The role of advection in the distribution of plankton populations at a moored 1-D coastal observatory

The degree to which advection modulates the distribution of plankton populations at a 1-D coastal observatory was assessed at station L4 in the western English Channel (50°15′N 4°13′W, depth 50 m), part of the Western Channel Observatory (WCO). Five tidal-cycle surveys were conducted, three in spring and two in summer 2010. Observations of the physical characteristics of L4 were obtained by using a moored acoustic doppler current profiler (ADCP) and a free-falling microstructure sensor (MSS). The moored ADCP highlighted the presence of vertical shear, with typical values of U during spring tides of ∼0.5 m s−1 at the surface and ∼0.2 m s−1 at the bed. The distribution of phyto- and zooplankton populations above a size threshold of 200 μm were examined using an in-line holographic imaging system, the Holocam. Variability in time as well as depth is a common feature throughout each of the surveys, with examples of recorded numbers of phytoplankton that ranged between 1300 L−1 and 2300 L−1 at the same depth but at different points within the tidal cycle. Further, at the same points in the tidal cycle the number of recorded zooplankton was also seen to vary, specifically with the identification of gelatinous planula in spring that increased the observed number to maximums of between 140 L−1 and 220 L−1 in the upper layer, considerably higher that the corresponding WP-2 net counts for a similar period. Specific aspects of the movement and transfer of plankton relating to advection and interaction with the pycnocline are identified, both across tidal cycles and seasons.

The relationship between the distribution of genetically distinct inbred lines and upper lethal temperature in Lasaea rubra

Lasaea rubra is an inbreeding bivalve species, living at most heights on rocky shores. Freshly collected animals from different shore heights showed significantly different upper median lethal temperatures (MLTs), with upper shore animals having higher MLTs than lower shore specimens. Experiments with animals acclimated for at least one month to a single temperature (15°C) demonstrated that these differences in upper MLT were unaffected by thermal acclimation. Electrophoretic investigation showed that the differences in thermal response had a genetic basis. Homogeneous populations of the high-water inbred line (‘Inbred line A’) had a higher MLT than homogeneous populations of ‘Inbred line C’ which was found on the middle and lower shore. No differences were detected between the MLTs of separate populations of Inbred lines A or C. A third inbred line (‘Inbred line B’) was found on the middle shore, but no homogeneous populations were found. However, indirect evidence suggests that Inbred line B has a thermal response intermediate between those of Inbred lines A and C. Study of populations made up of mixtures of inbred lines confirmed the relationship between upper MLTs and genetic composition of the population.

Continuous Plankton Records - Seasonal-Variations In The Distribution And Abundance Of Plankton In The North-Atlantic Ocean And The North-Sea

Charts are presented of the seasonal variations in the distribution of four phytoplankton and five zooplankton taxa in the North Atlantic and the North Sea. The main factors determining the seasonal variations appear to be the distribution of the main overwintering stocks, the current system and, in some instances, temperature control of the rate of population increase. Information is presented about the variation with latitude (over the range from 34° N to 65 ° N) of the seasonal regime of the plankton. On the assumption that there is a relationship between nutrient supply and vertical temperature stratification the main features of this variability can be interpreted. In the south (to about 43° N) nutrient limitation plus grazing appear to be dominant, resulting in a bimodal seasonal cycle of phytoplankton. North of about 60° N the system appears to be limited by the size of the phytoplankton stocks being grazed primarily by Calanus Finmarchicus and Euphausiacea. In an extensive zone, from about 44° N to 60° N, it would appear that the spring bloom of phytoplankton is under-exploited by grazing while in summer the zooplankton graze the daily production of the phytoplankton, the stocks of which are probably maintained by in situ nutrient regeneration. The implications, for at least this mid-latitude zone, that rates and fluxes of processes, as opposed to density dependent interactions between stocks, play a major role in the dynamics of the seasonal cycle is consistent with previously reported observations suggesting that physical environmental factors play a major role in determining year-to-year fluctuations in the abundance of the plankton.

Modelling the effects of climate change on the distribution and production of marine fishes: accounting for trophic interactions in a dynamic bioclimate envelope model

Climate change has already altered the distribution of marine fishes. Future predictions of fish distributions and catches based on bioclimate envelope models are available, but to date they have not considered interspecific interactions. We address this by combining the species-based Dynamic Bioclimate Envelope Model (DBEM) with a size-based trophic model. The new approach provides spatially and temporally resolved predictions of changes in species' size, abundance and catch potential that account for the effects of ecological interactions. Predicted latitudinal shifts are, on average, reduced by 20% when species interactions are incorporated, compared to DBEM predictions, with pelagic species showing the greatest reductions. Goodness-of-fit of biomass data from fish stock assessments in the North Atlantic between 1991 and 2003 is improved slightly by including species interactions. The differences between predictions from the two models may be relatively modest because, at the North Atlantic basin scale, (i) predators and competitors may respond to climate change together; (ii) existing parameterization of the DBEM might implicitly incorporate trophic interactions; and/or (iii) trophic interactions might not be the main driver of responses to climate. Future analyses using ecologically explicit models and data will improve understanding of the effects of inter-specific interactions on responses to climate change, and better inform managers about plausible ecological and fishery consequences of a changing environment.

