Removal Of Seagrass Research Articles

Propagule composition regulates the success of an invasive seaweed across a heterogeneous seascape

Abstract Propagule pressure is acknowledged as a key determinant of invasion success. Nonetheless, the role of morphological or physiological attributes of propagules (i.e. their quality) in regulating invader establishment has been little explored. In particular, no study has investigated how the presence of propagules differing in quality within an inoculum influences establishment across heterogeneous landscapes. We experimentally tested the hypothesis that the quality (+Fronds+Rhizoids; +Fronds−Rhizoids; −Fronds+Rhizoids) and the diversity (1, 2 and 3 fragment types) of vegetative fragments of the seaweed Caulerpa taxifolia determine their establishment success across seascapes consisting of bare sediments and patches of the seagrass Zostera muelleri exposed to different disturbance intensities (control, seagrass canopy clipping and total removal). After 6 weeks, seaweed biomass, stolon and frond length, frond and rhizoid number were generally greater in unvegetated habitats (bare sediments and total seagrass removal) than full or reduced seagrass canopies. The type and the diversity of types of fragments inoculated had significant effects on the final biomass and morphological features of C. taxifolia only in vegetated habitats. In control plots, inocula of fragments retaining both fronds and rhizoids achieved higher biomass, developed longer stolons and more fronds. In canopy clipping plots, mixed inocula of +Fronds+Rhizoids and −Fronds+Rhizoids fragments had the greatest biomass and stolon length. Synthesis. Assessing how propagules differing in quality perform in different habitats might be not sufficient to draw a comprehensive picture of invasion risk, as their establishment can be modulated by both negative and positive interactions among them. Propagule composition should be, therefore, considered as a further dimension of propagule pressure. Our results also suggest that the relevance of specific propagule traits for invader establishment decreases from intact to degraded habitats. Considering propagule size in terms of amount of competent propagules, rather than an absolute measure, would refine our ability of predicting invasion risk across habitats differing in biotic or abiotic conditions.

Growth and recovery after small-scale disturbance of a rapidly-expanding invasive seagrass in St. John, U.S. Virgin Islands

Seagrass meadows evolved in the presence of disturbances and have a wide variance in recovery rate that largely follow a trajectory of re-colonization and succession to pre-disturbance levels. Invasive species may gain a foothold within native seagrass beds after space is opened by disturbances that reduce seagrass cover. Here we use shoot density monitoring data to describe growth of the invasive seagrass Halophila stipulacea in Caribbean bays over a 5-year period and conduct a series of experiments using a combination of mesocosm, seagrass removal plots, and field measurements to quantify vegetative fragment survivorship and recovery after benthic disturbance. Shoot density increased rapidly in invaded bays, reaching average densities of approximately 600 shoots/m2 within 5 years of establishment. Seagrass cover was estimated to recover to pre-disturbance level 17–31 weeks after removal from vegetative propagation of neighboring plants outside the treatment plot. Mesocosm experiments found floating and settled fragments as small as 2 cm in length and containing at least one vertical shoot survived the 4-day trial and increased in both length and biomass. Empirical evidence here demonstrates that H. stipulacea is highly resilient to small-scale disturbance which we suggest is having a transformative impact on Caribbean seagrass communities.

Experimental harvest in a tropical seagrass meadow leads to shift in associated benthic communities

Seagrass meadows represent key ecosystems in coastal areas worldwide, hosting a great biodiversity of associated communities and thereby providing a large range of ecosystem services. In this study we present an experimental approach to investigate the effects of seagrass losses on related macrofauna assemblages. Over a three year period, seagrass canopies were removed in experimental plots and changes in epifauna, infauna and respective functional groups were recorded. The experimental removal of seagrass leaves resulted in a decline of 74% of overall macrofaunal abundance and the loss of several taxa. The immediate response of associated communities was followed by the establishment of an alternative assemblage, characterized by an increased number of bioturbators and deposit feeders. The colonization of disturbed seagrass plots by burrowing shrimps (Callianassidae) might have hindered the reestablishment of seagrass after the removal. Our findings highlight the important role of seagrasses as habitat forming species that provide relevant functioning and services in coastal ecosystems.

