Natural Sciences

Resource Partitioning Between Phytoplankton and Bacteria in the Coastal Baltic Sea

Sörenson E, Farnelid H, Lindehoff E, Legrand C. Resource Partitioning Between Phytoplankton and Bacteria in the Coastal Baltic Sea. Frontiers in Marine Science [Internet]. 2020 ;7. Available from: https://www.frontiersin.org/articles/10.3389/fmars.2020.608244/full?utm_source=F-AAE&utm_medium=EMLF&utm_campaign=MRK_1495887_45_Marine_20201201_arts_A
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

Eutrophication coupled to climate change disturbs the balance between competition and coexistence in microbial communities including the partitioning of organic and inorganic nutrients between phytoplankton and bacteria. Competition for inorganic nutrients has been regarded as one of the drivers affecting the productivity of the eutrophied coastal Baltic Sea. Yet, it is unknown at the molecular expression level how resources are competed for, by phytoplankton and bacteria, and what impact this competition has on the community composition. Here we use metatranscriptomics and amplicon sequencing and compare known metabolic pathways of both phytoplankton and bacteria co-occurring during a summer bloom in the archipelago of Åland in the Baltic Sea to examine phytoplankton bacteria resource partitioning. The expression of selected pathways of carbon (C), nitrogen (N), and phosphorus (P) metabolism varied over time, independently, for both phytoplankton and bacteria, indicating partitioning of the available organic and inorganic resources. This occurs regardless of eukaryotic plankton growth phase (exponential or stationary), based on expression data, and microbial community composition. Further, the availability of different nutrient resources affected the functional response by the bacteria, observed as minor compositional changes, at class level, in an otherwise taxonomically stable bacterial community. Resource partitioning and functional flexibility seem necessary in order to maintain phytoplankton-bacteria interactions at stable environmental conditions. More detailed knowledge of which organisms utilize certain nutrient species are important for more accurate projections of the fate of coastal waters.

 

Feeding Habits of Bigeye Tuna (Thunnus obesus) in the Western Indian Ocean Reveal a Size-Related Shift in Its Fine-Scale Piscivorous Diet

Lin C-H, Lin J-S, Chen K-S, Chen M-H, Chen C-Y, Chang C-W. Feeding Habits of Bigeye Tuna (Thunnus obesus) in the Western Indian Ocean Reveal a Size-Related Shift in Its Fine-Scale Piscivorous Diet. Frontiers in Marine Science [Internet]. 2020 ;7. Available from: https://www.frontiersin.org/articles/10.3389/fmars.2020.582571/full?utm_source=F-AAE&utm_medium=EMLF&utm_campaign=MRK_1495887_45_Marine_20201201_arts_A
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

This study analyzed the piscivorous diet of bigeye tuna (Thunnus obesus) through species identification of both fish and otolith remains in stomachs of 183 bigeye tuna collected in the western Indian Ocean. A total of 642 fish remains and 1,021 fish otoliths were examined. Prey items identified in the fish and otolith remains were not completely consistent. Although 12 items out of the 53 identified taxa were found in both remains, 20 items of fish remains were not found in otolith remains, and 21 items were added only from the otoliths. The main fish remains were Alepisauridae, which accounted for 13.9%. Most of the otoliths belonged to Myctophidae (49.5%) and Scopelarchidae (21.4%). Three prey items, namely Valenciennellus tripunctulatusEvermannella sp., and Zenion sp., were recorded for the first time in the diet of bigeye tuna from the region. The otolith remains substantially enhanced the taxonomic resolution of the diet. Bigeye tuna stomach contents were independent of location, depth, and time of catch but varied with tuna size. The proportion of dominant Myctophidae prey items decreased markedly as the tuna size increased, whereas the proportion of Macrouridae increased with size. In addition, larger bigeye tuna were found feeding on larger prey (Electrona risso and Scopelarchus analis), demonstrating that diet changes in both prey composition and size are related to the ontogeny of the fish.

Climatic and Oceanographic Controls on Coral Bleaching Conditions in the Maldivian Region

De Falco C, Bracco A, Pasquero C. Climatic and Oceanographic Controls on Coral Bleaching Conditions in the Maldivian Region. Frontiers in Marine Science [Internet]. 2020 ;7. Available from: https://www.frontiersin.org/articles/10.3389/fmars.2020.539869/full?utm_source=F-AAE&utm_medium=EMLF&utm_campaign=MRK_1495887_45_Marine_20201201_arts_A
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

The frequency of coral bleaching events has been increasing in recent decades due to the temperature rise registered in most regions near the ocean. Their occurrence in the Maldivian Archipelago has been observed in the months following the peak of strong El Niño events. Bleaching has not been uniform, and some reefs have been only marginally impacted. Here, we use satellite observations and a regional ocean model to explore the spatial and temporal variability of sea surface temperatures (SSTs), and quantify the relative magnitude of ENSO-related episodes with respect to the recent warming. In line with other studies, it is confirmed that the long-term trend in SST significantly increases the frequency of stress conditions for the Maldivian corals. It is also found that the interaction between currents and the steep bathymetry is responsible for a local cooling of about 0.2°C in the Archipelago during the warmest season, with respect to the surrounding waters. This cooling largely reduces the frequency of mortality conditions.

