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1.
Since the substantial loss of subtidal eelgrass (Zostera marina L.) in the 1930s, seagrass beds in the Wadden Sea are limited to the intertidal zone and dominated by Z. noltii Hornem. This study deals with the effect of vegetated tidal flats on quantities of mobile epifauna and proves empirically the function of seagrass canopies as a refuge for marine animals remaining in the intertidal zone at ebb tide. Drop-trap samples were taken in the Sylt-Rømø Bight, a shallow tidal basin in the northern Wadden Sea, on vegetated and unvegetated tidal flats during July and August 2002, and during the entire growth period of Z. noltii from May to September in 2003. The species composition in Z. noltii and bare sand flats showed minor differences since only two isopod species (Idotea baltica and I. chelipes) occurred on Z. noltii flats exclusively. Juvenile shore crabs (Carcinus maenas L.), brown shrimps (Crangon crangon L.) and common gobies (Pomatoschistus microps Krøyer) were also found abundantly on bare sand flats. However, the results showed significantly higher abundances and production of these dominant species on vegetated tidal flats. Additionally, the analyses of faunal size classes indicated higher percentages of small individuals in the seagrass bed during the entire sampling period. Despite drastic diurnal fluctuations of dissolved oxygen at low tide, faunal density in the residual water layer remaining in seagrass canopies at ebb tide was found to be consistently higher than that found in artificially created tide-pool units. Although species composition of mobile epifauna did not basically differ between vegetated and unvegetated tidal flats, Z. noltii beds are considered to contribute quantitatively to the function of tidal flats, as an extended juvenile habitat for some of the most important species of the Wadden Sea food web.Communicated by O. Kinne, Oldendorf/Luhe 相似文献
2.
Andreas M. Zipperle James A. Coyer Karsten Reise Eelo Gitz Wytze T. Stam Jeanine L. Olsen 《Marine Biology》2009,156(10):2139-2148
Genotypic structure and temporal dynamics of the dwarf seagrass, Zostera noltii, were studied in an intertidal meadow that has persisted since prior to 1936 near the Wadden Sea island of Sylt. Samples were
collected from two 10 × 10 m plots separated by 250 m from May 2002 to June 2005 and from four 1 × 1 m plots from June 2003
to September 2004. All the samples were genotyped with nine microsatellite loci. No genotypes were shared between the plots
separated by 250 m. Genetic diversity was higher in the Wadden Sea than in the other regions of its geographic range. The
average clone size (genets) (SD) in the two plots was 1.38 (0.26) and 1.46 (0.4) m2, respectively, with a range up to 9 m2
and <20% persisted for >4 years. A high genetic and genotypic diversity was maintained by annual recruitment of seedlings
despite a dramatic decrease in ramet density that coincided with the severe heat stress event of 2003. Fine-scale (1 m2) analysis
suggested that extensive loss of seagrass cover precluded space competition among the genets, while a persistent seed bank
prevented local extinction. Long-term persistence of Z. noltii meadows in the intertidal Wadden Sea was achieved by high genet turnover and frequent seedling recruitment from a seed bank,
in contrast to the low diversity observed in large and long-living clones of Z. noltii and other seagrasses in subtidal habitats. 相似文献
3.
María J. Darias Harry M. Murray Jeffrey W. Gallant Susan E. Douglas Manuel Yúfera Gonzalo Martínez-Rodríguez 《Marine Biology》2007,152(1):109-118
A restoration programme was introduced in the Mondego Estuary (Portugal) to recover seagrass beds of Zostera noltii endangered by eutrophication. A long-term survey of 10 years was used to assess the development of the processes involved,
focusing one of the key species (Cyathura carinata, Isopoda). The mitigation measures implemented since 1998 (nutrient loading reduction, freshwater circulation improvement
and seagrass bed protection) enhanced water quality and seagrass recovery, thus preventing the development of macroalgal blooms.
