Zostera Marina Beds Research Articles

Desiccation is a limiting factor for eelgrass (Zostera marina L.) distribution in the intertidal zone of a northeastern Pacific (USA) estuary

Intertidal irradiance, temperature, and aerial exposure were measured for two years in intertidal Zostera marina beds located in Yaquina Bay (Newport, OR, USA). These physical data were correlated with plant growth and other metrics measured at intervals during the study. Photosynthesis vs. irradiance (P vs. I) curves were determined by PAM fluorometry on plants along an intertidal gradient, and were used to estimate saturating irradiance (I k ) and daily hours of saturating irradiance (H sat ). Mean I k values were ∼64 μmol photons m -2 s -1 and H sat increased with increasing tidal position. Measurements taken during the second winter showed that H sat values in the low intertidal zone were within a critical range requiring eelgrass to use rhizome reserves to maintain carbon balance. However, plants continued to grow. Temperature differences across tidal gradients were not found to be physiologically important. These results suggested that temperature and irradiance were not limiting factors for intertidal Z. marina growth. High intertidal eelgrass, exposed to aerial conditions more frequently and for longer durations, exhibited signs of desiccation damage and appeared to have faster blade turn-over rates in spring and summer than their low intertidal neighbors. Thus, we concluded that the major factor limiting Z. marina in the upper intertidal zone was desiccation stress, which was acute and episodic rather than chronic.

Deterioration of eelgrass (Zostera marina L.) through destructive grazing by the gastropod Rissoa membranacea (J. Adams)

Deterioration of an eelgrass (Zostera marina) bed was observed in Skagerrak, southern Norway in August 2002. Compared with observations from previous years, there was a significant reduction in canopy height and shoot density. Simultaneously, high numbers of the gastropod Rissoa membranacea were observed. The proposed mechanism for this drastic loss of eelgrass leaves involves epidermal injuries caused by the grazing activity of the numerous snails, with subsequent leaf breakage. After 1 year, the canopy height had recovered, but shoot density was at the same level as in 2002.

광양만 잘피밭에 서식하는 단각류의 계절변동과 식성

On the basis of monthly samples, we investigated the seasonal variation and feeding habits of amphipods inhabiting Zostera marina beds in Gwangyang Bay. Dominant species <TEX>$(>1\%$</TEX> of the total number of amphipods) consist of 5 gammarids (Gammaropsis japonicus, Jassa slatteryi, Pontogenia rostrata, Atylus collingi and Ceinina japonica) and 1 caprellid (Caprella tsugarensis). Mean densities of amphipods varied from the highest of <TEX>$63,148\;ind.\;m^{-2}$</TEX> in-May to the lowest of <TEX>$1,247\;ind.\;m^{-2}$</TEX> in September. G. japonicus and J. slatteryi dominated in summer whereas C. japonica in autumn and winter. C. japonica was found to be a carnivorous feeder consuming mainly harpacticoid copepods and unidentified crustaceans, whereas G. japonicus, J. slatteryi, and C. tsugarensis consumed both phytoplankton and detritus. Seasonal densities of amphipods were significantly related with the shoot standing crop of the eelgrass and its epiphyte. Also densities of amphipods displayed significant difference in related with the shoot density of the eelgrass among sampling stations. These results suggest that the biological interactions between the eelgrass and amphipods as well as between the carnivorous and the herbivorous amphipods may be important in the seasonal variation of amphipods inhabiting Z. marine beds.

