Spatial variation in the recruitment of the intertidal barnacles Chthamalus montagui Southward and Chthamalus stellatus (Poli) (Crustacea: Cirripedia) over an European scale

Spatial variation in the recruitment of the intertidal barnacles Chthamalus montagui and Chthamalus stellatus was examined over an European scale. The study was carried out using standardised protocols at a series of locations. The five locations chosen (SW Ireland, NW Spain, SW Portugal and NW and NE Italy) span a large part of the range of these species in Europe. The spatial scales were location (hundreds of kilometres) and shore (thousands of metres).Estimates of total cumulative recruitment (cyprids and metamorphs) summed over the year (April 1997 to March 1998) showed substantial variation between locations which was dependent on the species. Recruitment was highest in SW Portugal for C. montagui and in SW Ireland and NW Spain for C. stellatus. Overall recruitment of C. montagui was higher than that of C. stellatus at all locations except SW Ireland, where recruitment of the two species was not significantly different. There were significant differences among shores in each location.The recruitment period of both species varied with location, with recruitment beginning earlier further south. In general, recruitment of C. montagui and C. stellatus was recorded in 8 months in NW Spain and NE Italy, while only in 7 months in SW Ireland. Recruitment of C. montagui occurred in 10 months in SW Portugal, but no recruits of C. stellatus were found. In all locations there was at least one distinct peak of recruitment. In SW Ireland both species showed only one peak of recruitment, a month after initiation. At the more southerly Atlantic locations, as well as in the Mediterranean, two unequal peaks of recruitment were generally seen. During recruit census, the number of cyprids, in comparison to metamorphs, found at any location was very low. In SW Ireland and NW Spain cyprids of both species were found, while in SW Portugal and in the Mediterranean, only cyprids of C. montagui were found.     

Patterns of adult abundance in Chthamalus stellatus (Poli) and C. montagui Southward (Crustacea: Cirripedia) emerge during late recruitment

The aim of this study was to investigate when adult distribution patterns are established in the barnacles Chthamalus stellatus and C. montagui. Adult ‘zones’ were identified by analysing field counts of both species at mid and upper shore heights. Monthly collections of cyprids, < 1 month old metamorphs and recruits (all metamorphosed individuals older than approximately 1 month) were made for C. stellatus and C. montagui in natural barnacle beds at six shores in SW Ireland. This was carried out over one year in 1996/1997, using a hierarchical sampling design. Abundance of total recruits (0-3 months old) was compared between adult zones after the main settlement season had ended. In addition, scales of variability in 0-3 month recruitment into adult zones were compared between the species at two scales: shores (1000s of metres) and sites within shores (10s of metres). Older recruits of each species, up to 11 months of age, were also compared between adult zones.The majority of settlement (measured as attached cyprids) occurred between August and October 1996. In October, there was no effect of adult zone on the abundance of total (0-3 month) recruitment up to that point in either species. Despite this homogeneity in recruitment between adult zones, significant spatial variation was found in 0-3 month recruits of both species at both of the scales examined. In C. stellatus the amount of variation associated with the larger scale (shore) was more than twice that of sites or of the residual variation (replicates within sites). 0-3 month recruitment in C. montagui was also most variable at the scale of shores but the residual variability (between replicates within site) was of similar magnitude to that of shores. Variability in 0-3 month C. montagui recruitment was relatively low at the scale of sites.There was a small but consistent input of recruits to adult zones over 9 months of the year, complicating the assessment of when adult patterns were set-up in these species. By June 1997, characteristic patterns of adult dominance had been established at all shores. Settlement had completely ceased by this time and individual barnacles were potentially 11 months old. Neither settlement nor early recruitment are significant in determining adult zonation patterns in these species. Instead, differential mortality patterns in individuals up to the age of 11 months are implicated in determining patterns of distribution of both species.     

