Life history of the sandy-beach amphipod Neohaustorius schmitzi (Crustacea: Haustoriidae)

Neohaustorius schmitzi Bousfield, the dominant macroscopic invertebrate on sandy beaches in North Carolina, USA, is strictly intertidal, and distributed from mean low tide to high tide, with an average density of 790/m². Location of greatest densities within the intertidal zone is dependent upon season and sex. An aggregated distribution is shown. N. schmitzi has 2 generations/year: a winter generation which lives about 8 months, and a summer generation which lives about 4 months. The reproductive season extends from February through October, with spring and summer peaks. Each female appears to produce only 1 brood of young. The number of young ranges from 2 to 14, depending upon the length and generation of the female.     

Population dynamics of the tanaid Hargeria rapax (Crustacea: Peracarida) in a tidal marsh

The tanaidacean Hargeria rapax (Harger, 1879) was sampled along intertidal transects semi-monthly at one site and quarterly at two other sites in salt marshes on Sapelo Island, Georgia, USA, from July 1985 to July 1986. Tanaids were most abundant near the mean highwater line and became progressively less abundant at lower intertidal elevations. Population density was greatest in the winter (December to February) when there were >29 000 individuals/m² at one high intertidal station. Although reproductive individuals were present most of the year, peaks in reproductive activity occurred in autumn (late August to early November) and spring (early March to mid June). An increase in population density coincided with increased reproductive activity only in autumn. Tanaid cohorts produced in the spring and summer rarely survived beyond 6 to 8 wk, but those produced in the autumn overwintered and lived 22 to 26 wk. The sex ratio among mature individuals was 2.8:1 (females: males). Mature females ranged in size from 2.2 to 3.9 mm total length (TL) and mature males were 2.3 to 4.1 mm TL; there was no significant sexual difference (Student's t-test, P>0.05) in the mean TL of mature individuals. The mean (±SD) size of brooding females was 2.9±0.32 mm TL and the mean (±SD) nunber of offspring/brood was 8.3±4.99 young/female. The timing of tanaid reproduction together with the effects of predation by juvenile fish and crustaceans may account for most of the spatial and temporal patterns of tanaid abundance observed in this study. There was a significant linear relationship (P<0.001, r ²=0.54) between the growth rate (GR, mm/d) of individuals and average daily air temperature (°C) described by the equation: GR=0.00178 (°C)-0.00971. The potential annual contribution of tanaid production to higher trophic levels, estimated from knowledge of standing stocks, growth rates and fecundity, was 5.71, 0.91 and 0.46 g dry wt/m² for high, mid and low intertidal areas, respectively. The high intertidal marsh, which supports the largest and most persistent standing stock of H. rapax, provides a rich foraging area for aquatic predators at high tide and an important source of recruits from which tanaid populations at lower intertidal elevations are recolonized after periods of intense predation pressure.     

Persistent blooms of surf diatoms along the Pacific coast,USA

Productivity was studied in two diatom species, Chaetoceros armatum T. West and Asterionella socialis Lewin and Norris, which form persistent dense blooms in the surf zone along the Pacific coast of Washington and Oregon, USA. Past observations have shown that surf-diatom standing stock usually declines in summer along with concentrations of nitrate and ammonium. Using the ¹⁴C method, photosynthetic rates in natural surf samples were measured monthly for one year (October 1981 through September 1982) at a study site on the Washington coast. Also measured were temperature, salinity, dissolved nutrients, particulate carbon and nitrogen (used as estimates of phytoplankton C and N), and chlorophyll a. Assimilation numbers (P _max) were higher in summer (5 to 8 g C g^-1 chl a h^-1) than in winter (3 to 4gC). Specific carbon incorporation rates (µ_max) showed no obvious seasonality, mostly falling within the range of 0.09 to 0.13 g C g^-1 C(POC) h^-1. The discrepancy between the seasonal trends for chlorophyll-specific and carbon-specific rates reflects a change in the carbon-to-chlorophyll ratio. Because of seasonal differences in daylength and light intensity, daily specific growth rates () are thought to be higher in summer than in winter. Neither ammonium enrichment assays nor particulate carbon-to-nitrogen ratios provided convincing evidence for nitrogen limitation during summer, and the observed changes in diatom abundance cannot be explained on this basis. Both the high diatom concentrations and their seasonal variations probably are due mainly to factors other than growth rates; two factors considered important are diatom flotation and seasonal changes in wind-driven water transport. C. armatum usually dominates the phytoplankton biomass in the surf zone, and evidence suggests that this species is strongly dominant in terms of primary production.Contribution No. 1391 of the School of Oceanography, University of Washington, Seattle, Washington, USA     

