Total
X-ray scattering and pair distribution function analysis
are combined with nuclear magnetic resonance spectroscopy to identify
key differences in structural properties between biogenic and synthetic
samples of amorphous calcium carbonate (ACC). Biogenic samples studied
are gastroliths taken from the American lobster and are composed of
hydrated ACC containing minor impurities. X-ray pair distribution
functions reveal that the short- and medium-range structure found
in synthetic ACC also occurs in gastrolith ACC, notably with atomic
pair correlations extending up to ∼10 Å. The 13C NMR spectra of gastrolith ACC show a distribution of carbonate
environments as seen in synthetic hydrated ACC. However, 1H NMR spectroscopy reveals that a mobile H2O component
and hydroxyl groups found in synthetic hydrated ACC are absent in
the gastrolith ACC. This difference may arise from differences in
local conditions of ACC formation. The 31P NMR results
indicate that inorganic phosphate is the principal form of the minor
phosphorus. Gastrolith that was allowed to age shows the presence
of calcite and vaterite, as well as residual ACC. 31P NMR
also reveals trace amounts of monetite (CaHPO4) in aged
samples, raising the possibility that fresh gastrolith ACC may contain
a minor component of amorphous calcium phosphate. The findings suggest
that important differences in the hydrous components between synthetic
and biogenic hydrated ACC influence stability of the amorphous phase
and its transformation to crystalline forms, thereby extending the
foundation for advanced materials applications in engineered systems.
American lobster (Homarus americanus) landings have more than quadrupled in the last two decades , coinciding with the collapse of Gulf of Maine groundfish fisheries such as Atlantic cod (Gadus morhua). Recently there has been speculation that the release of lobster from predatory control may have resulted in both lower predation rates and increased foraging areas. We used fine-scale acoustic telemetry within a 200 m × 250 m field enclosure to test the hypothesis that cod induce lobsters to decrease movement and seek refuge. We found a large amount of variation in the behavioral response of individual lobsters to predators; however, the addition of cod into the enclosure reduced maximum daily home range area and significantly reduced the distance traveled from shelter habitat area for all individuals. When predators were removed from the enclosure, lobsters responded by increasing home range area and significantly increasing the distance traveled from shelter habitat area. These results represent the first experimental evidence for American lobster range contraction and subsequent expansion in the presence and absence of cod, respectively.Résumé : Les débarquements de homards (Homarus americanus) ont plus que quadruplé au cours des deux dernières décennies , coïncidant avec l'effondrement des pêches aux poissons de fond, comme la morue (Gadus morhua), dans le golfe du Maine. Il a récemment été proposé que la disparition du contrôle des homards par la prédation puisse s'être traduite par des taux de prédation réduits et de plus grandes zones d'alimentation. Nous avons utilisé la télémétrie acoustique de haute résolution dans un enclos en mer de 200 m sur 250 m pour vérifier l'hypothèse voulant que la morue incite les homards à restreindre leurs déplacements et à trouver refuge. Nous avons noté d'importantes variations en ce qui concerne la réaction comportementale individuelle des homards à la présence de prédateurs; cela dit, l'ajout de morues dans l'enclos a entraîné une diminution de la superficie maximum du domaine vital quotidien et une diminution significative de la distance des excursions en dehors de la zone d'habitat refuge pour tous les individus. Quand les prédateurs étaient retirés de l'enclos, la superficie du domaine vital des homards augmentait et la distance des excursions en dehors de la zone d'habitat refuge augmentait significativement. Ces résultats constituent les premières preuves expérimentales de la contraction du domaine vital du homard en présence de morues et de son expansion en leur absence. [Traduit par la Rédaction]
Courtship behavior is well documented in captive lobsters. Sex pheromones contained in female urine and perceived by receptors on male antennules are thought to act as sex attractants or as signals necessary for pair formation. In this study, the lateral and medial antennules of male and female lobsters were removed. The result of these excisions were meant to indicate the gender-specific role of olfactory chemoreception in lobster courtship behavior. Removal of male antennules had little effect on pair bonding and mating. In contrast, removal of female antennules resulted in dramatic aberrations in behavior, including postmolt injuries and, in extreme cases, unsuccessful couplings and mortality. Therefore, female olfaction plays the more critical role in the normal reproductive behavior of Homarus americanus.
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