Seagrass Blades Research Articles

Diversity of Assimilatory Nitrate Reductase Genes From Plankton and Epiphytes Associated with a Seagrass Bed

Assimilatory nitrate reductase gene fragments were isolated from epiphytes and plankton associated with seagrass blades collected from Tampa Bay, Florida, USA. Nitrate reductase genes from diatoms (NR) and heterotrophic bacteria (nasA) were amplified by polymerase chain reaction (PCR) using two sets of degenerate primers. A total of 129 NR and 75 nasA clones from four clone libraries, two from each of epiphytic and planktonic components, were sequenced and aligned. In addition, genomic DNA sequences for the NR fragment were obtained from Skeletonema costatum and Thalassiosira weissflogii diatom cultures. Rarefaction analysis with an operational taxonomic unit cut-off of 6% indicated that diversity of the NR and nasA clone libraries were similar, and that sequencing of the clone libraries was not yet saturated. Phylogenetic analysis indicated that 121 of the 129 NR clones sequenced were similar to diatom sequences. Of the eight non-diatom sequences, four were most closely related to the sequence of Chlorella vulgaris. Introns were found in 8% of the Tampa Bay NR sequences; introns were also observed in S. costatum, but not T. weissflogii. Introns from within the same clone library exhibited close similarity in nucleotide sequence, position and length; the corresponding exon sequences were unique. Introns from within the same component were similar in position and length, but not in nucleotide sequence. These findings raise questions about the function of introns, and mechanisms or time evolution of intron formation. A large cluster of 14 of the 75 nasA sequences was similar to sequences from Vibrio species; other sequences were closely related to sequences from Alteromonas, alpha-proteobacteria and Marinomonas-like species. Biogeographically consistent patterns were observed for the nasA Tampa Bay sequences compared with sequences from other locations: for example, Tampa Bay sequences were similar to those from the South Atlantic Bight, but not the Barents Sea. The Tampa Bay NR clone libraries contained sequences that exhibited phylogenetic similarity with sequences from coastal New Jersey and Monterey Bay, USA. For both NR and nasA, the sequences formed phylogenetic clusters containing nitrate reductase gene fragments that were common to both plankton and epiphyte components, and sequences that were unique to just one component. The implication that some organisms may be differentially represented in epiphytic versus planktonic components of the community suggests that local environmental conditions may have ramifications for regulation of nitrate assimilation processes, community composition, and ecosystem function.

Temporal and spatial macrofaunal community changes along a salinity gradient in seagrass meadows of Akkeshi-ko estuary and Akkeshi Bay, northern Japan

Temporal and spatial variation of the macrofaunal community was investigated in seagrass meadows in Akkeshi-ko estuary and coastal area of Akkeshi Bay, northern Japan. We specifically addressed the question of how the salinity gradient in seagrass meadows affects the species richness, abundance and similarity of faunal groups classified based on the degree of association with the seagrasses, i.e. highly motile species that drift in the water column among seagrass blades (drift-fauna, DF group) and less motile species that are tightly associated with seagrass substrates (seagrass-associated fauna, SA group). A total of 70 species were collected semi-quantitatively using an epibenthic sledge, among which more than one third of the species were captured in all areas, and a quarter of species only in the marine area. Significant spatial variation in species richness, as well as a positive relationship between salinity and species richness was found for most sampling occasions and for both functional groups. Whereas, relationship between salinity and abundance of macrofauna was not clear although significant time and site interactions were found for both functional groups. Patterns of similarity of assemblages varied between the functional groups: clear differences by sampling sites were discerned for DF group but not for SA group. These results provided evidence that the macrofaunal community structures in seagrass beds varied with the salinity gradient, but the pattern differed with time and between functional groups, possibly due to the effect of biotic and abiotic factors that also changed with salinity.

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.

Feeding preferences of two seagrass grazing monacanthid fishes

Two seagrass grazing fishes, Meuschenia freycineti and Meuschenia trachylepis (Monacanthidae), were offered three choices of Posidonia australis seagrass blades of different epiphyte coverage and leaf age to determine whether these fishes exhibit a preference for epiphyte‐covered seagrass blades. Both species removed significantly more biomass of the epiphyte‐covered blades than of the two other blade types in multiple‐choice tests. This clear preference for epiphyte‐covered seagrass blades results in a preferred removal of older blades within the seagrass shoot of P. australis.