C. carinata was resilient to the occurrence of floods and macroalgal blooms, although both events caused dispersion of individuals. This
isopod was not much influenced by the changes occurring in the estuary, showing an unalterable population structure during
the entire study period. After 1998, its density and biomass became more stable at an inner unvegetated sand flat area, where
this isopod was most abundant; its population slightly increased in a bare mud flat at the middle section of the estuary;
but it could not establish successfully in a downstream Z. noltii bed, contrarily to other common estuarine species. Apart from other unknown reasons, the disrupted balanced between trematodes
and their hosts, caused by the eutrophication processes, may have an important role in the discontinuity of C. carinata at the Z. noltii bed. If the intertidal areas become fully restored to the original seagrass coverage, high prevalence and intensity trematodes
may prevent this isopod and other crustaceans from recovering within the intervened areas, by enhancing host mortality and
recruitment failure. In order to avoid this kind of situation, it may be necessary to survey the levels of parasite infestation
within the target hosts and safeguard areas where crustaceans present healthy populations. 相似文献
4.
Seasonal occurrence of the ctenophore Pleurobrachia pileus in the western Dutch Wadden Sea 总被引:2,自引:0,他引:2
Due to the short residence time of the water in the western Dutch Wadden Sea the ctenophore Pleurobrachia pileus has to be considered as an allochthonous species, which enters the estuary passively from the North Sea. The seasonal occurrence of this species in the Dutch Wadden Sea is a reflection of its abundance in the coatal zone of the North Sea and is characterized by a pronounced spring peak of up to 17000 individuals per 1000 m3 and a lower autumn peak with numbers up to 400 individuals per 1000 m3. Similar to other areas, predation by Beroë gracilis, another ctenophore species, may be a factor in controlling the P. pileus population in this region, although B. gracilis abundance is low. P. pileus is only important as a predator for a short time, i.e. the month of May, when it reaches maximum biomass values of up to 12 00 mgC per 1000 m3. Both the estimated potential consumption rates in comparison with the available food as well as the observed suboptimal growth rate of the population suggest that in the coastal zone of the North Sea area food conditions may not be optimal for P. pileus. 相似文献
5.
Cascading effects of hydrodynamics on an epiphyte–grazer system in intertidal seagrass beds of the Wadden Sea 总被引:3,自引:0,他引:3
This study examines experimentally how water movement may alter epiphyte-grazer systems in intertidal seagrass beds. Field observations in the Sylt-Rømø Bay (German Wadden Sea, SE North Sea) showed that the biomass of seagrass epiphytes was highest on seagrasses exposed to water movement, whereas at sheltered sites the epiphyte cover was negligible. In contrast, the seagrass shoot density and aboveground biomass was comparably sparse and the abundance of Hydrobia ulvae was extremely low at exposed areas, but showed maximum values at sheltered seagrass beds. Cross transplantation experiments and enclosure experiments between sheltered and exposed seagrass beds showed that adhering snails were washed off from seagrasses soon after transplantation into an exposed seagrass bed, and epiphytes started to grow. After 4 weeks the epiphyte biomass was similar to the that of the adjacent exposed seagrass bed. When heavily epiphytised seagrasses were transplanted from exposed into sheltered areas, the epiphytes were completely grazed down by immigrating snails within a week. Experiments carried out by means of an in situ "three-current-flume", modifying the entire current velocity, showed that snail density was significantly negatively correlated with increasing current velocity, whereas epiphyte biomass showed a significant positive correlation with current speed. These results suggest a cascading impact of hydrodynamics on an epiphyte-grazer system in intertidal seagrass beds, by directly affecting the density of grazers and indirectly leading to enhanced epiphyte growth, thereby inhibiting seagrass development. Additionally it shows that cascading effects within the trophic web cannot only be triggered by biotic interdependencies, but can also be caused by physical factors. 相似文献
6.
Joana F. M. F. Cardoso Johannes IJ. Witte Henk W. van der Veer 《Marine Biology》2007,152(6):1271-1282
In estuarine areas, bivalve species can be found in a variety of environments, where they experience large differences in
environmental conditions. In the present paper, the importance of different habitats (intertidal, subtidal and adjacent coastal
waters) for the persistence of the population was evaluated for the bivalve Macoma balthica (L.) in the western Dutch Wadden Sea estuary. Intra-specific variation in growth and reproductive output were followed during
the year and related to local abiotic conditions. Significant differences in growth and reproductive investment were found
between locations. Young individuals were mostly found in the intertidal area, where growth in terms of somatic mass was good.
