The Grass is Always Greener: Seagrass Ecology in South Florida

Transcription

1 The Grass is Always Greener: Seagrass Ecology in South Florida R.P. van Dam James W. Fourqurean Biological Sciences and Southeast Environmental Research Center, Florida International University Ocean Life Lecture Series, Florida Keys Cultural Center, Ley Largo February 17, 2012

2 Outline What are seagrasses? What is the global status of seagrass ecosystems? Seagrass services Seagrass history Seagrass pressures Seagrass response Human response What is the local status of the seagrasses in south Florida? signs of trouble in paradise

3 Seagrasses are flowering plants that live submerged in the sea

4 The seagrasses are an ecological group, NOT a taxonomical unit A plant is called a seagrass if it: 1. Grows when fully submerged 2. Is securely anchored by a root system 3. Is adapted to live in salt water 4. Has flowers that are pollinated under water 5. Can compete with other organisms in the sea

5 Seagrass or seaweed? 300 BC: Seagrasses are a type of seaweed - Theophrastus (300 BC), Enquiry into Plants

6 Evolution No. Species Seagrasses spp. Flowering plants 235,000 spp. Marine plants 60,000 spp. Phytoplankton 50,000 spp. Macroalgae - seaweeds 10,000 spp. Seagrasses (No. Genera) 7 tropical (Halodule, Cymodocea, Syringodium, Thalassodendron, Enhalus, Thalassia, Halophila), 5 temperate (Zostera, Phyllospadix, Heterozostera, Posidonia, Amphibolis) 1 cosmopolitan (Ruppia)

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12 LIFE CYCLE of Thalassia testudinum Seed Juvenile Female clone Female flower Fruit Juvenile Male clone Male flower

13 Seagrasses are abundant in tropical and temperate regions Halophila: Bocas del Toro, Panama Thalassia: Kuna Yala, Panama Ruppia: Morro Bay, USA Zostera: Ria Formosa, Portugal

14 Seagrass provides critical food source in tropical regions J. Kenworthy R.P. van Dam Manatee (Trichechus) In Thalassia meadow, Puerto Rico Green Sea Turtle (Chelonia) In Thalassia and Syringodium meadow, Yucatan, Mexico

15 Seagrass provides critical habitat in temperate regions G. Pergent G. Kendrick Seahorse (Hippocampus) In Cymodocea meadow, Mediterranian Sea Zebra fish (Girella) In Posidonia meadow, Perth, Western Australia

16 Seagrass provides valuable fisheries resources

17 Nutrient processors: Seagrass beds absorb and transform nutrients in the marine environment

18 Sediment stabilizers: seagrasses efficiently hold sediments in place, preventing resuspension and movement of sediment deposits- They reduce shoreline erosion and keep the water clear!

19 Seagrasses need: Clear water! Sandy or muddy bottom Stable salinity Moderate waves and currents

20 Seagrasses are valuable and threatened compared to other major marine habitats

21 Seagrasses evolved in a very different marine environment from today Hydorcharitaceae Cymodoceacea Posidoniaceae Zosteraceae

22 Seagrasses evolved in a very different marine environment from today Hydorcharitaceae Cymodoceacea An inconvenient truth timeline Posidoniaceae Zosteraceae

23 Seagrasses evolved in a very different marine environment from today Hydorcharitaceae Cymodoceacea Posidoniaceae Zosteraceae

24 Pressures to seagrass: human population Pacific northwest, seagrass use Egypt ca years ago Washington DC, 2006

25 Pressures to seagrass: human population Pacific northwest, seagrass use Egypt ca years ago Washington DC, 2006

26 Pressures to seagrass: human population Pacific northwest, seagrass use Egypt ca years ago Washington DC, 2006

27 Panama Canal, 1907 Pressures to seagrass: increased invasive species Ballast pumping Caulerpa taxifolia

28 Panama Canal, 1907 Pressures to seagrass: increased invasive species Ballast pumping Caulerpa taxifolia

29 Pressures to seagrass: increased nutrient input (Fertilizer and sewage) Fertilizer applied in agriculture Wastewater Treatment Plant Fertilizer applied to lawns

30 Fishing practices may also be changing seagrass meadows around the world

31 Reports of seagrass losses and the rates of decline are increasing dramatically Waycott et al PNAS

32 Drivers of seagrass loss 1. Water quality degradation from poor land use practices 2. Dredging and filling 3. Invasive species

