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.     

Comparison of mussel bed community between two intertidal mytilids Septifier virgatus and Hormomya mutabilis

Mussel bed community structure of two intertidal mytilids, Septifer virgatus (Wiegmann) and Hormomya mutabilis (Gould), whose beds were contiguous vertically on a rocky intertidal shore (Wakayama Prefecture, Japan), was compared between 1982 and 1983. In the upper S. virgatus bed, crustaceans and bivalves were dominant in terms of both number of individuals and biomass. There were three barnacle species representative of the epizoans, two isopods and one amphipod as mobile fauna, and two bivalves as infauna. The lower H. mutabilis bed supported virtually no epizoans or mobile fauna. Infaunal free-ranging polychaetes and sipunculids were dominant in terms of both number of individuals and biomass. The H. mutabilis bed contained a much greater amount of sediment than did the S. virgatus bed, and the interstices among individual H. mutabilis and among their byssal threads were filled with sediment. The biomass of six of nine species dominant in the S. virgatus bed was negatively correlated with the amount of sediment. Recruitment of these faunal assemblages into artificial mussel clumps was examined in mussel enclosure experiments, and a negative sediment effect in H. mutabilis clumps was detected for one isopod and one limpet species. Factors causing the differences between two mussel bed communities are discussed, focusing on the effects of sediment.     

Desiccation,higher temperatures and upper intertidal limits of three species of sea mussels (Mollusca: Bivalvia) in New Zealand

Distribution, abundance, and resistance adaptations to higher temperature and desiccation of three species of intertidal mussels (Mytilus edulis aoteanus, Perna canaliculus and Aulacomya maoriana) were studied in New Zealand. M. edulis aoteanus generally was more abundant upshore, with P. canaliculus dominating downshore. M. edulis aoteanus was more common than P. canaliculus on the outside of mixed-species clumps. Abundance of A. maoriana was variable, with individuals favouring damp habitats such as inside mussel clumps. In moving air at 75% relative humidity and at 20°C or 30°C, median lethal levels of water loss were similar for P. canaliculus and M. edulis aoteanus but lower for A. maoriana. Rates of desiccation varied inversely with size and were higher for P. canaliculus, due mainly to valve gaping with resultant loss of water from the mantle cavity. M. edulis aoteanus was more tolerant of higher water temperatures than were the other species. Success in colonizing upshore or more aerially exposed habitats seems to be related to ability of small mussels to tolerate desiccation, especially during hot, windy weather.     

Population and species diversity fluctuations in a rocky intertidal community relative to severe aerial exposure and sediment burial

From a series of 10 quarterly assessment between October 1975 and May 1978 (inclusive), fluctuations in abundance were determined for macroinvertebrates and macrophytes of a rocky intertidal community on Santa Cruz Island, California, USA. During afternoon low tides in late fall and winter of the first 2 yr of study, organisms of the upper and middle intertidal zones were subjected to prolonged aerial exposure. Many species there tolerated this exposure, but die-backs occurred for a barnacle (Chthamalus fissus/C. dalli) and several algae (Endocladia muricata, Pelvetia fastigiata f. gracilis, Corallina officinalis var. chilensis, Corallina vancouveriensis, Cylindrocarpus rugosus and Codium fragile). These die-backs were succeeded by blooms of Ulva californica and Porphyra perforata. In the upper and middle intertidal zones, the major cover organisms that could tolerate prolonged aerial exposure were disproportionately prevalent and appeared to be maintained by the periodic repression of species intolerant to such exposure. In February 1978, heavy rainfall caused sediment inundation of the middle and lower intertidal zones. This event was followed by declines in abundance of a barnacle (Tetraclita rubescens) and several algae (Pelvetia fastigiata f. gracilis and corallina spp.). Shannon-Wiener H species diversity fluctuated from a high in October to a low the following May during both 1975–1976 and 1976–1977 in conjunction with the period of increased daytime aerial exposure in late fall and winter. A further decline in diversity following sediment inundation in February 1978 contributed to a long-term trend of declining H species diversity (3.06 in October 1975 to 1.87 in May 1978). We hypothesize that predictable late fall to winter aerial exposure stresses, in combination with a random physical disturbance (sediment burial), exceeded an optimal intermediate level of disturbance predicted for maximal species diversity.     

