Seagrass Material Research Articles

The contributions of primary sources to fauna and the trophic structure in tropical seagrass areas: A case study from Thai waters

AbstractSeagrass provides habitat and resources for various organisms in coastal areas. However, the productivity of a seagrass meadow might vary by its size, which can influence the contribution of primary sources to fauna and the food web structure. This study uses stable isotopes to investigate the contribution of sources to faunas and the associated food web structure in two tropical seagrass meadows. The carbon (δ13C) and nitrogen (δ15N) stable isotopes of primary sources such as mangrove leaf, coastal and riverine particulate organic matter, seagrass material and associated fauna (fish, bivalves, gastropods, crab, shrimp) were investigated from samples collected seagrass meadows of different sizes, at Libong Island and Tharai Island in Thailand. The contribution of the primary sources to the fauna diet showed that seagrass material was the main food source for fauna in both sites. Moreover, the trophic niche did not overlap among the groups of each fauna guild, reflecting the support seagrass provides to resident fauna. The study emphasizes the important role of seagrass as a habitat and feeding ground in tropical coastal ecosystems.

Optimizing the restoration of the threatened seagrass Posidonia australis: plant traits influence restoration success

Restoration is an important activity to assist the recovery of damaged or degraded ecosystems. Accessing healthy donor material can be challenging when restoring threatened ecological communities, but careful selection of donor material may improve the success and cost‐effectiveness of restoration projects. We aim to optimize restoration of the threatened seagrass Posidonia australis by identifying the traits of donor material that best predict survival and establishment. To avoid collecting donor material from threatened populations, a recent restoration method focuses on using naturally detached fragments of P. australis collected from the shoreline, which are stored in outdoor tanks prior to planting. Here, we examine 10 morphological traits of P. australis fragments and other variables relating to collection method to identify which traits best predicted survival after replanting. Fragments with more shoots and less dead tissue (necrosis) in their leaves had higher survival 1 year after planting. Fragments that were stored longer in tanks prior to replanting had significantly higher survival rates. These results can refine the selection for donor material used in restoration and optimize the recently developed restoration technique for P. australis using beach‐cast seagrass material.

Beyond habitat boundaries: Organic matter cycling requires a system‐wide approach for accurate blue carbon accounting

AbstractAs coastal ecosystems become widely recognized for their capacity to sequester carbon (blue carbon), standard accounting methodologies for the generation of carbon credits are being developed. To ensure the applicability of these standards across blue carbon ecosystems, we investigated organic carbon provenance and burial in salt marshes and seagrass meadows of an arid, upwelling‐dominated Eastern Pacific lagoon. We found low carbon density in benthic sediments of Bahía de San Quintín (5.9 ± 0.5 mg C cm−3), only marginally higher in Zostera marina beds (6.9 ± 0.5 mg C cm−3), likely due to remineralization and hydrodynamically driven export of seagrass material, resulting in low carbon burial rates (4.5 ± 2.5 g C m−2 yr−1). Sediment organic carbon is mainly controlled by the fraction of fine sediment and its source is largely allochthonous, although sources differ spatially. Salt marshes at San Quintín derive 40% of their organic matter from autochthonous material and exhibit higher carbon burial rates (up to 414.7 ± 28.6 g C m−2 yr−1) and sediment carbon densities (32.0 ± 0.7 mg C cm−3) compared to benthic sediments. This study emphasizes the connectivity of blue carbon habitats with marsh plant detritus supplementing benthic carbon burial and incorporation of detrital eelgrass in marsh sediments. Our findings highlight the importance of allochthonous organic matter for carbon sequestration in blue carbon habitats, suggesting standard accounting practices that deduct allochthonous organic matter would miss the full potential for carbon burial.

"Neptune Balls" Polysaccharides: Disentangling the Wiry Seagrass Detritus.