Growth and longevity in the crustose red algaPetrocelis middendorffii

Petrocelis middendorffii is a non-calcareous encrusting red alga growing on rocks in the middle and upper intertidal zone. We have photographically followed the fate of 43 individual plants for periods up to 88 months at Waadah Island, near Neah Bay, Washington (USA). Growth is slow, with surface area increasing about 4% year^-1 for those individuals growing. Other plants were observed to decrease in total surface coverage, fragment, and eventually disappear. Plants on neighboring but not contiguous sample sites are not in synchrony, with some subpopulations increasing their total space coverage while others diminished theirs. Age estimates, based on a variety of growth interpretations, suggest that an average sized individual (123 cm²) will be from 25 to 87 years old. Recruitment and mortality rates appear low. The ecological traits ofP. middendorffii may be similar to those of other crustose heteromorphic benthic algae.     

Variation and persistence of the middle rocky intertidal community of central Chile,with and without human harvesting

Humans are an important intertidal predator in central Chile. Following a five-year study we report on the effects of the exclusion of humans from the rocky intertidal at Las Cruces, central Chile. The middle intertidal of harvested and non-harvested areas diverged in species diversity and composition during the experiment. In harvested areas the middle intertidal rocky shore was dominated throughout the study by a monoculture of mussels, Perumytilus purpuratus. When humans were excluded, the middle intertidal community switched to one dominated by barnacles (predominantly Jehlius cirratus and Chthamalus scabrosus); this community has persisted for at least three years, despite the presence of forces e.g. mussel larvae, that have the potential to alter the community structure. Such changes were mediated by the muricid gastropod Concholepas concholepas, a key-stone predator. As a consequence of the above changes, the species diversity, H', (primary space occupiers) in the non-harvested area increased from H'=0 at the beginning of the study in 1983 (when the middle intertidal community was dominated by mussels), to values ca H'=2 toward the middle of the study in 1984 (which coincided with the maximum predatory impact of C. concholepas) and subsequently decreasing to ca H'=0.5 at the end of the study in 1987 (when the middle intertida community was dominated by barnacles).Please address all correspondence to J. C. Castilla, Department of Zoology, University of Washington, Seattle, Washington 98195, USA, until March 1990     

Variation in life-history patterns between intertidal and subtidal populations of the meiobenthic copepod Microarthridion littorale

Life history patterns of the meiobenthic harpacticoid copepod Microarthridion littorale (Poppe) differed between intertidal and subtidal sites in a South Carolina, USA estuarine salt-marsh system. Throughout the summer and fall, densities of M. littorale were significantly greater intertidally than subtidally; however, for the remainder of the year the population sizes were not statistically different. Maximum densities occurred intertidally in July and subtidally in October. The number of eggs · gravid female^-1 was significantly greater subtidally than intertidally at all times. The mean length of all adults increased from summer to spring and was similar between areas. Birth rates and death rates paralleled one another in each area and with the exception of August, birth rates were higher subtidally than intertidally. Juvenile mortality appeared highest subtidally, the mortality apparently occurring in the early naupliar stages. The variation in life history patterns across the tidal gradient was likely the result of differences in food quality and quantity, increased exposure to potential epibenthic predators subtidally, and to differential competitive pressure in the 2 areas.     

