How fast do marine invertebrates burrow?

The burrowing of bivalves, arthropods, and echinoderms collected from tidal flats and shallow subtidal sediments of the Ogeechee estuary, Georgia, U.S.A was analyzed using time-elapse, X-ray analysis of thin-walled aquaria. The rate of sediment intrusion was determined for each animal. Burrowing rates ranged between 0.01 and 0.15 cm³/h for suspension-feeding animals. Deposit-feeding animals moved between 1 and 10 cm³ of sand per hour, approximately 10 to 100 times more sediment than the suspension feeders moved over similar times.Neoichnological experiments show that ten filter-feeding individuals could take as long as 115 yr to churn a 1 m² plot of sediment, by indexing the measured burrowing rates to realistic animal population densities. Ten such mobile deposit feeders as irregular echinoderms could bioturbate the same sediment in just 42 days. Under the maximum population densities modeled, the animals could bioturbate the sediment plot in 61 min. Given the reported results, qualitative interpretation of the rock record is possible: highly burrowed examples of the Skolithos Ichnofacies reflect high population densities and at least seasonal time spans. Highly burrowed examples of the Cruziana Ichnofacies may represent moderate population densities and short time spans.     

What to do in marine biotechnology?

During the symposium "Marine Biotechnology: Basics and Applications", held 25 February-1 March, 2003 in Matalasca?as, Spain, a special brainstorm session was organized. Two questions were addressed: 1, "What is the most desirable development in marine biotechnology"?; 2, "What is the most spectacular development in this field in your 'wildest' dreams"? The outcome of this session is reported in this paper. From the more than 250 ideas generated, concern for the environment and human health emerged as the most significant issues.     

Metagenomic marine nitrogen fixation--feast or famine?

Natural populations of bacteria in different environments can be astonishingly diverse, as was revealed graphically by large-scale sequencing of samples of their so-called metagenomes. Among the sequence datasets from four different samples of marine bacterial metagenomes, we noted that nitrogen fixation (nif) genes were conspicuous by their absence from three of them. However, in one sample, more than one-third of the bacteria appeared to have a complement of these genes. Here, some reasons behind this site-to-site variability and their implications for how molecular methods, involving large-scale sequencing and/or functional metagenomics, can best be used to describe bacterial diversity in natural environments are discussed.     

Will ocean acidification affect marine microbes?

The pH of the surface ocean is changing as a result of increases in atmospheric carbon dioxide (CO₂), and there are concerns about potential impacts of lower pH and associated alterations in seawater carbonate chemistry on the biogeochemical processes in the ocean. However, it is important to place these changes within the context of pH in the present-day ocean, which is not constant; it varies systematically with season, depth and along productivity gradients. Yet this natural variability in pH has rarely been considered in assessments of the effect of ocean acidification on marine microbes. Surface pH can change as a consequence of microbial utilization and production of carbon dioxide, and to a lesser extent other microbially mediated processes such as nitrification. Useful comparisons can be made with microbes in other aquatic environments that readily accommodate very large and rapid pH change. For example, in many freshwater lakes, pH changes that are orders of magnitude greater than those projected for the twenty second century oceans can occur over periods of hours. Marine and freshwater assemblages have always experienced variable pH conditions. Therefore, an appropriate null hypothesis may be, until evidence is obtained to the contrary, that major biogeochemical processes in the oceans other than calcification will not be fundamentally different under future higher CO₂/lower pH conditions.     

