Sensitivity and acclimation to UV radiation of zoospores from five species of Laminariales from the Arctic

Spores of five Laminariales from Arctic Spitsbergen were exposed in the laboratory to photosynthetically active radiation (PAR; 400–700 nm), PAR+UVA radiation (UVAR; 320–400 nm) and PAR+UVAR+UVB radiation (UVBR; 280–320 nm). Subsequently, germination was monitored over periods of 3, 6 and 9 days. The investigated species were the upper sublittoral Saccorhiza dermatodea, the upper to mid-sublittoral Alaria esculenta and Laminaria digitata, the mid-sublittoral L. saccharina and the lower sublittoral L. solidungula. The germination capacity decreased sharply after 16 h exposure to PAR+UVAR+UVBR in all species. However, S. dermatodea was able to recover from the damaging effects of UVBR. There was also a small increase in percentage germination of A. esculenta 6–9 days after the treatment. No recovery was evident in the other species. After 8 h exposure to PAR+UVA+UVB, L. digitata recovered completely, and L. saccharina and L. solidungula, partially. The only species susceptible to PAR+UVAR was L. solidungula. One prominent cytological feature of UVR-exposed spores was the enlargement of phenolic vesicles (physodes) (particularly seen in S. dermatodea and A. esculenta), which may have a protective function against UVR. Pilot experiments under natural irradiance conditions indicate that the PAR component of solar radiation exerts an additional stress. Overall the data show that zoospores of the species from the upper sublittoral are less sensitive to UVR or have the capacity to recover from UV stress in contrast to species from deeper waters, probably due to their UV protective and repair capabilities.Communicated by O. Kinne, Oldendorf/Luhe     

CO2 fixation and translocation in benthic marine algae. III. Rates and ecological significance of translocation in Laminaria hyperborea and L. saccharina

Translocation of ¹⁴C-labelled assimilates in Laminaria hyperborea and L. saccharina is strictly basipetal within the thallus. The lowermost 20 cm of the frond accumulates 71% (L. hyperborea) or 63% (L. saccharina) of the basipetallymoving translocate after a period of 96 h from initial feeding with NaH¹⁴CO₃. Whereas translocation was found to occur at all seasons in L. saccharina, which grows throughout the year, no translocation of newly synthesized photosynthate occurred in L. hyperborea in October, when no frond enlargement takes place, nor in January, when the new fond occurs as a tiny outgrowth. In L. hyperborea, organic material, assimilated by the old frond during the period of rapid growth, is exported at the rate of 0.5 mg C · dm^-2 · h^-1. In L. saccharina, 14 to 18 cm frond length are necessary for an elongation rate of the growing zone, situated in lowermost 10 cm of the frond, of 1 cm per week. The significance of translocation in the two Laminaria species is demonstrated by comparison of export rates with growth rates measured in situ and in the laboratory.Dedicated to Professor Dr. Otto Stocker on his 85th birthday.     

Growth and DNA damage in young Laminaria sporophytes exposed to ultraviolet radiation: implication for depth zonation of kelps on Helgoland (North Sea)

Growth as an integrative parameter of all physiological processes was measured in young sporophytes of temperate Laminaria digitata, Laminaria saccharina and Laminaria hyperborea exposed in the laboratory to irradiance consisting of either only photosynthetically active radiation (PAR) or to a spectrum including ultraviolet radiation (UVR) (PAR+UVA+UVB) by use of cut-off glass filters. Size increment was measured every 10 min over a period of 18–21 days using growth chambers with on-line video measuring technique. In the chamber, plants were grown at 10±2°C and 16:8 h light–dark cycles with 6 h additional UVR exposure in the middle of the light period. Tissue morphology and absorption spectra were measured in untreated young sporophytes while chlorophyll a content and DNA damage were measured in treated thalli at the end of the experiment. Sensitivity of growth under UVR was found to be related to the observed upper depth distribution limit of the upper sublittoral L. digitata, upper to mid sublittoral L. saccharina and lower sublittoral L. hyperborea. Tissue DNA damage is, however, dependent on thallus thickness which minimizes UVR effect where outer cell layers shade inner cells and provide longer pathlength for UVR. Exposure to UVR causes cellular, enzymatic and molecular damage. Presence of UV-absorbing compounds further reduces effective UVR from reaching physiological targets. The cost of producing higher amount of UV-absorbing compounds and effective DNA repair mechanism can, however, divert photosynthate at the expense of growth. Tissue chlorophyll a content was not significantly different between treatments suggesting a capacity for acclimation to moderate UVR fluence. Growth acclimation to repeated UVR exposure was observed within a period of 12 days while growth inhibition was observed after a longer UVR exposure period of 21 days. The results give further insight into the effects of UVR on the cellular level and show how ecological parameters such as the upper depth distribution limit are dependent on cellular processes.     

