Nucleic acid and protein levels in strobilating polyps of Chrysaora quinquecirrha and Aurelia aurita

Levels of DNA, RNA, and protein were measured in scyphistomae of the scyphozoans Aurelia aurita and Chrysaora quinquecirrha during strobilation. In synchronously developing populations of A. aurita, the amount of DNA per polyp increases 41 to 260% during strobilation, whereas RNA and protein remain relatively constant. The RNA/DNA ratio drops by about 50% during strobilation in both C. quinquecirrha and A. aurita, and protein/DNA decreases by 50% in A. aurita. Specific RNA reserves are probably not accumulated in advance of strobilation, since strobilation is blocked immediately in both species by 1 to 3 g/ml actinomycin D. The size and DNA content of polyps are usually increased by prolonged incubation at temperatures of 12° to 15°C, which facilitates strobilation; however, the RNA/DNA and protein/DNA ratios of such polyps are not significantly increased by the cold conditioning.Contribution No. 472 from the Virginia Institute of Marine Science.     

Carbon metabolism and strobilation in Cassiopea andromedea (Cnidaria: Scyphozoa): Significance of endosymbiotic dinoflagellates

Scyphopolyps and scyphomedusae of Cassiopea andromeda Forskål (Cnidaria, Scyphozoa) containing dinoflagellate endosymbionts (zooxanthellae) were investigated for rates and pathways of carbon fixation. Photosynthesis by the algae, accounting for 80 and 15 mol C h^-1 on a dry weight basis in medusae and polyps, respectively, by far exceeds dark incorporation of inorganic carbon by the intact association. Photosynthetic carbon fixation is operated via C₃ pathway of carbon reduction. DCMU-treatment (1×10^-6 M and 1×10^-5 M) completely inhibits light-dependent carbon assimilation. Major photosynthates presumably involved in a metabolite flow from algal symbionts to animal tissue are glycerol and glucose. A total of 5–10% net algal photosynthate appears to be seleased in vivo to the host. This is probably less than the energy supply ultimately required for the nutrition of the polyps and medusae. The presence of zooxanthellae proved to be indispensable for strobilation in the scyphopolyps. However, photosynthesis by algal symbionts as well as photosynthate release is obviously not essential for the initiation of ephyrae as is shown by DCMU-treatment, culture in continous darkness, and aposymbiotic controls. It is therefore concluded that strobilation is supported, but not triggered by algal photosynthetic activity. The induction of strobilation thus seems to depend on a more complex system of regulation.     

In vivo binding of a biologically active oligopeptide in vegetative buds of the scyphozoan Cassiopea andromeda: demonstration of receptor-mediated induction of metamorphosis

Vegetative buds of Cassiopea andromeda (Cnidaria, Scyphozoa) metamorphose into polyps in the presence of short synthetic peptides containing proline as the preterminal amino acid at the carboxyl terminus. In an in vivo assay, the binding of the biologically active hexapeptide ¹⁴C-dansyl-GPGGPA in buds was shown to be specific and saturable. Scatchard plot analysis of the specific binding data revealed a dissociation constant (K _D) of about 7 M. The total number of receptors was calculated to be approximately 1×10¹⁰ bud^-1 under saturation conditions. In correlation with the results of prior investigations, our finding of receptor-mediated induction of metamorphosis strongly supports the hypothesis that binding of biologically active peptides to receptors leads to initiation of phosphatidylinositol breakdown and activation of protein kinase C.     

Laboratory observations on the life history of Rhopilema verrilli (Scyphozoa: Rhizostomeae)

The life history of the scyphozoan Rhopilema verrilli is described from the planula to the young medusa stages. Planulae are retained within the gonadal tissue of the medusa until fully developed. On liberation, most planulae set and developed into small scyphistomae within 7 to 10 days. The scyphistoma differs from those of other described species in having an unusually large, clavate manubrium. The only means of asexual reproduction observed in the scyphistoma cultures involved the formation of podocysts. Strobilation was usually of the monodisc variety, although polydics strobilation was not infrequent. The process of strobilation was completed within 7 days at 20°C. Newly liberated ephyrae typically had 8 pairs of lappets, and 8 rhopalia. Ephyral development resembled that of the closely related rhizostome Rhizostoma pulmo. The cnidome of the planula and scyphistoma consisted of atrichous isorhizas (a atrichs) and microbasic heterotrichous euryteles, while that of the strobila and ephyra consisted of a atrichs, euryteles, and holotrichous haplonemesContribution No. 546 from the Virginia Institute of Marine Science, Gloucester Point, Virginia 23062, USA.     

