Seagrass Rhizomes Research Articles

Prolonged buoyancy and viability of Zostera muelleri Irmisch ex Asch. vegetative fragments indicate a strong dispersal potential

The establishment of clonal marine plant populations, including the seagrass Zostera muelleri (Zosteraceae), may be more dependent on the availability of viable vegetative fragments rather than seed. New populations may establish through long-distance dispersal of viable vegetative fragments, potentially increasing genetic diversity and resilience to anthropogenic or naturally occurring disturbance. A number of activities can dislodge vegetative fragments of Z. muelleri (leaves, rhizomes and roots) from the sediment. These fragments can remain positively buoyant, floating on the surface of the water. As the time since dislodgement increases, buoyancy may become reduced, causing fragments to move lower into the water column. However, what is not known is how long these fragments remain buoyant and potentially viable for recolonization. To address this knowledge gap, we collected wrack samples (n=125) of Z. muelleri from four Victorian estuaries. Fragments were floated in outside aquaria for up to ten weeks, with subsamples tested for metabolic activity using tetrazolium violet. Porosity of seagrass rhizomes was also investigated to understand the influence of lacunae (large air filled spaces within plant tissues) on the flotation of vegetative fragments. The average proportion of potentially viable fragments collected in wrack ranged from 3.6% (SD=2.23) to 11.2% (SD=5.9). While there was a steady decline in the buoyancy of fragments across the ten-week period, initial buoyancy was relatively high, with approximately 50% of the fragments remaining positively buoyant for the initial five weeks. The viability of fragments following flotation was high. One hundred percent of fragments (n=25 per assay) remained viable after floating for three weeks, with only a marginal decline (=96% viability) occurring after five weeks. When considered in conjunction with the highly porous nature of seagrass rhizomes (lacunae accounted for 45.2% of total volume), our findings indicate that the species may be capable of prolonged periods of transport dispersal within the marine environment.

Spatial and temporal patterns in the distribution of large bivalves in a permanently open temperate estuary: implications for management

To inform management, baseline ecological studies in estuaries must be implemented at spatial scales that accommodate both environmental gradients and likely anthropogenic pressures. We describe fine-scale spatial patterns in the abundances and size structure of large infaunal bivalves inhabiting shallow sand habitats in the lower reaches of a relatively undisturbed, permanently open, temperate estuary. Sampling over 3 years at 19 sites during the autumn, when freshwater influence was minimal, revealed that Soletellina alba, Wallucina assimilis and Paphies elongata were consistently the most abundant of nine species present. Although most abundant near the ocean entrance, S. alba was distributed widely and shells of differing lengths, and presumably ages, were present at most sites, suggesting that this species recruited continuously throughout the study area when conditions were appropriate. In contrast, W. assimilis and P. elongata occurred only near or in the entrance channel of the Nornalup Inlet in areas where seagrass rhizomes may grow and where oceanic influences caused relatively turbulent conditions, respectively. Sediment structure appeared to exert only a moderate and intermittent influence on the bivalve assemblage at some sites where particularly large grain sizes occurred. This study provides important baseline information on the distribution and abundance of large bivalves in this estuary. These species are likely to be important in the trophic ecology of this system and are potential indicators of disturbance and ecosystem health.

Osteology and Functional Morphology of the Forelimb of the Marine Sloth Thalassocnus (Mammalia, Tardigrada)

Thalassocnus is a genus of “ground sloths” known from Neogene deposits, for the great majority of specimens, of the Pisco Formation (Peru). Five species are recognized, their description being currently restricted, for the most part, to the skull, mandible, and dentition. The bones of the forelimb are here described, and compared among the species of Thalassocnus and to other pilosans. The main characteristics of the forelimb of Thalassocnus relative to other sloths are the shortness of the humerus and radius, and the specialized digits. Moreover, the late species of the genus are characterized by the development of the pronator ridge of the radius, stoutness of the ulna, widening of the proximal carpal row, and shortening of the metacarpals. Analogies with extant tetrapods are proposed in order to infer plausible aquatic functions of the forelimb of Thalassocnus. In addition to paddling, it is argued that the forelimb of Thalassocnus was involved in bottom-walking, a function similarly found in extant sirenians. However, the function of the forelimb of Thalassocnus differs drastically from that of the latter, since it was likely involved in an activity related to obtaining food such as uprooting seagrass rhizomes.