Each year, high amounts of dead seagrass material are washed ashore at beaches world-wide. In the Mediterranean region, the seagrass Posidonia oceanica is responsible for huge agglomerates of ball-like seagrass litter. As these are often removed due to touristic reasons, a reuse method would be a step towards a more ecologically oriented society. In this study, the main polysaccharide components were analyzed, in order to propose possible usage options. To do this, different aqueous fractions were extracted, analyzed by classical carbohydrate analysis methods (GC-FID/MS, colorimetric assay and elemental analysis), and purified by ion-exchange chromatography, as well as selective precipitation with a detecting agent for highly glycosylated glycoproteins. The obtained purified fractions were analyzed in detail and a linkage-type analysis of the most promising extract was conducted via permethylation. Only low amounts of glycoproteins, as well as medium amounts of the characteristic apiogalacturonan were likely to be present, while xylan seemed to be the most abundant polysaccharide in most fractions. A partial structural proposal showed general accordance with land plant xylans, presenting reuse options in the field of biofuel and bioplastic generation.

Gut microbial diversity and digestive function of an omnivorous shark

The intestinal microbiome of vertebrates has been shown to play a crucial role in their digestive capabilities. This is particularly true for omnivores and herbivores that rely on enteric microbes to digest components of plant material that are indigestible by host-derived enzymes. While studies of microbe-host interactions are becoming more frequent in terrestrial systems, studies of this type are still limited in marine systems, particularly for higher trophic level organisms. Although sharks are largely carnivorous, the bonnethead shark (Sphyrna tiburo) has been identified as an omnivore, given that it assimilates seagrass material in addition to proteinaceous prey items such as crustaceans. The mechanisms by which bonnetheads digest seagrass, including microbial digestion, are still unknown. We use digestive enzyme assays, histological imaging, measurements of microbial fermentation, and 16S rDNA sequencing to explore potential processes by which the bonnethead shark may digest and assimilate plant material. We found evidence of microbial fermentation (as evident by moderate short-chain-fatty-acid concentrations) as well as evidence of greater epithelial surface area in their spiral intestine compared to other gut regions. We identified specific orders of microbes that make up the majority of the bonnethead shark gut microbiome (Vibrionales, Clostridiales, Pseudomonadales, Mycoplasmatales, Rhizobiales, and others), some of which are known, in other organisms, to be involved in the production of enzymes responsible for the breakdown of chitin (found in crustacean shells) and components of cellulose (found in seagrass). Our results highlight that an organism from a stereotypical “carnivorous” group is capable of breaking down seagrass, including potential for some fiber degradation, as well as advances our knowledge of gut microbe community structure in sharks.

Spatial and Temporal Patterns in Macroherbivore Grazing in a Multi-Species Tropical Seagrass Meadow of the Great Barrier Reef

Macroherbivory is an important process in seagrass meadows worldwide; however, the impact of macroherbivores on seagrasses in the Great Barrier Reef (GBR) has received little attention. We used exclusion cages and seagrass tethering assays to understand how the intensity of macroherbivory varies over space and time in the seagrass meadows around Green Island (Queensland), and what impact this has on overall meadow structure. Rates of macroherbivory were comparatively low, between 0.25–44% of daily seagrass productivity; however, rates were highly variable over a one-year period, and among sites. Loss of seagrass material to macroherbivory was predominantly due to fish; however, urchin herbivory was also taking place. Macroherbivory rates were of insufficient intensity to impact overall meadow structure. No macroherbivory events were identified on video cameras that filmed in the day, indicating that feeding may be occurring infrequently in large shoals, or at night. While relatively low compared to some meadows, seagrass macroherbivory was still an important process at this site. We suggest that in this highly protected area of the GBR, where the ecosystem and food webs remain largely intact, macroherbivory was maintained at a low level and was unlikely to cause the large-scale meadow structuring influence that can be seen in more modified seagrass systems.