Seagrass Removal Leads to Rapid Changes in Fauna and Loss of Carbon

Seagrass habitats are important natural carbon sinks, with an average of ~14 kg C m−2 buried in their sediments. The fate of this carbon following seagrass removal or damage has major environmental implications but is poorly understood. Using a removal experiment lasting 18 months at Gazi Bay, Kenya, we investigated the impacts of seagrass loss on sediment topography, hydrodynamics, faunal community structure and carbon dynamics. Sediment pins were used to monitor surface elevation. The effects of seagrass removal on water velocity was investigated using Plaster of Paris dissolution. Sediment carbon concentration was measured at the surface and down to 50cm. Rates of litter decay at three depths in harvested and control treatments were measured using litter bags. Drop samples, cores, and visual counts of faunal mounds and burrows were used to monitor the impact of seagrass removal on the epifaunal and infaunal communities. Whilst control plots showed elevation, harvested plots were eroded (7.6 ± 0.4 and -15.8 ± 0.5 mm yr-1 respectively, mean ± 95% C.I). Carbon concentration in the surface sediments was significantly reduced with a mean carbon loss of 1.13 Mg C ha-1 in the top 5cm. Because sediment was lost from harvested plots, with a mean difference in elevation of 3cm, an additional carbon loss of up to 22.9 ± 2.4 Mg C ha-1 may have occurred over the 18 months. Seagrass removal had rapid and dramatic impacts on infauna and epifauna. There was a loss of diversity in harvested plots and a shift towards larger bodied, bioturbating species, with a significant increase in mounds and burrows. Buried seagrass litter decomposed significantly faster in the harvested compared with the control plots. Loss of seagrass therefore lead to rapid changes in sediment dynamics and chemistry driven in part by significant alterations in the faunal community.

Restoration enhances denitrification and DNRA in subsurface sediments of Zostera marina seagrass meadows

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 602:87-102 (2018) - DOI: https://doi.org/10.3354/meps12678 Restoration enhances denitrification and DNRA in subsurface sediments of Zostera marina seagrass meadows Lillian R. Aoki*, Karen J. McGlathery Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia 22904, USA *Corresponding author: lillian.aoki@virginia.edu ABSTRACT: Seagrasses exude oxygen and labile carbon into the sediment, which can stimulate microbial activity. However, it is not clear how seagrasses impact competing nitrate reduction processes, including nitrogen removal through denitrification and nitrogen retention through dissimilatory nitrate reduction to ammonium (DNRA). Using an in situ push-pull incubation method, we measured denitrification and DNRA rates in the root zone of a restored Zostera marina meadow, in adjacent unvegetated sediments, and in experimentally cleared plots within the meadow. Denitrification and DNRA rates in the meadow sediments were highly variable and contained ‘hotspots’ where maximum rates exceeded median rates by more than an order of magnitude. Hotspots were not observed in bare sediments, leading to average rates 4× greater in vegetated sediments than in bare sediments. In the meadow sediments, denitrification dominated over DNRA except in fall, during seagrass senescence, and after the experimental removal of seagrass. Extrapolated rates of annual nitrate removal via denitrification were greater in the vegetated sediments compared to bare sediments (0.62 compared to 0.16 g N m-2 yr-1) and accounted for 44% of annual N loading to the system. Similarly, annual DNRA rates were greater in the vegetated compared to bare sediments (0.45 and 0.12 g N m-2 yr-1, respectively). The restoration of the seagrass meadow thus increased both nitrogen removal and recycling, but removal via denitrification was the dominant process. The dominance of denitrification demonstrates how seagrass restoration can enhance the filter function of shallow coastal systems. KEY WORDS: Zostera marina · Denitrification · DNRA · Push-pull · Restoration Full text in pdf format PreviousNextCite this article as: Aoki LR, McGlathery KJ (2018) Restoration enhances denitrification and DNRA in subsurface sediments of Zostera marina seagrass meadows. Mar Ecol Prog Ser 602:87-102. https://doi.org/10.3354/meps12678 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 602. Online publication date: August 23, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Benthic meiofaunal community response to the cascading effects of herbivory within an algal halo system of the Great Barrier Reef.

