Correlations between weather and recruitment of Nassarius pauperatus,an intertidal gastropod with a planktotrophic larval stage

Recruitment of the intertidal gastropod Nassarius pauperatus (Lamarck) was estimated annually for more than a decade at three sites in South Australia. Recruitment varied temporally, but was relatively synchronous amongst sites, even though these were at least 10 km apart. The density of recruits at each site was negatively correlated with evaporation and also with several indices of temperature for February. We postulate that either high temperatures or desiccation cause the death of recently settled individuals, which may be unable to avoid these extremes by burrowing deeply into the substratum.     

A quantitative study of intertidepool movement of the wooly sculpin Clinocottus analis

Movements of the wooly sculpin Clinocottus analis between all pools in a designated area of a southern California (USA) intertidal zone were studied. Fish were captured during low tides, finclipped or bead-tagged, and released in the pool of capture. Percent recaptured in pool of first capture declined from 30 after 2 weeks to about 5 after 20 weeks. Percent recaptured in any pool in the study area declined from 50 after 2 weeks to 20 after 8 weeks, but remained at 20 through 16 weeks. A higher fidelity to an area of the intertidal zone than to a specific pool was suggested. Large fish exhibited higher probability of recapture than smaller individuals, indicating they become more sedentary with age. Changes in pool topography influenced percent recurrence in a pool, most likely as a consequence of changes in quality and quantity of cover available. Such responses to changes in specific pools and fidelity to intertidal areas containing several pools appear to be advantageous behavioral patterns in an environment where topographic change is frequent and often massive.     

Genetic differentiation independent of intertidal gradients in the pulmonate limpet Siphonaria kurracheensis

The intertidal limpet Siphonaria kurracheensis (Reeve, 1856) has a bimodal vertical distribution of abundance on rocky shores at Rottnest Island, Western Australia. An electrophoretic study of 5 polymorphic enzymes revealed no consistent genetic differences between adults high and low on the shore. Contrasting with this absence of a detectable genetic response to the steep environmental gradients in the intertidal zone, there were genetic differences among low-shore adults from different sites, and between adults and recruits. This genetic differentiation could be due to either localized selection or temporal variation in the genetic makeup of recruits.Communicated by G. F. Humphrey, Sydney     

Demography of the intertidal brown alga Pelvetia fastigiata in Southern California,USA

The demography of Pelvetia fastigiata was studied from 1973 through 1977 in the intertidal zone near La Jolla, California, USA. Populations were usually small and relatively stable as new recruits replaced older individuals that were lost; however, in 1977 high recruitment substantially increased total abundances. The survivorship of recruits was similar regardless of the season or year of recruitment. Mortality rates decreased with age, and the mean life expectancy continued to increase for at least 1 yr. Losses of juveniles were high; 50% lived 80 d and only 9% survived to the age of first reproduction (about 1.5 yr). Plants present at the start of the study had higher survivorship rates than new recruits, 19 and 7%, respectively, living more than 3 yr. Individuals within aggregations of large plants lived longer than most dispersed individuals, and aggregations remained intact throughout the study in spite of low recruitment. Established individuals had low mortality rates and populations probably relied on these persistent individuals for reproduction.     

Chaotic genetic patchiness in an intertidal limpet,Siphonaria sp.

Variation of 4 polymorphic enzymes was studied for 2 yr (1978 and 1979) in an undescribed species of Siphonaria, a pulmonate limpet, from a rocky shore at Rottnest Island, Western Australia. Depending on the locus, significant genetic differences were found among sites along 50 m of shore, between high and low portions of the shore within sites, between adults and recruits, and between recruits in the 2 yr. This genetic heterogeneity does not follow a simple, consistent pattern, but forms a shifting, ephemeral genetic patchiness best described as chaotic. This patchiness may result from temporal variation of numbers and genotypes of recruits, which leads to the proposal that planktonic dispersal, although causing uniformity on a large scale, can give rise to fine-scale genetic patchiness.     

