Bioclimatic conditions in Mexico City – an assessment

 Bioclimatic conditions have been assessed for a large urban area located in the tropical highlands of central Mexico using the indices (in °C) of resultant temperature (RT) and effective temperature (ET). The well-developed heat island effect the city generates, reduces the number of nights categorized as cold (ET between 5 and 15° C) to cool (ET from 15 to 18.5° C). Most days fall in the cold to cool range and during the warm season (April to June) the bioclimate of Mexico City is mostly within the neutral (comfort) range. The effect of the nocturnal (to the west) and daytime (to the east of the town) heat island is noticeable in the central and northern sectors. The daytime heat island located in these regions, albeit small (urban air temperature 2–3° C greater than rural), compared with the nocturnal heat island intensity (9–10° C) still adds energy to the already heated afternoon urban air. ET values in the north and central sectors approach the threshold for comfort (ET of 25° C) during the warm months around noon. It is not surprising to find that as the nocturnal heat island has increased over the years (1921–1985) as the city grew, so has the ET for the central district and indicating the dominating role of temperature in the ET index. Assessment of the diurnal cycle of bioclimatic conditions in downtown Mexico City by means of two empirical indices (effective temperature and thermopreferendum) throughout the years gave similar results to those obtained from the application of Fanger’s predicted mean vote (PMV) model. An attempt has been made to characterize four bioclimatic zones in the capital city. Received: 8 March 1994 / Revised: 15 July 1996 / Accepted: 9 September 1996     

The effect of temperature on larval pre-settlement duration and metamorphosis for the sponge, <Emphasis Type="Italic">Rhopaloeides odorabile</Emphasis>

Rising sea temperatures may potentially affect the dispersive larval phase of sessile marine invertebrates with consequences for the viability of adult populations. This study demonstrated that the planktonic larvae of Rhopaloeides odorabile, a common Great Barrier Reef sponge, survived and metamorphosed when exposed to temperatures up to 9°C above the annual maximum (~29°C). Planktonic larval duration of 54 h, at ambient temperatures (~28°C), were reduced to 18 h for larvae exposed to elevated temperatures (32–36°C). Moreover, at ambient temperatures larvae began metamorphosing after 12 h, but at 32–36°C this reduced to only 2 h. Larvae survived and could still metamorphose at temperatures as high as 38°C, but were no longer functional at 40°C. These results imply that predicted increases in sea surface temperature may reduce planktonic larval duration and dispersal capabilities, thereby contributing to population subdivision of the species.     

Evaluating the behaviour of different thermal indices by investigating various outdoor urban environments in the hot dry city of Damascus, Syria

Consideration of urban microclimate and thermal comfort is an absolute neccessity in urban development, and a set of guidelines for every type of climate must be elaborated. However, to develop guidelines, thermal comfort ranges need to be defined. The aim of this study was to evaluate the behaviour of different thermal indices by investigating different thermal environments in Damascus during summer and winter. A second aim was to define the lower and upper limits of the thermal comfort range for some of these indices. The study was based on comprehensive micrometeorological measurements combined with questionnaires. It was found that the thermal conditions of different outdoor environments vary considerably. In general, Old Damascus, with its deep canyons, is more comfortable in summer than modern Damascus where there is a lack of shade. Conversely, residential areas and parks in modern Damascus are more comfortable in winter due to more solar access. The neutral temperatures of both the physiologically equivalent temperature (PET) and the outdoor standard effective temperature (OUT_SET*) were found to be lower in summer than in winter. At 80 % acceptability, the study defined the lower comfort limit in winter to 21.0 °C and the upper limit in summer to 31.3 °C for PET. For OUT_SET*, the corresponding lower and upper limits were 27.6 °C and 31.3 °C respectively. OUT_SET* showed a better correlation with the thermal sensation votes than PET. The study also highlighted the influence of culture and traditions on people’s clothing as well as the influence of air conditioning on physical adaptation.     