Variability in drift macroalgal abundance in relation to biotic and abiotic factors in two seagrass dominated estuaries in the Western Gulf of Mexico

We examined the spatial and temporal variability in drift macroalgal abundance in two seagrass dominated estuarine systems on the Texas coast: Redfish Bay (in the Copano-Aransas Estuary) and Lower Laguna Madre. Measurements of benthic macroalgal variability were made in conjunction with a suite of biotic (seagrass biomass, percent cover, blade width and length, shoot density, epiphyte biomass, seagrass blade C:N ratios, and drift macroalgal abundance and composition) and abiotic (inorganic nitrogen and phosphorus concentrations, chlorophyll a, total suspended solids, light attenuation, salinity, temperature, total organic carbon and porewater NH4 + ) indicators. All parameters were measured at 30 sites within each estuary semiannually from July 2002 to February 2004. Principal components analysis (PCA) was used to examine relationships between drift macroalgal abundance and biotic and abiotic parameters. In both Redfish Bay and Lower Laguna Madre, drift macroalgal distribution was widespread, and during three of four sampling periods, abundance was equal to aboveground biomass of Thalassia testudinum, the dominant seagrass. Drift macroalgal abundance was highly variable within sites, between sites, and between seasons in both estuaries. No significant differences in drift macroalgal abundance were found between Redfish Bay and Lower Laguna Madre. In Redfish Bay, drift macroalgae (90.1 6 10.2 g m 22 ) tended to accumulate in bare patches within seagrass beds. In Lower Laguna Madre, drift macroalgae (72.7 6 10.7 g m 22 ) tended to accumulate in areas of dense seagrass cover rather than in bare areas. We found no relationship between drift macroalgal abundance and low (, 2 mM) water column nutrient concentrations, and although several of our measured parameters were related to drift macroalgal abundance, none alone sufficiently explained the variability in abundance noted between the two estuarine systems. The contrasting patterns of macroalgal accumulation between Redfish Bay and Lower Laguna Madre likely reflect differences in water circulation characteristics between the two regions as dictated by local physiography, including the shape and orientation of the lagoons, with seasonal variations in macroalgal abundance related to changes in freshwater inflow and nutrient loading.

Differential element assimilation by sea urchins Paracentrotus lividus in seagrass beds: implications for trophic interactions

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 306:125-131 (2006) - doi:10.3354/meps306125 Differential element assimilation by sea urchins Paracentrotus lividus in seagrass beds: implications for trophic interactions F. Tomas1,3,*, D. Álvarez-Cascos1, X. Turon2, J. Romero1 1Departament d’Ecologia, and 2Departament de Biologia Animal (Invertebrats), Universitat de Barcelona, Avenida Diagonal 645, 08028 Barcelona, Spain3Present address: Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, California 92093-0202, USA *Email: ftomasnash@ucsd.edu ABSTRACT: Despite increasing evidence that herbivory in seagrass systems is more important than previously considered, many factors regulating seagrass herbivory still need to be elucidated. In this study we evaluate the importance of epiphytes and seagrass blades in sea urchin nutrition using a multiple stable-isotope approach. Our aim is to contribute to the understanding of plant–herbivore interactions in seagrass beds. Stable-isotope ratios of carbon, nitrogen and sulphur of the sea urchin Paracentrotus lividus (Lamarck) were measured and compared to those of the potential food sources (i.e. the seagrass Posidonia oceanica [L.] Delile and its epiphytes) in a temperate seagrass meadow. Epiphytes and seagrass leaves had distinct δ13C (–18.7 vs. –12.8‰, respectively) and δ15N values (+6.4 vs. +3.6‰, respectively), while values for δ34S were closer (+19.4 vs. +17.0‰, respectively). Data from δ13C and δ34S indicated that both food sources contributed in approximately equal proportions (50%) to the bulk organic matter assimilated by Paracentrotus lividus, whereas δ15N measurements showed that approximately 90% of the nitrogen assimilated by the sea urchin is provided by epiphytes. Given the generally low nutritional quality of P. oceanica leaves, the data obtained suggest that epiphyte nitrogen is crucial in regulating the trophic relationships between the herbivore and the seagrass. Thus in P. oceanica meadows, epiphytes, particularly through nitrogen contribution, appear to be an essential component of the diet of important herbivores such as sea urchins. KEY WORDS: Plant–herbivore interactions · Epiphytes · Stable isotopes · Nitrogen · Food quality · Mediterranean · Posidonia oceanica Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 306. Online publication date: January 11, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Effects of habitat heterogeneity in seagrass beds on grazing patterns of parrotfishes

