Embryonic encapsulation and maternal incubation: Requirements for survival of the early stages of the estuarine gastropod Crepipatella dilatata

During their reproductive period, females of Crepipatella dilatata deposit their embryos in capsules that they then brood in the pallial cavity until juveniles emerge several weeks later, after passing through a transient veliger “larval” stage. Artificially excapsulated veligers of this species experimentally exposed to a wide range of salinities (5, 10, 15, 20, 25, and 30 psu) for six hours showed reduced activity at salinities of 15 and 20 psu, whereas encapsulated veligers exposed to those same salinities showed no reduction of activity. Artificially excapsulated veligers showed high mortality at salinities of 5 and 10 psu; encapsulated embryonic stages also showed high mortalities at 5 psu and serious sublethal effects at 10 psu in tests excluding maternal protection, showing that encapsulation alone does not provide complete protection from low salinity stress. Natural tidal cycles in the Quempillén River estuary also reduced embryonic survival at salinities of ≤ 10 psu when the capsules were exposed without maternal protection. In contrast, encapsulated embryos protected by their mothers survived well regardless of the salinity to which they were exposed, under both natural and laboratory-simulated estuarine tidal cycles. C. dilatata are able to develop in the estuary only because of maternal protection, since salinity levels in this environment sometimes decline to as low as 7 psu. Successful embryonic development in this estuary reflects the capacity of C. dilatata adults to detect dangerously low salinity levels and then seal themselves off from the environment for up to 50 hrs (O. Chaparro pers. obs.) when the salinity drops below 22.5 psu, allowing salinity to remain above this level within the pallial cavity despite continued salinity declines in the surrounding seawater.     

Effect of increased sediment sulfide concentrations on the composition of stable sulfur isotopes (δS) and sulfur accumulation in the seagrasses Zostera marina and Posidonia oceanica

The effect of increased sediment sulfide concentrations on the sulfur isotopic composition (δ³⁴S), total sulfur (TS) and elemental sulfur (S⁰) concentrations in plant tissues was studied for the two seagrasses Zostera marina (3 weeks in laboratory) and Posidonia oceanica (4 months in situ). Porewater sulfide concentrations were experimentally regulated and plants exposed to high sediment sulfide concentrations had δ³⁴S signals closer to the δ³⁴S of sulfide, whereas plants exposed to no / low sulfide concentrations had δ³⁴S signals closer to the δ³⁴S of seawater sulfate, indicating a higher sulfide invasion in plants exposed to high sulfide concentrations. The δ³⁴S varied between the plant tissues in both species with the leaves having more positive δ³⁴S signals than roots and rhizomes, indicating that sulfide was invading into the roots and moved to the other tissues through the lacunae. TS and S⁰ concentrations were higher in plants exposed to sulfide in both experiments suggesting that sulfur derived from sediment sulfide accumulated in the plants. The δ³⁴S signal in S⁰ was similar to sediment sulfide verifying that S⁰ found in the seagrasses originated from sediment sulfide. Direct comparisons of δ³⁴S in the two different seagrasses and across the treatments were not possible due to large differences in δ³⁴S of the sulfur sources. F_sulfide adjusted for these differences and may be a useful alternative, when δ³⁴S of the sulfur sources varies between study sites. There were no significant effects of sulfide exposure on plant growth and mortality in Z. marina and P. oceanica after 3 weeks and 8 weeks exposure, respectively, but P. oceanica showed indications of reduced growth and higher mortality after 16 weeks of sulfide exposure probably due to sulfide invasion/toxicity.     

