Organic and inorganic human-induced contamination of Posidonia oceanica meadows

In coastal environments, plants are used for phytoremediation of contamination. Organic and inorganic contaminants may be due to natural and/or anthropogenic sources. The aim of this study is to compare inorganic (trace metal) and organic (PAH) contamination in Posidonia oceanica and to analyse the relationship between these types of pollutants indeed very few studies have been interested in their correlations and common sources. P. oceanica leaves were collected in two sites exhibiting different levels of human-induced pressure. Higher values were recorded in the more polluted site (Toulon) for trace metals (Ag, Hg, Pb) as well as for PAHs (Medium Molecular Weight and High Molecular Weight) due to the presence of the city and/or harbour in proximity. For the first time in a coastal environment, correlations were observed between metals and PAHs.     

Comparing shoot population dynamics methods on Posidonia oceanica meadows

Prediction capacity of three main shoot population dynamics methods (age structure, net shoot recruitment per plagiotropic rhizome and shoot census) have been tested for a period of four years (2002-2006) on a Posidonia oceanica meadow. Accuracy of each method was checked by comparing measured and predicted densities at the end of the study period. Predicted densities came from the evolution of initial densities (measured in 2002) by a basic exponential model of population growth. The exponential model used the different net shoot recruitment rate estimates by each population dynamics method on three depths (upper, medium and lower limit) and three localities at each depth. Predictions performed by shoot census and net shoot recruitment per plagiotropic rhizome methods matched with measured densities at the end of the study period. Conversely, age structure method underestimated shoot densities at each depth, indicating an unreal decrease of shoot population in the meadow.     

Posidonia oceanica in the Marmara Sea

The seagrass Posidonia oceanica is a stenohaline species endemic to the Mediterranean Sea, where it normally lives at a salinity of between 36.5 and 39.5 ppt. Surveys carried out at the North-eastern distribution limits revealed large beds in the Dardanelles Strait and isolated beds in the Marmara Sea, where the salinity ranges between 21.5 and 28 ppt. Microsatellite analysis of these low-salinity tolerant P. oceanica beds, show different signs of genetic isolation: excess of heterozygosity and a presence of fixed alleles. These particularities are rarely found in the whole distributional range of the species. Moreover, all the populations considered in the analysis have a very low genetic diversity in comparison with most of the meadows sampled throughout the Mediterranean Sea. Taking into consideration the genetic data, rhizome expansion rate and the actual extent of the isolated beds in the Marmara Sea and knowing the reproductive rate and dissemination characteristics of P. oceanica, we hypothesize that the isolated population of the Marmara Sea has been established since the Middle Holocene, before the catastrophic intrusion of brackish water into the Marmara Sea and the strong and persistent flow coming from the Black Sea.     

Effects of salinity on leaf growth and survival of the Mediterranean seagrass Posidonia oceanica (L.) Delile

The main aim of this study was to estimate the effects of salinity variation on the Mediterranean seagrass Posidonia oceanica (L.) Delile and its attached epiphytes. Leaf growth and survival of this plant were tested in several short-term (15 days) mesocosms experiments under controlled conditions between February 2001 and November 2001. Plants collected from shallow meadows at Alicante (SE Spain), with an ambient salinity of 36.8-38.0 psu, were placed in tanks of 300 L with an additional overhead light and exposed to different salinity treatments (ranging from 25 to 57 psu) during 15 days. To estimate the mortality and growth recuperation, in some experiments shoots were returned to control salinity (38 psu). Leaf growth was measured in the laboratory where epiphytic fauna and flora were removed from leaves, with a razor blade, to determine their biomass.P. oceanica was negatively influenced by increased salinity. Shoots showed a significant decrease in growth and survival, whereas epiphyte biomass did not show a clear response because of their high variability. Maximum leaf growth occurred between 25 and 39 psu. In addition, plants suffered considerable mortality at salinities above 42 psu and below 29 psu, with 100% mortality at 50 psu. In salinities between 39 and 46 psu, surviving plants were able to regain their original growth rate when returned to normal seawater salinity (38 psu). These results suggest that P. oceanica is one of the most sensitive seagrasses to salinity increments it is more tolerant to salinity reductions (25.0-36.4 psu), perhaps due to the terrestrial origin of seagrasses.     