Spatio-temporal population dynamics of the sand snail Umbonium costatum: importance of ontogenetic migration and annual recruitment variability

The spatio-temporal population dynamics of the subtidal snail Umbonium costatum (Kiener) in Hakodate Bay, northern Japan, are described over a 9-yr period (1982 to 1988, 1992). Annual variations in recruitment success not only caused the highly variable age structure of the population, but also affected its distribution pattern. In heavy recruitment years (1982, 1984 and 1988), location of the densest population differed from the other years, and the areas with 0 yr old individuals were larger. Every year, the distribution of 0 yr olds was mostly restricted to inshore (within 320 m from shore), while the distribution of adults (>0 yr) was mostly restricted to offshore (>320 m from shore). Such patterns may be generated by ontogenetic migration of cohorts to offshore areas. Ontogenetic migration also could have buffered the large annual variation in spat distribution and maintained the small variation in the distribution of adults. (Prince et al. 1988). Density-related migration has also been reported in Acmaea digitalis (Frank 1965), Patella cochlear (Branch 1974) and Patelloida alticostata (Black 1977).Dense populations of the gastropod Umbonium costatum are found in some clean subtidal sandy-bottoms in Japan, e.g. inner part of Hakodate Bay. In the bay, the age structure of U. costatum revealed predominant year-classes. The 0 yr olds were restricted to the shallowest zone (<4 m depth) and most adult (<0 yr) cohorts were restricted to 6 to 7 m depths (Noda 1991a).This paper describes the temporal variability of population structure and distributional patterns of Umbonium costatum, and examines the distribution-regulating processes.     

Influence of seasonal food abundance and quality on the feeding habits of an opportunistic feeder,the intertidal crab <Emphasis Type="Italic">Pachygrapsus marmoratus</Emphasis>

The abundance of trophic sources on the intertidal zone is discontinuous and their supply can vary both in a predictable or unpredictable way. The Mediterranean semi-terrestrial crab Pachygrapsus marmoratus, is known, as adult, to entirely rely on the intertidal trophic sources, and, consequently, it faces the fluctuations of nutritional sources and quality. To clarify the relationships between the feeding habits of an Italian population of P. marmoratus and the temporal variation of its food sources, we carried out a 2-year sampling protocol. Data on seasonal variation in composition of intertidal food item assemblages, on the average content in N and C of the commonest algae, on seasonal changes in crabs feeding habits were collected and compared using a suite of multivariate and univariate techniques. Results showed that P. marmoratus takes advantage of the recruitment phase of the most common invertebrates, affecting and controlling the abundance even of those species whose adults are out of its reach. It can act both as a herbivore, and as a carnivore that shifts between bivalves, more abundant in spring/summer, and the periwinkle Melaraphe neritoides, during winter. In conclusion, we provide evidences on the food choice of this common rocky shore species, which is very plastic and capable of relying on many trophic sources, possibly influencing the abundance and/or the population structure of a number of intertidal populations.     

Genetic differentiation in the intertidal zone in populations of the alga Enteromorpha linza (Ulvales: Chlorophyta)

Genetic differentiation within the intertidal zone was examined in six populations of the asexually reproducing alga Enteromorpha linza growing in the Long Island Sound, USA. Four of the five populations sampled in 1981 showed significant differentiation between high and low intertidal positions with respect to the GOT-2 locus. The pattern of differentiation was consistent for samples collected at several times during the year with some seasonal modifications. Four additional polymorphic loci, resolved in 1982, identified a total of 13 five-locus genotypes or clones. Four of the six populations sampled in 1982 showed significant differences in clone frequency between high and low intertidal positions. Laboratory experiments revealed differences in response to temperature among the clones. At 24°C a high intertidal associated clone showed an increase in growth, while low intertidal associated clones showed decreased growth compared to growth at 15°C. These results suggest that the microgeographic differentiation observed for E. linza in the intertidal zone may in part be due to the differential adaptation of clones to different intertidal environments. Additional demographic information is needed for individual clones in order to determine the role longevity, reproductive output, recruitment and interclonal competition play in maintaining the observed differentiation.     

Correlations between Human Collecting and Intertidal Mollusc Populations on Rocky Shores

We tested whether the population structures of intertidal molluscs varied with the activity of human collectors in northern Port Phillip Bay, Victora, Australia. We examined eight sites, two of which had been protected for around 70 years by the area being used as a rifle range with the other six being visited frequently by human. The shores were examined in two different years, and in 1991 we counted humans and recorded their activities. At heavily visited shores, almost half of the people seen were simply walking, while 25% were actively collecting, despite regulations prohibiting the collection of intertidal gastritis. The remaining people were fishing or skydiving. At the protected shores, we observed only one collector and a handful of walkers over more than 20 observation periods, including weekdays, normal weekends, and holiday weekends. In 1989 and 1991, we compared size distributions of seven intertidal species between sites in the two categories. Four mollify species are taken for food and bait; the remaining three served as “controls”. The size distributions and abundance of noncarbonated species (alicized napalm, Leaderless viola, and emization ebonies) did not differ between visited and protected sites in either year, although most species did vary between individual sites. In contrast, three of the four collected species, alicize trampoliners, Austrocochlea constricta, and Nerita atramentosa, were significantly larger at the protected sites, and N. atramentosa was markedly less abundant at heavily visited sites. The fourth collected species, Turbo undulatus, has a distribution extending into the subtidal zone, and it is possible that intertidal populations ate replenished from deeper water. The changes in mean size of molluscs are well within the range reported from South America and South Africa under subsistence fishing, and they demonstrate that at least close to major urban centers, human recreational activities can have substantial effects in developed countries.     

