Survival Of Germlings Research Articles

Variations in epilithic microbial biofilm composition and recruitment of a canopy-forming alga between pristine and urban rocky shores

Brown algae of the genus Ericaria are habitat formers on Mediterranean rocky shores supporting marine biodiversity and ecosystem functioning. Their population decline has prompted attempts for restoration of threatened populations. Although epilithic microbial biofilms (EMBs) are determinant for macroalgal settlement, their role in regulating the recovery of populations through the recruitment of new thalli is yet to be explored. In this study, we assessed variations in microbial biofilms composition on the settlement of Ericaria amentacea at sites exposed to different human pressures. Artificial fouling surfaces were deployed in two areas at each of three study sites in the Ligurian Sea (Capraia Island, Secche della Meloria and the mainland coast of Livorno), to allow bacterial biofilm colonization. In the laboratory, zygotes of E. amentacea were released on these surfaces to evaluate the survival of germlings. The EMB's composition was assessed through DNA metabarcoding analysis, which revealed a difference between the EMB of Capraia Island and that of Livorno. Fouling surfaces from Capraia Island had higher rates of zygote settlement than the other two sites. This suggests that different environmental conditions can influence the EMB composition on substrata, possibly influencing algal settlement rate. Assessing the suitability of rocky substrata for E. amentacea settlement is crucial for successful restoration.

Differential responses of trailing-edge populations of a foundation alga to thermal stress

ABSTRACT Populations within the same species range edge may experience contrasting local conditions and exhibit diverse levels of environmental tolerance. This heterogeneity within a range boundary has seldom been considered in studies forecasting the impact of anthropogenic habitat alteration and climate change on species distributions. Moreover, any ecological prediction under changing environmental conditions requires a good understanding of the combined responses of organisms to multiple stressors, in particular the effects on key life cycle stages of species. The intertidal seaweed Fucus serratus is a dominant species on northern Atlantic shores and whose southern limit is in the NW Iberian Peninsula. We examined how early developmental stages of southern-edge populations of this foundation alga responded to the combined effects of environmental stressors, including salinity and aerial and seawater temperature. Four populations from two different areas of the NW Iberian coast were considered: two populations from open shores on the northern coast and two populations from the western rias on the Atlantic coast. The study findings revealed inter-population variability in the response to heat stress, with greater survival of germlings from the northern populations than those from western rias. Environmental conditions are still more benign within western rias, under the influence of strong summer upwelling events. The results also suggest the key role of aerial thermal stress in determining the southern limit of distribution of the target species. The future of these heterogeneous edge populations from NW Iberian Peninsula depends on trends in climate change and the ability of populations to cope with these. Environmental changes may already be occurring at rates that exceed the plastic and adaptive potential of edge populations in N Spain, while the future of western rias as climate refugia for this and other foundation alga is also uncertain.

Environmental factors impact the early life stages of Sargassum ilicifolium in laboratory

Global climate changes exert extreme effects on habitat-forming macroalgal species, including the extinction of algal populations in marine ecosystems. Algal conservation and management strategies applied during the crucial phases of early life stages require development. This study aims to investigate the effects of water temperature, irradiance, and salinity on the development of Sargassum ilicifolium germlings in a long-term laboratory system. The results showed that development varied under different environmental conditions. The growth (in terms of both length and relative growth rate) and survival of germlings were significantly affected by water temperature, irradiance, and salinity. Based on our findings, the optimum combination of environmental factors for the germlings was a temperature of 18 °C, irradiance of 100 μmol photons m−2 s−1, and salinity of 35 psu. This study reveals the environmental limitations on germling development in the early life stages of S. ilicifolium and provides important information for the conservation and restoration of S. ilicifolium. Knowledge of the essential environmental conditions for this developmental stage can be used to ensure successful recruitment and establishment of populations of S. ilicifolium in the future.

Are we ready for scaling up restoration actions? An insight from Mediterranean macroalgal canopies.