Patch dynamics of the Mediterranean seagrass Posidonia oceanica: Implications for recolonisation process

Patch dynamics of the Mediterranean slow-growing seagrass Posidonia oceanica was studied in two shallow sites (3–10 m) of the Balearic Archipelago (Spain) through repeated censuses (1–2 year⁻¹). In the sheltered site of Es Port Bay (Cabrera Island), initial patch density (October 2001) was low: 0.05 patches m⁻², and the patch size (number of shoots) distribution was bimodal: most of the patches had less than 6 shoots or between 20 and 50 shoots. Mean patch recruitment in Es Port Bay (0.006 ± 0.002 patches m⁻² year⁻¹) exceeded mean patch loss (0.001 ± 0.001 patches m⁻² year⁻¹), yielding positive net patch recruitment (0.004 ± 0.003 patches m⁻² year⁻¹) and a slightly increased patch density 3 years later (July 2004, 0.06 patches m⁻²). In the exposed site of S’Estanyol, the initial patch density was higher (1.38 patches m⁻², August 2003), and patch size frequency decreased exponentially with size. Patch recruitment (0.26 patches m⁻² year⁻¹) and loss (0.24 patches m⁻² year⁻¹) were high, yielding a slightly increased patch density in the area 1 year later (October 2004, 1.40 patches m⁻²). Most recruited patches consisted of rooting vegetative fragments of 1–2 shoots. Seedling recruitment was observed in Summer 2004 at both sites. Episodic, seedling recruitment comprised 30% and 25% of total patch recruitment in Es Port Bay and S’Estanyol, respectively. Patch survival increased with patch size and no direct removal was observed among patches of 5 shoots or more. Most patches grew along the study, shifting patch distribution towards larger sizes. Within the size range studied (1–150 shoots), absolute shoot recruitment (shoots year⁻¹) increased linearly with patch size (R² = 0.64, p < 4 × 10⁻⁵, N = 125), while specific shoot recruitment was constant (about 0.25 ± 0.05 year⁻¹), although its variance was large for small patches. Given the slow growth rate and the high survival of patches with 5 or more shoots, even the low patch recruitment rates reported here could play a significant role in the colonisation process of P. oceanica.     

Assessing effects of fishing prohibition on Posidonia oceanica seagrass meadows in the Marine Natural Reserve of Cerbère-Banyuls

The potential of alleviated fishing pressure measures established at the Marine Natural Reserve of Cerbère-Banyuls to affect phenological characters of P. oceanica, the main canopy-forming seagrass, was studied. Our results show differences in some leaf parameters between meadows under fishing prohibition measures compared to those without. In addition shallow P. oceanica meadows inside MPAs had lower non-structural carbohydrate content, yet are able to maintain themselves and, moreover, with an increased density. On the other hand, sexual reproduction was reduced inside protected areas.     

Recovery of deep Posidonia oceanica meadows degraded by trawling

The recovery capacity of meadows of the Mediterranean seagrass Posidonia oceanica (L.) Delile in an area affected by illegal trawling were assessed after protection by anti-trawling reefs. The differences in vegetative growth between two impacted and two undisturbed localities were tested using growth, shoot balance, aborted branches, and leaf and rhizome production of both plagiotropic and orthotropic rhizomes. The organic matter in sediments, silt clay fraction and light intensity incident on the bottom were also measured in order to evaluate the physical conditions. Environmental and plant variables were measured in three sites placed inside each locality. The vegetative growth was positive in both impacted and control meadows but growth rates were lower in impacted than in control meadows. Average growth, production and shoot balance were greater in plagiotropic rhizomes from undisturbed localities (40.7±1.75 vs. 28.4±1.34 mm/year, 1133±0.06 vs. 708±0.04 mg DW/shoot/year, 1.36±0.08 vs. 0.96±0.06 shoots/year, respectively). Significantly greater values were also found in undisturbed localities for orthotropic rhizomes in terms of shoot balance and rhizome production (0.07±0.01 vs. 0.01±0.003 shoots/shoot/year and 155 vs. 124 mg DW/shoot/year, respectively). Of the physical parameters measured, only light intensity differed significantly between impacted and undisturbed localities. This parameter was 15.5% to 67.6% lower in impacted localities than in undisturbed localities, and this is the factor that causes the retardation of vegetative growth. The results show that recovery of P. oceanica meadows is possible after eliminating the cause of the impact. However, the very low rates of vegetative growth may prolong the time to total recuperation to almost 100 years. Therefore, effective management of P. oceanica meadows should aim to prevent meadow loss.     