Settlement patterns of Chthamalus spp. at Praia da Oliveirinha (SW Portugal)

Recruitment of Chthamalus spp. is intense during spring and summer but the number of settled cypris larvae is very low when compared to the high number of Chthamalus spp. metamorphs. In the summer of 1997 at Praia da Oliveirinha (SW Portugal), two hypotheses were tested: 1) the cypris larvae of Chthamalus spp. metamorphose in one tidal cycle; and 2) the settlement of Chthamalus spp. is higher during diurnal high tide compared with nocturnal high tide. The results indicate that cypris larvae of Chthamalus spp. can metamorphose in one tidal cycle. The hypothesis of higher settlement during diurnal high tide could not be tested at the mid and upper levels of C. montagui distribution due to a significative heterogeneity of variances. At the lower level, the results support this hypothesis. In spite of these data having been collected on a single shore and on a few sampling dates, these results suggest that more studies using different spatial and temporal scales are needed to see if this pattern is general.     

Distribution and abundance of co-occurring chthamalid barnacles Chthamalus montagui and Chthamalus stellatus (Crustacea,Cirripedia) on the southwest coast of Portugal

Two co-occurring chthamalid barnacle species occur on the rocky shores of continental Portugal: Chthamalus stellatus (Poli) and Chthamalus montaguiSouthward. In the present study, patterns of distribution and abundance (density and percentage cover), both vertically (tidal level) and horizontally (wave action), were studied for each species on headlands (more wave action) and not on headlands (less wave action) and at two spatial scales (shore and site) and three tidal levels (low, mid and upper). Chthamalus montagui was significantly more abundant than C. stellatus in both degrees of wave action and at all tidal levels. Despite this great difference in abundance and considering each species individually, C. montagui was more abundant at mid tide-level, while C. stellatus was more abundant at the low tide-level, and C. montagui was less abundant on headlands, while C. stellatus was more abundant on headlands. Small-scale variability (between sites, tens of meters) of abundance of each species was detected, while differences on a larger scale (between shores, tens of kilometres) were not significant.     

Effect of rock type on the recruitment and early mortality of the barnacle Chthamalus montagui

Discontinuities in distribution of sessile species due to changes in available habitat have rarely been investigated. In the English Channel, soft sedimentary rocks including chalk could potentially present a barrier to eastward range extension of the southern barnacle Chthamalus montagui. To test the effect of rock type on recruitment and mortality, prepared settlement tiles of four calcareous rocks that form important platforms close to existing limits of distribution were fixed to the shore at a site in south-west England, known to have consistently high larval settlement. Prior to fixation, the roughness parameter “R_a” and Potential Settlement Sites (PSS) index was measured. Recruitment was monitored photographically on four occasions during the settlement season and subsequent mortality for 7 months after the settlement season. By the end of the settlement season, recruitment on the hard Kimmeridge Cementstone was significantly less than on the other three rock types and attributed to low surface roughness and fewest Potential Settlement Sites (PSS), yet only 28% of variance could be attributed to PSS. Post-recruitment mortality was more variable, however after 7 months there were significant differences between rock types. Simultaneous surveys of post-recruitment mortality in natural populations showed that although recruitment on chalk can potentially be high, survivorship was relatively low. Thus rock type could be influential in setting species geographical limits.     

The vertical distribution of Chthamalus montagui and Chthamalus stellatus (Crustacea,Cirripedia) in two areas of the NW Mediterranean Sea

