Physiological-Responses Of Mytilus-Edulis L To Parasitic Infestation By Mytilicola-Intestinalis

Various levels of infestation by Mytilicola had no effect on the rates of oxygen consumption by Mytilus edulis in laboratory experiments. However, high levels of infestation (> 10 parasites per mussel) caused a depression in the feeding rate of the host at high temperatures (22° or 23° C) and low ration (maintenance or sub-maintenance). This depression of feeding resulted in a decline in the scope for growth, which would result in time in a decline in the “condition” of the host. It is concluded that similar effects may occur in the field when large numbers of small parasites are present at a time of high metabolic demand and low food availability.

Population-Dynamics Of Mytilicola-Intestinalis In Mytilus-Edulis In South West England

The population dynamics of Mytilicola intestinalis Steuer in mussels (Mytilus edulis L.) from the River Lynher, Cornwall, England, have been studied over 3 years. By transplanting uninfested mussels from the River Erme, South Devon, into the Lynher mussel bed, the study was extended to the growth and development of new infestations under natural conditions. Female Mytilicola intestinalis are shown to breed twice, and two generations of parasites coexist for most of the year, with recruitment taking place in summer and autumn. One generation contributes its first brood to the autumn recruits before overwintering and contributing its second brood to the following summer's recruits. The other generation overwinters as juvenile and immature stages to contribute its two broods successively to the summer and autumn recruits. Environmental temperatures are believed to control the rates of development at all stages rather than acting as triggers in the onset or cessation of breeding at specific times. There is no evidence to support the contention that heavily infested mussels are killed, and parasite mortality is shown to be density-independent.

Relationship Between Infestation By Mytilicola-Intestinalis Steuer (Copepoda Cyclopoidea) And Condition Index Of Mytilus-Edulis In Southwest England

Seasonal cycles in the condition index of Mytilus edulis from three sites in southwest England are described. These are analysed in relation to host length, stage of gonad development and parasite burden by linear regression analysis. An effect on the condition index due to the presence of Mytilicola intestinalis can be detected only in the sublittoral mussels in those few winter months when the mean intensity of infestation is over about 25 parasites per host. In all cases studied, the magnitude of the effect due to variation in host length, stage of gonad development, seasonal cycles and environmental factors is greater than that due to parasitism.

North Atlantic climatic signals and the plankton of the European Continental Shelf

Climatic variability on the European Continental Shelf is dominated by events over the North Atlantic Ocean, and in particular by the North Atlantic Oscillation (NAO). The NAO is essentially a winter phenomenon, and its effects will be felt most strongly by populations for which winter conditions are critical. One example is the copepod Calanus finmarchicus, whose northern North Sea populations overwinter at depth in the North Atlantic. Its annual abundance in this region is strongly dependent on water transports at the end of the winter, and hence on the NAO index. Variations in the NAO give rise to changes in the circulation of the North Atlantic Ocean, with additional perturbations arising from El Ni (n) over tildeo - Southern Oscillation (ENSO) events in the Pacific, and these changes can be delayed by several years because of the adjustment time of the ocean circulation. One measure of the circulation is the latitude of the north wall of the Gulf Stream (GSNW index). Interannual variations in the plankton of the Shelf Seas show strong correlations with the fluctuations of the GSNW index, which are the result of Atlantic-wide atmospheric processes. These associations imply that the interannual variations are climatically induced rather than due to natural fluctuations of the marine ecosystem, and that the zooplankton populations have not been significantly affected by anthropogenic processes such as nutrient enrichment or fishing pressure. While the GSNW index represents a response to atmospheric changes over two or more years, the zooplankton populations correlated with it have generation times of a few weeks. The simplest explanation for the associations between the zooplankton and the GSNW index is that the plankton are responding to weather patterns propagating downstream from the Gulf Stream system. It seems that these meteorological processes operate in the spring. Although it has been suggested that there was a regime shift in the North Sea in the late 1980s, examination of the time-series by the cumulative sum (CUSUM) technique shows that any changes in the zooplankton of the central and northern North Sea are consistent with the background climatic variability. The abundance of total copepods increased during this period but this change does not represent a dramatic change in ecosystem processes. It is possible some change may have occurred at the end of the time-series in the years 1997 and 1998.