Feeding Habits of Rudarius ercodes in a Zostera marina Bed

Feeding habits of Rudarius ercodes collected from a Zostera marina bed in Jindong Bay, Korea were studied. R. ercodes was a omnivore which consumed mainly gammarid amphipods, polychaetes and eelgrass (z. marina). Its diets also included a small amount of copepods, urochordates and caprellid amphipods. R. ercodes showed ontogenetic changes in feeding habits. Small individuals less than 2cm SL fed mainly on copepods, however, gammarid amphipods and polychaetes were heavily selected with increasing fish size. The consumption of eelgrass by R. ercodes was <TEX>$10-20\%$</TEX> all size classes. The dietary breadth of R. ercodes were varied with fish size

Spatial variability in the epiphytic algal assemblages of Zostera marina seagrass beds

Within-bed variation of epiphytic algal assemblages was studied in 3 Zostera marina beds around Plymouth Sound (Devon, United Kingdom) in order to determine if distance from edge of bed affected the assemblage composition. Replicate seagrass samples were taken at 0, 1, 3 and 6 m along a transect running from the edge of each bed. Individual epiphytes were enumerated and placed into 6 'functional' groups: filamentous, foliose, corticated filamentous, corticated foliose, sac- cate and coralline. The abundance of each functional group did not vary with distance into each bed, nor was it related to measures of seagrass architecture or potential grazing pressure from gastropods. A positive relationship between amphipod abundance and total epiphytes suggest these crustaceans are influenced by epiphytes as an available substrate rather than exerting a grazing effect. Differ- ences amongst beds, however, were evident for filamentous, corticated filamentous and coralline functional groups. These groups comprised 99% of all epiphytes, resulting in the total algal abun- dance being different amongst beds. Similarly, the assemblage composition of the epiphytes was con- sistent within each bed, but differed amongst all 3 beds. Overall, therefore, epiphytic abundance and composition was not affected by distance from the edge of the bed, seagrass architecture or grazing pressure within the bed, but existence of within-bed variation cannot be completely ruled out due to the comparatively low power of the analysis. The only significant variation occurred at the amongst- bed level, probably due to variations in large-scale factors.

Abundance and early life history traits of young-of-the-year Sebastes inermis in a Zostera marina bed

: Young-of-the-year (YOY) Sebastes inermis uses seagrass beds as a temporary nursery ground after completing the planktonic stage in offshore waters. In the present study, the otolith microstructure was used to reveal the early life history of this species in a Zostera marina bed in Matsushima Bay, northern Japan. In 1998 and 1999, the settlement season began in early spring and catch per unit effort (CPUE) of YOY decreased markedly during the summer months. The smallest YOY S. inermis collected were 20 and 21 mm total length (TL) at 70–80 days after extrusion in 1998 and 1999, respectively. In both years, YOY that were extruded earlier (mostly in January) first appeared in the Zostera bed, and they were the first to leave, whereas those YOY extruded later (mainly in February) tended to stay beyond the summer in the Zostera belt. Birth dates of YOY showed two distinct cohorts, January and February, which showed a similar pattern of growth in both years; rapid growth after settlement peaking in May in 1998 (mean = 0.73 mm/day) and in April in 1999 (mean = 0.61 mm/day), decreasing during the summer months, with the lowest mean values in August in both years (mean = 0.40 mm/day for 1998 and 0.30 mm/day for 1999). In both years, the decrease in both CPUE and growth rates in summer months synchronized with a decline in biomass, density, leaf length and shoot weight of Z. marina. Total CPUE was higher in 1999 than in 1998, whereas the recent growth rate (i.e. 1 week before the fish were collected) was significantly higher in 1998 than in 1999, suggesting a density-dependent mechanism.

Material exchange and food web of seagrass beds in the Sylt-Rømø Bight: how significant are community changes at the ecosystem level?