Interactive effects of climate change and eutrophication on the dinoflagellate-bearing benthic foraminifer <Emphasis Type="Italic">Marginopora vertebralis</Emphasis>

Elevated sea surface temperatures caused by global climate change and increased nutrient concentrations resulting from land runoff both are stressors for calcifying coral reef organisms. Here, we test the hypothesis that increased temperature leads to bleaching in dinoflagellate-bearing foraminifera similar to corals and that increased nutrients through runoff can exaggerate stress on the holobiont. In an experiment manipulating temperatures alone, we have shown that mortality of Marginopora vertebralis increased with temperatures. Most individuals died after 7 days at 34°C, ~5°C above current summer maxima. Survival at 37 days was >98% at 28°C. After 7 days of exposure to 31 or 32°C, photosynthesis of the endosymbionts was compromised, as indicated by several photophysiological parameters (effective quantum yield and apparent photosynthetic rate). In a flow-though experiment manipulating both temperature (three levels, 26, 29 and 31°C) and nitrate concentrations (3 levels, ~0.5, 1.0 and 1.4 μmol l⁻¹ NO₃ ⁻), elevated temperature had a significant negative effect on most parameters measured. At 31°C, most photopigments (measured by UPLC) in the foraminifera were significantly reduced. The only pigment that increased was the photoprotective diatoxanthin. Several other parameters measured (maximum and effective quantum yield, O₂ production in light, organic carbon contents) also significantly decreased with temperature. Optode-based respirometry demonstrated that the presence of symbionts at elevated temperatures represents a net carbon loss for the host. Growth rates of M. vertebralis and mortality at the end of the experiment were significantly affected by both temperature increase and nitrate addition. We conclude that these foraminifera bleach in a similar fashion to corals and that global sea surface temperature change and nitrate increases are stressors for these protists. Furthermore, this provides support for the hypothesis that management of local stressors elevates resilience of coral reefs to global stressors.     

The influence of urban design on outdoor thermal comfort in the hot, humid city of Colombo, Sri Lanka

The outdoor environment is deteriorating in many tropical cities due to rapid urbanization. This leads to a number of problems related to health and well-being of humans and also negatively affects social and commercial outdoor activities. The creation of thermally comfortable microclimates in urban environments is therefore very important. This paper discusses the influence of street-canyon geometry on outdoor thermal comfort in Colombo, Sri Lanka. Five sites with different urban geometry, ground cover, and distance from the sea were studied during the warmest season. The environmental parameters affecting thermal comfort, viz. air temperature, humidity, wind speed, and solar radiation, were measured, and the thermal comfort was estimated by calculating the physiologically equivalent temperature (PET). The thermal comfort is far above the assumed comfort zone due to the combination of intense solar radiation, high temperatures, and low wind speeds, especially on clear days. The worst conditions were found in wide streets with low-rise buildings and no shade trees. The most comfortable conditions were found in narrow streets with tall buildings, especially if shade trees were present, as well as in areas near the coast where the sea breeze had a positive effect. In order to improve the outdoor comfort in Colombo, it is suggested to allow a more compact urban form with deeper street canyons and to provide additional shade through the use of trees, covered walkways, pedestrian arcades, etc. The opening up of the city's coastal strip would allow the sea breeze to penetrate further into the city.     

The thermal tolerance of crown-of-thorns (Acanthaster planci) embryos and bipinnaria larvae: implications for spatial and temporal variation in adult populations

To understand the role of sea temperature on the population biology of the crown-of-thorns sea star Acanthaster planci, the thermal window for embryonic and larval development was investigated. In two experiments, the response of embryos and larvae across 12 temperatures from 19.4 to 36.5 °C was quantified as the percentage of individuals reaching cleavage stage embryos, blastula, gastrula, early-bipinnaria, late-bipinnaria larvae or abnormal. Measurements were made at 7 times up to 72 h post-fertilisation, with the morphometrics of larvae measured in the 72-h sample. Acanthaster planci developed at temperatures between 19.4 and 33.2 °C, with a thermal window for development to the late-bipinnaria stage between 25.6 and 31.6 °C. Development rate, normal development and larval size were optimal at 28.7 °C, with development rates remaining relatively constant up to 31.6 °C. Rates of abnormality increased steadily (early embryonic stages) above 28.7 °C and was 100 % at temperatures approaching 33 °C. These experiments provide a more detailed insight into the response of A. planci developmental stages to temperature. The present day distribution of the species in eastern Australia overlap with the optimal thermal window for development to the late-bipinnaria stage (≈25–32 °C), implying a role of temperature in controlling population distributions and abundances. Despite this, short- or long-term temperature increases may not be a major modulator of the crown-of-thorns recruitment success, population dynamics and distribution in the future as no significant change in development rates, larval survival and growth occurred within this thermal window. Therefore, moderate (1–2 °C) increases in sea temperatures caused by El Niño or near-future ocean warming may not drive an increase in developmental and settlement success. Indeed, without any acclimation to warmer temperatures expected under near-future warming (+2 to 4 °C), climate change could ultimately reduce larval survival due to elevated mortality above the optimal development temperature.     