Spatial,temporal and structural variations of a Posidonia oceanica seagrass meadow facing human activities

The Bay of Saint-Cyr (Provence, France, Mediterranean Sea) is the site of two harbours, coastal urban development, trawling, boat anchoring and a sewage outfall. The Posidonia oceanica seagrass distribution was mapped with the help of aerial photographs, side scan sonar and GIS. In addition, the temporal variations of its distribution were studied by aerial photographs and GIS from 1955 to 2000. Finally, coverage and shoot density were measured via scuba-diving. This work reveals (i) the regression of the P. oceanica meadow at sites where harbours have been built, (ii) the occurrence of spaces within the meadow free of live P. oceanica (“intermattes”), which account for 8% of its surface area, (iii) a deep area where P. oceanica coverage and shoot density are low and (iv) evidence of regression, although modest, of the meadow at its lower limit. Nevertheless, the study site also exhibits an extensive and on the whole relatively healthy meadow whose limits have changed little over time.     

Isolation of putative type 2 metallothionein encoding sequences and spatial expression pattern in the seagrass Posidonia oceanica

Metallothioneins (MTs) are a group of proteins with low molecular mass and high cysteine content that bind to heavy metals and are thought to play a role in their metabolism and detoxification. Genes encoding MT-like proteins have been isolated in a number of plants. In this work we isolated nine MT-like sequences from copper- or cadmium-exposed plants of the seagrass Posidonia oceanica, a marine Angiosperm playing a major role in maintaining infralittoral ecosystems in the Mediterranean sea. These sequences, together with two other MT genes previously isolated from this species, show high similarities with genes encoding type 2 MTs. Neighbour-joining analysis, at both deduced protein and 3′-UTR sequence level, indicates that at least two subgroups occur within Posidonia type 2 MTs, showing, however, a strong sequence uniformity. Southern analysis of two type 2 MT-encoding sequences (Pomt2b and Pomt2f) belonging to the two different subgroups showed distinct hybridisation patterns. For both type 2 MTs, we have determined, by in situ technique, the expression domain in Posidonia plants. The members of these two MT subgroups show differences in their histological expression, with Pomt2b associated with proliferative tissues whereas Pomt2f is associated with lignified or suberized cell wall.     

Variability in patterns of growth and morphology of Posidonia oceanica exposed to urban and industrial wastes: contrasts with two reference locations

Urban and industrial wastes have been claimed to negatively affect Posidonia oceanica meadows, but few studies have addressed this issue by comparing disturbed locations with replicated reference locations. Here, we examined the general proposition that patterns of growth and morphology of P. oceanica exposed to urban and industrial effluents were different from those observed in reference meadows. Hypotheses were both on differences in mean values of response variables and on variation of these measures at a hierarchy of spatial scales (from centimetres to hundreds of metres). Results indicated a significant reduction in mean number of intermediate leaves at the outfall compared to reference locations, whereas the opposite pattern occurred for juvenile leaves. There were significant, though temporally variable differences in growth of rhizomes between disturbed and reference locations, with reduced growth at the outfall in 2 out of 3 years analysed. Measures of spatial variance in number of juvenile leaves and length of adult leaves at the scale of shoots were significantly larger at the outfall compared to reference locations. At the same scale, measures of spatial variance in length of juvenile and intermediate leaves were significantly lower at the putatively impacted location. Spatial variance in number of intermediate leaves was reduced at the outfall compared to reference locations at the scale of quadrats. Past values of spatial variance in number of leaves per shoot were lower at the outfall than at the two reference locations at the scale of shoots, whereas the opposite occurred at the scale of areas. None of the structural variables examined showed any difference between the putatively impacted location and the two reference locations, either in terms of mean response or as changes in spatial variance. These results indicated that integrating methods to examine present and past events of disturbance, including analyses to detect changes in spatial variance of response variables, may provide a powerful approach to the analysis of environmental impacts on P. oceanica.     