Material exchange, biodiversity and trophic transfer within the food web were investigated in two different types of intertidal seagrass beds: a sheltered, dense Zostera marina bed and a more exposed, sparse Z. noltii bed, in the Northern Wadden Sea. Both types of Zostera beds show a seasonal development of above-ground biomass, and therefore measurements were carried out during the vegetation period in summer. The exchange of particles and nutrients between seagrass beds and the overlying water was measured directly using an in situ flume. Particle sedimentation [carbon (C), nitrogen (N) and phosphorus (P) constituents] from the water column prevailed in dense seagrass beds. In the sheltered, dense seagrass bed, a net particle uptake was found even on windy days (7–8 Beaufort). Dissolved inorganic N and orthophosphate were mainly taken up by the dense seagrass bed. At times of strong winds, nutrients were released from the benthic community to tidal waters. In a budget calculation of total N and total P, the dense seagrass beds were characterised as a material sink. The seagrass beds with sparse Z. noltii were a source of particles even during calm weather. The uptake of dissolved inorganic N in the sparse seagrass bed was low but significant, while the uptake of inorganic phosphate and silicate by seagrasses and their epiphytes was exceeded by release processes from the sediment into the overlying water. Estimates at the ecosystem level showed that material fluxes of seagrass beds in the Sylt-Rømø Bight are dominated by the dense type of Zostera beds. Therefore, seagrass beds act as a sink for particles and for dissolved inorganic nutrients. During storms, seagrass beds are distinct sources for inorganic nutrients. The total intertidal area of the Sylt-Rømø Bight could be described as a sink for particles and a source for dissolved nutrients. This balance of the material budget was estimated by either including or excluding seagrass beds. Including the subtidal part, the function of the ecosystem as a source for particles increased, supposing that all seagrass beds were lost from the area. During the vegetation period, seagrass beds act as a storage compartment for material accumulated in the living biomass of the community. There was great biodiversity among the plant and animal groups found in intertidal seagrass beds of the Sylt-Rømø Bay, representing 50–86% of the total number of species investigated, depending on the particular group. Since most species are not exclusively seagrass residents, the loss of intertidal seagrass beds would be of minor importance for biodiversity at the ecosystem level. Food web structure in seagrass beds is different from other intertidal communities. Primary production and detritus input is high, but secondary production is similar to that of unvegetated areas, although the relative importance of the trophic guilds is different. The loss of seagrass beds leads to profound alterations in the food web of the total ecosystem. Historical as well as recent changes in material fluxes and energy flow due to man-made alterations to the ecosystem are discussed.

Habitat suitability of the Wadden Sea for restoration of Zostera marina beds

A conceptual model is proposed, describing potential Zostera marina habitats in the Wadden Sea, based on reported data from laboratory, mesocosm and field studies. Controlling factors in the model are dynamics, degree of desiccation, turbidity, nutrients and salinity. A distinction has been made between a higher and a lower zone of potential habitats, each suitable for different morphotypes of Z. marina. The model relates the decline of Z. marina in the Wadden Sea to increased sediment and water dynamics, turbidity, drainage of sediments (resulting in increased degree of desiccation) and total nutrient loads during the twentieth century. The upper and lower delineation of both the higher and the lower zone of potential Z. marina habitats appear to be determined by one or a combination of several of these factors. Environmental changes in one of these factors will therefore influence the borderlines of the zones. The lower zone of Z. marina will be mainly affected by increased turbidity, sediment dynamics, degree of desiccation during low tide and nutrient load. The higher zone will be affected by increases in water and sediment dynamics, desiccation rates and nutrient loads. Potential Z. marina habitats are located above approx. –0.80 m mean sea level (when turbidity remains at the same level as in the early 1990s) in sheltered, undisturbed locations, and preferably where some freshwater influence is present. At locations with a high, near-marine, salinity, the nutrient load has to be low to allow the growth of Z. marina. The sediment should retain enough water during low tide to keep the plants moist. Our results suggest that the return of Z. marina beds within a reasonable time-scale will require not only suitable habitat conditions, but also revegetation measures, as the changes in the environment resulting from the disappearance of Z. marina may impede its recovery, and the natural import of propagules will be unlikely. Furthermore, the lower zone of Z. marina may require a genotype that is no longer found in the Wadden Sea.