The anatomy of Lepetella sierrai (Vetigastropoda, Lepetelloidea): implications for reproduction, feeding, and symbiosis in lepetellid limpets

AbstractThe Lepetelloidea, a clade of small limpet‐shaped gastropods, can be used as a case study in continental margin and deep‐sea diversification. Lineages in this clade have been found associated with a combination of different substrates, including hydrothermal vents, seeps, wood, whale carcasses, polychaete tubes, chondrichthyan egg cases, seagrass rhizomes, algal holdfasts, crab carapaces, and sponges. Members of one lepetelloidean family, Lepetellidae, live on or inside empty tubes of members of the polychaete genus Hyalinoecia. The detailed morphology of a Mediterranean species, Lepetella sierrai Dantart & Luque 1944, was reconstructed in three dimensions from serial semi‐thin sections and compared with that of eleven other members of Lepetellidae. The hermaphroditic lepetellid limpets possessed a ciliated seminal groove, distinct testis and ovary with a common distal gonoduct, and a seminal receptacle containing mature sperm. A unique alimentary tract, with huge esophageal pouches, no true stomach, an extensive multilobed midgut, and short intestine, was present. Additionally, a bacteriocyte system throughout the entire mantle rim was revealed via light and transmission electron microscopy. This is the first recognized evidence for intracellular microbial symbiosis in lepetelloidean limpets. Semi‐thin sections showed evidence of a parasite, potentially a chitonophilid copepod, penetrating the body wall of the limpet. Hypotheses about reproductive biology, feeding, and symbiosis are presented based on anatomical features and knowledge of the habitat described herein.

The role of disturbance in promoting the spread of the invasive seaweed Caulerpa racemosa in seagrass meadows

Human disturbances, such as anchoring and dredging, can cause physical removal of seagrass rhizomes and shoots, leading to the fragmentation of meadows. The introduced green alga, Caulerpa racemosa, is widely spread in the North-West Mediterranean and, although it can establish in both degraded and pristine environments, its ability to become a dominant component of macroalgal assemblages seems greater in the former. The aim of this study was to estimate whether the spread of C. racemosa depends on the intensity of disturbance to the canopy structure of Posidonia oceanica. A field experiment was started in July 2010 when habitat complexity of a P. oceanica meadow was manipulated to simulate mechanical disturbances of different intensity: rhizome damage (High disturbance intensity = H), leaf removal (Low disturbance intensity = L), and undisturbed (Control = C). Disturbance was applied within plots of different size (40 × 40 cm and 80 × 80 cm), both inside and at the edge of the P. oceanica meadow, according to an orthogonal multifactorial design. In November 2011 (16 months after the start of the experiment), no C. racemosa was found inside the seagrass meadow, while, at the edge, the cover of the seaweed was dependent on disturbance intensity, being greater where the rhizomes had been damaged (H) than in leaf removal (L) or undisturbed (C) plots. The results of this study indicate that physical disturbance at the margin of seagrass meadows can promote the spread of C. racemosa.

Dispatches

Dispatches

Expansion into an Herbivorous Niche by a Customary Carnivore

Abstract. In expanding populations, individuals may increasingly be forced to use sites of relatively low quality. This process, named the “buffer effect,” was previously described for the Black-tailed Godwit (Limosa limosa islandica) in its use of nonbreeding sites in Great Britain and of breeding areas in Iceland. On the basis of diet analyses from droppings and stable isotopes, we describe a new case for the expanding French wintering population of the Black-tailed Godwit, an expansion accompanied by a drastic change in feeding strategy. In the 1990s, Black-tailed Godwits started using intertidal mudflats at Ile de Re, where they eat the rhizomes of seagrass (Zostera noltii) rather than the customary shellfish (Macoma balthica) eaten at both the preferred (initial) site (Aiguillon Bay) and the area occupied last (Yves to Marennes-Oleron bays). Individually color-marked godwits appeared faithful to both diet type and site, suggesting a cost of a change of strategy. This represents a first case of rhizom...