The Mediterranean Sea is characterised by a small tidal range (0.3–1 m). Despite this, intertidal communities are well established and their upper limits often extend above mean high water level. Organisms living in the intertidal region and in the supralittoral zone rely on both tides and wave action to perform their biological functions. Lack of food, desiccation and predation are common stresses in such a harsh environment. The present study deals with the vertical distribution of two species of intertidal barnacles, Chthamalus montagui Southward and Chthamalus stellatus (Poli), which are the main constituents of the barnacle belt along Mediterranean rocky shores. Previous work, carried out in the Atlantic, showed that where the distribution ranges of the two Chthamalus species overlap, C. montagui is more common in the upper barnacle zone while C. stellatus is dominant lower down. The main aims of our study are: (1) to establish if there is a relationship between position and extension of the barnacle belt on the shore and tidal range and/or wave exposure, (2) to test the hypothesis that in the study areas C. montagui is more abundant than C. stellatus high on the shore, and that the pattern is reversed lower down. Barnacle populations were monitored in summer 1998 in the Gulf of Genoa (Ligurian Sea) and in the Gulf of Trieste (North-Adriatic Sea). The two areas differ in tidal range and hydrodynamism, the former presenting quite strong wave action and a tidal range of 30 cm, the latter having limited wave action and 1 m tidal range. Three shores were randomly selected in each gulf and two transects on each shore. Counts of barnacles in 10 ^* 10 cm quadrats were done at different shore heights along each transect. The data was subjected to analysis of variance. Results showed that a more pronounced hydrodynamic regime corresponded to a shift of the barnacle belt towards the higher shore (Gulf of Genoa), while in more sheltered areas (Gulf of Trieste), the barnacle distribution was confined to the intertidal region. The relative spatial distribution of C. montagui and C. stellatus within the barnacle belt varied locally, even between transects on the same shore, and this obscured the distribution pattern along the vertical gradient. Nevertheless, it was still possible to conclude that at mid and high shore in Genoa, C. stellatus was more abundant than C. montagui, while in Trieste the pattern was reversed.     

Studies in the biochemistry of cirripede eggs. VII. Changes in the general biochemical composition during development of Chthamalus dentatus Krauss and Octomeris angulosa Sowerby

The carbohydrate, protein, total lipid, RNA, and DNA have been determined at four stages during the embryonic development in two chthamalids, Chthamalus dentatus Krauss and Octomeris angulosa Sowerby, from the South African coast. These values were compared with those of some cirripedes from the northern hemisphere. There is a relatively high utilization of lipids during the development as was previously found in Chthamalus montagui Southward. The relative volume specific energy content is similar to other cirripedes, but clearly higher than that of boreo-arctic balanids. The energy loss in C. dentatus is 54.4% of the initial energy content and that of Octomeris angulosa is 39.4%. This is lower than that found in Chthamalus montagui, but higher than that of all other cirripedes studied and especially the boreo-arctic species. The possibility of geographical significance of these differences is discussed.     

Chthamalus stellatus (Poli) und C. depressus (Poli) in der adria

A study has been made of the ecology of Chthamalus stellatus (Poli) and C. depressus (Poli) in the region of Rovinj (Yugoslavia). The distribution has been examined at several localities of different habitat conditions particularly with respect to wave action.     

Temporal scales of variation in settlement and recruitment of the mussel Perna perna (Linnaeus, 1758)

Population dynamics of many intertidal organisms are strongly affected by the abundance and distribution of larvae arriving on the shore. In particular, not only absolute numbers of settlers but also the degree of synchronisation of settlement can have a strong influence on whether density-dependent or density-independent processes shape adult shape populations. Temporal variation in rates of settlement and recruitment of the mussel Perna perna on the south coast of South Africa was investigated using a nested spatial design at different temporal scales. Variability in settlement at spring tides was examined at two temporal scales: lunar (to investigate the effect of state of the moon on settlement) and tidal (to investigate the influence of state of the tide on mussel settlement). Recruitment over neap tides was examined at one temporal scale, fortnight (to investigate the effect of date on mussel recruitment).Strong temporal variation was evident for both settlement and recruitment, but not at all time scales. Distinct peaks of settler/recruit abundance were observed during the lunar and neap tide studies. Recruitment intensity differed over the course of the year, and pulsing of recruitment was generally synchronised among locations. However, the strength of pulsing differed dramatically among locations, giving a significant interaction between fortnight and location. The finest temporal scale, investigated in the tidal study, did not reveal a significant effect of the state of the tide on settlement. The state of the moon (new or full) was not significant as a main factor (p = 0.052), although generally more settlers arrived on the shore during new moon. Phase of the moon appeared to have an effect on settler abundances, but only when and where densities were high.     

