Carbon content and nutritional condition of sardine larvae (Sardina pilchardus) off the Atlantic coast of Spain

As part of a “European Sardine/Anchovy Recruitment Program” (SARP), sardine larvae (Sardina pilchardus) were sampled off the Atlantic coast of Spain through the spawning season from March to June. The larvae were analysed for carbon and nitrogen content as a measure of nutritional condition and survival potential. There was no significant diel variation in larval carbon content, but there was a small significant diel variation in nitrogen; the absence of a strong diel signal in elemental composition was ascribed to the overnight retention of the gut contents. There was an increase in carbon content with increase in body length which reached an asymptote at ∼40% carbon content at a larval length of 20 mm. It is argued that larvae with a carbon content of <25% of body weight were nutritionally stressed, with the smaller larvae (<10 mm in length) appearing to be more vulnerable to food limitation. Although larvae with the lowest age-specific carbon content (poorest condition) occurred on the cruise with the lowest food availability, there was no consistent relationship between carbon content and food availability. While the successive monthly estimates of carbon content revealed differences in potential recruitment between months, these were not related to the birth-date distribution of the surviving juveniles. Received: 23 November 1998 / Accepted: 3 March 1999     

Feeding habits of the spotted flounder Citharus linguatula off the eastern coast of Spain

The composition of the diet of Citharus linguatula (L.) off the coast of the Gulf of Valencia, Spain, was determined between October 1989 and October 1990. The percentage of empty stomachs remained constant throughout the year, except for the period August to September, when a maximum was recorded coinciding with the reproductive period. Crustaceans (Mysidacea and Decapoda) and teleosts constituted the main prey. The composition of the prey ingested varied with predator size; small specimens contained a greater number of mysids in their stomachs, while decapods and fishes were more abundant in the stomachs of larger specimens. Diets varied seasonally: mysids were more important during autumn, whereas decapods were more important during winter and spring. Fishes were numerically most important in the diet in summer, but the frequency of occurrence was constant throughout the year.     

Daytime surface swarms of the euphausiid Thysanoessa inermis off the west coast of Hokkaido,northern Japan

Biological characteristics of the daytime swarming of the euphausiid Thysanoessa inermis (Krøyer) were examined off the west coast of Hokkaido in the northeast Sea of Japan between 1982 and 1987. Swarms were composed exclusively of fully mature individuals; males possessed spermatophores at the ejaculatory ducts and females had attached spermatophores at the thelycum. Females predominated in most swarms, while males or nearly balanced swarms were infrequently encountered. Fully mature females occurred in the late swarming season, usually mid-April. Examination of stomachs indicated that feeding activity was low during the daytime surface swarming behavior. The body sizes of swarming T. inermis occurring around Yagishiri Island were significantly larger than those found simultaneously off the Shakotan Peninsula. This suggests that the euphausiid populations of the two areas are different.     

Analysis of the structure of decapod crustacean assemblages off the Catalan coast (North-West Mediterranean)

We sampled the communities of decapod crustaceans inhabiting the depth zone between 3 and 871 m off the Catalan coast (North-West Mediterranean) from June 1981 to June 1983. The 185 samples comprised 90 species differing widely in their depth distributions. Multivariate analysis revealed four distinct faunistic assemblages, (1) littoral communities over sandy bottoms, (2) shelf communities over terrigenous muds, (3) upper-slope communitics, and (4) lower-slope or bathyal communities. The brachyuran crab Liocarcinus depurator is the most abundant species of the shelf assemblage, although L. vernalis dominates over the shallow sandy bottoms of the shelf. The dominant species of the upper-slope assemblage are nektobenthic species (Solenocera membranacea, Plesionika heterocarpus, Processa canaliculata), pelagic species (Pasiphaea sivado, Sergestes arcticus), and benthic species (Macropipus tuberculatus, Munida intermedia, Nephrops norvegicus). Aristeus antennatus comprise most of the biomass of the lower-slope community, which supports a greater diversity than the other assemblages. The main assemblages appear to be related to different hydrological characteristics, the extent of seasonal fluctuations, and to the changes in sediment structure associated with changes in the steepness of the bottom.     