Quantifying the cooling effect of rain events on outdoor thermal comfort in the southern coastal stations of the Caspian Sea

Pleasant outdoor thermal conditions depend on a wide range of climatic elements. The impact of rainfall events, as important climatic elements, on providing thermal comfort, has been less explored in the available literature. The work presented herein investigates the impact of Rainy Days as well as a Day Prior to (D_prior) and a Day Post rain (D_post) events on thermal conditions in the southern coastal region of the Caspian Sea. In this study, rainfall events during 1961–2017 observational period were categorized based on their intensity. Then, human thermal comfort during non-rainy (sunny) and rainy days was estimated and compared by using the radiation-driven Physiological Equivalent Temperature (PET) index, Universal Thermal Climate Index (UTCI) and Perceived Temperature (PT) index. Furthermore, difference between the average of thermal conditions in rainy days compared to a day prior and a day post rain events was calculated separately for comfort, cold and heat stress thresholds of each bioclimatic index. Finally, the correlation between the average of indices for rainy days and the frequency of rainfall events of each specific year was computed. Results suggested that overall average of studied indices for all rainy days is lower than the average for days prior and post the rain events. PET index has shown to be most impacted and reduced as a result of rain events and therefore more indicative of a cool ing effect. The observed difference in total average of PET in rainy days compared to non-rainy days were 8.30 °C, 5.86 °C and 8.85 °C for Babolsar, Rahst and Gorgan stations, respectively. Generally, the cooling effect of rain events on the temperature for a day prior rain events is higher than a day post rainfall. Finally, the trend analysis on rainy days in the studied period revealed that the average of bioclimatic indices in western stations (Babolsar and Rasht) are increasing whereas a decreasing trend was observed for Gorgan as more of an eastern station.     

Bioclimatic characterisation of an urban area: a case study in Bologna (Italy)

Summer bioclimatic discomfort is a significant public health problem. Bioclimatic characterisations of populations living in urban areas are usually very poor, although the risks are relatively higher in cities because of the phenomenon known as the “urban heat island”. We compared airport, rural, and urban bioclimatic conditions in terms of apparent temperature, Thom index, and temperature alone in several sites within a radius of approximately 25 km from the city of Bologna (Italy). The comparison between meteorological monitoring stations within and near the urban area showed the large impact of the urban heat island effect. Nighttime data showed the largest differences among the investigated sites. Minimum apparent temperatures at rural stations were about 3.5°C lower than the urban 30 m reference station, and 6°C lower than the 2 m urban site. The 2 m apparent temperature values within the urban area were several degrees higher (typically 2°C) than those taken above the roof, both for minimum and maximum values. Temporal trends in the different sites were highly correlated (generally above 0.90), but regression residuals were sometimes quite large. Finally, epidemiological implications are briefly addressed.     

The effects of increased constant incubation temperature and cumulative acute heat shock exposures on morphology and survival of Lake Whitefish (Coregonus clupeaformis) embryos

Increasing incubation temperatures, caused by global climate change or thermal effluent from industrial processes, may influence embryonic development of fish. This study investigates the cumulative effects of increased incubation temperature and repeated heat shocks on developing Lake Whitefish (Coregonus clupeaformis) embryos. We studied the effects of three constant incubation temperatures (2 °C, 5 °C or 8 °C water) and weekly, 1-h heat shocks (+3 °C) on hatching time, survival and morphology of embryos, as these endpoints may be particularly susceptible to temperature changes. The constant temperatures represent the predicted magnitude of elevated water temperatures from climate change and industrial thermal plumes. Time to the pre-hatch stage decreased as constant incubation temperature increased (148 d at 2 °C, 92 d at 5 °C, 50 d at 8 °C), but weekly heat shocks did not affect time to hatch. Mean survival rates and embryo morphometrics were compared at specific developmental time-points (blastopore, eyed, fin flutter and pre-hatch) across all treatments. Constant incubation temperatures or +3 °C heat-shock exposures did not significantly alter cumulative survival percentage (~50% cumulative survival to pre-hatch stage). Constant warm incubation temperatures did result in differences in morphology in pre-hatch stage embryos. 8 °C and 5 °C embryos were significantly smaller and had larger yolks than 2 °C embryos, but heat-shocked embryos did not differ from their respective constant temperature treatment groups. Elevated incubation temperatures may adversely alter Lake Whitefish embryo size at hatch, but weekly 1-h heat shocks did not affect size or survival at hatch. These results suggest that intermittent bouts of warm water effluent (e.g., variable industrial emissions) are less likely to negatively affect Lake Whitefish embryonic development than warmer constant incubation temperatures that may occur due to climate change.     