Benthic fauna play a crucial role in organic matter decomposition and nutrient cycling at the sediment-water boundary in aquatic ecosystems. In terrestrial systems, grazing herbivores have been shown to influence below-ground communities through alterations to plant distribution and composition, however whether similar cascading effects occur in aquatic systems is unknown. Here, we assess the relationship between benthic invertebrates and above-ground fish grazing across the ‘grazing halos’ of Heron Island lagoon, Australia. Grazing halos, which occur around patch reefs globally, are caused by removal of seagrass or benthic macroalgae by herbivorous fish that results in distinct bands of unvegetated sediments surrounding patch reefs. We found that benthic algal canopy height significantly increased with distance from patch reef, and that algal canopy height was positively correlated with the abundances of only one invertebrate taxon (Nematoda). Both sediment carbon to nitrogen ratios (C:N) and mean sediment particle size (μm) demonstrated a positive correlation with Nematoda and Arthropoda (predominantly copepod) abundances, respectively. These positive correlations indicate that environmental conditions are a major contributor to benthic invertebrate community distribution, acting on benthic communities in conjunction with the cascading effects of above-ground algal grazing. These results suggest that benthic communities, and the ecosystem functions they perform in this system, may be less responsive to changes in above-ground herbivorous processes than those previously studied in terrestrial systems. Understanding how above-ground organisms, and processes, affect their benthic invertebrate counterparts can shed light on how changes in aquatic communities may affect ecosystem function in previously unknown ways.

Small-scale removal of seagrass (Zostera marina L.): effects on the infaunal community

ABSTRACTEelgrass meadows are a common feature in shallow waters along the Norwegian coast, where they provide a habitat for a diverse infaunal community. Recreational boat anchoring and moorings physically scour seagrass and may affect the ecosystem functioning and resilience of the system to natural and anthropogenic disturbances. A small-scale eelgrass (Zostera marina) removal experiment was conducted to study the effects on macro- and meiofauna. Entire plants, including the rhizomes, were removed from 4 m2 patches in three eelgrass meadows in the inner Oslofjord in October 2010. Core samples were taken after a recovery period of 10 months, from the removed patches as well as from the surrounding meadow. Macrofauna (>500 μm) and meiofauna (63–500 μm) in the sediment were investigated for possible effects of the eelgrass removal. Macrofauna and meiofauna composition were site specific and therefore location was identified as the main determinant for the infaunal community. The eelgrass did not regrow within the recovery period and bare sediment patches with only single eelgrass shoots were present during the sampling. Our analyses support an influence of the removal on individual species, but not the complete community. In particular one species, the gastropod Peringia ulvae, was encountered in higher numbers in samples from the removed patches than in control samples. From a management perspective, such minor removal of eelgrass, on the scale of square metres, appears to have no long-lasting detrimental effect to the infaunal community in sheltered meadows with muddy sediments.

Implementing an outcomes-based approach to marine biodiversity offsets: lessons from the Great Barrier Reef

ABSTRACTEnvironmental offsets are widely used internationally, and are becoming a standard feature in project approvals in Australia, including in the Great Barrier Reef (‘GBR’) region. Marine ecosystems are unique, and novel approaches to offsets are needed. The GBR region offers an interesting case study in this regard, with new initiatives diverting offsets imposed on seagrass removal projects into programs aimed at reducing diffuse-source pollution. This article will analyse the offsets framework in the GBR region, and consider whether any safeguards or reforms are needed. It concludes that outcomes-based offset conditions should be used, with impacts on a marine ecosystem only offset by establishing or rehabilitating another marine ecosystem. Reducing diffuse-source pollution is a means to achieve this goal, but it should be merely a vehicle rather than the destination.

Observation of typhoon-induced seagrass die-off using remote sensing

Satellite remote sensing has been used as an effective tool to monitor and manage seagrass beds, but this tool is not appropriate to use in highly turbid waters along the coast of Korea. In this study, satellite data were used to identify the method for detecting seagrass beds in turbid bay waters and describing temporal changes over the past 24 years. Moreover, we found the cause of seagrass die-off phenomenon by observing the long-term satellite images and evaluating the impact of the typhoon on seagrass beds. All seagrass spectra from different sensors (Landsat TM/ETM+, Aster, Spot-4, and Kompsat-2) have low reflectance in green and high in NIR regions, whereas unvegetated seawater has the opposite spectrum features. A training area in the green band and Mahalanobis Distance Classification algorithm was adopted for classification and mapping of seagrass beds. The error matrix using the in situ reference data for Kompsat-2 image classification was 72.9% accurate. The average area of seagrass beds was 4.6 km2 from May 1990 to January 2012, and it was consistently >4.0 km2. A die-off of seagrass beds was observed in September 2012 after Typhoon Bolaven, Tembin, and Sanba consecutively passed the study site. When Typhoon Sanba passed the study site, it had sustained maximum wind speed (147.6 km h−1) during low tide, unlike the other typhoons. We found that the water column buffer did not have any effect on resistance of seagrass bed to disturbance, which led to greater damage. Additionally, the three sequential typhoons that passed through during the short time probably produced a cumulative effect. These results allow an understanding of past changes, and reveal the sudden and influential changes in seagrass distribution. As seagrass removal might have negative effect on other associated communities, comprehensive monitoring is required to ensure that disturbed seagrass habitats is recovered naturally.