Standing crop and leaf area index of the sublittoral Laminaria species near Helgoland

Standing crop values of Laminaria species sampled between 0 to 2 m depth in the sublittoral of Helgoland, a small rocky island in the southern North Sea, are similar to those reported by other workers from Norwegian or Scottish coasts. Below 2 m water depth, however, standing crop values are found to be reduced to a far greater extent with increasing depth than in the Norwegian or Scottish areas studied. Maximum standing crop values are not found in Laminaria digitata and L. saccharina growing just below the low water mark of spring tides, but in the upper L. hyperborea forest at 2 m depth. Population density and leaf area index (LAI) decrease with increasing depth (but not the average weight of individuals constituting the L. hyperborea forest). It is suggested that the depth at which LAI becomes 1 represents an important ecological threshold, since growth rates of L. hyperborea specimens appear to decrease at greater depths but not to increase above the threshold. Self-shading might equalize, to a certain extent, the quantity of underwater irradiance available to an individual phylloid at all depths at which a close vegetation of Laminaria species occurs.     

Temperature acclimation of respiration and photosynthesis in the brown algaLaminaria saccharina

Sporophytes of the brown algaLaminaria saccharina (L.) Lamour grown at 15°C contained significantly more chlorophylla (chla) than did similar plants grown at 5°C. The increase in chla in 15°C plants was due to increased numbers of photosystem II reaction centes, and possibly to increased photosynthetic unit size, compared with 5°C plants. These changes were associated with increased values (photosynthetic efficiencies) in 15°C-grownL. saccharina relative to 5°C-grown plants. The changes in together with reduced respiration rates allowed 15°C-grownL. saccharina to achieve net photosynthesis and light-saturated photosynthesis at a lower photon fluence rate (PFR) than 5°C plants when both groups were assayed at the same temperature (15°C). The photon fluence rates necessary to reach the compensation point and achieve light-saturated photosynthesis (I _c andI _k , respectively) increased with increasing incubation temperature inL. saccharina grown at both 5 and 15°C. However, acclimation responses to growth temperature compensated for the short-term effect of temperature onI _c andI _k . Consequently, plants grown at 5 and 15°C were able to achieve similar rates of light-limited photosynthesis, and similarI _c andI _k values at their respective growth temperatures. These responses are undoubtedly important for perennial seaweeds such asL. saccharina, which frequently grow in light-limited habitats and experience pronounced seasonal changes in water temperature.Please address all correspondence and requests for reprints to I.R. Davison     

Pheromone-based aggregation behaviour of the firebrat, <Emphasis Type="Italic">Thermobia domestica</Emphasis> (Packard) (Thysanura: Lepismatidae)

Summary. We tested the hypothesis that aggregation behaviour of the firebrat, Thermobia domestica (Packard) (Thysanura: Lepismatidae), an inhabitant of enclosed microhabitats, is mediated, at least in part, by a pheromone. Individual insects were released into the central chamber of a 3-chambered olfactometer and test stimuli were placed in lateral chambers. Paper discs previously exposed for 3 days to 10 female, male, or juvenile T. domestica were all preferred by female, male, or juvenile T. domestica over unexposed paper discs, indicating the presence of an aggregation/arrestment pheromone. In additional experiments, frass and scales from female T. domestica, tested singly and in combination, proved not to be the source of the pheromone. Physical contact was required for pheromone recognition, indicating that the pheromone arrests rather than attracts conspecifics. Arrestment by the long-tailed silverfish, Ctenolepisma longicaudata Escherich (Thysanura: Lepismatidae), but not by the common silverfish, Lepisma saccharina L. (Thysanura: Lepismatidae), to T. domestica exposed paper discs suggests closer phylogenetic relatedness between C. longicaudata and T. domestica, than between C. longicaudata and L. saccharina. Whether C. longicaudata or L. saccharina produce an aggregation signal, and whether T. domestica respond to this signal is unknown. Received 10 June 2002; accepted 30 September 2002.     

