Photosynthetic responses and daily carbon balance ofColpomenia peregrina: Seasonal variations and differences between intertidal and subtidal populations

The seasonal photosynthetic responses and daily carbon gain of upper intertidal, low intertidal and subtidal (3 to 4 m depth) populations ofColpomenia peregrina were examined over a 2 yr period (1986–1988) in Santa Catalina Island, California, USA. The populations showed significant differences in their photosynthetic responses, daily carbon balance and carbon-specific growth rates when normalized to tissue area or to chlorophyll content. The substantial plasticity with respect to photosynthetic responses shown byC. peregrina is considered to be an important factor in facilitating the colonization of both intertidal and subtidal habitats. This species appears to have a cellular carbon metabolism influenced by responses to season and tidal elevation. Highest net daily carbon balance, predicted carbonspecific growth rates and net growth efficiency were achieved in upper intertidal habitats during summer. These parameters decreased in winter and progressively declined with increasing depth as plants become increasingly exposed to low-light regimes. The diminishing net daily carbon balance and predicted carbon-specific field growth rates found during winter suggest that standing stock and lower subtidal limits of distribution ofC. peregrina are at least partly controlled by these two factors.     

Feeding preferences of periwinkles among four species ofFucus

A widely accepted view of intertidal community organizatiton in the NW Atlantic proposes that fucoid vegetation is maintained by the actions of predators which remove species competitively superior toFucus species. Herbivory is an important component of these predatory interactions, but has been studied largely with reference to the interaction betweenF. vesiculosus andLittorina littorea. There are many species of fucoids and herbivorous invertebrates on the shores of the NW Atlantic and this paper reports field and laboratory experiments performed in 1987 (in or near Halifax, Canada) on the effects of grazing by three species ofLittorina on adults and juveniles of four species ofFucus. In laboratory experiments, portions ofFucus species were presented singly (no choice) or together (multiple choice) to single species ofLittorina. AdultF. distichus was grazed to only a small extent.F. evanescens andF. vesiculosus adult tissues were heavily grazed in most laboratory experiments.F. spiralis adults were heavily grazed in no choice experiments, but were grazed only slightly in multiple choice tests. When adult fucoid tissues were exposed to a mixed suite of grazers in the field, onlyF. vesiculosus was grazed heavily. Tests done on adult tissues showed clearly thatFucus species are highly variable in their vunerability to grazers. Moreover, we found variability among periwinkle species in grazing rates on adultFucus. We also found a great disparity in the feeding rates of different periwinkle species on juveniles ofFucus. Therefore, it is not possible to extrapolate from a single periwinkle species/single fucoid species interaction when attempting to identify vegetation structuring processes.     

Community succession following massive ice-scour on a rocky intertidal shore: recruitment,competition and predation during early,primary succession

The importance of species interactions and recruitment variability was examined during the first year and a half of primary succession (1988–1989) on an exposed rocky seashore near Halifax, Nova Scotia. Previous work suggested that emergent rock on these shores is normally dominated by fucoid rockweeds because predatory whelks control the sessile animal competitors, mussels and barnacles, and because herbivorous littorinids control ephemeral algal competitors. Abundances of all species except seasonal ephemeral algae were very small throughout this experiment and we found no significant effects of carnivory, herbivory, plant-animal competition or plant-plant competition. A slight facilitation of Fucus recruitment is attributed to a thin mat of ephemeral, blue-green algae. Very few other studies have directly manipulated intertidal ephemeral algae. As primary succession may be very rare in this assemblage, these results may be specific to these circumstances, but they highlight the varying importance of species interactions with variable recruitment. In particular, it appears that variations in recruitment success may be important to community structure, even when recruitment is not limited by propagule supply. The scale of the study also provides insight into successional processes occurring after the recent, extensive ice-scour of exposed seashores in this region.     

Stability of sea urchin dominated barren grounds following destructive grazing of kelp in St. Margaret's Bay,Eastern Canada

Kelp regeneration was observed for the first time in St. Margaret's Bay, Nova Scotia, Canada in an area known to have been devoid of macroalgae for several years. The regeneration was destroyed by sea urchins within 10 months. Experimentally induced kelp regeneration met a similar fate under normal grazing pressure. At the lowest sea urchin biomass and density encountered re-establishment of mature kelp stands seems highly unlikely. The sea urchin population required to suppress kelp regeneration is fed by benthic microalgae. Diatoms and other pioneer algal community species were found in the guts of sea urchins. The mean standing crop of benthic microalgae was found to be, 2.2 g C m^-2 and production estimated as ca 15 g C m^-2yr^-1 at 8m depth. Most of the primary production of St. Margaret's Bay has been lost with the disappearing kelp populations.     