The effect of light on strobilation in the Chesapeake Bay Sea Nettle Chrysaora quinquecirrha

Previous work (Loeb, 1972) showed that strobílation could be induced in Chrysaora quinquecirrha (Desor) by subjecting polyps to a period of chilling followed by warming. It is shown here, that the onset of strobilation and the rate at which this process occurs in a population of C. quinquecirrha polyps is positively related to the amount of light received during chilling and in the period following warming. The absence of light during either period delays the onset of strobilation. The intensity of coloration of C. quinquecirrha polyps before strobilation appears to be correlated with the amount of light to which they have been exposed during chilling.     

Bud formation and metamorphosis inCassiopea andromeda (Cnidaria: Scyphozoa): A developmental and ultrastructural study

Asexual reproduction by formation of swimming buds which metamorphose directly into polyps plays a most important role in the propagation ofCassiopea andromeda (Cnidaria: Scyphozoa). (C. andromeda polyps, originally supplied by the Löbbecke Museum and Aquarium Düsseldorf, FRG, were cultured in our laboratories.) We have defined five budding stages and investigated epithelial recruitment and dynamics during bud formation using intracellular vital stains. The region of cell recruitment was found to encircle the budding site asymmetrically. The aboral side contributing considerably less to the developing bud than the oral and lateral sides. Furthermore, it was found that the epithelial flow involved in bud formation is part of a permanent apico-basal displacement of ectodermal cells. Light and electronmicroscopic investigations revealed that no drastic changes occur at the cellular level, neither in the ectoderm nor in the endoderm which both participate in bud formation. Scanning and transmissionelectron microscopic investigations of the swimming bud revealed that the ectoderm is composed of three, and the endoderm of two, cell types. Nerve elements have been detected near the mesoglea between both ecto- and endodermal cells. Amoebocytes are regularly found either at the basis of epidermal cells or within the mesoglea, whereas symbionts are located in the endoderm. Buds induced to metamorphose by a bacterial-inducing factor were used to investigate morphological and ultrastructural changes occurring during metamorphosis and scyphistoma morphogenesis. Metamorphosis starts with the settling of a bud, followed by the formation of the pedal disk in which desmocytes, as typical cnidarian adhesive structures, are differentiated. Metamorphosis is completed with the formation of the mouth and tentacles. Whereas metamorphosis of cnidarian planulae implies considerable changes at the cellular level, tissue remodeling processes prevail in bud metamorphosis ofC. andromeda.     

Accumulation of cadmium by Artemia salina

The relative importance of accumulation of cadmium by Artemia salina (L.) directly from solution and from ingested food has been studied at 3 cadmium concentrations (0.1, 1 and 10 ppm) under controlled experimental conditions. At each cadmium concentration, A. salina were exposed to cadmium in 4 ways; in solution; in solution in the presence of latex food particles; in solution with cadmium-rich Dunaliella tertiolecta as a food source; and to cadmium-rich D. tertiolecta alone. Net accumulation of cadmium by A. salina continued throughout 5 days exposure under all 4 conditions. When the brine shrimp were removed to cadmium-free conditions, their accumulated cadmium concentrations declined and levelled off to a stabilised plateau after 10 days. From consideration of these stabilised levels it was shown that at least 30% of cadmium accumulation directly from solution occurs via uptake through the alimentary tract. The ratio of cadmium accumulated from solution to cadmium accumulated from food was found to be 1:4.9, 1:6.7 and 1:1.1 at 0.1, 1 and 10 ppm Cd exposure, respectively. At lower cadmium exposures uptake from food is the major route for cadmium accumulation, but at higher exposures the cadmium-saturated food source displaced cadmium-rich water from the gut and therefore actually inhibited cadmium accumulation. This study, therefore, concludes that the food chain will be the major source of cadmium as long as the previous trophic level has the ability to accumulate the metal to such an extent as to make it more available to the consumer than by direct uptake from seawater.     