Effects of tidal inundation on benthic macrofauna associated with the eelgrass Zostera muelleri

Processes, such as sea level rise, that alter tidal inundation regimes have the potential to modify the structure of seagrasses and their dense and diverse faunal communities. This study tested the hypothesis that seagrass-dwelling invertebrate communities would vary across a tidal inundation gradient as a result of direct effects of tidal inundation and indirect effects, arising from changes in seagrass morphology across this gradient. First, we conducted mensurative sampling across tidal inundation gradients to assess how above- and below-ground seagrass biomass, and epi- and infaunal invertebrate communities co-varied with depth. Second, we ran a manipulative field experiment, utilising artificial seagrass rhizomes of varying morphologies, to separate out direct effects of tidal inundation on infaunal communities from indirect effects arising from changes in seagrass root morphology. Mensurative sampling revealed that the abundance and taxon richness of seagrass epi- and infauna, and the above- and below-ground biomass of seagrass each increased with depth across a tidal elevation gradient extending from the high intertidal to the shallow subtidal. The manipulative experiment revealed that the relative importance of direct and indirect effects of tidal inundation in determining the distribution and abundance of infauna were taxon-specific. In general, however, the facilitative effects of rhizome structure were more evident at the intertidal compared to the subtidal elevation. Our results indicate that changes to tidal inundation regime will affect seagrass-dwelling macroinvertebrates through a combination of direct and indirect effects. Therefore, future changes in tidal inundation should be taken into account in developing conservation plans for protecting seagrasses and the biodiversity they sustain.

Rytiodus heali, sp. nov., a new sirenian (Mammalia, Dugonginae) from the Miocene of Libya

ABSTRACT A species of the dugongine dugongid genus Rytiodus from the Miocene (Burdigalian–Langhian; 19–14 Ma) deposits of Jabal Zaltan (= Gebel Zelten), Libya, is re-described, considered a valid species differing from Rytiodus capgrandi from the lower Miocene (Aquitanian) of the Aquitaine Basin (SW France), and named Rytiodus heali. R. heali, together with R. capgrandi and Corystosiren varguezi appear to constitute a taxon of dugongines characterized by broad, mediolaterally compressed, blade-like tusks with enamel mainly on the medial side, and a modified nasal process of the premaxilla. They are regarded as specialized seagrass feeders, using their tusks in excavation of seagrass rhizomes. Rytiodus lived sympatrically with the generalist small-tusked halitheriine dugongid genus Metaxytherium.

Microsites play an important role for seedling survival in the seagrass Amphibolis antarctica

The contribution of recruitment to local population dynamics of plants is limited by production of seeds or availability of suitable sites for establishment of seedlings. Viviparous seedlings of the seagrass Amphibolis antarctica have been observed in great numbers within gaps in meadows of other seagrass species. We conducted a field experiment to assess the extent to which production of viviparous seedlings or availability of suitable sites limits recruitment of A. antarctica into gaps in seagrass meadows. At each of six gaps, seedlings of A. antarctica were transplanted at two densities onto three substrata; sand, seagrass matte (exposed rhizomes and sheath material) and established seagrass meadow. Seedling survival was tracked over 2 months and seedling survival half-lives were compared among treatments. Planting density had no effect on total survivorship, suggesting that increased seedling production would not increase recruitment rates. Physical dislodgement of seedlings by wave and current forces was the primary factor impeding successful recruitment. Of the substrata tested, the best potential establishment sites were associated with the matte of dead seagrass rhizome and sheath fibre. Seedlings entangled in seagrass matte fibres required greater force to remove, and we propose that the entangling nature of matte enhances seedling survival and establishment. The force needed to dislodge seedlings from sand was constantly exceeded by the current velocities acting upon seedlings during the study, and we suggest that the 100% loss of seedlings from sand was driven by hydrodynamic forcing. Seedling loss in the seagrass meadow plots was accelerated by contact with adult seagrass, which increased the rate of seedling dislodgement through the sweeping of leaves across the substratum. Recruitment in the population of A. antarctica examined in this study was limited by the availability of suitable establishment sites, such as those provided by the seagrass matte substratum along the fringe of meadow gaps. The ability of A. antarctica seedlings to recruit to seagrass meadow gaps allows local population persistence of this species in areas dominated by other seagrass species.