Diet of intertidal bivalves in the Ría de Arosa (NW Spain): evidence from stable C and N isotope analysis

We used natural abundance measurements of stable carbon and nitrogen isotopes and a short-term ¹⁵N-enrichment experiment to explore the importance of river-derived and autochthonous sources to the diet of intertidal suspension-feeding bivalves in the Ría de Arosa, an oceanic-dominated system in northwest Spain. Highly seasonal and intense phytoplankton "bloom" events occur in this estuary. However, relatively low phytoplankton standing crop and productivity are present during much of the year, suggesting that food sources other than phytoplankton must support bivalves during these periods. Bivalves (Cerastoderma edule, Tapes decussatus, Mytilus galloprovincialis) were sampled quarterly at four intertidal stations along the length of the estuary with increasing distance from the Ulla River. Muscle tissue was consistently enriched in ¹³C and ¹⁵N relative to stomach contents. The stable C isotope values of bivalves indicated that river-derived inputs were, at most, a minor component of diet. These values suggested the potential importance of benthic microalgae to bivalve diet much of the year and the incorporation of ¹⁵N label applied to the sediment surface into stomach contents and muscle tissue in a field experiment supported this conclusion. Other labeled components of the microbenthos such as bacteria could also have been ingested. ¹³C-depleted values of bivalves in May coincided with elevated offshore chlorophyll a concentrations, suggesting the increased use of a phytoplankton source during the spring. We propose that intertidal suspension-feeding bivalves in this estuary use primarily resuspended microbenthos during periods of low phytoplankton concentration, but that phytoplankton increases in relative dietary importance during bloom events.Communicated by P.W. Sammarco, Chauvin     

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.     

Gamete production,somatic growth and multiple-locus enzyme heterozygosity inMytilus edulis

Mussels,Mytilus edulis L., were collected from the lower shore in Stony Brook Harbor, New York, USA, in April 1984. The mussels were in spawning condition at the time of collection. Mantle weight was used as an index of fecundity and somatic tissue weight and growth rate were measured so that the relative production of gametes and somatic tissue with age could be calculated. For each individual mussel the genotypes at loci coding for five enzymes were determined. Somatic tissue production exceeds gamete production for the first two and a half years of life, but thereafter it declines and is exceeded by gamete production. There is a positive correlation between multiple-locus enzyme heterozygosity and fecundity in mussels which have grown beyond the size at which gamete production starts to exceed somatic production. There is no correlation between heterozygosity and fecundity in younger individuals. We conclude that the higher scope for growth of more heterozygous bivalves, described elsewhere, is translated into allocation of energy to somatic growth during early life and into gamete production in later life. Our observations perhaps explain why, in other studies, the correlation between growth rate and heterozygosity in bivalves is manifested most clearly when young individuals are examined.     

Functional morphology and zonation of three species of sea anemones from rocky shores in southern Chile

Three species of sea anemones, clearly exhibiting zonation on the shore, are grouped into intertidal [Phymactis clematis (Drayton, 1846), Anthothoe chilensis (Lesson, 1830)] and infralittoral [Antholoba achates (Drayton, 1846)] forms. A series of observations revealed that intertidal forms have the ability to retain water in the coelenteron during exposure to air,/while the infralittoral form cannot do so. This different behaviour is attributed to morphological characteristics, such as the specific body shape and the structure of the sphincter and retractor muscles. These features, in combination with specific abiotic factors of the various habitats under consideration, determine the upper limits of distribution of each species, while zonation below these limits seems to be affected in addition by biological interactions.     

A comparative study of metabolic energy expenditure in the limpets Patella cochlear,P. oculus and P. granularis

Oxygen consumption of 3 species of Patella was measured in air and water at various temperatures. Measurements at constant temperature over a full tidal cycle showed no tidal or light-dark rhythms. Measurements under conditions simulating natural tidal, temperature and day-night cycles allowed calculation of daily respiratory energy budgets. P. cochlear occurs low on the shore, but experiences a food shortage due to intense intraspecific competition. Its rate of respiration is moderate, but metabolic expenditure is kept low because exposure to air is brief and body temperatures seldom rise above 23°C. P. cochlear has a respiratory rate-temperature (R-T) curve which peaks at 20°C and forms a plateau between 20° and 32.5°C. The midshore P. oculus has abundant food and adopts an exploitative strategy. Growth rate is very high, and this high turnover of energy is linked with a high metabolic rate, high Q10 (temperature coefficient) values, high body temperatures during the day-time low tide, and a respiratory R-T curve peaking at 32.5°C. Small P. oculus occur mainly in intertidal pools and respire faster in water, while larger individuals occur on bare rocks and respire faster in air over the upper temperature range. In contrast, the upper-shore P. granularis has little food, and conservation of energy is essential, particularly as its growth rate is moderate and its reprocurve output high. Respiratory losses are reduced by suppression of the R-T curve and low Q10 values, resulting in relative independence of temperature. Small P. granularis occur low on the shore and respire slower in water. Larger individuals occur at high levels due to migration, and respire slower in air. This further reduces respiratory energy losses. The patterns of respiration in these 3 species are thus related to food availability, resulting in exploitative or conservationist strategies.     

