Seagrass

Differences in fish community structure between different estuaries, lagoons and bays can be very large, and generalisations are complicated by the use of a wide variety of sampling methods. In the present study, fish communities of subtidal seagrass beds and sandy seabeds in 13 marine embayments of a single Caribbean island were therefore sampled using a uniform method. The objective of the study was to determine whether the seagrass and sandy seabed habitats of various embayments are characterised by typical fish assemblages which differ in terms of taxa (species, families), size classes (life stages) and functional groups (ecological species groups, feeding time and diet). This was linked to the hypothesis that differences in fish assemblages between habitats in different embayments are larger at taxonomic levels than at the level of functional groups. A second objective was to determine the most useful discriminating features between the two habitat types. The above hypothesis was rejected, since differences in fish assemblages from different seagrass and sandy seabed sites did not increase from functional to taxonomic level, but from size class to diet/species to family/feeding time to ecological species group. However, the seagrass and sandy seabed habitats could each be characterised by typical fish assemblages which differed in taxonomical and functional group composition, irrespective of differences in environmental and biotic variables between the embayments in which these habitats were situated. The two habitat types could be best characterised on the basis of fish family, ecological species group, feeding time and size distribution. Seagrass beds mainly harboured nocturnally active nursery species (Haemulidae, Lutjanidae, etc.), whose relative abundance was related to vegetation (mainly seagrass) cover. Sandy seabeds mainly harboured diurnally active bay species (Gerreidae, etc.) whose relative abundance was related to cover of bare sand. Similarities in taxonomical and functional traits of fish species predicted whether they occurred more abundantly in seagrass beds or in sandy seabeds.

Seagrasses represent the unique re-colonization of the marine ecosystem by angiosperms. As their terrestrial relatives, seagrasses are important habitat providers but in contrast, their microbiomes are still poorly known. The microbial community associated with terrestrial plants is intensively studied and plays an important role in plant fitness. The close relation of seagrasses to terrestrial plants suggests a resemblance in survival strategies, including the creation of a microbiome distinct of the surrounding environment. To obtain more knowledge regarding seagrass microbiomes and their intra- and interspecies differentiation, samples of three tropical seagrass species occurring around the island of Curaçao, the invasive Halophila stipulacea and the natives Halodule wrightii and Thalassia testudinum, were collected. Root and leaf-associated microbes were separately analyzed using high throughput Illumina sequencing of the region V5-V7 of the 16S rRNA gene. Sequences were aligned and clustered into Operational Taxonomic Units (OTUs). Results displayed the occurrence of a seagrass-specific microbiome, distinct from that of the surrounding seawater and sediment. The existence of a species and tissue (root/leaf) specific bacterial community and structure was detected, along with a bacterial community that was shared among the seagrasses. OTUs belonging to the shared seagrass community were mostly of the orders rhizobiales. Desulfobacterales was the most abundant order associated with the roots and Rhodobacterales with the leaves of the three seagrass species. Species-specific bacteria are represented mostly by OTUs of the same orders as the common OTUs, along with a few species-specific orders. The high abundant and widespread bacterial OTUs were identified to be mostly associated with sulfur and nitrogen cycling, which point towards the importance of these processes in seagrass fitness.

The Spaanse Water is a relatively turbid, 3.19 km2 inland bay of virtually oceanic salinities and contains the largest seagrass, algal and mangrove areas of the Curaçao Underwater Park. During 1989 and 1990, a quantitative community assessment of the larger attached flora and fauna of the seagrass and algal meadows of the bay was conducted at 151 6 m2 stations using a quadrat sampling technique.

A total of 13 different assemblages were distinguished. Shallow assemblages were dominated by Thalassia testudinum and Halimeda opuntia. As depth increased and light levels decreased, Thalassia gave way to increased coverages of especially H. opuntia, H. incrassata, Cladophora sp. and Caulerpa verticillata. In areas with significant availability of hard substrate an assemblage characterised (though not dominated) by corals was found at depths of 0–2 m, while sponges were concentrated at depths of about 4 m. The richest assemblages were found in shallow areas with high light levels and where a mix of both hard and soft substrate occurred. Assemblages with the lowest species richness were typically associated with low light intensities, soupy muds or homogeneous sandy sediments of high grain size.