Posidonia oceanica as a Source of Chromophoric Dissolved Organic Matter for the Oligotrophic NW Mediterranean Coast

Posidonia oceanica is a well-recognized source of dissolved organic matter (DOM) derived from exudation and leaching of seagrass leaves, but little is known about its impact on the chromophoric fraction of DOM (CDOM). In this study, we monitored for two years the optical properties of CDOM in two contrasting sites in the Mallorca Coast (Balearic Islands). One site was a rocky shore free of seagrass meadows, and the second site was characterized by the accumulation of non-living seagrass material in the form of banquettes. On average, the integrated color over the 250–600 nm range was almost 6-fold higher in the beach compared with the rocky shore. Furthermore, the shapes of the CDOM spectra in the two sites were also different. A short incubation experiment suggested that the spectral differences were due to leaching from P. oceanica leaf decomposition. Furthermore, occasionally the spectra of P. oceanica was distorted by a marked absorption increase at wavelength < 265 nm, presumably related to the release of hydrogen sulfide (HS−) associated with the anaerobic decomposition of seagrass leaves within the banquettes. Our results provide the first evidence that P. oceanica is a source of CDOM to the surrounding waters.

Expanding Greenland seagrass meadows contribute new sediment carbon sinks

The loss of natural carbon sinks, such as seagrass meadows, contributes to grenhouse gas emissions and, thus, global warming. Whereas seagrass meadows are declining in temperate and tropical regions, they are expected to expand into the Arctic with future warming. Using paleoreconstruction of carbon burial and sources of organic carbon to shallow coastal sediments of three Greenland seagrass (Zostera marina) meadows of contrasting density and age, we test the hypothesis that Arctic seagrass meadows are expanding along with the associated sediment carbon sinks. We show that sediments accreted before 1900 were highly 13C depleted, indicative of low inputs of seagrass carbon, whereas from 1940’s to present carbon burial rates increased greatly and sediment carbon stocks were largely enriched with seagrass material. Currently, the increase of seagrass carbon inputs to sediments of lush and dense meadows (Kapisillit and Ameralik) was 2.6 fold larger than that of sparse meadows with low biomass (Kobbefjord). Our results demonstrate an increasing important role of Arctic seagrass meadows in supporting sediment carbon sinks, likely to be enhanced with future Arctic warming.

Seagrass digestion by a notorious 'carnivore'.

What an animal consumes and what an animal digests and assimilates for energetic demands are not always synonymous. Sharks, uniformly accepted as carnivores, have guts that are presumed to be well suited for a high-protein diet. However, the bonnethead shark (Sphyrna tiburo), which is abundant in critical seagrass habitats, has been previously shown to consume copious amounts of seagrass (up to 62.1% of gut content mass), although it is unknown if they can digest and assimilate seagrass nutrients. To determine if bonnetheads digest seagrass nutrients, captive sharks were fed a 13C-labelled seagrass diet. Digestibility analyses, digestive enzyme assays and stable isotope analyses were used to determine the bonnethead shark's capacity for digesting and assimilating seagrass material. Compound-specific stable isotope analysis showed that sharks assimilated seagrass carbon (13.6 ± 6.77‰ δ13C mean ± s.d. for all sharks and all amino acid types analysed) with 50 ± 2% digestibility of seagrass organic matter. Additionally, cellulose-component-degrading enzyme activities were detected in shark hindguts. We show that a coastal shark is digesting seagrass with at least moderate efficiency, which has ecological implications due to the stabilizing role of omnivory and nutrient transport within fragile seagrass ecosystems.

3-D Morphological Change Analysis of a Beach with Seagrass Berm Using a Terrestrial Laser Scanner

Along many Mediterranean coasts, the detached seagrass material of Posidonia oceanica creates seagrass berms that control the structure and morphodynamics of sandy beaches. Here, we show how Terrestrial Laser Scanner remote sensing data allows analyzing the 3-D morphologic change of beaches where this characteristic geomorphic structure is present. We propose a methodology for estimating accretion/erosion (almost −200 m3 in our study) by considering the sand dominated and seagrass berms as two independent elements. For this purpose, two different sampling dates (named scenarios A and B, before and after an erosive heavy storms period, respectively) recorded in a microtidal pocket-beach (300 m2) with these characteristic geomorphic structures have been modeled in 3-D. The present approach constitutes a cost-efficient, accurate, and quick tool to survey the sand volume in natural and artificial replenished beaches. The innovative approach, which can be considered as a conceptual and methodological starting point, can be useful to examine long-term and high-precision data sets in future studies of the morphodynamic evolution of these characteristic Mediterranean beaches.