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 303:113-121 (2005) - doi:10.3354/meps303113 Effects of habitat heterogeneity in seagrass beds on grazing patterns of parrotfishes Silvia Maciá1, 3, *, Michael P. Robinson1, 2 1Hofstra University Marine Laboratory, PO Box 90, St. Ann’s Bay, Jamaica, West Indies2Department of Biology, University of Miami, PO Box 249118, Coral Gables, Florida 33124, USA3Present address: Barry University, School of Natural and Health Sciences, 11300 NE 2 Avenue, Miami Shores, Florida 33161, USA *Email: smacia@mail.barry.edu ABSTRACT: Habitat heterogeneity, particularly patchiness in seagrass cover, greatly affects the community dynamics of seagrass ecosystems. Heterogeneity in seagrass habitats can also be caused by unvegetated patches within the otherwise continuous seagrass cover. Blowouts are bare areas with an eroding edge that forms a vertical wall, often with overhanging seagrass roots and rhizomes. Fishes, including parrotfishes, aggregate in these blowouts. These aggregations of herbivorous fishes might influence the structure of the adjacent seagrass habitat. We compared parrotfish Sparisoma spp. grazing patterns at different distances from the edge of blowouts in seagrass beds (mainly Thalassia testudinum) at St. Ann’s Bay, Jamaica, by counting and measuring the number of bite marks on the seagrass blades. The percentage of grazed blades, number of bites per blade, and total area of seagrass removed by grazing all increased with increasing distance from the edge of the blowout. However, the size of the bite marks, which is indicative of the size of the fish that made them, was significantly larger near the blowout than at further distances. Few large bites were found at distances greater than 4 m from the blowout, while small bites were more abundant at distances further from the edge. These data suggest that larger fishes feed in closer proximity to the shelter of the blowouts, while smaller fishes avoid the blowout edge. Both seagrass morphology and parrotfish grazing characteristics were significantly different among the blowouts used in the study, indicating that blowouts in and of themselves increase the structural heterogeneity of seagrass beds. Thus, blowouts affect the structure of seagrass ecosystems directly and indirectly (via their effects on the grazing behavior of parrotfishes). KEY WORDS: Habitat heterogeneity · Grazing · Blowouts · Parrotfishes · Thalassia testudinum · Seagrass Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 303. Online publication date: November 21, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Compensatory effects of boat wake and dredge spoil disposal on assemblages of macroinvertebrates

Estuarine assemblages are exposed to multiple disturbances that overlap in time and space. Along the Atlantic Intracoastal Waterway (east coast, United States), two disturbances that frequently co-occur are the production of wake by boats and the disposal of sediment dredged from boat channels. Boat wake generally coarsens sediments by eroding finer particles while deposition of dredge spoil decreases mean grain size. If previously demonstrated effects of boat wake on infauna are due to coarsening of grain size, deposition of dredge spoil on wake affected sites may, through compensatory effects, prevent an effect of wake from being detected. Epifaunal assemblages associated with seagrass blades that are more likely to be structured by hydrodynamic forces than granulometry may instead be affected by boat wake irrespective of the previous deposition of fine materials. To test these hypotheses, in fauna and epifauna were sampled in patchy seagrass habitat at sites with and without boat wake that were affected by historic deposition of dredge spoil and at sites without wake that had not received dredge spoil. Sediment granulometry and infaunal assemblages differed between sites with and without dredge spoit but not between spoil affected sites differing in exposure to wake. Epifaunal assemblages differed between sites with and without wake irrespective of sediment granulometry. The effect of wake on epifauna was primarily due to lesser abundances of the gastropodBittiolum varium and the slipper limpet,Crepidula fornicata, at wake exposed sites. These results suggest that because of their opposing effects on sediment granulometry, boat-wake and sediment disposal may have compensatory effects on infaunal assemblages. The detection of an effect of wake on epifauna despite the absence of a sedimentological effect of the disturbance shows that ecological impacts do not necessarily mirror physical effects and should be considered separately when adopting strategies of management.