Extensive loss of macroalgal forests advocates for large-scale restoration interventions, to compensate habitat degradation and recover the associated ecological functions and services. Yet, restoration attempts have generally been limited to small spatial extensions, with the principal aim of developing efficient restoration techniques. Here, the success of outplanting Cystoseira amentacea v. stricta germlings cultured in aquaria was experimentally explored at a scale of tens of kms, by means of a multifactorial experimental design. In the intertidal rocky shores of SE Italy, locations with a continuous distribution for hundreds of meters or with few thalli forming patches of few centimeters of C. amentacea canopy were selected. In each location, the effects of adult conspecifics and the exclusion of macrograzers (salema fish and sea urchins) on the survival of germlings were tested. We evaluated the most critical determinants of mortality for germlings, including the overlooked pressure of mesograzers (e.g. amphipods, small mollusks, polychaetes). Despite the high mortality observed during outplanting and early settlement stages, survival of C. amentacea germlings was consistently favored by the exclusion of macrograzers, while the presence of adult conspecifics had no effects. In addition, the cost analysis of the interventions showed the feasibility of the ex-situ method, representing an essential tool for preserving Cystoseira forests. Large scale restoration is possible but requires baseline information with an in-depth knowledge of the species ecology and of the areas to be restored, together with the development of specific cultivation protocols to make consistently efficient restoration interventions.

Warming impacts on early life stages increase the vulnerability and delay the population recovery of a long‐lived habitat‐forming macroalga

Abstract Understanding the combined effects of global and local stressors is crucial for conservation and management, yet challenging due to the different scales at which these stressors operate. Here, we examine the effects of one of the most pervasive threats to marine biodiversity, ocean warming, on the early life stages of the habitat‐forming macroalga Cystoseira zosteroides, its long‐term consequences for population resilience, and its combined effect with physical stressors. First, we performed a controlled laboratory experiment exploring the impacts of warming on early life stages. Settlement and survival of germlings were measured at 16°C (control), 20°C, and 24°C, and both processes were affected by increased temperatures. Then, we integrated this information into stochastic, density‐dependent integral projection models. Recovery time after a major disturbance significantly increased in warmer scenarios. The stochastic population growth rate (λs) was not strongly affected by warming alone, as high adult survival compensated for thermal‐induced recruitment failure. Nevertheless, warming coupled with recurrent physical disturbances had a strong impact on λs and population viability. Synthesis. The impact of warming effects on early stages may significantly decrease the natural ability of habitat‐forming algae to rebound after major disturbances. These findings highlight that, in a global warming context, populations of deep‐water macroalgae will become more vulnerable to further disturbances, and stress the need to incorporate abiotic interactions into demographic models.

Responses of Germlings to Acute Environmental Stress

The responses of Sargassum thunbergii germlings to high temperature, low salinity, desiccation, combined thermal and osmotic stress (35 ºC combined with 12 psu), anthracene, and eutrophication were examined. Probit regression analysis results showed that the median lethal time (LT50) values of high temperature decreased with the increase in temperature. The 24 h median lethal temperature was 36.9 ºC. For salinity treatment, the LT50 value of fresh water was 47.6 h. Survival rates of germlings were over 60% when germlings were exposed to salinities ranging from 27 psu to 7 psu at a time interval of 108 h post-treatment. The LT50 values of desiccation and combined thermal and osmotic stress (35 ºC combined with 12 psu) were 7.0 h and 9.8 h, respectively. Anovas showed that germlings were inhibited by high concentrations of anthracene (5 mg L-1 and 10 mg L-1) with low survival rates of below 50% and low relative growth rates of below 1% after 25 days of culture; however, low concentrations (0.01-1 mg L-1) had no significant effects. In addition, neither severe eutrophication nor disproportionality of N/P showed any significant effect on the survival and growth of germlings. Of the environmental stresses tested, possible occurrence of high temperature of 40 ºC and combined thermal and osmotic stress directly impacted the survival of germlings, suggesting that the deterioration of S. thunbergii bed may be related more to increasing extreme climatic events.