These areas were not favourable for adult individuals, since growth in shell length was low and many individuals did not reproduce.
In the subtidal, where the highest densities were found, somatic and gonadal mass indices were low. Coastal areas had the
lowest densities and showed high growth in terms of shell length and body mass. The habitat with the highest reproductive
effort per individual was not the most important habitat in terms of reproductive output due to differences in density and
in size of the habitat type. For M. balthica, the subtidal habitat contributed the most to the reproductive output of the western Dutch Wadden Sea population although
the highest reproductive output per individual was in the coastal area. 相似文献
7.
Potential impact of a toxic dinoflagellate (Alexandrium excavatum) bloom on survival of fish and crustacean larvae 总被引:8,自引:0,他引:8
During the last 20 yr the western half of the Dutch Wadden Sea has undergone significant eutrophication: concentrations of P and N compounds and planktonic algae have roughly doubled, as has primary production. Though oxygen levels are often low in summer, anoxic areas are small and rare due to strong tidal mixing. During the 1970 to 1990 period, macrozoobenthos was sampled annually at 15 stations at Balgzand, a 50-km2 tidal-flat area in the westernmost part of the Wadden Sea. Not only did the estimates of total numbers, biomass, and production double during these two decades, but significant changes in the composition of the benthic community were observed, too: (1) the numerical proportion of polychaetes increased at the expense of molluscs and crustaceans, (2) the overall mean weight per individual of the macrozoobenthos decreased (numbers of individuals of small-sized species increased more rapidly than those of large-sized species), and (3) though absolute numbers and biomass of all feeding types increased, the share of carnivores declined and that of deposit feeders increased; the proportion of suspension feeders showed little change. This study refers to true macrobenthos only (1-mm sieve) and further excludes two taxa (Corophium spp. andHydrobia ulvae) which occasionally exercised an undue influence on numbers. Mass mortalities caused by low oxygen concentrations were of a small-scale nature only. Total number of species fluctuated without a clear trend. As a consequence of the increasing numerical densities, trends in species numbers were slightly increasing when expressed per unit of area and slightly decreasing when estimated per 100 individuals (by rarefaction). 相似文献
8.
Fernando G. Brun Fabio Cummaudo Irene Olivé Juan José Vergara José Lucas Pérez-Lloréns 《Marine Biology》2007,151(5):1917-1927
Disaggregating seagrass meadows and studying its components separately (clones, ramets, shoots) can provide us insights on
meadow dynamics and growth patterns. The clonal growth, dependent upon clonal rules may regulate and impose constraints to
plant architecture and, therefore, determine how individual clones evolve into the environment. In order to investigate the
relationship between clonal growth rules and clone architecture, the belowground network architecture of single-clones of
the seagrass Zostera noltii was studied. Networks were traced in situ after washing out the overlying sediment, and network characteristics were measured
using digital analysis: area covered by clone, total rhizome length, type of rhizomatic axes (main, secondary, tertiary, quaternary),
number and length of the internodes, branching angles and branching frequencies. This approach revealed that Z. noltii is able to develop into large clones integrating up to 300 internodes, 676 cm of rhizome, 208 shoots and 4,300 cm2 of plant area. Internodal length depended on both, the distance to the apical shoot (time effect) and the axes type (apical
dominance effect). However, average branching angle was independent of axis type (average 58.3 ± 0.75), but varied significantly
depending on the distance from the apical shoot. This average branching angle allows Z. noltii maximize the rate of centrifugal expansion, maintaining a high density in colonized areas to produce close stands but also
minimizing the investment in belowground biomass and ramets overlapping. The clonal architecture of Z. noltii seems to be regulated by the interaction of both, apical dominance strength and clonal integration distance. Moreover, clonal
growth rules and growth pattern seem to constrain clonality through (clonal) plant architecture regulations (i.e. branching
is restricted in secondary axes, similar average branching angles regardless the axes, the higher the distance to the apex
the higher the number of internodes in secondary axes, shorter internodes in secondary and tertiary axes). Future research
efforts should focus on how these complex relationships between apical dominance and clonal integration interact to elucidate
the temporal (seasonal) and spatial scales of both processes and the outcome at the plant architectural level. 相似文献
9.