Further observations on the ecology of Chthamalus depressus (Poli)

An account is given of the forms of Chthamalus depressus (Poli). An extreme hypobiotic form common in caves is described; it is shown that all forms may be found in very restricted localities (even on a single boulder) according to different micro-habitats. Some biometrical data on the species and regressions of the several variables are given; they indicate that thickness tends to increase with exposure.The effect of exposure on growth-form is considered and compared with similar data on the laying down of the shell in molluscs. Thickening of the shell is believed to be due to withdrawal of the mantle tissue under wave action. The effect of light on the penetration of algae is discussed; animals growing in darkness have no endolithic algae. Erosion is considered to be due to mechanical forces acting on shells much weakened by endolithic algae.The changes on transplantation to Scotland have been observed, and measurements of the growth rate made; growth is slow, but somewhat greater under conditions of total immersion.The reproductive and moulting cycles, fertility, and general behaviour have been determined and the results compared with similar data on C. stellatus (Poli).The results are discussed in relation to the ecology of C. depressus and, in particular, relative to possible competition with C. stellatus.     

A histological and scanning electron microscope study of the formation of the wall plates in Chthamalus depressus (Poli)

Because of the small amount of pigmentation the difficulties associated with earlier histological work on Chthamalus stellatus (Poli) are absent in extreme hypobiotic C. depressus (Poli). The formation of the wall plates has been investigated by normal histological techniques and supported by scanning electron microscopy. The wall plates are covered by epicuticle which in its continuity resembles that of Acasta spongites; the epicuticle is strongly ribbed and the plate has more or less regularly spaced, volcano-like outgrowths. The various cell-types and the part they play in the expansion of the basis and growth of the wall plate are described. A series of ‘bridging’ cells are present and lie between the lower part of the last completely formed ‘scale’ and the basal cells. Growth is considered from the evolutionary point of view and in relation to the forms assumed under natural conditions, in particular to the capacity of the animal to adapt to changes in the rock surface.     

Chemotaxonomy of Hypericum genus from Portugal: Geographical distribution and essential oils composition of Hypericum perfoliatum, Hypericum humifusum, Hypericum linarifolium and Hypericum pulchrum

The geographical distribution and analysis of the essential oils of species from three sections of Hypericum L. (Guttiferae/Clusiaceae/Hypericaceae) from Portugal are presented. Hypericum perfoliatum (section Drosocarpium) grows wild in the centre and south of Portugal; Hypericum humifusum and Hypericum linarifolium are both from section Oligostema, the former occurring throughout the country, while the second is distributed mainly in the north and centre; Hypericum pulchrum (section Taeniocarpium) is confined to the littoral north of Portugal. The essential oils were obtained by distillation–extraction, hydrodistillation and distillation in a modified Marcusson apparatus from the dried aerial parts of the different populations and were analysed by GC and GC–MS. Monoterpene hydrocarbons constituted the main fraction in all oils (43–69%, 53–85%, 28–45% and 48–65% for H. perfoliatum, H. humifusum, H. linarifolium and H. pulchrum, respectively). Sesquiterpene hydrocarbons (2–13%, 6–18%, 21–27% and 16–18%, respectively) and a third fraction of non-terpenic compounds (20–29%, 3–16%, 2–14% and 5–11%, respectively) from the four species attained relatively high amounts in all oils. Within each species, no major differences were detected in the essential oil composition, despite the fact that different locations, phenological phases and extraction methodologies were used. Notwithstanding the dominance of α-pinene in all four species' oils, cluster and principal components analysis on the identified components showed that the range of α-pinene, β-pinene and n-nonane supported a separation of the four species. The essential oil composition of the four species showed some qualitative resemblances, which correlate well with the taxonomical classification based on morphological characters.     