Phenology and demography of a marine specialist herbivore: Placida dendritica (Gastropoda: Opisthobranchia) on the central coast of Oregon

The occurrence of small specialist herbivores in marine rocky intertidal communities has been largely ignored. From 1984 to 1989, the phenology and demography of the common oligophagous ascoglossan opisthobranch Placida dendritica A.& H. was documented at several sites along the central coast of Oregon, USA. P. dendritica was found on the low intertidal green algae Codium setchellii Gardn., C. fragile (Sur.) Har. and Bryopsis corticulans Setch. during spring and summer. Ascoglossan abundance on Codium spp. varied spatially and temporally. Peak density usually occurred in May or June. Maximum ascoglossan live mass was 4 to 6 mg on Codium spp. and 100 mg on B. corticulans. Larval recruitment of P. dendritica to algal hosts was continuous during spring and summer. Rapid recruitment (200 to 400 sea slugs thallus^-1mo^-1) of newly metamorphosed ascoglossans to C. setchellii in wave-protected areas suggests that high densities of competent larvae occurred in nearshore waters and/or that larvae were efficient at locating algal hosts. Ascoglossan growth was rapid, with less than one month elapsing from larval settlement to adult sexual maturity. Therefore, populations of P. dendritica were composed of many overlapping generations. Movement of adult ascoglossans among thalli of C. setchellii was rapid. Continuous larval settlement and adult movement enabled P. dendritica not only to locate and colonize its algal hosts quickly but also to maintain a persistent association with algal hosts during spring and summer.     

Allocation of organic material and energy to the holdfast,stipe, and fronds inPostelsia palmaeformis (Phaeophyta: Laminariales) on the California coast

Postelsia palmaeformis were collected from the lower intertidal at Pigeon Point, California, USA, in May 1987, and the proximate composition and allocation of energy to the various body components were determined. The holdfast and stipe have a proximate composition (% dry weight) of ca. 40% ash, 5.3% protein, 1% lipid, 2% soluble carbohydrate, and 55% insoluble carbohydrate. The fronds have a proximate composition of ca. 25% ash, 6.5% protein, 2% lipid, 3% soluble carbohydrate, and 65% insoluble carbohydrate. The energetic level was ca. 12 kJ g^-1 dry wt and ca. 19 kJ g^-1 ash-free dry wt. The relative proportion of three plant components varied, comprising 26, 39, and 35% wet wt and 20, 42, and 38% kJ for the holdfast, stipe, and fronds, respectively. A plant with a basal stipe diameter of 33 mm contains 114 g wet wt and 266 kJ. The maximal density found in May 1987 was 826 plants, 49 301 g wet wt, and 106 157 kJ m^-2.P. palmaeformis differs in these characteristics from another intertidal pheophyte,Durvillaea antarctica, that is found in a high-energy intertidal zone.     

Seasonal abundance,distribution and growth of postlarval and juvenile grass shrimp (Palaemonetes pugio) in a Georgia,USA, salt marsh

Postlarval and juvenile grass shrimp (Palaemonetes pugio Holthuis) ≦15 mm total length (TL) were abundant at low tide in shallow aquatic microhabitats (i.e. puddles and films of residual tidal water) in the intertidal zone of a salt marsh on Sapelo Island, Georgia, USA from 1982 to 1984. The highest concentrations of young P. pugio occurred at 190 to 200 cm above mean low water, ∼10 to 20 cm below mean high water. The intertidal distributions of young grass shrimp expanded and contracted with changes in tidal amplitude. Postlarval grass shrimp (6 to 8 mm TL) continuously recruited into the intertidal marsh population from May until October, but densities varied in a regular pattern with peaks in abundance occurring at ∼2-week intervals, corresponding to spring tide periods in the lunartidal cycle. Although present nearly year-round in the intertidal marsh, juveniles (9 to 15 mm TL) were most abundant from August to October. Apparent growth rates of individuals up to 15 mm TL averaged 0.268±0.026 (mean±95% C.I.) mm d^-1 from May to October and 0.070±0.032 mm d^-1 in November and December. Unlike larger aquatic organisms, which can forage in the emergent marsh only when it is flooded by the tide, juvenile grass shrimp have constant access to intertidal resources. Although potentially important predators in this system, the role of young P. pugio in the trophic organization of salt marsh benthic invertebrate assemblages has yet to be examined. Contribution No. 576 of the University of Georgia Marine Institute     

Ingestion-independent rates of ammonium excretion by the copepod Calanus pacificus

