Natural Seagrass Research Articles

Response of eelgrass Zostera marina to CO2 enrichment: possible impacts of climate change and potential for remediation of coastal habitats

Projected increases in dissolved aqueous con- centrations of carbon dioxide (CO2(aq)) may have significant impacts on photosynthesis of CO2-limited organisms such as seagrasses. Short-term CO2(aq) enrichment increases photo- synthetic rates and reduces light requirements for growth and survival of individual eelgrass Zostera marina L. shoots grow- ing in the laboratory under artificial light regimes for at least 45 d. This study examined the effects of long-term CO2(aq) enrichment on the performance of eelgrass growing under natural light-replete (33% surface irradiance) and light-limited (5% surface irradiance) conditions for a period of 1 yr. Eelgrass shoots were grown at 4 CO2(aq) concentrations in outdoor flow-through seawater aquaria bubbled with industrial flue gas containing approximately 11% CO2. Enrichment with CO2(aq) did not alter biomass-specific growth rates, leaf size, or leaf sugar content of above-ground shoots in either light treatment. CO2(aq) enrichment, however, led to significantly higher reproductive output, below-ground biomass and vege- tative proliferation of new shoots in light-replete treatments. This suggests that increasing the CO2 content of the atmo- sphere and ocean surface will increase the area-specific pro- ductivity of seagrass meadows. CO2(aq) enrichment did not affect the performance of shoots grown under light limitation, suggesting that the transition from carbon- to light-limited growth followed Liebig's Law. This study also demonstrated that direct injection of industrial flue gas could significantly increase eelgrass productivity; this might prove useful for restoration efforts in degraded environments. The broader effects of CO2(aq) enrichment on the function of natural seagrass meadows, however, require further study before deliberate CO2 injection could be considered as an engineer- ing solution to the problem of seagrass habitat degradation.

The impact of extreme flooding events and anthropogenic stressors on the macrobenthic communities’ dynamics

Marine and coastal environments are among the most ecologically and socio-economically important habitats on Earth. However, climate change associated with a variety of anthropogenic stressors (e.g. eutrophication) may interact to produce combined impacts on biodiversity and ecosystem functioning, which in turn will have profound implications for marine ecosystems and the economic and social systems that depend upon them. Over period 1980–2000, the environment of the Mondego estuary, Portugal, has deteriorated through eutrophication, manifested in the replacement of seagrasses by opportunistic macroalgae, degradation of water quality and increased turbidity, and the system has also experienced extreme flood events. A restoration plan was implemented in 1998 which aimed to reverse the eutrophication effects, especially to restore the original natural seagrass ( Zostera noltii) community. This paper explores the interactions between extreme weather events (e.g. intense floods) and anthropogenic stressors (e.g. eutrophication) on the dynamics of the macrobenthic assemblages and the socio-economic implications that follow. We found that during the previous decade, the intensification of extreme flooding events had significant effects on the structure and functioning of macrobenthic communities, specifically a decline in total biomass, a decline in species richness and a decline in suspension feeders. However, the earlier eutrophication process also strongly modified the macrobenthic community, seen as a decline in species richness, increase in detritivores and a decline in herbivores together with a significant increase in small deposit-feeding polychaetes. After the implementation of the management plan, macrobenthic assemblages seemed to be recovering from eutrophication, but it is argued here that those earlier impacts reduced system stability and the resilience of the macrobenthic assemblages, so that its ability to cope with other stressors was compromised. Thus, heavy flooding in the Mondego region during the recovery process had more severe effects on these assemblages than expected, effectively re-setting the recovery clock, with significant socio-economic impacts (e.g. high mortality of fish in fish farms, and a large decline of economically important species, such as the bivalves Scrobicularia plana and Cerastoderma edule). The frequency and magnitude of these extreme events is predicted to increase in future years [IPCC WGI, 2001. Climate change 2001: the scientific basis, contribution of working group I to the third assessment report of the Intergovernmental Panel on Climate Change (IPCC). In: Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., van der Linden, P.J., Xiaosu, D. (Eds.), Cambridge University Press, UK, 944 p.] and there is a risk that impacted ecosystems will never recover fully, with far-reaching consequences for human well being.