The influence of temperature variations and thermal pollution on various aspects of the biology of the prawn Palaemon pacificus (Stimpson)

The influence of different temperatures 10, 15, 20, and 25°C on the food consumption, growth, moulting rate, and respiration of Palaemon pacificus (Stimpson) from Langebaan Lagoon, west coast of South Africa, was studied under laboratory conditions. At 10°C mortality was high so that food consumption and moulting rate could not be determined as these were very low. At higher temperatures, food consumption was found to be temperature dependent, the rate at 25°C being twice that at 15°C. Growth rate was most favourable at 25°C. At 28°C growth rate was lower than at 20°C but higher than at 15°C. The intermoult period was 17 days at 15°C, and 11 and 10 days at 20, and 25°C, respectively. It seems that from an energetic point of view, 25°C is the most favourable temperature for P. pacificus. Several indices of growth efficiency at different temperatures are presented. The appearance of this prawn in South African west coast localities such as Langebaan during the summer and its disappearance during winter, can be explained by its temperature preferences. The possibility that thermal pollution from a nuclear power station may be beneficial to this prawn, is discussed.     

Thermal habitat of adult Atlantic salmon Salmo salar in a warming ocean

The year-round thermal habitat at sea for adult Atlantic salmon Salmo salar (n = 49) from northern Norway was investigated using archival tags over a 10 year study period. During their ocean feeding migration, the fish spent 90% of the time in waters with temperatures from 1.6–8.4°C. Daily mean temperatures ranged from −0.5 to 12.9°C, with daily temperature variation up to 9.6°C. Fish experienced the coldest water during winter (November–March) and the greatest thermal range during the first summer at sea (July–August). Trends in sea-surface temperatures influenced the thermal habitat of salmon during late summer and autumn (August–October), with fish experiencing warmer temperatures in warmer years. This pattern was absent during winter (November–March), when daily mean temperatures ranged from 3.4–5.0°C, in both colder and warmer years. The observations of a constant thermal habitat during winter in both warmer and colder years, may suggest that the ocean distribution of salmon is flexible and that individual migration routes could shift as a response to spatiotemporal alterations of favourable prey fields and ocean temperatures.     

Seasonal and year-to-year variations in the growth of Zostera marina L. (eelgrass) in the lower Chesapeake Bay

Seasonal and year-to-year variations in the growth of Zostera marina L. were measured at three sites in two locations in the lower Chesapeake Bay between 1978 and 1980. The maximum values for the 1979 above- and belowground standing crop ranged from 161–336 g dry wt m⁻² and 61–155 g dry wt m⁻², respectively, leaf length was 19.6–59.7 cm and shoot density 1418–2576 shoot m⁻². Values for 1980 tended to be greater and may be related to climatical differences between the two years. Maximum values were usually recorded in the months of June and July when water temperatures were between 20 and 25°C. Significant loss of leaves occurred in July and August, when water temperatures ranged between 25 and 30°C, while new shoots began to appear more rapidly in late September as water temperatures dropped below 20°C. The greatest increase in all growth parameters occurred from April to June during which time reproductive shoots were present, and accounted for up to 25% of the total number of shoots.     

Freezing and desiccation injury resistance in the filamentous green alga Klebsormidium from the Antarctic, Arctic and Slovakia