Nitrogen cycling in two temperate Zostera marina beds:seasonal variation

Exchange of dissolved inorganic N (DIN) between 2 eelgrass vegetated sediments and the water column along with denitrification, plant uptake and loss of N were measured monthly throughout a full year. The eelgrass beds acted as strong sinks for DIN in the spring and summer months. In autumn the beds acted as DIN sources, whereas during the winter months the beds had reestablished their sink capacity, although exchange rates were much lower than during the spring. The seasonal variation in DIN exchange between the water column and eelgrass beds was mainly controlled by the balance between benthic N-mineralization and plant N-uptake, while denitrification was of minor importance. Although plants and probably other associated primary producers were the dominant N sink, there was no accumulation of N in the living biomass on an annual scale. Model calculation of eelgrass decomposition furthermore suggested that most of the N bound to sloughed plant material was liberated to the environment within 1 yr. Only during the spring summer period was more nitrogen taken up by the beds than was released via decomposition of plant material. Therefore only in that period could the beds be considered as N sinks. The uptake of DIN by the eelgrass beds was significantly higher than the DIN uptake at unvegetated sites during the spring and summer period, whereas outside this period there was no significant difference between DIN fluxes measured at vegetated and unvegetated sites. Denitrification activity in the eelgrass vegetated sediments was similar to the activity in unvegetated sediments. It is suggested that the presence of eelgrass will not alter estuarine N-retention on an annual scale. However, during the spring and summer period when eelgrass beds are superior DIN sinks compared to unvegetated sediments, the temporal retention of N in the eelgrass biomass and detritus pool may reduce nutrient availability for other phototrophic organisms. The presence of eelgrass in N-limited areas may therefore reduce pelagic primary production.

Spatial and diurnal distribution of invertebrate and fish fauna of a Zostera marina bed and nearby unvegetated sediments in Damariscotta River, Maine (USA)

Fish, epibenthos and macroinfauna were collected in a Zostera marina bed and nearby unvegetated sediments in the estuary of the Damariscotta River, on the mid-coast of Maine. Samples of epibenthic fauna and fish were collected at low tides both during day and night, and samples of infauna at low tides during the day. The mean density of Zostera shoots in the study area was 335 m −2. Abundance and species number of fish were greater at night than during the day and greater in eelgrass beds ( Z. marina) than in unvegetated habitats. Daytime fish collections were dominated by Atlantic silversides ( Medinia medinia), while juvenile winter flounder ( Pseudopleuronectes americanus) dominated night collections. Also Zostera-associated epifaunal abundances and number of species were significantly higher at night than during the day. Mysis stenolepis, Idotea balthica and Littorina obtusata were dominant species in the epifauna samples. Of the total of 37 invertebrate species encountered, only five occurred both in the infaunal and epifaunal samples. Nineteen different taxa were collected from the benthic core samples. The most abundant invertebrate infaunal taxa were sipunculids, the polychaete Nereis virens, and oligochaetes. Infaunal invertebrate abundances and species diversity were significantly higher in eelgrass beds than in unvegetated sediments. The abundance and number of species of benthic invertebrates were also positively correlated to seagrass biomass. Community diversity values ( H′) were relatively low but fit well in the general pattern of decreasing diversity towards northern latitudes.

Effect of habitat fragmentation on the macroinvertebrate infaunal communities associated with the seagrass Zostera marina L.