Monitoring morphological changes along the coast of Huelva (SW Spain) using soft-copy photogrammetry and GIS

This contribution deals with the use of different sources of data (field surveys with total station and GPS, air photographs and topographic maps) as well as their integrated digital treatment in a GIS context to quantify the morphological changes in a ridge of coastal dunes in the southwest of Spain. The results show very high and increm enting rates of foredune retreat significant losses of foredune surface and a clear negative sedimentary balance (lowering and inland migration) in its recent evolution (1979–1996). Two processes can explain this evolution: (1) marine erosion and (2) the reactivation of aeolian deflation. The combined use of GPS (code/phase) and soft-copy photogrammetry seem to provide the best for monitoring future changes.     

Growth,mortality and yield-per-recruit of deep-water royal red prawns (Haliporoides sibogae) off eastern Australia,using the length-based MULTIFAN method

The MULTIFAN method of Fournier et al. was used to analyse a series of monthly length-frequency distributions of deep-water royal red prawns (Haliporoides sibogae de Man, 1907, Solenoceridae) for the estimation of growth, mortality and yield-per-recruit. Length data were collected from commercial catches made between Latitude 33° and 35°S from November 1988 to May 1990. MULTIFAN distinguished six cohorts in the royal red prawn population, aged at 6 mo intervals from about 1.5 to 4 yr. Most prawns were between 2 and 3 yr of age. Females and males were fully recruited at 23.1 and 21.5 mm carapace length (CL) respectively, when about 2 yr old. Females grew faster and reached larger sizes at age than males (growth coefficient, K=0.37 yr^-1 and asymptotic length, L =48.3 mm CL for females, and K=0.49 yr^-1 and L =33.5 mm CL for males). Total mortality (Z) was estimated at 1.6 and 1.2 yr^-1 for females and males, respectively. Approximate values for natural mortality (M) ranged from 0.6 to 0.7 yr^-1 for females, and from 0.4 to 0.8 yr^-1 for males. Analysis of yield-per-recruit suggested that while the current yield could possibly be increased by decreasing the length at first capture (L _c ), there seems to be little potential for an increase in yield from increased fishing effort in the area currently fished.     

Cross-shelf variation in calanoid copepod production during summer 1996 off the Oregon coast, USA

The fecundity of nine species of adult female calanoid copepods, and molting rates for copepodite stages of Calanus marshallae were measured in 24 h shipboard incubations from samples taken during the upwelling season off the Oregon coast. Hydrographic and chlorophyll measurements were made at approximately 300 stations, and living zooplankton were collected at 36 stations on the continental shelf (<150 m depth) and 37 stations offshore of the shelf (>150 m depth) for experimental work. In our experiments, maximum egg production rates (EPR) were observed only for Calanus pacificus and Pseudocalanus mimus, 65.7 and 3.9 eggs fem^-1 day^-1 respectively, about 95% of the maximum rates known from published laboratory observations. EPR of all other copepod species (e.g., C. marshallae, Acartia longiremis and Eucalanus californicus) ranged from 3% to 65% of maximum published rates. Fecundity was not significantly related to body weight or temperature, but was significantly correlated with chlorophyll a concentration for all species except Paracalanus parvus and A. longiremis. Copepod biomass and production in on-shelf waters was dominated by female P. mimus and C. marshallae, accounting for 93% of the adult biomass (3.1 mg C m^-3) and 81% of the adult production (0.19 mg C m^-3 day^-1). Biomass in the off-shelf environment was dominated by female E. californicus, P. mimus, and C. pacificus, accounting for 95% of the adult biomass (2.2 mg C m^-3) and 95% of the adult production (0.08 mg C m^-3 day^-1). Copepodite (C1-C5) production was estimated to be 2.1 mg C m^-3 day^-1 (on-shelf waters) and 1.2 mg C m^-3 day^-1 (off-shelf water). Total adult + juvenile production averaged 2.3 mg C m^-3 day^-1 (on-shelf waters) and 1.3 mg C m^-3 day^-1 (off-shelf waters). We compared our measured female weight-specific growth rates to those predicted from the empirical models of copepod growth rates of Huntley and Lopez [Am Nat (1992) 140:201-242] and Hirst and Lampitt [Mar Biol (1998) 132:247-257]. Most of our measured values were lower than those predicted from the equation of Huntley and Lopez. We found good agreement with Hirst and Lampitt for growth rates <0.10 day^-1 but found that their empirical equations underestimated growth at rates >0.10 day^-1. The mismatch with Hirst and Lampitt resulted because some of our species were growing at maximum rates whereas their composite empirical equations predict "global" averages that do not represent maximum growth rates.     