The freezing and desiccation tolerance of 12 Klebsormidium strains, isolated from various habitats (aeroterrestrial, terrestrial, and hydro-terrestrial) from distinct geographical regions (Antarctic — South Shetlands, King George Island, Arctic — Ellesmere Island, Svalbard, Central Europe — Slovakia) were studied. Each strain was exposed to several freezing (−4°C, −40°C, −196°C) and desiccation (+4°C and + 20°C) regimes, simulating both natural and semi-natural freeze-thaw and desiccation cycles. The level of resistance (or the survival capacity) was evaluated by chlorophyll a content, viability, and chlorophyll fluorescence evaluations. No statistical differences (Kruskal-Wallis tests) between strains originating from different regions were observed. All strains tested were highly resistant to both freezing and desiccation injuries. Freezing down to −196°C was the most harmful regime for all studied strains. Freezing at −4°C did not influence the survival of studied strains. Further, freezing down to −40°C (at a speed of 4°C/min) was not fatal for most of the strains. RDA analysis showed that certain Antarctic and Arctic strains did not survive desiccation at +4°C; however, freezing at −40°C, as well as desiccation at +20°C was not fatal to them. On the other hand, other strains from the Antarctic, the Arctic, and Central Europe (Slovakia) survived desiccation at temperatures of +4°C, and freezing down to −40°C. It appears that species of Klebsormidium which occupy an environment where both seasonal and diurnal variations of water availability prevail, are well adapted to freezing and desiccation injuries. Freezing and desiccation tolerance is not species-specific nor is the resilience only found in polar strains as it is also a feature of temperate strains. Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia. This paper is dedicated to the memory of the late Dr. Bohuslav Fott (1908–1976), Professor of Botany at the Charles University in Prague, to mark the centenary of his birth.     

Heat-Resistance and Heat-Shock Response in the Nosocomial Pathogen <Emphasis Type="Italic">Enterococcus faecium</Emphasis>

We have characterized the heat-shock response of the nosocomial pathogen Enterococcus faecium. The growth of E. faecium cells was analyzed at different temperatures; little growth was observed at 50°C, and no growth at 52°C or 55°C. In agreement, a marked decrease of general protein synthesis was observed at 52°C, and very light synthesis was detected at 55°C. The heat resistance of E. faecium cells was analyzed by measuring the survival at temperatures higher than 52°C and, after 2 h of incubation, viable cells were still observed at 70°C. By Western blot analysis, two heat-induced proteins were identified as GroEL (65 kDa) and DnaK (75 kDa). Only one isoform for either GroEL or DnaK was found. The gene expression of these heat-shock proteins was also analyzed by pulsed-labeled experiments. The heat-induced proteins showed an increased rate of synthesis during the first 5 min, reaching the highest level of induction after 10 min and returning to the steady-state level after 20 min of heat treatment. Received: 29 March 2002 / Accepted: 5 July 2002     

Mean radiant temperature in idealised urban canyons—examples from Freiburg, Germany

Studies on the thermal comfort of humans in urban areas require meteorological data such as air temperature, air humidity, wind speed, and short- and long-wave fluxes. In such studies radiation fluxes can be expressed by the mean radiant temperature—a parameter with high variability in urban areas due to variability in global radiation. Wind speed in urban areas is influenced by urban obstacles and their orientation. Both mean radiant temperature and wind speed can be modified or changed by different height-to-width ratios or orientation of urban structures. Modifications to these parameters by typical urban structures (represented by the height-to-width ratio) can result in variation of mean radiant temperature over a range of more than 30°C, which can correspond to three levels of thermal stress. The results presented here provide a possible means of comparing different urban configurations in different climate regions.     

Effect of change in ambient temperature on core temperature during the daytime

In this study, the hypothesis is tested that continuous increases in ambient temperature (T_a) during daytime would give elevated core and skin temperatures, and consequently better thermal sensation and comfort. Rectal temperature (T_re), skin temperatures and regional dry heat losses at 7 sites were continuously measured for 10 Japanese male subjects in three thermal conditions: cond. 1, stepwise increases in T_a from 26 °C at 9 h00 to 30 °C at 18 h00; cond. 2, steady T_a at 28 °C from 9 h00 to 18 h00 and cond. 3, stepwise decreases in T_a from 30 °C at 9 h00 to 26 °C at 18 h00. Oxygen consumption was measured and thermal sensation and comfort votes were monitored at 15 min intervals. Body weight loss was measured at 1 h intervals. While T_re increased continuously in the morning period in any condition, it increased to a significantly greater (p?<?0.05) 36.9?±?0.3 °C at 18 h00 in cond. 1 relative to 36.7?±?0.28 °C in Cond. 2 and 36.5?±?0.37 °C in cond. 3. Better thermal comfort was observed in the afternoon and the evening in Cond.1 as compared with the other 2 conditions. Thus, a progressive and appropriate increase in T_a may induce optimal cycle in core temperature during daytime, particularly for a resting person.     

