''Thalassia testudinum'', commonly known as turtlegrass, is a
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of
marine
Marine is an adjective meaning of or pertaining to the sea or ocean.
Marine or marines may refer to:
Ocean
* Maritime (disambiguation)
* Marine art
* Marine biology
* Marine debris
* Marine habitats
* Marine life
* Marine pollution
Military
* ...
seagrass
Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the orde ...
. It forms meadows in shallow sandy or muddy locations in the
Caribbean Sea
The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...
and the
Gulf of Mexico
The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...
. Turtle grass and other seagrasses form
meadows
A meadow ( ) is an open habitat, or field, vegetated by grasses, herbs, and other non-woody plants. Trees or shrubs may sparsely populate meadows, as long as these areas maintain an open character. Meadows may be naturally occurring or artifici ...
which are important habitats and feeding grounds. The grass is eaten by turtles and herbivorous fish, supports many
epiphyte
An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called phoroph ...
s, and provides habitat for juvenile fish and many invertebrate taxa.
Description
''Thalassia testudinum'' is a
perennial
A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wide ...
grass growing from a long, jointed
rhizome
In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...
. The rhizome is buried in the
substrate deep, exceptionally down to . Some nodes are leafless but others bear a tuft of several erect, linear leaf blades.
These are up to long and wide and have rounded tips. The flowers grow on short stalks in the axils of the leaves and are greenish-white, sometimes tinged pink, and are followed by seed pods.
Distribution and habitat
Turtle grass grows in meadows in calm shallow waters throughout the Caribbean Sea and the Gulf of Mexico, and as far north as
Cape Canaveral
, image = cape canaveral.jpg
, image_size = 300
, caption = View of Cape Canaveral from space in 1991
, map = Florida#USA
, map_width = 300
, type =Cape
, map_caption = Location in Florida
, location ...
in Florida. Extensive meadows can be formed on muddy sand, and coarse sandy and clayey seabeds, especially those with a
calcareous
Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.
In zoology
''Calcareous'' is used as an adje ...
content. This grass favours high-salinity waters with low
turbidity
Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality.
Fluids can ...
, such as calm lagoons. It cannot grow in fresh water but some growth is possible at a
salinity
Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...
of 10 parts per thousand. The plant's preferred salinity range is 25 to 38.5 parts per thousand with a temperature range of . It is found from the low-tide mark down to depths of , depending on water clarity. It often grows in meadows with other seagrasses where it is the
climax species
Climax species, also called late seral, late-successional, K-selected or equilibrium species, are plant species that can germinate and grow with limited resources; e.g., they need heat exposure or low water availability. They are the species wit ...
.
[
Its temporal range spans from the ]Middle Eocene
The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', "dawn ...
to present.
Reproduction
Turtle grass can reproduce both through vegetative and sexual reproduction
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...
. The main propagation method is by extension of the underground rhizome
In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...
, or stem. This increase in rhizome length results in asexual ramets, or clonal colonies
A clonal colony or genet is a group of genetically identical individuals, such as plants, fungi, or bacteria, that have grown in a given location, all originating vegetatively, not sexually, from a single ancestor. In plants, an individual in s ...
which are genetic replicates of the parent plant. Although asexual propagation results in an increase in the size of the turtle grass bed, extensive asexual reproduction limits genetic diversity
Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species. It is dis ...
and can put the meadow at severe risk if there is a disease outbreak.[ It has been found that where plants have been damaged mechanically, such as by the propellers of boats, the cut ends of rhizomes are unable to grow and holes may develop in the turtle grass meadow.][
Turtle grass can also sexually reproduce through the production of underwater flowers and ]hydrophily
Hydrophily is a fairly uncommon form of pollination whereby pollen is distributed by the flow of waters, particularly in rivers and streams. Hydrophilous species fall into two categories:
(i) Those that distribute their pollen to the surface o ...
. Turtle grass is dioecious
Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...
, which means that there are separate male and female plants, each which produce an imperfect flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanism ...
containing only one sex. Sexual reproduction takes place from April to July depending on location, though flowering has been observed during warm winters in Tampa Bay, Florida.[Moffler MD, Durako MJ and Grey WF. 1981. Observations on the reproductive ecology of ''Thalassia testudinum'' (Hydrocharitaceae). Aquatic Botany. 10: 183-187.] The small flowers are each borne by a peduncle. Female plants typically grow one green flower, while males often produce three to five pink or white flowers.[Orpurt PA and Boral, LL. 1964. The flowers, fruits and seeds of ''Thalassia testudinum'' Konig. Bulletin of Marine Science. 14: 296-302.] At night when male flowers are fully mature, they release mucilaginous pollen into the water column. The following morning, female flowers open.
There are two methods of pollination: hydrophily
Hydrophily is a fairly uncommon form of pollination whereby pollen is distributed by the flow of waters, particularly in rivers and streams. Hydrophilous species fall into two categories:
(i) Those that distribute their pollen to the surface o ...
and biotic pollination. In hydrophilic pollination, the pollen grains are carried through the water column by tides or currents and deposited upon an open pistillate
Gynoecium (; ) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more) ''pistils'' ...
flower. Underwater video cameras have more recently revealed crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
s, polychaete
Polychaeta () is a paraphyletic class (biology), class of generally marine invertebrate, marine annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that ...
s, and amphipods
Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descri ...
swimming towards open male flowers. These creatures were attracted to the seagrass’s nutritious mucilage
Mucilage is a thick, gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion. The direction of their movement is always opposite to that of the secretion of m ...