Physical and biological gradients in a submarine cave on the Western Mediterranean coast (north-east Spain)

Submarine caves are semi-closed subsystems within the marine littoral ecosystem. One of the most striking features is the progressive reduction of the number of phyla, species, and biomass towards the interior of such a cave. The decrease in biomass has been explained as the result of low exchange rates of the water inside the caves which limit the supply of oxygen and food particles from the exterior. Many authors have proposed that this reduced exchange rate is associated with the occurrence of marked gradients in temperature, salinity, oxygen and light. Measurement of faunal abundance of a cave in the littoral zone of the Medes Islands (Catalonia, north-east Spain) made between June 1983 and July 1984, revealed a zonation similar to that in other Mediterranean caves. Animal biomass decreased from 260 g ash-free dry weight m^-2 at the entrance to 80 g ash-free dry weight m^-2 at the end of the cave (50 m from the mouth). A special technique for remote water-sampling was developed to avoid problems due to turbulence caused by divers in this semi-closed system. This involved the installation of a series of plastic tubes at different points along the axis of the cave. The water was brought to the surface using a battery-powered electric pump. The reliability of this method was verified by comparing the results with samples collected directly by divers. Sampling both in winter and summer showed no longitudinal gradients for temperature, salinity, oxygen, chlorophylla and the number and volume of suspended particles. These results suggest that there is a constant circulation within the cave which guarantees water-exchange. The decrease in biomass cannot be explained by physico-chemical gradients due to insufficient exchange with the external system. On a finer scale, however, along the walls of the cave there may exist boundary layers that are not affected by the general circulation. This could account for the observed decrease in the biomass of benthic organisms.     

Relationship between zooplankton distribution,geographic characteristics and hydrographic patterns off the Catalan coast (Western Mediterranean)

Astract Northern anchovy larvae, Engraulis mordax, were collected on five cruises covering the Southern California Bight, one cruise in April 1984, four cruises in January, February and May 1986. The amounts of triacylglycerol, cholesterol and polar lipid were measured in individual anchovy larvae as indicators of their nutritional condition. There was a significant difference in each of the size-specific lipid components between the stations for four of the five cruises. This indicates that all the ocean habitats within a cruise were not equal in promoting growth (and presumably survival) in the anchovy larvae. There were also differences between cruises, where the percentage of the larvae judged to be in poor condition varied from 8 to 27%. Canonical correlation analyses revealed a significant relationship in most cases between the larval fish parameters and the physical and biological data collected from each occupied station. Cholesterol and triacylglycerol were the most important larval components, and the short-term energy storage component in the copepod Calanus pacificus was the most important station component. The data, however, are not sufficient to identify and characterize stations in the field which produce anchovy larvae in good condition.     

Reproductive biology of the red alga Polysiphonia lanosa (Ceramiales) in the Bay of Fundy, Canada

The purpose of this investigation was to establish reproductive phenology of the dioecious marine floridean red alga Polysiphonia lanosa (L.) Tandy. Specifically, the distribution and frequencies of male and female plants, timing of their sexual maturity, fecundity and success of fertilization were investigated. The presence of cystocarps was taken as an indication of syngamy. Populations of P. lanosa in the Bay of Fundy reproduce in spring, summer and autumn. Both male and female filaments were present in equal abundance at all sampling locations, grew in close proximity, and occurred with equal abundance at all elevations above chart datum. During the growing season most of the mature plants contained reproductive organs with apparently functional gametangia containing gametes the structure and behavior of which conformed to those reported in the literature for other species of the genus. Male and female plants of P. lanosa matured synchronously during late May to early July at all collecting sites. The ratio of spermatia to carpogonia calculated for the sampled population was high, 3000–4800 spermatia:1 carpogonium. At the end of the growing season (late October) the fertilization success was at its maximum of 50 to 90% and at its minimum in July at 24%. The three free-living life-history phases (females, males and tetrasporophytes) were abundant and occurred with equal frequency, indicating that a complete life cycle was common at the studied location. Received: 10 December 1996 / Accepted: 16 January 1997     

Growth and production of Euphausiacea (Crustacea) in the Rockall Trough

The euphausiid fauna of the Rockall Trough has been sampled in time series at approximately two-monthly intervals between 1973 and 1976 between surface and depths greater than 2000 m. Length/frequency histograms have modes that are coherent for periods of at least 4 to 6 mo, indicating that populations are being sampled. Rates of growth were determined for six species. Epipelagic species have winter checks to the growth rates, but such checks are absent in the growth of Thysanopoda acutifrons, Nematobranchion boöpis and Stylocheiron maximum. Ratios of annual production: biomass were determined and are all within the previously determined range of values for epipelagic and coastal populations. Lack of a winter check to the growth rate in deep-living species enables these potentially to have overall rates of growth comparable to those of temperate, epipelagic, shelf and coastal species.     