Highly efficient photoprotective responses to high light stress in Sargassum thunbergii germlings, a representative brown macroalga of intertidal zone

Photosynthetic responses to sudden exposure to high light stress (600μmolphotonsm−2s−1) and the potential for subsequent recovery were assessed in Sargassum thunbergii germlings grown under three different light intensities of 10μmolphotonsm−2s−1 (low light, LL), 60μmolphotonsm−2s−1 (moderate light, ML) and 300μmolphotonsm−2s−1 (high light, HL). The photosynthetic activity (maximum photochemical efficiency, Fv/Fm; rapid light curves, RLCs; non-photochemical quenching, NPQ) was estimated by chlorophyll fluorescence using a pulse amplitude modulated fluorometer. All treatments exhibited high capacity for dynamic photoinhibition, with the fast reaction kinetics of Fv/Fm during both inhibition and recovery period, and with the rapid induction of maximum NPQ (within minutes). HL-germlings characteristically demonstrated a high NPQ value of approx. 5.5, allowing a flexible and reversible response to stress. Besides the significant contribution of NPQ to photoprotection, photosynthetic capacity (ETRmax) in LL-germlings was as great as that in HL-germlings, suggesting that energy dissipation through photochemical electron transport system could also reduce probability of photodamage. NPQ in S. thunbergii germlings appeared to be not directly controlled by a transthylakoid proton gradient (ΔpH) due to the lack of “light activated state”. Furthermore, inhibition of xanthophyll cycle with DTT considerably blocked NPQpre induction of preillumated germlings, and a slow NPQ relaxation occurred upon disruption of ΔpH by NH4Cl, collectively indicating the importance of xanthophyll cycle to NPQ. These results suggested that S. thunbergii germlings could tolerate sudden high light by down-regulation of photosynthetic capacity, based on highly efficient photoprotective responses, including energy dissipation through xanthophyll cycle and photosynthetic electron transport. The photoprotection was efficiently independent on the light history of germlings. The high photosynthetic plasticity with immediate response to rapidly changing light may be a central feature explaining the survival of germlings in highly variable light environments of intertidal habitat.

Alexandrium fundyense cyst viability and germling survival in light vs. dark at a constant low temperature

Both observations and models suggest that large-scale coastal blooms of Alexandrium fundyense in the Gulf of Maine are seeded by deep-bottom cyst accumulation zones (“seed beds”) where cysts germinate from the sediment surface or the overlying near-bottom nepheloid layers at water depths exceeding 100m. The germling cells and their vegetative progeny are assumed to be subject to mortality while in complete darkness, as they swim to illuminated surface waters. To test the validity of this assumption we conducted laboratory investigations of cyst viability and the survival of the germling cells and their vegetative progeny during prolonged exposure to darkness at a temperature of 6°C, simulating the conditions in deep Gulf of Maine waters. We isolated cysts from bottom sediments collected in the Gulf of Maine under low red light and incubated them in 96-well tissue culture-plates in culture medium under a 10:14h light:dark cycle and under complete darkness. Cyst viability was high, with excystment frequency reaching 90% in the illuminated treatment after 30 days and in the dark treatment after 50 days. Average germination rates were 0.062 and 0.038d−1 for light and dark treatments, respectively. The dark treatment showed an approximately 2-week time lag in maximum germination rates compared to the light treatment. Survival of germlings was considerably lower in the dark treatment. In the light treatments, 47% of germinated cysts produced germlings that were able to survive for 7 days and produce vegetative progeny, i.e., there were live cells in the well along with an empty cyst at least once during the experiment. In the dark treatments 12% of the cysts produced germlings that were able to survive for the same length of time. When dark treatments are scaled to take into account non-darkness related mortality, approximately 28% of the cysts produced germlings that were able to survive for at least 7 days. Even though cysts are able to germinate in darkness, the lack of illumination considerably reduces survival rate of germling cells. In addition to viability of cysts in surface sediments and the near-bottom nepheloid layer, survivability of germling cells and their vegetative progeny at aphotic depths is an important consideration in assessing the quantitative role of deep-coastal cyst seed beds in bloom formation.