The relationship between food ingested and NH ₊ ⁴ excretion rate was investigated for female Calanus pacificus collected in August, 1982, from the San Juan Archipelago, Washington State, USA. The copepods were preconditioned to 6 densities of the diatom Thalassiosira weissflogii (0 to 10⁴ cells ml^–1) for 30 h before the experiment. The experiment was conducted with nutrients added in excess to maintain equal rates of NH ₊ ⁴ uptake by the diatoms at all densities. Although ingestion rates of C. pacificus varied from 0 to over 20% of body N d^–1 at the different food levels, excretion was a constant 6.6 nM NH ₊ ⁴ copepod^–1 h^–1 or about 10% of body N d^–1. This ingestion-excretion relationship, which is consistent with previous respiration and fecundity studies, suggests that the ecological dominance of C. pacificus only under conditions of high food abundance may be due to a dramatic increase in its growth efficiency as ingestion increases above the level supporting a constant metabolic rate. The maintenance of a constant level of metabolism during relatively short periods of low food abundance may be advantageous if it allows the copepod to exploit more effectively short-term variability in its food resulting from environmental heterogeneity or vertical migration.Contribution No. 1360 from the School of Oceanography, University of Washington, Seattle, Washington 98195, USA     

Genetic evidence of self-fertilization in the sea anemone Epiactis prolifera

Biochemical genetic variation provided evidence for the mode of reproduction of brooded young in the sea anemone Epiactis prolifera Verrill, 1869. Individuals of E. prolifera are female when small but hermaphroditic when large (i.e., gynodioecious); juveniles are brooded externally on the column. Brooding individuals collected from 6 intertidal sites (5 in central California and 1 in Washington State, USA) in the spring and summer of 1980 were assayed for gene-enzyme variation by starch-gel electrophoresis. Three of 12 enzyme loci were polymorphic; phosphoglucose isomerase appeared to be encoded by two, closely linked loci. Genotypic frequencies deviated markedly from expected random mating proportions. Only three heterozygotes were found; two were heterozygous at all three polymorphic loci, and the other was polymorphic at the two PGI loci. All 158 juveniles from 25 brooding individuals were assayed (2–19 juveniles per parent). Juveniles on homozygous adults were always identical to their parent. However, brooded young of heterozygous individuals were not identical to their parent. but showed 1:2:1 phenotypic segregation ratios consistent with reproduction by self-fertilization. This genetic evidence together with findings of marked heterozygote deficiencies and genetic identity of homozygous adults and their brooded young supports the conclusion that E. prolifera usually reproduces by self-fertilization, and cross-fertilization is rate.     

Spatial variation in dimethylsulfoniopropionate (DMSP) production in <Emphasis Type="Italic">Ulva lactuca</Emphasis> (Chlorophyta) from the Northeast Pacific

Although dimethylsulfoniopropionate (DMSP) has a variety of functions in marine macroalgae including that of a cryoprotectant, an osmolyte, a way to remove excess sulfur and energy, an antioxidant, and an allelopathic precursor, the latter two functions are believed to be the most important in Ulva lactuca L. (=U. fenestrata) in intertidal populations on the coast of Washington state, USA. The present study found significant variation in DMSP concentrations among U. lactuca collected in May 2005 from six sites ranging from 47°54.45′N (Possession Point, Whidbey Island, WA, USA) to 48°30.55′N (Shannon Point Beach, Anacortes, WA, USA), and also among individuals within sites, and among tissues (basal tissues near the holdfast, middle of the blades, and tips). Concentrations ranged from 37 to 224 μmol g⁻¹ fresh mass (FM). In several 10-day experiments between July 2001 and August 2004 with U. lactuca collected from several places on the coast of Washington, the effects of nutrient level (DIN), light intensity and wavelength, and grazing by the herbivorous gastropod Lacuna vincta, were examined. None of these manipulations resulted in DMSP concentrations that differed significantly from controls, and variance in DMSP concentrations within each experiment was very low. Although DMSP concentrations in U. lactuca may be affected by factors not tested in these experiments, it is also possible that the observed spatial differences reflect constitutive genotypic or phenotypic differences among geographically separated U. lactuca populations or among cryptic Ulva species. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Estimates of outcrossing rates and of inbreeding depression in a population of the marine angiosperm Zostera marina