10.
J. J. Beukema 《Marine Biology》1988,99(3):425-433
The ABC-method proposed by Warwick (1986) for detecting pollution effects on marine zoobenthic communities, was tested on distribution patterns of numbers and biomass among species in macrozoobenthos samples taken annually for 13 yr in a uniform way at 15 tidal-flat stations in the western part of the Dutch Wadden Sea. Along the margins of the tidal-flat area studied, where exposition to either drainage or water movements is extreme, the k-dominance plots for numbers were generally situated above those for biomass. In these areas values for biomass and species richness were relatively low and a few small-sized species such asCorophium volutator andHydrobia ulvae were very numerous. In the central part of the area, where environmental conditions are less severe, values for biomass and species richness were higher. Biomass was dominated by large adults ofMya arenaria, Mytilus edulis and/orArenicola marina. However, in only a restricted part of this area were plots for numbers consistently below biomass plots. In most of the central area high numbers ofH. ulvae occasionally occurred, causing plots for numbers to be situated above those for biomass during such periods. There appears to be no reason to interprete a high abundance ofH. ulvae as a sign of pollution or any other kind of disturbance or stress. It is concluded that the ABC method cannot be applied to tidal flat communities without reference to long-term and spatial series of control samples. In areas where such smallsized and sometimes numerous species asH. ulvae occur in strongly fluctuating numbers, the method appears useless for assessing the pollution status of a benthic community. 相似文献
11.
Martin Gullström Charlotte Berkström Marcus C. Öhman Maria Bodin Mattis Dahlberg 《Marine Biology》2011,158(7):1483-1495
Although herbivorous fish form critical linkages between primary producers and higher trophic levels, the major factors regulating
their spatial structure in seagrass systems remain poorly understood. The present study examined the parrotfish Leptoscarus vaigiensis in seagrass meadows of a tropical embayment in the western Indian Ocean. Stomach content analysis and direct field observations
showed that L. vaigiensis is an efficient grazer, feeding almost exclusively on seagrass leaves. Seagrass shoot density was highly correlated to all
density variables (total, juvenile and subadult) and juvenile biomass of L. vaigiensis, while subadult biomass was predicted by distance to neighbouring coral habitat. Moreover, density and biomass of predatory
fish (piscivores) were predicted by seagrass canopy height and the distribution patterns of predators followed those of L. vaigiensis. Hence, factors at local (seagrass structural complexity and feeding mode) and landscape scale levels (seascape context and
distribution of piscivores) likely mutually structure herbivorous fish communities. The findings underscore the importance
of incorporating multiple scale-dependent factors when managing coastal seagrass ecosystems and their associated key species. 相似文献
12.
Mangrove forests and seagrass beds frequently occur as adjacent habitats in the temperate waters of southeastern Australia.
At low tide when fish cannot occupy mangroves they might utilise adjacent habitats, including seagrass. We first sampled small
fish from seagrass beds close to and far from mangroves in the Pittwater estuary, NSW, Australia. Seagrass beds close to mangroves
had a greater density of fish species than beds far from mangroves (close: mean 16.0 species net−1, SE 1.0; far: 13.2, 1.3; P < 0.05). In particular, juvenile fish were in greater densities near to than far from mangroves (close: 5.3, 0.4; far: 3.1,
0.4; P < 0.05). We then sampled the mangrove forests during the high tide and seagrass beds during the low tide, in beds along a
continuum of distances from mangroves. Multivariate analysis showed that fish assemblages differed with distance from mangroves,
and the differences were attributed to the composition of the fish assemblage (i.e. presence/absence of fish species), not
the abundances of individual species. In particular, fish that utilise mangrove forests at high tide were found in greater
species densities and species richness in seagrass nearer to mangroves. A negative relationship was found between the density
of mangrove-utilising fish species and the distance of the bed from mangroves (R
2 = 0.37, P < 0.05). This confirms the important connectivity between mangroves and seagrass for fish in temperate Australian waters. 相似文献
13.