Complex Interactions of Temperature, Light and Tissue Damage on Seagrass Wasting Disease in Zostera marina

Jakobsson-Thor S, Brakel J, Toth GB, Pavia H. Complex Interactions of Temperature, Light and Tissue Damage on Seagrass Wasting Disease in Zostera marina. Frontiers in Marine Science [Internet]. 2020 ;7. Available from: https://www.frontiersin.org/articles/10.3389/fmars.2020.575183/full?utm_source=F-AAE&utm_medium=EMLF&utm_campaign=MRK_1467818_45_Marine_20201027_arts_A
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

The temperate seagrass species eelgrass Zostera marina can be infected by the wasting disease pathogen Labyrinthula zosterae, which is believed to have killed about 90% of the seagrass in the Atlantic Ocean in the 1930s. It is not known why this opportunistic pathogen sometimes becomes virulent, but the recurrent outbreaks may be due to a weakening of the Z. marina plants from adverse environmental changes. This study investigated the individual and interactive effects of multiple extrinsic factors (temperature, light, and tissue damage) on the host-pathogen interaction between Z. marina and L. zosterae in a fully crossed infection experiment. The degree of infection was measured as both lesion coverage and L. zosterae cell concentration. We also investigated if the treatment factors affect the chemical defense of the host, measured as the inhibitory capacity of seagrass extracts in bioassays with L. zosterae. Finally, gene expression of a set of targeted genes was quantified in order to investigate how the treatments change Z. marina’s response to infection. Light had a pronounced effect on L. zosterae infection measured as lesion coverage, where reduced light conditions increased lesions by 35%. The response to light on L. zosterae cell concentration was more complex and showed significant interaction with the temperature treatment. Cell concentration was also significantly affected by physical damage, where damage surprisingly resulted in a reduced cell concentration of the pathogen. No treatment factor caused detectable decrease in the inhibitory capacity of the seagrass extracts. There were several interactive effects between L. zosterae infection and the treatment factors on Z. marina growth, and on the expression of genes associated with immune defense, phenol synthesis and primary metabolism, showing that the molecular reaction toward L. zosterae infection depends on prevailing environmental conditions. Our study shows that individual or interactive effects of light, temperature and tissue damage can affect multiple aspects of host-pathogen interactions in seagrasses. These results highlight the complexity of marine host-pathogen systems, showing that more multi-factorial investigations are needed to gain a better understanding of disease in marine plants under different environmental conditions.

Extreme Effects of Extreme Disturbances: A Simulation Approach to Assess Population Specific Responses

Reed J, Harcourt R, New L, Bilgmann K. Extreme Effects of Extreme Disturbances: A Simulation Approach to Assess Population Specific Responses. Frontiers in Marine Science [Internet]. 2020 ;7. Available from: https://www.frontiersin.org/articles/10.3389/fmars.2020.519845/full?utm_source=F-AAE&utm_medium=EMLF&utm_campaign=MRK_1467818_45_Marine_20201027_arts_A
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

In South Australia, discrete populations of bottlenose dolphins inhabit two large gulfs, where key threats and population estimates have been identified. Climate change, habitat disturbance (shipping and noise pollution), fishery interactions and epizootic events have been identified as the key threats facing these populations. The Population Consequences of Disturbance (PCoD) framework has been developed to understand how disturbances can influence population dynamics. We used population estimates combined with population specific bioenergetics models to undertake a partial PCoD assessment, comparing how the two populations respond to the identified regional threats. Populations were modeled over a 5 year period looking at the influence of each disturbance separately. As expected, the most extreme epizootic and climate change disturbance scenarios with high frequency and intensity had the biggest influence on population trends. However, the magnitude of the effect differed by population, with Spencer Gulf showing a 43% and Gulf St Vincent a 23% decline under high frequency and high impact epizootic scenarios. Epizootic events were seen to have the strongest influence on population trends and reproductive parameters for both populations, followed by climate change. PCoD modeling provides insights into how disturbances may affect different populations and informs management on how to mitigate potential effects while there is still time to act.

