NeoBiota 21: 65–79, doi: 10.3897/neobiota.21.4963
Wrack burial reduces germination and establishment of the invasive cordgrass Spartina densiflora
Ahmed M. Abbas 1, Alfredo E. Rubio-Casal 1, Alfonso de Cires 1, Enrique Figueroa 1, Javier J. Nieva 2, Jesús M. Castillo 1
1 Departamento de Biología Vegetal y Ecología, Facultad de Biología, Universidad de Sevilla, Avd. Reina Mercedes, s/n.-41012 Sevilla, España
2 Departamento de Biología Ambiental y Salud Pública, Universidad de Huelva, Campus del Carmen, 21071 Huelva, España

Corresponding author: Jesús Castillo (

Academic editor: J. Jeschke

received 5 March 2013 | accepted 13 October 2013 | Published 17 April 2014
(C) 2014 Ahmed M. Abbas. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
For reference, use of the paginated PDF or printed version of this article is recommended.

Citation: Abbas AM, Rubio-Casal AE, de Cires A, Figueroa E, Nieva JJ, Castillo JM (2014) Wrack burial reduces germination and establishment of the invasive cordgrass Spartina densiflora. In: Capdevila-Argüelles L, Zilletti B (Eds) Proceedings of 7th NEOBIOTA conference, Pontevedra, Spain. NeoBiota 21: 65–79. doi: 10.3897/neobiota.21.4963


Germination and emergence of halophytes may decrease significantly by seed burial in dead plant material, or wrack, which is common and abundant in tidal marshes. The effects of plant debris (wrack) burial on seed germination and seedling establishment of Spartina densiflora, an invasive cordgrass, were studied under greenhouse conditions and compared with field observations. Five wrack burial depths were applied: control without wrack, 1 cm (1235 ± 92 g DW wrack m-2), 2 cm (3266 ± 13 g DW m-2), 4 cm (4213 ± 277 g DW m-2), and 8 cm (6138 ± 227 g DW m-2). Sediment pH, electrical conductivity, redox potential and temperature were recorded. Quiescence increased with wrack load up to ~20% at 8 cm deep. Germination decreased with wrack load from 96% to 14%, which could be related with anoxic conditions under the debris since sediment redox potential was as low as -83 ± 7 mV at 8 cm. Germination percentage increased and quiescent and dormant percentages decreased at higher daily sediment temperatures and with higher daily temperature fluctuations, conditions that were recorded without or under low loads of wrack. Spartina densiflora did not show primary dormancy, but its seeds entered into a non-deep physiological dormancy below 1 cm deep in plant debris. The establishment of S. densiflora seedlings was also greatly reduced by wrack burial since only 6 seedlings (11 ± 5 % of germinated seeds) emerged above plant debris from 1 cm and all seedlings died from deeper than 1 cm. S. densiflora seedling development was also reduced by wrack burial. The inverse relationship between germination and emergence of S. densiflora with wrack burial recorded in our study is useful to predict its invasion dynamics and to plan the management of invaded marshes.


Coastal marshes, physiological dormancy, plant debris, seedling, Spartina densiflora


Most salt marsh environments are unpredictable for plants, because of the occurrence of both salinity and flooding stress (Cantero et al. 1998). When conditions for seed germination are not favorable, ungerminated seeds of halophytes often remain under enforced dormancy in the soil and serve as a transient or persistent seed bank (Ungar 1995). Thus, seed banks are particularly important in maintaining populations of halophytes in saline marshes (Coteff and Van Auken 2006). Salt marshes are among the most heavily invaded systems in the world (Grosholz 2002). The ability of introduced species to bank seeds can contribute to invasion success, since seeds can persist while waiting for favorable conditions. This ability is especially useful in environments where opportunities for seed germination are infrequent or unpredictable such as salt marshes (Parker et al. 1989). Management of invasive species in salt marshes can be challenging because monitoring and control must continue for at least as long as their seeds persist in the seed bank (Panetta and Timmins 2004).

Rafts of dead plant material, or wrack, are common and abundant in tidal marshes. Due to high primary productivity rates and low consumption rates by herbivorous, halophytes, such as eelgrasses and cordgrasses, produce high quantities of wrack, especially in dye-back areas. This wrack is added up to that transported by rivers to salt marshes in estuaries. Then, tidal creeks provide corridors for wrack transport into salt marshes where it can disturb plant communities (Reidenbaugh and Banta 1980; Bertness and Ellison 1987; Valiela and Rietsma 1995; Tolley and Christian 1999; Brewer et al. 1998; Minchinton 2002). As part of the natural disturbance regime, deposited wrack mats often create bare spots by killing not only the surface vegetation, but also the below-ground biomass (Hartman 1988). Seeds of different salt marsh plants can germinate in the spaces opened by wrack accumulation, playing a key role in plant distribution (Hartman et al. 1983; Pennings and Richards 1998), but germination and emergence may decrease significantly by seed burial in plant debris. Buried seeds are recruited only when they are brought back to the surface by disturbances (Facelli and Pickett 1991). However, these effects are poorly understood since there is a general lack of research that examines the effects of wrack burial in salt marshes.

