ABSTRACT
A global survey of coral reefs reveals that overfishing is driving resident shark species toward extinction, causing diversity deficits in reef elasmobranch (shark and ray) assemblages. Our species-level analysis revealed global declines of 60 to 73% for five common resident reef shark species and that individual shark species were not detected at 34 to 47% of surveyed reefs. As reefs become more shark-depleted, rays begin to dominate assemblages. Shark-dominated assemblages persist in wealthy nations with strong governance and in highly protected areas, whereas poverty, weak governance, and a lack of shark management are associated with depauperate assemblages mainly composed of rays. Without action to address these diversity deficits, loss of ecological function and ecosystem services will increasingly affect human communities.
Subject(s)
Conservation of Natural Resources , Coral Reefs , Extinction, Biological , Sharks , Skates, Fish , Animals , Humans , Fisheries , BiodiversityABSTRACT
Cyclic tetrameric complexes have been prepared by the reaction of Pd(en)Cl2 or Pd(dapol)Cl2, or their nitrato analogues, with Na2(5'GMP) in aqueous solution, where en=1,2-diaminoethane, dapol=1,3-diamino-2-propanol, and 5'GMP=guanosine 5'-monophosphate. Addition of certain small molecules containing hydrophobic groups resulted in the expansion of the tetramer to a cyclic hexamer with strong bonding of one guest per hexameric host. At pH 5-6, the guest molecule can be a cation, anion, or neutral, and those species containing trimetylsilyl and t-butyl groups bonded the most strongly. The size of the central cavity of the [Pd(en)(5'GMP)]6 host has been estimated to be 5.2 A. Formation of the host-guest complex caused a large upfield shift (Deltadelta) of 2.5-2.9 ppm in the 1H NMR spectrum of the most highly affected guest protons, which were those in closest proximity to the guanine nucleobases. NOESY spectra were used to determine the interaction sites between the host and the guest. Apparent association constants determined at 26 degrees C and pD 5.4 for the [Pd(en)(5'GMP)]6-DSS and [Pd(en)(5'GMP)]6-t-butanol systems, where DSS is 3-(trimethylsilyl)-1-propanesulfonate anion, were 1.36+/-0.11x10(4) and 2.74+/-0.95x10(4) M(-3/2), respectively. The Pd(dapol)-5'GMP system forms hexameric host-guest complexes, similar in nature to those of the Pd(en)-5'GMP system. The molecular and crystal structures of Pd(dapol)Cl2 are also reported.