Transversal profiles of carbon assimilation in the fronds of three Laminaria species

The brown macroalgae Laminaria digitata (Huds.) Lamour., L. hyperborea (Gunn.) Foslie, and L. saccharina (L.) Lamour. (Laminariales, Phaeophyceae) have been investigated for carbon assimilation and assimilate biosynthesis in different tissues (meristoderm, cortex, medulla) of stipes and blades. Carboxylation via ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) and phosphoenolpyruvate carboxykinase (EC 4.1.32) follows a transversal gradient from the outer to the inner tissues with maximum activity of enzymatic CO₂ fixation in the meristoderm. Such transversal profiles are also recorded for photosynthetic and dark carbon assimilation as well as for kinetics of assimilate ¹⁴C-labelling in isolated tissues. Differential chemical constitution of the blade and stipe tissues examined and results from assimilate biosynthesis are discussed with regard to a transversal translocation of photosynthates from meristodermal to cortical and medullar cells.     

The section Digitatae of the genus Laminaria (Phaeophyta) in the northern and southern Atlantic: crossing experiments and temperature responses

Hybridization experiments between seven north and south Atlantic Laminaria species were carried out. Morphologically normal F₁ sporophytes developed from the following crosses among south Atlantic species: L. pallida x L. schinzii, L. pallida x L. abyssalis and L. schinzii x L. abyssalis. Normal F₁ sporophytes also resulted from the crosses L. digitata (north Atlantic) x L. pallida (south Atlantic) and L. digitata (north Atlantic) x L. abyssalis (south Atlantic). Hybrids between north Atlantic L. ochroleuca and south Atlantic L. pallida, L. schinzii and L. abyssalis and between north Atlantic L. digitata and south Atlantic L. schinzii initially developed as normal sporophytes but became deformed later on and further development was retarded. No hybrids resulted from attempted crosses between northeastern Atlantic L. saccharina and L. abyssalis from Brazil. Temperature tolerance, relative growth rates and temperature demands for gametogenesis revealed the existence of a warm temperate group within the digitate Laminaria species consisting of L. ochroleuca, L. pallida, L. schinzii and L. abyssalis. Hybridization experiments and temperature responses suggest that north Atlantic L. digitata and L. ochroleuca are still similar to south Atlantic Laminaria species, confirming the speculation that a transequatorial migration of a warm-temperate L. ochroleuca-like ancestor may have taken place.     

Physiological ecology of four Polysiphonia species (Rhodophyta,Ceramiales)

Photosynthesis and respiration of 4 species of the marine red algal genus Polysiphonia were evaluated under a variety of light, temperature and salinity conditions. The manometric results were compared with the local distribution and abundance of each species. The species can be separated into two distinct categories based on their overall distribution and temperature optima: (1) cold water plants [P. lanosa (L.) Tandy and P. elongata (Hudson) Sprengel], with peak photosynthesis at 21° to 24°C, but with active photosynthesis as low as 5°C; (2) plants with warm-water affinities [P. nigrescens (Hudson) Greville and P. subtilissima Montagne], having photosynthetic optima at 27° to 30°C, and exhibiting little or no photosynthesis below 10°C. The plants from the first group exhibit thermal injury at temperatures of 25°C and show a narrow tolerance to low salinities during periods of high temperatures. The plants from the second group show thermal injury at 30°C and have a wider tolerance to low salinities. The horizontal distribution of the 4 Polysiphonia species within the Great Bay Estuary System of New Hampshire, USA, is primarily governed by their tolerances to high temperatures and low salinities. The temperature optimum for each of the species corresponds to its particular estuarine distribution. Thus, P. subtilissima, having the highest temperature optimum, penetrated furthest into the Estuary, while P. lanosa, having the lowest temperature optimum, was restricted to the more coastal stations. There was a good correspondence between the natural distribution patterns and the manometric results.Published with the approval of the Director of the New Hampshire Agricultural Experiment Station as Scientific Contribution No. 731.Scientific Contribution No. 4 of the Jackson Estuarine Laboratory.     