Effects of Houseboats on Organisms of the La Parguera reserve, Puerto Rico

As coastal development increases so too does the number of artificial floating and permanent structures. It has been postulated that because of their size, many houseboats are similar to permanent structures in that they shade a significant portion of the benthos and thereby limit production by benthic flora. On the other hand, these structures can benefit biotic communities by providing sites for attachment of organisms in a substrate-limited environment and both habitat and food sources for fish. In this study, we examined whether houseboats benefit or harm the ecological integrity of a typical seagrass dominated system, at La Parguera, Puerto Rico. We performed a benthic survey to compare the diversity and health of seagrasses under houseboats to that at control locations. Species diversity (0-0.79) varied significantly among sites, but this variability was not attributed to the houseboats. Rather, the variability appeared related to the proximity of the study locations to new development along the shoreline. Average seagrass blade density and length were 52.7 blades/m(-2) and 23.6 cm, respectively. Neither parameter differed between houseboat and control areas; however, both varied significantly among sites. In addition, boat hulls were heavily encrusted with invertebrates. The overall averages of species diversity and richness of sessile organisms on hulls of the houseboats were 1.13 and 4.83, respectively. Fish also utilized these structures. Our results indicate that houseboats did not directly harm the seagrass communities at La Parguera primarily because of sound environmental management of wastes and mooring techniques.

A comparison between fluid shear stress reduction by halophytic plants in Venice Lagoon, Italy and Rustico Bay, Canada—analyses of in situ measurements

A series of in situ experiments on bed stability were carried out at three sites across Venice Lagoon using the benthic annular flume—Sea Carousel. Turbulence measurements were made at a range of flow speeds over different vegetated beds as well as ‘smooth’ muddy beds. The drag induced by the various bed types was estimated using flow deceleration. Bed shear stress was also estimated using three methods, and the results were compared with the bed shear stress as determined over a smooth bed in a laboratory equivalent of Sea Carousel—Lab Carousel. The stress was found to increase with increasing bed roughness and with the addition of vegetation in the form of the sea grasses Cymodocea nodosa and Zostera noltii. The stress was also found to be affected by the bending of the sea grass blades under flow velocities exceeding 0.4 m s −1, the sea grasses became flattened and the shear stress was found to decrease to produce skimming flow. It was concluded that the presence of sea grasses decreases erosion due to (1) stress reduction and (2) stabilization of the bed, thus reduction of the distribution of sea grass beds in Venice Lagoon will likely enhance bed erosion and hence habitat destruction. Stress was also reduced by an increase in levels of turbidity level in the water column.

Simulated herbivory and the dynamics of disease in Thalassia testudinum

An experiment was conducted in a Thalassia testudinum bed in SW Florida to examine the effect of simulated green turtle Chelonia mydas L. herbivory on the intensity of infection by Labyrinthula, which causes wasting disease in seagrass. Four pairs of 4.0 m 2 plots were established at the site, with each pair containing one plot subjected to simulated herbivory and the other serving as an unmanipulated control. Labyrinthula infection appeared abruptly during April, reached maxi- mum levels in May, and decreased to zero by September 2002. In plots subjected to simulated her- bivory, clipped seagrass blades were more likely to be infected than new blades emerging from clipped short shoots. Three months after clipping, disease levels in the new blades were not sig- nificantly different between simulated herbivory and control plots. These results suggest sea turtle herbivory is not likely to reduce disease levels in T. testudinum.