The austral cordgrass, Spartina densiflora Brongn. (Poaceae) is invading salt marshes in southern Europe, Northwest Africa and the West Coast of North America (Bortolus 2006). In invaded marshes, Spartina densiflora develops very dense populations where large amounts of dead matter are deposited (Nieva et al. 2001; Castillo et al. 2008). Moreover, Spartina densiflora seeds float so they are dispersed by currents and tides together with plant debris (Howard and Sytsma 2013). One of the keys to the success of Spartina densiflora invasion is its ability to produce large quantities of viable seeds (Nieva et al. 2001a, b). Spartina densiflora produces many seedlings in intertidal mudflats but its recruitment is very low in marsh zones where wrack is accumulated.

While cordgrasses (Spartina genus) are one of the most abundant and frequent halophytes in salt marshes, there have not been any studies that examined how their seeds and seedlings respond to wrack burial. We examined under controlled greenhouse conditions the impact of five wrack burial depths (0, 1, 2, 4 and 8 cm) on germination, seed viability and seedling establishment of Spartina densiflora. Main abiotic factors conditioning seed germination and seedling establishment in salt marshes (sediment pH, electrical conductivity, redox potential and temperature) were also recorded for every wrack treatment. We hypothesized that Spartina densiflora germination and establishment would be reduced by wrack burial due to anoxia and/or low temperature fluctuations.

Seed and wrack collection

Spartina densiflora seeds were collected in August 2009 from multiple mature individuals chosen at random from a population growing at the periphery of an accreting, well-drained intertidal lagoon at Odiel Marshes (Southwest Iberian Peninsula; 37°08' - 37°20'N, 6°45' - 7°02'W; Fig. 1); see Castellanos et al. (1994) for a description of the site. Seeds were stored at 5 °C, under dry conditions and in darkness after harvest until the beginning of the experiment. Wrack was collected from the mean higher high water (MHHW) from the same marsh and it consisted of dead culms and leaves of different plant species (~50% of the debris was dead Spartina densiflora) together with pieces of shells (diameter < 1.0 cm). Collected wrack was checked for the presence of Spartina densiflora seeds and none was found, probably because seeds are dispersed before dead spiked shoots are transported by tides and currents.

Figure 1.

Location of the Odiel Marshes on the Atlantic coast of Southwest Iberian Peninsula (37°08'-37°20'N, 6°45'-7°02'W), and the sampling point where Spartina densiflora seeds were collected (1).

Wrack treatments

A greenhouse experiment was conducted from December 2009 to February 2010, since most Spartina densiflora seeds germinate during winter, to test the effects of wrack burial on seed germination, and emergence and growth of seedlings of Spartina densiflora. The mean disseminule size of Spartina densiflora was 9.67 ± 0.15 mm by 1.47 ± 0.02 mm (n = 50) and its mean weight was 3.0 ± 0.1 mg (range: 1.3-4.2 mg). Mean Spartina caryopsis size was 4.68 ± 0.08 mm by 0.98 ± 0.02 mm (n = 50) and its weight was 2.0 ± 0.1 mg (range: 1.3–3.0 mg). Four replicates of 25 seeds were sown at 1 cm depth in clean sand in plastic containers measuring 18 cm width, 22 cm length and 11 cm height (containing ~1.6 kg of clean sand). The sand was collected from the same marsh where the seeds were obtained and it was sieved through 0.5-mm mesh size filling to eliminate pre-existing seeds and other plant material. A control treatment was set up without any seeds added in order to test whether the sand we used contained seeds. Five wrack burial treatments were conducted: control (no wrack was added above the sand surface), 1 cm (1235 ± 92 g DW wrack m-2), 2 cm (3266 ± 13 g DW m-2), 4 cm (4213 ± 277 g DW m-2), and 8 cm (6138 ± 227 g DW m-2) of wrack burial depth. These treatments were decided following our field observations in Odiel Marshes (Southwest Iberian Peninsula) where Spartina densiflora is very abundant (Nieva et al. 2001a). Each container had 25 seeds at one depth, so there were five treatments with four containers (replicates) per depth (n = 4 per treatment; n = 20, including all treatments together). Containers were irrigated gently once a day with water to ensure the moisture of the soil remained within 70% of its water-holding capacity. Fresh water (< 0.5 psu) was used to avoid salinity effects on germination since we wanted just to record seed responses to burial and avoid high salinity effects. Spartina densiflora is a facultative halophyte that can germinate, establish and develop in freshwater conditions (Nieva et al. 2001b; Castillo et al. 2005). The containers had small holes on the bottom to allow drainage, but these were covered with strips of cloth to prevent the loss of sand.

