Home About us Contact
|
Home About us Contact | ||
|
|
||
Pelagic Habitats (pelagic + habitat)
Selected AbstractsFood composition, habitat use and growth of stocked and native Arctic charr, Salvelinus alpinus, in Lake Muddusjärvi, FinlandFISHERIES MANAGEMENT & ECOLOGY, Issue 4 2002K. KAHILAINEN Habitat use, growth and food composition of native and stocked Arctic charr, Salvelinus alpinus (L.), were studied in the subarctic Lake Muddusjärvi, northern Finland, to investigate reasons for poor stocking success. Samples were collected with pelagic and epibenthic gill nets. Stocked and native charr occurred in similar epibethic habitats, whereas pelagic habitat was avoided. Native charr grew fast after shifting to piscivory. Growth rate of stocked charr was slow because only a small proportion of stocked fish became piscivorous during the first year after stocking. During the first lake year, stocked charr divided into slow-growing planktivores and fast-growing piscivores. Piscivorous stocked and native charr consumed only whitefish, Coregonus lavaretus (L.), as their prey. Small-sized (<10 cm) whitefish were preferred when shifting to piscivory. [source] Pelagic and benthic net production of dissolved inorganic carbon in an unproductive subarctic lakeFRESHWATER BIOLOGY, Issue 3 2007JAN ÅBERG Summary 1. Both the pelagic and benthic net dissolved inorganic carbon (DIC) productions were measured in situ on four occasions from June to September 2004, in the unproductive Lake Diktar-Erik in subarctic Sweden. The stable isotopic signal (,13C) of respired organic material was estimated from hypolimnion water data and data from a laboratory incubation using epilimnion water. 2. Both pelagic and benthic habitats were net heterotrophic during the study period, with a total net DIC production of 416 mg C m,2 day,1, of which the pelagic habitat contributed approximately 85%. The net DIC production decreased with depth both in the pelagic water and in the sediments, and most of the net DIC production occurred in the upper water column. 3. Temporal variations in both pelagic and benthic DIC production were small, although we observed a significant decrease in pelagic net DIC production after the autumn turnover. Water temperature was the single most important factor explaining temporal and vertical variations in pelagic DIC production. No single factor explained more than 10% of the benthic net DIC production, which probably was regulated by several interacting factors. 4. Pelagic DIC production, and thus most of the whole-lake net production of DIC, was mainly due to the respiration of allochthonous organic carbon. Stable isotope data inferred that nearly 100% of accumulated DIC in the hypolimnion water had an allochthonous carbon source. Similarly, in the laboratory incubation using epilimnion water, c. 85% of accumulated DIC was indicated to have an allochthonous organic carbon source. [source] A Middle Ordovician cephalopod fauna from Cuzco Province, southern Perú and its palaeobiogeographical significanceGEOLOGICAL JOURNAL, Issue 1 2007David H. Evans Abstract A small cephalopod assemblage collected during the 1930s by J. A. Douglas from the Middle Ordovician San José Formation of Cuzco Province is redescribed. Although small in number (four taxa) and poorly preserved, this assemblage contains a representative of the ellesmerocerid family Eothinoceratidae and a probable member of the Arionoceratidae (Orthocerida). One taxon may be closely related to Protocycloceras harringtoni Cecioni from northern Argentina. The presence of a particular group of eothinoceratids, here and elsewhere in South America indicate a link with western Gondwana. The relatively diminutive size of the arionoceratids suggests homeomorphy with those Silurian forms associated with a pelagic habitat and indicates a relatively offshore site for this assemblage. Copyright © 2006 John Wiley & Sons, Ltd. [source] Phylogenetic analyses of ribosomal DNA-containing bacterioplankton genome fragments from a 4000 m vertical profile in the North Pacific Subtropical GyreENVIRONMENTAL MICROBIOLOGY, Issue 9 2008Vinh D. Pham Summary High-throughput identification of rRNA gene-containing clones in large insert metagenomic libraries is difficult, because of the high background of host ribosomal RNA (rRNA) and rRNA genes. To address this challenge, a membrane hybridization method was developed to identify all bacterial small subunit rRNA-containing fosmid clones of microbial community DNA from seven different depths in the North Pacific Subtropical Gyre. Out of 101,376 clones screened, 751 rDNA-containing clones were identified that grouped in ,60 different clades. Several rare sequences only remotely related to known groups were detected, including a Wolbachia -related sequence containing a putative intron or intervening sequence, as well as seven sequences from Order Myxococcales not previously detected in pelagic habitats. Stratified, depth-specific population structure was evident within both cultured and uncultured lineages. Conversely, some eurybathyal members of the genera Alcanivorax and Rhizobium shared identical small subunit ribosomal DNA sequences that were distributed from surface waters to the 4000 m depth. Comparison with similar analyses in Monterey Bay microbial communities revealed previously recognized, as well as some distinctive, depth-stratified partitioning that distinguished coastal from open ocean bacterioplankton populations. While some bias was evident in fosmid clone recovery in a few particular lineages, the overall phylogenetic group recovery and distributions were consistent with previous studies, as well as with direct shotgun sequence data from the same source DNA. [source] Fight or flight: antipredator strategies of baleen whalesMAMMAL REVIEW, Issue 1 2008JOHN K. B. FORD ABSTRACT 1The significance of killer whale Orcinus orca predation on baleen whales (Mysticeti) has been a topic of considerable discussion and debate in recent years. Discourse has been constrained by poor understanding of predator-prey dynamics, including the relative vulnerability of different mysticete species and age classes to killer whales and how these prey animals avoid predation. Here we provide an overview and analysis of predatory interactions between killer whales and mysticetes, with an emphasis on patterns of antipredator responses. 