Effects of salinity on respiration and nitrogen excretion in two species of echinoderms

The 30-d survival limit of Eupentacta quinquesemita and Strongylocentrotus droebachiensis is 12–13 S. The activity coefficient (1 000/righting time in seconds) of stepwise acclimated sea urchins declined from 16.3 at 30 S to 3.5 at 15 S. Oxygen consumption rates (QO₂) of both species held at 30 S and 13°C were highest in June and lowest in December. During the summer, when environmental salinity is most variable in southeastern Alaska, the QO₂ of both species held at 30, 20 and 15 S varied directly with salinity. Perivisceral fluid PO₂ varied directly with acclimation salinity in sea urchins, but not in sea cucumbers. Perivisceral fluid oxygen content of acclimated sea urchins was significantly lower at 15 and 20 S than at 30 S due to reduced PO₂ and extracellular fluid volume at the lower salinities. The QO₂ of both species varied directly with ambient salinity during a 30-10-30. semidiurnal pattern of fluctuating salinity. No change occurred in the average QO₂ of either species over a 15-30-15. semidiurnal pattern of fluctuating salinity. Sea urchin perivisceral fluid PO₂ declined as ambient salinity fluctuated away from the acclimation salinity in both cycles and increased as ambient salinity returned to the acclimation salinity. Total nitrogen excretion of stepwise acclimated sea cucumbers declined significantly from 30 to 15 S, but there was no salinity effect on total nitrogen excretion in sea urchins. Ammonia excretion varied directly with salinity in stepwise acclimated sea cucumbers (67–96% of total nitrogen excreted), but there was no salinity effect on ammonia excretion (89–95% of total nitrogen excreted) of sea urchins. Urea excretion did not vary with salinity in sea cucumbers (2–4% of total nitrogen excreted) or sea urchins (2–9% of total nitrogen excreted). Primary amines varied inversely with salinity in sea cucumbers (2–30% of total nitrogen excreted), but did not vary with salinity in sea urchins (2–4% of total nitrogen excreted). The oxygen: nitrogen ratio of both species indicated that carbohydrate and/or lipid form the primary catabolic substrate. The O:N ratio did not vary as a function of salinity. Both species are more tolerant to reduced salinity than previously reported, however, rates of oxygen consumption and/or nitrogen excretion are modified by salinity as well as season.     

Life history and settlement preferences of the edible jellyfish Catostylus mosaicus (Scyphozoa: Rhizostomeae)

 The life history and settlement preferences of larvae of Catostylus mosaicus (Scyphozoa: Rhizostomeae) (Quoy and Gaimard, 1824) were investigated in New South Wales, Australia, over a 2 mo period beginning in November 1998. The life history consisted of an alternation between a sexual, medusoid stage and an asexual, polypoid stage, and was similar to that described for other rhizostomes. Planula larvae were brooded by the adults. Approximately 4 d after collection, larvae settled on a variety of substrata including wood, sandstone, shell, seagrass and glass, and metamorphosed into four-tentacled polyps. The number of tentacles increased and polyps strobilated when they had between 12 and 20 tentacles. Strobilation occurred within 15 d of settlement, but only polyps that settled on the concave surfaces of the shells strobilated. Both monodisk and polydisk strobilation was observed. Ephyrae were raised for one month and were observed developing oral arms. Polyps reproduced asexually via the formation of podocysts, by production of buds, and by partial fission. Received: 30 April 1999 / Accepted: 27 August 1999     

Sexual and asexual reproduction of Anthopleura dixoniana (Anthozoa: Actiniaria): periodicity and regulation

Reproduction of the sea anemone Anthopleura dixoniana (Haddon and Shackleton) from the high intertidal zone of southern Taiwan (120°41 E; 22°01N) was studied from April 1987 through March 1989. A. dixoniana spawns once a year, in July, and divides asexually by longitudinal fission throughout the year, with a peak in July. During the spawning season, sea anemones>3 mm pedal dise diameter can be sexed, and display a 1:1 sex ratio. Dividing sea anemones are significantly larger than non-dividing individuals, and increase in body size before fission. Under laboratory conditions, individuals kept at 28 C and fed had larger oocytes and a higher division rate than those kept at 18, 22, 25 or 32°C or starved. The division rate significantly influenced the oocyte diameter. The present study revealed for the first time, that a long photoperiod (14 h hight:10 h dark) significantly enhances the growth of oocytes in A. dixoniana under laboratory conditions.     

