Seasonal variations in the stable isotopic composition and the skeletal density pattern of the coralPorites lobata (Gulf of Eilat,Red Sea)

The stable carbon and oxygen isotopic compositions of the massive coralPorites lobata collected from the Gulf of Eilat, Red Sea, in May 1987 were measured along the vertical growth axis. The isotopic compositions show annual periodicity. The variations along the isotopic profile, compared with the X-radiography, indicate that the high-density bands are enriched in¹⁸O and deposited during the season of lowest water temperature (winter). In contrast, the low-density bands are depleted in¹⁸O and deposited during the warmest seawater temperatures (summer). The stable carbon and the oxygen isotopic ratios are negatively correlated with a shift in phase. During the season of higher water temperatures and light intensity values (summer), the skeleton is depleted in¹⁸O and enriched in¹³C and vice versa for the winter time. The shift between the carbon and the oxygen isotopic curves reflects the shift between the seasonal light intensities and seasonal temperature variations in the shallow water. The oxygen isotope ratio was used to detect the seasonal variations in seawater temperatures. The coral aragonitic skeleton is depleted in¹⁸O compared to apparent equilibrium with ambient seawater. The disequilibria range from (ca.) -3.10 to -3.50 with an average value of 3.40. The isotope fractionation behavior during skeleton precipitation is discussed in light of the environmental variables.     

Oxygen- and carbon-isotope analyses of the articulate brachiopodLaqueus californianus: a recorder of environmental changes in the subeuphotic zone

This study is the first systematic attempt to use oxygen and carbon isotopes in modern brachiopods to investigate seasonality and growth rates. A comparison of oxygen-isotope analyses of shells of living specimens ofLaqueus californianus dredged from 80 and 130 m off Santa Catalina Island, California, to available hydrographie data indicates that this articulate brachiopod secretes its shell in or close to oxygen isotopic equilibrium with ambient seawater. Periodic oxygen-isotope depletions appear to result from El Nino events. Unexpectedly low ¹³C values associated with the 1983 El Nino may be explained by increased bacterial activity or organic loading into the Southern California Bight associated with these warm-water pulses. Growth rates determined from annual cycles in ¹⁸O records are variable, but generally average between 2 and 3 mm yr^–1 for mature individuals. Because of the longevity ofL. californianus,¹⁸O profiles provide high-resolution seasonal temperature records spanning one to two decades. Our data suggest that oxygen isotopes in brachiopod shells can be utilized as monitors of environmental change in the subeuphotic zone.     

Combined sclerochronologic and oxygen isotope analysis of gastropod shells (Gibbula cineraria, North Sea): life-history traits and utility as a high-resolution environmental archive for kelp forests

The grey top-shell, Gibbula cineraria is a common member of temperate to cold water kelp forest communities, but its longevity and the age structure of its populations remains unresolved. Combined measurements of shell growth rates (sclerochronology) and oxygen isotope composition allow analysis of rate and timing of shell growth. Eight specimens were analyzed from the southern North Sea (near Helgoland, German Bight). Three age groups were identified but external measurements (width, height, ornamentation patterns and number of whorls) and shell weight are not adequate for ontogenetic age discrimination. Stable oxygen isotope data is consistent with shell growth during the interval from April to December in isotopic equilibrium with seawater, and growth increments exhibit strong tidal controls with fortnightly bundles well preserved. Reliable environmental proxy data (water temperature) can be extracted from the shell aragonite using conventional stable oxygen isotope analyses, with a temporal resolution of days attainable during intervals of maximum growth, but annual extremes are not always recorded in the shell. While demonstrating the utility of G. cineraria as a environmental and potential paleoenvironmental proxy for kelp forest habitats, its longevity has been significantly overestimated.     

Seasonal patterns of growth and storage in Laminaria longicruris in relation to differing patterns of availability of nitrogen in the water

The annual cycles of growth and of internal storage of nitrogen and carbon in Laminaria longicruris were compared at three sites in Nova Scotia, Canada. One site had abundant nitrogen all year round, on account of local upwelling, one had abundant nitrogen for only four months and the last was intermediate in this respect. Where nitrogen was abundant year round, growth followed the seasonal pattern of light, and there was little storage of either carbon or inorganic nitrogen. Where nitrogen was only abundant in the sea in winter, growth accelerated at this time and continued throught early summer while internal reserves of nitrogen were utilized. Carbon was stored in summer and used for growth in the fall. At the intermediate site, larger reserves of nitrogen were built up in winter and a high growth rate was maintained through most of the summer. Smaller carbon reserves were accumulated and growth was minimal in winter. Experiments in which plants were transplanted between sites were not conclusive, but suggested that plants at different sites may have genetic differences.     