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.

High tolerance to fluctuating salinity allows Sargassum thunbergii germlings to survive and grow in artificial habitat of full immersion in intertidal zone

In this study, a four-way factorial experimental design (three temperatures, four salinities, two frequencies and three durations of osmotic stress) was used to test the tolerance of Sargassum thunbergii germlings shortly released from fertile thalli to osmotic stress. Results showed that the growth and survival of germlings were significantly affected by salinity and duration of osmotic stress, rather than by osmotic frequency. In addition to the main effects, all two-way, three-way and four-way interactions between the four stresses on the growth were significant. Germlings showed quick growth with relative growth rate (RGR, % day −1) over 16% when cultured at 32 psu combined with 30 °C. Although growths of germlings subjected to hypo-osmotic and hyper-osmotic conditions were significantly inhibited, RGRs over 12% were obtained except for those at 35 °C with the RGRs below 10%. In comparison to growth, survival was more tolerant to osmotic stress. Germlings showed high survivals over 60% when exposed to most osmotic stresses, by the end of experiment. Only under extreme conditions (12 psu for 4 h or 8 h at 35 °C) were the survivals reduced to below 10%. Although the effects of osmotic stress on the growth and survival were significant, germlings exhibited quick growth and high survival under most conditions. And those extreme conditions which had great destructive effect on germlings barely exist in field. Therefore, the construction of artificial tanks is feasible for the restoration of S. thunbergii beds in the intertidal zone.

Tolerance of Sargassum thunbergii germlings to thermal, osmotic and desiccation stress

The construction of artificial seaweed beds in the intertidal zone is a challenge due to extreme levels of physical stress. In order to provide a basis for the construction using the dispersal of microscopic juveniles, a three-way factorial experimental design was used to evaluate the tolerance of Sargassum thunbergii germlings shortly released from fertile thalli to temperature, salinity and desiccation in this study. Results revealed that temperature, salinity and desiccation significantly affected the growth and survival of germlings. Germlings showed rapid growth with relative growth rate (RGR, % day −1) over 16% when cultured at 25 °C and full immersion in normal seawater. Although growths of germlings subjected to moderate conditions were significantly inhibited, RGRs over 13% were obtained. The RGRs of germlings below 10% were observed only at 35 °C and 9 h desiccation treatments. In comparison to growth, survival was less affected by physical stress. Germlings showed low mortalities below 10% under appropriate conditions (25 °C and 30 °C combined with full immersion), and below 60% under moderate conditions, by the end of experiment. However, the mortality rates increased to over 90% under extreme conditions (9 h desiccation and 35 °C combined with full immersion in salinity of 12). These results showed that S. thunbergii germlings had high tolerance to physical stresses. In addition to the main effects, both two-way and three-way interactions between temperature, salinity and desiccation were significant. Based on the magnitude of effect, desiccation was the predominant factor affecting both growth and survival. According to the results, construction of artificial tanks in natural habitat to minimize desiccation may be an effective strategy for S. thunbergii restoration using germlings.

An investigation of the relationship between sediment particles size and the development of green algal mats (Ulva prolifera) on the intertidal flats of Muan, Korea

The relationship between median grain size of sediments and the abundance in the wild of green algal mats (Ulva prolifera) on the intertidal flats of Muan, Korea, were investigated. The impact of substratum particle size on the growth and survival of germlings was examined in the laboratory. In the wild, the average annual density of algal mats was 7,950 ind m−2. The algal mats mainly occurred in sands and exhibited patchy distribution. Statistical analysis indicates significant spatial analysis differences and a significant relationship between density and the ratio of sands to silts, suggesting that the distribution and density of this species were related to particle size. In laboratory experiments, the survival rate of U. prolifera germlings was the lowest value (22%) on sediments with a median grain size of 63–125 μm. Laboratory experiments have generally shown a positive relationship between attachment or survival of the alga and substratum particles size. Our laboratory results indicate a clear link between germling settlement/survival and substratum particle size. These results explain the spatial differences in abundance observed in the field in relation to the distribution and ratio of sands to silt on the Muan flats.