1. The effect of habitat fragmentation was investigated in two adjacent, yet separate, intertidal Zostera marina beds in the Salcombe Estuary, Devon, UK. The seagrass bed on the west bank comprised a continuous meadow of ca. 2.3 ha, whilst the bed on the east bank of the estuary was fragmented into patches of 6–9 m2. 2. Three 10 cm diameter core samples for infaunal macroinvertebrates were taken from three stations within each bed. No significant difference was found in univariate community parameters between beds, or in measured seagrass parameters. However, multivariate analysis revealed a significant difference in community composition, due mainly to small changes in species abundance rather than differences in the species present. 3. The species contributing most to the dissimilarity between the two communities were polychaetes generally associated with unvegetated habitats (e.g. Magelona mirabilis) and found to be more common in the fragmented bed. 4. A significant difference in median grain size and sorting coefficient was recorded between the two beds, and median grain size was found to be the variable best explaining multivariate community patterns. 5. The results of the study provide evidence for the effects of habitat fragmentation on the communities associated with seagrass beds, habitats which are of high conservation importance. As the infaunal community is perhaps intuitively the component least likely to be affected by fragmentation at the scale observed, the significant difference in community composition recorded has consequences for more sensitive and high-profile parts of the biota (e.g. fish), and thus for the conservation of seagrass habitats and their associated communities. Copyright © 1999 John Wiley & Sons, Ltd.

Effects of changes in seagrass shoot density and leaf height on abundances and distribution patterns of juveniles of three gobiid fishes in a Zostera marina bed

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 183:87-94 (1999) - doi:10.3354/meps183087 Effects of changes in seagrass shoot density and leaf height on abundances and distribution patterns of juveniles of three gobiid fishes in a Zostera marina bed Masahiro Horinouchi*, Mitsuhiko Sano Department of Global Agricultural Sciences, Graduate School of Agricultural and Life Sciences, University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan *E-mail: adiver@hongo.ecc.u-tokyo.ac.jp ABSTRACT: The effects of changes in the structural complexity of a seagrass Zostera marina habitat on the densities of juveniles of 3 gobiid fishes, Pterogobius zonoleucus, Chaenogobius heptacanthus and Chasmichthys gulosus, were investigated by field experimentation at Moroiso and Aburatsubo Bays, Miura Peninsula, Japan. Following seagrass manipulation, involving reduction of leaf heights and shoot densities as well as complete removal of seagrass, juvenile densities of all 3 gobiids were found to be higher in those quadrats with sparser or shorter seagrass, the abundance in the seagrass-cleared quadrat always being greater than that in the control. In the quadrat with the lowest shoot density, juveniles resided among the shoots, and were evenly distributed over a horizontal plane. In the quadrat with the shortest seagrass, juveniles appeared above the canopy, and were positioned as in the seagrass-cleared quadrat, i.e. near the surrounding walls of untreated seagrass. By contrast, in the experimental patches lacking surrounding walls of unmanipulated seagrass, no juveniles appeared. The results indicated that water column-distributed juveniles of the 3 gobiid species prefer sparser seagrass and open areas close to the wall of untreated seagrass. KEY WORDS: Habitat complexity · Seagrass bed · Gobiid juveniles Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 183. Publication date: July 06, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Development of Eelgrass(Zostera marina) Bed Utilizing Sand Drift Control Mats

Field observation for the development of eelgrass(Zostera marina) beds was conducted off Kushiki beach, Naruto, Tokushima Prefecture. Chemical fiber mats were used to control the sand drift. Square seeds bags with side 30 cm long were laid under the mats in November and December 1995 and also in January 1996. In May 1996, the amount of eelgrass germinated per unit area reached up to 100/m2. The results of numerical analysis indicated that the velocity inside mat decreases when the velocity at the upper boundary becomes large. A small amount of circulating flow takes place with the occurrence of vertical flow, which seems to relate to the diffusion of suspended sediment. Sediment concentration near the bed, averaged over a wave period, is about 10 ~ 30% of that without mat. The seeding method presented in this study is demonstrated to be one effective means for the development of eelgrass beds.

