Investigations of artificial sediments from two deep-sea in situ recolonization experiments deployed for one year at the central HAUSGARTEN station IV during ARK-XIX/3c

Commercial exploitation and abrupt changes of the natural conditions may have severe impacts on the Arctic deep-sea ecosystem. The present recolonisation experiment mimicked a situation after a catastrophic disturbance (e.g. by turbidites caused by destabilized continental slopes after methane hydrate decomposition) and investigated if the recolonisation of a deep-sea habitat by meiobenthic organisms is fostered by variations innutrition and/or sediment structure. Two "Sediment Tray Free Vehicles" were deployed for one year in summer 2003 at 2500 m water depth in the Arctic deep-sea in the eastern Fram Strait. The recolonisation trays were filled with different artificial and natural sediment types (glass beads, sand, sediment mixture, pure deep-sea sediment) and were enriched with various types of food (algae, yeast, fish). After one year, meiobenthos abundances and various sediment related environmental parameters were investigated. Foraminifera were generally the most successful group: they dominated all treatments and accounted for about 87% of the total meiobenthos. Colonizing meiobenthos specimens were generally smaller compared to those in the surrounding deep-sea sediment, suggesting an active recolonisation by juveniles. Although experimental treatments with fine-grained, algae-enriched sediment showed abundances closest to natural conditions, the results suggest that food availability was the main determining factor for a successful recolonisation by meiobenthos and the structure of recolonised sediments was shown to have a subordinate influence.

Diversity of abyssal agglutinated foraminifera from Cenomanian to Santonian sediments of the North Atlantic

Benthic foraminiferal assemblages of distinctive taxonomic composition occur at the top of benthic fossil-free black shales which correspond to the anoxic event at the Cenomanian/Turonian boundary in the North Atlantic abyssal DSDP/ODP sites 386, 398, 603 and 641. These assemblages consist of minute, thin-walled agglutinated foraminifera with low specific diversity of 2 to 4 species, variable abundance and dominance of few taxa (Haplophragmoides, Rhizammina and Glomospira). The species are inferred to be opportunistic, able to survive in low-oxygen environments and to be pioneers recolonizing the seafloor after cessation of bottom-water anoxia. Most species are characterized by test morphologies with high surface/volume ratios and single-layered wall structures, with loosely agglutinated grains, and small amounts of organic cement for agglutination. These features are best observed in material from ODP Hole 641A which has exceptional foraminiferai preservation because of its shallow burial depth. The successive appearance of benthic foraminifera after the anoxic event is probably controlled by the continuous reoccurrence of more oxygenated bottom- and interstitial-water conditions. With the final development of oxic bottom-water conditions in the Turonian, a rapid radiation of deep-water agglutinated foraminifera occurred in the North Atlantic.

Rarefied allelic richness of the ground beetle Abax parallelepipedus in Germany

Although genetic diversity is one of the key components of biodiversity, its drivers are still not fully understood. While it is known that genetic diversity is affected both by environmental parameters as well as habitat history, these factors are not often tested together. Therefore, we analyzed 14 microsatellite loci in Abax parallelepipedus, a flightless, forest dwelling ground beetle, from 88 plots in two study regions in Germany. We modeled the effects of historical and environmental variables on allelic richness, and found for one of the regions, the Schorfheide-Chorin, a significant effect of the depth of the litter layer, which is a main component of habitat quality, and of the sampling effort, which serves as an inverse proxy for local population size. For the other region, the Schwäbische Alb, none of the potential drivers showed a significant effect on allelic richness. We conclude that the genetic diversity in our study species is being driven by current local population sizes via environmental variables and not by historical processes in the studied regions. This is also supported by lack of genetic differentiation between local populations sampled from ancient and from recent woodlands. We suggest that the potential effects of former fragmentation and recolonization processes have been mitigated by the large and stable local populations of Abax parallelepipedus in combination with the proximity of the ancient and recent woodlands in the studied landscapes.

Gametogenic cycle of Mesodesma donacium

Large-scale environmental patterns in the Humboldt Current System (HCS) show major changes during strong El Niño episodes, leading to the mass mortality of dominant species in coastal ecosystems. Here we explore how these changes affect the life-history traits of the surf clam Mesodesma donacium. Growth and mortality rates under normal temperature and salinity were compared to those under anomalous (El Niño) higher temperature and reduced salinity. Moreover, the reproductive spatial-temporal patterns along the distribution range were studied, and their relationship to large-scale environmental variability was assessed. M. donacium is highly sensitive to temperature changes, supporting the hypothesis of temperature as the key factor leading to mass mortality events of this clam in northern populations. In contrast, this species, particularly juveniles, was remarkably tolerant to low salinity, which may be related to submarine groundwater discharge in Hornitos, northern Chile. The enhanced osmotic tolerance by juveniles may represent an adaptation of early life stages allowing settlement in vacant areas at outlets of estuarine areas. The strong seasonality in freshwater input and in upwelling strength seems to be linked to the spatial and temporal patterns in the reproductive cycle. Owing to its origin and thermal sensitivity, the expansion and dominance of M. donacium from the Pliocene/Pleistocene transition until the present seem closely linked to the establishment and development of the cold HCS. Therefore, the recurrence of warming events (particularly El Niño since at least the Holocene) has submitted this cold-water species to a continuous local extinction-recolonization process.

(Table 1) Distribution of Cretaceous-Tertiary benthic foraminifers in ODP Hole 129-802A

Reworked shallow-water larger and deep-water calcareous benthic foraminifers were recovered from foraminiferal packstones and nannofossil chalks in Hole 802A. The autochthonous zeolitic pelagic claystone is characterized by late Campanian abyssal agglutinated foraminifers that allow correlation with the North Atlantic and the adjacent Pigafetta Basin. Assemblages of DendrophryalRhizammina in graded beds within the zeolitic claystone indicate reworking through entrainment in the flocculent E layer of turbidites, rather than recolonization following a biosiliceous event. Background sedimentation of the claystone took place below the carbonate compensation depth. The nannofossil chalk contains reworked lower bathyal to abyssal calcareous foraminifers of late Paleocene to early Miocene age. The topmost bed of the nannofossil chalk unit commences with an algal foraminiferal packstone containing Lepidocyclina sumatrensis, Heterostegina borneensis, Amphistegina hauerina, Asterigerina marshallana, and A. tentoria, which indicate that the source area was a shallow-water reef and allow the bed to be dated as early Miocene. The absence of obviously younger planktonic microfossils in the graded bed indicates that the resedimentation event was generally contemporaneous with original deposition and took place during an early Miocene global sea-level highstand. An early Miocene shallow-water assemblage is also seen in the graded beds at the base of a volcaniclastic turbidite sequence overlying the nannofossil chalks. Resedimentation of this unit was associated with volcanic activity some distance away.