Predation by gulls on crabs in rocky intertidal and shallow subtidal zones of the Gulf of Maine

Most organisms in intertidal areas are marine in origin; many have distributions that extend into the subtidal zone. Terrestrial predators such as mammals and birds may exploit these animals during low tide and can have considerable effects on intertidal food webs. Several studies have shown that avian predators are capable of reducing densities of sessile and slow-moving intertidal invertebrates but very few studies have considered avian predation on mobile invertebrate predators such as crabs. In this study, we investigated predation by Great Black-backed Gulls (Larus marinus Linnaeus) on three species of crabs (Cancer borealis Stimpson, Cancer irroratus Say, and Carcinus maenas Linnaeus). The study was at Appledore Island, ME (a gull breeding island) and 8 other sites throughout the Gulf of Maine, including breeding islands and mainland sites. On Appledore Island, intertidal and subtidal zones provided over one-third of prey remains found at gull nests, and crabs were a substantial proportion (∼ 30% to 40%) of the total remains. Similarly, collections of prey remains from intertidal areas indicated that crabs were by far the most common marine prey. C. borealis was eaten far more often and C. irroratus and C. maenas less often than expected at each site. Comparing numbers of carapaces to densities of crabs in low intertidal and shallow subtidal zones at each site, we estimated that gulls remove between 15% and 64% of C. borealis during diurnal low tides. The proportion of C. borealis eaten by gulls was independent of proximity to a gull colony. Approximately 97% of the outer coast of Maine is within 20 km of a breeding island. Thus, a lot of gull predation on crabs may occur throughout the Gulf of Maine during summer months. Crabs are important predators of other invertebrates; if predation by gulls reduces the number of crabs in intertidal and shallow subtidal areas, gulls may have important indirect effects on intertidal food webs.     

ATP25, a new nuclear gene of Saccharomyces cerevisiae required for expression and assembly of the Atp9p subunit of mitochondrial ATPase

We report a new nuclear gene, designated ATP25 (reading frame YMR098C on chromosome XIII), required for expression of Atp9p (subunit 9) of the Saccharomyces cerevisiae mitochondrial proton translocating ATPase. Mutations in ATP25 elicit a deficit of ATP9 mRNA and of its translation product, thereby preventing assembly of functional F(0). Unlike Atp9p, the other mitochondrial gene products, including ATPase subunits Atp6p and Atp8p, are synthesized normally in atp25 mutants. Northern analysis of mitochondrial RNAs in an atp25 temperature-sensitive mutant confirmed that Atp25p is required for stability of the ATP9 mRNA. Atp25p is a mitochondrial inner membrane protein with a predicted mass of 70 kDa. The primary translation product of ATP25 is cleaved in vivo after residue 292 to yield a 35-kDa C-terminal polypeptide. The C-terminal half of Atp25p is sufficient to stabilize the ATP9 mRNA and restore synthesis of Atp9p. Growth on respiratory substrates, however, depends on both halves of Atp25p, indicating that the N-terminal half has another function, which we propose to be oligomerization of Atp9p into a proper size ring structure.