Sediment redox potential, electrical conductivity and pH were recorded at the end of the experiment in February 2010 at 1 cm depth in the sand. pH was recorded in the laboratory after adding distilled water to the soil (1:1, soil: distilled water, v/v) (pH/redox Crison with the electrode M-506). Soil salinity was measured as electrical conductivity (conductivity meter, Crison-522) after pH (1:2, soil: distilled water, v/v)). Redox potential was determined with a portable meter and electrode system in the greenhouse (Crison pH/mV p-506). Mean, maximum and minimum daily sediment temperature were recorded at 0, 1, 2, 4 and 8 cm depths using an electronic thermometer (SA880SSX, Germany) recording from 8 a.m. to 8 p.m. every 4 hours for 3 days (n = 3). Average daily air temperature during the experiment was 18.5 ± 0.5 °C, varying between a mean low temperatures of 10.4 ± 1.6 °C and a mean maximum temperature of 34 ± 3.5 °C. Mean daily air relative humidity was 74.5 ± 2.6%, varying between 32.5 ± 5.5% and 92.5 ± 1.1%.

Emerged seedlings from beneath the wrack were counted every 24 h (Cui et al. 2007). The experiment continued until no additional emergence was observed during 10 days. At the end of the experiment, the wrack and the sand were carefully removed and those seedlings that died before raising the wrack surface were counted and ungerminated seeds were collected. At the end of the experiment, shoot and root length were measured on all seedlings and the number of roots counted. Germination percentage was calculated as the number of germinated seeds by the total number of seeds per treatment. Seedling emergence percentage was calculated as the number of seedlings raising above the wrack surface by the number of germinated seeds per treatment. Seedling aerial growth rate was recorded as the difference in emerged seedling height between two consecutive measures (in two days period) divided by the number of days.

Ungerminated seeds were transferred to 0.5-cm depth in sand and germination and emergence percentages were recorded until no more seeds germinated for 10 days. Germinated seeds were considered to be in a quiescent state, which is different than true seed dormancy and occurs when a seed fails to germinate because external environmental conditions are not appropriate (Baskin and Baskin 1985). Then, ungerminated seeds were soaked in water at 30 °C for 24 h. Seed coats were cut and the embryo was soaked in 1% tetrazolium chloride (Panreac Quimica S.A., Barcelona, Spain) for 24 h at 30 °C. Pink embryos were scored as alive and considered to be in dormancy (Baskin and Baskin 2004). Non-coloured seeds were considered to be dead. Quiescence, dormancy and mortality percentages were calculated in relation to the total number of seeds per treatment.

Statistical analysis

Analyses were carried out using SPSS 12.0 (SPSS Inc, USA). Data were tested for homogeneity of variance and normality with the Brown-Forsythe test and the Kolmogorov-Smirnov test, respectively (P < 0.05). Plant traits were compared between treatments by one-way analysis of variance (ANOVA, F-test). Tukey Honest Significant Difference (HSD) test between means was calculated only if the F-test was significant (P < 0.05). The effect of wrack load on seedling growth rate between two treatments was analyzed using a Student t- test. Pearson correlation coefficient and linear regressions were calculated between abiotic factors, germination and seedling traits, and the wrack load. When a biotic characteristic was correlated with two or more abiotic environmental factors, multiple regression analysis was carried out to explore relative weights (β). Deviations were calculated as standard errors of the mean (SEM).

Abiotic environment

Sediment pH increased with the wrack burial load from 6.2 ± 0.5 in the control treatment to 7.7 ± 0.1 under 8 cm (r = 0.96, P < 0.01, n = 20). Electrical conductivity changed from 0.11 ± 0.00 to 0.23 ± 0.00 mS cm-1. Sediment redox potential varied between -83 ± 7 mV under 8 cm of wrack and +255 ± 5 mV without wrack burial (Table 1). Mean daily sediment temperature decreased at higher depths (r = -0.61, P < 0.05, n = 20), but without showing significant differences between treatments, varying between 12.3 ± 1.0 °C for the control treatment and 10.1 ± 0.8 °C at 4 and 8 cm (ANOVA, F = 0.39, P > 0.05). Maximum daily sediment temperature changed between +25.0 ± 0.8 °C for the control treatment and +21.7 ± 0.3 °C at 1 cm (ANOVA, F = 2.02, P > 0.05), decreasing also when wrack burial depth increased (r = -0.36, P > 0.05, n = 20). Minimum daily temperature varied between +10.4 ± 0.4 °C at 8 cm and +7.9 ± 1.0 °C for the control treatment (ANOVA, F = 0.86, P > 0.05), increasing with depth (r = 0.81, P < 0.0001, n = 20). Daily variation between maximum and minimum temperatures decreased at higher depths (r = -0.62, P < 0.05, n = 20), varying between 17.7 ± 1.4 °C for the control treatment and 12.4 ± 0.3 °C at 8 cm (ANOVA, F = 2.46, P < 0.05) (Table 1).