Maximising establishment success of Amphibolis antarctica seedlings

Coastal developments of all scales impact on seagrass meadows. Mitigation for loss of seagrass ecosystems is increasingly being required by regulatory agencies to compensate for coastal developments and while many attempts have been made to transplant seagrasses, there are concerns about the long-term viability of these efforts, as well as the sustainability of harvesting natural seagrass material for transplantation. The present pilot study demonstrates a novel way of maximising establishment of Amphibolis antarctica seedlings. Seedlings were planted and tethered using an innovative spiral peg, in a bare sand area adjacent to a mature Amphibolis meadow in Shoalwater Bay, Western Australia. Survival and growth were monitored over two years. After two years, 29.4% of seedlings survived into well-established mature plants. By enhancing establishment success of seedlings it is anticipated that more rapid and sustainable rehabilitation of Amphibolis seedlings will be possible.

First experimental evidence of corals feeding on seagrass matter

We present the first experimental evidence of a coral (Oulastrea crispata) ingesting and assimilating seagrass material. Tropical seagrass meadows export a substantial portion of their productivity and can provide an important source of nutrients to neighbouring systems such as coral reefs; however, little is known about the mechanisms of this link. To investigate whether seagrass nutrient uptake via coral heterotrophy is possible, we conducted a feeding experiment with seagrass particulate and dissolved organic matter. Using gut extractions and stable isotope analyses, we determined that O. crispata ingested 15N-enriched seagrass particles and assimilated the nitrogen into its tissue at a rate of 0.75 μg N cm−2 h−1. Corals took up nitrogen from dissolved matter at a comparable rate of 0.98 μg N cm−2 h−1. While other ecological connections between seagrass meadows and reef ecosystems are well known, our results suggest a previously unstudied direct nutritional link between seagrasses and corals.

Meiofauna and harpacticoid copepods in different habitats of a Mediterranean seagrass meadow

This study investigated whether associated meiobenthic communities, especially harpacticoid copepods, differed amongst habitats. Five pre-defined habitats within and next to thePosidonia oceanicaseagrass meadow were sampled: living seagrass canopy leaves (LL), small (SMF) and large (LMF) macrophytodetritus fragment accumulations and sand, bare (BS) and covered (CS). The highest meiofauna abundances were recorded in the BS for the core sampled habitats (BS, CS, SMF and LMF) and in the LMF for seagrass material habitats (SMF, LMF and LL). Harpacticoid copepods were the most abundant taxon in all habitats. The assemblage composition at copepod family level showed two distinct habitats clusters: a leaf (LMF and LL) and a sediment cluster (BS, CS and SMF). Subsequently, stable isotope analyses were conducted to analyse the relationship between copepods and their potential food sources in seagrass material habitats. Based on δ13C isotopic analyses and SIAR mixing model, harpacticoid copepods relied for 70% on epiphytes and for 30% onP. oceanicaleaf material in the LMF and LL habitats.

Development of a DNA Barcoding System for Seagrasses: Successful but Not Simple

Seagrasses, a unique group of submerged flowering plants, profoundly influence the physical, chemical and biological environments of coastal waters through their high primary productivity and nutrient recycling ability. They provide habitat for aquatic life, alter water flow, stabilize the ground and mitigate the impact of nutrient pollution. at the coast region. Although on a global scale seagrasses represent less than 0.1% of the angiosperm taxa, the taxonomical ambiguity in delineating seagrass species is high. Thus, the taxonomy of several genera is unsolved. While seagrasses are capable of performing both, sexual and asexual reproduction, vegetative reproduction is common and sexual progenies are always short lived and epimeral in nature. This makes species differentiation often difficult, especially for non-taxonomists since the flower as a distinct morphological trait is missing. Our goal is to develop a DNA barcoding system assisting also non-taxonomists to identify regional seagrass species. The results will be corroborated by publicly available sequence data. The main focus is on the 14 described seagrass species of India, supplemented with seagrasses from temperate regions. According to the recommendations of the Consortium for the Barcoding of Life (CBOL) rbcL and matK were used in this study. After optimization of the DNA extraction method from preserved seagrass material, the respective sequences were amplified from all species analyzed. Tree- and character-based approaches demonstrate that the rbcL sequence fragment is capable of resolving up to family and genus level. Only matK sequences were reliable in resolving species and partially the ecotype level. Additionally, a plastidic gene spacer was included in the analysis to confirm the identification level. Although the analysis of these three loci solved several nodes, a few complexes remained unsolved, even when constructing a combined tree for all three loci. Our approaches contribute to the understanding of the morphological plasticity of seagrasses versus genetic differentiation.