—a carbohydrate-rich substance that houses pollen. As the invertebrates feed on the mucilage, excess pollen grains stick to their bodies. They move from flower to flower, feeding and spreading the pollen from male to female.
Seeds begin to develop in about 2–4 weeks if fertilization occurred. Female turtle grass fruits develop into green capsule about 20–25 mm in diameter and can include 1-6 small seeds. After about 8 weeks of growth, the fruit undergoes dehiscence (botany)
Dehiscence is the splitting of a mature plant structure along a built-in line of weakness to release its contents. This is common among fruits, anthers and sporangia. Sometimes this involves the complete detachment of a part; structures that op ...
, which releases neutrally buoyant seeds into the water column. If an event occurs producing significant water turbulence, an immature fruit may break off from the peduncle. This buoyant fruit acts as a transportation vessel as it continues to develop. The fruit will moved around by wind, currents, and tides until it eventually splits open to release the negatively buoyant seedlings into a new area. If the new location has favorable environmental conditions, the seedling will begin to grow. This is one way viviparous
Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the m ...
seedlings can start new patches of seagrass.[
]
Ecology
Turtle grass and other seagrasses form meadows which are important habitats and feeding grounds. Associated seagrass species include ''Halophila engelmannii
''Halophila engelmannii'' is a species of seagrass in the Hydrocharitaceae family. It is referred to by the common names star grass and Engelmann's seagrass and grows underwater on shallow sandy or muddy sea floors. It is native to the Bahamas, t ...
'' and ''Syringodium filiforme
''Syringodium filiforme'', commonly known as manatee grass, is a species of marine seagrass. It forms meadows in shallow sandy or muddy locations in the Caribbean Sea and the Gulf of Mexico, and is also found in the Bahamas and Bermuda
) ...
''. Many epiphyte
An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called phoroph ...
s grow on the grasses, and algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
, diatom
A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
s and bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
l films cover the surface of the leaf blades. The grass is eaten by turtles, herbivorous parrotfish
Parrotfishes are a group of about 90 fish species regarded as a Family (biology), family (Scaridae), or a subfamily (Scarinae) of the wrasses. With about 95 species, this group's largest species richness is in the Indo-Pacific. They are found ...
, surgeonfish
Acanthuridae are the family of surgeonfishes, tangs, and unicornfishes. The family includes about 86 extant species of marine fish living in tropical seas, usually around coral reefs. Many of the species are brightly colored and popular in ...
, and sea urchin
Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...
s, while the leaf surface films are a food source for many small invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
s.[ Decaying turtle grass leaves are responsible for the majority of detritus in meadow areas. This grass is subject to periodic dieback episodes in the ]Florida Bay
Florida Bay is the bay located between the southern end of the Florida mainland (the Florida Everglades) and the Florida Keys in the United States. It is a large, shallow estuary that while connected to the Gulf of Mexico, has limited exchange o ...
area. One such episode in 1987 killed off a large proportion of the plants and the resulting increased sedimentation and greater growth of epiphytes on the remaining plants caused a secondary dieback event. The areas affected have since been reseeded and planted with rhizomes and have recovered. In general, the population of this grass is stable.[
Rhizomatous green algae in the genus '']Caulerpa
''Caulerpa'' is a genus of seaweeds in the family Caulerpaceae (among the green algae). They are unusual because they consist of only one cell with many nuclei, making them among the biggest single cells in the world. A species in the Mediterran ...
'' often live among the grasses and many animal make seagrass meadow
A seagrass meadow or seagrass bed is an underwater ecosystem formed by seagrasses. Seagrasses are marine (saltwater) plants found in shallow coastal waters and in the brackish waters of estuaries. Seagrasses are flowering plants with stems and ...
s their home. These include bivalves
Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...
and other molluscs
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant taxon, extant species of molluscs are recognized. The number of fossil sp ...
, polychaete worms
Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are m ...
, amphipods
Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descri ...
, juvenile fish (which hide among the leaf blades), sea urchin, crab
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...
s, and caridean shrimps.[
]
Relationship to humans
Along with ''Thalassia hemprichii
''Thalassia hemprichii'', called Pacific turtlegrass, is a widespread species of seagrass in the genus '' Thalassia'', native to the shores of the Indian Ocean, the Red Sea, and the western Pacific Ocean. Its growth rate increases with CO2 enrich ...
'' (which shares its common name with ''Thalassia testudinum''), turtle grass makes its way into the aquarium trade and it may be cropped at 12 in/30 cm.[(2012): Beautiful Seagrasses – Keeping True Flowering Plants in Your Marine Aquarium, Reefland.com. ]
'. In: Reefland.com
/ref>
References
External links
*
{{Authority control
Seagrass
Hydrocharitaceae
Biota of the Atlantic Ocean
Plants described in 1805