Autecology of Fucus distichus ssp. distichus (Phaeophyceae: Fucales) in Nova Scotia,Canada

The autecology of Fucus distichus L. ssp. distichus was investigated at several sites on the Atlantic coast of Nova Scotia, Canada, throughout a 2-year period. This species is confined to high-littoral rock pools at exposed sites, where there appears to be little competition from other organisms. Water temperature, salinity, dissolved oxygen, and hydrogen-ion concentrations underwent both considerable seasonal and short-term variation. Pools with extremes of salinity did not contain F. distichus ssp. distichus. Receptacles are formed during winter, and by late spring they are cast. Sporelings were first visible during September; their development was slow, and these plants did not become reproductive until the second year. During the period February to May, rapid growth of new fronds occurred; an increase in both length and bulk of the plants resulted from this growth. Fronds of mature plants continued to elongate slowly throughout the summer and the early autumn with the formation of receptacles in winter. Plants were frequently damaged, which resulted in regeneration of new fronds from the wounded surface.Issued as NRCC No. 14510     

Stable isotope profiles from subtropical marine gastropods of the family Fasciolariidae: growth histories and relationships to local environmental conditions

Oxygen and carbon stable isotope profiles were constructed for two species of large subtropical gastropods of the family Fasciolariidae—Triplofusus giganteus and Fasciolaria tulipa—from the Florida Keys and the Bahamas, to evaluate their life history and to assess their potential as paleoenvironmental proxies. Oxygen isotope profiles revealed T. giganteus and F. tulipa grew their shells for 6 and 3 years, respectively. Both mollusks show faster growth rates during the first half of their lifespan. Mean annual temperatures (MAT) derived from oxygen isotopes for T. giganteus were 26.5 °C and for F. tulipa were 26.7 °C, both matching instrumental MATs of 26.7 and 26.5 °C for the Florida Keys. Both shells, however, failed to record entire mean annual temperature ranges (MART). Fasciolaria tulipa yielded a calculated MART of 5.6 °C compared with a measured MART of 9.3 °C, and T. giganteus showed a calculated MART of 6.9 °C compared with a measured MART of 9.4 °C. Carbon isotopes of T. giganteus were ambiguous and reveal no significant relationships with trends in nutrient concentrations (N and P), dissolved oxygen, and dissolved organic carbon, although they did exhibit more negative values concomitant with landfall of Hurricane Irene and trended to increasing values with ontogeny that could reflect migration. Carbon isotopes in F. tulipa were lower during winters, possibly reflecting seasonal upwelling or seagrass-mediated carbon cycling.     

Reproductive cycle and gametogenesis in the black abalone Haliotis cracheroidii (Gastropoda: Prosobranchiata)

Seasonal changes in gonald size and stages of gametogenesis in the black abalone Haliotis cracheroidii were related to changes in environmental parameters. H. cracheroidii showed an annual reproductive cycle terminating in a synchronized spawning in late summer. Gametogenesis was initiated immediately after spawning. Gametes were present in the gonad through the winter months. Gametogenesis was initiated a second time in the spring months. Maximal gonad growth (to a gonad index of 20%) occurred during summer months prior to spawning. Changes in gonad size andperiods of initiation of gametogenesis revealed no apparent correlation with changes in seasonal water temperature. Changes in gonad size showed no apparent relation to change in day length. Total polysaccharide levels in foot tissue changed seasonally, indicating that food availability is probably not a factor in directly regulating gonad growth. Gonad index data for the chiton Katharina tunicata (collected over a 10 year period) showed no apparent correlation to seasonal change in water temperature.     

Functional clustering of varved lake sediment to reconstruct past seasonal climate

Annually laminated (varved) lake sediments constitutes excellent environmental archives, and have the potential to play an important role for understanding past seasonal climate with their inherent annual time resolution and within-year seasonal patterns. We propose to use functional data analysis methods to extract the relevant information with respect to climate reconstruction from the rich but complex information in the varves, including the shapes of the seasonal patterns, the varying varve thickness, and the non-linear sediment accumulation rates. In particular we analyze varved sediment from lake Kassjön in northern Sweden, covering the past 6400 years. The properties of each varve reflect to a large extent weather conditions and internal biological processes in the lake the year that the varve was deposited. Functional clustering is used to group the seasonal patterns into different types, that can be associated with different weather conditions. The seasonal patterns were described by penalized splines and clustered by the k-means algorithm, after alignment. The observed (within-year) variability in the data was used to determine the degree of smoothing for the penalized spline approximations. The resulting clusters and their time dynamics show great potential for seasonal climate interpretation, in particular for winter climate changes.     