Herbicide-induced macrophyte-to-phytoplankton shifts in Japanese lagoons during the last 50 years: consequences for ecosystem services and fisheries

As expressed in the Ramsar Convention, the wise use of wetlands, including coastal lagoons, is one of the greatest environmental concerns across the globe. Seagrass beds are the key element for sustaining coastal lagoon ecosystems. Eutrophication, especially by nitrogen and phosphorus, has degraded many coastal waters and has been invoked as a major cause of seagrass disappearance worldwide. Seagrass had been used as fertilizer in Japan, and the removal of seagrass contributed to the decline of nutrients in the water. The shifts of primary producers from rooted macrophytes to phytoplankton occurred simultaneously between the mid-1950s and 1965 in Japan—presumably because of the wide use of herbicides for rice paddies. Increased phytoplankton induced the increase of fishery yield of clam on one hand and non-edible biofouling species on the other. Because a phytoplankton-dominated ecosystem is easily oxygen depleted at the bottom with the accumulation of organic matter of phytoplankton origin, preventing hypoxia is the key factor to maintain high secondary production for bivalve fisheries and sustainable use of the ecosystem of coastal lagoons.

Habitat-Mediated Facilitation and Counteracting Ecosystem Engineering Interactively Influence Ecosystem Responses to Disturbance

Recovery of an ecosystem following disturbance can be severely hampered or even shift altogether when a point disturbance exceeds a certain spatial threshold. Such scale-dependent dynamics may be caused by preemptive competition, but may also result from diminished self-facilitation due to weakened ecosystem engineering. Moreover, disturbance can facilitate colonization by engineering species that alter abiotic conditions in ways that exacerbate stress on the original species. Consequently, establishment of such counteracting engineers might reduce the spatial threshold for the disturbance, by effectively slowing recovery and increasing the risk for ecosystem shifts to alternative states. We tested these predictions in an intertidal mudflat characterized by a two-state mosaic of hummocks (humps exposed during low tide) dominated by the sediment-stabilizing seagrass Zostera noltii) and hollows (low-tide waterlogged depressions dominated by the bioturbating lugworm Arenicola marina). In contrast to expectations, seagrass recolonized both natural and experimental clearings via lateral expansion and seemed unaffected by both clearing size and lugworm addition. Near the end of the growth season, however, an additional disturbance (most likely waterfowl grazing and/or strong hydrodynamics) selectively impacted recolonizing seagrass in the largest (1 m2) clearings (regardless of lugworm addition), and in those medium (0.25 m2) clearings where lugworms had been added nearly five months earlier. Further analyses showed that the risk for the disturbance increased with hollow size, with a threshold of 0.24 m2. Hollows of that size were caused by seagrass removal alone in the largest clearings, and by a weaker seagrass removal effect exacerbated by lugworm bioturbation in the medium clearings. Consequently, a sufficiently large disturbance increased the vulnerability of recolonizing seagrass to additional disturbance by weakening seagrass engineering effects (sediment stabilization). Meanwhile, the counteracting ecosystem engineering (lugworm bioturbation) reduced that threshold size. Therefore, scale-dependent interactions between habitat-mediated facilitation, competition and disturbance seem to maintain the spatial two-state mosaic in this ecosystem.

Patterns of seagrass biomass removal by two temperate Australian fishes (Monacanthidae)

Despite the global significance of nearshore seagrass beds, little is known of their trophodynamic processes. Herbivory by seagrass fishes is thought to be significant but some species previously suspected to be herbivores may be largely detritivorous. Patterns of grazing on the seagrass Posidonia australis by two abundant monacanthid fishes, Meuschenia freycineti and Meuschenia trachylepis, were determined by calculating the removal of seagrass biomass in three Australian estuaries over 14 months. M. freycineti removed significantly more seagrass biomass than M. trachylepis but seagrass biomass removed by both species varied widely across the three estuaries over time. Median amounts of seagrass removal were generally low for all sites compared with standing stock biomass of P. australis leaves and its epiphytes. Nevertheless, grazing by the two species caused high localised rates of removal (up to 90 mg dry weight of P. australis with epibiota per m2) in winter, the season when seagrass growth is least. Such removal rates are far greater than those reported for any other fish grazer in P. australis. These two fish species directly affect seagrass biomass and potentially alter the trophodynamics of P. australis seagrass beds, especially when grazing intensity is high during the season of lowest seagrass growth.