Boat anchoring on Posidonia oceanica beds in a marine protected area (Italy, western Mediterranean): effect of anchor types in different anchoring stages

Seagrasses worldwide are noted for suffering from mechanical damage caused by boat anchoring. This is particularly so in sites highly frequented by boaters (marine protected areas or coastal urbanised areas). In the last decades, different strategies have been put into practice to reduce such impacts on seagrasses (i.e. by anchoring bans or by deploying boat moorings). More recently, in consideration that few marine protected area (MPA) management bodies or local administrations have the resources to enforce their anchorage regulations, the self-regulatory approach based on education and information of boaters has been preferred in several cases. At present, however, very little is known on the correct anchoring practices to ensure the safeguarding of seagrasses. The aim of the present study was to experimentally quantify in the field the damage caused to Posidonia oceanica shoot density by anchoring. A multifactorial experiment was designed to test whether the damage is dependent on (1) different anchor types (Hall, Danforth and Folding grapnel), (2) the use of a chain vs. a rope, (3) the three anchoring stages (anchor fall, dragging/lock-in and weighing), and finally (4) whether the pattern is consistent among different locations of the meadow.As expected, the three anchor types employed in the present study differed in the levels of damage inflicted on the P. oceanica meadows of the Ustica Island MPA. In particular, the use of the Hall type anchor seems to be preferable to minimise this impact in comparison with the other two anchor types. Moreover, the effect on the meadow of the three anchor types is greatly dependent on the anchoring stage. These results confirm that the weighing stage is the critical stage of the anchoring process. The number of damaged shoots of P. oceanica was not affected by the presence of the chain. These patterns were consistent between locations.In the long term, even anchoring on P. oceanica by small boats using low-impact anchors may potentially have detrimental consequences. For this reason, we suggest that in vulnerable sites, it is preferable to implement an educational program based on information of boaters on correct anchoring practices and anchor typology to use, rather than adopting strong restrictions to boat anchoring or deploying mooring buoys. Although the use of these management strategies is still recommended in the case of anchorage frequented by bigger vessels using heavier anchors and chains.     

A small-scale analysis of the spatial structure of a Posidonia oceanica meadow off the Island of Ischia (Gulf of Naples,Italy): Relationship with the seafloor morphology

Posidonia oceanica L. (Delile), an endemic species of the Mediterranean, forms extensive meadows which are continuously endangered by anthropic impacts. The availability of up-to-date information about interannual changes in shoot density of meadows and the knowledge of its expansion capabilities are crucial elements for the development of effective protection plans. Conversely, spatial ecology is becoming an increasingly important component of resource management, and the use of quantitative data for constructing prognosis maps of the dynamics of ecosystem degradation and restoration by nonlinear simulation methods is a topical field of landscape ecology. Unfortunately, little is known on spatial patterns of shoot density of P. oceanica on a small scale, despite their increasing use as indicators of the status and/or trends of meadows. The spatial structure of a continuous P. oceanica meadow, extending from 1 to 33 m depth in Lacco Ameno (Gulf of Naples, Italy), is investigated here by the “kriging” technique, a method widely used for geostatistical purposes. The analysis detected peculiar spatial patterns of shoot density and facilitated a small-scale (square meters) model of the distribution of P. oceanica. The highest shoot densities were found at the shallow stand (430 shoots m⁻², on the average, with a peak of 1000 shoots m⁻² in a relatively small area, at 1 m depth) and the lowest at the deep stand (average density <300 shoots m⁻² below 15 m depth). A high degree of patchiness was found in the shallow stand, down to 10 m depth. Nestlike patterns with a rounded shape, characterized by shoot density radially decreasing from the center, were demonstrated mainly in the shallow stand. An opposite trend was detected in one case, where the main nestlike pattern was characterized by a decrease of density towards the center. Nestlike patterns may be generated by the confluence and overlap of stolons expanding from proximal areas. The comparison of density and depth models indicated that the shape of the seafloor influences the density structure of meadows and the growth patterns of P. oceanica.     

Physiological responses of the seagrass Posidonia oceanica to elevated organic matter content in sediments: An experimental assessment

Here we studied the effects of adding organic carbon and nutrients to sediment on the physiology and survival of the seagrass Posidonia oceanica in a field experiment in the Medes Islands (NE Spain). Nine randomly selected plots were established at a depth of 10 m; three were enriched with organic carbon (OM treatment), three with organic carbon and nutrients (OMN treatment), and three were kept as controls (CON). The experiment was performed over 5 months and sampling of plants and sediments was done in March, May and July 2002. Sediment sulfide pools and pore water ammonium concentrations increased significantly in OM and OMN plots, both treatments showing increased reducing conditions in the sediment. Plants in these two treatments showed higher mortality and lower biomass compared to plants from CON plots. The greatest effects on seagrass occurred in the OMN plots, indicating a synergistic effect of organic carbon and nutrient additions. Treatments had significant effects on plant nitrogen (N) and phosphorous (P) metabolism, shown by an increase in free amino acid (FAA) content, a change in FAA composition and a lack of increase in N and P tissue content. Treated plants showed higher g-aminobutyric acid (GABA) and malate concentrations and lower concentrations of non-structural carbohydrates compared to CON, indicating that anaerobic respiration in below-ground tissues occurred. Several of the physiological changes shown by P. oceanica can be interpreted as adaptations to anoxia exposure. However, the increased mortality in treated plots demonstrates that this seagrass does not tolerate highly reduced sediments.     