Growth dynamics of the seagrass <Emphasis Type="Italic">Halophila nipponica</Emphasis>, recently discovered in temperate coastal waters of the Korean peninsula

Seagrass species in the genus Halophila are usually distributed in tropical or subtropical areas, but a Halophila species identified as H. nipponica was first observed in temperate coastal regions of Korea in 2007. Since this species mainly occurs in warm temperate regions influenced by warm currents, we hypothesized that H. nipponica may exhibit different growth patterns from those of other temperate seagrass species in Korea, instead showing similar growth dynamics to tropical/subtropical species. The growth and morphology of H. nipponica in relation to coincident measurements of environmental factors were investigated from July 2008 to September 2009 to examine the growth dynamics of this species. Water temperature at the study site ranged from 9.7°C in January to 25.1°C in August. Shoot density, biomass, and productivity exhibited significant seasonal variation, increasing during summer and decreasing during winter. Productivity was severely restricted to nearly ceasing at water temperatures less than 15°C, and winter minimum growth lasted until May. The optimal temperature for H. nipponica growth was approximately 25°C, which was the maximum water temperature at the study site, and no growth reduction in high summer water temperature was observed. Thus, H. nipponica on the temperate coast of Korea exhibited a distinctly different growth pattern from those of temperate seagrass species in Korea, which have shown great reductions in growth at water temperatures higher than 20°C. Higher below- to above-ground ratio and leaf burial into sediments with shorter leaf petioles during winter might be overwintering strategies in this species. The growth patterns of H. nipponica at the study site imply that this species still possess the tropical characteristics of the genus Halophila.     

Age determination of the soft-shell clam Mya arenaria using shell internal growth lines

Shells of known-age Mya arenaria have revealed an internal annual growth pattern in this bivalve. The number of external growth rings on the shell exterior does not correspond to the age of the clams. This study provides an alternative method to using external annual rings for age determination. The internal growth lines are visible in thin sections when the shells are cut from the umbo to the ventral margin. The lines are formed by late spring of each year prior to spawning and are probably in response to decreased winter growth. When the 7 year olds were examined it was difficult to distinguish the most recent growth line and the inner shell layer. This could result in ages being underestimated. This annual pattern of internal growth lines could be useful to biologists and paleoecologists engaged in population studies.     

Using social network analysis tools in ecology: Markov process transition models applied to the seasonal trophic network dynamics of the Chesapeake Bay

Ecosystem components interact in complex ways and change over time due to a variety of both internal and external influences (climate change, season cycles, human impacts). Such processes need to be modeled dynamically using appropriate statistical methods for assessing change in network structure. Here we use visualizations and statistical models of network dynamics to understand seasonal changes in the trophic network model described by Baird and Ulanowicz [Baird, D., Ulanowicz, R.E., 1989. Seasonal dynamics of the Chesapeake Bay ecosystem. Ecol. Monogr. 501 (59), 329–364] for the Chesapeake Bay (USA). Visualizations of carbon flow networks were created for each season by using a network graphic analysis tool (NETDRAW). The structural relations of the pelagic and benthic compartments (nodes) in each seasonal network were displayed in a two-dimensional space using spring-embedder analyses with nodes color-coded for habitat associations (benthic or pelagic). The most complex network was summer, when pelagic species such as sea nettles, larval fishes, and carnivorous fishes immigrate into Chesapeake Bay and consume prey largely from the plankton and to some extent the benthos. Winter was the simplest of the seasonal networks, and exhibited the highest ascendency, with fewest nodes present and with most of the flows shifting to the benthic bacteria and sediment POC compartments. This shift in system complexity corresponds with a shift from a pelagic- to benthic-dominated system over the seasonal cycle, suggesting that winter is a mostly closed system, relying on internal cycling rather than external input. Network visualization tools are useful in assessing temporal and spatial changes in food web networks, which can be explored for patterns that can be tested using statistical approaches. A simulation-based continuous-time Markov Chain model called SIENA was used to determine the dynamic structural changes in the trophic network across phases of the annual cycle in a statistical as opposed to a visual assessment. There was a significant decrease in outdegree (prey nodes with reduced link density) and an increase in the number of transitive triples (a triad in which i chooses j and h, and j also chooses h, mostly connected via the non-living detritus nodes in position i), suggesting the Chesapeake Bay is a simpler, but structurally more efficient, ecosystem in the winter than in the summer. As in the visual analysis, this shift in system complexity corresponds with a shift from a pelagic to a more benthic-dominated system from summer to winter. Both the SIENA model and the visualization in NETDRAW support the conclusions of Baird and Ulanowicz [Baird, D., Ulanowicz, R.E., 1989. Seasonal dynamics of the Chesapeake Bay ecosystem. Ecol. Monogr. 501 (59), 329–364] that there was an increase in the Chesapeake Bay ecosystem's ascendancy in the winter. We explain such reduced complexity in winter as a system response to lowered temperature and decreased solar energy input, which causes a decline in the production of new carbon, forcing nodes to go extinct; this causes a change in the structure of the system, making it simpler and more efficient than in summer. It appears that the seasonal dynamics of the trophic structure of Chesapeake Bay can be modeled effectively using the SIENA statistical model for network change.     