Archival tagging of subadult and adult common thresher sharks (Alopias vulpinus) off the coast of southern California

The common thresher shark (Alopias vulpinus) is a secondary target species of the California drift gillnet fishery (CA-DGN) and supports a growing recreational fishery in California waters. This study used archival tags to examine the movement patterns and habitat preferences of common threshers of the size range captured in the CA-DGN (>120 cm fork length). Depth and temperature-logging archival tags were deployed on 57 subadult and adult common threshers in the Southern California Bight. Tags from five individuals (8.8%) were recovered, and 154 days of data were successfully obtained from four of these. By night, shark movements were primarily limited to waters above the thermocline, which ranged in depth from 15 to 20 m. Sharks were significantly deeper by day, and daytime vertical distribution consisted of two distinct modes: a ‘shallow mode’ (wherein sharks occupied only the upper 20 m of the water column) and a ‘deep mode’ (characterized by frequent vertical excursions below the thermocline). This modal switch is interpreted as relating to regional differences in abundance of surface-oriented prey and prey in deeper water. Maximum dive depth was 320 m, greatest dive duration was 712 min, minimum temperature experienced during a dive was 9.1°C, and dive descent rate was significantly greater than ascent rate. Sharks inhabited waters corresponding to a sea surface temperature range of 16 to 21°C. The nocturnal depth distribution of common threshers has implications for management of drift gillnet deployment depths in the CA-DGN.     

Distribution and abundance of fish larvae off the coast of West Pakistan

The material was collected during 4 different cruises on the shelf off the coast of W. Pakistan in November–December, 1964 and in March, 1967 and 1968. The hydrography as well as the zooplankton-biomass distribution are briefly described. A total of 5777 larval fish were taken in 33 positive vertical hauls by an Indian Ocean Standard Net. The number of larvae in positive hauls ranged from 2 to 1262 larvae haul^-1. The most productive area of the ichthyoplankton was the waters south of Karachi, covered during the Machera Cruise, where 828 to 1262 larvae haul^-1 were obtained. The larvae were identified to species, genera or family. Sardinella sindensis (specific identification uncertain) larvae dominated in abundance. The other abundant larvae belonged to Benthosema spp., Amentum commersonii, Vinciguerria spp. and Diaphus spp. Larval distributions and abundances are described. Aggregation and spawning of adult Sardinella (sindensis) in the waters off the coast of W. Pakistan in November/December, 1964, are discussed. Presumably, the waters south of Karachi represent good feeding grounds for s. (sindensis) larvae. Displacement volume, length and weight relationships of various larval size groups have been studied and a high rate of larval mortality (at a length of 5.0 to 8.5 mm) observed.     

Genetic structure of the subtidal red alga Delisea pulchra

We used random amplified polymorphic DNA (RAPDs) to examine small-scale spatial genetic structure in the red alga Delisea pulchra (Greville) Montagne at two locations near Sydney, Australia. We examined genetic structure among plants at four spatial scales ranging from 2 km apart down to <50 cm apart between locations, among sites within locations, among quadrats within sites, and among plants within quadrats. Haploid stages of D. pulchra were absent from the populations studied, suggesting that they are maintained through asexual reproduction of diploid plants. Consistent with this, we found that 19 RAPD phenotypes scored in this study had multiple individuals, indicating the presence of clones in these populations. However, there were no RAPD phenotypes common to two locations separated by only 2 km. Analysis of molecular variance revealed that strong genetic differences occurred between plants from these two locations, with 46.3% of the total genetic variation occurring at this scale, most probably reflecting limited gene flow. Within each location, <25% of the genetic variation was attributable to differences among sites or quadrats, indicating gene flow at those smaller scales. Most of the variation within each location occurred at the smallest spatial scale, among plants within 0.25 m² quadrats. Nonetheless, some pairwise genetic distances (φST) between sites or quadrats within locations were large, indicating some genetic divergence on smaller scales. Genetic distance was independent of spatial distance within both locations, suggesting that fine-scale differences within locations were most probably caused by variation in fine-scale patterns of water movement or fine-scale natural selection. We assessed the impact of one potential selective agent, grazing sea urchins, on the fine-scale genetic structure of D. pulchra. There was no evidence that grazing by sea urchins affected the genetic structure of D. pulchra. In combination with demographic data, our results indicated that local populations of D. pulchra within locations were relatively open and that fine-scale genetic structure was probably constrained by gene flow. At the larger scale however, strong genetic differentiation indicated little gene flow between locations and restricted dispersal of spores. Received: 22 April 1999 / Accepted: 29 November 1999     