Macroalgal growth on bivalve aquaculture netting enhances nursery habitat for mobile invertebrates and juvenile fishes

Destruction and degradation of biogenic nursery habitats, such as seagrass and coral/ oyster/polychaete reefs, threaten coastal fisheries worldwide. We tested the hypothesis that macroal- gae and epifauna growing upwards from protective plastic mesh used in bottom clam culture substi- tutes for seagrass as a nursery habitat for mobile invertebrates and juvenile fish. By quantifying bio- mass of epibiota in each season and by seining both day and night on 11 occasions from August 1997 to April 1999, biogenic habitat structure and habitat use by mobile invertebrates and juvenile fishes were quantified on hard clam Mercenaria mercenaria aquaculture leases that were using 2 alter- native grow-out methods and on 2 natural habitats, a seagrass bed (Zostera marina and Halodule wrightii) and an unstructured sandflat. The macroalgal/epifaunal biomass per unit bottom area was significantly greater on aquaculture mesh than on the sandflat but did not differ significantly from the natural seagrass biomass density on most sampling dates. Community structure of mobile inverte- brates and juvenile fishes utilizing clam leases was more similar to that of seagrass than sandflat habitats. Community similarity among the structured habitats, the seagrass and the 2 lease types, was greater than the similarity between night and day within any given habitat. The total numbers of mobile invertebrates summed over all 11 dates were 75 times greater in the seagrass than in the sandflat habitat, whereas the structural habitat provided by epibiota attached to bottom mesh on leases provided a 44-fold enhancement of invertebrates over the corresponding counts on unstruc- tured sandflat. Utilization by juvenile fishes was 3 times greater in seagrass and 3 to 7 times greater in epibiota on mesh in clam leases than on sandflat habitat. For example, juvenile reef fishes exhib- ited almost equal utilization of epibiota on leases and seagrass while remaining absent over the sand- flat, which lacked emergent structure. Thus, the biogenic habitat provided largely by macroalgal growth on protective bottom mesh of clam leases supports elevated densities of mobile invertebrates and juvenile fishes similar to that of natural seagrass habitat, thereby representing a previously un- documented ecosystem benefit of bivalve aquaculture. This ecological role for structural habitat rising above clam aquaculture leases is consistent with a broader recognition that artificial reefs, plastic seagrass, oyster shell mounds, and other emergent bottom structures provide habitat services.

Lack of epifaunal response to the application of salt for managing the noxious green alga Caulerpa taxifolia in a coastal lake

Since the discovery of the green alga Caulerpa taxifolia in Lake Macquarie (New South Wales, Australia) in 2001, the New South Wales Department of Primary Industries (Fisheries) has attempted various control methods, including covering the alga with granulated sea salt to induce osmotic shock and cell lysis. In Lake Macquarie, C. taxifolia often occurs in patches within beds of the native seagrass Zostera capricorni. Although the effects of the salt treatment on blades of Z. capricorni and infauna have been shown to be minimal, there have been no tests of any effects on other native biota, including seagrass epifauna. In this study, we tested the general hypothesis that the abundance and diversity of epifauna would be reduced by salting. We used a ‘Beyond BACI’ experimental design whereby epifaunal invertebrates were sampled 3 months, 6 weeks and 6 days before and then again after salting. Epifaunal abundances at the putatively impacted (salted) location were compared to those at 4 control locations (where no salt was applied). Abundances of most organisms varied significantly among times and locations with no evidence of the consistent effect of salting on diversity or abundance of epifauna. The study represents an example of the use of large-scale managerial action as a scientific experiment.