Direct measurements of light attenuation by epiphytes on eelgrass Zostera marina

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 238:73-79 (2002) - doi:10.3354/meps238073 Direct measurements of light attenuation by epiphytes on eelgrass Zostera marina Mark J. Brush*, Scott W. Nixon Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882-1197, USA *E-mail: brush@vims.edu ABSTRACT: Declines in the seagrass Zostera marina L. in estuaries and lagoons have been attributed in part to reductions in irradiance reaching the seagrass blades. Epiphytes growing on Z. marina have the potential to attenuate a large fraction of the light that would otherwise reach the blades. This problem has previously been studied by measuring light penetration through homogenized epiphytic slurries or through glass slides fouled with epiphytes. However, the latter may not represent the natural succession or species composition found on live Z. marina leaves and the former does not preserve the structure of the epiphytic complex. Further, past studies have not measured attenuation across the full range of epiphytic densities found in the field. In this study, we measured light penetration across a wide range of epiphytic densities by holding scraped and unscraped Z. marina blades over a submerged light sensor. Results compared well with past studies at low epiphyte densities, with strong reductions in light penetration as density increased. However, at higher densities, penetration leveled off to a relatively constant value as the epiphytes floated out from the edges of the blade. Studies using slurries did not capture this phenomenon and thus predicted decreasing penetration down to 0%. KEY WORDS: Epiphytes · Light attenuation · Seagrass · Zostera marina Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 238. Online publication date: August 08, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

The influence of freshwater runoff on biomass, morphometrics, and production of Thalassia testudinum

Efforts to restore more natural freshwater flows in South Florida will impact Biscayne Bay. In order to evaluate possible effects of decreased freshwater discharge on the seagrass Thalassia testudinum, we determined the biomass, density, morphometrics (width, length, number of blades per shoot) and production of T. testudinum twice a year for 2 year at sites exposed to varying degrees of freshwater runoff. Responses to freshwater discharge varied between the sampling years. The only morphometric variable to be influenced by freshwater runoff in both years was blade width with width of seagrass blades being less at sites influenced by freshwater runoff than at sites with limited influence of freshwater runoff. In 1996, no other parameters differed among the three freshwater conditions considered; canal discharge, sheet-flow runoff, and limited freshwater runoff. In addition, all measured parameters were greater in summer (wet season) than in winter (dry season) in 1996. In 1997, biomass, shoot weight, shoot production, and areal shoot production all were greater at sites on the eastern side of the bay that experience limited influence from freshwater runoff compared to sites on the western side of the bay that experience large amounts of freshwater runoff from sheet-flow and canal discharge. In 1997, only length of seagrass showed a significant increase from winter to summer. Factors thought to be responsible for these interannual differences are winter temperatures and seasonal rainfall amounts. The winter of 1996 was much colder than the winter of 1997, and 1997 experienced an unusually rainy dry season thus increasing the amount of time during the year that freshwater runoff would be influencing sites on the western side of the bay. Based on these results, reduced freshwater inflow to Biscayne Bay should have a positive effect on T. testudinum provided detrimental hypersaline conditions do not occur.

Herbivorous fish assemblages and herbivory pressure on Laamu Atoll, Republic of Maldives

While herbivory is recognized as a fundamental process structuring coral reef communities, herbivore assemblages and processes are poorly described for reefs in the Indian Ocean region. We quantified herbivorous fish assemblage structure (abundance and diversity) in Laamu Atoll, Republic of Maldives, in four reef habitat types: faro reef flats, faro reef slopes, inner and outer atoll reef slopes (20 sites in total). Herbivorous fish assemblages, representing a total of 30 species, grouped strongly by habitat type, with the highest absolute abundance observed on faro reef flats and lowest abundance on inside atoll rim reef slopes. Removal of Thalassia seagrass blades by ambient herbivore assemblages was used in a bioassay to assess relative herbivory pressure among four habitat types (eight sites). Also, at one site a choice herbivory assay was performed to assess herbivore preference among four benthic plants across three depth zones. Relative herbivory, as indicated by Thalassia assays, was highest on inside atoll rim reef slopes and lowest on outside atoll rim reef slopes. Thalassia consumption did not correspond to overall herbivorous fish abundance, but corresponded more closely with parrotfish abundance. In the choice assays, herbivores showed strong preferences among plant types and consumption of most plant types was higher at mid-depth than in the shallow reef flat or deep reef knoll zones.