Seasonal Analysis of Zoobenthos Associated with a Zostera marina L. Bed in Gulbahce Bay Aegean Sea, Turkey

Abstract. seasonal sampling of three stations in Gulbahce Bay Aegean Sea for the zoobenthic organisms associated with a Zostera marina bed was carried out during 1993–94. Temperature, salinity and oxygen were recorded each sampling period. A total of 7 taxonomic groups were determined: Polychaeta was the dominant group comprising 77 % of the total taxa and individuals, followed by Crustacea, Bivalvia and other groups such as Nemertea. Sipuncula, Turbellaria and Phoronida. Of the 108 taxa encountered, the polychaetes Notomastus latericeus and Caulleriella alata accounted for 49 % of the total populations. The species abundance did not show major changes among seasons, with highest values in fall 982 indiv. ·m‐2 and lowest in spring 754 indiv. ·m‐2. Diversity and evenness of the samples were relatively high and fairly constant, and were affected by the dominance levels of the species.

Considerations On Some Species of Hippolyte (Decapoda, Caridea) From Southern European Waters, H. Niezabitowskii, H. Holthuisi, and H. Varians

[Preliminary samples taken from Zostera marina beds on the Mediterranean coast of southern Spain, have allowed us to obtain three species of Hippolyte. One of them, Hippolyte niezabitowskii, represents the first record for Spain and the western Mediterranean. Also, the morphology of the present material shows clear differences with that of specimens from the Adriatic and Ionian seas. A complementary description and some considerations on a presumably subspecific status are given. The capture of many specimens belonging to the complex H. varians-H. holthuisi (H. holthuisi represents a new record for the area) has allowed us to make a comparative analysis between populations from the Alboran Sea and from the Gulf of Cadiz, which has established the existence of consistent differences between these., Preliminary samples taken from Zostera marina beds on the Mediterranean coast of southern Spain, have allowed us to obtain three species of Hippolyte. One of them, Hippolyte niezabitowskii, represents the first record for Spain and the western Mediterranean. Also, the morphology of the present material shows clear differences with that of specimens from the Adriatic and Ionian seas. A complementary description and some considerations on a presumably subspecific status are given. The capture of many specimens belonging to the complex H. varians-H. holthuisi (H. holthuisi represents a new record for the area) has allowed us to make a comparative analysis between populations from the Alboran Sea and from the Gulf of Cadiz, which has established the existence of consistent differences between these.]

Diel cycles of sulphate reduction rates in sediments of a Zostera marina bed (Denmark)

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 15:97-102 (1998) - doi:10.3354/ame015097 Diel cycles of sulphate reduction rates in sediments of a Zostera marina bed (Denmark) Vibeke Blaabjerg1, Kim N. Mouritsen2, Kai Finster1,* 1Department of Microbial Ecology and 2Department of Marine Ecology, Institute of Biological Sciences, University of Aarhus, DK-8000 Aarhus, Denmark *Addressee for correspondence. E-mail: kai@bio.aau.dk Sulphate reduction was investigated over 24 h cycles in Zostera marina-bearing sediments. The experiments were carried out at the beginning (April) and end (August) of the growing season of the eelgrass. The sulphate reduction rates were 3 times higher in August (~90 mmol SO42- m-2 d-1) than in April. In both periods, the sulphate reduction rates were significantly higher in the light than in the dark. The stimulation in the light may be due to increased root exudation of organic matter related to photosynthetic activity. The exuded organic carbon accounted for approximately 2 to 4% of the total amount of carbon fixed by the plants. The sulphate reduction rates responded rapidly to shifts from dark to light and vice versa, indicating the presence of a limited pool of labile organic matter in the sediment. A positive correlation between sulphate reduction rates and root+rhizome biomass was observed in April and August during the daytime and in August but not April in the dark. Light-stimulated sulphate reduction · Marine · Anaerobic · Seagrasses Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 15, No. 1. Publication date: May 22, 1998 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1998 Inter-Research.