A decline in the abundance and condition of a native bivalve associated with Caulerpa taxifolia invasion

Caulerpa taxifolia is a fast-spreading invasive seaweed that threatens biodiversity in temperate Australian estuaries. To date, little is known about its effects on infauna. In the present study, we describe variation in demographic and life-history traits of the abundant infaunal bivalve, Anadara trapezia, in C. taxifolia and uninvaded habitats (seagrass and unvegetated sediments) at multiple sites across three estuaries in south-eastern New South Wales. Densities of A. trapezia were always lower in C. taxifolia than on unvegetated sediment, and lower in C. taxifolia than in seagrass at three out of four sites where they were compared. Dry tissue weight of A. trapezia was also lower in C. taxifolia than on unvegetated sediment at most sites, but was only lower in C. taxifolia than in seagrass at one of four sites. Populations were dominated by larger individuals (>45 mm length), but smaller individuals (35–45 mm length) were more common in C. taxifolia and seagrass. A. trapezia shell weight and morphology was variable and appeared weakly affected by invasion. Generally, our findings are consistent with the hypothesis that A. trapezia is negatively affected by C. taxifolia. However, C. taxifolia invasion appears complex and, at some places, its effects may not differ from those of native seagrass. There is a need for manipulative studies to understand the mechanisms underlying the effects of C. taxifolia on infauna.

Habitat associations of estuarine species: Comparisons of intertidal mudflat, seagrass (Zostera marina), and oyster (Crassostrea gigas) habitats

The complexity of habitat structure created by aquatic vegetation is an important factor determining the diversity and composition of soft-sediment coastal communities. The introduction of estuarine organisms, such as oysters or other forms of aquaculture, that compete with existing forms of habitat structure, such as seagrass, may affect the availability of important habitat refugia and foraging resources for mobile estuarine fish and decapods. Fish and invertebrate communities were compared between adjacent patches of native seagrass (Zostera marina), nonnative cultured oyster (Crassostrea gigas), and unvegetated mudflat within a northeastern Pacific estuary. The composition of epibenthic meiofauna and small macrofaunal organisms, including known prey of fish and decapods, was significantly related to habitat type. Densities of these epifauna were significantly higher in structured habitat compared to unstructured mudflat. Benthic invertebrate densities were highest in seagrass. Since oyster aquaculture may provide a structural substitute for seagrass being associated with increased density and altered composition of fish and decapod prey resources relative to mudflat, it was hypothesized that this habitat might also alter habitat preferences of foraging fish and decapods. The species composition of fish and decapods was more strongly related to location within the estuary than to habitat, and fish and decapod species composition responded on a larger landscape scale than invertebrate assemblages. Fish and decapod species richness and the size of ecologically and commercially important species, such as Dungeness crab (Cancer magister), English sole (Parophrys vetulus), or lingcod (Ophiodon elongatus), were not significantly related to habitat type.

Phytotoxic activity of caulerpenyne from the Mediterranean invasive variety of Caulerpa racemosa: a potential allelochemical

Allelopathy has been postulated as a factor in the colonisation success of Caulerpa racemosa var. cylindracea, an introduced chlorophyte alga which has become invasive in the Mediterranean Sea. In order to reveal their possible phytotoxic activity, secondary metabolites were isolated from a population growing in the Gulf of Naples (Italy) and tested on leaf tissue of the native seagrass Cymodocea nodosa, which often co-occurs with Caulerpa in nature. The seaweed metabolites were identified by 1H and 13C NMR analysis and leaf portions of C. nodosa were exposed to crude diethyl ether extract and purified compounds in the laboratory, under controlled conditions of irradiance and temperature for a period of 144 h. Eventual changes in the photosynthetic performance of the seagrass tissue following the treatment were tested by monitoring its optimal quantum yield with a pulse amplitude modulated (PAM) fluorometer. One of the identified compounds, caulerpenyne, showed a phytotoxic effect, while the other purified metabolites did not reveal any effect at the assayed concentrations. Thus, our results seem to suggest a possible allelopathic activity of caulerpenyne, which may play a role in the successful competition of the invasive C. racemosa var. cylindracea with native macrophytes, such as seagrasses.