Derivation of the reduced life cycle of <Emphasis Type="Italic">Thecoscyphus zibrowii</Emphasis> Werner, 1984 (Cnidaria,Scyphozoa)

The species Thecoscyphus zibrowii Werner, 1984 has an exceptional life cycle, which lacks a medusa stage but develops an extraordinary structure (egg sac) for reproduction. Investigation of the life cycle, as well as anatomical and histological studies of the different developmental stages of T. zibrowii were performed to provide evidence for a possible homology of the egg sac with the medusa stage and to determine whether the reduced metagenesis of T. zibrowii is derived from strobilation. The egg sac showed several characteristics, which were compared to those of coronate medusae. The ectodermis of the egg sac had a plate-like appearance and was completely ciliated as is typical for coronate medusae. The number and the location of the gonads were similar to those of coronate medusae. The cnidocysts were significantly larger in the egg sac than in the polyp. A size difference of cnidocysts in the medusa and the polyp stage is known for several Coronatae. Characteristics of egg sac formation were compared to characteristics of strobilation. The formation of the early operculum was similar in T. zibrowii and N. eumedusoides. The constriction of egg sac and strobila occurred in the same mode and the gastric cavities of two egg sacs stayed in contact in a similar fashion to the gastric cavities of the strobila discs. The developmental zones of cnidoblasts of the egg sac and polyp were separated during the formation of the egg sac which showed a similar developmental gradient to a strobila. The existence of all of these consistent characteristics makes it very likely that the egg sac structure was homologous to a medusa. The species T. zibrowii would therefore be derived from a metagenetic ancestor. This species has reduced the medusa generation to the greatest extent within the Nausithoidae and has demonstrated thus far the endpoint of a regressive evolution of the medusa generation.     

Global phylogeography of<Emphasis Type="Italic"> Cassiopea</Emphasis> (Scyphozoa: Rhizostomeae): molecular evidence for cryptic species and multiple invasions of the Hawaiian Islands

The upside-down jellyfish Cassiopea is a globally distributed, semi-sessile, planktonically dispersed scyphomedusa. Cassiopea occurs in shallow, tropical inshore marine waters on sandy mudflats and is generally associated with mangrove-dominated habitats. Controversy over the taxonomy of upside-down jellyfishes precedes their introduction to the Hawaiian Islands during the Second World War, and persists today. Here we address the global phylogeography and molecular systematics of the three currently recognized species: Cassiopea andromeda, C. frondosa, and C. xamachana. Mitochondrial cytochrome c oxidase I (COI) sequences from Australia, Bermuda, Fiji, the Florida Keys, the Hawaiian Islands, Indonesia, Palau, Panama, Papua New Guinea, and the Red Sea were analyzed. Highly divergent COI haplotypes within the putative species C. andromeda (23.4% Kimura 2-parameter molecular divergence), and shared haplotypes among populations of two separate putative species, C. andromeda and C. xamachana from different ocean basins, suggest multiple anthropogenic introductions and systematic confusion. Two deeply divergent Oahu haplotypes (20.3%) from morphologically similar, geographically separate invasive populations indicate long-term (14–40 million years ago) reproductive isolation of phylogenetically distinct source populations and cryptic species. Data support at least two independent introductions to the Hawaiian Islands, one from the Indo-Pacific, another from the western Atlantic/Red Sea. Molecular phylogenetic results support six species: (1) C. frondosa, western Atlantic (2) C. andromeda, Red Sea/western Atlantic/Hawaiian Islands (3) C. ornata, Indonesia/Palau/Fiji (4) Cassiopea sp. 1, eastern Australia (5) Cassiopea sp. 2, Papua New Guinea and (6) Cassiopea sp. 3, Papua New Guinea/Hawaiian Islands.Communicated by P.W. Sammarco, Chauvin     

Influence of salinity and temperature on the oxygen consumption in young juveniles of the Indian prawn Penaeus indicus