Table 1.

Wrack load (g m-2), sediment pH, redox potential (mV), electrical conductivity (mS cm-1), daily mean, maximum and minimum sediment temperature (°C), and the difference between maximum and minimum temperature (°) (n = 3) for five wrack burial depths. Different letters indicate significant differences between treatments (ANOVA, P < 0.05) (n = 5).

Wrack depth (cm) Wrack load (g m-2) pH Redox potential (mV) Conductivity (mS cm-1) Daily sediment temperature (°C)
Mean Maximum Minimum Max-Min
0 0 ± 0a 6.2 ± 0.5a +255 ± 5a 0.23 ± 0.00a 12.3 ± 1.0a 25.0 ± 0.8a 7.9 ± 1.0a 17.7 ± 0.2a
1 1235 ± 92b 6.9 ± 0.3b +247 ± 2a 0.20 ± 0.02a 10.4 ± 0.9a 21.7 ± 0.3a 9.4 ± 0.5a 13.0 ± 0.3b
2 3266 ± 13c 7.1 ± 0.5b +229 ± 3b 0.16 ± 0.00b 10.2 ± 0.9a 22.5 ± 0.1a 9.7 ± 0.5a 13.1 ± 0.0b
4 4213 ± 277d 7.3 ± 0.1c +157 ± 11c 0.13 ± 0.01c 10.1 ± 0.8a 22.7 ± 0.8a 10.1 ± 0.4a 12.7 ± 0.1b
8 6138 ± 227e 7.7 ± 0.1d -83 ± 7d 0.11 ± 0.00d 10.1 ± 0.8a 22.5 ± 0.0a 10.4 ± 0.4a 12.4 ± 0.3b
Germination and establishment

The time to first emergence of Spartina densiflora was 23 days after the start of the experiment at control treatment and 37 days at 1 cm wrack depth. Germination decreased when wrack load increased (r = -0.84, P < 0.0001, n = 20), showing the highest value without wrack (96 ± 4%) and decreasing significantly under 8 cm deep (ANOVA, P < 0.05) (Fig. 2).

Figure 2.

Germination, quiescence, dormancy and mortality of Spartina densiflora seeds for five wrack burial depths.

Germination percentage decreased at lower redox potentials (r = 0.65, P < 0.005, n = 20; β = -0.599), varying from 96 ± 4% at the control treatment with sediment redox potential +255 ± 5 mV to less than 15% under 8 cm deep with negative redox potential -83 ± 7 mV. In addition, germination percentage increased at lower minimum daily sediment temperature (r = -0.95, P < 0.0001, n = 20; β = -3.669) (Fig. 2).

Quiescence and dormancy percentages increased with wrack load (r = 0.67, P< 0.05, n = 20; r = 0.70, P < 0.001, n = 20, respectively). Quiescent percentage increased at higher minimum daily sediment temperature (r = 0.57, P < 0.05, n = 20; β = 3.265) and at lower redox potentials (r = -0.56, P < 0.01, n = 20; β = 0.495). No dormant seeds were recorded for the control treatment where seed mortality was the lowest (4%; 4 seeds). Dormancy and mortality increased to ~50% of the ungerminated seeds under wrack (Fig. 2). Dormant seed percentage and seed mortality increased mainly at higher daily minimum sediment temperature (r = 0.70, P < 0.001, n = 20; r = 0.81, P < 0.0001, n = 20, respectively).

No seedling emerged from deeper than 1 cm depth since every seedling died before emerging above the wrack surface. Minimum seedling mortality was recorded for the control treatment (7 ± 3% of germinated seeds) (ANOVA, P < 0.05). The highest seedling emergence percentage occurred without wrack (93 ± 3%) and only 6 seedlings emerged from under 1 cm of wrack (11 ± 5%) (Table 2).

Table 2.

Emergence and mortality rates of germinated seeds for five wrack burial depths. Different letters indicate significant differences between wrack burial depths for the same trait (ANOVA, P < 0.05).

Wrack depth (cm) Emergence (%) Mortality (%)
0 93 ± 3a 7 ± 3a
1 11 ± 5b 89 ± 5b
2 0 ± 0c 100 ± 0c
4 0 ± 0c 100 ± 0c
8 0 ± 0c 100 ± 0c

Seedlings in the control treatment were much taller and had longer and more roots than those growing from under 1 cm of wrack and also than those seedlings dying under the wrack at 2, 4 and 8 cm (Fig. 3). These results also showed a higher aerial growth rate for seedlings at the control treatment (0.11 ± 0.01 cm day-1) than those growing from under 1 cm of wrack (0.02 ± 0.01 cm day-1) (t-test; P < 0.05).

Figure 3.