Proximate nutrient analyses of four species of submerged aquatic vegetation consumed by Florida manatee (Trichechus manatus latirostris) compared to romaine lettuce (Lactuca sativa var. longifolia).

Free-ranging Florida manatees (Trichechus manatus latirostris) consume a variety of sea grasses and algae. This study compared the dry matter (DM) content, proximate nutrients (crude protein [CP], ether-extracted crude fat [EE], nonfiber carbohydrate [NFC], and ash), and the calculated digestible energy (DE) of sea grasses (Thalassia testudinum, Halodule wrightii, and Syringodium filiforme) collected in spring, summer, and winter, and an alga (Chara sp.) with those of romaine lettuce (Lactuca sativa var. longifolia). Neutral-detergent fiber (NDF), acid-detergent fiber (ADF), and lignin (L) measured after ash-extraction were also compared. Results of statistical tests (C = 0.01) revealed DM content was higher in aquatic vegetation than in lettuce (P = 0.0001), but NDF and ADF were up to threefold greater, EE (P = 0.00001) and CP (P = 0.00001) were 2-9 times less, and NFC (P = 0.0001) was 2-6 times lower in sea grass than in lettuce, on a DM basis. Chara was lower in NDF, ADF, L, EE, CP, and NFC relative to lettuce on a DM basis. Ash content (DM basis) was higher (P = 0.0001), and DE was 2-6 times lower in aquatic vegetation than in lettuce. Sea grass rhizomes had lower L and higher ash contents (DM basis) than sea grass leaves. Based on the nutrient analyses, romaine lettuce and sea grasses are not equivalent forages, which suggests that the current diet of captive Florida manatees should be reassessed.

The food of the miosirenAnomotherium langenwieschei (Siegfried) — indirect proof of seaweed or seagrass by xenomorphic oyster fixation structures in the Upper Oligocene (Neogene) of the Doberg, Bünde (NW Germany) and comparisons to modernDugong dugon (Müller) feeding strategies

The palaeoecology of two large oyster species of the Doberg (North Germany) are described. The Upper Oligocene large oysterPycnodonte (Crenostrea) callifera (Lamarck 1819) has unusual fixation structures in the form of large elongated negative impressions on the right and convex xenomorphic structures on the left valve. The heavy oysters ofP. (C.)callifera must have already been attached in their larval stage to the base of stapes of macro algae on which they sometimes built colonies with several individuals. Balanids and serpulids on the algae were overgrown. On the second medium-sized and flat oyster speciesOstrea (Ostrea) cf.digitalina (Eichwald 1830) of the Upper Oligocene, different xenomorphic structures are present. These are thin elongated fixation negatives with concentric rings. The radial sculptured oysters must have been attached onto the Upper Oligocene seagrass rhizomes, such as recentOstrea species do in the Mediterranean Sea.Ostrea started the attachment in the larval stage on the roots in between sea grass meadows which covered the shallow coastal shore seafloor. Both plant groups, seagrass and brown macroalgae, indicate very shallow and moderately warm water conditions and were important food plants of the Oligocene miosirenAnomotherium langenwieschei (Siegfried 1965) that was found at the Doberg as a nearly complete skeleton. Another skeleton of this species was found within the “Middle Oliogocene, uppermost Rupelian” in the Kassel Bay at Schaumburg-Hoof; and finally a single massive rib find of late Lower Oligocene age (Bohlener Schichten) proves for the first time this miosiren in the Leipzig Bay was present during the latest Rupelian. An overlapping of both species can be proved at this time (uppermost Rupelian) with finds of both north of the Rhenish Massif, and in the Leipzig Bay. In Espenhain both species occur in the Bohlener Schichten. Here the only known articulated skeleton remain ofHalitherium schinzii (Kaup 1838) can be reported. This eosirenia was possibly hunted by a large shark, most probablyIsurus of which several teeth were found in-between the disarticulated skeleton. At the minimum it was strongly scavenged, which is indicated by many shark bite scratch marks found all over the ribs and vertebrae. The north Rhenish Massif and western Kassel Bay was different with its Upper Oligocene carbonate environment; only here miosirenia found seagrass as their main food source. In the other siliciclastic dominated Cologne Bay and Leipzig Bay the eosireniaHalitherium could have fed during the Rupelian on seaweeds, but possibly also on other food sources.