Seagrass beds and intertidal invertebrates: an experimental test of the role of habitat structure

The majority of field experiments have been carried out on relatively small spatial and short temporal scales, but some of the most interesting ecological processes operate at much larger scales. However, large-scale experiments appropriate to the landscape, often have to be carried out with minimal plot replication and hence reduced statistical power. Here, we report the results of such a large scale, un-replicated field experiment on the Mondego estuary, Portugal, which nevertheless provides compelling evidence of the importance of habitat structure for invertebrate community composition and dynamics. In this estuary, seagrass beds have suffered a dramatic decline over the last 20 years, associated with changes in invertebrate assemblages. In addition, the most abundant species in the system, Hydrobia ulvae, displays distinctly different population structures in those sites. The aim of the field experiment was to test the hypothesis that these differences are related to enhanced survival of snails due to protection from avian or fish predators so that they can grow to larger body sizes in the more complex habitat provided by seagrass. We tested this hypothesis through a large-scale experiment using artificial seagrass beds over a 12-month period. Adult snail densities were higher in the artificial bed plots compared to controls. However, these differences emerged only slowly, related to snail growth rate. This suggests that protection from epibenthic predators can have a significant effect on population structure and hence biomass and productivity of key species in this system. However, the invertebrate assemblage in artificial seagrass plots and the natural seagrass bed, remained statistically separate by the end of the experiment.

Polychaete assemblages as indicators of habitat recovery in a temperate estuary under eutrophication

From 1980 to 2000, the Mondego estuary (Portugal) suffered dramatic changes due to eutrophication, leading to a decline in seagrass beds and changes in community structure, namely a decline in species richness and replacement of herbivores by detritivores. Because the conservation status of the estuary was being compromised, a restoration project was implemented in 1998 in order to restore the original natural seagrass habitat. This project included several restoration/management measures, including the protection of the remaining seagrass patches and improvement of the hydraulic conditions through modifying sluice opening regimes, thereby reducing the nutrient loading in the southern arm of the estuary. In addition, several stakeholder forums were convened to inform local people of the ecological and economic importance of the area. In this paper we evaluate the success of this management plan as judged by changes in the polychaete assemblages. In the year following implementation of the restoration measures, the total biomass of polychaetes increased markedly, a pattern also seen in the overall macrobenthic community. Biomass recovery was faster and more pronounced compared to density recovery, probably because many larger species were able to attain adult body size (e.g. Hediste diversicolor). The polychaetes Alkmaria romijni and Capitella capitata, considered as indicators of nutrient enrichment and pollution of estuarine systems, gradually declined over time. A general increase in species diversity was observed after the application of the restoration/management measures. These changes indicate that the restoration project has been successful and that polychaetes can be considered representative indicators of the wider macrobenthic community, with considerable savings in time and effort for monitoring programmes.

Edge effects and patch size in seagrass landscapes: an experimental test using fish

Edge effects and bed size are 2 main landscape-scale parameters that may affect fish in seagrass. We tested their influence on the species richness per unit area and density of fish in 6 Zostera capricorni seagrass beds ranging in size from 2300 to 211 200 m 2 , in the Pittwater estuary, NSW, Australia. The effect of edge interacted with bed size. The species richness was lower in edge than inner regions of the larger beds, but did not differ between regions in smaller beds, in which the species richness was similar to the inner regions of large beds. The density of fish (all species combined) varied with bed size in 1 of the 2 seasons sampled, but not with region. The densities of some individual species were lower in the larger beds compared to smaller beds (5 species), while others were greater (3 species), although for some species this was inconsistent between seasons. We then tested whether species richness and abundance were responding to patch area, perimeter, or perimeter: area ratio (P:A ratio) using artificial seagrass units (ASUs) of different shapes and sizes. All ASU designs had similar total abundances of fish species (per ASU), yet 1 design was smaller in area, so these smaller ASUs had greater species richness per unit area. The ASUs were smaller than the natural seagrass beds, and it seems that, although edge effects appeared in large natural seagrass beds, in smaller patches the total area rather than amount of edge influenced the species richness.

