Showing posts with label nutrients. Show all posts
Showing posts with label nutrients. Show all posts

Friday, May 20, 2016

Diatom of the month – May 2016: Rhopalodia gibba

May 20, 2016 0
by Luca Marazzi*
Rhopalodia gibba belongs to the epithemioid group, that is to say it has valves symmetric about a line (bilateral symmetry), but asymmetrical to the apical (longitudinal) axis, the raphe system is well developed, enclosed within a canal, and positioned near the valve margin1. It is longer and more slender than other species such as the lunate R. gibberula, and the more arched R. musculus; it is found in the benthos, attached to substrata such as plant (epiphytic), or gliding more freely and opportunistically2. Interestingly, R. gibba seems to have declined significantly in the United Kingdom due to agricultural intensification and associated large use of nitrogen fertilizers. In fact, this pennate (bilaterally symmetric) diatom species lives in nitrogen poor habitats, but it has evolved an endosymbiosis with cyanobacteria that fix nitrogen3. So it does not like when there is too much nitrogen around, and loses its competitive edge against other fellow diatoms and algae, but it’s quite happy with abundant phosphorus…

  Rhopalodia gibba in valve and girdle view (scalebars = 10 µm; from Hebron Swamp, Cheboygan Co, MI; photos by P. Kociolek www.westerndiatoms.colorado.edu); (top right) a specimen of the lunate R. gibberula (www.fcelter.fiu.edu); R. gibba with cyanelles (inset above), its endosymbiotic cyanobacteria: https://microscopesandmonsters.wordpress.com; cell length ~ 100 µm & max width ~ 20 µm).

 

…such as in some areas of the Everglades, where R. gibba can tolerate high phosphorus (P) concentrations (> 800 μg P g−1) in the periphyton mats4. This species has been found to dominate primary production in restored prairie wetlands in South Dakota that had persistent high P levels.5 Moreover, it is well adapted to high conductivity and alkalinity, such as in boreal wetlands in Wood Buffalo National Park(in Northeast Alberta, Canada); here R. gibba lives in yellow diatom ponds (!), nesting sites of whooping cranes6. The diatom ponds are shallow spring-fed, alkaline wetlands with bicarbonate, sulphate, calcium and magnesium. In these open habitats, cranes can see predators well, and they find their favored nesting material, bulrush6. So preserving the habitats of these glass-celled algae that fix nitrogen thanks to cyanobacteria living in their cells, we end up conserving large charismatic species too (and viceversa), from the bottom to the top of the food chain.


                        Ponded wetland in Wood Buffalo National Park (source: www.emaze.com).


A whooping crane (source: http://cranetrust.org); this large bird uses diatom ponds as nesting habitats.


* Postdoctoral Associate in Dr. Evelyn Gaiser's lab at Florida International University.

1. Source: https://westerndiatoms.colorado.edu/taxa/morphology/epithemioid

2. M. Kelly “More about Croft Kettle” - https://microscopesandmonsters.wordpress.com/tag/rhopalodia-gibba/

3. Round, F. E., R. M. Crawford, and D. G. Mann. 1990. The Diatoms: Biology and Morphology on the Genera.       Cambridge University Press, Cambridge, U.K.
4. Gaiser E.E., McCormick P.V., Hagerthey S.E. & Gottlieb A.D. (2011) Landscape Patterns of Periphyton in the Florida Everglades, Critical Reviews in Environmental Science and Technology, 41(S1), 92–120.
5.   Mayer P.M. & Galatowitsch S.M. (2001) Assessing ecosystem integrity of restored prairie wetlands from species production–diversity relationships Hydrobiologia, 443, 177–185.
6.   Tilmoney K., Zoltai S.C. & Goldsborough L.G. (1997) Boreal diatom ponds: a rare wetland associated with
    nesting whooping cranes. Wetlands, 17, 539–51.
Tags # Algae # Diatoms # Education and Outreach Continue Reading
By at No comments:
Labels: , , , ,

Tuesday, January 14, 2014

More Out-of-Town Visitors

January 14, 2014 0
More Out-of-Town Visitors

This post was written by guest blogger Mike Bush, a grad student in FIU's aquatic ecology lab (http://faculty.fiu.edu/~trexlerj/).
__________________________________________________________________________
http://i2.cdn.turner.com/cnn/dam/assets/131205211533-01-whales-1205-horizontal-gallery.jpg
Boaters trying to push whales back to deep waters. Photo from CNN.com
       This will be another post on some wide-ranging animals that only occasionally visit the Everglades.  Last time I talked about small songbirds, but I’ll scale up a bit for this round. 
About a month ago, a pod of around 50 short-finned pilot whales beached themselves on a remote shore in the southwestern part of Everglades National Park.  Normally these are deep-water beasts, but for whatever reason, this particular group of animals navigated several miles through shallow sandy shoals, only to end up stranded. Pilot whales are well-known for mass strandings, and the reasons for these strandings are unknown but are thought to be related to sick individuals trying to gain some respite.  The tight-knit social structure of the animals then may lead to other animals following their sick brethren into shallow water.  Another theory is that the animals may get move in to shallow areas inadvertently and are unable to successfully navigate back out using echolocation.  Whatever the reason, this is actually just one of several strandings that have happened in Florida in the last few years.  Through the efforts of some very hard working park service staff and volunteers, it is thought that upwards of half of the animals may have survived the rescue effort.  Eleven whales were later found on a beach in the Lower Keys, thought to be from this group.  They may have survived the rescue effort but may have been too weakened to survive for a trip back out to deeper waters.  Before this post depresses you too much, remember that short-finned pilot whales are species of least concern for conservation efforts, meaning that they are an abundant animal and the loss of 20-30 animals shouldn’t be detrimental to the persistence of the species.  Also, and perhaps more importantly, this was a natural event, and a couple dozen whale bodies (these guys can get to be almost 20 feet long!) will feed a lot of smaller animals out in the shallow sandbars.  I heard several reports of small sharks feeding on the carcasses, and the whales will also provide food for countless crabs, fishes, and seabirds, thus providing an important nutrient subsidy for a large stretch of the food chain.
       The recent stranding just goes to show that even though the Everglades is known for alligators, storks, and panthers, a massive swath of the park is marine, and sometimes we get visitors of a larger sort.
       There’s a whole slew of articles out there on the strandings.  Here’s a link to the most recent article, published by the Miami Herald: http://www.miamiherald.com/2013/12/09/3808627/eleven-pilot-whales-from-everglades.html.
 
