Carcharhinus_falciformis_bahamas

April 22 – Silky Sharks Are Highly Impacted By Purse Seining at FADs

Bycatch of non-target species is a chronic problem in pelagic purse seine fisheries.  In the Western and Central Pacific tuna fishery, 95% of the elasmobranch by-catch is composed of juvenile silky sharks (Carcharinus falciformis), which are attracted to fish aggregating devices (FADs) deployed by fisherman to aggregate skipjack and yellowfin tuna.  Currently, sharks captured during purse seining operations are released alive, but little is known regarding their survival rate once released.  We discussed a paper by Hutchinson et al. (2015) that sought to determine the post-release survival of silky sharks captured in the Pacific purse seine fishery and identified the point during fishing operations when silky sharks endure injuries that ultimately lead to mortality.  The study revealed that 84% of sharks released after being captured in the purse seine ultimately die after being released and early removal of sharks from the net is the key to increasing their chances of survival. –Travis

Image via Joi Ito

www.mantis.cz/mikrofotografie

April 15 – Forams Provide High-Resolution Climate Record from Santa Barbara Basin

Sediment cores collected from the Santa Barbara basin have recorded changes in ocean circulation and climate change from the past 20,000 years. Previous paleo-climate research has been focused in the North Atlantic basin, however this research provides evidence that ocean basins in the Pacific are just as useful in reconstructing climate change over the Holocene. Radiocarbon dating, sediment analysis, and benthic foraminifera provide evidence for four major global cooling and warming events, which also correspond with changes in ocean circulation. The first event was the last Ice age, followed by the Bolling-Allerod warming period (~14.5 kya), the Little Ice Age (~11 kya), and finally the modern warming event. In conclusion, the Santa Barbara basin in the Pacific ocean provides excellent evidence of changes in global climate over the past 20,000 years. – Jacque

Image via By Dr. Josef Reischig, CSc.

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April 8 -Coccolith Abundance on the Rise with Increasing Ocean pCO2

The goal of this paper was to investigate the increase of coccolithophore abundance in the North Atlantic since the 1960s, with one of the major theories being the rising concentrations of carbon dioxide in the North Atlantic as the driving factor. Basic information was provided about coccolithophores, such as being calcifying primary producers that live in ocean surface waters . The accepted paradigm up until this point was that increases in atmospheric CO2 would drive an increase in pCO2 in the ocean, thereby contributing to ocean acidification that would be detrimental to organisms with calcareous exoskeletons. Random forest models were implemented to determine which variables may have the greatest effect on coccolith occurrence over the multiple decades that were sampled. The results of these models concluded that increasing CO2 concentrations are the main predictor of occurrence on both a local and global scale. –Shawna

Image via NEON ja/Richard Bartz talk/Papa Lima Whiskey

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April 1 – Bottom-Up Processes Regulate Population Dynamics of Leatherbacks

Leatherback sea turtles (Dermochelys coriacea) are currently listed as endangered by IUCN Red List (IUCN 2014), for which major contributors to their decline among all worldwide nesting populations include egg poaching, incidental fishery mortality, loss of nesting beaches, and the harvest of nesting females. Despite their worldwide endangered status, nesting populations in the Western Atlantic and Western Indian Ocean are increasing or stable while those in Pacific Ocean have been facing a drastic declines for the past few decades. This has been paradoxical, leading some scientists to suggest that ENSO (El Nino Southern Oscillation) is highly influencing the decreasing population trends within the Pacific region, in addition to other natural factors. High energy reserves prior to the nesting season are vital for successful reproduction and are also a function of foraging ground condition; this is driven by bottom-up effects associated with net primary production (NPP). This study reveals that foraging grounds used by the Western Atlantic and Indian Ocean populations produce high and consistent mean and maximum NPP enhanced by various physical factors. In contrast, foraging areas used by the Pacific populations exhibit the lowest regional NPP and seasonal variations result in low abundance and poor quality of food resources. These differences in NPP quantity and consistency among foraging grounds have largely driven the differences between Atlantic/Indian and Pacific Ocean populations, impacting body size and therefore clutch sizes of mature females. Consequently, higher reproductive output and more frequent nesting events will enhance the population’s growth rate. While egg harvesting and fishery mortality are the primary threats to the Pacific nesters, low resource quality and availability in their foraging grounds influenced by bottom-up and climatic variations also appear to be doing this population no favors on their road to recovery. –Ayaka

Image via US FWS SE Region

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March 25 -Constructing Your Own Niche

A relatively new concept within the framework of evolution, ‘niche construction’ aims to identify the ramifications of organismal modifications to their natural environment. Any alteration made by an organism to the organism-environment functional relationship will lead to a redefining of its own realized niche, possibly as well as that of neighboring organisms and future generations. These environmental modifications can then lead to new selective pressures, resulting in changes in allele frequencies within a population. While still widely unstudied, niche construction offers an explanation for the active modification of environmental pressures that shape a population and ecosystem. Despite the long-held belief that natural selection is only imposed upon on a species, these authors propose that the species may actually affect selection. This concept is an important addition to the field of evolution and our understanding of how organisms interact with their environment. – Nathan

Image via DickDaniels

  • Article – Niche Construction
  • Citation – Odling-Smee, F. J., Laland, K. N., & Feldman, M. W. (1996). Niche construction. The American Naturalist147(4), 641-648.
  • Presenter – Nathan, Marine Mammal Physiology Lab
SI Neg. 96-10756. Date: 1996.

A Wheeler's Goby fish poking out of a hole in the Indo-Pacific Coral Reef Ecosystem Exhibit in the Smithsonian's National Museum of Natural History. Fish species: Amblyeleotris wheeleri 

Credit: Carl C. Hansen (Smithsonian Institution)

March 11 – Two Sympatric Goby Species Exhibit High Resource Overlap

The authors attempted to detect the degree of prey resource overlap between two similar species of Gobiid fishes (Gobionellus boleosoma and Gobionellus shufeldti), and determine their impact on the meiobenthic community. Since both species were found in the same location, it was believed that they would use resource partitioning to reduce competition for overlapping resources. Since they both feed on the benthos, it was also hypothesized that they would also affect the meiobenthic community via feeding activities.

Although there were several issues with methods (including at least one hungry raccoon), the authors found that there was an unexpected high degree of overlap prey selection for both G. boleosoma and G. shufeldti. Additionally, both species did affect the meiobenthic community through feeding with general decreases in benthic taxa as time and abundance of both Gobiid species increased. Some prey taxa (i.e., nematodes and ostracods) displayed increased density patterns with depth, which the authors posited may indicate an attempt to escape predation by burrowing deeper into sediments. – Marissa

Image via Carl Malamud

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March 4 -Geographic Range and Taxonomy Explain Extinction Risk in Marine Life

This journal article uses the fossil record to predict the extinction risk of a variety of marine taxa. The authors assessed the intrinsic risk, or extinction risk, of marine taxa present in the 23 million years between the Neogene and the Pleistocene using a model that evaluated the geographic range size and taxonomic membership in bivalves, gastropods, echinoids, sharks, mammals, and scleractinian corals. They then used the same model to predict the intrinsic risk of modern genera in the same six taxonomic groups. After geographically mapping their findings, they found that the tropics have the highest intrinsic risk for many of the taxa. However, the vulnerability of extinction for many of the taxa will rely not only on intrinsic risk, but climate velocity and anthropogenic effects as well. This intrinsic risk model creates a baseline to identify taxa and ecosystems that could benefit from conservation efforts. – Sarah

Image via Pyenson et al., 2014