Hidden structural heterogeneity enhances marine hotspots’ biodiversity

Studies in terrestrial and shallow-water ecosystems have unravelled the key role of interspecific interactions in enhancing biodiversity, but important knowledge gaps persist for the deep sea. Cold-water coral reefs are hotspots of biodiversity, but the role of interspecific interactions and “habitat cascades” (i.e. positive effects on focal organisms mediated by biogenic habitat formation) in shaping their biodiversity is unknown. Associations between macrofaunal hosts and epifauna were examined in 47 stations at the Mingulay Reef Complex (northeast Atlantic). In total, 101 (group level) and 340 (species level) unique types of facultative associations formed by 43 hosts and 39 epifaunal species were found. Molluscs and empty polychaete tubes had higher values for the type and number of host-epifaunal associations, the Shannon–Wiener (H) and Margalef (d) indices of the epifauna than the rest of the taxonomic groups (p < 0.05). Hosts’ body size, orientation, surface smoothness, and growth form explained a significant amount of variability (32.96%) in epifauna community composition. Epifaunal species richness (S), H and d were 27.4 (± 2.2%), 56.2 (± 2.8%) and 39.9 (± 2.3%) of the respective values for the total sessile communities living on coral framework. This is intriguing as coral framework is orders of magnitude larger than the size of macrofaunal hosts. It is suggested that bivalves, tunicates and empty polychaete tubes increase habitat heterogeneity and enhance biodiversity through “habitat cascades”, in a similar way that epiphytes do in tropical rainforests. Most macrofaunal habitat suppliers in the studied cold-water coral reef are calcified species and likely susceptible to ocean acidification. This indicates that the impacts of climate change on the total biodiversity, structure and health of cold-water coral reefs may potentially be more severe than previously thought.

     

Carbon or nitrogen limitation in marine copepods?

The elemental limitation of copepod production can be studiedusing stoichiometric models, which balance carbon (C) and nitrogen(N) in ingested food and predator biomass, and assume that theelement in shortest supply is used as efficiently as possible.A model of this type was developed which has two important features:(i) it is assumed that a maximum N net production efficiencyof 1.0 is possible, although assimilation of N may be <1.0;and (ii) assimilation of C in the gut is handled by dividingfood into biochemical compounds. Model results suggested thatmarine copepods should commonly be limited by C, owing to theirlow C net production efficiency, and the low food C:N ratiostypical of the upper ocean. Nevertheless, the work demonstratedthat copepods might still preferentially ingest protein-richprey to maximize production because the associated C is easilyassimilated. A comparison of model predictions with two experimentalstudies, however, revealed that in the studies copepods werenot utilizing N as efficiently as would be expected by stoichiometrictheory. This finding suggests that copepod nutrition is morecomplicated than simple elemental limitation by C or N: imbalancesof specific compounds, such as essential amino acids, may becontrolling production. In addition, the nutritional requirementsof copepods may vary on a seasonal basis in a complex manner.     

The prevalence of Toxoplasma gondii in polar bears and their marine mammal prey: evidence for a marine transmission pathway?

Little is known about the prevalence of the parasite Toxoplasma gondii in the arctic marine food chain of Svalbard, Norway. In this study, plasma samples were analyzed for T. gondii antibodies using a direct agglutination test. Antibody prevalence was 45.6% among polar bears (Ursus maritimus), 18.7% among ringed seals (Pusa hispida) and 66.7% among adult bearded seals (Erignathus barbatus) from Svalbard, but no sign of antibodies were found in bearded seal pups, harbour seals (Phoca vitulina), white whales (Delphinapterus leucas) or narwhals (Monodon monoceros) from the same area. Prevalence was significantly higher in male polar bears (52.3%) compared with females (39.3%), likely due to dietary differences between the sexes. Compared to an earlier study, T. gondii prevalence in polar bears has doubled in the past decade. Consistently, an earlier study on ringed seals did not detect T. gondii. The high recent prevalence in polar bears, ringed seals and bearded seals could be caused by an increase in the number or survivorship of oocysts being transported via the North Atlantic Current to Svalbard from southern latitudes. Warmer water temperatures have led to influxes of temperate marine invertebrate filter-feeders that could be vectors for oocysts and warmer water is also likely to favour higher survivorship of oocycts. However, a more diverse than normal array of migratory birds in the Archipelago recently, as well as a marked increase in cruise-ship and other human traffic are also potential sources of T. gondii.     

Algalytic activity of α-mannosidase on harmful marine microalgae

-D mannose is present on the surface of thetoxic dinoflagellate Cochlodinium polykrikoides.When exposed to the enzyme -mannosidase, livecells of C. polykrikoides lost motility, roundedup, swelled gradually, and then lysed. The enzymedemonstrated a wide spectrum of lytic activity towardthe harmful algal species of the family Gymnodiniales,Alexandrium tamarense and Eutreptiellagymnastica, but showed less effect on useful feedalgae such as Chaetoceros calcitrans, Dunaliella salina, Isochrysis galbana, and Navicula pelliculosa.     