Despite the great diversity of pollination and fertilization mechanisms observed in marine plants, little is known about the causes or maintenance of this variation. In this study, I estimated outcrossing rates and levels of inbreeding depression in Zostera marina L. (eelgrass), providing the first empirical test of hypotheses about the evolution of breeding systems in plants with submerged flowers. This study also addressed temporal separation of female and male flowering (dichogamy) in eelgrass as a mechanism promoting an outcrossing mating system, and whether the mating system in eelgrass is related to the degree of dichogamy in the field. Outcrossing rates (0<t<1) estimated from two polymorphic allozyme loci indicate that the Z. marina population in intertidal and subtidal habitats in False Bay, Washington, USA, was highly outcrossing in both 1991 (intertidal t=0.905, subtidal t=1.0) and 1992 (intertidal t=0.775, subtidal t=0.611). The outcrossing rates were positively associated with the degree of dichogamy in 1992; intertidal plants exhibited a greater temporal separation of female and male flowering and a higher outcrossing rate than did subtidal plants. Inbreeding depression at seed set was estimated from hand pollinations (self- and outcross) on 20 reproductive individuals from the False Bay population. Averaged across all maternal parents, a greater proportion of outcrossed flowers set seed than selfed flowers; i.e., inbreeding depression was detected. Plants exhibited genetic variation for inbreeding depression, detected as a significant pollination treatment × maternal family interaction in a log-likelihood analysis. By the end of the seed-maturation period (7 mo after intial seed set) some families showed outbreeding depression, i.e., greater fitness in progeny derived from selfing than in progeny from outcrossing. The inbreeding depression in the False Bay population may be an important selective factor contributing to the maintenance of dichogamy and an outcrossing mating system, as proposed for aquatic plants.     

Depletion of heavy isotopes of oxygen and hydrogen in tissue water of intertidal plants: implications for water economy

Stable oxygen and hydrogen isotope ratios of leaf and thallus water of the intertidal seagrasses Phyllospadix scouleri and P. torreyi and the marine algae Egregia menziesii, Gelidium coulteri, and Corallina vancouverensis from three locations in California, USA, were determined in 1987. Compared with subtidal seawater, most plant-water samples were depleted in the heavy isotopes ¹⁸O and deuterium. Depletion of heavy isotopes was greatest in plants growing at the highest intertidal elevations. This was an unexpected result, because enrichment of heavy isotopes occurs during evapotranspiration in terrestrial plants. Two possible mechanisms for this isotopic depletion are proposed: direct uptake of heavy isotope-depleted water vapor and preferential diffusion of ¹⁶O and ¹H into littoral plants from water remaining in the intertidal zone at low tide.     

Distribution,movement and diet of the snailSearlesia dira in the intertidal community of San Juan Island,Puget Sound,Washington

Searlesia dira Reeve is a locally abundant, carnivorous gastropod that occurs from Alaska to central California. I studied populations of this snail at a variety of sites on San Juan Island in order to provide information on their distribution and abundance and to analyze their community role, i.e., their potential impact on their prey populations and their dietary overlap with co-occurring invertebrate predators. I established permanent transects, both random and in crevices, at three areas of differing exposure to wave action. On these transects I recorded the number and size ofS. dira, activity, distance to nearest neighbor, other organisms present, and tidal height on four phases of the mixed semi-diurnal tidal cycle. The results are (1) an increase in density with increase in substrate relief, (2) an occurrence of highest densities in moderately exposed and exposed sites rather than in protected ones, (3) an increase in mean size with increase in depth along the intertidal gradient, (4) an increase in both total activity and feeding success on the high water immediately following an extreme minus low tide occurring during the daytime in the summer, (5) a relative restriction of feeding success to that high tide, and (6) a similarity of the diet to the relative abundance of the main observed prey for most areas. The main exceptions are chitons and one lower intertidal limpet, all of which are taken in excess of their apparent abundance and especially in the middle intertidal. The upward extension of some lower intertidal prey populations, such as chitons, may be limited by the increased susceptibility of individuals at the upper margin of the population to predators such asS. dira; susceptibility appears to be increased after periods with a higher probability of increased physiological stress, such as extreme low tides on summer days.     