Population ecology of the low-shore chitons Onithochiton quercinus and Plaxiphora albida

Populations of two chitons, Onithochiton quercinus (Gould, 1846) and Plaxiphora albida (Blainville, 1825) were sampled at five sites in the low-shore algal community at Cape Banks, New South Wales, Australia, from January 1985 to February 1988. Both species were abundant, reaching densities of 96 and 45 m^-2, respectively and grew to 80 mm in length. O. quercinus and P. albida were found on the solitary ascidian Pyura stolonifera and on the substratum in amongst the foliose macroalgae which dominate this community. Size-frequency data were used to estimate the rates of growth, mortality and longevity, and time of recruitment. Growth of both species was rapid for the first 3 yr and slowed thereafter. O. quercinus and Plaxiphora albida had similar longevities and were estimated to live for at least 6 yr. Reproductive samples were also collected to identify when sexual maturity occurred, to clarify the reproductive periodicity, and to examine the sex ratios of the two species. Both species spawned over a discrete period in early autumn and there was no evidence of the bi-annual spawning reported in a previous study. Recruitment of O. quercinus and P. albida occurred during autumn, but recruits could not be quantified owing to their cryptic nature. The microhabitats occupied by the recruits of both species included the empty shells of the barnacle Austromegabalanus nigrescens, the spaces between the calcareous tubes of the polychaete Galeolaria caespitosa, and the space amongst the algae on Pyura stolonifera. Both species reached reproductive maturity at 2 yr of age. The sex ratios of both species were consistent with the results of a previous study: P. quercinus had a sex ratio of almost 2:1 biased in favour of males, and Plaxiphora albida exhibited a sex ratio of 1:1. The study suggested that populations of O. quercinus and P. albida could persist in the low-shore algal community in the absence of recruitment. This, together with their large size and consumption of macroalgae suggests that they have the potential to affect the structure and dynamics of this intertidal community.     

Influence of predation by a crab on the distribution of the size-groups of three intertidal gastropods in South Australia

Two South Australian rocky intertidal platforms were sampled in April 1981 and December 1982 (Marino Rocks) and in December 1982 (Lady Bay), respectively. Three snail species, Nerita atramentosa Reeve, 1855, Bembicium nanum (Lamarck, 1822) and Austrocochlea concamerata (Wood, 1828), exhibited shore-level size-gradients, with smaller individuals occupying the higher intertidal levels. The reef crab (Ozius truncatus M.-Edwards, 1834), whose distribution overlaps that of the gastropods, is an important predator of these gastropods. The shore-level distribution of shell sizes can be explained by differential selection against smaller individuals by reef crabs. The decreased density of small snails at lower intertidal levels may be the result of either their consumption by reef crabs and/or their movement to higher shore levels where crab predation is less intense.     

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     

Measurement of chlorophyll fluorescence reveals mechanisms for habitat niche separation of the intertidal seagrasses <Emphasis Type="Italic">Thalassia hemprichii</Emphasis> and <Emphasis Type="Italic">Halodule uninervis</Emphasis>

In Taiwan, Thalassia hemprichii dominates the upper intertidal zone, whereas Halodule uninervis occupies the lower intertidal zone. We tested the hypothesis that T. hemprichii is better adapted to high irradiance and more resistant to air exposure than H. uninervis. The photosynthetic efficiency, damage, and extent of recovery were determined by measuring chlorophyll fluorescence using pulse amplitude modulated fluorometry. Both species growing in tidal pools, in response to high irradiance alone, revealed a small depression in maximal quantum yield of photosystem II (Fv/Fm) at noon. The second experiment compared the effect of air exposure alone and the combined effect of air exposure with high irradiance by interposing a shading screen on both species, growing in the intertidal zone over a diurnal cycle. Values of Fv/Fm of both the shaded and irradiated T. hemprichii remained high at low tide. However, H. uninervis exhibited a marked depression following air exposure and a synergistic depression under the combined effect. The experimental manipulations of exposure time demonstrated that the tolerance of T. hemprichii to the combined effect was longer and the recovery from air exposure following re-submersion was better than those of H. uninervis. Both species were more susceptible to the combined effect in the dry season than in the wet season. Our results suggest that air exposure is more important than high irradiance in constraining the distribution of H. uninervis in the upper intertidal zone. This was confirmed by transplantation experiments in which a rapid decline of H. uninervis was observed after transplantation into the upper intertidal zone. In the lower intertidal zone, measurements of the response of the photosynthetic electron transport rate to irradiance demonstrated that the transplanted T. hemprichii exhibited a sun-type response and H. uninervis a shade-type response.     