Some aspects of the thermal tolerance of Trichomya hirsuta (Mollusca: Bivalvia) of Eastern Australia

The upper temperature tolerance range for Trichomya hirsuta L. is described for acclimation temperatures of 10° to 32°C at 30% S. Changes in thermal resistance with time are described along with the incipient lethal temperatures. The eurythermicity for the species is 240.7 C°-squared. The ultimate upper incipient lethal temperature is 35.1°C. Definition of the incipient sublethal temperature is given, and is equal to 32°C. Diet effects are shown not to be significant in short-term lethal experiments, but indicate that unfed mussels reduce their resistance after prolonged exposure to high temperatures. Size was also shown to have no effect on resistance and tolerance. A comparison of the tolerance triangle of T. hirsuta with those of the temperate species Mytilus edulis and Mya arenaria revealed that the 24-h LT₅₀ minus 2.2 C° approximates the incipient lethal temperature. The eurythermicities of the temperate species are Mytilus edulis, 363 C°-squared; and Mya arenaria, 415 C°-squared.     

Ecological energetics of the seaweed zone in a marine bay on the Atlantic coast of Canada. I. Zonation and biomass of seaweeds

An intertidal and underwater survey of the zonation of seaweed in St. Margaret's Bay, NovaScotia, Canada showed 8 major zones as one proceeded away from shore: (1) Fucus and Ascophyllum; (2) Chorda with filamentous browns; (3) Chondrus crispus; (4) Zostera marina; (5) Laminaria digitata with L. longicrusis; (6) Laminaria longicruris; (7) L. longicruris with Agarum cribrosum; (8) Agarum cribrosum with Ptilota serrata. Zostera occurred at the same level as O. crispus but replaced it in sheltered water. Ascophyllum was more abundant in sheltered water. L. digitata was confined to the more exposed, steeper shore. The average horizontal extent of the seaweed zone was 369 m, and the greatest depth of significant amounts of seaweed 20 to 30 m. Laminaria longicruris contributed 36% of the total biomass, and Laminaria spp. and Agarum together constituted 83%, while intertidal seaweeds contributed less than 10% of the biomass. The estimated average total biomass per m of shore line was 1,481 kg fresh weight, 326 kg dry weight, 98 kg carbon, or 980x10³ kcal. When averaged over the whole area of the bay, the corresponding figures were 1.38 kg/m² fresh weight, 0.30 kg/m² dry weight, 91 g/m² carbon or 912 kcal/m². Dry matter of Laminaria was 15 to 27% of fresh weight in blades, 10 to 12% in stipes. The dry matter content of blades was least in spring and highest in autumn, but carbon content and calorific value of dry matter showed little difference with species or season.Contribution to the International Biological Programme CCIBP 108.Bedford Institute Contribution BI 249.     

Effects of temperature on fertilization and early cleavage of some tropical echinoderms,with emphasis on Echinometra mathaei

Select temperatures, above normal, are shown to reduce success of fertilization and normal early cleavage in the laboratory for the echinoderms Acanthaster planci (L.), Culcita novaeguineae Muller and Troschel, Linckia laevigata (L.), Echinometra mathaei (de Blainville), and Diadema savignyi Michelin. The data indicate that cleavage is more sensitive to increased temperature than is fertilization. Upper tolerance limits for early cleavage in most of the species examined is near 34.0°C. The early developmental stages of A. planci were the most sensitive to elevated temperature, and those of E. mathaei, the least sensitive. Further experiments with E. mathaei showed that unfertilized ova were still viable, dividing normally when fertilized after 2 h exposure at 36.0°C. The ova were significantly less viable after 3 h. Early cleavage stages of E. mathaei were resistant to 36.0°C for exposure times of up to 40 min, but were inhibited beyond this period. It is suggested that the ability of E. mathaei to develop normally at 34.0°C (6C° above ambient temperature) and to withstand limited exposure to 36.0°C may account for the wide distribution of this species in habitats which are often subjected to broad temperature fluctuations, such as reef flats.Contribution No. 46 from the University of Guam Marine Laboratory.     

