considered to constitute the diet of the microplankton can become part of the diet of organisms higher in the food-chain. The micronekton was dominated by the amphipod Themisto compressa, whose pellets also contained the marine snow signature. Shipboard incubation experiments with this species indicated that (1) it does consume marine snow, and (2) its gut-passage time is sufficiently long for material it has eaten in the upper water to be defecated at its day-time depth of several hundred meters. Plankton and micronekton were collected with nets to examine their vertical distribution and diel migration and to put into context the significance of the flux of material in the guts of migrants. “Gut flux” for the T. compressa population was calculated to be up to 2% of the flux measured simultaneously by drifting sediment traps and <5% when all migrants are considered. The in situ abundance and distribution of marine snow aggregates (>0.6 mm) was examined photographically. A sharp concentration peak was usually encountered in the depth range 40 to 80 m which was not associated with peaks of in situ fluorescence or attenuation but was just below or at the base of the upper mixed layer. The feeding behaviour of zooplankton and nekton may influence these concentration gradients to a considerable extent, and hence affect the flux due to passive settling of marine snow aggregates.

Fishery Exploitation and Stock Assessment of the Endangered Nassau Grouper, Epinephelus Striatus (Actinopterygii: Perciformes: Serranidae), in the Turks and Caicos Islands

The Nassau grouper, Epinephelus striatus (Bloch, 1792), is an endangered species that has been historically overexploited in numerous fisheries throughout its range in the Caribbean and tropical West Atlantic. Data relating fishery exploitation levels to stock abundance of the species are deficient, and protective regulations for the Nassau grouper are yet to be implemented in the Turks and Caicos Islands (TCI). The goal of this study was to conduct a stock assessment and evaluate the exploitation status of the Nassau grouper in the TCI. Materials and methods. Calibrated length cohort analysis was applied to published fisheries data on Nassau grouper landings in the TCI. The total lengths of Nassau groupers among the catches of spearfishers, lobster trappers, and deep sea fishers on the island of South Caicos during 2006 and 2008 were used with estimates of growth, natural mortality, and total annual landings to derive exploitation benchmarks. Results. The TCI stock experienced low to moderate fishing mortality (0.28, 0.18) and exploitation rates (0.49, 0.38) during the period of the study (2006, 2008). However, 21.2%-64.4% of all landings were reproductively immature. Spearfishing appeared to contribute most to fishing mortality relative to the use of lobster traps or hydraulic reels along bank drop-offs. Conclusion. In comparison with available fisheries data for the wider Caribbean, the results reveal the TCI as one of the remaining sites, in addition to the Bahamas, with a substantial Nassau grouper stock. In light of increasing development and tourism in the TCI, continued monitoring is essential to maintain sustainable harvesting practices.