Seasonality and thallus ontogeny of edible seaweed Monostroma latissimum (Kützing) Wittrock (Chlorophyta, Monostromataceae) from Tosa Bay, Kochi, Japan

Monostroma latissimum (Kutzing) Wittrock is an intertidal rock-dwelling green algal species of commercial importance in Japan. This article reports on the seasonality of its growth and occurrence from three distinct habitats of marine and estuarine regions in Tosa Bay, Japan, for two consecutive growth seasons. Thallus lengths of individuals and environmental parameters were monitored monthly between November 2005 and July 2007. Culture studies were carried out to establish the species-level identity of the specimens. Nuclear encoded ITS 1 (Internal Transcribed Spacer 1) sequences reveal that the naturally occurring strain of M. latissimum has identical nucleotide sequences to those of the commercially cultivated strain from the Shimanto river estuary. We have also found that the two strains are cross-fertilizing. Seasonal fluctuations in thallus length were found to be distinctive to the habitat where the strain grows and re-occur annually. Algal cover was highest during winter months and lowest during the summer. However, we found only a very weak positive correlation between chosen environmental parameters and thallus length. Appearance and decay of thalli occurred earlier in high saline habitats. Therefore, it is likely that salinity influences the maturation of microscopic sporophytes or the growth and survival of germlings in M. latissimum.

Effects of filamentous algae and deposited matter on the survival of Fucus vesiculosus L. germlings in the Baltic Sea

As a result of increased nutrient levels in the Baltic Sea during thepast 50 years, mass developments of filamentous algae have become a commonfeature along the Swedish east coast and deposition of organic matter has alsoincreased. To test whether these two factors have any effects on the early lifestages of Fucus vesiculosus a number of laboratory andfield studies were conducted. The amount of epilithic and epiphytic filamentousalgae on F. vesiculosus and the amount of deposited matterin the littoral zone were quantified during the two reproductive periods ofF. vesiculosus, early summer (May–June) and lateautumn (September–October). Both filamentous algae (Cladophoraglomerata) and deposited matter (introduced either before or aftersettlement of fertilized eggs) were shown to significantly decrease the numberof surviving germlings. The survival of germlings seeded on stones withfilamentous algae, or seeded on culture dishes concurrently with the lowestconcentration of deposited matter (0.1 g dm−2),was 5% or less. In the field, the amount of filamentous algae was significantlyhigher during F. vesiculosus summer reproduction, whereasthe amount of deposited matter collected in traps was significantly higherduring the period of autumn reproduction. The greatest biomass of filamentousalgae was observed at sheltered sites. Based on the negative effects offilamentous algae and deposited matter on Fucusrecruitmentand the observation of local and seasonal differences in abundance offilamentous algae and deposition, we suggest that the prerequisites for thesurvival of either summer or autumn-reproducing populations of F.vesiculosus in the Baltic Sea may differ locally.

Distribution, dynamics and in situ seeding potential of Scrippsiella hangoei (Dinophyceae) cyst populations from the Baltic Sea

