Advection Of Larvae Research Articles

Predicting larval dispersal of the vase tunicate Ciona intestinalis in a Prince Edward Island estuary using a matrix population model

Despite sporadic observations of the vase tunicate, Ciona intestinalis, on boats and mooring structures in Charlottetown Harbour, Prince Edward Island, the species has not established a population in the harbour nor dispersed the ~12 km downstream to Hillsborough Bay, an important source of blue mussel (Mytilus edulis) spat for the PEI aquaculture industry. A population matrix model used in conjunction with an oceanographic model suggests that advection of larvae from the harbour to the spat production area requires more than one or two generations, and the use of intermediate settlement nodes, such as navigational aids and aquaculture sites located in the upper part of Hillsborough Bay, as ‘stepping stones’. Maintaining potential settlement nodes in a tunicate-free condition could delay oceanographic dispersal of C. intestinalis within the estuary. According to observations of colonial tunicate dispersal in 2010, most likely originating from colonies established in the same locations where C. intestinalis inoculations have been detected, dispersal was occurring in the vicinity of one of the nodes identified by the model as priorities to be monitored for early detection of tunicate settlement, but had not yet reached the other node. A major finding is that the dispersal of solitary tunicates by oceanographic processes, often considered uncontrollable, is evidently amenable to management through monitoring and cleaning of the intermediate settlement nodes.

Environmental control of Northeast Atlantic mackerel (Scomber scombrus) recruitment in the southern Bay of Biscay: case study of failure in the year 2000

We investigate the effect of strong meteorological perturbations in early spring on the success of mackerel (Scomber scombrus) recruitment in the N/NW Iberian area (southern Bay of Biscay) for the period 1999–2008. In 2000, the year of the most pronounced recruitment failure on record, two consecutive multidisciplinary surveys sampled hydrographic conditions and mackerel eggs, larvae and post-larvae over the main mackerel spawning grounds of the north and northwest coast of the Iberian Peninsula. Analysis of egg and larval abundance and birthdates based on the otoliths of mackerel juveniles caught between July and October 2000 showed that there were no survivors from the early spring spawns, indicating a massive loss of early spawning effort. Moreover, the abundance of 1-year-old mackerel estimated from an acoustic survey carried out in 2001 was the lowest observed within the 1999–2008 time series. This low or null survival from the early spawns in 2000 could be due to the meteorological and oceanographic conditions of that spring, in particular two storm events in April after a relatively calm March. The first storm event from the north caused strong local wind in the southern Bay of Biscay but a weak oceanographic response. The second storm event from the southwest was mainly felt west of Galicia and caused a notable increase in shelf currents and a shift of the hydrographical structure along the shelf. Detailed analysis of strong wind pulses in early spring within the historical recruitment record suggests that strong local turbulence generated by high wind speeds and advection of larvae caused by the enhancement of shelf currents can contribute to reduced recruitment. Our observations indicate that, in 2000, both mechanisms were present.

Genetic structure of a recent climate change-driven range extension

The life-history strategies of some species make them strong candidates for rapid exploitation of novel habitat under new climate regimes. Some early-responding species may be considered invasive, and negatively impact on 'naïve' ecosystems. The barrens-forming sea urchin Centrostephanus rodgersii is one such species, having a high dispersal capability and a high-latitude range margin limited only by a developmental temperature threshold. Within this species' range in eastern Australian waters, sea temperatures have increased at greater than double the global average rate. The coinciding poleward range extension of C. rodgersii has caused major ecological changes, threatening reef biodiversity and fisheries productivity. We investigated microsatellite diversity and population structure associated with range expansion by this species. Generalized linear model analyses revealed no reduction in genetic diversity in the newly colonized region. A 'seascape genetics' analysis of genetic distances found no spatial genetic structure associated with the range extension. The distinctive genetic characteristic of the extension zone populations was reduced population-specific F(ST), consistent with very rapid population expansion. Demographic and genetic simulations support our inference of high connectivity between pre- and post-extension zones. Thus, the range shift appears to be a poleward extension of the highly-connected rangewide population of C. rodgersii. This is consistent with advection of larvae by the intensified warm water East Australian current, which has also increased Tasmanian Sea temperatures above the species' lower developmental threshold. Thus, ocean circulation changes have improved the climatic suitability of novel habitat for C. rodgersii and provided the supply of recruits necessary for colonization.

Vertical migrations of fish larvae: Eulerian and Lagrangian observations in the Eastern English Channel

The Eastern English Channel is known for its strong hydrodynamics. Tidal and residual currents are reinforced by the south-western dominant wind and drift waters from the English Channel to the North Sea. Previous spatial studies have shown that the advection of larvae could differ from one species to another. Flounder (Pleuronectes flesus) larvae were found offshore, drifting to the north until the fins were formed; then they were found near the coast. However, sole (Solea solea) larvae remained in coastal waters during their development. The difference in larval spatial distribution is assumed to be related to the interaction between vertical migration and advection by alternative tidal currents, leading to a selective tidal stream transport. To describe the vertical distribution of these larvae, two strategies were used. First, a Eulerian study was carried out with samples taken at the same geographical location every 1.5 h for 41 h. Ichthyoplankton were collected in the water mass using a Bongo net and with a suprabenthic multi-net sledge, at four layers above the sea bed, between 0.1 and 1.4 m. Secondly, to enable water movement to be disregarded, a Lagrangian study was carried out by using a Bongo net every 3 h, following a drifting buoy for 3 days. The results show that even during the youngest stages, sole larvae are able to perform tidal and diel vertical migration. We assume that they may limit their advection to the North Sea because of their upward migration during ebb and at night, which may enable them to remain in the same area dealing with the currents. Flounder larvae begin their vertical migration at the stage of notochord flexion, which ends their drift to the north. The larvae reach the bottom of the water column, particularly during ebb when they are concentrated in the first 40 cm above the bottom. This behaviour favours their advection during flow, leading to efficient and fast transport towards the coast.