Starch grain morphology of the seagrasses Halodule wrightii, Ruppia maritima, Syringodium filiforme, and Thalassia testudinum

Starch grains are a ubiquitous component of plants that have been used in tandem with phytoliths, pollen, and macrofossils to reconstruct past floral diversity. This tool has yet to be fully explored for aquatic plants, specifically seagrasses, which lack phytoliths and are rarely preserved as macrofossils or pollen. If starch grains in seagrasses are morphologically distinct, this method has the potential to improve seagrass identification in the fossil record in such cases where its starch is preserved (e.g. scratches and occlusal surfaces of tooth enamel from seagrass consumers). The goals of this study were twofold: (1) to determine if starch is present in seagrass material and (2) to assess how starch grain morphology differs between different seagrasses. This study focused on four abundant and ecologically distinct seagrasses from the Caribbean: Halodule wrightii, Ruppia maritima, Syringodium filiforme, and Thalassia testudinum. Starch grains were observed in all species except S. filiforme. Grains from H. wrightii are typically observed in side-on orientation, are sub-round to angular, and are fairly small (3-19 μm, end-on). Grains of R. maritima are small spherical grains (4–8 μm) that have a centric hilum and a straight extinction cross with a median angle between the arms of 90°. Grains from T. testudinum are large (9–31 μm, end-on), conical in side-on and round/sub-round in end-on orientation, have a slightly eccentric hilum with an obvious particle, and prominent lamellae. Visual assessment and comparative statistics demonstrate that the morphology of starch grains from T. testudinum, R. maritima, and H. wrightii are significantly different. With more extensive research, there is potential for the positive identification of starch grains from an unknown seagrass. The ability to identify seagrass from starch grains could facilitate the identification of seagrasses in the fossil record and supply information on seagrass evolution and distribution, climate effects on seagrass distribution, and the diets of seagrass consumers.

Redefining the trophic importance of seagrasses for fauna in tropical Indo-Pacific meadows

Fauna species living in seagrass meadows depend on different food sources, with seagrasses often being marginally important for higher trophic levels. To determine the food web of a mixed-species tropical seagrass meadow in Sulawesi, Indonesia, we analyzed the stable isotope ( δ 13C and δ 15N) signatures of primary producers, particulate organic matter (POM) and fauna species. In addition invertebrates, both infauna and macrobenthic, and fish densities were examined to identify the important species in the meadow. The aims of this study were to identify the main food sources of fauna species by comparing isotopic signatures of different primary producers and fauna, and to estimate qualitatively the importance of seagrass material in the food web. Phytoplankton and water column POM were the most depleted primary food sources for δ 13C (range −23.1 to −19.6‰), but no fauna species depended only on these sources for carbon. Epiphytes and Sargassum sp. had intermediate δ 13C values (−14.2 to −11.9‰). Sea urchins, gastropods and certain fish species were the main species assimilating this material. Seagrasses and sedimentary POM had the least depleted values (−11.5 to −5.7‰). Between the five seagrass species significant differences in δ 13C were measured. The small species Halophila ovalis and Halodule uninervis were most depleted, the largest species Enhalus acoroides was least depleted, while Thalassia hemprichii and Cymodocea rotundata had intermediate values. Fourteen fauna species, accounting for ∼10% of the total fauna density, were shown to assimilate predominantly (>50%) seagrass material, either directly or indirectly by feeding on seagrass consumers. These species ranged from amphipods up to the benthic top predator Taeniura lymma. Besides these species, about half of the 55 fauna species analyzed had δ 13C values higher than the least depleted non-seagrass source, indicating they depended at least partly for their food on seagrass material. This study shows that seagrass material is consumed by a large number of fauna species and is important for a large portion of the food web in tropical seagrass meadows.