POPULATION DENSITIES AND DIVERSITIES OF EPIPHYTAL FORAMINIFERA ON NEARSHORE SUBSTRATES, NEVIS, WEST INDIES

Research Article| July 01, 2007 POPULATION DENSITIES AND DIVERSITIES OF EPIPHYTAL FORAMINIFERA ON NEARSHORE SUBSTRATES, NEVIS, WEST INDIES Brent Wilson; Brent Wilson 1 Petroleum Geoscience Unit, Department of Chemical Engineering, The University of the West Indies, St. Augustine, Trinidad, West Indies 1Correspondence author. E-mail: bwilson@eng.uwi.tt Search for other works by this author on: GSW Google Scholar Ann Ramsook Ann Ramsook Petroleum Geoscience Unit, Department of Chemical Engineering, The University of the West Indies, St. Augustine, Trinidad, West Indies 2Present address: Petroleum Company of Trinidad and Tobago Limited, Pointe-a-Pierre, Trinidad, West Indies. Search for other works by this author on: GSW Google Scholar Author and Article Information Brent Wilson 1 Petroleum Geoscience Unit, Department of Chemical Engineering, The University of the West Indies, St. Augustine, Trinidad, West Indies Ann Ramsook 2Present address: Petroleum Company of Trinidad and Tobago Limited, Pointe-a-Pierre, Trinidad, West Indies. Petroleum Geoscience Unit, Department of Chemical Engineering, The University of the West Indies, St. Augustine, Trinidad, West Indies 1Correspondence author. E-mail: bwilson@eng.uwi.tt Publisher: Cushman Foundation for Foraminiferal Research Received: 30 Dec 2005 Accepted: 17 Nov 2006 First Online: 03 Mar 2017 Online ISSN: 1943-264X Print ISSN: 0096-1191 © 2007 Journal of Foraminiferal Research Journal of Foraminiferal Research (2007) 37 (3): 213–222. https://doi.org/10.2113/gsjfr.37.3.213 Article history Received: 30 Dec 2005 Accepted: 17 Nov 2006 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Brent Wilson, Ann Ramsook; POPULATION DENSITIES AND DIVERSITIES OF EPIPHYTAL FORAMINIFERA ON NEARSHORE SUBSTRATES, NEVIS, WEST INDIES. Journal of Foraminiferal Research 2007;; 37 (3): 213–222. doi: https://doi.org/10.2113/gsjfr.37.3.213 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search Abstract Foraminiferal population densities and diversities were monitored on calcareous algae and seagrass in two Caribbean bays, one of which has been polluted by a leaking septic tank, and samples were collected monthly over a year-long period. Population densities on seagrass blades were measured using the mass of dried leaves. On other substrates, population densities were computed as the number of foraminifera per gram of detritus (diatom frustrules, sand, particulate organic matter) washed from the plants. Densities on the heads (capitulae) of the alga Penicillus capitatus in both bays were three times higher than those on either the alga Halimeda opuntia or on exposed seagrass (Syringodium filiforme, Thalassia testinudum) rhizomes and basal leaf bosses. The input of organic matter into one bay may have impacted the assemblage species composition, but it did not affect population densities. The short life span of P. capitatus, coupled with the more dense populations it supports, implies that assemblages on this alga may contribute proportionally more foraminiferal tests to the sediment than do those on other plants.Population dynamics showed that entire foraminiferal communities on all plants fluctuated independently of one another, whether on different plants in the same bay or on the same plants in different bays. This suggests that nearshore foraminifera are patchily distributed and that the populations in the patches wax and wane independently. Population diversities fluctuated from month to month and were significantly higher in the polluted bay. However, monthly diversities and population densities were not correlated. Species dominance was greater in the windward, unpolluted bay. Differences in dominance within each bay suggest that Penicillus capitatus capitulae support a pioneering foraminiferal community, whereas long-lived seagrass rhizomes bear a climax community. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Use of tusks in feeding by dugongid sirenians: Observations and tests of hypotheses