Underwater video as a monitoring tool to detect change in seagrass cover

To date seagrass monitoring has involved the removal of seagrass from its environment. In fragile or highly disturbed systems, monitoring using destructive techniques may interfere with the environment or add to the burden of disturbance. Video photography is a form of non-destructive monitoring that does not require the removal of seagrass or interference with the environment and has the potential to be a valuable tool in monitoring seagrass systems. This study investigated the efficacy of video photography as a tool for detecting change in seagrass cover, using the temperate Australian species Amphibolis antarctica (Labill.) Sonder ex Aschers. Using visual and random point estimates of seagrass cover from video footage, it was possible to determine the minimum sample size (number of random video frames) needed to detect change in seagrass cover, the minimum detectable change in cover and the probability of the monitoring design committing a Type II error. Video footage was examined at three scales: transects (m apart), sites (km apart) and regions (tens of km apart). Using visual and random point estimation techniques, a minimum sample size of ten quadrats per transect was required to detect change in uniform and variable seagrass cover. With ten quadrats it was possible to identify a minimum detectable change in cover of 15% for uniform and 30% for variable seagrass cover. Power analysis was used to determine the probability of committing a Type II error from the data. Region level data had low power, corresponding to a high risk of committing a Type II error. Site and transect level data had high power corresponding to a low risk of committing a Type II error. Based on this study's data, managers using video to monitor for change in seagrass cover are advised to use data from the smaller scale, for example, site and transect level data. By using data from the smaller scale, managers will have a low risk of incorrectly concluding there has not been a disturbance when one has actually occurred.

Seasonal and small-scale spatial variability of herbivory pressure on the temperate seagrass Posidonia oceanica

Despite increasing evidence that herbivory on seagrasses can be substantial in nearshore systems, there is only scarce experimental data on the direct quantification of seagrass removal by herbivores. To help fill this gap, and to evaluate the hypothesis that herbivory on the Mediterranean seagrass Posidonia oceanica (L.) Delile is generally low, we assessed the patterns of grazing pressure variability and its effects on seagrass in an undisturbed meadow in the NW Mediter- ranean. We quantified herbivore density and grazing pressure through both direct (tethering exper- iment) and indirect (through marks of herbivore attacks) measurements. Although grazing varied greatly both temporally and spatially, our results show that whereas consumption by the sea urchin Paracentrotus lividus is relatively minor, P. oceanica is intensely grazed by the fish Sarpa salpa in summer. During this period, fish are very abundant at a depth of 5 m, with consumption rates that temporarily exceed seagrass production, which is at its yearly minimum. This imbalance between consumption and production causes the appearance of mowed patches that can be seen from early summer to September; seagrass biomass is reduced by 50% in such patches. Through direct mea- surements of consumption, our study has revealed that P. oceanica consumption by herbivores can be substantial with respect to the total annual production and much higher than previously estimated through indirect measurements. Thus, it becomes apparent that estimation of consumption rates by indirect methods can grossly underestimate the importance of herbivory in seagrass ecosystems, which leads us to strongly advocate the use of direct methods whenever possible.

Seagrass Removal Causes Problems in Mauritius

Seagrass Removal Causes Problems in Mauritius

In situ nitrogen fixation associated with seagrasses in the Gulf of Elat (Red Sea)