Climate change impacts on China’s marine ecosystems

Reviews in Fish Biology and Fisheries - Globally, climate change impacts on marine ecosystems are evident in physical, chemical, and biological processes, and are generally more extensive in faster...     

What can biological barcoding do for marine biology?

The idea of using nucleotide sequences as barcodes for species identification has stirred up debates in the community of taxonomists and systematists. We argue that barcodes are potentially extremely useful tools for taxonomy for several reasons. Barcodes may, for example, help to identify cryptic and polymorphic species and give means to associate life history stages of unknown identity. Barcode systems would thus be particularly helpful in cases when morphology is ambiguous or uninformative and would provide tools for higher taxonomic resolution of disparate life forms. Comparative analysis of short DNA sequences may also represent heuristic access cards to a deeper understanding of evolutionary relationships between organisms. However, barcodes are the “essence” of species identities no more than taxonomic holotypes are “the species”. It makes no sense to think that morphology and other biological information about organisms can be made obsolete by barcode systems. The biological significance of matching or diverging nucleotide sequences will still have to be the subject of taxonomic decisions that must be open for scrutiny. It is imperative, therefore, that barcodes are associated with specimen vouchers.     

Do marine phytoplankton follow Bergmann's rule sensu lato?

Global warming has revitalized interest in the relationship between body size and temperature, proposed by Bergmann's rule 150 years ago, one of the oldest manifestations of a ‘biogeography of traits’. We review biogeographic evidence, results from clonal cultures and recent micro‐ and mesocosm experiments with naturally mixed phytoplankton communities regarding the response of phytoplankton body size to temperature, either as a single factor or in combination with other factors such as grazing, nutrient limitation, and ocean acidification. Where possible, we also focus on the comparison between intraspecific size shifts and size shifts resulting from changes in species composition. Taken together, biogeographic evidence, community‐level experiments and single‐species experiments indicate that phytoplankton average cell sizes tend to become smaller in warmer waters, although temperature is not necessarily the proximate environmental factor driving size shifts. Indirect effects via nutrient supply and grazing are important and often dominate. In a substantial proportion of field studies, resource availability is seen as the only factor of relevance. Interspecific size effects are greater than intraspecific effects. Direct temperature effects tend to be exacerbated by indirect ones, if warming leads to intensified nutrient limitation or copepod grazing while ocean acidification tends to counteract the temperature effect on cell size in non‐calcifying phytoplankton. We discuss the implications of the temperature‐related size trends in a global‐warming context, based on known functional traits associated with phytoplankton size. These are a higher affinity for nutrients of smaller cells, highest maximal growth rates of moderately small phytoplankton (ca. 10² µm³), size‐related sensitivities for different types of grazers, and impacts on sinking rates. For a phytoplankton community increasingly dominated by smaller algae we predict that: (i) a higher proportion of primary production will be respired within the microbial food web; (ii) a smaller share of primary production will be channeled to the classic phytoplankton – crustacean zooplankton – fish food chain, thus leading to decreased ecological efficiency from a fish‐production point of view; (iii) a smaller share of primary production will be exported through sedimentation, thus leading to decreased efficiency of the biological carbon pump.     

Why are marine adaptive radiations rare in Hawai'i?

Islands can be sites of dynamic evolutionary radiations, and the Hawaiian Islands have certainly given us a bounty of insights into the processes and mechanisms of diversification. Adaptive radiations in silverswords and honeycreepers have inspired a generation of biologists with evidence of rapid diversification that resulted in exceptional levels of ecological and morphological diversity. In this issue of Molecular Ecology, tiny waterfall‐climbing gobies make a case for their place among Hawaiian evolutionary elite. Moody et al. ( 2015 ) present an analysis of gene flow and local adaptation in six goby populations on Kaua'i and Hawai'i measured in three consecutive years to try to disentangle the relative role of local adaptation and gene flow in shaping diversity within Sicyopterus stimpsoni. Their study shows that strong patterns of local selection result in streams with gobies adapted to local conditions in spite of high rates of gene flow between stream populations and no evidence for significant genetic population structure. These results help us understand how local adaptation and gene flow are balanced in gobies, but these fishes also offer themselves as a model that illustrates why adaptive diversification in Hawai'i's marine fauna is so different from the terrestrial fauna.     