Most living and fossil sea cows of the subfamily Dugonginae (Dugongidae, Sirenia, Mammalia) are characterized by large upper incisor tusks, which are thought to play an important role (at least primitively) in feeding on seagrass rhizomes. Testing this hypothesis is difficult, because the only extant tusked sirenian (Dugong dugon) is morphologically and perhaps behaviorally aberrant. The tests attempted here involve examination of stomach contents of wild Recent dugongs, experiments using plastic replicas of diverse tusks to harvest seagrasses, gross anatomical observations on tusks and skulls, measurements of tusk tip geometry, and observations of microwear on tusks. We conclude that (a) male D. dugon (with erupted tusks) do not consume more rhizomes than females (without erupted tusks); (b) the tusks do not play a significant role in feeding in the modern dugong; (c) larger, more bladelike tusks are more effective at harvesting rhizomes, but the effect of shape was not experimentally separated from the effect of exposed tusk length; (d) some fossil dugongines show apparent cranial adaptations for downward and backward cutting motions of their large, bladelike tusks; (e) geometry of wear surfaces is consistent with use of at least the more bladelike tusks as cutting instruments; (f) preliminary observations of microwear in D. dugon do not indicate more than occasional use of the tusks in purposeful harvesting of rhizomes, and then only opportunistically by large adult males. The hypothesis of such tusk use by extinct dugongines (in contrast to the living species) is so far corroborated, but available data and tests do not suffice to establish this conclusively.

Guilds among epiphytal foraminifera on fibrous substrates, Nevis, West Indies

The nearshore foraminifera of the oligotrophic Caribbean region are predominantly epiphytal, living on calcareous algae and seagrasses. However, their community ecology (interactions between and associations among species) is little understood. Cluster analysis is used here to identify guilds among the epiphytal foraminifera, a guild being a group of species that forms an arena of intense competition within which species' niches overlap considerably in habitat, time and food. Samples were collected monthly between September 1994 and August 1995 from (a) calcareous algae and (b) seagrass rhizomes and leaf bosses from two bays around Nevis, northern Lesser Antilles. One bay was impacted by organic enrichment from a leaking septic tank. Data from both bays were combined to form a metapopulation, analysis of which was conducted using common species (i.e., those that formed > 1% of the recovery from any substrate in either bay). Q-mode cluster analysis using populations on all substrates of common species clearly separated the two bays, despite sampling of the same substrate in both, indicating that the bays occupy different biofacies. However, Q-mode analysis did not separate the different substrates in the individual bays. R-mode cluster analysis of the two-bay metapopulation based on common species revealed three clusters that are interpreted as guilds: Guild I A higher-energy guild intolerant of nutrient enrichment. Guild II A guild of rapidly-reproducing opportunists on short-lived substrates. Guild III A lower-energy guild tolerant of nutrient enrichment. These guilds are not limited to any one bay, but vary in proportion between the two, Guild I being most prolific in the virtually pristine back-reef bay on the windward side of the island, and Guilds II and III forming a greater proportion of the epiphytal foraminiferal fauna in the bay impacted by lower-energy waves and a flux of organic matter. Guild II shows a preference for the bushy capitulae of the alga Penicillus capitatus. In cross-correlation of 12-month time-series for the three guilds, the virtually pristine bay showed that they bloomed sequentially, at intervals of 4 months. The recognition of guilds clears the way for improved understanding of the foraminiferal community ecology of nearshore areas. Nearshore sediments in the Caribbean yield primarily foraminifera washed from phytal substrates. The palaeoecology of these assemblages can now be interpreted with greater confidence.