Shoot and root lengths (cm) and root number of Spartina densiflora seedlings for five wrack burial depths (seedlings from deeper than 1 cm were found dead and did not emerge above the wrack surface). Different letters indicate significant differences between wrack depths for the same trait (ANOVA, P < 0.05).


This study shows that germination and establishment of Spartina densiflora, an invasive cordgrass in Europe, North America and North Africa, is greatly limited by wrack burial.

Sediment pH increased with wrack burial load, which may be related to the presence of shells in the debris that would add carbonate to the sediment. However, Spartina densiflora germination would not be altered within the narrow recorded pH range (6.2–7.7) (Curado et al. 2010). Similarly, electrical conductivity varied within a range (0.11–0.23 mS cm-1) that would not influence Spartina densiflora germination significantly (Castillo et al. 2005). In contrast, sediment redox potential under the debris may have affected germination under 8 cm of wrack since it was as low as -83 ± 7 mV, and germination decreased and quiescence increased at low redox potentials as it has been described previously in anaerobic environments under organic material in lakes (Rich and Wetzel 1978) and in accordance with our hypothesis. Negative values of redox potential can decrease Spartina densiflora germination in the field (Mateos-Naranjo et al. 2008). Sediment anoxia affects seeds by consuming oxygen resulting from degradation of organic matter (Wu et al. 2009). Thus, poor soil aeration may induce quiescence (Vleeshouwers et al. 1995).

The highest germination was recorded without debris (96%), decreasing markedly (to values between 21–43%) between 1 and 4 cm deep with positive redox potentials (> +150 mV). Therefore, other environmental factors in addition to anoxia seemed to be limiting Spartina densiflora germination under the debris. The effects of burial on germination can be mediated by changes in the light regime as it has been described for some halophytes (Pons 1992; Khan and Gul 2002), which is not the case for Spartina densiflora germination that is similar in light and darkness under fresh water conditions (Nieva et al. 2001b). However, synergistic effects between light and other abiotic factors cannot be excluded. Germination of Spartina densiflora increased at lower sediment daily minimum temperatures, conditions that were recorded without or under low loads of wrack, indicating that burial probably caused an unsuitable temperature environment for germination (Benvenuti et al. 2000). Thus, quiescence and dormant seed percentages increased at higher sediment minimum temperatures. In temperate regions, many grass species require exposure to low winter temperatures to come out of dormancy (Baskin and Baskin 1998). Sensitivity to temperature fluctuation functions as a depth- or gap-detecting mechanism; in this way, germination is activated when temperature fluctuation increases at unvegetated areas exposed directly to solar radiation (Thompson and Grime 1983). Furthermore, allelopathic effects from the plant debris inhibiting the germination of Spartina densiflora seeds cannot be excluded (Li et al. 2010; Sieg and Kubanek 2013).

Spartina densiflora did not show primary dormancy since all its seeds germinated or died (only 4%) without wrack in optimal conditions. Instead, Spartina densiflora seeds entered a non-deep physiological dormancy (Baskin and Baskin 1988) under the plant debris. Dormancy percentage increased with higher daily minimum temperature determining a lower daily temperature variation under the wrack. Secondary dormancy may be induced by environmental factors such as high CO2 levels produced by debris decomposition (Harper and Obeid 1967), poor aeration (Simpson et al. 1989) and low temperature fluctuations (Baskin and Baskin 1998). Longer seed dormancy at greater depths within the debris would be ecologically advantageous because seeds would survive in the dormant state in the seed bank until the upper layer of wrack would be removed. Nevertheless, wrack burial increased seed mortality.

The establishment of Spartina densiflora seedlings was also greatly influenced by wrack. Only six seedlings emerged above the plant debris from a burial depth of 1 cm, while no seedling emerged from deeper than 1 cm (wrack load > 3 kg DW m-2). The seedling of Spartina densiflora has just one thin and sharp cotyledon that grows easily along an axis, being able to emerge straight away from 4 cm depth in water (Abbas et al. 2012) and in sand (A.M. Abbas, personal observation). In contrast, when a seedling grew within wrack it had to find the few hollows left open in the wrack as is reflected in its cotyledon growing in curves. Every Spartina densiflora seedling dying within the debris was shorter than 2 cm, which seemed to be the longest length they were able to grow under these conditions. The dense structure of the debris would prevent Spartina from emerging from deeper than 1 cm due to the exhaustion of food reserves before getting to the surface (Martínez et al. 1992; Bond et al. 1999). It has been previously described how deeply sown seedlings in sediment died before emerging in wetlands (Hartleb et al. 1993; Jurik et al. 1994; Wang et al. 1994; Dittamar and Nelly 1999; Spencer and Ksander 2002; Ke and Li 2006). Live and dead standing biomass of Spartina patens (Aiton) Muhl prevented seedling emergence of subordinate annuals and perennials in coastal marshes (Brewer and Grace 1990; Baldwin et al. 1996). Spartina densiflora seed germination and quiescence presented a gradual response to wrack burial but seed dormancy, seed and seedling mortality and seedling emergence showed a threshold dynamic in response to wrack burial, increasing markedly even under just 1 cm depth. These results characterized Spartina densiflora as a very sensitive species to wrack burial during the establishment period, which may limit its invasion in those marshes accumulating high debris loads.