Changes in the oceanic northeast Pacific plankton populations; what may happen in a warmer ocean

The Continuous Plankton Recorder has been sampling the northeast Pacific on a routine basis since 2000. Although this is a relatively short time series still, climate variability within that time has caused noticeable related changes in the plankton. The earlier part of the time series followed the 1999 La Nina and conditions were cool, but conditions between 2003 and 2005 were anomalously warm. Oceanic zooplankton have responded to this warming in several ways that are discernible in CPR data. The seasonal cycle of mesozooplankton biomass in the eastern Gulf of Alaska has shifted earlier in the spring by a few weeks (sampling resolution is too coarse to be more accurate). The copepod Neocalanus plumchruslflemingeri is largely responsible as it makes up a high proportion of the spring surface biomass and stage-based determinations have shown an earlier maximum in warmer years across much of the northeast Pacific, spanning nearly 20 degrees of latitude. Summer copepod populations are more diverse than in spring, although lower in biomass. The northwards extension of southern taxa in the summer correlates with surface temperature and in warmer years southern taxa are found further north than in cooler years. These findings support the importance of monitoring the open ocean particularly as it is an important foraging ground for large fish, birds and mammals. Higher trophic levels may time their reproduction or migration to coincide with the abundance of particular prey which may be of a different composition and/or lower abundance at a particular time in warmer conditions.

Shortened duration of the annual Neocalanus plumchrus biomass peak in the Northeast Pacific

The calanoid copepod Neocalan us plumchrus (Marukawa) is a dominant member of the spring mesozooplankton in the subarctic North Pacific and Bering Sea. Previous studies have shown interdecadal and latitudinal variation in seasonal developmental timing, with peak biomass occurring earlier in years and places with warmer upper ocean temperatures. Because N. plumchrus normally has a single dominant annual cohort, its seasonal timing can be indexed from measurements of total population biomass or by following progressive changes in stage composition. Early studies empirically found that peak upper ocean biomass occurred when about half of the pre-dormant population had reached copepodite stage 5 (C5). However, more recent comparisons derived from recent Continuous Plankton Recorder (CPR) data now show peak biomass when a larger fraction (> 80%) of the population is at C5. CPR samples the surface 10 to 15 m, but comparisons to depth-resolved BIONESS data show that this discrepancy is not an artefact of sampling depth. Other causes are either a prolongation of duration of pre-dormant C5 or a narrowing of the age range making up the annual cohort. We assessed changes in cohort width using a modification of Greve's cumulative percentile method, and found that average cohort widths in the Alaska Gyre were significantly narrower in 2000-2007 than in 1957-1965 (1968-1980 were intermediate). Net tow sampling of Strait of Georgia populations showed a similar significant narrowing of cohorts in the 2003-2005 sampling period. This study provides evidence that in addition to the shift to an earlier occurrence of peak biomass reported previously, the duration of the peak has also decreased in the last decade.

Variability in northwards extension of warm water copepods in the NE Pacific

The Continuous Plankton Recorder has been deployed in the NE Pacific on two intersecting transects since 2000. Many deployments included a temperature sensor providing in situ temperature data to supplement the species abundance data for 1300 samples. Twenty-nine copepod taxa were sufficiently abundant to examine their temperature-related distributions. Groups of warm- and cold-water species were identified, with overlapping distributions between 48 and 588N. Recent fluctuations in ocean climate, from the warmest year on record in 2005 to one of the coldest in decades in 2008, provided ideal conditions to observe temperature-related interannual variability. The abundance and northwards extension of warm water species were significantly positively correlated with mean annual temperature and the Pacific Decadal Oscillation. The cold water species showed no correlations with temperature/Pacific Decadal Oscillation (PDO) within the study region; however, if the 4 years of sampling that extended south to 398N were examined separately, there was a strong relationship between temperature/PDO and the southern extent of subarctic copepods. Under warm ocean conditions, the range overlap of the two groups will increase as warm water species extend northwards, causing an increase in copepod diversity. Since warm water species are generally smaller and nutritionally poorer, this has implications for higher trophic levels