Horizontal and vertical distribution of cirripede cyprid larvae in an upwelling system off the Portuguese coast

The distribution of cirripede cyprids in relation to associated oceanographic conditions was obtained from a grid survey and intensive vertical sampling at a fixed station located 21 km off the northwest Portuguese coast in May 2002. Analysis of cyprid length composition allowed separation of 3 species groups. Chthamalus montagui, Pollicipes pollicipes and Balanus perforatus were largely restricted to the neuston layer and showed only low-amplitude vertical migration. Most C. stellatus cyprids only appeared in the upper 20 m at night, a migration which did not appear to be affected by physical conditions in the water column, but some differences in the vertical migration pattern between days were probably related to varying light penetration. C. montagui is the most abundant adult species found along the Portuguese coast, but C. stellatus cyprids, at densities of up to 8.7 ind. m–3, were the most common sampled in all depth strata at the fixed station. Cyprid horizontal distribution was mainly restricted to an offshore band along the inner shelf, where highest densities were 11 to 15 ind. m–3. This distribution pattern was considered to result from upwelling-favourable wind conditions, creating fronts along the shelf in which the cyprids become concentrated. Cyprid vertical migration, in association with current vertical shear and onshore movement of fronts during upwelling-relaxation periods, may be the mechanisms returning cyprids to the coast to settle. The regularity of these events in the region falls within the period of cyprid viability.

Use of Continuous Plankton Recorder information in support of marine management: applications in fisheries, environmental protection, and in the study of ecosystem response to environmental change

The Continuous Plankton Recorder (CPR) survey was conceived from the outset as a programme of applied research designed to assist the fishing industry. Its survival and continuing vigour after 70 years is a testament to its utility, which has been achieved in spite of great changes in our understanding of the marine environment and in our concerns over how to manage it. The CPR has been superseded in several respects by other technologies, such as acoustics and remote sensing, but it continues to provide unrivalled seasonal and geographic information about a wide range of zooplankton and phytoplankton taxa. The value of this coverage increases with time and provides the basis for placing recent observations into the context of long-term, large-scale variability and thus suggesting what the causes are likely to be. Information from the CPR is used extensively in judging environmental impacts and producing quality status reports (QSR); it has shown the distributions of fish stocks, which had not previously been exploited; it has pointed to the extent of ungrazed phytoplankton production in the North Atlantic, which was a vital element in establishing the importance of carbon sequestration by phytoplankton. The CPR continues to be the principal source of large-scale, long-term information about the plankton ecosystem of the North Atlantic. It has recently provided extensive information about the biodiversity of the plankton and about the distribution of introduced species. It serves as a valuable example for the design of future monitoring of the marine environment and it has been essential to the design and implementation of most North Atlantic plankton research.

Determination Of Fine-Scale Vertical-Distribution Of Microbes And Meiofauna In An Intertidal Sediment

A simple sampling device is described which produces thin (1 mm) sections of sediment cores. The sampler has been tested on fine sand of an intertidal sandflat and used to study the vertical distribution, over part of a tidal cycle in August, 1981, of migrating algae in the surface 20 mm of sand. Two species of Diplonies and one of Navicula showed marked changes in vertical distribution as the sandflat was flooded, but the distribution of bacteria in the sime samples did not show any change with tidal state. Spatial separation of different species of harpacticoid oppepods within the surface 20 mm of sand has also been demonstrated using this sampler, and the results suggest that different species may occupy particular fine-scale spatial niches within the sand column. The depth separation of nematode species was less well defined, except for two species with apparently the same feeding mode which were isolated from one another vertically.

Coccolithophore species as indicators of surface oceanographic conditions in the vicinity of Azores islands

During summer 2008 and spring 2009, surface oceanographic surveys were carried out around three islands of the Azores archipelago (Terceira, Sao Miguel and Santa Maria) to assess the phytoplankton distribution and associated physico-chemical processes. The Azores archipelago is a major feature in the biogeochemical North Atlantic Subtropical Gyre (NAST) province although its influence on the productivity of the surrounding ocean is poorly known. Surface phytoplankton was studied by microscopy and HPLC (High Precision Liquid Chromatography). The mean values for biomass proxy Chlorophyll a (Chla) ranged from 0.04 to 0.55 mu g L-1 (Chla maximum = 0.86 mu g L-1) and coccolithophores were the most abundant group, followed by small flagellates, Cyanobacteria, diatoms and dinoflagellates being the least abundant group. The distribution of phytoplankton and coccolithophore species in particular presented seasonal differences and was consistent with the nearshore influence of warm subtropical waters from the south Azores current and colder subpolar waters from the north. The satellite-derived circulation patterns showed southward cold water intrusions off Terceira and northward warm water intrusions off Santa Maria. The warmer waters signal was confirmed by the subtropical coccolithophore assemblage, being Discosphaera tubifera a constant presence under these conditions. The regions of enhanced biomass, either resulting from northern cooler waters or from island induced processes, were characterized by the presence of Emiliania huxleyi. Diatoms and dinoflagellates indicated coastal and regional processes of nutrient enrichment and areas of physical stability, respectively.