Spartina densiflora seedling development was also significantly reduced by wrack burial. Seedlings growing without wrack were ~5.8 cm tall at the end of the experiment while seedlings emerging from 1 cm deep under the wrack were ~2 cm tall (including their buried part), coinciding with lower growth rates. In adittion, seedlings in the control treatment had longer and more roots. In this sense, it has been reported that phytotoxins generated in anaerobic decomposition can inhibit the growth of freshwater plants (Barko and Smart 1986; Maun and Lapierre 1986).

Our experimental results are in accordance with our field observations. In tidal salt marshes, wrack is accumulated mainly coinciding with the mean higher high water. We have observed in the field (Odiel Marshes) that the wrack depth in these areas ranges from 2 to 14 cm. In these marshes, we have seen no Spartina densiflora seedling growing from within the wrack. Just very few Spartina adult clumps were observed within the debris areas, which seemed to have established before wrack accumulation or within open patches in the wrack. Spartina densiflora tussocks accumulate high densities of dead tillers in middle and high marshes (Nieva et al. 2001a) and when this necromasa is detached from the tussocks is accumulated as wrack. In view of our results, as Spartina densiflora invades a location it would decelerate its own invasion rate through the accumulation of wrack that may limit its establishment.


Data gathered during this study confirmed an inverse relationship between germination and emergence with wrack burial for the invasive cordgrass Spartina densiflora. Germination decreased from 96% without wrack to 14% at 8 cm deep in debris (ca. 6 kg DW m-2). No seedling emerged above the wrack surface for seeds germinated at wrack burial depths greater than 1 cm (a wrack load of ca. 1 kg DW m-2). The results from this study improved our understanding of Spartina densiflora invasion and they are useful to predict invasion dynamics and to plan the management of invaded marshes. Thus, wrack may be used to limit Spartina densiflora colonization and should not be removed from those areas sensible to the invasion of this cordgrass.


This work was supported by a Ph.D scholarship of Egyptian Government-Ministry of Higher Education (cultural affairs and missions sector). We thank Jesús and Jose at the Greenhouse Facility of the University of Seville.

