Evidence for the use of non-detrital dissolved organic matter by microheterotrophs on plant detritus in a woodland stream

SUMMARY 1. Recent studies provide evidence for the use of exudates from living plants by epilithic microheterotrophs in streams. This study investigated the possible use of such non-detrital sources of dissolved organic matter (DOM) by streatn microheterotrophs colonizing leaf litter. Biomass of bacteria and of fungi accumulating in situ on autumn-shed leaves in flow-through troughs from which light was excluded was compared to that accumulating on leaves in troughs open to natural illumination.
2. In experiments repeated at different times of year and in different stream sections, greater biomass of microheterotrophs consistently accumulated on the leaf detritus in troughs open to natural illumination. Differences in water temperature or in grazing of leaf surfaces by macroinvertebrates could not account for these consistent differences. Further, greater microheterotroph biomass accumulated on light- and dark-incubated leaves in a stream section relatively open to sunlight, compared to corresponding leaves in a section heavily shaded by canopy and understorey vegetation.
3. These and other results suggest that, to some yet undetermined extent, detritus-associated microheterotrophs use non-detrital DOM. This conclusion is consistent with a priori predictions based on consideration of microbial energetics involved in the use of detrital versus non-detrital DOM.
4. Studies of trophic pathways in streams and other aquatic habitats have failed to assess some potentially important sources of non-detrital DOM. The ability of available techniques to assess the relative roles of detrital and non-detrital sources of DOM is evaluated, and alternative approaches to this problem are suggested.     

The West African species of Bathygobius (Teleostei: Gobiidae) and their affinities

The circumtropical gobiid fish genus Bathygobius Bleeker, 1878 is discussed and defined in terms of external features, including the head lateral-line system, and osteology. Three West African species are recognized and redescribed: the amphiatlantic B. soporalor (Valenciennes, 1837) and two endemics, B. burtoni (O'Shaughnessy, 1875) and B. casamancus (Rochebrune, 1880). West African B. soporator differs significantly from western Atlantic material only in average values for predorsal scales and some body proportions, so that separation of eastern and western Atlantic populations as morphological species is not warranted. The affinities of the West African Bathygobius species are examined by means of phenetic (presence-only group-average clustering) and cladistic (Camin-Sokal, Dollo and Wagner) numerical processing of a binary database comprising 46 character states in 15 Operational Taxonomic Units (OTUs) formed by species of Bathygobius. Results do not indicate close common ancestry between the West African endemic species and B. soporator , which has probably colonized West Africa from the New World. The implications of various cladistic schemes for the relationships of certain other American species are also noted.     

CHANGES IN CLICK SOURCE LEVELS WITH DISTANCE TO TARGETS: STUDIES OF FREE-RANGING WHITE-BEAKED DOLPHINS LAGENORHYNCHUS ALBIROSTRIS AND CAPTIVE HARBOUR PORPOISES PHOCOENA PHOCOENA

ABSTRACT

Probably all odontocetes use echolocation for spatial orientation and detection of prey. We used a four hydrophone “Y” array to record the high frequency clicks from free-ranging White-beaked Dolphins Lagenorhynchus albirostris and captive Harbour Porpoises Phocoena phocoena. From the recordings we calculated distances to the animals and source levels of the clicks. The recordings from White-beaked Dolphins were made in Iceland and those from Harbour Porpoises at Fjord & Baelt, Kerteminde, Denmark during prey capture. We used stringent criteria to determine which clicks could be defined as being on the acoustic axis. Two dolphin and nine porpoise click series could be used to track individual animals, which presumably focused on the array hydrophones or a fish right in front of the array. The apparent source levels of clicks in the individual tracks increased with range. One individual White-beaked Dolphin and three Harbour Porpoises regulate their output signal level to nearly compensate for one-way transmission loss while approaching a target. The other dolphin regulated the output differently. For most of the recordings the sound level at the target remains nearly constant and the echo level at the animal increases as it closes on the target.