Routine oxygen consumption of very young juveniles (0.1 g) of Penaeus indicus H. Milne Edwards was significantly influenced by ambient temperature and weight of the animal, but not by ambient salinity, when tested at salinities (7, 21, and 35) to which they had been long-term (over 10 days) acclimated. Standard oxygen consumption of young juvenile prawns (1 to 3 g), subjected to step-wise changes in ambient salinity, from sea water to low salinity waters (2 to 6), and measured after short-term (24 h) salinity acclimation at each step, was lowest at salinities where prawns such as those tested occur naturally (10 to 15). The metabolic rates do not appear to have a direct relation to the osmotic gradient, even when the influence of interfering activity is eliminated. It appears that factors other than osmotic gradient will have to be sought in order to explain the metabolic patterns of P. indicus in relation to salinity.     

The zooplankton of the inshore waters of Dar es Salaam (Tanzania,S. E. Africa) with observations on reactions to artificial light

From 18th December, 1968 to 5th January, 1970, zooplankton samples were taken in darkness and using artificial light in selected areas of the Dar es Salaam coast (Tanzania, S. E. Africa). Surface sea temperature was measured on most occasions, salinity for the first 7 months only. The neritic waters of Dar es Salaam experience a warm period during January to March and a cool period during July to September. The annual salinity cycle is not known. Thirtysix dark and 17 light zooplankton samples were analysed; where possible, organisms were identified to species, others to generic or higher taxonomic level. The principal taxa and their mean percentage proportions (figures in parentheses) in the dark samples were: Calanoida (49. 1), Larvacea (11. 9), Corycaeus spp. (6.4), Cypridina sinuosa (5.6), Oithona spp. (4.8), caridean larvae (4.0), Sagitta spp. (3.8), Euterpina (2.1), Lucifer (1.2), Oncea (1.2), calyptopis larvae (1.0), Hydromedusae (1.0), Euconchoecia chierchiae (1.0), Creseis acicula (1.0), brachyuran zoeae (0.8), Ctenophora (0.5), Mysidacea (0.5), fish eggs (0.5), postlarval bivalves (0.5), postlarval gastropods (0.5), Cumacea (0.1), Gammaridea (0.1) and Hyperiidea (0.1). Evadne tergestina and Thalia democratica abound in waters at certain times of the year only and then virtually disappear. The remaining groups were numerically unimportant most of the time. Almost every major group showed an annual cycle of abundance; greater numbers were recorded either for the entire or part of the period February to August, compared to the period September to November. From the end of January to early August, 1969, the average numbers per haul of total zooplankton were about three times greater than for the period mid-August to mid-November. During February-March and July-August, several oceanic indicators were observed together in the neritic waters. Artificial light induced the following changes in night zooplankton: Mysidacea, Leptochela sp., Hyperiidea, Cypridina sinuosa, brachyuran megalopae and fish larvae were attracted towards artificial light and aggregated densely under the lamp; Calanoida, Corycaeus spp., Macrosetella, Microsetella and Euterpina avoided regions of strong illumination and aggregated in dim-lit areas; Lucifer, Creseis acicula and postlarval gastropods were more abundant in dim-lit samples compared to dark hauls; caridean larvae, brachyuran zoeae and larvaceans were less abundant in high-intensity light samples compared to dark hauls on the same nights.This work was performed at the Department of Zoology, University of Dar es Salaam, Tanzania, S.E. Africa.     

Adaptations to osmotic stress in the fresh-water euryhaline teleost Tilapia mossambica. IV. Changes in blood glucose,liver glycogen and muscle glycogen levels

Some aspects of osmoregulation energetics have been studied in the euryhaline teleost Tilapia mossambica (Peters) acclimated to media of different salinities. In stress media (75 and 100% sea water) the blood glucose of the fish increases significantly, accompanied by a corresponding increase in oxygen consumption and cytochrome-oxidase activity, suggesting that oxidative degradation of blood glucose is the predominant energy source for osmotic work in these stress media. It is likely that the variations in the blood-glucose level as a function of acclimation to the heterosmotic media —except the natural fresh-water medium — are governed by the combined effects of salinity of the medium and blood-medium osmotic gradient, rather than by the effect of any one of them separately. Perhaps, metabolic homoeostasis is in operation in the natural fresh-water medium. Depletion of muscle glycogen at significant levels is noticed only in stress media. Presumably, there is an augmentation of oxidative metabolism with glycolysis to meet the exacting energy demands for heavy osmotic work in high-stress media. Prior acclimation to 75% sea water (24.375 S) facilitates subsequent acclimation to 100% sea water (32.50 S) with less energy cost —an instance of facilitation acclimation. Smaller individuals of T. mossambica osmoregulate with less energy expenditure than larger ones. Thus, smaller individuals are osmotically more efficient.     