Fish assemblages in habitats dominated by Caulerpa taxifolia and native seagrasses in south-eastern Australia

Seagrass beds in estuaries are important habitats and nursery grounds for a great vari- ety of fishes, including many economically important species. The introduction of the invasive green alga Caulerpa taxifolia could potentially threaten the seagrasses of south-eastern Australia. This study examined the implications of the spread of C. taxifolia on ichthyofauna in 2 estuaries in central New South Wales. Fish assemblages were compared among adjacent habitats of C. taxifolia and 2 seagrass species (Posidonia australis and Zostera capricorni). Fish were sampled using a small beam trawl to test for differences among habitats in (1) the species composition of the fish assemblages, (2) total abundance and species richness of fishes, and (3) abundances of major fish families. Fish assemblages separated into 3 significantly distinct groupings based on habitat. Total abundances of fishes were similar among habitats; however, species richness was lower in C. taxifolia. The fish assemblages in C. taxifolia were largely characterised by high abundances of gobiid fishes, similar to those in Z. capricorni, and few or no syngnathid and monacanthid species when compared to sea- grass fish assemblages. This suggests that if C. taxifolia competitively replaces native seagrass beds in the estuaries of New South Wales, the resulting change in habitat may also cause a change in fish assemblages. This could reduce the abundances of some protected and economically important fish species but may also increase abundances of other opportunistic fishes.

Seagrass recovery in the Delmarva Coastal Bays, USA

Zostera marina (eelgrass) in the coastal bays of the Delmarva Peninsula, USA, declined precipitously in the 1930s due to the pandemic wasting disease and a destructive hurricane in 1933. This resulted in major changes in many of the ecosystem services provided by this seagrass, such as loss of bay scallops ( Argopecten irradians) and disappearance of brant ( Branta bernicla). Natural recovery of Z. marina, possibly deriving from either small remnant stands or undocumented transplant projects after the demise of Z. marina, has been significant in four northern bays, with over 7319 ha reported through 2003 compared to 2129 ha in 1986, an average expansion rate of 305 ha year −1. This rapid spread was likely due to seeds and seed dispersal from recovering beds. However, no recovery had occurred in the southern coastal bays prior to restoration efforts, possibly due to both their distance from potential donor beds, restricted entrances to the bays, and the narrow time period when seeds are available for colonization via rafting reproductive shoots carrying viable seeds. Survival and expansion of small test plots (4 m 2) in these southern coastal bays between 1997 and 2000 demonstrated that propagule supply, rather than water quality, was limiting seagrass recovery in these bays. In 2001, we initiated a large-scale Z. marina restoration effort in the southern coastal bays utilizing seeds, while simultaneously monitoring water quality using spatially and temporally intensive water quality mapping techniques. Between 2001 and 2004, approximately 24 million seeds harvested from natural, dense beds in Chesapeake Bay were broadcast into experimental plots ranging in size from 0.2 to 2 ha in four coastal bays having no seagrass, totaling approximately 46 ha through 2004. Successful germination (estimated at 5–10% of seeds broadcast), growth and expansion of Z. marina in and around these plots over this 3-year test period, as well as water quality data, suggest conditions are appropriate for plant growth. Low-level aerial photographs in 2004 showed 38% of the bottom in 52–0.4 ha plots was covered by vegetation. Increasing Z. marina coverage will have important implications for fisheries and waterfowl but may potentially conflict with aquaculture, which is rapidly expanding in this region. Continued recovery will depend on maintaining good water quality to avoid the macro-algal accumulations and phytoplankton blooms that have characterized other coastal lagoons. The patterns of natural seagrass recovery and the results of restoration efforts we describe here, as well as seagrass recoveries from wasting disease outbreaks, anoxic events, hurricanes, and propeller scarring reported elsewhere, suggest that seeds and seed dispersal play an important role in the recovery and expansion of these beds.