Effects of Salinity and Nutrient Addition on Mangrove Excoecaria agallocha

Effects of salinity on seed germination and growth of young (1 month old) and old (2-year old) seedlings of Excoecaria agallocha were investigated. Combined effects of salinity and nutrient level were also examined on old seedlings. Seed germination was best at 0 and 5 psu salinity. 15 psu salinity significantly delayed root initiation and decreased final establishment rate. All seeds failed to establish at 25 psu salinity. Young seedlings performed best at 0 and 5 psu, but growth was stunned at 15 psu, and all seedlings died within 90 days at 25 psu. Old seedlings grew best at salinities below 5 psu and they survived the whole cultivation at 25 psu. This indicated that E. agallocha increased salt tolerance over time. Gas exchange was significantly compromised by salinities above 15 psu but evidently promoted by high nutrient. Proline accumulated considerably at high nutrient, and its contents increased from 0 to 15 psu but decreased at 25 psu salinity. Lipid peroxidation was aggravated by increasing salinity beyond 15 psu but markedly alleviated by nutrient addition. These responses indicated that E. agallocha was intolerant to high salinity but it can be greatly enhanced by nutrient addition.     

Tropical seagrass species tolerance to hypersalinity stress

The long-term sustainability of seagrasses in the subtropics and tropics depends on their ability to adapt to shifts in salinity regimes, particularly in light of present increases in coastal freshwater extractions and future climate change scenarios. Although there are major concerns world-wide on increased salinity in coastal estuaries, there is little quantitative information on the specific upper salinity tolerance of tropical and subtropical seagrass species. We examined seagrass hypersalinity tolerance under two scenarios: (1) when salinity is raised rapidly simulating a pulsed event, such as exposure to brine effluent, and (2) when salinity is raised slowly, characteristic of field conditions in shallow evaporative basins; the first in hydroponics (Experiments I and II) and the second in large mesocosms using intact sediment cores from the field (Experiment III). The three tropical seagrass species investigated in this study were highly tolerant of hypersaline conditions with a slow rate of salinity increase (1 psu d⁻¹). None of the three species elicited total shoot mortality across the range of salinities examined (35–70 psu over 30 days exposures); representing in situ exposure ranges in Florida Bay, a shallow semi-enclosed subtropical lagoon with restricted circulation. Based on stress indicators, shoot decline, growth rates, and PAM florescence, all three species were able to tolerate salinities up to 55 psu, with Thalassia testudinum (60 psu) and Halodule wrightii (65 psu) eliciting a slightly higher salinity threshold than Ruppia maritima (55 psu). However, when salinity was pulsed, without a slow osmotic adjustment period, threshold levels dropped 20 psu to approximately 45 psu for T. testudinum. While we found these three seagrass species to be highly tolerant of high salinity, and conclude that hypersalinity probably does not solely cause seagrass dieoff events in Florida Bay, high salinity can modify carbon and O₂ balance in the plant, potentially affecting the long-term health of the seagrass community.     

Development and mortality of the first naupliar stages of Eurytemora affinis (Copepoda, Calanoida) under different conditions of salinity and temperature

As a prevalent species complex in temperate estuaries and salt marshes of the Northern Hemisphere, populations of Eurytemora affinis that inhabit these environments must be adapted to salinity fluctuations. Some populations have invaded freshwater environments. In this work, we focus on the combined effects of temperature and salinity fluctuations on mortality rates and development time of the first naupliar stages under starvation. Two temperatures (10 and 15 °C) and eight salinities, ranging from 0 to 35 psu are investigated. We show (i) that among all experimental conditions the optimal temperature and salinity for naupliar survival and development are 15 psu and 15 °C, and (ii) that only the most extreme salinities (i.e. 0 and 35 psu) have a negative effect on naupliar survival. Nauplii develop faster and reach a higher developmental stage at 15 than at 10 °C, independent of salinity. The relevance of this metabolic adaptive pattern is discussed in the general framework of in situ behavior, tidal forcing and biogeographic variability, as well as the potential sources of the observed individual variability.     