Utilization of DOC from seagrass rhizomes by sediment bacteria: 13C-tracer experiments and modeling

Seagrasses are widely recognized as contributing to net ecosystem primary production and to supporting heterotrophy in estuarine systems. We investigated the linkage between seagrass (Thalassia testudinum) rhizosphere carbon exudation and sediment bacteria. In microcosms, we sim- ulated summer conditions and enriched the water column DIC (dissolved inorganic carbon) pool with 13 C, then followed the tracer into the sediment porewater DOC (dissolved organic carbon) and the bacterial biomarkers (phospholipid fatty acids, PLFAs). Subsequently, we developed an inverse analysis of the seagrass microcosm system and calculated the flux of carbon between biological and geochemical compartments. After 18 d, the bacterial pool was enriched by about Δ +4‰, while the DOC pool was enriched by about Δ +50 to +60‰. We estimate that about 15 to 30% of gross primary production was exuded from the root/rhizome and that this accounts for about 41 to 61% of the car- bon required by sediment bacteria. Mineralization of detrital seagrass leaf material or refractory sea- grass DOC rhizodeposition may account for the other 38 to 59% of the bacterial carbon demand. We suggest that the sediment bacteria in the seagrass rhizosphere rapidly utilize labile DOC and, conse- quently, build up 13 C label in the refractory DOC pool. Our results conclusively show a direct linkage between seagrass carbon exudation and sediment biogeochemical processes.

Changes in nutrient content and stable isotope ratios of C and N during decomposition of seagrasses and mangrove leaves along a nutrient availability gradient in Florida Bay, USA

The decomposition of the mangrove Rhizophora mangle and the seagrass Thalassia testudinum was examined using litterbags along a natural gradient in nutrient availability. Seagrass leaves had a higher fraction of their biomass in the labile pool (57%), compared to mangrove leaves (36%) and seagrass rhizomes (29%); the overall decomposition rates of the starting material reflected the fractionation into labile and refractory components. There was no relationship between the N or P content of the starting material and the decomposition rate. Nutrient availability had no influence on decomposition rate, and mass was lost at the same rate from litterbags that were buried in the sediment and litterbags that were left on the sediment surface. The dynamics of N and P content during decomposition varied as a function of starting material and burial state. N content of decomposing mangrove leaves increased, but seagrass rhizomes decreased in N content during decomposition while there was no change in seagrass leaf N content. These same general patterns held for P content, but buried seagrass leaves increased in P content while surficial leaves decreased. δ13C and δ15N changed by as much as 2‰ during decomposition.

Near infrared spectroscopy as a rapid and inexpensive means of dietary analysis for the marine herbivore, dugong Dugong dugon

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 257:259-266 (2003) - doi:10.3354/meps257259 Near infrared spectroscopy as a rapid and inexpensive means of dietary analysis for the marine herbivore, dugong Dugong dugon Jessica André, Ivan R. Lawler* School of Tropical Environment Studies and Geography, James Cook University, Townsville, Queensland 4811, Australia *Corresponding author. Email: ivan.lawler@jcu.edu.au ABSTRACT: The objective of this study was to evaluate the potential of near infrared reflectance spectroscopy (NIRS) to estimate the botanical composition of seagrass mixtures in the stomach contents of dugongs more rapidly and cost-effectively than by conventional means. NIRS estimation of dietary composition is achieved by developing calibration equations that relate NIR spectra of samples to laboratory-derived values for botanical composition. Once calibration equations have been developed, these characteristics can be estimated for further samples from their spectra alone. We developed calibration equations using samples from the stomachs of 26 dugongs (from a total data set of 128 dugongs) and validated them against a further set of 14 stomach samples. Nine dietary components were identified, 5 of which made up less than 5% of the total diet. Acceptable calibrations were obtained for the major components of dugong diets: seagrass rhizomes (pooled across all species) and the leaves of the seagrasses Thalassia hemprichii, Syringodium isoetifolium and Cymodocea species. We did not attain satisfactory calibrations for minor (<10%) dietary components. NIRS is a valid method for obtaining rapid information on the main components of the dugong diet. With larger calibration sets and fresh samples it should also be able to provide information on minor dietary components. NIRS is applicable to dietary studies of marine herbivores and should thus be of value to marine ecologists generally. KEY WORDS: Near-infrared spectroscopy · Dietary analysis · Herbivory · Dugong · Seagrass Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 257. Online publication date: August 07, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Role of decomposition of mangrove and seagrass detritus in sediment carbon and nitrogen cycling in a tropical mangrove forest