Abbas AM, Rubio-Casal E, De Cires A, Figueroa ME, Castillo JM (2012) Burial effects on seed germination and seedling emergence of two halophytes of contrasting seed size. Weed Research 52: 269-276. doi: 10.1111/j.1365-3180.2012.00913.x
Baldwin AH, McKee KL, Mendelssohn IA (1996) The influence of vegetation, salinity, and inundation on seed banks of oligohaline costal marshes. American Journal of Botany 83: 470–479. doi: 10.2307/2446216
Barko JW, Smart RM (1986) Sediment-related mechanisms of growth limitation in submersed macrophytes. Ecology 67: 1328-1340. doi: 10.2307/1938689
Baskin JM, Baskin CC (1985) The annual dormancy cycle in buried weed seeds: A continuum. Bioscience 35: 492-498. doi: 10.2307/1309817
Baskin CC, Baskin JM (1988) Seeds, Ecology, Biogeography, and Evolution of Dormancy and Germination. Academic Press, London.
Baskin CC, Baskin JM (1998) Seeds – Ecology, Biogeography and Evolution of Dormancy and Germination. Academic Press, San Diego.
Baskin JM, Baskin CC (2004) A classification system for seed dormancy. Seed Science Research 14: 1-16. doi: 10.1079/SSR2003150
Benvenuti S, Macchia M, Miele S (2000) Light, temperature and burial depth effects on Rumex obtusifolius seed germination and emergence. Weed Research 41: 177-188. doi: 10.1046/j.1365-3180.2001.00230.x
Bertness MD, Ellison AM (1987) Determinants of pattern in a New England salt marsh plant community. Ecological Monographs 57: 129-147. doi: 10.2307/1942621
Bond WJ, Honig M, Maze KE (1999) Seed size and seedling emergence: An allometric relationship and some ecological implications. Oecologia 120: 132-136. doi: 10.1007/s004420050841
Bortolus A (2006) The austral cordgrass Spartina densiflora Brong.: its taxonomy, biogeography and natural history. Journal of Biogeography 33: 158-168. doi: 10.1111/j.1365-2699.2005.01380.x
Brewer JS, Grace JB (1990) Plant community structure in an oligohaline tidal marsh. Vegetatio 90: 93-107. doi: 10.1007/BF00033019
Brewer JS, Levine JM, Bertness MD (1998) Interactive effect of elevation and burial with wrack on plant community structure in some Rhode Island salt marshes. Journal of Ecology 86: 125–186. doi: 10.1046/j.1365-2745.1998.00241.x
Cantero JJ, Leon R, Cisneros JM, Cantero A (1998) Habitat structure and vegetation relationships in central Argentina salt marsh landscapes. Plant Ecology 137: 79-100. doi: 10.1023/A:1008071813231
Castellanos EM, Figueroa ME, Davy AJ (1994) Nucleation and facilitation in saltmarsh succession: interactions between Spartina maritima and Arthrocnemum perenne. Journal of Ecology 82: 239-248. doi: 10.2307/2261292
Castillo JM, Rubio-Casal E, Redondo S, Álvarez-López AA, Luque T, Luque C, Nieva FJ, Castellanos EM, Figueroa ME (2005) Short-term responses to salinity of an invasive cordgrass. Biological Invasions 7: 29-35. doi: 10.1007/s10530-004-9626-9
Castillo JM, Mateos-Naranjo E, Nieva FJ, Castellanos EM, Figueroa ME (2008) Plant zonation at salt marshes of the endangered cordgrass Spartina maritima invaded by Spartina densiflora. Hydrobiologia 614: 363-371. doi: 10.1007/s10750-008-9520-z
Coteff C, Van Auken OW (2006) Sampling requirements for estimation of the soil seed bank of a west Texas salt marsh. Texas Journal of Science 58: 349-370.
Cui J, Yu-lin L, Ha-lin Z, Yong-zhong S, Sam D (2007) Comparison of Seed Germination of Agriophyllum squarrosum (L.) Moq. and Artemisia halodendron Turcz. Ex Bess, Two Dominant Species of Horqin Desert, China. Arid Land Research and Management 3: 165-179. doi: 10.1080/15324980701426306
Curado G, Rubio-Casal E, Figueroa ME, Castillo JM (2010) Germination and establishment of the invasive cordgrass Spartina densiflora in acidic and metal polluted sediments of the Tinto river. Marine Pollution Bulletin 60: 1842-1848. doi: 10.1016/j.marpolbul.2010.05.022
Dittamar LA, Nelly RK (1999) Wetland seed bank response to sedimentation varying in loading rate and texture. Wetlands 19: 341-351. doi: 10.1007/BF03161765
Facelli JM, Pickett STA (1991) Plant litter: its dynamics and effects on plant community structure. Botanical Review 57: 1-32. doi: 10.1007/BF02858763
Grosholz ED (2002) Ecological and evolutionary consequences of coastal invasions. Trends in Ecology and Evolution 17: 22-27. doi: 10.1016/S0169-5347(01)02358-8
Harper JL, Obeid M (1967) Influence of seed size and depth and sowing on the establishment and growth of varieties of fiber and oils seed flax. Crop Science 7: 527-532. doi: 10.2135/cropsci1967.0011183X000700050036x
Hartleb CF, Madsen JD, Boylen CW (1993) Environmental factors affecting seed germination in Myriophyllum spicatum L. Aquatic Botany 45: 15-25. doi: 10.1016/0304-3770(93)90049-3
Hartman J, Caswell H, Valiela I (1983) Effects of wrack accumulation on salt marsh vegetation. In: Cabioch C, Glemaree M, Samain J (Eds) Proceedings of the 17th European Marine Biology Symposium. Olsen and Olsen, Fredensborg, 99-102.
Hartman JM (1988) Recolonization of small disturbance patches in a New England salt marsh. American Journal of Botany 75: 1625-1631. doi: 10.2307/2444678