C. H. Peterson 《Marine Biology》1982,66(2):159-170
In 57 l-m2 samples within a meadow of Halodule wrightii in Bogue Sound, North Carolina, USA, densities of the clams Mercenaria mercenaria and Chione cancellata were positively associated with seagrass cover. Where seagrass was experimentally removed, marked individuals of both clam species exhibited high rates of mortality in fine sand sediments during two successive experiments spanning 13 months. In the unaltered (control) seagrass meadow, M. mercenaria density remained constant over 13 months and C. cancellata density declined at a slower rate than in the unvegetated plots. Seagrass provides these clams with a refuge from whelk (Busycon carica, B. contrarium, and B. canaliculatum) predation, the major cause of mortality and population decline in experimentally unvegetated plots. In 2 factorial field experiments in unvegetated substratum in which densities of M. mercenaria and C. cancellata were varied independently, first over 5 levels (0 X, 1/2X, 1 X, 2 X, 4 X) and subsequently over 4 levels (0 X, 1/4 X, 1 X, 4 X), there was no repeatable intra- or interspecific effect of density on percent survival, or on the rate of any mortality type. Whelk predation fell preferentially on larger size classes of both species, whereas factors which contribute to clam disappearance usually acted more intensely on smaller sizes. Experimental exclusion of large predators by caging demonstrated that even in unvegetated substratum survivorship of both clam species was high in the absence of whelks and other predators. Individuals of C. cancellata live closer to the sediment surface than those of M. mercenaria, which may explain why seagrass does not serve as effectively to protect them from whelk predation. The mechanism of whelk inhibition may depend upon sediment binding by the H. wrightii root mat, which produces a demonstrable decrease in the physical penetrability of surface sediments. 相似文献
14.
Eelgrass (Zostera marina L.) in the Dutch Wadden Sea historically covered an area varying from 65–150 km2 in the eulittoral as well as the sublittoral zones. At present, this area comprises less than 1 km2 eulittoral eelgrass stands, with an associated decrease in habitat diversity. The causes for this decline are presumably
connected with the ‘wasting disease’ and the closure of the former Zuiderzee in the early 1930s resulting in increased tidal
range and increased currents. After a slight recovery of the eelgrass populations on the intertidal flats a definite decline
started in the early 1970s, possibly connected to increased turbidity. The present water quality and turbidity do not negatively
influence eelgrass growth up to a depth of at least 0.6m below Mean Sea Level. Based on mesocosm experiments and field experiments
it is concluded that re-establishment of eelgrass should be possible in sheltered bays and on unexposed tidal flats. The most
suitable depths for a reintroduction are those between 0 and 20–40 cm below mean sea level. 相似文献
15.
Eelgras (Zostera marina L.) in the Dutch Wadden Sea historically covered an area varying from 65–150 km2 in the eulittoral as well as the sublittoral zones. At present, this area comprises less than 1 km2 eulittoral eelgrass stands, with an associated decrease in habitat diversity. The causes for this decline are presumably
connected with the ‘wasting disease’ and the closure of the former Zuiderzee in the early 1930s resulting in increased tidal
range and increased currents. After a slight recovery of the eelgrass populations on the intertidal flats a definite decline
started in the early 1970s, possibly connected to increased turbidity. The present water quality and turbidity do not negatively
influence eelgrass growth up to a depth of at least 0.6m below Mean Sea Level. Based on mesocosm experiments and field experiments
it is concluded that re-establishment of eelgrass should be possible in sheltered bays and on unexposed tidal falts. The most
suitable depths for a reintroduction are those between 0 and 20–40 cm below mean sea level. 相似文献
16.
