Rectified tidal transport in Lofoten–Vesterålen, northern Norway

Vestfjorden in northern Norway, a major spawning ground for the northeast Arctic cod, is sheltered from the continental shelf and open ocean by the Lofoten–Vesterålen archipelago. The archipelago, however, is well known for hosting strong and vigorous tidal currents in its many straits, currents that can produce significant time-mean tracer transport from Vestfjorden to the shelf outside. We use a purely tidally driven unstructured-grid ocean model to look into non-linear tidal dynamics and the associated tracer transport through the archipelago. Of particular interest are two processes: tidal pumping through the straits and tidal rectification around islands. The most prominent tracer transport is caused by tidal pumping through the short and strongly non-linear straits Nordlandsflaget and Moskstraumen near the southern tip of the archipelago. Here, tracers from Vestfjorden are transported tens of kilometers westward out on the outer shelf. Further north, weaker yet notable tidal pumping also takes place through the longer straits Nappstraumen and Gimsøystraumen. The other main transport route out of Vestfjorden is south of the island of Røst. Here, the transport is primarily due to tracer advection by rectified anticyclonic currents around the island. There is also an anticyclonic circulation cell around the island group Mosken–Værøy, and both cells have flow speeds up to 0.2 m s−1, magnitudes similar to the observed background currents in the region. These high-resolution simulations thus emphasize the importance of non-linear tidal dynamics for transport of floating particles, like cod eggs and larvae, in the region.

Rectified tidal transport in Lofoten-Vesterålen, Northern Norway

Vestfjorden in Northern Norway, a major spawning ground for the Northeast Arctic cod, is sheltered from the continental shelf and open ocean by the Lofoten-Vesterålen archipelago. The archipelago, however, is well known for hosting strong and vigorous tidal currents in its many straits, currents that can produce significant time-mean tracer transport from Vestfjorden to the shelf outside. We use a purely tidally-driven unstructured-grid ocean model to look into the nonlinear tidal dynamics and the associated tracer transport through the archipelago. Of particular interest are two processes: tidal pumping through the straits and tidal rectification around islands. The most prominent tracer transport is caused by tidal pumping through the short and strongly nonlinear straits Nordlandsflaget and Moskstraumen near the southern tip of the archipelago. Here tracers from Vestfjorden are transported tens of kilometers westward out on the outer shelf. Further north, weaker yet notable tidal pumping also takes place through the longer straits Nappstraumen and Gimsøystraumen. The other main transport route out of Vestfjorden is south of the island of Røst. Here the transport is primarily due to tracer advection by rectified anticyclonic currents around the island. There is also an anticyclonic circulation cell around the islands of Mosken-Værøy, and both cells have have flow speeds up to 0.2 m/s, magnitudes similar to the observed background currents in the region. These high-resolution simulations thus emphasize the importance of nonlinear tidal dynamics for transport of cod eggs and larvae in the region.

Drivers of nano- and microplanktonic community structure in a Patagonian tidal flat ecosystem

ABSTRACT Tidal flats are exceptionally dynamic coastal ecosystems. Tides are their main source of energy, whose influence decreases landwards (as land elevation increases), thus shaping physical, chemical and biological gradients. In this study, we assess whether the structure of nano- and microplankton varies along a spatial gradient in San Antonio Bay (SAB, SW Atlantic), a semi-desert coastal ecosystem with a wide tidal flat and a macrotidal regime. We hypothesize that the tidal effect shapes SAB’s both taxonomical groups and size spectrum. The seasonal sampling of 9 sites revealed that diatoms and small flagellates were the most abundant groups, together accounting for over 75% of total density in practically all sites and seasons. High densities of meroplanktonic stages of Ulva lactuca were recorded in spring at the innermost sites, accounting for over 95% of all planktonic cells. Slopes of the size spectrum analysis were in line with highly productive inshore waters (mean, −0.64) and showed that larger phytoplankton was the main contributor to total biomass, despite its decreasing importance toward inner sites. The spatial and seasonal variations found for lower trophic web compartments provide evidence of the importance of tidal transport in ruling phytoplankton structure in tidal flats under strong macrotidal regimes.

Small scale variability of geomorphological settings influences mangrove-derived organic matter export in a tropical bay

Organic matter (OM) exchanges between adjacent habitats affect the dynamics and functioning of coastal systems, as well as the role of the different primary producers as energy and nutrient sources in food webs. Elemental (C, N, C : N) and isotope (δ13C) signatures and fatty acid (FA) profiles were used to assess the influence of geomorphological setting in two climatic seasons on the export and fate of mangrove OM across a tidally influenced tropical area, Gazi Bay (Kenya). The main results indicate that tidal transport, along with riverine runoff, play a significant role in the distribution of mangrove organic matter. In particular, a marked spatial variability in the export of organic matter from mangroves to adjacent habitats was due to the different settings of the creeks flowing into the bay. Kinondo Creek acted as a mangrove retention site, where export of mangrove material was limited to the contiguous intertidal area, while Kidogoweni Creek acted as a “flow-through” system, from which mangrove material spread into the bay, especially in the rainy season. This pattern was evident from the isotopic signature of primary producers, which were more 13C-depleted in the Kinondo Creek and nearby, due to the lower dilution of the DIC pool, typically depleted as an effect of intense mangrove mineralization. Despite the trapping efficiency of the seagrass canopy, suspended particulate OM showed the important contribution of mangroves across the whole bay, up to the coral reef, as an effect of the strong ebb tide. Overall, mixing model outcomes and FA profiles indicated a widespread mixed contribution of both allochthonous and autochthonous OM sources across Gazi Bay. Moreover, FAs indicated a notable contribution of brown macroalgae and bacteria in both sediment and particulate pools. These results suggest that ecological connectivity in Gazi Bay is strongly influenced by geomorphological setting, which may have far-reaching consequences for the functioning of the whole ecosystem and the local food webs.

The quick and the dead: larval mortality due to turbulent tidal transport

Marine populations are typically connected over greater spatial scales than their terrestrial counterparts due to many species having a highly dispersive, planktonic larval phase. However, high levels of larval mortality in the plankton may reduce connectivity between populations. The effect of turbulence on larval mortality was investigated under natural conditions in a field experiment. Larvae were collected before and after being subjected to turbulent tidal flow from a marine reserve, with differential mortality being observed between taxa. Thin-shelled veligers of gastropods and bivalves showed significantly increased mortality, while barnacle nauplii and cyprids, bryozoan cyphonaute larvae and polychaete trochophores showed no effect of turbulent tidal transport. Where appropriate, marine reserve design should account for the reduced connectivity between populations associated with turbulent tidal transport between reserve and adjacent areas.