Seasonal variation of excystment pattern of the planktonic oligotrich ciliate Strombidium conicum

Cysts of the planktonic oligotrich ciliate Strombidium conicum were isolated from sediment samples, collected monthly in Onagawa Bay on the northeastern Pacific coast of Japan, and incubated under laboratory conditions of 20 °C in light. The excystment ability changed seasonally in a regular manner, which was demonstrated by alternation of three characteristic seasonal patterns of the cumulative excystment curve, i.e., rapid, delayed and transitional patterns. While the transitional excystment pattern was characteristic during the period from spring to midsummer, the rapid pattern occurred during late summer to early winter. The pattern changed again to transitional in midwinter and finally returned to the delayed pattern in late winter or early spring. We suggest that mud temperature was the most determinative factor of this seasonality in excystment ability. Such synchronization of annual excystment helps this species to proliferate rapidly and maintain the vegetative part of the population in the upper water column for a longer period of time where it is subjected to the dispersion process due to water movement. Received: 17 September 1996 / Accepted: 18 November 1996     

A comparative seasonal study of two populations of Hypnea musciformis from the East and West Coasts of Florida,USA I. Growth and chemistry

Dry weight levels of the red alga Hypnea musciformis (Wulfen) Lamouroux from Atlantic and Gulf of Mexico coastal sites in florida, USA were lowest in the late winter and early spring, increasing through the summer and highest in the fall. There was a two-month lag in the Gulf coast population's dry weight pattern, indicating differing growth patterns. Chlorophyll a, phycoerythrin and phycoerythrin/chlorophyll a ratios were highest in the winter and lowest in the summer for both populations. Total pigment levels for H. musciformis from the Atlantic coast site were significantly greater than those of the Gulf coast. Protein and carbohydrate percentages were inversely related in both populations, with carbohydrate levels highest in summer and protein levels highest in winter. The Gulf coast population contained significantly more protein than the Atlantic coast plants. Carrageenan levels were highest in spring and lowest in fall, the Atlantic coast population generally had higher levels than the Gulf coast population. The differences in seasonal patterns and levels of the chemical constituents were reflected by distinct morphological characteristics for each population. The Atlantic coast population was larger, darker, more coarse in texture and possessed more crozier branch tips than the Gulf coast plants. These distinctions represent acclimitization responses that relate to habitat differences.     

Temporal life history plasticity of the Southern Ocean squid <Emphasis Type="Italic">Todarodes filippovae</Emphasis> from waters off Tasmania,Australia

Population dynamics and maturity parameters were analysed for seasonal samples of the oceanic ommastrephid squid Todarodes filippovae from off the coast of Tasmania Australia from 2002 to 2004. Based on assumed daily periodicity in statolith increments, T. filippovae had a life cycle of about a year with the sexually dimorphic females reaching their larger size by predominantly growing faster than males. Due to the small sample size of males, analysis was undertaken on female individuals only. Growth in all samples was best described by a power curve and varied annually, with significantly faster growth in 2001 compared to the subsequent 2 years. Seasonal growth rates also varied with autumn- and winter-hatched squid significantly faster than summer-hatched squid. Spring growth rates were intermediate but not significantly different to the other three seasons. Peak hatching periods occurred in late autumn and early winter. ANOVA revealed a season × year interaction for mantle length and total body weight. Pairwise comparisons showed that the annual differences were likely driven by smaller squid in autumn 2002 compared to autumn samples in the other 2 years. Pairwise comparisons also revealed seasonal differences with winter-caught squid smaller than those from the majority of other samples. There were no seasonal effects on mature female gonad weights but females caught in 2002 had significantly lighter gonad weights than females from the following 2 years. There were no consistent trends among seasons or years in the age structure of mature females. This study revealed the plasticity and flexibility in growth and maturity parameters in this species, with a preference for faster growth during cooler periods.     