The respiratory metabolism of Tilapia mossambica (Teleostei)

Tilapia mossambica (Teleostei) weighing 5 to 80 g were acclimated at 30°C to salinities of 0.4 (tap water), 12.5 (50% sea water) and 30.5 (100% sea water). Their respiration was measured at routine activity and the partial pressure of ambient oxygen gradually reduced from 250 to 50 mm Hg. Respiration is salinity-dependent; the proportionate ability to use oxygen in any one salinity is — above the critical pO₂ —the same in all experimental groups. This ability is a function of temperature and increases from 15° to 30°C, becoming temperature independent from 30° to 40°C as long as the pO₂ remains above 150 mm Hg. At 50 mm Hg pO₂, the limiting effect of oxygen causes a decrease in metabolic rate. This limiting effect is minimal in 80 g fish kept in an isotonic medium (12.5 S), allowing greater scope for activity and a higher rate of oxygen uptake.     

Ammonium enhancement of dark carbon fixation and nitrogen limitation in zooxanthellae symbiotic with the reef coralsMadracis mirabilis andMontastrea annularis

The nutrient status (limitation vs sufficiency) of dinoflagellates (zooxanthellae) symbiotic with reef corals in Bermuda was assessed in 1989 and 1990 by measuring the enhancement of dark carbon fixation with 20 M ammonium by isolated symbionts. A colony ofMadracis mirabilis was kept in the laboratory and fed daily or starved for one month. Symbionts from fed portions of the colony had ammonium-enhancement ratios (NH _4dark ⁺ ; SW_dark;SW=seawater without added ammonium) similar to those of the original field population (1.2 to 1.3). Ammonium-enhancement ratios increased with starvation of the host (x1.7) as did values forV _D:V _L [(ammonium dark rate-seawater dark rate): light rate in seawater]. Both parameters indicated decreasing nitrogen sufficiency of the algae when the host was not fed, but starvation appeared to affect these algae less than symbionts of sea anemones. Field samples of zooxanthellae fromM. mirabilis (Three Hill Shoals and Bailey's Bay Flats) yielded results similar to those for fed corals, but those taken from Bailey's Bay Flats in May 1990 yielded exceptionally high values for enhancement (>3) andV _D:V _L indicating pronounced nitrogen limitation at the time of sampling. We sampled zooxanthellae from populations ofMontastrea annularis at 8 m (Three Hill Shoals) and 24 m (Soldier's Point) depths. Enhancement andV _D:V _L values for zooxanthellae from the 8 m corals were density-dependent: symbionts from corals with normal symbiont densities displayed the most nitrogen limitation (enhancement values=1.4 to 2.0), while those from bleached corals with lower density exhibited enhancement andV _D:V _L values typical of nitrogen-sufficient algae. Symbionts isolated from the 25 m corals yielded the highest values, and appeared to exhibit the least nitrogen-sufficiency for this species.     

Grazing and ingestion rates of nauplii,copepodids and adults of the marine planktonic copepod Calanus helgolandicus