Restoration flows for the Colorado River estuary, México: estimates from oxygen isotopes in the bivalve mollusk Mulinia coloradoensis (Mactridae: Bivalvia)

Because of competing demands for freshwater, restoration of estuaries requires estimates of inflows to sustain key species. In this study we estimated the pre-dam salinities of the Colorado River estuary by using oxygen isotopes in subfossil shells of the bivalve mollusk Mulinia coloradoensis. Since the construction of upstream dams and water diversions, average salinity in the estuary has increased to 38 practical salinity units (psu) and the population of M. coloradoensis has decreased by ~90%. In the pre-dam estuary, specimens grew when salinity ranged from 22 to 33?psu at the mouth of the river while populations 40?km distant grew at salinities from 30 to 38?psu. The river flow needed to reduce salinities at the mouth of the river to those recorded in the most distant localities (40?km from river??s mouth) ranges from 120 to 290?m³?s^?1. If these flows were sustained for a year, they would total 7?C16?% of the river??s annual average historical flow (~1.8?×?10¹⁰?m³).     

Salinity tolerances of 62 strains of Pflesteria and Pfiesteria-like heterotrophic flagellates (Dinophyceae)

The salinity tolerance of 62 strains of Pfiesteria and Pfiesteria‐like heterotrophic dinoflagellates was measured. All strains were acclimated at 12 psu for at least 1 year before experimentation. Strains isolated from the Chesapeake Bay and Neuse River systems tolerated lower salinities than strains isolated from the Wilmington River system (P< 0.005). Swimming cells were still observed after 5 days at 0.5 psu for one strain, and at 1 psu for most other Chesapeake Bay and Neuse River strains. Swimming cells for the Wilmington River were still observed after 5 days at 3–5 psu, but no swimming cells were observed at ≤ 2 psu. With regard to the upper salinity tolerance, the Wilmington River strains tolerated higher salinities than the Chesapeake Bay and Neuse River systems (P< 0.005). Most Wilmington River strains were swimming after 5 days at salinities ≥ 50 psu, whereas the Chesapeake Bay and Neuse River system strains rarely had swimming cells at salinities exceeding 35–45 psu. For all three water systems and for both lower and higher salinities, cells apparently encysted in many instances. However, when salinities were returned to 12 psu, swimming cells often re‐appeared. Statistically significant geographic differences in salinity tolerance suggest a geographic adaptation has occurred and that salinity tolerance is under genetic control. The results also suggest there is diversity among the strains.     

EFFECT OF SALINITY ON PSEUDO‐NITZSCHIA SPECIES (BACILLARIOPHYCEAE) GROWTH AND DISTRIBUTION1

Salinity varies widely in coastal areas that often have a high abundance of Pseudo‐nitzschia H. Peragallo. Pseudo‐nitzschia is abundant in Louisiana waters, and high cellular domoic acid has been observed in natural samples but no human illness has been reported. To assess the threat of amnesic shellfish poisoning (ASP), we examined the effect of salinity on Pseudo‐nitzschia occurrence in the field and growth in the laboratory with special emphasis on the salinity range where oysters are harvested (10–20 psu). In Louisiana coastal waters, Pseudo‐nitzschia spp. occurred over a salinity range of 1 to >35 psu, but they occurred more frequently at higher rather than lower salinities. Seven species were identified, including toxigenic species occurring at low salinities. In culture studies, seven clones of three species grew over a salinity range of 15 to 40 psu, some grew at salinities down to 6.25 psu, and most grew at salinities up to 45 psu. Tolerance of low salinities decreased from Pseudo‐nitzschia delicatissima (Cleve) Heiden to P. multiseries (Hasle) Hasle to P. pseudodelicatissima (Hasle) Hasle emend. Lundholm, Hasle et Moestrup. In conclusion, although Pseudo‐nitzschia was more prevalent in the field and grew better in the laboratory at higher salinities, it grew and has been observed at low salinities. Therefore, the probability of ASP from consumption of oysters harvested from the low salinity estuaries of the northern Gulf of Mexico is low but not zero; animal mortality events from toxin vectors other than oysters at higher salinity on the shelf are more likely.     