Role of peat organic matter on isotopic composition of most abundant benthic organisms in intertidal habitats of SW Iceland

The transfer of peat organic matter (OM) from tidal pools of upper littoral to downstream rocky shores and its potential incorporation into marine biota were investigated using the stable isotope approach. Samplings were carried out in September 2004 in two SW Icelandic sites (Osar and Hvassahraun), where we selected (1) areas with shores where grass gently declined towards rocks and, on reaching the sea line, formed small tidal peat pools and (2) areas where grass and rocky shores were not contiguous, rather the grass lower limits were several hundreds of meters back from the shore. In both grass and no grass areas, in the intertidal zone, all benthic organisms and all potential OM sources were sampled. Dominant macroalgae were Ascophyllum nodosum ([Linnaeus] Le Jolis) and Fucus vesiculosus Linnaeus. In grass sites, organisms partially reflected the isotopic composition of peat OM, while in no grass sites, peat represented only a negligible amount of available OM, or its signal was totally absent from the environment. Intertidal organisms could rely on peat both directly by suspension feeding, grazing or scavenging and indirectly by predation (crabs) on low level consumers (barnacles).     

Effects of detrital non-native and native macroalgae on the nitrogen and carbon cycling in intertidal sediments

The decay of non-native and native seaweed mixing may modify sediment biogeochemistry and organic matter transfers within benthic food webs according to their composition and biomass. The non-native species Sargassum muticum was deliberately added to the sediment of an intertidal sandflat at different biomass and mixed to the native species Ulva sp. and Fucus vesiculosus. The sediment porewater was then ¹³C and ¹⁵N enriched to test whether both detrital diversity and biomass influenced the transfer of porewater carbon and nitrogen to the sediment and to the macrofauna consumers. More ¹⁵N-nitrogen was mobilized to sediments and macrofauna when the 3-species detrital mixing was buried, probably because this mixing provided species-specific compounds such as polyphenols due to the presence of S. muticum and F. vesiculosus, as well as large amounts of nitrogen due to the presence of Ulva. Our study revealed the importance of detrital diversity and non-native seaweeds for the nitrogen cycling in the benthic food web.     

Photosynthesis in air and in water of Acanthophora najadiformis growing within a narrow zone of the intertidal

In this work, we investigated photosynthetic gas exchange responses of the red alga Acanthophora najadiformis (collected in 1991 from a shore near Netanya, Israel) to heating, light, inorganic carbon and desiccation of the thalli. This was done to elucidate some of the contributing causes for its particular restricted vertical distribution within the lower intertidal zone of the Israeli Mediterranean rocky shore. In contrast to other common intertidal species, the photosynthetic performance of A. najadiformis was very sensitive to desiccation and to high temperature, and these factors may thus prevent the alga from growing above the surge zone. On the other hand, this species photosynthesized five times faster in air than in water (provided it was kept highly hydrated), and this may be the reason why it does not succeed in competing with other algae in the subtidal which use HCO ₃ ^- more efficiently.This paper is in partial fulfillment of a Ph.D. study by R. Einav in cooperation with the Department of Ecology, University of Bielefeld (under supervision of Prof. Dr. S. W. Breckle), under a cooperative arrangement between Tel Aviv and Bielefeld Universities     

Patterns of mussel recruitment in southern Africa: a caution about using artificial substrata to approximate natural recruitment

Quantifying sessile marine invertebrate recruitment often requires destructive sampling or extrapolation from artificial substrata, the latter introducing the danger of artifacts. We measured intertidal mussel recruitment into mussel beds and into brushes at three-month intervals for five years across 3,200 km of southern Africa and determined substrata effects on recruitment rate. Recruitment into mussel beds showed a strong, coast-wide gradient, with high recruitment on the West coast, diminishing on the South coast, and increasing slightly on the East coast. At scales of 10 s of km, brushes reflected natural temporal recruitment variability, with a strong significant linear correlation between recruitment into brushes and into mussel beds. However, the relationship became semi-logarithmic when comparing among locations at a scale of 100 s of km. Artificial substrata thus reflect local natural settlement well but may be a poor indicator of it when spatial scales are large, particularly when mussel bed topography is complex, or localities have very different recruitment densities.     

