3 research outputs found
Development of a prototype for submarine communications in shallow waters
The Telecommunications Marine Laboratory (TML) of the University of
Cádiz takes part in a research project to study the intertidal sediments of the Bay
of Cádiz. The collection of samples from the seabed and the transmission of data
to the surface are performed by a Mini Profiler with four channels (MP4), which is
supplied by UNISENSE. Each channel processes the samples collected by a single
sensor. For power, control, and data transmission, a special wiring that connects the
submerged subsystem with the surface subsystem is used. The tension transmitted
by the cable to the MP4 structure makes its handling and positioning under water
more difficult. This article explains the technological solution developed by the TML
to replace some wiring from the MP4. For the prototype, two underwater acoustic
modems have been used and an electronic system has been developed based on the
Arduino platform, in order to multiplex, digitize, and transmit the data collected by
the MP4 sensors, eliminating the need to use wiring. The submerged subsystem has
an autonomous power supply by a battery.Peer Reviewe
Microbenthic Net Metabolism Along Intertidal Gradients (Cadiz Bay, SW Spain): Spatio-Temporal Patterns and Environmental Factors
Microphytobenthos (MPB), the photosynthetic primary producing component of
microbenthos, shows variable patterns in its biomass distribution along the intertidal
gradient as a result of the interactions of factors such as light, tides, temperature,
and grazing pressure. These patterns have been studied more extensively in northern
European estuaries than southern European coastal systems. Even less information is
available regarding temporal changes in MPB primary production rates in these systems.
For this reason, we followed the seasonal changes in net production in light and dark
respiration rates (determined by oxygen microelectrodes) and MPB biomass (estimated
by sediment chlorophyll a) along the intertidal gradient of the inner Cadiz Bay during
a year. Sediment cores were collected along two transects (five sampling stations per
transect) with distinct sediment granulometry: one muddy [Puerto Real (PR)] and one
muddy-sandy transect [San Fernando (SF)]. Our results show that MPB biomass and
net production increased seawards reaching their maxima in winter. In contrast to what
is observed in northern European systems, the higher solar irradiance and temperatures
occurring in summer in southern Spain likely inhibit MPB production. In Cadiz Bay,
spatial patterns of MPB biomass and net production depended on season and location
due to the environmental heterogeneity observed. Environmental variables, analyzed
by principal component analysis (PCA), were used to explain the variability of MPB
metabolism by multiple regression. Selected principal component (PC) axes explained
60% of the net production in light and 41% of the dark respiration rates variability
in PR, while they only accounted for 25% of the same rates in SF. The differences
observed between transects and the variability in the environmental variables explaining
them highlight the importance of considering the spatial heterogeneity of our system to
estimate the contribution of MPB to the inner Cadiz Bay productivity. In our case, this
contribution is significant accounting for up to 49% of the total benthic production of the
inner Cadiz Bay intertidal sediments, confirming previous global estimates
Diel patterns of microphytobenthic primary production in intertidal sediments: the role of photoperiod on the vertical migration circadian rhythm
Diel primary production patterns of intertidal microphytobenthos (MPB) have been attributed to short-term physiological changes in the photosynthetic apparatus or to diel changes in the photoautotrophic biomass in the sediment photic layer due to vertical migration. Diel changes in primary production and vertical migration are entrained by external factors like photoperiod and tides. However, the role of photoperiod and tides has not been experimentally separated to date. Here, we performed laboratory experiments with sediment cores kept in immersion, in the absence of tides, with photoperiod or under continuous light. Measurements of net production, made with O-2 microsensors, and of spectral reflectance at the sediment surface showed that, in intertidal sediments, the photoperiod signal was the major driver of the diel patterns of net primary production and sediment oxygen availability through the vertical migration of the MPB photoautotrophic biomass. Vertical migration was controlled by an endogenous circadian rhythm entrained by photoperiod in the absence of tides. The pattern progressively disappeared after 3 days in continuous light but was immediately reset by photoperiod. Even though a potential contribution of a subjective in situ tidal signal cannot be completely discarded, Fourier and cross spectral analysis of temporal patterns indicated that the photosynthetic circadian rhythm was mainly characterized by light/dark migratory cycles