A field colonization experiment with meiofauna and seagrass mimics: effect of time, distance and leaf surface area

From a conservation point of view, it is essential to know how fast an ecosystem can recover after physical disturbance. Meiofauna and especially harpacticoid copepods are abundant in seagrass beds and are therefore useful to study ecosystem recovery after disturbance. In the western Caribbean coast, a fragmented Thalassia testudinum seagrass bed was selected to conduct a colonization field experiment by means of plastic seagrass mimics. Meiofauna colonization, with special emphasis on harpacticoid copepods, was followed in relation to: (1) colonization time (2, 4, 6, 10, 14 and 21 days); (2) distance to source of colonizers (close and far series) and (3) leaf surface area to colonize (small, medium, large). Colonization was recorded after 2 days with average meiofauna densities of 480 ind/100 cm2 (close) and 1350 ind/100 cm2 (far) of leaf surface area, while on average 400 ind/100 cm2 were collected from the natural seagrass plants. In this early phase, the meiofauna diversity was high, with on average 8 taxa. A longer period of colonization (21 days) showed an increased meiofaunal density and diversity (average density: 3220 ind/100 cm2, 13 taxa). Increasing meiofauna colonization with time is probably related to the development of a biofilm making the leaf more attractive for meiofauna. The effect of distance was not so pronounced as that of time. Total absolute densities were highest in the far series (5 m away from natural seagrass patch), mainly because of nematode densities. Meiofauna diversity was lower in the far series than in the close series (at the border of the natural seagrass patch). A larger individual leaf surface area did not affect the overall meiofauna densities but had a significant positive effect on copepod densities. Larger surface areas promoted the presence of epiphytic copepod families such as Tegastidae and Dactylopusiidae. Overall, we found a rapid recovery of meiofauna in fragmented seagrass beds with primary colonizers (both nematodes and benthic opportunistic copepods) originating from the sediment and later colonizers as epiphytic copepods and their nauplii from the local seagrass regeneration pool.

Comparison of restored and natural seagrass beds near Corpus Christi, Texas

Structural equivalence between seagrass restoration sites and adjacent natural seagrass beds on the mid Texas coast was assessed six times between April 1995 and May 1997. Throw traps and corers were used for quantitative sampling. Restoration sites were 2.7 to 6.6 yr old when first sampled and 3.7 to 8.2 yr old when last sampled. There were few significant differences in water column, seagrass, or sediment characteristics, in fish and decapod (nekton) densities, or in nekton and benthos community compositions between restored and natural seagrass habitats at any time during the study period. Differences in densities of dominant benthic invertebrates were regularly observed, with greater densities of more taxa observed in natural seagrasses than in restored beds. Densities of Class Oligochaeta and the polychaetePrionospio heterobranchiata are proposed as potential indicators of structural equivalence in restored seagrasses. This study indicates that seagrass restorations in the vicinity of Corpus Christi, Texas, exhibit minimal quantitative differences in community structure (except for benthos) relative to adjacent natural seagrass beds after 3 to 5 yr.

Scaling of ramet size and spacing in seagrasses: implications for stand development

The scaling between shoot mass and spacer length was examined across 23 seagrass species by compiling field and literature data on architectural and stand features. The distance between shoots programmed in seagrass architecture was scaled at the 0.24 power of shoot mass. The predicted distance between neighboring shoots resulting from the scaling relationship investigated was compared with the spacing observed in 79 crowded natural seagrass stands. Seagrass architecture predicted 50% of the variability of the distance between neighbors observed in natural stands. Moreover, the growth programme of seagrass species predicted 29% of the variance of maximum aboveground biomass developed by seagrass meadows. The close agreement between the shoot density and biomass developed by closed natural stands and that predicted from seagrass architecture suggested that the upper limit to density and aboveground biomass, such as that defined by the self-thinning law, is already imprinted within the basic architecture of seagrasses (i.e. spacer length in between consecutive shoots).