Diving behaviour of dugongs, Dugong dugon

The diving behaviour of 15 dugongs (Dugong dugon) was documented using time-depth recorders (TDRs), which logged a total of 39,507 dives. The TDRs were deployed on dugongs caught at three study sites in northern Australia: Shark Bay, the Gulf of Carpentaria and Shoalwater Bay. The average time for which the dive data were collected per dugong was 10.4±1.1 (S.E.) days. Overall, these dugongs spent 47% of their daily activities within 1.5 m of the sea surface and 72% less than 3 m from the sea surface. Their mean maximum dive depth was 4.8±0.4 m (S.E.), mean dive duration was 2.7±0.17 min and the number of dives per hour averaged 11.8±1.2. The maximum dive depth recorded was 20.5 m; the maximum dive time in water >1.5 m deep was 12.3 min. The effects of dugong sex, location (study site), time of day and tidal cycle on diving rates (dives per hour), mean maximum dive depths, durations of dives, and time spent ≤1.5 m from the surface were investigated using weighted split-plot analysis of variance. The dugongs exhibited substantial interindividual variation in all dive parameters. The interaction between location and time of day was significant for diving rates, mean maximum dive depths and time spent within 1.5 m of the surface. In all these cases, there was substantial variation among individuals within locations among times of day. Thus, it was the variation among individuals that dominated all other effects. Dives were categorised into five types based on the shape of the time-depth profile. Of these, 67% of dives were interpreted as feeding dives (square and U-shaped), 8% as exploratory dives (V-shaped), 22% as travelling dives (shallow-erratic) and 3% as shallow resting dives. There was systematic variation in the distribution of dive types among the factors examined. Most of this variation was among individuals, but this differed across both time of day and tidal state. Not surprisingly, there was a positive relationship between dive duration and depth and a negative relationship between the number of dives per hour and the time spent within 1.5 m of the surface after a dive.     

Predator-prey interaction between hatchery-reared Japanese flounder juvenile, Paralichthysolivaceus, and sandy shore crab, Matutalunaris: daily rhythms, anti-predator conditioning and starvation

Predator-prey interaction between sandy shore crab, Matuta lunaris (Forskål, 1775), and juvenile Japanese flounder, Paralichthys olivaceus (Temminck et Schlegel), was investigated under controlled laboratory conditions. Possibility of training and conditioning hatchery-reared flounder to avoid predators was also examined. Crabs took over 75% of their daily ration at night when they were given access to prey 24 h a day. Large (64.8±5.4 g)- and medium (30.68±3.33 g)-sized crabs ate ca. 5.5±1.45 and 3.9±1.99 individuals of flounder (TL=4.96±0.23 cm) a day, respectively. When flounder juveniles that have experienced predation pressure by crabs encountered predators again, they exhibited better survival compared to the naive fish. Flounder juveniles were also conditioned either using small and, thus, benign predators, or large crabs over fence. The conditioned fish with either method were better able to avoid capture by crabs than naive fish, revealing that learning process should play an important role in their predator avoidance. Anti-predator performance was also compared between starved and fed flounder juveniles. Fed fish were rarely eaten by predators after 3 h of exposure, whereas starved fish continued to be eaten. Our results suggest that stock-enhancement program of Japanese flounder can be improved by applying proper feeding protocol and conditioning to avoid predators prior to release. Present research supports the idea that behavioural and ecological consideration for the target species is indispensable for the success of stock enhancement.     

The interplay of substrate nature and biofilm formation in regulating Balanus amphitrite Darwin, 1854 larval settlement

The settlement of marine larvae is influenced by a wide range of physical and biological factors. It is still poorly known how the nature of substrate and the biofilm can interact in regulating settlement patterns of invertebrate larvae. Here we use laboratory experiments focused on settlement behaviour of the barnacle Balanus amphitrite. The aim of this work is to understand whether: (i) the nature of substratum can affect biofilm formation and its structure, (ii) the nature of substratum can affect B. amphitrite larval settlement, (iii) the age of the biofilms and the nature of substrate can interact in influencing larval settlement.Four kinds of substrata (marble, quartz, glass, and cembonit) were biofilmed under laboratory conditions for 5, 10 and 20 days at the temperature of 28 °C. Settlement response was investigated with 5-day-old cyprids. Biofilms were quantitatively and qualitatively analysed by scanning electron microscopy. The settlement of B. amphitrite larvae significantly differed among substrata; also, the patterns of development of biofilm assemblages changed with substrate. In addition, the larval attractiveness of different substrates tends to disappear with biofilm age.     