The distribution and seasonal dynamics of cyst populations of the spring bloom dinoflagellate Scrippsiella hangoei were studied in surface sediments on the southwest coast of Finland, Baltic Sea. In situ germination was assessed by monitoring the fraction of empty cysts and chlorophyll a fluorescence in cyst populations at different coastal sites throughout the annual cycle. Scrippsiella hangoei resting cysts were widely distributed in the study area and occurred in exceptionally large numbers (magnitudes of 10 4 -10 6 cysts cm -3 ) at all sampling locations between the innermost parts of the coastal archipelago and the open Gulf of Finland. The decreases in cyst number in winter and the increases occurring in late spring reflected the dynamics of germination and encystment of the species. Chlorophyll fluorescence appeared in mid-winter in -40% of cysts from well-aerated basins and 6-15% of cysts from temporarily anoxic sediments. A generally low increase in the proportion of empty cysts indicated that only a part of the potentially germinable cysts actually germinates. Given the high cyst concentrations in the sediments, the potential for germination is considerable, despite the environmentally and physiologically determined losses. In contrast, the size of the vegetative inoculum is very low, indicating that the survival of germlings is problematic under harsh winter conditions. This is an unusual life cycle strategy; however, the early release of cells into the water column provides a high probability for successful bloom initiation under the unpredictable meteorological conditions in winter and early spring, which often lead to the sudden onset of favourable growth conditions.

The interactive effects of adult canopy, germling density and grazing on germling survival of the rockweed Ascophyllum nodosum

Mortality soon after settlement is typically high and spatial distribution of germlings is usually very variable in seaweeds. This is the case for Ascophyllum nodosum (L.) Le Jol, which is a very common brown alga on sheltered rocky shores of the northern Atlantic. In this paper, the interactive effects of several factors on the survival of germlings of A. nodosum were investigated using an experiment carried out on the Swedish west coast. The general hypothesis that the combination of littorinid grazing, adult canopy and germling density affect the survival of germlings was tested. Two densities of zygotes were seeded onto small outplant discs in the laboratory. After 4 wk, the discs were transplanted onto the shore in plots, which were composed of all possible combinations of adult canopy and Littorinid grazing. Germling survival was calculated at 2 different points in time (after 5 and 23 d on the shore). After 5 d, there was no effect of grazers in the presence of canopy. In contrast, in areas cleared of canopy, survival was extremely low where grazers were present, but high where grazers were removed. At this stage, higher survival was observed at low density under an adult canopy and the opposite trend was observed in cleared areas. Mortality rates were not constant over time. In the presence of gastropods, instantaneous mortality rates were higher during the first 5 d than over the whole experimental period. Thus, the first period constituted the mast vulnerable phase for A. nodosum germlings. After 23 d, there was a trend far germling survival to decrease in the presence of grazers, regardless of other factors. This result suggests that grazers may affect the patterns of recruit distribution at later stages and the transition probabilities to macrorecruits.

Do littorinids affect the survival of Ascophyllum nodosum germlings?

The survival of germlings of the brown alga Ascophyllum nodosum on the west coast of Sweden were investigated in two field experiments. In the first experiment the role of Littorina fabalis, L. littorea, L. obtusata and L. saxatilis for the survival of 5 days old germlings were tested at two spatial scales, by comparing plots cleared of Littorina spp with plots holding the natural composition of the snails. The second experiment tested the effect of Littorina littorea and the exclusion of mesoherbivores other than littorinids on the survival of 13 days old germlings placed in cages. The treatments were cages with and without L. littorea and two mesh sizes (1.4 and 6.3 mm respectively), where the finer mesh was thought to exclude the mesoherbivores. There were no detectable effects of Littorina spp in the first experiment despite a low survival of the germlings. Significant differences in the survival of germlings were found between plots within a shore on a spatial scale of 2 to 30 m, but no significant differences were found between shores about 1 km apart. In the second experiment L. littorea had a negative effect on the survival of the germlings, and there was a lower level of survival of the juveniles in the cages with a larger mesh size compared to those with a finer mesh size. It is suggested that the difference in effect between the cages with different mesh sizes is due to the difference of accessibility for mesoherbivores of different sizes and that it is not caused by physical alterations by the cages. Our experiments showed that Littorina spp had no effect on the survival of germlings of A. nodosum unless in cages at abundances higher than those naturally occurring in the area at this time. Further, the experiments suggest that other mesoherbivores such as isopods and amphipods are important grazers on A. nodosum germlings.