The influence of burrowing thalassinid shrimps on the distribution of intertidal seagrasses in Willapa Bay, Washington, USA

Two species of seagrasses frequently co-occur with extensive thalassinid shrimp populations and aquaculture operations in the intertidal zone of estuaries along the west coast of North America. Although thalassinid shrimp are known to be strong bioturbators and affect both aquaculture operations and benthic intertidal community structure, few studies have investigated shrimp–seagrass interactions. Application of the pesticide carbaryl to control shrimp populations for oyster aquaculture in Willapa Bay, Washington provided us with an experimental tool to investigate one such interaction. We found that the seagrass Zostera japonica colonized areas where ghost shrimp ( Neotrypaea californiensis) had been removed via carbaryl application. We applied carbaryl to small (900 m 2) experimental plots and compared seagrass colonization on these to that on control plots where shrimp remained abundant (100 m −2). The cumulative proportion of Z. japonica seeds and sprouts was slightly higher in the surface layer of treated plots (presumably due to the lack of shrimp bioturbation distributing them to depth), but seedling abundance was not significantly different between treated (no shrimp) and untreated control plots when they first emerged in early spring. As the season progressed however, and shrimp became more active, fewer seedlings survived in the untreated areas, and those that did survive grew much more slowly than those in the treated plots. We suspect that this was due to the effects of shrimp bioturbation and either light limitation (shoots that survived were much smaller) or direct burial and loss. Although it is an introduced plant, the natural distribution of Z. japonica is high in the intertidal zone and it is often separated from its congener Zostera marina by an expansive sandflat that is dominated by the ghost shrimp N. californiensis in west coast estuaries. The treatment of intertidal oysterbeds with carbaryl clearly reduces abundance of shrimp in this zone and we documented the same pattern of seagrass colonization on a commercial oyster bed and lack of seagrass in an adjacent unsprayed area. Density of native seagrass Z. marina shoots was also enhanced in plots treated with carbaryl, but only at lower tidal elevations or in intertidal pools where it could survive. We believe the removal of shrimp will continue to broaden the distribution of Z. japonica in Washington coastal estuaries where carbaryl use is permitted and add an interesting perspective to this controversial management issue.

Fauna of Natural Seagrass and TransplantedHalodule wrightii(Shoalgrass) Beds in Galveston Bay, Texas

AbstractWe compared nekton and benthos densities and community compositions in a natural mixed seagrass bed dominated byHalodule wrightii(shoalgrass) with those found in three shoalgrass transplant sites and adjoining sand habitats in western Galveston Bay, Texas, U.S.A. Quantitative drop traps and cores were used to compare communities up to seven times over 36 months post‐transplant where transplant beds survived. Total densities of fishes, decapods, annelids, benthic crustaceans, and most dominant species were significantly higher in natural seagrass than in transplanted shoalgrass or sand habitats during most sampling periods. On occasion, fish and decapod densities were significantly higher in transplanted shoalgrass than in adjoining sand habitats. No consistent faunal differences were found among transplant sites before two of three sites failed. Taxonomic comparison of community compositions indicated that nekton and benthos communities in natural seagrass beds were usually distinct from those in transplanted beds or sand habitats, which were similar. We conclude that reestablishing a shoalgrass bed that resembles a natural seagrass bed and its faunal communities in the Galveston Bay system will take longer than 3 years, provided that transplants persist.

Susceptibility of the Invasive Seaweed Caulerpa taxifolia to Ionic Aluminium

The tropical green seaweed, Caulerpa taxifolia has been invading the northwestern Mediterranean Sea since 1984, and has been discovered recently in California. This strain of C. taxifolia has proved an aggressive colonist, capable of vigorous growth on a variety of substrates. It can displace the native seagrasses and seaweeds, and its progress remains unchecked by grazers, which either avoid it or are poisoned by it. A variety of unsuccessful attempts have been made to curtail its spread. In this report we document the susceptibility of C. taxifolia to ionic aluminium. The exposure of whole fronds to 1 mM AlCl3 causes complete inhibition of photosynthesis in less than 2 hours. The effect is irreversible. The ecologically important seagrass Posidonia oceanica is unaffected by this treatment. The unusually low internal pH of 4.0 found in Caulerpa taxifolia may explain its vulnerability to aluminium poisoning, since the highly toxic Al3+ ion predominates at low pH. The results of this study provide the basis for the development of an environmentally sound means of selectively reducing the dominance of the aggressive strain of C. taxifolia in areas where it adversely affects the native plants and animals.

