L16 - Seagrass Flashcards
What are seagrasses?
Marine plants. Produce flowers, fruits and seeds. Flowering plant = Angiosperm
What is seagrass classification?
Class - monocotyledons, order - alismatales. Families (4 of 14) - hydrocharitaceae, posidoniaceae, zosteraceae, cymodoceaeceae. Alismatales comprise flowering plants of aquatic and marshy habitats. Only monocotyledons know to have green embryos no endosperm.
What do seagrasses have?
Have a true root system, an internal vascular system. Clonal, rhizomatous plants (a necessary adaptation for angiosperm growth in the high-energy marine environment). Rhizome is responsible for vegetative propagation. Angiosperm; produces flowers and seed for broadcasting over greater distances. Mostly monoecious (has both male and female reproductive units) perennials but some may become annuals under stressful conditions.
What are seaweeds?
No vascular system, often floating, do not produce flowers and seeds. If anchored uses holdfast, not roots
What are seagrass flowers?
Enhalus acoroides flowers (male), halophola ovalis flower, Zostera sp. flowers, cymodosea nodosa flower, thalassia hemprichii flower.
What are seagrass flowers & fruits?
Enhalus acoroides fruit, Enahlis acoroides fruit. Enhalus acaroides female flowers with tiny male flowers, posidonia australis fruits
What is hydrophilous pollination?
Pollen from male flower disperses and must find a female flower on a different plant for pollination to occur
What are the bees of the sea?
Tiny crustaceans pollinate underwater plants. Seagrass pollen swirls. Underwater invertebrates can ferry pollen between flowers.
What are some seagrass seeds?
A posidonia fruit. Zostera marina. These raw seeds are edible - said to taste like chestnuts
What can seagrass clones be?
Very old, some seagrasses have been found to have a min age estimate of between 80,000 and 200,000 yrs old
What are the anatomical adaptations of seagrass leaves?
Lack stomata; thin cuticle to allow gas and nutrient exchange. Large thin-walled aerenchyma (air channel) to facilitate gas diffusion within leaf provides buoyancy to leaves (to reach light).
What are the anatomical adaptations of seagrass roots & rhizomes?
Oxygen transport to the roots creates an oxic environment around the roots, facilitating nutrient uptake. All produce root hairs.
Where are they found?
About 60 species found globally from Arctic to Southern oceans. Found in tropical and temperate regions
What are tropical seagrass?
Fringing reef flat, protected lagoon, mainland coastal, deep water >15m
What are temperate seagrass?
Subtidal, intertidal
What environmental conditions might seagrass require?
Light, nutrients, shelter, CO2, Oxic mud or sand, saline water (0-56ppt), suitable temp (0-30degC)
Why do seagrass need high light?
Light requirements (% surface irradiance - SI). Minimum 5%, most species >18%. Depth - intertidal to 60m
What happens if there are too many nutrients?
Low light, Nutrients cause excess algal growth. Balance for optimal seagrass habitat.
What do seagrass meadows require?
Sheltered conditions
What habitat are seagrasses fully?
Marine, wide salinity tolerance, 0-99ppt tolerance, 0-56ppt growth. Salinity influences the distribution and growth of a single species as well as modifying competitive interactions so that species replacements occur
What are the effects of temp change?
Research examples: Campbell et al., 2006 found certain species more tolerant to thermal stress than others. Implications for climate change where temperatures are predicted to rise.
What are seagrass meadows susceptible to?
Change
What do seagrasses supply in ecosystems?
Very important, support thousands of marine species, improve water quality, protect coastlines, cycle nutrients and create habitat corridors between coral reefs and mangroves. Biodiversity, food, oxygen, carbon storage, shelter, habitat corridors, water quality, nutrient cycling, climate resilience, livelihoods
What lives in seagrass?
Seagrass meadows are important habitat. Small invertebrates and fish are more abundant in seagrass meadows. Habitat modification and substrate stabilisation by seagrasses leads to a rich infaunal communty. Leaves provide place to hide from predators. In turn the rich faunal community is a source of prey for larger predators. Is used for foraging
What herbivores are found in seagrasses?
Dugong (Dugong dugon) - consumes up to 40kg, Green turtle (Chelonia mydas) - consumes up to 2kg.
Feeding for shorebirds?
Herbivores grazing on the seagrass tissue, piscivorous birds feed on young fish in seagrass. Wading birds forage on inverts in seagrass, targeted predation on bivalves, piscivorous birds feed offshore.
What are the threats to seagrass?
Global decline of seagrasses, approximately 58% of seagrass meadows globally have lost part of their distribution. Documented losses of seagrass meadows globally since 1980 are equivalent of 2 football fields per hour.
What are some threats to seagrass ecosystems?
Agricultural run-off, temp increase, urban infrastructure, urban & industrial run-off, cooling water from power stations. Sea level rise, boating, harvesting, invasive species, aquaculture, ocean acidification, dredging.
How can we protect and secure a future for seagrasses?
Increased knowledge of seagrass ecosystems leading to more monitoring and protection. Water quality improvements has led to recovery in some places. Successful seagrass restoration.