Feeding habits of the dungeness crab Cancer magister as determined by the index of relative importance

Specimens of the Dungeness crab Cancer magister, were collected subtidally and intertidally from an estuary in Washington State, USA in June and September 1980, and January, April, May and July, 1981. Gut contens of freshly collected crabs were analyzed by the Index of Relative Importance; for each prey taxon, this method measured frequency of occurrence, percentage of total biomass, and percentage of total numbers consumed. The most important higher taxon eaten was fish; however, the most important prey genus was the shrimp Crangon spp. There was greater predation on Crangon spp. at night at the intertidal site, and during winter and spring when the shrimp were most abundant there. Feeding activity, as indicated by a weight-specific gut-fullness index, showed no consistent diel pattern. There were significant ontogenetic changes in feeding patterns: first-year crabs preyed primarily on very small bivalves or small crustaceans including their conspecifics; second-year crabs preferred Crangon spp. and fish, and third-year crabs preyed less on Crangon spp. and more on fish. Such changes in feeding habits with ege could be purely due to mechanics of food handling, but might also reduce competition among age groups of crabs, possibly partitioning resources within the estuary. Findings are discussed in terms of optimal foraging and compared to other similar studies.Contribution No. 599, School of Fisheries, University of Washington, Seattle, Washington 98195, USA     

Heterotrophic bacteria in Long Island Sound

Correlated with a study of heterotrophic bacteria from cultures of larval bivalve molluses, bacteria were studied from the water column over an oyster bed in Lont Island Sound, USA. Samples taken biweekly for 1 year showed bacterial densities ranging from 1.2x10³/ml in summer to 3.8x10⁴/ml in winter. Variation in seasonal density mirrored that of phytoplankton. Gram-negativ rods constituted 99% of the isolate. Eight genera were identified, but 92.3% of these were Achromobacter, Flavobacterium, and Pseudomonas. Pseudomonads dominated the summer flora, whereas flavobacteria were most abundant in spring. Types varied seasonally, but proteolytic, lipolytic, and amylolytic activity appeared independent of season.     

Mangrove fish-communities in tropical Queensland,Australia: Spatial and temporal patterns in densities,biomass and community structure

Regular daylight sampling over 13 mo (February 1985–February 1986) in and adjacent to intertidal forested areas, in small creeks and over accreting mudbanks in the mainstream of a small mangrove-lined estuary in tropical northeastern Queensland, Australia, yielded 112 481 fish from 128 species and 43 families. Species of the families Engraulidae, Ambassidae, Leiognathidae, Clupeidae and Atherinidae were numerically dominant in the community. The same species, with the addition ofLates calcarifer (Latidae).Acanthopagrus berda (Sparidae) andLutjanus agentimaculatus (Lutjanidae) dominated total community biomass. During high-tide periods, intertidal forested areas were important habitats for juvenile and adult fish, with grand mean (±1 SE) density and biomass of 3.5±2.4 fish m^–3 and 10.9±4.5 g m^–3, respectively. There was evidence of lower densities and less fish species using intertidal forests in the dry season (August, October), but high variances in catches masked any significant seasonality in mean fish biomass in this habitat. On ebb tides, most fish species (major families; Ambassidae, Leiognathidae, Atherinidae, Melanotaeniidae) moved to small shallow creeks, where mean (±1 SE) low-tide density and biomass were 31.3±12.4 fish m^–2 and 29.0±12.1 g m^–2, respectively. Large variances in catch data masked any seasonality in densities and biomasses, but the mean number of species captured per netting in small creeks was lowest in the dry season (July, August). Species of Engraulidae and Clupeidae, which dominated high-tide catches in the forested areas during the wet season, appeared to move into the mainstream of the estuary on ebbing tides and were captured over accreting banks at low tide. Accreting banks supported a mean (±1 SE) density and biomass of 0.4±0.1 fish m^–2 and 1.7±0.3 g m^–2, respectively, at low tide. There were marked seasonal shifts in fish community composition in the estuary, and catches in succeeding wet seasons were highly dissimilar. Comparison of fish species composition in this and three other mangrove estuaries in the region revealed significant geographic and temporal (seasonal) variation in fish-community structure. Modifications and removal of wetlands proposed for north Queensland may have a devastating effect on the valuable inshore fisheries of this region, because mangrove forests and creeks support high densities of fish, many of which are linked directly, or indirectly (via food chains) to existing commercial fisheries.Contribution No. 493 from the Australian Institute of Marine Science     