The average grazing and ingestion rates of all stages of the marine planktonic copepod Calanus helgolandicus (Calanoida) from nauplius stage IV to adults were measured experimentally at 15°C in agitated cultures. The chain-forming diatom Lauderia borealis and the unarmoured dinoflagellate Gymnodinium splendens were offered as food. The food concentrations were close to natural conditions and ranged from 36 to 101 g of organic carbon per liter. The medium body weights expressed in g of organic carbon of almost all larval stages raised at 49 g C/1 were identical with the weight of the same stages caught in the Pacific Ocean off La Jolla, California, USA. In a log-log system, grazing and ingestion rates increased almost linearly with increasing body weight. Grazing rates ranged from 4 to 21 ml/day/nauplius stage IV to 286 ml to 773 ml/day/female. Ingestion rates increased from 0.2 g to 0.8 g C/day/nauplius stage IV to 18 g to 69 g C/day/female. Grazing and ingestion rates per unit body weight decreased gradually with increasing body weight. The daily ingested amount of food decreased from 292 to 481% of the body weight (g C) of nauplius stage V to 28–85% of the body weight of adult females. Grazing and ingestion performances of all stages increased with increasing particle size. Grazing rates decreased and ingestion rates increased with increasing food concentrations. The published data on food intake of the different age groups of C. helgolandicus show that the young stages of herbivorous planktonic copepods can play a major part in the consumption of phytoplankton in the sea due to their high grazing and ingestion rates.     

Acclimation and tolerance of Artemia salina to copper salts

The brine shrimp Artemia salina L. was acclimated in sea water with cupric chloride, acetate, carbonate, and sulphate, each at concentrations of 0.1, 0.05 and 0.025 ppm Cu⁺⁺, together with sea water controls. Growth inhibition was observed in all four compounds, generally in direct relationship to the concentration. It was least in sulphate, and increased progressively in chloride, acetate and carbonate in that order. No inhibition however was observed in carbonate at 0.025 ppm Cu⁺⁺. In toxicity tests, 2-week old larvae from each solution were exposed to concentrations of 10, 7.5, 5, 2.5 and 1 ppm Cu⁺⁺ of the same compounds, together with unacclimated larvae of the same age. Similar tests were held with 6-week old adults acclimated (a) in 0.1 ppm Cu⁺⁺ (chloride, acetate and sulphate) using the same concentrations and (b) in 0.5 ppm Cu⁺⁺ (carbonate), using 150, 125, 100, 75, and 50 ppm Cu⁺⁺. Toxicity to unacclimated larvae and adults differed with the compounds, carbonate being the least toxic, followed by sulphate, chloride and acetate in increasing order. Larvae acclimated in chloride (0.025 ppm Cu⁺⁺) and sulphate (0.1 and 0.5 ppm Cu⁺⁺) showed an increased tolerance to 1 and 2.5 ppm Cu⁺⁺ compared to untreated controls. Tolerance was not enhanced from 5 ppm Cu⁺⁺ upwards. In both compounds, adults acclimated in 0.1 ppm Cu⁺⁺ showed an increased tolerance to concentrations between 1 and 7.5 ppm Cu⁺⁺ compared to controls. Larval mortality in carbonate was below 50% in all test solutions. Adults acclimated at 0.5 ppm Cu⁺⁺ showed an increased tolerance to 50 ppm Cu⁺⁺ compared to controls. Considerable precipitation occurred with the high levels of this compound, thus effecting the final concentrations. No acclimation effect was observed in acetate for either larvae or adults. It is suggested that in A. salina, copper toxicity depends on the particular form of the metal, and that this difference is also evident in growth inhibition and in the potential acquisition of increased tolerance through exposure to low concentrations.     

Effect of sunlight intensity and albinism on the covering response of the Caribbean sea urchin<Emphasis Type="Italic"> Tripneustes ventricosus</Emphasis>

At Discovery Bay, Jamaica, Tripneustes ventricosus lives in beds of the turtle grass Thalassia testudinum. Especially during daylight hours, it covers its aboral surface with fragments of this plant and other objects. Normally pigmented, wild-type sea urchins covered themselves significantly less with Thalassia when sunlight was experimentally decreased to 66% or 32% ambient intensity. Consistent with this result, naturally occurring sea urchins exhibited significantly less covering at a deep (3.5 m) site than at a shallow (1 m) site, where light intensities at the bottom were 619 and 946 mol s^–1 m^–2, respectively. The graded covering response to light intensity suggests that covering is a defense against damaging solar radiation. Albino sea urchins covered themselves significantly more with Thalassia than wild-type sea urchins in both full and 66% sunlight. In addition, at the shallow site where they accounted for about 4% of the population, they showed significantly greater covering than wild-type urchins. The greater covering response of albino sea urchins suggests a greater susceptibility to solar radiation.Communicated by P. W. Sammarco, Chauvin