33 Research effort on seagrasses increasing, but lagging behind other coastal habitats.

34 Within widely accessed media, reports of seagrass are lacking

35 Bottom line: less seagrass research done AND it isn t broadly publicized

36 Seagrasses on a global scale Extensive seagrass losses have occurred in temperate and tropical regions Nutrients and sediment inputs are the primary pressures Research and understanding of seagrass communities is increasing BUT despite a lot of effort, the importance and issues of seagrass habitats are still lagging behind other coastal communities in effective communication to the public and ultimately policy makers

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38 A broad variety of seagrass habitats in south Florida

39 Thalassia testudinum Turtle grass Many (most) seagrasses are dioecious

40 Syringodium filiforme Manatee grass

41 Halodule wrightii Shoal grass

42 Halophila decipiens A monoecious seagrass

43 Halophila engelmanni

44 Halophila johnsonni

45 Ruppia maritima Widgeon grass

46 Synoptic Benthic Habitat Surveys

47 Synoptic Surveys: Species distributions Thalassia testudinum Halophila decipiens Syringodium filiforme Halodule wrightii

48 As nutrient inputs to seagrass beds increase, species shifts occur and seagrasses get displaced by seaweeds, then by phytoplankton

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50 Long-term changes in seagrass bed composition suggest nutrients are becoming more plentiful Braun Blanquet Density Site 273 Thalassia Syringodium Halodule Calcareous Green* Braun Blanquet Density 5 Site

51 Changes in relative abundance of primary producers At 19 of 30 sites, species composition has shifted in a manner consistent with increased nutrient availability Green: Thalassia getting denser Red: Thalassia decreasing in relative importance

52 Leaf tissue N content (% of dry weight) As nutrient inputs increase, the amounts of important plant nutrients in the seagrass leaves changes providing a sentinel for nutrient addition Oligotrophic P-limited Eutrophication Eutrophication Nutrient-replete N:P = 30:1 Oligotrophic N-limited Leaf tissue P content (% of dry weight) Seagrass Leaf N:P Progressive eutrophication or light reduction

53 The relative importance of the two important plant nutrients nitrogen and phosphorus change across the landscape in south Florida Thalassia testudinum N:P of leaves P-limited N-limited

54 Some seagrass meadows in south Florida are changing in ways that indicate nutrient pollution N:P of Thalassia Site 267 Y= x r 2 =0.171, p=

55 Long-term changes in N:P consistent with increases in nutrients

56 Changes in water management in south Florida will cause a change in the distribution of seagrass species and the animals that live in the seagrass beds Kilometers

57 Deep, C-rich soils underlay seagrass meadows 0 0 C org generally decreases downcore in Florida Bay seagrass soils. Buried peats have high C org Depth (cm) Depth (cm) Depth (cm) Depth (cm) Bob Allen Keys Russel Bank Organic C content (% of dry wt) Organic C content (% of dry wt) Nine Mile Bank Trout Cove Organic C content (% of dry wt) Organic C content (% of dry wt)

58 Seagrasses store about as much C as forested ecosystems 1200 Ecosystem C storage (Mg C org ha -1 ) Boreal Living Biomass Soil C org Temeprate Tropical Upland Oceanic Mangrove * * * * * * * * * * Seagrass

59 There are about 18,000 km 2 of seagrass beds in south Florida

60 A very rough estimate of carbon stored in the top meter of seagrass soils in south Florida: 18,000 km 2 of seagrasses 594 tons CO 2 e ha -1 1 x 10 9 tons CO 2 e stored in the soils! Anthropogenic CO 2 e flux is about 29 x 10 9 tons y -1

61 Summary points Seagrasses in south Florida The Keys are home to some of the most expansive and important seagrass beds on earth Rapid population increases adjacent to oligotrophic marine ecosystems in south Florida may have deleterious effects on those ecosystems, as in so many other places in the world Changes are occurring in south Florida seagrass beds that are consistent with increased nutrient availability in the system. These changes are relatively subtle, we have not witnessed large-scale permanent loss of seagrass beds in the Keys. There is time to act!

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63 Are we describing locallyinduced changes, responses to larger-scale processes, or natural cycles?

64 Sister taxa in Atlantic and Indopacific

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