Physiological activity of Porphyra in relation to eulittoral zonation

Eulittoral seaweeds at different tidal elevations are exposed to various frequencies and durations of emergence. Their physiological activities (e.g. nutrient uptake) may be affected by water loss during emersion. We used three Porphyra species from different tidal elevations to test whether species at different vertical elevations on the shore respond differently to the increasingly non-marine environment, in terms of their physiological activities including nutrient uptake, tissue carbon, nitrogen and phycoerythrin contents. Simulated tidal cycles produced water losses of 0%, 40 ± 10% and 90 ± 5% tissue water. Emersion was stressful for all species regardless of their habitat. It was more stressful to nitrate and phosphate uptake for the sublittoral species P. yezoensis than eulittoral species, P. umbilicalis and P. leucosticta. Interestingly, tissue N for thalli that had been emerged and then re-submerged was significantly higher than those of continuously submerged individuals. During exposure, tissue N contents of all species declined but recovered quickly (e.g. within 30 min) after re-submergence. This result suggests that emersion-induced N release may constitute an undescribed biogeochemical pathway linking marine, terrestrial, and atmospheric N reservoirs.     

Fine-scale spatial and temporal variation in settlement of the intertidal mussel Perna perna indicates differential hydrodynamic delivery of larvae to the shore

Scales of spatial and temporal variation in the settlement of early and late plantigrades of the mussel Perna perna to artificial substrata were measured on the south coast of South Africa. One study examined daily settlement over one month at three sites of similar tidal height and aspect. The sites were separated by 100′s of m with 5 replicated artificial settlement substrata approximately 1 m apart within each site. Early (< 0.5 mm) and large late plantigrades (1 - 3.5 mm) dominated samples with few individuals of 0.5-1 mm. Settler abundance showed clear peaks, synchronised among sites and apparently following spring tides, though the relationship between tide and settlement was not significant. Two-way ANOVA indicated significant spatial variation, which varied with time, at the 100 m-scale among sites. A second study investigated the local effects of substratum aspect. Seaward facing surfaces had consistently lower settlement (but higher adult cover) than horizontal and landward facing surfaces, this effect was significant for large late plantigrades. This suggests that either juveniles migrate after settlement, or that post-settlement mortality differs markedly among aspects. The high degree of temporal variation at the scale of days and weeks was expected, but the results also suggest a degree of pulsing in settlement, with maximum intensities around spring tide. A previous study of nearshore waters indicated a common pool of larvae at scales of 100 s m. Thus, consistent ranking of sites for all size classes of settlers indicates predictably differential hydrodynamic delivery of larvae to sites separated by 100 s m. The effect of aspect on settlement highlights the importance of smaller scale hydrodynamics, suggesting that the stronger turbulence experienced by seaward facing surfaces may affect larval settlement negatively.     

Genetic structure and distribution of Gelidium elegans (Gelidiales,Rhodophyta) in Korea based on mitochondrial cox1 sequence data

Gelidium elegans Kützing is commonly found in Korea, China, and Japan, and is the economically most important agarophyte in the northwest Pacific. To assess the genetic structure of the Korean species, we analyzed 1200 base pairs of the mitochondrial cox1 gene from 272 individuals collected from 36 locations. A total of 34 haplotypes were found, most of which were unique, including 27 (79%) ‘private’ haplotypes. The nucleotide and haplotype diversities of cox1 within G. elegans were 0.711 ± 0.028 (H) and 0.00736 ± 0.00038 (π), respectively. The distribution of cox1 haplotypes, pairwise F_ST values, results of neutrality tests, AMOVA, and mismatch distribution revealed the existence of a deep genetic break between central Pacific Japan and all the other locations, corresponding to the surface seawater current patterns as well as the genetic signature of potential demographic expansion.     