Acquisition of continuous plankton recorder data

The Continuous Plankton Recorder has been deployed on a seasonal basis in the north Pacific since 2000, accumulating a database of abundance measurements for over 290 planktonic taxa in over 3,500 processed samples. There is an additional archive of over 10,000 samples available for further analyses. Exxon Valdez Oil Spill Trustee Council financial support has contributed to about half of this tally, through four projects funded since 2002. Time series of zooplankton variables for sub-regions of the survey area are presented together with abstracts of eight papers published using data from these projects. The time series covers a period when the dominant climate signal in the north Pacific, the Pacific Decadal Oscillation (PDO), switched with unusual frequency between warm/positive states (pre-1999 and 2003-2006) and cool/negative states (1999-2002 and 2007). The CPR data suggest that cool negative years show higher biomass on the shelf and lower biomass in the open ocean, while the reverse is true in warm (PDO positive) years with lower shelf biomass (except 2005) and higher oceanic biomass. In addition, there was a delay in plankton increase on the Alaskan shelf in the colder spring of 2007, compared to the warmer springs of the preceding years. In warm years, smaller species of copepods which lack lipid reserves are also more common. Availability of the zooplankton prey to higher trophic levels (including those that society values highly) is therefore dependent on the timing of increase and peak abundance, ease of capture and nutritional value. Previously published studies using these data highlight the wide-ranging applicability of CPR data and include collaborative studies on; phenology in the key copepod species Neocalanus plumchrus, descriptions of distributions of decapod larvae and euphausiid species, the effects of hydrographic features such as mesoscale eddies and the North Pacific Current on plankton populations and a molecularbased investigation of macro-scale population structure in N. cristatus. The future funding situation is uncertain but the value of the data and studies so far accumulated is considerable and sets a strong foundation for further studies on plankton dynamics and interactions with higher trophic levels in the northern Gulf of Alaska.

Rapid biogeographical plankton shifts in the North Atlantic Ocean

Large-scale biogeographical changes in the biodiversity of a key zooplankton group (calanoid copepods) were detected in the north-eastern part of the North Atlantic Ocean and its adjacent seas over the period 1960–1999. These findings provided key empirical evidence for climate change impacts on marine ecosystems at the regional to oceanic scale. Since 1999, global temperatures have continued to rise in the region. Here, we extend the analysis to the period 1958–2005 using all calanoid copepod species assemblages (nine species assemblages based on an analysis including a total of 108 calanoid species or taxa) and show that this phenomenon has been reinforced in all regions. Our study reveals that the biodiversity of calanoid copepods are responding quickly to sea surface temperature (SST) rise by moving geographically northward at a rapid rate up to about 23.16 km yr−1. Our analysis suggests that nearly half of the increase in sea temperature in the northeast Atlantic and adjacent seas is related to global temperature rises (46.35% of the total variance of temperature) while changes in both natural modes of atmospheric and oceanic circulation explain 26.45% of the total variance of temperature. Although some SST isotherms have moved northwards by an average rate of up to 21.75 km yr−1 (e.g. the North Sea), their movement cannot fully quantify all species assemblage shifts. Furthermore, the observed rates of biogeographical movements are far greater than those observed in the terrestrial realm. Here, we discuss the processes that may explain such a discrepancy and suggest that the differences are mainly explained by the fluid nature of the pelagic domain, the life cycle of the zooplankton and the lesser anthropogenic influence (e.g. exploitation, habitat fragmentation) on these organisms. We also hypothesize that despite changes in the path and intensity of the oceanic currents that may modify quickly and greatly pelagic zooplankton species, these organisms may reflect better the current impact of climate warming on ecosystems as terrestrial organisms are likely to significantly lag the current impact of climate change.