Salinity tolerance of Avicennia marina (Forssk.) Vierh. from Gujarat coasts of India

Greenhouse experiments were conducted to assess the effects of soil salinity on emergence, growth, water status, proline content and mineral accumulation of seedlings of Avicennia marina (Forssk.) Vierh. NaCl was added to the soil and salinity was maintained at 0.2, 2.5, 5.1, 7.7, 10.3, 12.6, 15.4, 17.9, 20.5, 23.0, 25.6 and 28.2 psu. A negative relationship between seedling emergence and salt concentration was obtained. Nevertheless, this mangrove is highly salt tolerant during germination. Growth of seedlings was significantly promoted by low salinity and optimum growth was obtained at 15.4 psu. Higher salinities inhibited plant growth. Growth and dry matter accumulation in tissues followed the same optimum curve. Water potential of tissues became significantly more negative with increasing salinity, and proline content significantly increased. Moreover, water potential and proline content of tissues displayed an S-curve with the inflection point below ∼10 psu. The concentration of Na in tissues increased significantly, whereas K, Ca, Mg, N and P content decreased.     

Interacting effects of temperature and salinity on Bonamia sp. parasitism in the Asian oyster Crassostrea ariakensis

The proposition to introduce the Asian oyster Crassostrea ariakensis to the mid-Atlantic region of the USA is being considered with caution, particularly after the discovery of a novel microcell haplosporidian parasite, Bonamia sp., in North Carolina. Although this parasite was found to be pathogenic in C. ariakensis under warm euhaline conditions, its persistence in C. ariakensis exposed to various temperature and salinity combinations remained unresolved. In this laboratory experiment, we tested the influence of temperature in combination with a wide range of salinities (10, 20 and 30 psu) on Bonamia sp. Temperature was either changed from warm (>20 °C) to cold (6 °C for 6 weeks) and back to warm or maintained constant and warm. Warm temperature was associated with higher host mortality than cold temperature, suggesting that temperature influenced Bonamia sp. pathogenicity. The effect of salinity was revealed under warm temperature with highest mortality levels observed in infected C. ariakensis exposed to 30 psu. When temperature was increased following low-temperature exposure, Bonamia sp. was not detected; however sub-optimal experimental conditions may have contributed to this result, making it difficult to draw conclusions regarding the reemergence of the parasite after low-temperature exposure. Although the overwintering of Bonamia sp. in C. ariakensis will need to be further investigated, the results presented here suggest that Bonamia sp. may be able to persist in C. ariakensis under a combination of low temperature and meso- to euhaline salinities.     

Maximum standard metabolic rate corresponds with the salinity of maximum growth in hatchlings of the estuarine northern diamondback terrapin (Malaclemys terrapin terrapin): Implications for habitat conservation

I evaluated standard metabolic rates (SMR) of hatchling northern diamondback terrapins (Malaclemys terrapin terrapin) across a range of salinities (salinity = 1.5, 4, 8, 12, and 16 psu) that they may encounter in brackish habitats such as those in the Maryland portion of the Chesapeake Bay, U.S.A. Consumption of O₂ and production of CO₂ by resting, unfed animals served as estimates of SMR. A peak in SMR occurred at 8 psu which corresponds closely with the salinity at which hatchling growth was previously shown to be maximized (salinity ∼ 9 psu). It appears that SMR is influenced by growth, perhaps reflecting investments in catabolic pathways that fuel anabolism. This ecophysiological information can inform environmental conservation and management activities by identifying portions of the estuary that are bioenergetically optimal for growth of hatchling terrapins. I suggest that conservation and restoration efforts to protect terrapin populations in oligo-to mesohaline habitats should prioritize protection or creation of habitats in regions where average salinity is near 8 psu and energetic investments in growth appear to be maximized.     

Influence of salinity, nutrients and light on the germination and growth of Enteromorpha sp. spores