Growth histories of strombid snails from Bermuda recorded in their O-18 and C-13 profiles

The isotopic ratios ¹⁸O/¹⁶O and ¹³C/¹²C show an annal periodicity in the strombid snails Strombus gigas and S. costatus from Bermuda. S. gigas appears to have a constant displacement of 0.5 from oxygen isotopic equilibrium, whereas S. costatus fractionates the oxygen istopes in accordance with established fractionation relationships. With this tool, the growth in strombid snails during different stage can readily be determined on one and the same snail. A 24.8 cm long S. gigas showed an age of 7, a 19.3 cm long S. costatus of 5, and a 7.8 cm long S. costatus of 2 years. From the annual range in oxygen isotopes, growth restricted to warmer periods of the year is assumed. The abundances of ¹⁸O and ¹³C tend to be positively correlated in adult S. gigas and S. costatus speciments, but were inversely related in a juvenile S. costatus.     

Age and growth of the fan mussel Pinna nobilis from south-east Spanish Mediterranean seagrass (Posidonia oceanica) meadows

The calcitic and aragonitic shell of the fan mussel Pinna nobilis L. contains a record of the environmental changes experienced during its growth. Stable-isotope analyses of oxygen (¹⁸O:¹⁶O) in shell carbonate from the calcitic outer shell-layer have been used to validate the periodicity of clearly defined concentric rings on the aragonitic posterior adductor-muscle scar and to estimate the age and growth of fan mussels growing in Posidonia oceanica (L.) meadows at four locations on the south-east Spanish Mediterranean coast. The stable oxygen-isotope records obtained at intervals along a profile across the shell surface enabled seasonal changes in water temperature to be established, and hence seasonal patterns of shell growth to be inferred. Muscle-scar rings were found to be deposited annually in the shell in the spring and early summer (a period of increasing water temperatures), and represent an interruption in the migration of the posterior adductor muscle along the inner surface of the shell. In small pinnids (<25 cm) accretion of the shell is rapid during the first year, but in the second year it is distinctly slower than at the same time the previous year. This slowing down in growth during the second year coincides with the appearance of the “first” distinct muscle-scar ring, indicating that Pinna nobilis does not form a muscle-scar ring during its first year of shell growth. Maximum growth rates were recorded amongst pinnids from Carboneras, where they achieved a length of 59 cm in 8 yr, whilst those from Aguamarga were estimated to be the oldest (attaining a length of 45 cm in 13 yr). Received: 26 January 1998 / Accepted: 8 October 1998     

Seasonal growth of the benthic amphipodsPontoporeia affinis andP. femorata in a Baltic archipelago in relation to environmental factors

An intensive field study of three depth zones in 1980 revealed different seasonal patterns of growth in the deposit-feedingPontoporeia affinis Lindström andP. femorata Kröyer (Crustacea, Amphipoda) in the northern Baltic Sea, SW coast of Finland. The study areas were situated in the outer archipelago at depths of 21 to 25 m and 26 to 30 m and in the sea zone at 46 m. InP. affinis growth rates decreased with increasing depth, but the same seasonal pattern was evident at all depths: growth began in spring, increased to a maximum in early or midsummer, and decreased again or ceased altogether by autumn. In the archipelago the 1 + age group attained its maximum growth rate in May–June and the 0 + age group clearly later, in June–July. InP. femorata the growth rates of all age groups were more even, having only slight peaks in summer and autumn. The seasonal variation in growth ofPontoporeia spp. was not directly dependent on sedimentation of the spring phytoplankton bloom, but was more closely connected with seasonality of temperature and total benthic metabolism. Because estimates of annual food consumption byPontoporeia spp. exceeded bacterial and meiofaunal production, these species must have derived the majority of their energy demands from dead organic detritus. BothPontoporeia species are probably strictly food-limited in the area. The cessation of growth seemed to coincide with the approach of a plateau of total biomass, suggesting food competition. Different timing of growth between the age groups ofP. affinis suggests differences in sources or utilization of food; differences betweenP. affinis adP. femorata may indicate interspecific competition or different food.     