Tags # animal movement # nutrients # Subsidies Continue Reading
By at No comments:
Labels: , ,

Tuesday, January 7, 2014

Exploring the Outer Reaches of the Everglades

January 07, 2014 0

 This post was written by guest blogger Emily Nodine, a PhD candidate in FIU's Periphyton Lab (http://algae.fiu.edu/research/).

When people think about today’s Everglades or the “River of Grass,” they generally think of Lake Okeechobee, Everglades National Park, and the canals and water control structures in between.  But the watershed is actually much larger than that.  Lake Okeechobee does serve as the headwaters of the Everglades; prior to human alteration, Lake Okeechobee would slowly overflow southward during very wet periods, forming the shallow, slow-flowing sheet of water that earned it the title “River of Grass.”  Today, the Hoover Dike prevents this and the water flow is strictly controlled, mostly released to the east and west coasts via the St. Lucie and Caloosahatchee Rivers, but also southward to the Everglades through an extensive system of canals and water control structures.  But the water in Lake Okeechobee came from somewhere else, too.

Lake Okeechobee sits at the mouth of the Kissimmee River and several smaller creeks that drain much of highlands central Florida as far north as Orlando.  Much like Lake Okeechobee and the Everglades, the Kissimmee River has also been through dramatic hydrological alteration and subsequent restoration efforts.  Once a meandering 103-mile waterway with a floodplain 1 to 3 miles across, the Kissimmee River was transformed during the 1960s to a 56-mile canal 300 feet wide and 30 feet deep.  Within the next couple of years, the South Florida Water Management District and U.S. Army Corps of Engineers plan to complete backfilling of a large section of the canal and removing water control structures in order to restore ecological integrity to 40 square miles of the river-floodplain system and 12,000 acres of wetlands.  Already, flora and fauna that disappeared following the canalization have begun to return.  Additional details about the restoration project can be found at http://my.sfwmd.gov/portal/page/portal/xweb%20protecting%20and%20restoring/kissimmee%20river.


Little of the Everglades watershed has been left untouched by hydrological alterations.  While restoration efforts such as the one-mile bridge on Tamiami Trail aim to deliver more water southward to the Everglades, estuaries at the outflows of the St. Lucie and Caloosahatchee Rivers  suffer from the effects of too much freshwater.  Historically, the Caloosahatchee River’s headwater was a small wetland pond west of Lake Okeechobee called Lake Hicpochee.  During early efforts to drain the Everglades for farmland in the late 1800s, a canal was dug connecting Lake Hicpochee to Lake Okeechobee, allowing the Caloosahatchee to become a major outflow for the larger lake.  Through subsequent canalization and installation of water control structures, the Caloosahatchee, like the Kissimmee River, was transformed.  Today, freshwater is released through a series of lock and dam structures down the Caloosahatchee to relieve pressure on the aging Hoover Dike that surrounds Lake Okeechobee, causing an influx of eutrophic water to the Charlotte Harbor estuary that results in adverse effects on seagrasses, oyster beds, and water quality.
My research is focused on the Charlotte Harbor watershed, which sometimes feels peripheral to the work of FCE LTER scientists in the Everglades, but I remind myself how important this region is as part of the Greater Everglades Ecosystem.  There are three major inflows into Charlotte Harbor, and they couldn’t be more different.  The Caloosahatchee, which is near my home, is highly managed and cut off from marine influence by water control structures (except during severe storms, when these are occasionally breached); the Peace River, which is naturally enriched in phosphorus and has been extensively mined for fertilizer; and the Myakka River, which is relatively pristine, with much of its watershed set aside as conservation lands and parks.
My goal is to understand the differences among these systems and how they influence inputs to Charlotte Harbor over time.  I am studying the diatom communities across this watershed in order to interpret long term changes from sediment cores taken from the estuary.  Diatoms are single-celled algae that provide clues about past environments because they are indicators of specific environmental conditions and they preserve in sediments, allowing us to determine what past conditions were based on which diatoms are present.  Specifically, I am interested in how they are distributed along environmental gradients, and how this changes in response to a disturbance such as a tropical storm or hurricane.  By studying what diatoms occur in these waterways before and after storms, I hope to identify a signal of hurricane activity that can be detected in sediment cores and help us to understand how these types of storms have affected south Florida ecosystems on large time scales.
Tropical Storm Debby, in June 2012, provided an excellent opportunity to investigate changes across the watershed.  During the dry season, diatom assemblages are strongly related to a salinity gradient across the watershed.   But following the storm, diatom communities changed in different ways across the various regions of the watershed.   Next, I hope to identify patterns in these differences to help us understand drivers of the type or direction of changes, such as whether anthropogenic alteration causes a different response to disturbance compared to more pristine areas.

Tags # conservation # Emily Nodine # Myakka River Continue Reading
By at No comments:
Labels: , , , , , , ,