Abundance, population structure and microhabitat use of compound ascidians in a Fijian seagrass bed, with special reference to Didemnum molle

Six species of compound ascidians found in a Fijian seagrass bed dominated by Syringodium isoetifolium were divided into two groups, each occupying somewhat different microhabitats provided by the seagrass. Didemnum molle and Lissoclinum bistratum, both with algal symbiont Prochloron sp., were abundant in high light microhabitats. D. molle was mostly attach to seagrass blades (maximum colony density: 980m-2), while L. bistratum occurred both on seagrass and sediment surfaces in places with sparse seagrass cover (maximum colony density: 11, 500m-2). Trididemnum clinides also had the symbiont Prochloron sp., but it mostly occupied dark microhabitats such as the sheaths of the seagrass. The other 3 species, Didemnum cuculiferum, D. sp. cf. albopunctatum and Trididemnum discrepans, lacked algal symbionts and were rare, all occupying dark places such as seagrass sheaths in areas with dense seagrass cover. Sympatric ascidians, thus, co-exist in seagrass beds and show a different microhabitat use. Ascidians were not distributed evenly over the area of the seagrass bed, but were concentrated in an area between 30 and 84m from the shore, independent of the distribution of seagrass biomass. In dense seagrass patches, light intensities varied greatly between the top and the basal part of the seagrass, and persistence and stability of seagrass as an attachment substrate were also different between leaf blades and sheaths. Populations of D. molle on the seagrasses included many smaller colonies. There were no colonies as large as those in the population on the more stable nearby rock substrates. The small size of the seagrass blades (1.5mm in diameter), their short lifetime (1.5mo) and their lower persistence and stability as an attachment substrate may explain the small size of the colonies on the seagrass.

Factors influencing the association patterns of Hippolyte zostericola and Palaemonetes intermedius (Decapoda: Natantia) with seagrasses of the Indian River Lagoon, Florida

The ecological role and the association of Hippolyte zostericola (Smith, 1873) (Decapoda: Natantia) with different seagrass species in the Indian River Lagoon (Florida, USA) were investigated through field sampling and the analysis of diet, size–frequency distributions and laboratory experiments. Gut contents suggested that H. zostericola is a mesograzer which may be important in the transfer of primary production to higher trophic levels. Population size–frequency distributions showed a polymodal pattern variable according to the site. Preference experiments indicated that choice of seagrass species is not influenced by the available surface area of seagrass blades, nor by the presence of epiphytic food. Significant responses of the shrimp to the ambient light field, mediated by the seagrass canopy, were detected. A clear negative phototropism was observed for H. zostericola which may be an adaptive response to improve avoidance of visual predators.

Settlement and recruitment of the abalone Haliotis cyclobates Péron, 1816

The settlement preference, distribution and juvenile recruitment distribution of Haliotis cyclobates were investigated in a seagrass meadow in Gulf St Vincent, South Australia, in 1993 and 1994. Samples of hard substratum and seagrass were collected from seagrass patches and open areas and examined for newly settled and 0+ recruits. Hard substrata consisted of small rocks, large bivalve shells and bottles. Twelve newly settled recruits (<3 mm) were found: 11 on seagrass and one on hard substratum. Settlement onto seagrass blades is the first field example of an abalone species settling naturally onto soft substratum. 0+ recruits (4–9 mm) were found from March to October, indicating a single spawning and settlement season. 0+ recruits were found on small isolated patches of hard substratum in open and seagrass areas, suggesting that post-settlement migration may have some influence on recruitment patterns. The results indicate that the early life history of Haliotis cyclobates is adapted for enhancing recruitment into seagrass areas. Settlement onto seagrass blades is different from that observed for other species of abalone, and clarification of the specific settlement cue may contribute to the understanding of abalone settlement behaviour.

Patch dynamics and response to disturbance of the seagrass Zostera novazelandica on intertidal platforms in southern New Zealand