Phenology of the Mediterranean seagrass Posidonia oceanica (L.) Delile: Medium and long-term cycles and climate inferences

The results of 15 years of monitoring of Posidonia oceanica in the “Cinque Terre” Marine Protected Area (NW Mediterranean) are presented. Seasonal data on meadow characteristics (cover and shoot density), plant phenology (leaf number, leaf length and width, leaf brown portion, undamaged leaves), lepidochronology, leaf epiphyte cover and herbivore pressure collected from three stations at 5, 10 and 17 m depth were compared. Time-series analyses showed both medium-term (5 < years) and long-term cycles (from 5 to more than 20 years). The comparison of annual cycles with sea surface temperatures (SST) and rainfall showed correlations that differed in relation to depth and, in the case of epiphytes, with each side (internal and external) of the leaf blade. Meadow parameters (visual cover, shoot percent cover) and plant parameters (leaf number, number of undamaged leaves, number of scales shoot⁻¹) showed a positive trend in accordance with the rise of air and sea surface temperature recorded over these last decades. Shoot density and leaf width showed exceptions. Leaf length, leaf brown portion length and the number of undamaged leaves shoot⁻¹ showed positive or negative long-term trends, whose variability could not be related to climate data alone. The two major groups of epiphytes (encrusting algae and the bryozoan Electra posidoniae) showed negative trends. Grazing variability could be explained only partially by climate parameters. Epiphyte cover was found to be related to the NAO index.In conclusion, data showed that the effects of the climate change in terms of both sea surface temperature rising and rainfall decreasing may affect the growth cycles of P. oceanica on two levels: on a decadal level, with positive or negative trends in meadow and plant characteristics and in epiphyte cover; on yearly and seasonal levels, influencing endogenous plant growth rhythms, as in the case of leaf production cycle.     

Secondary metabolites of Posidonia oceanica (Posidoniaceae)

Posidonia oceanica Delile is an endemic of the Mediterranean Sea. P. oceanica is one of the few marine higher plants of the Mediterranean and plays a significant role in coastal ecosystems of the Mediterranean Sea. In the past, a number of phytochemical investigations with different focus were carried out. The results of these investigations are summarized and appraised here. A total of 51 natural products was reported from P. oceanica, including phenols, phenylmethane derivatives, phenylethane derivatives, phenylpropane derivatives and their esters, chalkones, flavonols, 5α-cholestanes, and cholest-5-enes. Many of the compounds reported for P. oceanica were, however, not detected by appropriate phytochemical methods and some most probably represent artifacts and are no genuine natural products.     

An improved method to monitor the health of seagrass meadows based on kriging

This paper focuses on the spatial pattern of the shoot density of the seagrass Posidonia oceanica through kriging methods. Kriging is a group of geostatistical techniques to predict the value of a field at an unobserved location from observations of its value at nearby locations. The results of an ordinary kriging of both raw values of shoot density and normalized shoot density with reference to a density vs. depth model (Dn) were compared. Results confirmed the existence of spatially organized parameters other than depth that influence patterns of P. oceanica shoot density. Although still requiring additional testing for complete validation, Dn mapping appears to be a valuable tool to (1) infer causes for the meadow's condition and to design a cost-effective field survey; (2) define areas where protection policies should be undertaken.     

不同群落中米氏冰草和羊草的年龄结构动态

米氏冰草和羊草都是根茎型禾草,是典型的无性系植物。采取单位面积挖掘取样法,对呼伦贝尔沙地植被次生演替过程中的米氏冰草和羊草种群分株年龄结构进行调查。结果表明,在单生和混合群落中,米氏冰草分株分别由3和4个年龄级组成,羊草均由2个年龄级组成;米氏冰草分株数量和生物量年龄结构变化基本一致,即随着生长年限的延长,呈减少低龄级和增加高龄级比例的趋势,使单生群落中始终为增长型,但接近于稳定型,混生群落中由增长型变为稳定型。羊草分株数量和生物量年龄结构在连续2a均为明显的增长型。羊草各龄级平均单株生产力均高于米氏冰草,平均是米氏冰草的5.2倍。米氏冰草和羊草种群分株年龄结构的变化,蕴含着米氏冰草种群的优势地位将被羊草种群取代的趋势。     