Contribution of warm habitat to cold-water fisheries

A central tenet of landscape ecology is that mobile species depend on complementary habitats, which are insufficient in isolation, but combine to support animals through the full annual cycle. However, incorporating the dynamic needs of mobile species into conservation strategies remains a challenge, particularly in the context of climate adaptation planning. For cold-water fishes, it is widely assumed that maximum temperatures are limiting and that summer data alone can predict refugia and population persistence. We tested these assumptions in populations of redband rainbow trout (Oncorhynchus mykiss newberrii) in an arid basin, where the dominance of hot, hyperproductive water in summer emulates threats of climate change predicted for cold-water fish in other basins. We used telemetry to reveal seasonal patterns of movement and habitat use. Then, we compared contributions of hot and cool water to growth with empirical indicators of diet and condition (gut contents, weight–length ratios, electric phase angle, and stable isotope signatures) and a bioenergetics model. During summer, trout occurred only in cool tributaries or springs (<20 °C) and avoided Upper Klamath Lake (>25 °C). During spring and fall, ≥65% of trout migrated to the lake (5–50 km) to forage. Spring and fall growth (mean [SD] 0.58% per day [0.80%] and 0.34 per day [0.55%], respectively) compensated for a net loss of energy in cool summer refuges (–0.56% per day [0.55%]). In winter, ≥90% of trout returned to tributaries (25–150 km) to spawn. Thus, although perennially cool tributaries supported thermal refuge and spawning, foraging opportunities in the seasonally hot lake ultimately fueled these behaviors. Current approaches to climate adaptation would prioritize the tributaries for conservation but would devalue critical foraging habitat because the lake is unsuitable and unoccupied during summer. Our results empirically demonstrate that warm water can fuel cold-water fisheries and challenge the common practice of identifying refugia based only on summer conditions.     

Stable isotopes in southern right whale (Eubalaena australis) baleen as indicators of seasonal movements,feeding and growth

Ratios of stable carbon and nitrogen isotopes were examined in the baleen of 11 southern right whales originating from South Africa, including one neonate, six juveniles and four adults. Oscillations in carbon isotope ratios were marked, and indicated feeding north of or at the Subtropical Convergence (STC) alternating with feeding south of the STC. There was an inverse relationship in juveniles between the periodicity of the oscillations and the length of the baleen plate, indicating a reduction in baleen growth with age. The size of the periodicity predicted for the smallest juvenile plate was equivalent to the length of the baleen at 1 yr of age as estimated from the rate of baleen growth in calves, suggesting that the oscillations in carbon isotope ratios were annual events. On this assumption, the timing of the formation of the most recent carbon enrichment peak could be calculated for each individual, given the date of death and the rate of baleen growth in the preceding year; formation occurred over a period of 100 d from January to April (mean in February). A similar analysis indicated that valleys in the nitrogen isotope ratios were formed between January and June (mean in April), and enrichment peaks between August and May (mean in December). These patterns were not inconsistent with previous scenarios of southern right whale migration, if the enrichment peaks in carbon isotopes were taken to represent feeding just north of the STC, the subsequent decline in enrichment levels to represent feeding south of the STC in autumn, and the persistence of an isotopic signature characteristic of high latitude plankton throughout the winter and early spring to indicate that feeding essentially ceased when the northern migration began, and did not resume until the southern migration was under way. The oscillations in nitrogen isotope ratios would support this interpretation, if they were assumed to represent cycles of starvation and recovery. A comparison with baleen growth rates for bowhead whales allowed the ages of the six juveniles to be assessed. Their size at age, when compared to the lengths and growth rates of calves measured photogrammetrically, suggested that growth in body length of southern right whales slows markedly between weaning and 1 yr, and may be almost negligible from 1 to 4 yr of age.     

Continuous plankton records: overwintering and annual fluctuations in the abundance of zooplankton

A study of seasonal variations in the pattern of year-to-year changes, for 1948 to 1982, in the abundance of four zooplankton taxa (Pseudocalanus elongatus Acartia clausi, Calanus finmarchicus and Hyperiidea) for the North Sea suggests that an element of the variations, represented at least in part by a quasi-linear downward trend, has its origins in winter and its occurrence through the year is a function of inherent persistence. A downward linear trend is the dominant pattern in the annual fluctuations in abundance of many species of zooplankton throughout the north-east Atlantic and the North Sea. It is argued that it is reasonable to extrapolate from the limited data set included in the detailed study and to assume a winter origin for the pattern wherever it occurs. Some implications for ideas about the dynamics of the plankton ecosystem are considered.