Variations in number and biomass of benthic bacteria were examined in the surface sediments of a Mediterranean seagrass bed [Posidonia oceanica (L.) Delile] in the Gulf of Marconi (northwestern Mediterranean Sea) from 1990 to 1991. The annual dynamics of benthic bacterial density and biomass were compared to changes in elemental (organic C and total N) and biochemical (lipids, proteins, carbohydrates) composition of sediment organic matter, as well as to microphytobenthic biomass, dissolved inorganic nutrients and ATP. Bacterial densities exhibited marked seasonal variations (5.12 to 322.7x108 cells g-1 sediment dry wt) with highest values in late spring. Bacterial standing stocks (15.8 to 882.33 g C g-1 of sediment dry wt) were high. Bacterial biomass did not correlate with organic C, total N or to specific biochemical components, but correlated significantly with chlorophyll a, ATP and porewater phosphate concentrations. There is evidence that benthic bacteria were responding to variations of algal biomass. Bacterial biomass accounted, on average, for 30% of total living carbon (calculated on the basis of the ATP concentrations) and 8.4% of total organic carbon. 相似文献
17.
Katsumasa Yamada Kazutaka Takahashi Carole Vallet Satoru Taguchi Tatsuki Toda 《Marine Biology》2007,150(5):905-917
Spatial and seasonal distribution pattern, life history and production of three species of Neomysis (Mysidacea) which commonly occur in northwestern subarctic Pacific coastal waters, were investigated throughout the year
in the Akkeshi-ko estuary, northern Japan. The most abundant species Neomysis awatschensis (annual mean density: 179.8 inds. m−2, biomass: 108.8 mg DW m−2) occurred at the inner part of the estuary including low salinity areas with no clear preference for the seagrass bed. The
second most abundant Neomysis mirabilis (mean density: 95.8 inds. m−2, biomass: 90.1 mg DW m−2) occurred at relatively saline seagrass site throughout the year. Occurrence of Neomysis czerniawskii in the estuary was limited to the seagrass bed during summer when their population mainly consisted of juveniles, suggesting
that this species is a seasonal migrant between the estuary and the marine environment. Both N. awatschensis and N. mirabilis populations were composed of two generation types, a larger sized overwintering and smaller sized spring/summer generations;
however, each species had a different reproductive strategy. N. awatschensis was characterized by fast growth to maturity at a smaller size than N. mirabilis with a relatively high fecundity during warm season, suggesting that this species is an r-strategist which can utilize opportunistically
a wide variety of habitats. In contrast, the seagrass bed resident N. mirabilis was a K-strategist which matures at a larger size producing fewer but larger offspring. The annual production of N. awatschensis (0.57–0.70 g DW m−2, mean of the whole estuary) and N. mirabilis (0.58–0.68 g DW m−2, mean of the seagrass bed) at their respective habitats was comparable. Consequently, species-specific life history and distribution
pattern are concluded to allow Neomysis spp. to coexist in the estuary and the high carrying capacity of seagrass bed is suggested to contribute to maintain their
high biomass level. 相似文献
18.
We have analyzed the composition, diversity, density and biomass of a temporal series of samples taken in a Tubularia indivisa community, which dominates a shipwreck in the North Sea waters (N 51°23′,730–E 02°29′,790, 17 nautical miles from the coast,
30 m depth). This shipwreck has structures emerging up to 8 m above the seabed. Water temperature ranged from 4.2°C in March
to 20.3°C in August. Salinity showed few variations around 33.9 psu. Bottom tidal currents followed a semi-diurnal cycle and
were preferentially NE oriented with 84% of them in the range 0.25–0.75 m s−1. The mean value for total suspended matter was 6.2 mg l−1 with large variations on a monthly scale. The species richness of samples varied from 15 in October to 42 in August with
a mean value of 33 species. Diversity indices were higher during autumn and winter because of the strong dominance of a few
crustacean species during the warmer months. The total density of individuals ranged from 6,500 ind m−2 in October to 445,800 ind m−2 in July, most of these individuals belonging to the amphipod species Jassa herdmani. The biomass of the T. indivisa community varied from 9 g AFDW m−2 in October to 1,106 g AFDW m−2 in July, with T. indivisa itself constituting between 59 and 82% of the total biomass. The biomass of T. indivisa was positively correlated with species richness and with the density of 23% of the species identified on this community,
suggesting that T. indivisa plays an important structural role in this habitat. This was further confirmed by the number of species associated with T. indivisa which was generally superior to 55% of the sorted species. Multivariate analysis indicated strong differences between spring/summer−autumn/winter
assemblages mostly but not solely due to the abundance patterns of species. These findings support the conclusion that shipwrecks
in Belgian waters allow the development of assemblages dominated by a high biomass of T. indivisa which in turn provides shelter for high densities and biomass of epizoites. These assemblages will further show large monthly
variations in densities and composition due to large variation in T. indivisa biomass under an apparent repetitive annual cycle.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
19.
