Hydro-Sedimentary Study of a Tidal River: Case Study of the Arvand River in Iran

The present field study investigated hydraulic and sediment in tidal conditions. Measurements were made for two stations at neap tide and spring tide for 13-hour periods at no-dimensional depths of 0.2, 0.6 and 0.8 of the water level each time. In these measurements, the parameters of velocity, direction of flow, electrical conductivity, temperature and depth were measured directly, and to determine the amount of suspended sediments per hour, 3 samples of one litre from the mentioned depths were measured by the instantaneous vertical sampler and taken to a laboratory. An examination of the depth charts of the suspended sediments concentration for all stations, and in both the neap tide and the spring tide, showed that, in general the suspended sediments concentration increased with increasing depth. Moreover, the deep distribution of sediments concentration showed that the values obtained in the laboratory corresponded well with the values calculated from the Rouse equation, and as the depth increases, the sediments concentration usually increases.

All you can eat: the functional response of the cold-water coral Desmophyllum dianthus feeding on krill and copepods

The feeding behavior of the cosmopolitan cold-water coral (CWC) Desmophyllum dianthus (Cnidaria: Scleractinia) is still poorly known. Its usual deep distribution restricts direct observations, and manipulative experiments are so far limited to prey that do not occur in CWC natural habitat. During a series of replicated incubations, we assessed the functional response of this coral feeding on a medium-sized copepod (Calanoides patagoniensis) and a large euphausiid (Euphausia vallentini). Corals showed a Type I functional response, where feeding rate increased linearly with prey abundance, as predicted for a tentaculate passive suspension feeder. No significant differences in feeding were found between prey items, and corals were able to attain a maximum feeding rate of 10.99 mg C h−1, which represents an ingestion of the 11.4% of the coral carbon biomass per hour. These findings suggest that D. dianthus is a generalist zooplankton predator capable of exploiting dense aggregations of zooplankton over a wide prey size-range.

Spatial distribution of the Black Sea copepod, Calanus euxinus, estimated using multi-frequency acoustic backscatter

The copepod Calanus euxinus is a key prey species for fish in the Black Sea. To estimate the distribution and biomass of the late developmental stages of this species in July 2013, we analysed multi-frequency (38, 120, and 200 kHz) echo-sounder data from a fisheries survey of the Black Sea. The dependence of acoustic backscatter on frequency, i.e. the frequency response, was estimated for daytime scattering layers, which were confirmed by net catches to be dense, post-copepodite-stage (C4) aggregations of C. euxinus with prosome lengths greater than 2 mm. The high-resolution acoustic observations revealed that the nighttime, shallow distribution was bounded by the lower portion of the thermocline and that the daytime, deep distribution was bounded by oxygen. The dense and isolated aggregations were observed in seawater with a specific density, σT, of between 15.2 and 15.9 kg m−3. These results show that fisheries acoustic surveys, typically targeting only commercially exploited fish species, may also provide information on the lower trophic levels and thereby serve as an ecosystem-monitoring tool.