Extraordinarily high earthworm abundance in deposits of marine macrodetritus along two semi-arid beaches

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 361:181-189 (2008) - DOI: https://doi.org/10.3354/meps07351 Extraordinarily high earthworm abundance in deposits of marine macrodetritus along two semi-arid beaches Grey T. Coupland*, Justin I. McDonald School of Plant Biology (M090), Faculty of Natural and Agricultural Sciences, University of Western Australia, Crawley, Western Australia 6907, Australia *Email: greyc@cyllene.uwa.edu.au ABSTRACT: Earthworms are common in most soil profiles; however, the abundance of earthworms varies greatly among habitats. The euryhaline earthworm Pontodrilus litoralis was recorded in extraordinarily high numbers in wrack material deposited on arid beaches along the western Australian coastline. Based on worm abundance in 20 × 20 × 20 cm plots, we estimated worm densities to be as high as 4875 m–2 at one site. Mean (±SE) worm density was 3200 ± 466 m–2 for the north Leeman site, with a minimum density of 750 m–2 at the Point Louise site (1940 ± 475 m–2). Using estimates of consumption by earthworms from previous research, we calculated that earthworms could consume approximately 19 kg m–2 yr–1 of wrack material deposited at Point Louise and 31 kg m–2 yr–1 at north Leeman. The densities and associated potential consumption rates of worms recorded in the wrack habitat well exceed any records of worm populations in other natural systems. The only similar estimates are those from artificially created habitats, such as manure heaps. Stable isotope analyses suggest that the earthworms (mean δ13C –15.9 and δ15N 6.9) were consuming the more ephemeral algal component (mean δ13C –21.5 and δ15N 3.7) of the wrack in preference to the more persistent seagrass material (mean δ13C –12.4 and δ15N 2.1). The extraordinary densities of earthworms in wrack habitat have implications for the rate of wrack turnover along beach habitats and incorporation of marine-derived nutrients into what is essentially a nutrient-poor terrestrial coastal system. High earthworm densities in the wrack also indicate that wrack as a habitat is a potential hotspot for diversity and metabolism, probably exceeding records for other more stereotypically rich habitats, such as rainforests. KEY WORDS: Coastal systems · Detached macrophytes · Land–water interface · Nutrient turnover · Wrack Full text in pdf format PreviousNextCite this article as: Coupland GT, McDonald JI (2008) Extraordinarily high earthworm abundance in deposits of marine macrodetritus along two semi-arid beaches. Mar Ecol Prog Ser 361:181-189. https://doi.org/10.3354/meps07351 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 361. Online publication date: June 09, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Beach-cast seagrass material fertilizes the foredune vegetation of Mediterranean coastal dunes

Stable nitrogen isotopes were used to assess the relevance of debris from the seagrass Posidonia oceanica as a source of inorganic nutrients for the members of three functional groups of plants (camephytes, geophytes, and C3 perennial grasses) in three coastal dune systems of Minorca (Balearics Archipelago, western Mediterranean). The δ 15N of foredune camephytes and geophytes was usually higher than that of atmospheric nitrogen and often was not statistically different from that of P. oceanica debris. Conversely, the δ 15N of camephytes and geophytes collected in hinddunes and matorral areas was not statistically different from that of atmospheric nitrogen and usually lower than that of P. oceanica. Two-way ANOVA revealed a strong and significant effect of habitat on the δ 15N of camephytes and geophytes, without any significant effect of the functional type or a significant interaction term. Although the δ 15N of the C3 perennial grasses from the foredunes was never statistically different from that of beach-cast seagrass material and that of perennial C3 grasses from the matorral was always significantly lower than that of beach-cast seagrass material, Student's t-test was unable to reveal statistically significant differences between the C3 grasses from the foredunes and the matorral, due to the high standard deviation. The foliar nitrogen contents of foredune plants other than grasses were higher than those of plants from the hinddune and matorral sites, and the foliar C:N ratios were much lower. However, the differences between the grasses growing in the foredunes and in the matorral were not statistically significant for foliar N content or the foliar C:N ratio. On the whole, this evidence strongly supports the hypothesis that beach-cast P. oceanica material is a relevant source of nitrogen for the vegetation of Mediterranean foredunes.