Aims: In the marine biological literature sea-grass beds are generally regarded as being more or less similarly structured, and typically indicated as the sea-grass ecosystem. This assumption regarding their structure is discussed and rejected, as regarded on a worldwide scale sea-grass beds show considerable variation in many qualities to be elucidated in this paper. Study area: Sea-grass beds of the world. Methods: A combination of the formation approach and the phytosociological approach is applied, using genera (instead of species) and some structural vegetation characteristics as variables. The study of sea-grass beds with the two mentioned approaches is elucidated, and the history of their application for the classification is outlined. Results: Six well-defined classes of sea-grass communities are recognised on a global scale (top-down). The classification of the sea-grass communities is presented in the form of an identification key. The descriptions are based on floristic composition, physical structure (stratification, rooting system), relation to the substrate (soft substrate or rock), and degree of permanence (from annual presence to millennia). Conclusions: The assumption that sea-grass communities may be considered as more or less similarly structured ecosystems is an unjustified simplification, as the world’s sea-grass beds show, apart from differences in the species composition, considerable variations in their structure, persistence and performance. They have been accepted as a ‘formation’ in its own right. Seagrass communities are well distinguished from all other plant communities, and show only occasionally some overlap with communities of brackish and continental salt waters. Descriptions of sea-grass communities are generally based on the dominant angiosperm component, and thus present in fact only taxo- or merocoenoses. Consequently, they may show considerable regional variations, and even within the same area, if the algal flora, the fauna and environmental parameters, such as exposition to wave action, salinity, and substrate are being considered. The importance of the proposed classification is that comparisons of sea-grass communities can be made at the right level, and that generalisations should be considered in a more critical manner.

There has been a recent increase in public awareness of environmental issues as the effects of climate change have become ever more noticeable in our daily lives. As we enter a new decade, it becomes useful to review what conservation efforts have worked so far, and take inventory of what efforts will be required for the future. Starting with the constitutional referendum creating the Caribbean Netherlands (Bonaire, St. Eustatius and Saba (BES), the response to conservation challenges of all six Dutch Caribbean islands have varied. Since 2010, the BES islands have seen an overall increase in funding support and conservation actions, and therefore presumably also saw greater improvements when compared to Aruba, Curaçao and Sint Maarten, though clearly not enough (Sanders et al, 2019).

The goal of this Transboundary Species special edition of BioNews is to provide an update on the latest published research results and highlight the need for transboundary protection. These species know no boundaries, and thus move between the Dutch Caribbean islands and beyond. Their protection will require broadscale conservation efforts which cover the entire Caribbean, including the six Dutch Caribbean islands. Collaboration between all six islands is of the utmost importance. This is one of the Dutch Caribbean Nature Alliance’s (DCNA) main goals: working together and sharing skills, knowledge and resources to maintain a solid network and support nature conservation in the entire Dutch Caribbean.

Contents

Introduction - by the Editors.
Address - by M. A. POURIER, Minister of Economic Development.
Address- by Mr. A. R. W. SINT JAGO, Lieutenant Governor of Bonaire.
Illuminated Address to Mr. L. D. GERHARTS- by Mr. J. A. CONNELL, President Caribbean Conservation Association.

I.            FLAMINGOES

J. Rooth: Ecological aspects of the flamingos on Bonaire. Resumen: Aspectos ecológicos de los flamencos en Bonaire.
A. Sprunt: A new Colombian site for the American flamingo (Phoenicopterus ruber).
B. de Boer & J. Rooth: Notes on a visit to Chichiriviche (Venezuela).
I. Kristensen: Discussion on flamingo problems.
 

II.           0IL POLLUTION

J. H. B. W. Elgershuizen & H. A. M. de Kruijf: abstract: Toxic effects of crude oils and dispersant to the stony coral Madracis mirabilis,
J. H. B. W. Elgershuizen, R. P. M. Bak & I. Kristensen: abstract: Oil sediment removal in corals.
H. S. George: Position-determination of oil pollution by aerial photographs and its interpretation.
L. T. Giulini: La contaminación del ambiente marino por los hidrocarburos. Abstract: Marine pollution by oil.
G. P. Canevari: Some remarks regarding the utility and mechanisms of chemical dispersants.
 