Intrusion of Kuroshio Helps to Diminish Coastal Hypoxia in the Coast of Northern South China Sea

Lui H-K, Chen C-TArthur, Hou W-P, Liau J-M, Chou W-C, Wang Y-L, Wu C-R, Lee J, Hsin Y-C, Choi Y-Y. Intrusion of Kuroshio Helps to Diminish Coastal Hypoxia in the Coast of Northern South China Sea. Frontiers in Marine Science [Internet]. 2020 ;7. Available from: https://www.frontiersin.org/articles/10.3389/fmars.2020.565952/full?utm_source=F-AAE&utm_medium=EMLF&utm_campaign=MRK_1467818_45_Marine_20201027_arts_A
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

Since half a century ago, the number and area of dead zones (dissolved oxygen (DO) < 2 mg L–1 or 30% saturation) in the coastal oceans has increased dramatically. As widely recognized, the increased terrestrial nutrient and organic matter inputs are the two main factors causing the eutrophication of many coastal oceans. Here we show with decadal observed time series data from stations off the Pearl River Estuary and in the northern South China Sea (nSCS) that a strong intrusion into the nSCS of the West Philippine Sea (WPS) seawater in the form of Kuroshio branch occurred during the warm phase of the Pacific Decadal Oscillation (PDO) around 2003–2004 and 2015–2016 (also a strong El Niño event). Consequently, the DO concentration increased but NO3 and PO43– concentrations decreased in the subsurface layers of the nSCS. The WPS seawater was observed to reach the hypoxic area off the Pearl River Estuary in 2003–2004. Likely, due to the oxygen supply carried by the Kuroshio, little hypoxia developed. Yet, anoxic condition developed in the cold phase of PDO or strong La Niña years with weak Kuroshio intrusions.

Swim with the tide: Tactics to maximize prey detection by a specialist predator, the greater sea snake (Hydrophis major)

Udyawer V, Goiran C, Chateau O, Shine R. Swim with the tide: Tactics to maximize prey detection by a specialist predator, the greater sea snake (Hydrophis major) Somers CM. PLOS ONE [Internet]. 2020 ;15(10):e0239920. Available from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0239920
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

The fitness of a predator depends upon its ability to locate and capture prey; and thus, increasing dietary specialization should favor the evolution of species-specific foraging tactics tuned to taxon-specific habitats and cues. Within marine environments, prey detectability (e.g., via visual or chemical cues) is affected by environmental conditions (e.g., water clarity and tidal flow), such that specialist predators would be expected to synchronize their foraging activity with cyclic variation in such conditions. In the present study, we combined behavioral-ecology experiments on captive sea snakes and their prey (catfish) with acoustic tracking of free-ranging sea snakes, to explore the use of waterborne chemical cues in this predator-prey interaction. In coral-reef ecosystems of New Caledonia, the greater sea snake (Hydrophis major) feeds only upon striped eel catfish (Plotosus lineatus). Captive snakes became more active after exposure to waterborne chemical cues from catfish, whereas catfish did not avoid chemical cues from snakes. Movement patterns of tracked snakes showed that individuals were most active on a rapidly falling tide, which is the time when chemical cues from hidden catfish are likely to be most readily available to a foraging predator. By synchronizing foraging effort with the tidal cycle, greater sea snakes may be able to exploit the availability of chemical cues during a rapidly falling tide to maximize efficiency in locating and capturing prey.

Assessing the effectiveness of different sea turtle nest protection strategies against coyotes

Lovemore TEJ, Montero N, Ceriani SA, Fuentes MMPB. Assessing the effectiveness of different sea turtle nest protection strategies against coyotes. Journal of Experimental Marine Biology and Ecology [Internet]. 2020 ;533:151470. Available from: https://www.sciencedirect.com/science/article/pii/S0022098120303051?dgcid=raven_sd_search_email
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

Depredation of sea turtle nests, where a nest is either partially or completely predated by a predator, is particularly detrimental to the reproductive output of sea turtles and consequently a concern for sea turtle conservation efforts globally. To minimize depredation of sea turtle nests, several protective strategies have been trialed against different predators. However, although information on their effectiveness exists, information on the effectiveness of strategies aiming to mitigate depredation by coyotes, which is an issue at loggerhead turtle, Caretta caretta, nesting beaches in Florida and globally is inexistent. To inform future management of sea turtle nest depredation by coyotes, this study evaluated the effectiveness of three nest protection strategies (self-releasing metal cage, self-releasing plastic cage, and self-releasing metal screen). Further, to obtain insights into coyote behavior during depredation activities and inform management strategies, we used infrared camera surveillance to monitor sea turtle nests. Self-releasing plastic cages were found to be the most effective strategy at mitigating coyote depredation on loggerhead nests. Our findings provide important information for consideration when developing depredation mitigation strategies in the region and globally.