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 189:275-288 (1999) - doi:10.3354/meps189275 Patch dynamics and response to disturbance of the seagrass Zostera novazelandica on intertidal platforms in southern New Zealand Deborah L. Ramage*, David R. Schiel** Marine Ecology Research Group, Zoology Department, University of Canterbury, Private Bag 4800, Christchurch 1, New Zealand *Present address. Zoology Department, University of Queensland, Queensland 4072, Australia **Addressee for correspondence. E-mail: d.schiel@zool.canterbury.ac.nz ABSTRACT: We examined the patch dynamics of the intertidal seagrass Zostera novazelandica on 2 reef platforms in order to understand the processes governing the establishment, maintenance and mortality of patches. The size distribution of patches at 3 tidal heights (low, mid and high shore) was assessed. Eighty patches, ranging in initial size from 0.1 to 2.4 m2 surface area, were tagged and video image analysis was used bi-monthly for 14 mo to calculate rates of expansion and contraction of these patches. Permanently marked 150 m2 areas of reef were monitored monthly to record patch recruitment and mortality. Initially, 75% of patches were <0.5 m2. All patches decreased in size during winter, probably due to increased wave action, and expanded during spring and summer. The proportional expansion and contraction of patches was independent of initial patch size. At the end of the study the size distribution of patches was similar to the initial distribution. Patch mortality was restricted to those <0.4 m2, of which 60% disappeared during the study. Larger patches suffered partial mortality through fragmentation. No large patches were formed through the amalgamation of smaller patches. Seedlings recruited into small sediment pockets in tidepools during spring, but few survived through summer because of removal by wave action. Experimental perturbation of patches resulted in increased erosion followed by decreased growth rates and, in many small patches, mortality. Removing only seagrass blades, however, resulted in increased production of new shoots relative to controls. Overall, seagrass patches are susceptible to disturbance, successful recruitment by seedlings may be rare or at least episodic, and populations are probably long-lived and depend on slow vegetative growth for maintenance and expansion. KEY WORDS: Seagrass · Patch dynamics · Disturbance · Zostera novazelandica · Intertidal · New Zealand Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 189. Publication date: November 26, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Microalgae on seagrass mimics: Does epiphyte community structure differ from live seagrasses?

The role of seagrasses in regulating epiphytes is a question of central importance for understanding structuring processes in seagrass communities. This study tests the hypothesis that seagrasses are not simply bare substrata for microalgal attachment, but rather influence community composition by altering competitive interactions between different microalgal groups. The effects of wave exposure, depth, seagrass species and seagrass type (mimic vs. live blades) on eelgrass ( Zostera marina L.) and shoalgrass ( Halodule wrightii Ascher) epiphyte community structure were examined using manipulative field experiments. Relative abundances of major microalgal groups were determined using high-performance liquid chromatographic measurements of diagnostic photopigments. Exposure to wave energy, depth, and seagrass species did not affect epiphyte total biomass. However, epiphyte biomass was significantly greater on live than mimic blades. Diatom biomass was higher under conditions of low wave energy, in deep habitats and on mimic blades. Cyanobacterial biomass was higher in high energy habitats and on live seagrass blades. Although diatoms had a significantly higher biomass on mimic blades, their biomass contribution relative to cyanobacteria was higher on live seagrass blades. The differences in epiphyte community structure on live vs. mimic seagrass blades suggest that competitive interactions between seagrass and epiphytes may result in selection against cyanobacteria or for diatoms. Another possibility is that seagrasses modify the microenvironment on blade surfaces in a way that alters the outcome of competitive interactions between major algal groups (i.e., diatoms and cyanobacteria).

Regrowth of the seagrass Thalassia testudinum into propeller scars

Regrowth of turtle grass, Thalassia testudinum Banks ex Konig, into existing propeller scars and artificial cuts was studied in a mangal estuary located in Tampa Bay, Florida. Sediments from scars and cuts and adjacent grass beds were not significantly different in relation to particle size distribution and levels of calcium carbonate. Significantly lower concentrations of total organic matter and extractable ammonium but not phosphate were detected in scars. Increases in ammonium levels coincided with the expansion of T. testudinum into a propeller scar. Seagrass blade morphology and productivity did not significantly differ in short shoots growing along the edges of scars or cuts relative to those in adjacent seagrass beds. Rhizome architectural studies revealed that apical meristems were few in number (19 to 38% of rhizomes) and randomly orientated in undisturbed grass beds (31 to 53% oriented toward center). In contrast, a greater percentage of apical meristems (78 to 88%) along the edges and in scars or cuts were directed towards the center. Full regrowth required an average of 3.5 to 4.1 years in existing propeller scars and could take up to 7.6 years in artificial cuts. The lack of changes in shoot productivity and limited production of rhizome meristems in T. testudinum result in slow regrowth in propeller cuts. The management implication is that turtle grass meadows will show long-term damage from propeller scars if not protected.