Carbon economy and nutrition of the alloparasitic red alga Harveyella mirabilis

Rhodomela confervoides (Huds.) Silva (Ceramiales: Rhodophyta) infected with the alloparasitic Harveyella mirabilis (Reinsch) Reinke (Cryptonemiales: Rhodophyta) was investigated with particular regard to rates of carbon fixation, patterns of soluble and insoluble assimilates, and transfer of reduced carbon from the photoautotrophic basiphyte to the fully heterotrophic epiphyte by means of ¹⁴C-labelling experiments. Gross carbon input by photosynthesis in Rh. confervoides accounted for about 53 g Cd^-1 when based on a biological unit (average individual of 200 mg fresh weight). Some 3% of the remaining net carbon gain (equivalent to about 0.7 g Cd^-1) was transferred from Rh. confervoides to its alloparasite, H. mirabilis (biological unit 0.5 mg fresh weight). Chromatographic examination showed that soluble ¹⁴C was translocated to and stored by H. mirabilis as mannosidoglycerate (=digeneaside) and probably a variety of amino acids. A certain proportion of soluble radiocarbon imported is converted by H. mirabilis to glycerolgalactoside (=floridoside). The bulk of imported ¹⁴C was recovered from the polymeric fraction, mainly from floridean starch.     

Brood production and lineage discrimination in the red harvester ant (Pogonomyrmex barbatus)

In contrast to the system of caste determination in most social insects, reproductive caste determination in some populations of Pogonomyrmex barbatus has a genetic basis. Populations that exhibit genetic caste determination are segregated into two distinct, genetic lineages. Same-lineage matings result in female reproductives, while inter-lineage matings result in workers. To investigate whether founding P. barbatus queens lay eggs of reproductive genotype, and to determine the fate of those eggs, we genotyped eggs, larvae, and pupae produced by naturally inseminated, laboratory-raised queens. We show that founding dependent lineage queens do lay eggs of reproductive genotype, and that the proportion of reproductive genotypes decreases over the course of development from eggs to larvae to pupae. Because queens must mate with a male of each lineage to produce both workers and female reproductives, it would benefit queens to be able to distinguish males of the two lineages. Here we show that P. barbatus males from the two genetic lineages differ in their cuticular hydrocarbon profiles. Queens could use male cuticular hydrocarbons as cues to assess the lineage of males at the mating aggregation, and possibly keep mating until they have mated with males of both lineages.     

Unexpected reproductive strategy of Sardinella aurita off the coast of Venezuela

Biological sampling of Spanish sardine (Sardinella aurita Valenciennes, 1847) off the coast of Venezuela from 1956 to 1989 was used to study the reproductive strategy and migration pattern of the population. Whereas in many pelagic fishes the energy re-allocation necessary for reproduction usually occurs optimally at the end of the upwelling season when planktonic production reaches a maximum, in the present study a 5 mo delay was observed. This suggests that energy was stored as lipids early in the season and released later via metabolism for gamete production. Major reproduction did not occur in an area and at a time when offshore transport and turbulence were low, which is also unusual for a pelagic fish species. These results are discussed in terms of the life cycle of the Spanish sardine and its possible migratory patterns. The reproductive strategy of this population apparently gives priority to optimising food availability for the offspring and not to preventing eggs and larvae being transported offshore. The presence of “retention” areas could explain this unexpected strategy. Received: 4 November 1996 / Accepted: 20 December 1996     

Ultrastructure of tetrasporogenesis in the red alga Osmundea spectabilis var. spectabilis (Rhodomelaceae: Ceramiales: Rhodophyta)