Production dynamics of eelgrass, Zostera marina was examined in two bay systems (Koje Bay and Kosung Bay) on the south coast of the Korean peninsula, where few seagrass
studies have been conducted. Dramatically reduced eelgrass biomass and growth have been observed during summer period on the
coast of Korea, and we hypothesized that the summer growth reduction is due to increased water temperature and/or reduced
light and nutrient availabilities. Shoot density, biomass, morphological characteristics, leaf productivities, and tissue
nutrient content of eelgrass were measured monthly from June 2001 to April 2003. Water column and sediment nutrient concentrations
were also measured monthly, and water temperature and underwater irradiance were monitored continuously at seagrass canopy
level. Eelgrass shoot density, biomass, and leaf productivities exhibited clear seasonal variations, which were strongly correlated
with water temperature. Optimal water temperature for eelgrass growth in the present study sites was about 15–20°C during
spring period, and eelgrass growths were inhibited at the water temperature above 20°C during summer. Daily maximum underwater
photon flux density in the study sites was usually much higher than the light saturation point of Z. marina previously reported. Densities of each terminal, lateral, and reproductive shoot showed their unique seasonal peak. Seasonal
trends of shoot densities suggest that new eelgrass shoots were created through formation of lateral shoots during spring
and a part of the vegetative shoots was transformed into flowering shoots from March. Senescent reproductive shoots were detached
around June, and contributed to reductions of shoot density and biomass during summer period. Ambient nutrient level appeared
to provide an adequate reserve of nutrient for eelgrass growth throughout the experimental period. The relationships between
eelgrass growth and water temperature suggested that rapid reductions of eelgrass biomass and growth during summer period
on the south coast of the Korean peninsula were caused by high temperature inhibition effects on eelgrass growth during this
season. 相似文献
20.
Meiofauna on the seagrass Thalassia testudinum: population characteristics of harpacticoid copepods and associations with algal epiphytes 总被引:1,自引:0,他引:1
The composition and abundance of bladedwelling meiofauna was determined over a 15 mo period (1983–1984) from a Thalassia testudinum Banks ex König meadow near Egmont Key, Florida, USA. Harpacticoid copepods, copepod nauplii, and nematodes were the most abundant meiofaunal taxa on T. testudinum blades. Temporal patterns in species composition and population life-history stages were determined for harpacticoid copepods, the numerically predominant taxon. Sixteen species or species complexes of harpacticoid copepods were identified. Harpacticus sp., the most abundant harpacticoid, comprised 47.8% of the total copepods collected, and was present throughout the study. Copepodites dominated the population structures of the blade-dwelling harpacticoid species on most collection dates. Ovigerous females and/or copepodites were always present, indicating continuous reproductive activity. Results suggest that epiphytic algae influence meiofaunal abundance on seagrass blades, as densities of most meiofaunal taxa at Egmont Key were positively associated with percent cover of epiphytic algae throughout the study. The majority of significant correlations between meiofaunal density and cover of epiphytic algae involved filamentous algae, although encrusting algae dominated the epiphytic community. It appears that resources provided by epiphytic algae to seagrass meiofauna (additional food, habitat, and/or shelter from predation) may be associated with algal morphology. 相似文献