Leaf dynamics and production of a Zostera marina bed near its southern distributional limit

Through biweekly census, from January to December 1987, leaf dynamics and production of a perennial, intertidal population of Zostera marina L., were studied near the southern distributional limit of the species (30°N) in Baja California, Mexico. Shoots had an average of 4.0 leaves, and 1.0 new leaf appeared every week. The average number of new leaves per shoot was highest from May to August, while the average number of leaves present per shoot peaked during the September–December period. A maximum leaf area index of 4.1 m 2 m −2 was recorded at the end of the summer. Growth and production were continuous during the year, and annual means were 10 m m −2 d −1, and 0.9 g dry wt m −2 d −1 respectively, with peak values in September. Growth and production were positively correlated with light and water temperature. This southern population presents a summer condition (May to October) during which, values increase and reach their maximum, and a winter condition (November to April) with low values. Intertidal zone shoots are characterized by their small size and high dynamics, with an average plastochrone interval value of 8.2 days, an average lifetime of a leaf of 37.6 days, and an annual turnover rate of 9.71 yr −1. Environmental stability apparently allows vegetative activity to proceed throughout the year.

Community structure and spatial variation of benthic invertebrates associated with Zostera marina (L.) beds in the northern Baltic Sea

The distribution and bed structure of eelgrass ( Zostera marina L.), and its importance for associated faunal communities in the coastal areas of the northern Baltic Sea are poorly known. The spatial distribution of the fauna associated with Zostera was studied at five localities in SW Finland in 1993–1994. Zostera was common on all localities, but the beds varied in terms of area (1–5 m diameter), density (50–500 shoots/m 2) and blade length (20–110 cm). A total of about 40 species or taxa were recorded. The zoobenthic infauna showed significant spatial differences, and total abundance and species diversity were significantly higher in the Zostera beds than in adjacent bare sand. The total abundance in Zostera ranged from 25 000 to 50 000 ind/m 2 and in sand from 2500 to 15 000 ind/m 2 The mean number of species in Zostera ranged from 5.9 to 8.8 spp ( H′ = 1.76–2.54) and in sand from 2.2 to 5.5 spp ( H′ = 1.67–2.31). The epifauna in Zostera was numerically dominated by grazing gastropods (Hydrobiidae) and copepods. The epifauna is an important community component, which contributes to the total diversity of the Zostera assemblage. These systems are among the most species-rich components of the shallow soft-bottom ecosystems in the northern Baltic Sea. The mechanisms structuring both the Zostera and the ambient sand-bottom habitats are presented.

Sediment sulfur dynamics related to biomass- density patterns in Zostera marina (eelgrass) beds

Sediment sulfur dynamics related to biomass- density patterns in Zostera marina (eelgrass) beds

Nursery role of seagrass beds: enhanced growth of juvenile blue crabs ( Callinectes sapidus Rathbun)

The role of submerged aquatic vegetation in supporting enhanced growth of Callinectes sapidus was investigated through field and laboratory experiments. In predator-free enclosures (1 m 2) in the lower York River, Virginia, juvenile blue crabs within Zostera marina (L.) beds grew faster than crabs in enclosures deployed outside the beds. First stage crabs were introduced into vegetated or un vegetated enclosures at either 10 or 50 crabs m −2. After the 6 wk experimental period, both survival and growth were significantly higher in vegetated treatments (growth was estimated by change in “volume,” the product of carapace width, length and depth). In fiberglass mesocosms (2.67 m × 1.33 m × 0.67 m) divided into vegetated and unvegetated halves, juvenile blue crabs grew faster in the vegetation, consistent with field findings. Where differences existed between density treatments in field enclosures, juvenile crabs grew faster in high density than in low density treatments. Aggregate crab growth (summed “volumes” of all recaptured individuals) for vegetated enclosures was greater than for unvegetated enclosures. Potential contribution of cannibalism was sufficient to explain some within-habitat density effects, but was not sufficient to account for the entire aggregate differences, suggesting that food may not be limiting within the seagrass beds even at 50 crabs m −2. These results show that early stage blue crabs receive a substantial growth advantage, in addition to the refuge function shown in other studies, from their association with seagrass beds. This trophic advantage may be experienced by juveniles of other species that utilize vegetated nursery areas and may help explain the ontogenetic habitat shifts that characterize many life histories.