Combining heat-transfer and energy budget models to predict thermal stress in Mediterranean intertidal mussels

Recent studies have emphasised that organisms can experience physiological stress well within their geographic range limits. Developing methods for mechanistically predicting the presence, absence and physiological performance of organisms is therefore important because of the ongoing effects of climate change. In this study, we merged a biophysical–ecological (BE) model that estimates the aquatic (high tide) and aerial (low tide) body temperatures of Mytilus galloprovincialis with a Dynamic Energy Budget (DEB) model to predict growth, reproduction and mortality of this Mediterranean mussel in both intertidal and subtidal environments. Using weather and chlorophyll-a data from three Mediterranean sites along the Italian coasts, we show that predictions of sublethal and lethal (acute) stress can potentially explain the observed distribution (both presence and absence) of mussels in the intertidal and subtidal zones, and the maximum size of animals in the subtidal zones. Importantly, our results suggest that different mechanisms limit the intertidal distribution of mussels, and that these mechanisms do not follow a simple latitudinal gradient. At the northernmost site (Palermo), M. galloprovincialis appears to be excluded from the intertidal zone due to persistent exposure to lethal aerial temperatures, whereas at the southernmost sites (Porto Empedocle and Lampedusa) sublethal stress is the most important driver of mussel intertidal distribution. Our predictions provide a set of hypotheses for future work on the role of climate change in limiting intertidal distribution of mussels in the Mediterranean.     

Predators influence the tidal distribution of oysters (Crassostrea virginica)

Biotic and abiotic conditions can separately and synergistically influence the abundance and distribution of species and create vertical zonation patterns in marine systems. In Corpus Christi Bay, TX, USA, eastern oysters (Crassostrea virginica) are limited to intertidal habitats, while in adjacent estuaries, oysters not only grow subtidally, but thrive in these areas to the extent they are a viable commercial fishery. The purpose of this study was to assess how predators and abiotic conditions affect oyster mortality and growth at different tidal elevations. Anecdotal evidence suggests that abiotic conditions, primarily hypoxia and salinity, as well as oyster disease, limits oysters to intertidal areas. Yet, in Corpus Christi Bay, oysters are absent from subtidal areas where hypoxia is not known to occur. Infection by Perkinsus marinus (Dermo) is common in the study area, but previous work suggests that infection rates do not increase when oysters are transplanted subtidally. We investigated oyster tidal distributions by transplanting newly settled oysters into intertidal and subtidal areas. Predation on oysters was significantly greater in subtidal as compared to intertidal habitats. When protected from predators using cages, oyster survival significantly increased. Further, oysters in subtidal areas allocated significantly more resources to shell growth than did those in intertidal areas, and oysters are known to grow heavier shells in response to predators. Oyster settlement was not statistically different between inter and subtidal areas, and abiotic conditions measured during the study did not exceed known tolerance limits for oysters. Previous studies have shown that abiotic conditions influence oyster mortality and the success of restored oyster reefs. Our findings indicate that predators can also affect oyster distribution, and their effects should be evaluated when developing plans for oyster management and restoration.     

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     

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.     

Carbon emission associated with respiration and calcification of nine gastropod species from the intertidal rocky shore of Western Europe

Intertidal rocky shores are characterized by vertical zonation that results from the interplay between environmental conditions, organism physiology, and species interactions. Metabolism of intertidal organisms is highly variable between species and it changes with vertical position along the intertidal gradient. The present study aimed to quantify the carbon metabolism of nine intertidal rocky shore gastropods, in order to clarify their respective roles in carbon production during emersion and immersion. The influences of monthly temperature variation and tidal level were tested for each species. Analyses were performed in the laboratory using the infrared gas analyzer method for measuring aerial respiration rates, and the dissolved inorganic carbon and total alkalinity technique for measuring aquatic respiration rate and calcification. Hourly carbon fluxes were calculated for the mean annual temperature of 13 °C measured in both air and underwater in the study area. Respiration rates were similar for emersion (8–25 μmol CO₂ g AFDW^?1 h^?1) and immersion (10–23 μmol DIC g AFDW^?1 h^?1). For all species, underwater respiration fluxes were more influenced by monthly temperature variation than by air fluxes, probably as an adaptation to the rapid changes occurring during emersion. Calcification was an important factor influencing annual carbon fluxes for all studied species; every species showed different calcification rates according to its size and position on the intertidal zone. Annual carbon emissions were calculated using the mean immersion/emersion time of each species. Intertidal gastropod carbon emission was primarily influenced by body biomass and their vertical position within the intertidal zone.     