Settlement and Density of Juvenile Fish Assemblages in Natural, Zostera Capricorni (Zosteraceae) and Artificial Seagrass Beds

Few studies have validated the use of artificial seagrass to study processes structuring faunal assemblages by comparison with natural seagrass. One metric (fish recruitment) for evaluating the use of artificial seagrass was used in the present study. Settlement and recruitment of juvenile fish was estimated in natural, Zostera capricorni Aschers, and artificial seagrass in Botany Bay, NSW, over 6 consecutive days. Tarwhine, Rhabdosargus sarba, dominated the catch from both habitats, and there was no significant difference in abundance of recruits among the habitats. This was at least partly caused by large spatial and temporal variation in abundance. Daily abundances of R. sarba recruits suggested movement between seagrass beds, but could not be confirmed without tagging individual fish. Rhabdosargus sarba settlers were less abundant than recruits, but were also patchily distributed amongst natural and artificial seagrass beds. Most other species were also found in similar abundance in the two habitats, except stripey, Microcanthus strigatus, which was more abundant in artificial seagrass. Overall, fish assemblages in natural and artificial seagrass were similar. Artificial seagrass may therefore be useful for monitoring settlement and recruitment of juvenile fishes to disturbed habitats, to predict the success of habitat remediation. However, if artificial seagrass is used to model processes occurring in natural seagrass, it is necessary to consider species-specific responses to the artificial habitat.

Effects of the invasive, nonindigenous seagrass Zostera japonica on nutrient fluxes between the water column and benthos in a NE Pacific estuary

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 254:69-80 (2003) - doi:10.3354/meps254069 Effects of the invasive, nonindigenous seagrass Zostera japonica on nutrient fluxes between the water column and benthos in a NE Pacific estuary Scott T. Larned1,2,* 1Coastal Ecology Branch, United States Environmental Protection Agency, 2111 SE Marine Science Drive, Newport, Oregon 97365, USA 2Present address: National Institute of Water and Atmospheric Research, PO Box 8602, Christchurch, New Zealand *Email: s.larned@niwa.co.nz ABSTRACT: The effects of Z. japonica on dissolved nutrient fluxes between the water column and the benthos in Yaquina Bay, Oregon, USA were examined. Nutrient fluxes in Zostera japonica habitats were compared to those in adjacent unvegetated sediment in warm and cool seasons, and in daylight and darkness. In daylight, Z. japonica habitats were net sinks for nitrate (NO3), ammonium (NH4) and dissolved reactive phosphorus (DRP) in the warm season, and for NO3 and DRP in the cool season. At night in the warm season, Z. japonica habitats were net sinks for NO3 and NH4. Unvegetated sediments were net sources of NH4 to the water column in daylight in both seasons, and net sinks for NO3 at night in the warm season. On a diel basis, Z. japonica habitats habitats were net sinks for NO3 and NH4, and unvegetated sediments were net sources of NH4. Porewater NO3 and NH4 concentrations in unvegetated sediments were twice those in Z. japonica habitats. Nutrient fluxes in abutting monospecific patches of Z. japonica and the native seagrass Z. marina were also compared. Both species were sinks for NO3, NH4 and DRP. NO3 influx rates per unit above-ground biomass were higher in Z. japonica habitats, but areal rates of NO3 influx were higher in Z. marina habitats, reflecting the latterŒs higher biomass. The data demonstrate that Z. japonica invasions alter water column-benthos nutrient fluxes. These alterations may in turn affect pelagic primary production. At current biomass levels, Z. japonica is estimated to remove 50 to 60 mole dissolved inorganic nitrogen (DIN) h-1 and 0.2 to 2.2 mole DRP h-1 from the Yaquina Bay water column, and continued expansion of Z. japonica in the estuary could lead to substantial reductions in nutrient availability. KEY WORDS: Estuary · Invasion · Nonindigenous species · Nutrient flux · NE Pacific · Porewater · Seagrass · Sediment · Zostera japonica Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 254. Online publication date: June 04, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.