In many shallow coastal areas worldwide, several species of opportunistic macroalgae (mainly Chlorophyta) have an excessive growth, as a consequence of eutrophication processes. Therefore, bloom-forming macroalgae become the dominant primary producers within these coastal systems. However, frequently the ecology and the ecophysiology of adult macroalgae have been insufficient to explain their seasonal abundances. Thus, it is essential to understand the factors that regulate the germination and growth of spores of opportunistic green macroalgae. In the present work, we assessed the effects of nutrients (N and P), salinity and light on the germination and growth of Enteromorpha spores. Overall, the results highlight the fact that, such as for adult macroalgae, spore germination and growth are adversely affected by low salinities. Growth of the spores is significantly decreased at 5 psu, while salinities of 20 and, especially of 35 psu, clearly promote the spore growth. Additionally, Enteromorpha spores seem to be particularly sensitive to PO₄-P limitation and to NH₄-N toxicity, which suggests a higher sensitivity to the variation of external nutrient concentrations than adult macroalgae. The present results contribute to increase the understanding about the factors that control macroalgal growth at its early phases of development. In particular, the results suggest that the growth of spores from opportunistic green macroalgae is strongly salinity-dependent. Consequently, in highly hydrodynamic systems such as most shallow estuaries, salinity variations may play a determinant role in the yearly abundances of green macroalgae, since it controls macroalgal growth from the spores to the adults.     

Does scope for growth change as a result of salinity stress in the amphipod Gammarus oceanicus?

Physiological performance (feeding, metabolism, growth and excretion) across a broad range of salinity (5-30 psu) were determined for the benthic amphipod Gammarus oceanicus, a species of marine origin inhabiting brackish waters of the southern Baltic Sea. Feeding rates decreased with increasing salinity, whereas the nutritive absorption efficiency increased. Faeces production and ammonia excretion rates decreased strongly from the lowest to the highest salinity by 60% and 58%, respectively. Increasing salinity was accompanied by a reduction in the metabolic rate from 438 J g^− 1 dry wt d^− 1 (5.1 mW g^− 1) at 5 psu to 245 J g^− 1 (2.8 mW g^− 1) at 30 psu. Individuals were able to maintain a positive energy balance at all experimental salinities. The greatest values for scope for growth were recorded at the environmental salinity (7 psu) with a mean of 769 J g^− 1 dry wt d^− 1 (8.7 mW g^− 1).     

Comparing salinity tolerance in early stages of the sporophytes of a non-indigenous kelp (Undaria pinnatifida) and a native kelp (Saccharina latissima)

The short-term effects of low salinities on the survival of germlings of an introduced kelp Undaria pinnatifida and a native kelp Saccharina latissima were assessed under laboratory conditions. This experiment was designed to compare the differential stress tolerance to salinity of the early life history stages of sporophytes of these two kelps that co-occur on European Atlantic coasts. Germlings (young sporophytes) of both species were exposed for 4 days to salinities ranging from 31 (control) to 26, 21, 16, 11, and 6 psu. Afterwards, they were post-cultured in control seawater (31 psu) for another 4 days to corroborate the viability of injured germlings. Results showed that germlings of the introduced kelp were less resistant to low salinity, surviving to as low as 16 psu; whereas the germlings of the native kelp survived in salinities as low as 11 psu. Despite the observed differences, both species are relatively tolerant to low salinity. Our observations also indicated that, at least in a short term, gametophytes of both species were able to survive in salinities as low as 6 psu. The significance of low-salinity tolerance to the distribution of these kelps and for their offshore cultivation is discussed.     

Seagrass Proliferation Precedes Mortality during Hypo-Salinity Events: A Stress-Induced Morphometric Response

Halophytes, such as seagrasses, predominantly form habitats in coastal and estuarine areas. These habitats can be seasonally exposed to hypo-salinity events during watershed runoff exposing them to dramatic salinity shifts and osmotic shock. The manifestation of this osmotic shock on seagrass morphology and phenology was tested in three Indo-Pacific seagrass species, Halophila ovalis, Halodule uninervis and Zostera muelleri, to hypo-salinity ranging from 3 to 36 PSU at 3 PSU increments for 10 weeks. All three species had broad salinity tolerance but demonstrated a moderate hypo-salinity stress response – analogous to a stress induced morphometric response (SIMR). Shoot proliferation occurred at salinities <30 PSU, with the largest increases, up to 400% increase in shoot density, occurring at the sub-lethal salinities <15 PSU, with the specific salinity associated with peak shoot density being variable among species. Resources were not diverted away from leaf growth or shoot development to support the new shoot production. However, at sub-lethal salinities where shoots proliferated, flowering was severely reduced for H. ovalis, the only species to flower during this experiment, demonstrating a diversion of resources away from sexual reproduction to support the investment in new shoots. This SIMR response preceded mortality, which occurred at 3 PSU for H. ovalis and 6 PSU for H. uninervis, while complete mortality was not reached for Z. muelleri. This is the first study to identify a SIMR in seagrasses, being detectable due to the fine resolution of salinity treatments tested. The detection of SIMR demonstrates the need for caution in interpreting in-situ changes in shoot density as shoot proliferation could be interpreted as a healthy or positive plant response to environmental conditions, when in fact it could signal pre-mortality stress.     