Routine oxygen consumption of Mugil cephalus,Liza dumerili and L. richardsoni at Different temperatures and salinities

Oxygen consumption studies were undertaken with 3 mullet species to determine b, the exponent of w, as well as a, as indices of metabolic rate in the equation M=aw ^bwhere M=metabolic rate, a=the intensity of metabolism, W=body weight, and b=the exponent of w. This was done under 5 experimental temperatures (13°, 18°, 23°, 28°, 33°C) for Mugil cephalus and Liza dumerili at 1 and at 35 S, and for L. richardsoni at 35S only. Mean b values were approximately 0.85. The a values depended on temperature, and increased according to Van't Hoff's law except for L. dumerili (1 S) and L. richardsoni (35 S) for a temperature increase from 23° to 28°C. It was found that handling had a profound influence on metabolic rate and led to considerably increased consumption rates during the first 8 h after introduction into the respiration chambers. Fasting in L. dumerili resulted in a total drop of 27% in oxygen consumption over a period of 6 days, of which 10% occurred over the first 24 h. Oxygen consumption displayed diurnal rhythms during the 6 day period, with lowest consumption rates at midday and midnight and highest just after sunrise and sunset.     

Autecological investigation on marine diatoms 3. Thalassiosira nordenskioeldii and Chaetoceros diadema

The temperature range for the best competitive position by growth of Thalassiosira nordenskioeldii Cleve has been determined by comparing generation times. It ranges from-1.5° to 6°C. At these temperatures, especially at lower light intensities, it was one of the fastest growing species, whereas above 6°C many other species grew faster. High light intensities at increasing temperatures became damaging. A flowering of the cold oligo-eurytherm diatom T. nordenskioeldii occurs not only in the upper layers, but can also occur at greater depth simultaneously, because decreasing daylengths at 6°C had the least influence on its growth. Continuous light at 6°C had a positive influence on its growth. The start of the T. nordenskioeldii spring flowering under the Arctic Sea Ice is discussed in connection with the occurrence of enclosed marine diatoms in Polar Sea Ice. The influence of the winter temperature on the spring flowering of the North Sea, the southern border for flowerings of T. nordenskioeldii, is discussed. For Chaetoceros diadema (Ehrenberg) Gran the best competitive position by growth is reached at-1.5° to about 6°C. It has the best opportunity of reaching high cell numbers at the lowest temperatures of the range. The occurrence of the cold oligo-eurytherm diatom Ch. diadema in plankton samples at temperatures above 10°C need not be incorret, for the species did grow in cultures at 12° and 16°C. The wrong interpretation of the experimentally determined optimum temperature of e.g. T. nordenskioeldii caused a discrepancy between experimental results and field data that does not exist. The question is discussed whether ecologically it is relevant to talk about a temperature optimum. On account of the results of T. nordenskioeldii the question of the adaptation of diatom cultures for the start of the real experiments is discussed.     

Feeding and nutritional ecology of the sea urchin strongylocentrotus drobachiensis in Maine,USA