Tetrasporogenesis in Osmundea spectabilis (Postels and Ruprecht) K.W. Nam var. spectabilis proceeds through three developmental stages. A uninucleate tetraspore mother cell with synaptonemal complexes depicted during early prophase of meiosis I comprises the youngest stage. Subsequently, the nuclear envelope obtains a highly irregular profile and is surrounded by perinuclear endoplasmic reticulum (ER) and numerous mitochondria. Proplastids with peripheral thylakoid and numerous straight-profiled dictyosomes are present. Dictyosome vesicles discharge their contents, initiating tetraspore wall formation. A four-nucleate tetraspore mother cell is formed prior to tetrahedral cleavage. During the second stage of tetraspore formation the nuclei are very irregular in outline and move toward the central region where they fuse. The formation of fibrous vacuoles originates from the fibrous vacuole associated organelles (FVAOs). Thylakoid formation from concentric lamellar bodies (CLBs) seems to occur in plastids. Extremely hypertrophied dictyosomes with two tightly compressed and densely laminated mid-regions produce vesicles which contribute to enlargement of the fibrous vacuoles. During the second stage of tetraspore development striated vesicles are formed and starch granule formation increases. Mature tetraspores are characterized by numerous cored vesicles and abundant starch granules. Plastids have a fully developed system of internal thylakoids, and cleavage is usually complete at this stage. Mature tetraspores are surrounded by a bi-layered wall and the tetrasporangial wall. Unbranched, tubular structures connecting the plasmalemma with the peripheral sheets of ER are possibly involved in wall deformation. A distinct blebbing nuclear envelope appears to sequester vesicles into the cytoplasm.     

Reproductive dynamics of the sea urchin Paracentrotus lividus on the Galicia coast (NW Spain): effects of habitat and population density

We studied the spatial variability in the size at first maturity and the reproductive cycle of Paracentrotus lividus in Galicia, contributing key information for the exploitation and management of this resource. The size at maturity varied between 20.4 (±1.2 SE) mm and 27.9 ± 1.2 mm and was smaller in areas of low population density where sea urchins do not form patches. Using a nonlinear model, we analysed the effect of depth, body size, sex and population density on the temporal pattern of the gonad index. The maximum and minimum indices were obtained at 4 m depth in the months before and after the spring spawning, respectively. The depth also affected the cycle phase, and the sea urchins at 4 m depth spawned 9.4 ± 3.0 days later than the sea urchins at 8 m depth and 20.5 ± 3.0 days later than those at 12 m depth. Moreover, the sea urchins living in patches showed a slight increase in gonad size as a consequence of the better-quality habitat. This shows that there is no intraspecific competition in this area despite the high population densities reached (18.5 kg m^?2).     

High-temperature tolerance of photosynthesis in the red alga Chondrus crispus

Chondrus crispus (Stackhouse) is a perennial red seaweed, common in intertidal and shallow sublittoral communities throughout the North Atlantic Ocean. In the intertidal zone, C. crispus may experience rapid temperature changes of 10 to 20C° during a single immerison-emerision cycle, and may be exposed to temperatures that exceed the thermal limits for long-term survival. C. crispus collected year-round at Long Cove Point, Chamberlain, Maine, USA, during 1989 and 1990, underwent phenotypic acclimation to growth temperature in the laboratory. This phenotypic acclimation enhanced its ability to withstand brief exposure to extreme temperature. Plants grown at summer seawater temperature (20°C) were able to maintain constant rates of lightsaturated photosynthesis at 30°C for 9 h. In contrast, light-saturated photosynthetic rates of plants grown at winter seawater temperature (5°C) declined rapidly following exposure to 30°C, reached 20 to 25% of initial values within 10 min, and then remained constant at this level for 9 h. The degree of inhibition of photosynthesis at 30°C was also dependent upon light intensity. Inhibition was greatest in plants exposed to 30°C in darkness or high light (600 mol photons m^-2s^-1) than in plants maintained under moderate light levels (70 to 100 mol photons m^-2s^-1). Photosynthesis of 20°C-acclimated plants was inhibited by exposure to 30°C in darkness or high light, but the degree of inhibition was less than that exhibited by 5°C-grown plants. Not only was light-saturated photosynthesis of 20°C plants less severely inhibited by exposure to 30°C than that of 5°C plants, but the former also recovered faster when they were returned to growth conditions. The mechanistic basis of this acclimation to growth temperature is not clear. Our results indicate that there were no differences between 5 and 20°C-grown plants in the thermal stability of respiration, electron transport associated with Photosystems I or II, Rubisco or energy transfer between the phycobilisomes and Photosystem II. Overall, our results suggest that phenotypic acclimation to seawater temperature allows plants to tolerate higher temperatures, and may play an important role in the success of C. crispus in the intertidal environment.