Assessment of intertidal growth and capacity adaptations in suspension-feeding bivalves

Curves relating instantaneous growth rate to aerial exposure were determined for six species of bivalves in laboratory and shore experiments. A dimensionless index equatable with the relative intertidal growth performance of a species was calculated by integration of the growth curve after converting both growth rate and aerial exposure to decimal fractions. Intertidal growth performance of the bivalves tested corresponded well with their natural levels of occurrence on the shore, and improved in the following order: Modiolus modiolus < Argopecten irradians < Ostrea edulis < Mytilus edulis < Crassostrea virginica. Geukensia demissa, for which an index value could not be determined, grew faster intertidally than subtidally. The relative contributions made to intertidal growth performance by energy-conserving and energy-supplementing capacity adaptations were assessed by resolving the growth curves into energy-input and energy-loss components. The rate of energy loss due to intertidal exposure was lower in the high-shore species, and also less affected by harsher subaerial conditions, than in the low-shore species. Moreover, M. edulis and C. virginica showed abilities to supplement energy input such that growth per unit immersion time was better at certain intertidal levels than subtidally. Energy conservation and supplementation in these forms made roughly equal contributions to their improved intertidal growth relative to species occurring lower on the shore.     

Wave exposure effects on population structure and recruitment in the mussel <Emphasis Type="Italic">Perna perna</Emphasis> suggest regulation primarily through availability of recruits and food,not space

Recruitment and population structure of Perna perna in low shore mussel beds were investigated over 15 months at six sites along the south coast of South Africa. Initial, subjective classification of sites as wave exposed or wave sheltered (three of each) was confirmed using the dissolution of cement blocks to measure average water flux and dynamometers for maximum wave force. Recruitment occurred throughout the year, but recruit (1–5 mm) densities were significantly higher from January to April 1996 on both shore types. Recruit densities were positively correlated with adult (>15 mm) densities for both shore types (P < 0.05) but the correlations were extremely weak (r ² < 0.06 in each case). In areas with 100% cover, adult size (mean and maximum lengths) was greater on exposed sites, but density showed the reverse and was negatively correlated with maximum wave strength (r = −0.84). Despite differences in adult densities and sizes, biomass, which is a product of the two, showed no significant difference between the two shore types (ANOVA P > 0.05). Thus wave exposure dramatically affects density, recruitment and mussel size, but not recruitment timing or biomass where there is 100% cover, and mediates a three-way interaction among food supply, larval supply and intraspecific competition for space. In contrast to shores with saturation recruitment, mussel biomass here appears to be limited by recruit supply and constraints of food, especially on sheltered shores, while density is regulated through intraspecific competition for space primarily on exposed shores and at small spatial scales.     

Population structure,northern range limit,and recruitment variation in the intertidal limpet Lottia scabra

The northern range limit of the intertidal limpet Lottia scabra is Cape Arago, Oregon (43°N), where adult survival is excellent, the population is small (<300), and recruitment is low; the range limit may be set by limited recruitment. Between June 2012 and March 2013, 25 sites from the middle of the species range (33°N) to Cape Arago were sampled and population size frequency distributions, densities, and nearest neighbor distances were compared to the amount of rocky and sandy shore and kelp bed size. North and south of 37°N, the densities of new recruits averaged 22 and 86 m^?2, respectively. This shift was associated with the range limit of Macrocystis pyrifera kelp beds; we hypothesize that slower currents in M. pyrifera beds may limit larval dispersal leading to higher recruitment. North and south of 40°N, adult density averaged <1 and 458 m^?2, respectively, with the species absent from many sites to the north. This shift was associated with a sharp drop in the amount of rocky shoreline and an increase in uninhabitable sandy shore. Near the northern range limit, >80 % of the individuals were solitary and may be unable to spawn successfully. Recruitment at Cape Arago was infrequent and likely due to self-recruitment. This study suggests that the range limit was set by the absence of M. pyrifera and too little rocky shore leading to high larval wastage, low settlement, low population densities, and, due to an Allee effect, very small effective population sizes.