The elemental composition and in situ decomposition of detritus of Rhizophora apiculata and Enhalus acoroides were studied in mangrove and seagrass bed sediments in the Bangrong man- grove, Phuket, Thailand, and compared with controlled laboratory flux incubations. At the field site detritus was buried in litter-boxes in the sediments and changes in particulate organic carbon and nitrogen in detritus and sediments were followed for up to 2 mo. In the flux incubations the sediments were amended with mangrove and seagrass leaves and rhizomes, and the exchange of oxygen, CO2, dissolved organic carbon (DOC) and inorganic nitrogen was measured across the sediment-water interface for 43 d. The decomposition of seagrass leaves was rapid both in situ and in the laboratory, whereas about 40% of the mangrove leaves remained after 43 d, and no decomposition could be detected for the seagrass rhizome detritus. There was an immediate increase in sediment oxygen uptake (SOU) in the seagrass sediments followed by an increase in CO2 production after the addition of detritus, whereas the SOU remained low in the mangrove sediments. The C:N ratios decreased in the carbon-rich mangrove leaves and seagrass rhizome detritus, but increased in the less carbon-rich seagrass leaves during the decomposition. The decrease in C:N ratio was attributed to colonization by bacteria which incorporated nitrogen from the overlying water column or from the indigenous particulate organic nitrogen pool in the sediments. The mineralised carbon from the plant detritus was recovered as CO2, whereas no accumulation or release of DOC was found. The effect of amend- ment with mangrove detritus on the nitrogen fluxes was minor, whereas the uptake of nitrate and release of ammonium was enhanced with the seagrass leaves. About 32 to 36% of the mineralised nitrogen from the seagrass leaves was released across the sediment-water interface, where it became available for primary producers or exported to adjacent ecosystems

Effects of sea urchin grazing on seagrass (Thalassodendron ciliatum) beds of a Kenyan lagoon

We present the results of experimental and descriptive field studies on the effects of dense sea urchin aggregations on seagrass beds in the Mombasa lagoon (Kenya). The study area was dominated by the slow-growing seagrass Thalassodendron ciliatum (49.6% cover), and supported an average sea urchin density of 1.6 m -2 , mostly Tripneustes gratilla (90%). In the T. ciliatum meadows, 39% of the cover was heavily grazed by the sea urchins (more than 75% dead shoots), 23.4% was moderately grazed (more than 50% dead shoots) and 38.5% was slightly grazed (19.8% dead shoots). We observed 5 aggregations (fronts) of T. gratilla in the study area (5000 m 2 ), 4 of these within the T. ciliatum meadows. These aggregations were linear in structure, with mean densities of 10.4 m -2 , and left in their wake a 'trailing edge' area of defoliated seagrass rhizomes (85% dead shoots). Graz- ing rates were measured in 2 ways: marked permanent quadrats along the fronts, and sea urchin addition experiments. The first method produced grazing rates of 1.8 ± 0.43 shoots m -2 d -1 , and the second produced slightly higher values of 5 ± 0.86 shoots m -2 d -1 . New shoot recruitment was esti- mated from the marked permanent quadrats in the fronts as 0.32 shoots m -2 d -1 . Simple models indi- cated that the return interval (i.e. the average frequency of the passage of sea urchin fronts through a seagrass patch) for the 'sea urchin grazing fronts' was 99 or 34 mo, depending on the method used, and that T. ciliatum recovery time was 44 mo. We conclude that the sea urchin aggregations observed in the Mombasa lagoon control T. ciliatum density by grazing its exposed apical tips.