Effect of temperature on early development of the Pacific mussel <Emphasis Type="Italic">Mytilus trossulus</Emphasis> (Bivalvia: Mytilidae) in sea water polluted by copper ions

The effects of water temperatures of 7, 15 and 20°C and pollution of sea water by copper ions in concentrations of 0.005 and 0.01 mg/l on the early development of the Pacific mussel Mytilus trossulus were studied. It was shown that copper additives were most toxic at the initial stages of development, from fertilization up to the veliger stage. It was determined that larvae of the Pacific mussel were able to adapt to copper at a concentration of 0.005 mg/l. The copper toxicity increased to a greater extent with an increase in water temperature from its average value of 15°C, than with a temperature decrease.     

Seasonal variations in abundance, development and vertical distribution of Calanus finmarchicus, C. hyperboreus and C. glacialis in the East Icelandic Current

The seasonal variation in abundance and development of Calanusfinmarchicus, Calanus hyperboreus and Calanus glacialis in relationto hydrography and chlorophyll (Chl) a was studied in the Arcticwaters of the East Icelandic Current to the north-east of Icelandfrom March 1995 to February 1996. The sampling was carried outat approximately monthly intervals on a transect of five stationsextending from 67°00'N, 13°55'W to 68°00'N, 12°40'W.In April, May and June, vertical distribution was also investigated.Spring warming of the surface waters began in May, with maximumtemperatures recorded in August (~5°C, mean for uppermost50 m). Below 75 m, temperature remained at <0°C throughoutthe year. The spring bloom of phytoplankton started in earlyMay and the highest Chl a concentrations were measured duringlate May to early June (~1 mg Chl a m^-3). Calanus finmarchicusdominated in terms of numbers (~75%), while C. hyperboreus dominatedbiomass (~76%). Calanus glacialis occurred only in low numbers(~1%) and was only a small portion of biomass (~0.7%). The abundanceof all species was low during the winter and peaked once duringsummer: C. finmarchicus in July (~16 000 ind. m^-2) and C. glacialisand C. hyperboreus in June (~370 and ~7700 ind. m^-2, respectively).The biomass of C. finmarchicus had two maxima, in April (~1.9g m^-2) and July (~1.5 g m^-2), while C. hyperboreus peaked inJune (~12.3 g m^-2). Calanus finmarchicus was estimated to spawnin early May at about the start of the spring bloom, while C.hyperboreus spawned prior to the spring bloom, in late Februaryto early March. On the basis of copepod stage distribution,C. finmarchicus was considered to have a 1-year life cycle andC. hyperboreus at least a 2-year life cycle.     

The effect of Sea Water and Temperature on the Germination Behaviour of Crithmum maritimum

The seeds of Crithmmm maritimum L. were germinated floating on various concentrations of sea water up to 50% at constant temperatures of 5, 10, 15, 20, and 25°C and at alternating temperatures of 5 and 15°C. 5 and 25°C. and 15 and 25°C. Significantly higher germination was obtained at alternating than at constant temperature. When two constant temperatures at which no germination occurred were alternated, good germination was obtained. There was reduced germination and increase in time of first germination as sea water concentration increased, in the absence of sea water, high temperature caused not only severe inhibition of germination but also permanent injury to the seeds. The results help to explain the germination behaviour of the species in nature.     

Prevailing sea surface temperatures inhibit summer reproduction of the kelp Laminaria digitata at Helgoland (North Sea)

The impact of abiotic factors on kelp sporophyte reproduction has rarely been investigated. Laminaria digitata (Hudson) J.V. Lamouroux is one of the few summer fertile Laminaria species worldwide and reproduction is subjected to relatively high water temperatures. We investigated the impact of prevailing summer temperatures (~18°C in August) on the induction of sporangia, meiospore release, and germination at the island of Helgoland (North Sea). At Helgoland, fertile sporophytes are found between April and December with a maximum in late summer. While released meiospore numbers were constant between June and October, germination rates decreased significantly in summer. Short‐term exposure of mature sori to 17°C–22°C induced a significantly higher meiospore release indicating enhancement of sporulation by elevated temperatures. Induction of sporangia on vegetative blade disks was not possible at 20°C, and fertility was only 20% at 18°C–19°C, but it was 100% in cool temperatures of 1°C–10°C. It was shown for the first time in a kelp species that “sporogenesis” is the life‐cycle process with the narrowest temperature window compared to growth or survival of the sporophyte or reproduction, growth, and survival of the gametophyte. We incorporated several parameters (induction time, fertile area, and relative fertility) into a “Reproductive efficiency index.” This indicates that sporogenesis of L. digitata is a cold‐adapted process with an optimum at (5)–10°C. The results show that the population at Helgoland is at its reproduction limit despite the existence of other geographically more southerly located populations.