Recruitment, early survival and growth of the Mediterranean red coral Corallium rubrum (L 1758), a 4-year study

Recruitment, early survival and growth rates of the precious Mediterranean red coral Corallium rubrum (L 1758) are poorly known. We examined these life history traits by means of artificial long-term settlement plates. Eighteen marble tiles placed off the coast of Leghorn (Tuscany, Italy) at two depths (25 and 35 m) were photographed monthly over the 4-year period from 1998 to 2002. Overall, 864 transparencies were examined to follow the individual life histories of red coral colonies belonging to four successive cohorts. Red coral planulae settled on tiles each year between July and September. Overall, 388 settlers colonized the tiles (244 at 25 m and 144 at 35 m), and their respective densities varied between 12.37±6.1 and 2.75±2.4 dm⁻². Heavy mortality affected these colonies (−24.35±9.12 colonies % y⁻¹), but, after 4 years, the tiles still harboured a persistent population (19±4.97 and 9.75±2.87 colonies dm⁻², respectively, at 25 and 35 m) with positive net recruitment rates. Only in 1999 did the net recruitment rate show a negative trend, although only at the shallower depth. At the same time (late summer 1999), a thermal anomaly affected several epibenthic communities in the Ligurian Sea. After 4 years, the tiles were removed, and the colonies that settled on them were measured. The average annual growth rate of colonies was low (0.62±0.19 mm y⁻¹ in diameter), and a marked reduction in growth with age was observed. Our findings suggest that the populations of this slow-growing long-lived octocoral exhibit a high capacity for colonization and seem to be quite resilient to environmental variability.     

Nutritional value of the cryptophyte Rhodomonas lens for Artemia sp.

Juvenile or adult Artemia sp. are often used as live prey for the rearing of early life stages of some crustacean, fish and cephalopod species. The improvements of both Artemia growth and its biochemical composition are key issues for the suitable use of Artemia biomass in these rearing processes. In this study we evaluated the growth and survival rates of Artemia fed with the cryptophyte Rhodomonas lens in comparison with different microalgal species commonly used in aquaculture: the prasinophyte Tetraselmis suecica, the prymnesiophyte Isochrysis galbana Parke, and the eustigmatophyte Nannochloropsis gaditana. Microalgae were cultured semi-continuously in nutrient saturated conditions and with a daily renewal rate of 30% of the volume of cultures, to obtain biomass of controlled and optimized composition. Considerable differences in Artemia growth were observed, as well as in the survival rate. At day 8 of rearing, Artemia fed R. lens had the highest length (4.9 ±0.6 mm, P < 0.001), followed by individuals fed T. suecica (4.2 ± 0.7 mm), I. galbana (3.6 ± 0.7 mm) and finally those fed N. gaditana (1.5 ± 0.2 mm). The survival rate of Artemia fed N. gaditana (18 ± 3%) was much lower (P < 0.001) than values found for the remaining groups (69 to 88%). The growth rate of Artemia obtained with R. lens was in general much higher than with other microalgal diets previously reported in the literature. The higher protein content of R. lens could explain the higher growth obtained with this species, but differences of Artemia growth with the different diets could not be explained solely on the basis of the gross composition of microalgae. Factors such as cell size and digestibility all seem to contribute to the results observed. Another trial was carried out to investigate differences in Artemia growth and on its biochemical composition when fed the best two diets: R. lens or T. suecica. The fatty acid (FA) and total amino acid (AA) composition of both microalgal species and the composition of Artemia were assessed as well. As found in the first experiment individuals fed R. lens (group ARHO) grew faster than those fed T. suecica (group ATET), attaining 3.6 ± 0.3 mm and 3.2 ± 0.4 mm (P < 0.001), respectively, after 5 days of rearing. The much higher AA content obtained in R. lens may be on the basis of the higher growth obtained with this species. Protein and carbohydrate levels in Artemia juveniles were very similar in both groups (64-68% of dry weight, and 8-10%, respectively). Lipid was slightly lower in ARHO (12%) than in ATET (15%, P < 0.01). Regarding the FA composition, juveniles from group ARHO contained higher levels of eicosapentaenoic acid (EPA, 6.2%) than juveniles from ATET (4.1%, P < 0.01), whereas docosahexaenoic acid (DHA) was only found in juveniles from ARHO (1.1%). Taking into account that the daily productivity of R. lens culture was higher than, or at least equal, the remaining microalgal species this cryptophyte is confirmed as an excellent diet to optimize the growth of Artemia, as well as to improve its biochemical composition.