Plankton Community Changes From Warm to Cold Winters in the Oligotrophic Subtropical Ocean

Armengol L, Franchy G, Ojeda A, Hernández-León S. Plankton Community Changes From Warm to Cold Winters in the Oligotrophic Subtropical Ocean. Frontiers in Marine Science [Internet]. 2020 ;7. Available from: https://www.frontiersin.org/articles/10.3389/fmars.2020.00677/full?utm_source=F-AAE&utm_medium=EMLF&utm_campaign=MRK_1406443_45_Marine_20200818_arts_A
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

Subtropical gyres are large areas of the ocean characterized by high stratification, low nutrients, and low primary production. The Canary Current System (CanCS) shows a rather strong seasonal thermocline during most of the annual cycle, which erodes through convective mixing from January to March promoting the so-called Late Winter Bloom (LWB). Atmospheric deposition from the Sahara desert is also another key feature of the CanCS providing additional nutrients to the euphotic zone. As a consequence of global warming, these oligotrophic regimes systems are expanding and the temperature increase affects phytoplankton, and reverberate on the food web structure and biogeochemical cycles. In the CanCS, the effect of warming and dust deposition on the planktonic community remains poorly know. Here, we show the effects of a 0.5°C increase in ocean temperature during two consecutive years. During 2011, winter temperature allowed the development of the LWB, promoting the increase of autotrophic cells and the coexistence of the microbial loop and the “classic” trophic web. The former predominated before and after the LWB, while the latter prevailed during the LWB. The rather high temperature during 2010 prevented the LWB development, causing highly oligotrophic conditions and episodic events of Saharan dust contributing to nutrient inputs. During this warm year, we found a dominance of small cells such as nanoflagellates and dinoflagellates, and surprisingly high biomass of mesozooplankton, hinting at the “tunneling effect” as an alternative trophic pathway (rapid uptake of phosphate by prokaryotes which are consumed by flagellates and then by zooplankton). These changes show the impact of a slight increase in temperature in this oligotrophic system and how future scenarios in the context of global warming could promote considerable shifts in the trophic web structure.

Few Herbivore Species Consume Dominant Macroalgae on a Caribbean Coral Reef

Dell CLA, Longo GO, Burkepile DE, Manfrino C. Few Herbivore Species Consume Dominant Macroalgae on a Caribbean Coral Reef. Frontiers in Marine Science [Internet]. 2020 ;7. Available from: https://www.frontiersin.org/articles/10.3389/fmars.2020.00676/full?utm_source=F-AAE&utm_medium=EMLF&utm_campaign=MRK_1406443_45_Marine_20200818_arts_A
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

Coral reefs have changed radically in the last few decades with reefs in the Caribbean now averaging 13% coral cover and 40% macroalgal cover (mostly Dictyota and Lobophora). So, it is time we re-evaluate which species are key to the process of herbivory in these new conditions. The role herbivorous fishes play in controlling macroalgae is often considered by managers and researchers at a guild or family level, but greater resolution is needed to understand the impact of herbivores more fully. We performed feeding assays and behavioral observations of fish feeding to quantify the removal of the most common macroalgae by different herbivorous fish species. In total, we ran 34 h-long trials using Dictyota and Lobophora across two sites and conducted over 34 h of observation of 105 fish from eight species in the Cayman Islands, Caribbean. We show that many nominal herbivores did not consume macroalgae but instead targeted the epibionts on macroalgae and other substrates. In fact, only three fish taxa consumed macroalgae as a significant proportion of their feeding: one species of surgeonfish (Acanthurus coeruleus), one species of parrotfish (Sparisoma aurofrenatum), and the third, the chubs (Kyphosus spp.), is a group of species which is not consistently considered as part of the herbivore community in the Caribbean. From our observations, an individual A. coeruleus can consume ∼44 g of Dictyota per day, while S. aurofrenatum can consume ∼50 g and Kyphosus spp. can consume ∼100 g. These values are significantly more than all other herbivorous fish species and suggest these three taxa are key macroalgal consumers in the Caribbean. These results highlight that disentangling the role of individual herbivore species is necessary for critical species to be identified and protected. Furthermore, as reef conditions change, we need to re-evaluate the key functions and species to be more effective at protecting and managing these important ecosystems. With far higher macroalgal coverage than in the past, the few browsing species that remove macroalgae may be increasingly important in promoting reef health.

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