III.          REEFS

J. L. Hunt & J. Araud: Coral distribution in the Bahia de Patanemo, Venezuela.
H. G. Gamiochipi: Parques submarinos en el Caribe Mexicano.
C. Noome & I. Kristensen: abstract: Necessity of conservation of slow growing organisms like Black Coral. Resumen: Necesidad de medidas conservacionistas con respecto a organismos de lento crecimiento tales como el Coral Negro.
A. Corsten, I. Corsten-Hulsmans & H. A. M. de Kruijf: abstract: Recolonization experiments of the coral reef fish Gramma Ioreto, the Royal Gramma.
C. den Hartog: The role of seagrasses in shallow waters in the Caribbean.
E. Towle: abstract: Reef communities and human interference: a positive view.
D. Stewart: abstract: Human participation in reef communities.
 

Addresses of the authors.
List of participants.
Netherlands Antilles National Parks Foundation- information.
 

Seagrass beds are highly productive coastal ecosystems providing a large array of ecosystem services including !sheries and carbon sequestration. As seagrasses are known to be highly sensitive to anthropogenic forcing, we evaluated the use of trace metal concentrations in seagrasses as bioindicators for trace metal pollution of coastal regions at both global and local scale. We carried out a meta-analysis based on literature data to provide a global benchmark list for trace metal accumulation in seagrasses, which was lacking in literature. We subsequently carried out a case study at the Caribbean islands of Curaçao and Bonaire to test for local-scale differences in trace metal concentrations in seagrasses, and
internal metal allocation. The benchmark and local study show that trace metal concentrations in seagrass leaves, regardless of the species, can vary over a 100e1000-fold range, and are related to the level of anthropogenic pressure, making seagrasses highly valuable indicators.

google scholar link

Raw data of seagras monitoring on Lac, Bonaire. 

At 49 locations 6 square meter quadrants are investigated. The coverage per seagrass species is measured per quadrant using a 10 by 10 cm grid. 

Observed species:

• Thalassia testudinum (Turtlegrass, Species code: Tt) - IUCN Red List
• Syringodium filiformi (Manatee Grass, Species code Sf) - IUCN Red List
• Halodule beaudettei (Shoal grass, Species code Hy - IUCN Red List
• Halophila stipulacea (Species code: Hs) - IUCN Red List
   
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Seagrasses are found in shallow salty and brackish waters in many parts of the world, from the tropics to the Arctic Circle. Seagrasses are so-named because most species have long green, grass-like leaves.They are often confused with seaweeds, but are actually more closely related to the flowering plants that you see on land. Seagrasses have roots, stems and leaves, and produce flowers and seeds. They evolved around 100 million years ago, and today there are approximately 72 different seagrass species that belong to four major groups. Seagrasses can form dense underwater meadows, some of which are large enough to be seen from space. Although they often receive little attention, they are one of the most productive ecosystems in the world. Seagrasses provide shelter and food to an incredibly diverse community of animals, from tiny invertebrates to large fish, crabs, turtles, marine mammals and birds. Seagrasses provide many important services to people as well, but many seagrasses meadows have been lost because of human activities. Work is ongoing around the world to restore these important ecosystems.

Contents of document:

• Introduction
• What are seagrasses
• Growth and reproduction
• Biodiversity
• Ecosytem benefits
• Threats and conservation
• Seagrass at the Smithsonian
• Additional resources
• More like this

Document retrieved from Smithsonian Ocean portal at 22 March 2018

Shoot organization in seagrasses varies from the unspecialized condition of Enhalus and Posidonia to the highly differentiated shoot systems of plants like Halophila, Thalassodendron and Thalassia. In the former type proliferation of vegetative meristems seems to be an unordered process, whereas in the latter type proliferation can be very ordered. In some examples, e.g. Syringodium, proliferation of rhizomes is not regularized in shoot organization but is largely a consequence of perturbation by the environment. Since production of new organs and proliferation of indeterminate shoot systems is dependent entirely on continually active meristems, with either a limited tendency to form resting meristems or often no such ability at all, seagrasses show a high degree of meristem dependency.