Contrasting responses of seagrass transplants (Posidonia australis) to nitrogen, phosphorus and iron addition in an estuary and a coastal embayment

Addition of nutrients to sediments has been proposed as a means of enhancing transplantation success in seagrasses. The effects of nutrient and iron additions to natural sediments on the growth and morphology of Posidonia australis transplants were evaluated in underwater plots in two contrasting environments: a coastal embayment (Princess Royal Harbour) with sandy sediments and little riverine input, and an estuary (Oyster Harbour) with organic-rich sediments and subject to seasonal river flow from a large rural catchment. Sixty six planting units spaced 1 m apart were transplanted in situ in each location. Nitrogen (N) and phosphorus (P) were added in a randomized factorial design using slow release fertilizer granules at the start of the experiment and repeated every 4-5 months for 2 years. In a concurrent experiment, chelated iron Fe EDTA was added to modify the sediment sulphur cycle.In Oyster Harbour, the addition of N significantly increased leaf N concentrations but reduced total biomass and biomass of leaves. Addition of P significantly increased leaf P concentrations and number of living leaves per transplant, leaf area, leaf length, length of longest rhizome axis and total rhizome length. Combined N + P addition resulted in a significant increase in leaf P concentrations and leaf area per plant only. In Princess Royal Harbour, addition of N produced significant increases in leaf variables (total and leaf biomass, number of shoots and living leaves, leaf area, and leaf length) but there were no significant differences observed in below ground plant parts (rhizomes). Addition of P had no significant effects on any growth measurements. Addition of N + P combined increased number of living leaves and leaf area significantly. δ¹⁵N in mature leaf tissue were significantly more negative for N and N + P treatments at both locations.Our results indicated that N limitation was occurring in the coastal embayment, Princess Royal Harbour whereas in the more estuarine Oyster Harbour, P was limiting plant growth. Addition of FeEDTA produced equivocal results at both sites and we suggest these results are confounded by the addition of N and C in the EDTA. We caution the use of nutrient addition to transplants of slow growing seagrasses such as P. australis without a thorough understanding of the nutrient status of the system, estuarine or coastal embayment, in which they are to be transplanted.     

Seagrass light acclimation: 2-DE protein analysis in Posidonia leaves grown in chronic low light conditions

Posidonia oceanica meadows are among the most valuable coastal systems in the Mediterranean basin. They provide nursery and forage areas for many commercially important species, including juvenile mollusc, finfish, and crustaceans. In the Mediterranean Sea, P. oceanica beds have recently suffered from progressive die-offs attributed to lower light availability from elevated water turbidity. In order to understand adaptive low-light responses of this seagrass, we compared the protein expression in plants collected from turbid waters (low-light) with plants collected from pristine-clear waters (high-light). More than 2600 proteins were detected in leaves from both sites. Among them, 26 proteins were differentially expressed in low-light conditions, 12 of which were identified through MASCOT analyses. The remaining 14 proteins, did not receive significant identity scores due to a lack of genomic and proteomic information in available databases. Nevertheless, we observed a 30% down-regulation of RuBisCo large subunit in low-light acclimated leaves. Whereas, enzymes involved in carbohydrate cleavage (1-fructose-bisphosphate aldolase, nucleoside diphosphate kinase, and beta-amylase) were upregulated in low-light conditions. Electron microscopy studies also revealed substantial changes in the stroma lamellae/grana ratios in chloroplasts receiving low-light, possibly as a mechanism for re-establishing optimal PSI/PSII ratios. Furthermore, under low-light conditions, four components of the ubiquitin/mediated proteolysis pathway (26 S proteasome regulatory, proteasome beta type 1, proteasome 7 D beta type, and proteasome alpha 7), and the perchloric acid soluble translation inhibitor protein, were upregulated. This suggests that, in P. oceanica leaves, enhanced protein turnover mediates acclimation to low-light conditions. Also, enzymes involved in defending against cellular stress (superoxide dismutase, pyridoxine, and 2-caffeic-acido-methyl transferase) were differentially expressed in low-light regime. Subsequent aquaria studies involving P. oceanica transplants maintained in low- and high-light conditions, also demonstrate RuBisCo down-regulation and proteasomes upregulation in low-light acclimated plants.