Simple procedures to assess and compare the ecological niche of species

Hutchinson's (1957; Cold Spring Harbour Symp Quant Biol 22:415-427) niche concept is being used increasingly in the context of global change, and is currently applied to many ecological issues including climate change, exotic species invasion and management of endangered species. For both the marine and terrestrial realms, there is a growing need to assess the breadth of the niches of individual species and to make comparisons among them to forecast the species' capabilities to adapt to global change. In this paper, we describe simple non-parametric multivariate procedures derived from a method originally used in climatology to (1) evaluate the breadth of the ecological niche of a species and (2) examine whether the niches are significantly separated. We first applied the statistical procedures to a simple fictive example of 3 species separated by 2 environmental factors in order to describe the technique. We then used it to quantify and compare the ecological niche of 2 key-structural marine zooplankton copepod species, Calanus finmarchicus and C. helgolandicus, in the northern part of the North Atlantic Ocean using 3 environmental factors. The test demonstrates that the niches of both species are significantly separated and that the coldwater species has a niche larger than that of its warmer-water congeneric species.

Effects of formalin preservation on stable carbon and nitrogen isotope signatures in Calanoid copepods: implications for the use of Continuous Plankton Recorder Survey samples in stable isotope analyses

Preserved and archived organic material offers huge potential for the conduct of retrospective and long-term historical ecosystem reconstructions using stable isotope analyses, but because of isotopic exchange with preservatives the obtained values require validation. The Continuous Plankton Recorder (CPR) Survey is the most extensive long-term monitoring program for plankton communities worldwide and has utilised ships of opportunity to collect samples since 1931. To keep the samples intact for subsequent analysis, they are collected and preserved in formalin; however, previous studies have found that this may alter stable carbon and nitrogen isotope ratios in zooplankton. A maximum ~0.9‰ increase of δ15N and a time dependent maximum ~1.0‰ decrease of δ13C were observed when the copepod, Calanus helgolandicus, was experimentally exposed to two formalin preservatives for 12 months. Applying specific correction factors to δ15N and δ13C values for similarly preserved Calanoid species collected by the CPR Survey within 12 months of analysis may be appropriate to enable their use in stable isotope studies. The isotope values of samples stored frozen did not differ significantly from those of controls. Although the impact of formalin preservation was relatively small in this and other studies of marine zooplankton, changes in isotope signatures are not consistent across taxa, especially for δ15N, indicating that species-specific studies may be required. Copyright © 2011 John Wiley & Sons, Ltd.

Diet of auklet chicks in the Aleutian Islands, Alaska: similarity among islands, interspecies overlap, and relationships to ocean climate

Seabirds are effective samplers of the marine environment, and can be used to measure resource partitioning among species and sites via food loads destined for chicks. We examined the composition, overlap, and relationships to changing climate and oceanography of 3,216 food loads from Least, Crested, and Whiskered Auklets (Aethia pusilla, A. cristatella, A. pygmaea) breeding in Alaska during 1994–2006. Meals comprised calanoid copepods (Neocalanus spp.) and euphausiids (Thysanoessa spp.) that reflect secondary marine productivity, with no difference among Buldir, Kiska, and Kasatochi islands across 585 km of the Aleutian Islands. Meals were very similar among species (mean Least–Crested Auklet overlap C = 0.68; Least–Whiskered Auklet overlap C = 0.96) and among sites, indicating limited partitioning of prey resources for auklets feeding chicks. The biomass of copepods and euphausiids in Least and Crested Auklet food loads was related negatively to the summer (June–July–August) North Pacific Gyre Oscillation, while in Whiskered Auklet food loads, this was negatively related to the winter (December–January–February) Pacific Decadal Oscillation, both of which track basin-wide sea-surface temperature (SST) anomalies. We found a significant quadratic relationship between the biomass of calanoid copepods in Least Auklet food loads at all three study sites and summer (June–July) SST, with maximal copepod biomass between 3–6°C (r 2 = 0.71). Outside this temperature range, zooplankton becomes less available to auklets through delayed development. Overall, our results suggest that auklets are able to buffer climate-mediated bottom-up forcing of demographic parameters like productivity, as the composition of chick meals has remained constant over the course of our study.