In situ nitrogen fixation associated with the seagrass Halophila stipulacea, at the northern Gulf of Elat (Red Sea), is eight to ten times higher than that of nearby plant-free areas. A daily cycle of nitrogen fixation is evident, with rates during the day being seven times greater than during the night. Removal of seagrass leaves only from a patch within a seagrass bed gradually decreases nitrogen fixation activity, reaching the rates of plant-free areas after ten hours. A method devised for the in situ measurement of nitrogen fixation rates using belljars is described in detail. Nitrogen fixation rates in situ are higher than in the laboratory and lack the lag period typical to laboratory measurements. In laboratory experiments using intact plant samples, glucose enhances nitrogen fixation rates both in light and dark. Photosystem II inhibitor (3-3,4-dichloro-phenyl-1,1-dimethylurea) doubles nitrogen fixation rates in light. Both field and laboratory results indicate that light is essential for nitrogen fixation activity in the H. stipulacea bed possibly through its effect on cyanobacterial population that occupy the aerobic niches of the phyllosphere and on photosynthetic Rhodospirillacean bacteria that inhabit the anaerobic ones. Nitrogen fixation rates evident in H. stipulacea beds in situ account for a considerable portion of the biomass production by the seagrasses. The dependence of high nitrogenase activity by the diazotrophs on the presence of the seagrasses indicates the great importance of the seagrass community to the nitrogen cycle in its highly oligotrophic surroundings of the Gulf of Elat.

Effects of changes in seagrass shoot density and leaf height on the abundance of juveniles of Acentrogobius pflaumii in a Zostera marina bed

The effects of changes in the structural complexity of a seagrass (Zostera marina) habitat on the density of juveniles of the streaked goby, Acentrogobius pflaumii, were investigated by field experimentation at Moroiso Bay, Miura Peninsula, Japan. The experimental design, which included seven treatments plus a control, included reduction of seagrass shoot densities and leaf heights as well as complete removal of seagrass. Throughout the study period, juvenile densities remained similar among the experimental quadrats, including the completely cleared quadrat. On the other hand, juveniles did not appear over the bare sandy substratum surrounding the experimental seagrass bed. Within the bed, prey densities were high, being similar among the experimental quadrats, whereas prey were relatively scarce over the surrounding bare substratum. This result suggested that streaked goby juveniles were not attracted to the structure of the Zostera bed per se and that their distribution patterns may be determined by other factors, such as prey availability.

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.

Effects of removal of seagrass canopy on assemblages of small, motile invertebrates

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 118:129-137 (1995) - doi:10.3354/meps118129 Effects of removal of seagrass canopy on assemblages of small, motile invertebrates Connolly, R. M. To test the importance of seagrass canopy to epifaunal invertebrates in a southern Australian estuary, patches of the short, fine-leaved seagrass Zostera muelleri Irmisch ex Aschers. were cleared of canopy. All other factors were known to be consistent with seagrass presence, and a procedural control was used to measure any effects of the method used to remove seagrass. Effects on epifauna were measured as changes in abundance and biomass of key taxa and in total production, and as differences amongst assemblages, tested using an analysis of similarity (ANOSIM) randomisation routine. Removal of seagrass canopy had a weak but detectable effect on epifauna over and above the slight effect caused by the disturbance concomitant with seagrass removal. Epifauna associated with habitat from which seagrass had been removed did not, however, match that from areas unvegetated prior to the experiment. The epifauna from these previously unvegetated areas were characterised by low abundance and biomass of several key taxa, apart from 1 group, cumaceans, which were far more common in this habitat. The results suggest that the overriding importance of Z. muelleri to epifauna is not simply the presence of seagrass canopy, and explanations of the higher abundance of epifaunal invertebrates in vegetated compared to unvegetated habitats based merely on the presence of seagrass canopy are not supported. Zostera . Macrofauna . Crustacea . Predation . ANOSIM Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 118. Publication date: March 09, 1995 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 1995 Inter-Research.

Behaviour and Ecology of the Dugong, Dugong Dugon (Sirenia): Observations in Shoalwater and Cleveland Bays, Queensland.

Dugongs (Dugong dugon) were studied in 2 bays in north Queensland from shore and small boats. Population in favoured areas of one bay was 5/km shoreline and 4 to 8% were juveniles. Feeding was the most common activity. The dugongs dived and grazed, apparently using their rostral disc to gouge a serpentine track through the bottom sediment. Removal of sea grass was calculated to be 78% from the tracks selected by observers or 59% from a random sample; both were thought to be underestimated. Dugongs tended to move on after 5 or 6 days when 30% of an area had been grazed. They left inshore sea grass beds before low tide to avoid being stranded, so their feeding was governed by the 25-h cycle of 2 high and 2 low tides daily. Inshore feeding was not restricted to hours of darkness. The most commonly eaten sea grasses were Zostera capricorni, Halophila decipiens and H. ovalis. From published work, it was thought that the dugongs specialized in whatever seagrass species were most readily available. Owing to opacity of the water, they could not be observed under water. Mean length of the 9 faecal pellets found on shore was 8.98 mm; the pellets included plant fibre.