Howard VH, Sytsma MD (2013) Potential ocean dispersal of cordgrass (Spartina spp.) from core infestations. Invasive Plant Science and Management 6: 250-259. doi: 10.1614/IPSM-D-12-00042.1
Jurik TW, Wang SC, Van der Valk AG (1994) Effects of sediment load on seedling emergence from wetland seed banks. Wetlands 14: 159-165. doi: 10.1007/BF03160652
Ke X, Li W (2006) Germination requirement of Vallisneria natans seeds: implications for restoration in Chinese lakes. Hydrobiologia 559: 357-362. doi: 10.1007/s10750-005-1276-0
Khan MA, Gul B (2002) Some ecophysiological aspects of seed germination in halophytes. In: Liu X, Liu M (Eds) Halophytes Utilization and Regional Sustainable Development of Agriculture. Meteorological Press of China, Beijing, 59-68.
Leyer I, Pross S (2009) Do seed and germination traits determine plant distribution patterns in riparian landscapes? Basic Applied Ecology 10: 113–121. doi: 10.1016/j.baae.2008.01.002
Li J, Peng SL, Chen LY, Wang RL, Ni GY (2010) Use of Sonneratia apetala allelopathy to control Spartina alterniflora weed. Allelopathy Journal 25: 123-131.
Martínez ML, Valverde T, Moreno-Casasola P (1992) Germination response to temperature, salinity, light and depth of sowing of ten tropical dune species. Oecologia 92: 343-353. doi: 10.1007/BF00317460
Mateos-Naranjo E, Redondo-Gomez S, Cambrolle J, Figueroa ME (2008) Growth and photosynthetic responses to copper stress of an invasive cordgrass, Spartina densiflora. Marine Environmental Research 66: 459-465. doi: 10.1016/j.marenvres.2008.07.007
Maun MA, Lapierre J (1986) Effects of burial by sand on seed germination and seedling emergence of four dune species. American Journal of Botany 73: 450-455. doi: 10.2307/2444088
Minchinton TE (2002) Disturbance by wrack facilitates spread of Phragmites australis in a coastal marsh. Journal of Experimental Marine Biology and Ecology 281: 89-107. doi: 10.1016/S0022-0981(02)00438-0
Nieva FJ, Diaz-Espejo A, Castellanos EM, Figueroa ME (2001a) Field variability of invading populations of Spartina densiflora Brong. grown in different habitats of the Odiel marshes (SW Spain). Estuarine, Coastal and Shelf Science 52: 515-527. doi: 10.1006/ecss.2000.0750
Nieva FJ, Castellanos EM, Figueroa ME (2001b) Effects of light and salinity on seed germination in the marsh invader Spartina densiflora Brong., 1829 (Gramineae) from Gulf of Cadiz–Spain. Boletín de la Real Sociedad Española de Historia Natural 96: 117-124.
Panetta FD, Timmins S (2004) Evaluating the feasibility of eradication for terrestrial weed incursions. Plant Protection Quarterly 19: 5-11.
Parker VT, Simpson RL, Leck MA (1989) Pattern and process in the dynamics of seed banks. In: Leck MA, Parker VT, Simpson RL. Ecology of soil seed banks. Academic Press, Inc, San Diego, USA, 367–384.
Pennings SC, Richards CL (1998) Effects of wrack burial in salt-stressed habitats: Batis maritima in a southwest Atlantic salt marsh. Ecography 21: 630-638. doi: 10.1111/j.1600-0587.1998.tb00556.x
Pons T (1992) Seed responses to light. In: Fenner M (Ed) Seeds The Ecology of Regeneration in Plant Communities (2nd edition). CAB International, Wallingford, UK, 259-282.
Reidenbaugh TG, Banta WC (1980) Origin and effects of tidal wrack in a Virginia salt marsh. Gulf Research Reports 6: 393-401.
Rich PH, Wetzel RG (1978) Detritus in the lake ecosystem. American Naturalist 112: 57-71. doi: 10.1086/283252
Sieg RD, Kubanek J (2013) Chemical ecology of marine angiosperms: opportunities at the interface of marine and terrestrial systems. Journal of Chemical Ecology 39: 687-711. doi: 10.1007/s10886-013-0297-9
Simpson RL, Leck MA, Parker VT (1989) Seed banks: general concepts and methodological issues. In: Leck MA, Parker VT, Simpson RL (Eds) Ecology of Soil Seed Banks. Academic Press, Inc, San Diego, California, USA, 3-21.
Spencer DF, Ksander GG (2002) Sedimentation disrupts natural regeneration of Zannichellia palustris in Fall River, California. Aquatic Botany 73: 137-147. doi: 10.1016/S0304-3770(02)00016-5
Thompson K, Grime JP (1983) A comparative study of germination responses to diurnally-fluctuating temperatures. Journal of Applied Ecology 20: 141-156. doi: 10.2307/2403382
Tolley PM, Christian RR (1999) Effects of increased inundation and wrack deposition on a high salt marsh plant community. Estuaries 22: 944–954. doi: 10.2307/1353074
Ungar IA (1995) Seed germination and seed-bank ecology in halophytes. In: Kigel J, Galili G (Eds) Seed Development and Germination. Marcel Dekker, Inc., New York, USA, 529-544.
Valiela I, Rietsma CS (1995) Disturbance of salt marsh vegetation by wrack mats in Great Sippewissett marsh. Oecologia 102: 106-112.
Vleeshouwers LM, Bouwmeester HJ, Karssen CM (1995) Redefining seed dormancy: An attempt to integrate physiology and ecology. Journal of Ecology 83: 1031-1037. doi: 10.2307/2261184
Wang S, Jurik TW, Van der Valk AG (1994) Effects of sediment load on various stages in the life and death of cattail (Typha glauca). Wetlands 14: 166-173. doi: 10.1007/BF03160653
Wu J, Cheng S, Liang W, He F, Wu Z (2009) Effects of sediment anoxia and light on turion germination and early growth of Potamogeton crispus. Hydrobiologia 628: 111-119. doi: 10.1007/s10750-009-9749-1