2Responses of baleen whales to predatory advances and attacks by killer whales appear to fall into two distinct categories, which we term the fight and flight strategies. The fight strategy consists of active physical defence, including self-defence by single individuals, defence of calves by their mothers and coordinated defence by groups of whales. It is documented for five mysticetes: southern right whale Eubalaena australis, North Atlantic right whale Eubalaena glacialis, bowhead whale Balaena mysticetus, humpback whale Megaptera novaeangliae and grey whale Eschrichtius robustus. The flight strategy consists of rapid (20,40 km/h) directional swimming away from killer whales and, if overtaken and attacked, individuals do little to defend themselves. This strategy is documented for six species in the genus Balaenoptera. 3Many aspects of the life history, behaviour and morphology of mysticetes are consistent with their antipredator strategy, and we propose that evolution of these traits has been shaped by selection for reduced predation. Fight species tend to have robust body shapes and are slow but relatively manoeuvrable swimmers. They often calve or migrate in coastal areas where proximity to shallow water provides refuge and an advantage in defence. Most fight species have either callosities (rough and hardened patches of skin) or encrustations of barnacles on their bodies, which may serve (either primarily or secondarily) as weapons or armour for defence. Flight species have streamlined body shapes for high-speed swimming and they can sustain speeds necessary to outrun pursuing killer whales (>15,20 km/h). These species tend to favour pelagic habitats and calving grounds where prolonged escape sprints from killer whales are possible. 4The rarity of observed successful attacks by killer whales on baleen whales, especially adults, may be an indication of the effectiveness of these antipredator strategies. Baleen whales likely offer low profitability to killer whales, relative to some other marine mammal prey. High-speed pursuit of flight species has a high energetic cost and a low probability of success while attacks on fight species can involve prolonged handling times and a risk of serious injury. [source] Lake morphometry predicts the degree of habitat coupling by a mobile predatorOIKOS, Issue 8 2009Rebecca Dolson Habitat coupling is an ecosystem process whereby semi-discontinuous habitats are connected through the movement of energy and nutrients by chemical, physical or biological processes. One oft-cited example is that of littoral,pelagic coupling in lakes. Theory has argued that such habitat coupling may be critical to food web dynamics, yet there have been few empirical studies that have quantified ecological factors that affect the degree of habitat coupling in ecosystems. Specifically, the degree to which habitat coupling occurs across important physical gradients has largely been ignored. To address this, we investigate the degree of littoral habitat coupling (i.e. the degree to which a top predator lake trout, Salvelinus namaycush, derives energy from the littoral zone) along a gradient of lake shape, where lake shape modifies the relative quantity of coupled epilimnetic benthic and pelagic habitats within each lake. Herein we demonstrate that littoral habitat coupling is intensified in simple circular lakes compared to their reticulate counterparts in seven Canadian Shield lakes. Although the more reticulate lakes had larger areas of epilimnetic benthic habitat, littoral food sources comprised 11% compared to 24% of lake trout diet in reticulate and circular lakes, respectively. This heightened interaction in circular lakes also appears to translate into increased omnivory in more circular lakes compared to reticulate lakes such that lake trout of circular lakes have a significantly lower trophic position than lake trout of reticulate lakes (F1,5=6.71 p=0.05). These results suggest that it is the accessibility of littoral production via thermal refugia, and not the amount of littoral production, that determines the degree to which lake trout couple littoral and pelagic habitats in lakes. [source] Intraspecific competition drives multiple species resource polymorphism in fish communitiesOIKOS, Issue 1 2008Richard Svanbäck It has been hypothesized that inter-specific competition will reduce species niche utilization and drive morphological evolution in character displacement. In the absence of a competitor, intra-specific competition may favor an expansion of the species niche and drive morphological evolution in character release. Despite of this theoretical framework, we sometimes find potential competitor species using the same niche range without any partitioning in niche. We used a database on test fishing in Sweden to evaluate the factors (inter- and intraspecific competition, predation, and abiotic factors) that could influence habitat choice of two competitor species. The pattern from the database shows that the occurrence of perch and roach occupying both littoral and pelagic habitats of lakes in Sweden is a general phenomenon. Furthermore, the results from the database suggest that this pattern is due to intra-specific competition rather than inter-specific competition or predation. In a field study, we estimated the morphological variation in perch and roach and found that, individuals of both species caught in the littoral zone were more deeper bodied compared to individuals caught in the pelagic zone. Pelagic perch fed more on zooplankton compared to littoral perch, independent of size, whereas the littoral perch had more macroinvertebrates and fish in their diet. Pelagic roach fed more on zooplankton compared to littoral roach, whereas littoral individuals fed more on plant material. Furthermore, we sampled littoral and pelagic fish from another lake to evaluate the generality of our first results and found the same habitat associated morphology in both perch and roach. The results show a consistent multi-species morphological separation in the littoral and pelagic habitats. This study suggests that intra-specific competition is possibly more important than inter-specific competition for the morphological pattern in the perch-roach system. [source] | |||||||||||||