Antioxidant defences in marine fish—II. Elasmobranchs

1. Tissues from four ray species and two shark species were examined concerning Superoxide dismutase and catalase content, and malonaldehyde and tocopherol concentrations.2. Livers displayed the highest Superoxide dismutase and catalase content in all species examined. Sharks exhibited higher mean enzyme contents than rays (3.6 and 2.4 nmol SOD g⁻¹ wet tissue, 185 and 120 pmol catalase g⁻¹ wet tissue).3. Tocopherol was detected in liver from all species, in kidney and in ovary from one ray and one shark species, and in shark cristaline in a range of 0.1–4.8 nmol g⁻¹ wet tissue.4. The content of antioxidant enzymes in elasmobranchs was lower than that of teleosts, and seems to follow the overall metabolic oxygen consumption or activity level from each fish major taxonomic group.5. Liver peroxidation as measured as MDA/TBARS concentration, revealed very high values (range of 1.5–4.5 μmoles g⁻¹ wet tissue), approximately one order of magnitude higher when compared with mammals.     

Fiji’s largest marine reserve benefits reef sharks

To provide more information about whether sharks benefit from no-take marine reserves, we quantified the relative abundance and biomass of reef sharks inside and outside of Namena, Fiji’s largest reserve (60.6 km²). Using stereo baited remote underwater video systems (stereo-BRUVs), we found that the abundance and biomass of sharks was approximately two and four times greater in shallow and deep locations, respectively, within the Namena reserve compared to adjacent fished areas. The greater abundance and biomass of reef sharks inside Namena is likely a result of greater prey availability rather than protection from fishing. This study demonstrates that marine reserves can benefit sharks.     

Can heterotrophic bacteria be important to marine light absorption?

The contribution of heterotrophic bacteria to particulate lightabsorption in the ocean has been traditionally considered insignificantas compared to that of phytoplankton and detritus. This viewhas been based on the general preswnption that heterotrophicmarine bacteria do not contain pigments with significant absorptionin the visible spectral range. However, there exist heterotrophicbacteria that synthesize carotenoid pigments, and carotenoid-richstrains of bacteria have often been isolated from natural seawatersamples taken in the open and coastal ocean. Because carotenoidsabsorb strongly in the blue spectral region, the heterotrophicbacteria may contribute more to marine light absorption thanhas been assumed. In order to make preliminary assessment ofsuch a contribution, we measured the absorption of a strainof carotenoid-containing heterotrophic bacteria (CHB) grownin the laboratory under differing conditions of light and nutrientavailability. These measurements showed that absorption cross-sectionsof CHB in the blue could be at least twice, and possibly oneorder of magnitude, higher than those of non-pigmented heterotrophicbacteria (NHB). In addition, the absorption features of CHBwere conserved under the differing light and nutrient conditions.We conclude that the role of heterotrophic bacteria in marinelight absorption needs to be re-evaluated. This will requirefurther laboratory studies to quantify the absorption cross-sectionsof marine bacteria with improved accuracy, as well as the developmentof a technique for the recognition and enumeration of CHB cellsin the ocean.     

Gloom and doom? The future of marine capture fisheries

Predicting global fisheries is a high-order challenge but predictions have been made and updates are needed. Past forecasts, present trends and perspectives of key parameters of the fisheries--including potential harvest, state of stocks, supply and demand, trade, fishing technology and governance--are reviewed in detail, as the basis for new forecasts and forecasting performance assessment. The future of marine capture fisheries will be conditioned by the political, social and economic evolution of the world within which they operate. Consequently, recent global scenarios for the future world are reviewed, with the emphasis on fisheries. The main driving forces (e.g. global economic development, demography, environment, public awareness, information technology, energy, ethics) including aquaculture are described. Outlooks are provided for each aspect of the fishery sector. The conclusion puts these elements in perspective and offers the authors' personal interpretation of the possible future pathway of fisheries, the uncertainty about it and the still unanswered questions of direct relevance in shaping that future.