Shrimp burrow in tropical seagrass meadows: An important sink for litter

The abundance, burrow characteristics, and in situ behaviour of the burrowing shrimps Neaxius acanthus (Decapoda: Strahlaxiidae) and Alpheus macellarius (Decapoda: Alpheidae) were studied to quantify the collection of seagrass material, to identify the fate of this collected material, and to determine the importance of these burrowing crustaceans in the nutrient (nitrogen and phosphorus) cycling of two tropical seagrass meadows on Bone Batang, South Sulawesi, Indonesia. Alpheus macellarius harvested 0.70 g dry weight (DW) burrow −1 d −1 seagrass material, dominantly by active cutting of fresh seagrass leaves. Neaxius acanthus collected 1.66 g DW burrow −1 d −1, mainly detached leaves which floated past the burrow opening. The A. macellarius and N. acanthus communities together collected in their burrows an amount of seagrass leaf material corresponding to more than 50% of the leaf production in the meadows studied. The crustacean species studied might therefore fulfil an important function in the nutrient cycling of tropical meadows. In the burrow most of the collected material is shredded into pieces. The burrows of both species had special chambers which serve as a storage for seagrass leaf material. Neaxius acanthus incorporated most of the material into the burrow wall lining, which is made of small sediment particles and macerated seagrass leaves. Phosphate concentrations measured in N. acanthus burrows compared with pore-water and water-column concentrations suggests that a substantial amount of the seagrass material undergoes decomposition in the burrows. Oxygen levels measured in these water bodies are indicative for a possible exchange of water between the burrow and its surroundings, most likely supported by the shrimps irrigating their burrows. By collecting leaf material in their burrows, nutrients that are otherwise lost from the seagrass meadow associated with detached leaves and leaf fragments carried away in the water column, are maintained in the meadow and may form an important source of recycled nutrients.

The contribution of scarid herbivory to seagrass ecosystem dynamics in the Indo-Pacific

The functional importance of herbivory is well established within terrestrial ecosystems yet within marine ecosystems, specifically seagrass beds, consumption by herbivores has generally been considered to be of little importance due to its minor contribution to turnover of growth. The present paper challenges this assumption within the Indo-Pacific and shows that scarid (parrotfish) herbivory may have a functionally important role in the export of seagrass detrital material. Estimation of scarid herbivory on dominant Indo-Pacific seagrass species was conducted using a three pronged approach. We estimated: background levels of scarid seagrass bites; in-situ rates of grazing using tethering experiments; and seagrass grazing effect per individual scarid, which was scaled up to estimate the grazing effects of the local scarid population. All research was carried out within the Wakatobi Marine National Park, Indonesia. Research found scarid herbivory to be an important process within an Indo-Pacific seagrass bed causing the loss of up to ten times (average, four times) the daily seagrass growth. T. hemprichii was found to be lost at a rate of 0.28 ± 0.08 g DW day −1, while E. acoroides was lost at a rate of 2.85 ± 0.43 g DW day −1. We propose that such high rates of seagrass consumption are the combined effects of seasonally high grazing rates by resident scarids and short-term effects from shoals of juvenile reef scarids. Scarid grazing was indiscriminate between seagrass species and grazing was dependant on seagrass availability rather than nutritional quality. In conclusion, the present research finds scarids to be major herbivores within an Indo-Pacific seagrass bed; they not only take up carbon into the food chain through direct seagrass consumption, but also make an important indirect contribution to the detrital food chain through the export of discarded decaying seagrass material.