ALBERT

Description: The planktonic foraminifer Globigerinoides sacculifer (Brady) was cultured under two different light intensities and in continuous darkness. High light intensity (HLI = 4oo-soo einsteins/m2/s) resulted in a longer lifespan, a greater number of chambers formed, and a larger final shell size compared with individuals cultured under low light intensity (LLI = 20-50 einsteins/m2/s) or in continuous darkness. Shell growth rates were unaffected by increasing light intensity, but gametogenesis was delayed. Continuous darkness induced a rapid onset of gametogenesis in organisms with shell lengths larger than 250 m. Feeding frequency had a greater effect on growth and reproduction than light intensity under conditions of LLI and HLI, but continuous darkness had an overriding effect on growth and reproduction owing to the rapid onset of gametogenesis which terminated the life of the mother cell. Our previous data indicated that the longevity of G. sacculifer was dependent on feeding frequency, and that G. sacculifer cultured under LLI had a lifespan of approximately 2-4 weeks. Present results suggest that the lifespan can vary from a minimum of 8 days for organisms fed daily in continuous darkness to a maximum of 54 days for organisms fed once every 7 days and maintained in HLI. It is concluded that individual G. sacculifer attain a shell size greater than 6oo ,urn only if they maintain their position in the euphotic zone. Prolonged existence below the euphotic zone would result in premature death or gametogenesis following stunted shell growth.

Description: Symbiotic luminous bacteria have been described in, and cultured from, a number of species offish and cephalopod. Indeed only in these two groups are extracellular luminous bacteria believed to be utilized as a source of light (see Buchner (1965) and Herring (1978) for references). Despite several earlier investigations of such symbioses in cephalopods the bacteria in these animals have not been adequately identified, nor has the extent of their role been clarified. The ultrastructural relationships between bacteria and the tissues of the squid accessory nidamental gland have been investigated in the non-luminous species Loligo pealei (Lesueur) (Bloodgood, 1977) and Sepia officinalis L. (Van den Branden et al. 1979) but no comparative work on luminous species has been undertaken apart from that on Heteroteuthis dispar (Rüppell), whose photophore does not contain typical luminous bacteria (Dilly & Herring, 1978; cf. Leisman, Cohn & Nealson, 1980). The order Sepioidea contains five families, among which are the two families Sepiolidae and Spirulidae. Though the presence of luminous bacteria is known in some sepiolids (as well as in certain loliginids (order Teuthoidea)) some doubt remains about the source of light in the photophore of Spirula spirula Hoyle. The steady luminescence of this species has prompted speculation that bacteria may be involved (Harvey, 1952). In this paper we compare the anatomy and ultrastructure of the photophores of both Sepiola and Spirula in order to clarify some of these problems.

Description: The structural setting of the Maltese Islands is governed by two rift systems of different ages and trends and the interference of both. Accompanying faults are exposed at many places along cliffs and belong to the most spectacular phenomena of rift faulting of the world. Malta is part of a wide shelf bridge that connects the Ragusa platform of southern Sicily and the Tripolitanian platform of northern Libya. The archipelago is underlain by a continental crust of African provenance. The older rift generation traversing the islands strikes about 50° to 70° to create a basin-and-range structure on western Malta, Comino and eastern Gozo. This micro-province is framed by two master faults at an average distance of 14 km. Crustal extension started during the Early Miocene, as observed by growth faulting and sedimentary dikes parallel to the future rift. A syndepositional uparching of about 200 m has preceded the physiographical rifting in post-Middle Miocene times. Discrete dip-slip faulting created an external wedge block, split by internal tilt blocks of antithetic character, both compensating an average 15% crustal spreading normal to the rift axis. Shoulder upwarping of approximately 120 m has evolved synchronously with the rifting. Structures of the first generation are crosscut by still active, second-generation rift faults, which on Malta strike about 120°, but on Gozo between 80° and 90°. These faults are associated with the Pantelleria rift, whose deep trough sets immediately south of the islands. Rifting was mainly originated during Late Miocene/Early Pliocene time to continue in parts up to the Present. A set of transform faults runs through the straits on both sides of Comino to form a complicated en echelon or Riedel shear structure on easternmost Gozo and westernmost Malta. Shoulder upwarping related to the Pantelleria rift has considerably tilted the block of Malta NNE-ward and caused the inundated river valleys of the natural harbour of Valletta. The superimposition of two rift structures of different trends has been caused principally by a rotation of the controlling stress regime about 10 m.y. ago. The active Afro—Eurasian collision front is located about 200 km north and northwest of the islands. A contemporary change of plate tectonic stresses is discussed to explain the intraplate rift pattern on Malta as foreland-specific reactions to plate tectonic processes.

Description: Generally, oxidative regeneration of phosphate from anoxic sediments is by microbially mediated sulfate reduction processes. Stoichiometric modelling of such reactions takes into consideration varying proportions of ‘decomposable’ organically bound P to account for the ratios among nutrients in depth-concentration profiles of near-surface sediments. New results of interstitial water composition from sediments underlying the water masses influenced by coastal upwelling of the eastern boundary current system off Peru indicate that dissolution of phosphatic fish debris represents a mechanism for remineralization of phosphate comparable to or larger in magnitude than that by oxidative regeneration of organically bound P. Dissolved interstitial phosphate from fish debris is revealed by an excess amount of phosphate over that predicted from a simple stoichiometric oxidative regeneration model and by anomalously high dissolved interstitial fluoride concentrations. Phosphate flux estimates based on diffusion from the sediment suggest that this mechanism may generate up to 10% of the nutrient pool in the waters of the Peru undercurrent. Partitioning of P among the two sources reveals further that fish debris phosphate is about four times more important than organically bound P in nutrient generation from sediments of the Peru continental margin. Not only does this mechanism of regeneration affect the nutrient cycling but may also control widespread phosphorite formation in this area.

Description: Investigations of formation-fluid salinities in a transect from western Georgia to the edge of the Blake Plateau off the coast of Georgia show surprisingly similar hydrochemical features offshore and onshore. A fresh-brackish wedge of groundwater (〈25 g/kg total dissolved solids) lies beneath the shelf to a depth of ∼ 900 m. On land, brackish waters extend to a maximum depth of ∼ 1.2 km below sea level in Lowndes County, Georgia. In deeper horizons, hypersaline brines (〉 100 g/kg) occur in Lower Cretaceous (?) strata. These strata have a pronounced evaporitic (anhydritic) character in the offshore segment. Strong salinity gradients in interstitial waters signify buried evaporite deposits at drill sites beneath the Blake Plateau.