Space partitioning and interactions in an intertidal sand-burrowing amphipod guild

A nine-year study at a moderately exposed, fine sand intertidal beach at Long Sands, Maine, USA identified marked seasonal changes in the foci of sand-burrowing amphipod activities. These included seasonal population movements, degree of interspecific horizontal overlap, life stage segregation within and between species, and sand depth stratification. Behavioral interactions related to competition for available space are considered important in affecting the distribution and abundance of amphipod species, and community structure. Significant negative correlations were shown between the abundance and upper distributional limits of the smaller, lower shore Acanthohaustorius millsi and the abundance of the larger, higher shore species Haustorius canadensis. Tolerance limits to a variety of prevailing physical factors alone, were not considered a serious obstacle to occupation of higher intertidal level sands by A. millsi. Summer brooding females of both species occupied similar 5 to 10 cm sand depths, but were strongly segregated horizontally. Laboratory coexistence experiments during the reproductive period showed increased mortality of adults and negligible reproductive output of A. millsi when in combination with H. canadensis compared to controls where the former species was alone. A third species, Amphiporeia virginiana, occupied primarily very shallow sand (0 to 2.5 cm), and performed seasonal movements opposite in direction to A. millsi and H. canadensis. The presence, amount, and refinement of biological interactions across the wave exposure gradient requires further study. Until then, we consider as inappropriate the blanket designation of all types of intertidal sand communities as physically controlled.     

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     

Observations on the biology of Donax trunculus and D. vittatus at Ile d'Oléron (French Atlantic coast)

Observations have been made on the biology of two species of the bivalve genus Donax, on two beaches, Vertbois and St. Trojan, on the Ile d'Oléron, French Atlantic coast. The two species displayed different vertical distribution: D. trunculus Linné in the intertidal; and D. vittatus (da Costa) between low-water spring tide (LWST) and 5 to 6m depth, with only the fringe of the population extending to the shore. D. trunculus also showed differential distribution by size or age, the youngest individuals being highest on the shore, and the oldest near LWST. The two species exhibited a similar pattern of seasonal recruitment and growth, but in both there were differences in growth characteristics between the two beaches, individuals at St. Trojan growing to a larger size than those at Vertbois. The mean pattern of mortality in the two areas was similar, and productivity per 100 recruits surviving to the first winter following settlement was greater at St. Trojan than at Vertbois. For D. trunculus the mean population density at Vertbois was higher and the production per unit area on the two beaches was similar. Production to biomass (B) and elimination to biomass (B) ratios were similar for the two beaches for both species, and while production was greater for D. trunculus at both beaches, the B and B ratios were higher for D. vittatus. Comparisons with other published data reveal that the rate of growth of D. trunculus is similar throughout its range from Brittany to the Mediterranean Sea, while that of D. vittatus shows more variation. In both species, there is a trend of increasing P/B and E/B ratios from north to south throughout the geographical range.     

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.     

Desiccation enhanced nitrogen uptake rates in intertidal seaweeds

Desiccation increased nitrate and ammonium uptake rates upon resubmergence in late summer populations of the intertidal macroalgae Gigartina papillata (C.Ag.) J.Ag., Enteromorpha intestinalis (L.) Grev., Fucus distichus L., and Pelvetiopsis limitata (Setch) Gardn. The ratio of nitrogen uptake rates in desiccated plants to rates in hydrated plants (controls) was correlated with the position of the species in the intertidal zone. Gracilaria pacifica Abbott., the species occurring at the lowest shore level, showed no enhancement of nitrogen uptake following desiccation. The high intertidal species such as P. limitata and F. distichus showed a two-fold enhancement of nitrate and ammonium uptake following more extensive desiccation (>30%) and continued uptake even following severe desiccation (50 to 60%). After the plants had been desiccated, the increase in nitrate uptake rates upon submergence lasted much longer than a similar enhancement of ammonium uptake. The duration of the enhanced nitrate uptake was similar to the time required for total rehydration but the uptake rates were not related to the state of rehydration. The potential contribution that this enhanced nitrogen uptake following desiccation could make to total nitrogen procurement for growth is discussed. The experiments were carried out in 1979 or 1980 and repeated in 1981.This paper is dedicated to Dr. R. F. Scagel on the occasion of his retirement for his outstanding contribution to phycology     

Desiccation as a factor in the intertidal zonation of barnacles

Four species of balanomorph barnacles, Balanus crenatus Brugière, B. balanoides (L.), Elminius modestus Darwin and Chthamalus stellatus (Poli), were studied to assess the susceptibility of intertidal barnacle species to desiccation. Known sized samples of barnacles were exposed to controlled desiccating conditions and subsequent survival and water loss were determined. It is clear that the ability to live high on the shore is dependent on a reduction of the overall permeability to water loss. Because of greater surface area to volume ratios, small stages are particularly prone to desiccation. In normal intertidal emersion periods, small stages of B. crenatus particularly, and also of B. balanoides and E. modestus which are similar in their desiccation resistance, would be susceptible to desiccation at normal temperatures and low humidities. Large barnacles would be more prone to death from high temperatures when the tide is out. The spat of C. stellatus, although surviving much longer than spat of larger dimensions of the other species, must also be prone to prolonged emersion conditions at high shore levels.