No zone is always greener: variation in the performance of<Emphasis Type="Italic"> Fucus gardneri</Emphasis> embryos,juveniles and adults across tidal zone and season

The responses of the different stages of an organisms life-cycle to different environments can have important implications for their persistence in those habitats. The marine intertidal zone is considered among the most stressful of all marine environments, because daily exposure at low tide results in daily fluctuations in a range of important environmental factors. In this study we examined the link between daytime exposure and the performance of embryos, juveniles and adults of the seaweed Fucus gardneri across zones and seasons on San Juan Island, Washington, USA. Specifically we asked: (1) whether three measures of performance for F. gardneri: growth rates, surface area of reproductive tissue and survivorship differed between high- and mid-intertidal zones, and among months throughout the year and, then, (2) whether total daytime exposure within each zone each month was a good predictor of variation in these measures of performance. At our study site, seasonal differences in the timing of low tides result in long periods each day during summer of very harsh conditions (exposure to the air, high temperatures and low humidity) compared to winter when exposure to the air during the day is virtually absent. Contrary to the expectation of lower performance in the high zone, we found no consistent differences between zones over the entire year in any measure of performance for any stage. For nearly all traits, there were significant differences among months and, importantly, significant interactions between zone and month. Thus, for each stage there were some months when thalli in the high zone performed better and some months when thalli in the mid-zone performed better. Regressions between total daytime exposure and performance each month indicated some stage-specific effects. Larger thalli appeared more strongly affected by the amount of exposure per month; there were significant negative relationships between total daytime exposure and (1) growth rates of medium and large adults in the high zone and (2) the surface area of reproductive tissue of medium adults in the high zone and small adults in the mid-zone. The lowest survivorship for all stages occurred in the 2–3 months that followed summer, suggesting a cumulative effect of long daytime exposure in summer on survivorship. Post-settlement survivorship of embryos was very low throughout the year, with only 2 out of 5395 seeded zygotes surviving to a visible size. One-month post-settlement survivorship ranged from 0% to 16.7%, and there were no differences in the survivorship curves between high- and mid-intertidal zones for each cohort. Although it is often assumed that the performance of intertidal species is lower in high-intertidal zones because of exposure to environmental extremes for longer, our results do not support this paradigm. Instead, they indicate a complex and fluctuating pattern of variation in the performance of different stages of the F. gardneri life-cycle throughout the year in different intertidal zones.Communicated by M.S. Johnson, Crawley     

The effects of sand movement on intertidal seaweeds and selected invertebrates at Bound Rock,New Hampshire,USA

A seasonal study of sand movement and the benthic intertidal organisms at Bound Rock, New Hampshire, USA was conducted between November, 1973 and February, 1975. The site is subjected to irregular sand fluctuations, as well as diurnal, neapspring and major summer sand intrusions. The abundance and distribution of intertidal species was interrelated with the historical sand fluctuations at the area. For example, the lower limits of Mytilus edulis, Balanus balanoides and Porphyra umbilicalis approximated the highest summer sand elevations. Highly abraded rock surfaces in the lower intertidal zone were dominated by opportunistic annuals (e.g. Enteromorpha spp.) and perennial psammophytic or sand-loving seaweeds (e.g. Ahnfeltia plicata and Sphacelaria radicans). Overall, the intertidal seaweed populations at Bound Rock showed a lower number of perennials and fewer species than adjacent rocky shores. The low species diversity of seaweeds at the study site is attributable to unstable environmental conditions and a limited number of habitats. Even so, several psammophytic microhabitats are evident at Bound Rock depending upon the extent of sand burial and abrasion. The morphological and reproductive adaptations of several psammophytic species are discussed.Published with the approval of the Director of the New Hampshire Agricultural Experiment Station as Scientific Contribution No. 812.Scientific Contribution No. 53 of the Jackson Estuarine Laboratory.