Environmental influences on the formation and germination of hibernacula in the brackish-water bryozoan Victorella pavida Saville Kent, 1870 (Ctenostomata: Victorellidae)

Brackish-water and fresh-water bryozoans produce asexually derived dormant propagules that allow survival of unfavourable conditions and provide a potential means of dispersal. The propagules of brackish-water ctenostome bryozoans are called hibernacula. We monitored the life-cycle of the brackish-water ctenostome Victorella pavida Saville Kent, 1870 in its natural habitat and investigated, in laboratory cultures, the influence of temperature and salinity on the production and germination of hibernacula and on subsequent colony growth. V. pavida is a protected species in the UK, where its only locality is at Swanpool lagoon, Falmouth. Colonies were collected from Swanpool monthly from January 2004 to January 2005. Hibernaculum germination appeared to be triggered by increased water temperature (c. 13 °C) in the lagoon in March and April. In culture, germination was triggered by transfer from 5 °C to 19 °C in a range of salinities; subsequent colony growth was affected by salinity, with strongest growth at 13, 18 and 36 psu, and reduced growth at 5 and 9 psu. At 3.5 psu, hibernacula germinated, but there was no further development. At 36 psu there was an initial lag in growth, but after 30 d the colonies were comparable with those kept at 18 psu. Hibernaculum formation by colonies occurred from June to October, with production increasing towards October. Hibernacula appear not to have long-term viability but merely to permit survival from one year to the next. The results suggest that any changes in the hydrographic regime at Swanpool could have significant consequences for the survival of V. pavida.     

The effect of salinity on the growth,toxin production,and morphology of <Emphasis Type="BoldItalic">Nodularia spumigena</Emphasis> isolated from the Gulf of Gdańsk,southern Baltic Sea

Culture experiments on the toxic Nodularia spumigena strain NSGG-1 isolated from the Gulf of Gdańsk showed a significant effect of salinity on growth and nodularin production. Growth of the NSGG-1 strain, was optimal between 7 and 18 psu, lower at 3 and 24 psu and was significantly inhibited at the extreme salinities of 0 and 35 psu. Nodularin (NOD) content of N. spumigena, estimated by the NOD/Chla ratios, correlated positively with salinity and increased from 0 to 35 psu. The NOD/Chla ratio on day 10 of growth was high, and, reached the maximum at day 30. A sudden increase in salinity from 7 to 18 and 35 psu resulted in plasmolysis of Nodularia cells. Salinity was also observed to have other effects on NSGG-1; the filaments were longest at 7 psu, while an increased number of akinetes were formed at 35 psu. The number of heterocytes was markedly reduced at the extreme salinities. This latter finding might explain why Nodularia blooms do not occur outside a certain salinity range in nitrogen-deficient waters.     

Interactive effects of salinity and water depth on the growth of Melaleuca ericifolia Sm. (Swamp paperbark) seedlings