Field observations on the emergence rhythm of the Norway lobsterNephrops norvegicus,using different methods

The emergence ofNephrops norvegicus (L.) from their burrows was studied on several fishing grounds around Scotland at 28 to 62 m depth. Various methods were used: sampling by trawl and baited creels, observations by television and time-lapse cameras. Peak emergence generally occurred around dusk and dawn. In shallow water (30 m) there was also a significant level of activity during the intervening night period. Day/night variations in the size composition of catches suggest that relatively more time is spent out of the burrow with increasing size. There was good agreement between the various methods employed, suggesting that trawl and camera avoidance has little influence on the pattern of emergence observed. The use of bait in some experiments confirmed that emergence is essentially a feeding activity.     

The genetic basis of morphological differentiation in some Laminaria populations

Clinal differentiation of stipe traits in Laminaria (simplices) populations occurs on a gradient of exposure to wave action. Crossability tests and the production of fertile hybrids established interfertility between populations from the extremes of the morphological range. Reciprocal transplantation experiments between exposed and sheltered sites did not produce significant changes in stipe morphology. Quantitative genetic analysis of the degree of resemblance between relatives indicated a relatively high genetic component in the interpopulation differentiation. This is consistent with the results of the transplantation experiments. Within-population heritability estimates at the exposed site were low, perhaps because of intensive local stabilising selection which acts to reduce genetic variability. The question of conspecificity of L. saccharina and L. longicruris in view of these results is discussed.     

Swimming performance and endurance of the Norway lobster Nephrops norvegicus

The swimming behaviour of the Norway lobster, Nephrops norvegicus (L.), was studied in the laboratory. The lobsters were stimulated to swim repeatedly until they failed to respond to a single tactile stimulus. The position of the initiating stimulus on the body determined the height of the escape path above the bottom of the tank. A stimulus to the rostrum resulted in a low swimming trajectory, rarely exceeding a height of 0.1 m. A similar tactile stimulus to the abdomen produced higher mean swimming trajectories up to 0.5 m. Several parameters of swimming performance and endurance were measured for each swimming sequence, including distance, duration, mean and maximum velocities and the frequency and number of tail beats. Results showed no significant differences in the average swimming performance and endurance of males and females, but there was a sex difference in the relationship between swimming performance and N. norvegicus size.     

Differential responses of honeybee (<Emphasis Type="BoldItalic">Apis mellifera</Emphasis>) patrilines to changes in stimuli for the generalist tasks of nursing and foraging

Which task a social insect worker engages in is influenced by the worker’s age, genotype and the colony’s needs. In the honeybee, Apis mellifera, genotype influences both the age a worker switches tasks and its propensity of engaging in specialist tasks, such as water collecting, which only some workers will perform. In this study, we used colonies with natural levels of genetic diversity and manipulated colony age demography to drastically increase the stimuli for the generalist tasks of foraging and nursing, which all workers are thought to engage in at some point in their lives. We examined the representation of worker patrilines engaged in nursing and foraging before and after the perturbation. The representation of patrilines among foragers and nurses differed from that of their overall colony’s population. In the case of foraging, over- and underrepresentation of some patrilines was not simply due to differences in rates of development among patrilines. We show that replacement foragers tend to be drawn from patrilines that were overrepresented among foragers before the perturbation, suggesting that there is a genetic component to the tendency to engage in foraging. In contrast, the representation of patrilines in replacement nurses differed from that in the unperturbed nursing population. Our results show that there is a genetic influence on even the generalist tasks of foraging and nursing, and that the way patrilines in genetically diverse colonies respond to increases in task stimuli depends upon the task. The possible significance of this genetic influence on task allocation is discussed. Electronic supplementary material Supplementary material is available in the online version of this article at doi: and is accessible to authorized users.     

A Water Allocation Decision‐Support Model and Tool for Predictions in Ungauged Basins in Northeast British Columbia,Canada

Pressures on water resources due to changing climate, increasing demands, and enhanced recognition of environmental flow needs result in the need for hydrology information to support informed water allocation decisions. However, the absence of hydrometric measurements and limited access to hydrology information in many areas impairs water allocation decision‐making. This paper describes a water balance‐based modeling approach and an innovative web‐based decision‐support hydrology tool developed to address this need. Using high‐resolution climate, vegetation, and watershed data, a simple gridded water balance model, adjusted to account for locational variability, was developed and calibrated against gauged watersheds, to model mean annual runoff. Mean monthly runoff was modeled empirically, using multivariate regression. The modeled annual runoff results are within 20% of the observed mean annual discharge for 78% of the calibration watersheds, with a mean absolute error of 16%. Modeled monthly runoff corresponds well to observed monthly runoff, with a median Nash–Sutcliffe statistic of 0.92 and a median Spearman rank correlation statistic of 0.98. Monthly and annual flow estimates produced from the model are incorporated into a map‐ and watershed‐based decision‐support system referred to as the Northeast Water Tool, to provide critical information to decision makers and others on natural water supply, existing allocations, and the needs of the environment.