Feeding of Calanus finmarchicus and Oithona similis on the microplankton assemblage in the Irminger Sea, North Atlantic

The present investigation reviews published data on the feeding rates and prey selection of Oithona similis females, Calanus finmarchicus nauplii and females in the Irminger Sea in April/May and July/August 2002. Our aim was to examine how the feeding rates and prey selection of these three copepod stages respond to concomitant changes in microplankton community composition and prey abundance. Copepods typically ingested prey overall according to its ambient concentration although significant species and stage-specific differences in prey-type ingestion and selection were apparent. Despite being of comparable weight, the ingestion rates of C. finmarchicus nauplii were always higher than those of the O. similis females. Moreover, C. finmarchicus nauplii and O. similis females fed preferentially on diatoms and ciliates respectively, whereas adult female C. finmarchicus showed limited prey selectivity. Copepod grazing impact on total and on ciliates/dinoflagellates standing stock was <0.5 and <2%, respectively. We attribute this result to a combination of low grazing rates, low copepod abundance and low microplankton biomass, all of which are indicative of the non-bloom conditions under which these experiments were conducted. The differences in copepod feeding rates and prey selection we report reflect species and stage-specific eco-physiological adaptations, which may act as important driving forces for marine ecosystem structuring and functioning.

Temporal and spatial variability of Oithona spp. abundance and phenology in the North Atlantic, North Pacific and Southern Ocean using the CPR data

The genus Oithona is considered the most ubiquitous and abundant copepod group in the world oceans. Although they generally make-up a lower proportion of the total copepod biomass, because of their high numerical abundance, preferential feeding for microzooplankton and motile preys, Oithona spp. plays an important role in microbial food webs and can provide a food source for other planktonic organisms. Thus, changes in Oithona spp. overall abundance and the timing of their annual maximum (i.e. phenology) can have important consequences for both energy flow within marine food webs and secondary production. Using the long term data (1954-2005) collected by the Continuous Plankton Recorder (CPR), the present study, investigates whether global climate warming my have affected the long term trends in Oithona spp. population abundance and phenology in relation to biotic and abiotic variables and over a wide latitudinal range and diverse oceanographic regions in the Atlantic, Pacific and Southern Ocean.

Biologging, Remotely-Sensed Oceanography and the Continuous Plankton Recorder Reveal the Environmental Determinants of a Seabird Wintering Hotspot

Marine environments are greatly affected by climate change, and understanding how this perturbation affects marine vertebrates is a major issue. In this context, it is essential to identify the environmental drivers of animal distribution. Here, we focused on the little auk (Alle alle), one of the world’s most numerous seabirds and a major component in Arctic food webs. Using a multidisciplinary approach, we show how little auks adopt specific migratory strategies and balance environmental constraints to optimize their energy budgets. Miniature electronic loggers indicate that after breeding, birds from East Greenland migrate .2000 km to overwinter in a restricted area off Newfoundland. Synoptic data available from the Continuous Plankton Recorder (CPR) indicate that this region harbours some of the highest densities of the copepod Calanus finmarchicus found in the North Atlantic during winter. Examination of large-scale climatic and oceanographic data suggests that little auks favour patches of high copepod abundance in areas where air temperature ranges from 0uC to 5uC. These results greatly advance our understanding of animal responses to extreme environmental constraints, and highlight that information on habitat preference is key to identifying critical areas for marine conservation.