The sea urchin strongylocentrotus drobachiensis exhibited a high degree of food selectivity, whether foods were presented singly or in combination. Foods ranked from most to least preferred were, in summer, Laminaria longicruris, Chondrus crispus, Corallina officinalis, Ascophyllum nodosum, and Agarum cribrosum, whereas in winter A. nodosum and A. cribrosum exchanged ranks. Food preference was not correlated with caloric content but, because of higher feeding rates on preferred foods, caloric intake was positively correlated with preference. Similarly, food absorption rankings were not correlated with food preference, with the exception of gravimetric efficiencies in winter. However, the absorption of L. longicruris, the most preferred alga, was highest in all measurements. Growth and reproductive development of S. drobachiensis on single species diets were positively correlated with food preference. Highest values occurred with animals fed L. longicruris. Urchins transferred from non-preferred to preferred diets showed increased somatic and reproductive growth compared to control animals on the original, non-preferred diets. Conversely, when transferred from preferred to non-preferred diets, urchins showed reduced growth compared to controls. No combination diet tested supported significantly better gonadal growth than L. longicruris: 25% C. crispus supported slightly better somatic growth than L. longicruris alone. These data support the view that S. drobachiensis has evolved a feeding strategy resulting in the maximization of growth and reproduction.     

Preliminary rearing experiments on the larvae of Sergestes lucens (Penaedia,Natantia, Decapoda)

Sergestes lucens Hansen, a mesopelagic shrimp fished commercially in Suruga Bay, Japan, was successfully reared from egg to post-larval stage V under laboratory conditions. Chaetoceros ceratosporum and Artemia nauplii were found to be satisfactory food in the laboratory during rearing. Growth, mortality, food preference, and feeding and swimming activities during the various developmental stages were investigated. Temperature changes greatly affected the speed of development and the mortality of the larvae. The optimum temperature range for larval development was 18° to 25°C. The growth rate (length) of larval stages was as rapid as 0.16mm/ day at 20 °C and 0.21 mm/day at 23 °C. The larvae first started feeding on phytoplankton at elaphocaris stage I, and then gradually became predators in the post-larval stages. It is suggested that the critical period for the species occurs in the elaphocaris stages. Environmental data, vertical distribution of the species, and data obtained from laboratory experiments suggest that the fluctuation in the abundance of S. lucens is greatly influenced by the water temperature at around 50 m from June to August. Feeding mechanisms observed in the post-larval stages are described.     

Light and temperature demands for growth and reproduction of laminarian gametophytes in southern and central California

The gametophytes of 9 laminarian species (4 from southern California, and 5 from central California, USA) became fertile in the unicellular stage (female gametophytes) or in a few-celled stage (male gametophytes), when appropriate temperatures and a sufficiently high quantum irradiance in the blue part of the spectrum were supplied. Vegetative growth, leading to the formation of filamentous gametophytes was light-saturated at relatively low irradiances (4 W m^-2; equivalent to about 2 nE cm^-2 sec^-1 or an illuminance of 1000 lux), whereas 2 to 3 times this irradiance in continuous fluorescent cool white light was needed to induce the majority of the gametophytes to become fertile. An illuminance of 8300 lux did not inhibit the development of the gametophytes from southern Californian species. Egregia menziesii exhibited an exceptionally low quantum demand for induction of fertility. Gametophytes of species from central and southern California differed in regard to their temperature optimum for growth (12°C in the former, 17°C in the latter) and their upper temperature limit for reproduction (17°C in the former, 20°C in the latter).     

Seasonal variation in ecophysiological patterns in macroalgae from an Arctic fjord. I. Sensitivity of photosynthesis to ultraviolet radiation