Melaleuca ericifolia Sm. (Swamp paperbark) is a common tree species in freshwater and brackish wetlands in southern and eastern Australia. The survival of this species in many wetlands is now threatened by increased salinity and inappropriate water regimes. We examined the response of 5-month-old M. ericifolia seedlings to three water depths (exposed, waterlogged and submerged) at three salinities (2, 49 and 60 dS m⁻¹). Increasing water depth at the lowest salinity did not affect survival, but strongly inhibited seedling growth. Total biomass, leaf area and maximum root length were highest in exposed plants, intermediate in waterlogged plants and lowest in submerged plants. Although completely submerged plants survived for 10 weeks at the lowest salinity, they demonstrated negative growth rates and were unable to extend their shoots above the water surface. At the higher salinities, M. ericifolia seedlings were intolerant of waterlogging and submergence: all plants died after 9 weeks at 60 dS m⁻¹. Soil salinities increased over time, and by Week 10, exceeded external water column salinities in both the exposed and waterlogged treatments. In exposed sediment, ∼90% of plants survived for 10 weeks at 60 dS m⁻¹ even though soil salinities reached ∼76 dS m⁻¹. No mortality occurred in the exposed plants at 49 dS m⁻¹, and small but positive relative growth rates were recorded at Week 10. We conclude that at low salinities M. ericifolia seedlings are highly tolerant of sediment waterlogging, but are unlikely to tolerate prolonged submergence. However, at the higher salinities, M. ericifolia seedlings are intolerant of waterlogging and submergence and died rapidly after 5 weeks exposure to this combination of environmental stressors. This research demonstrates that salinity may restrict the range of water regimes tolerated by aquatic plants.     

A high-throughput method for measuring growth and loss rates in microalgal cultures

A miniaturized and low-cost assay for algal growth and loss rates, and estimation of compensation light was developed and optimized. Microalgal cultures were grown in white 96-well microplates to estimate specific growth rates at six temperatures, five salinities and eight light levels. Data from black 24-well microplates at six temperatures, five salinities and five light conditions were used in addition to estimate loss rates and compensation light. Absorption and reflection of light were different in the white and black microplates. Growth rates were estimated from daily in vivo fluorescence (IVF) measurements using a microplate reader fitted with a fluorometer. To validate the microplate algal growth assay, IVF was compared with cell counting by flow cytometry. Maximal growth rate for the test alga Pseudochattonella farcimen (Heterokonta) was estimated to 0.52?±?0.05 day^?1 at optimal temperatures ranging from 9 to 14°C and salinities 18–26 psu. Lowest value of compensation light as photosynthetic photon flux density (PPFD) was 4.2?±?1.2 μmol photons m^?2 s^?1, and lowest saturation light, 34.1?±?3.7 μmol photons m^?2 s^?1, was observed in the temperature range 5–11°C and salinity range 23–28 psu. Minimum loss rate was obtained at temperatures 5–8°C and salinities 26–31 psu. Blooms of P. farcimen have been recorded in nature under conditions similar to those minimizing loss rates rather than maximizing growth rates in this study. The microalgal assay described here allows for a large number of conditions to be tested, and accurate optimal conditions for growth and loss rates to be obtained.     

Acclimation of the intertidal red alga Bangiopsis subsimplex (Stylonematophyceae) to salinity changes

The effect of salinity on growth, photosynthetic performance and osmotic acclimation was investigated in the eulittoral red algal species Bangiopsis subsimplex (Stylonematophyceae). The strain grew in a broad salinity range between 1 and 70 psu showing optimum growth between 10 and 50 psu. The saturation point I_k of the photosynthesis irradiance curves ranged between 153 and 83 μmol photons m^− 2 s^− 1 at all salinities and indicates an adaptation of B. subsimplex to moderate radiation conditions. Adjustments on the photosynthetic level (non-photochemical quenching) were sufficient to prevent damage to the photosynthetic apparatus as F_v/F_m values were constantly high (> 0.7) even when grown at the most hypo- and hypersaline conditions. As main low molecular weight carbohydrates, B. subsimplex contains the heteroside digeneaside and the polyol sorbitol. Digeneaside concentration was low and almost unchanged after hypersaline treatment (< 20 μmol g^− 1 DW), i.e. it did not play a role in osmotic acclimation. By contrast, sorbitol levels increased linearly from 150 to 380 μmol g^− 1 DW with increasing salinities between 5 and 60 psu, indicating its important function as an osmolyte and compatible solute under hypersaline conditions. The data presented are consistent with the natural habitat of B. subsimplex, i.e. the upper eulittoral zone.