Marine macroalgae inhabiting Arctic coastal ecosystems are exposed to pronounced seasonal variations in the radiation regime, including harmful UVB radiation. This study presents the first data on the seasonal changes in the sensitivity of macroalgal photosynthesis towards UV exposure by comparing under-ice, clear-water and turbid-water conditions characteristic for late winter, spring and summer. Various brown (Laminaria saccharina, L. digitata, L. solidungula, Saccorhiza dermatodea, Desmarestia aculeata), red (Palmaria palmata, Devaleraea ramentacea) and one green macroalgal species (Monostroma aff. arcticum) were collected at the same water depth throughout the seasons in the Kongsfjord (Spitsbergen, Svalbard, Norway). Maximum quantum yield (F_v/F_m) and maximum photosynthetic electron transport rates (ETR_max) were determined immediately after collection, after 2 h exposure to artificial UV radiation and after 18 h recovery in dim white light. Photosynthesis of the studied species showed different responses depending on their morpho-functional and physiological characteristics, their life strategies, phenology and depth distribution. Within the genus Laminaria, maximum quantum yield of adult specimens of the deep-water species L. solidungula was most strongly UV sensitive. Adult L. saccharina exhibited a lower UV sensitivity than a 6-month-old specimen. Inhibition of photosynthesis after UV exposure remained at the same level throughout the study period, both in adult L. saccharina and S. dermatodea. However, adult specimens of L. saccharina collected in May showed partial recovery only, whereas photosynthesis of specimens from both species collected later recovered fully. D. aculeata exhibited a remarkable decrease of UV sensitivity during the study period. Photosynthesis of specimens collected under the ice was strongly inhibited by UV, but the degree of inhibition decreased during spring and summer. Concomitantly ETR_max values were low after UV exposure in specimens collected in June, but increased later in the season. P. palmata exhibited a relatively flexible response. Photosynthesis in specimens collected under the ice in June or in turbid water in July/August was relatively strongly inhibited; specimens collected during sunny periods and in clear water in spring showed a much lower degree of photoinhibition after UV exposure. The seasonal pattern of low/high ETR_max values in spring/summer is probably a characteristic of the life strategy of this species. The UV sensitivity of D. ramentacea exhibited a similar seasonal pattern. In M. aff. arcticum, UV sensitivity increased and ETR_max values decreased during the study period, reflecting the life strategy of this annual late winter/spring species. The physiological basis for the seasonal changes in UV sensitivity of photosynthesis is presented in a companion paper (this issue).     

Effects of temperature on activity,food consumption rates,and gut passage times of seaweed-eating<Emphasis Type="Italic"> Tegula</Emphasis> species (Trochidae) from California

Previous feeding studies on herbivorous marine snails rarely have focused on temperature effects on food intake. If temperature affects food intake, ectothermic snails may experience difficulty obtaining sufficient nutritional resources, limiting their ability to sustain populations at suboptimal temperatures. We hypothesized that the feeding responses of Tegula species would correspond with temperatures characteristic of their geographic distributions. We determined activity, consumption rates, and gut passage times at 11°C, 15°C, 19°C, and 23°C for three Tegula species with distinct thermal distributions: T. brunnea (cold water), T. aureotincta (warm water), and individuals from warm- and cold-water populations of T. funebralis, a broadly distributed species. Activity and consumption rates of T. aureotincta increased with increasing temperature, but were highest for T. brunnea at 19°C, a temperature rarely achieved in habitats occupied by this species, and lowest at 11°C. Warm-water T. funebralis showed significantly lower activity and consumption rates at 11°C, whereas cold-water T. funebralis consumed food fastest at 15°C and were most active at 23°C. Temperature affected gut passage time only in T. aureotincta. These data suggest that temperature might influence the northern limit of T. aureotincta by affecting activity and food consumption rates. T. brunneas activity and ability to consume food were not hindered by warmer temperatures despite the present day restriction of this species to colder waters. Also, widely separated (>300 km) T. funebralis populations may be adapted to regional conditions based on the different temperature responses of northern and southern snails.Communicated by P.W. Sammarco, Chauvin     

Effects of temperature on the mortality and growth of Hawaiian reef corals

Three common species of Hawaiian reef corals, Pocillopora damicornis (L.), Montipora verrucosa (Lamarck) and Fungia scutaria Lamarck, were grown in a temperature-regulated, continuous-flow sea water system. The skeletal growth optimum occurred near 26°C, coinciding with the natural summer ambient temperature in Hawaii, and was lowest at 21° to 22°C, representing Hawaiian winter ambient. Levels of approximately 32°C produced mortality within days. Prolonged exposure to temperatures of approximately 30°C eventually caused loss of photosynthetic pigment, increased mortality, and reduced calcification. Corals lived only 1 to 2 weeks at 18°C. The corals showed greater initial resistance at the lower lethal limit, but ultimately low temperature was more deleterious than high temperature. Results suggest that a decrease in the natural water temperature of Hawaiian reefs would be more harmful to corals than a temperature increase of the same magnitude.Contribution No. 504 of the Hawaii Institute of Marine Biology.