you're reading...

Biological oceanography

Best of both worlds: stromatolites of the intertidal zone

Rishworth, G. M., R. Perissinotto, T. G. Bornman, and D. A. Lemley, 2017, Peritidal stromatolites at the convergence of groundwater seepage and marine incursion: Patterns of salinity, temperature and nutrient variability, Journal of Marine Systems 167:68-77. http://doi.org/10.1016/j.jmarsys.2016.11.010

Opportunities to study stromatolites, layered forms of ancient microbial structures called microbialites, are few and far between. They only occur in a few places around the world, including South Africa, where Rishworth et al. examined the conditions that support  stromatolites. Considering the limited understanding and rarity of intertidal stromatolites, this research has potential to shed light on microbial processes and their role in shaping biological coastal communities.

What in the world is a microbialite?

Microbialites are reef-like structures, often referred to as “living rocks”, made of calcium carbonate and are inhabited by diverse communities of bacteria, algae, cyanobacteria, and diatoms. They form their own mini-ecosystem, and primarily occur in salty shallow environments, but a few microbialites occur in the intertidal zone, experiencing great fluctuations in salinity, nutrients, and temperature of the water.

Featured image: A photo of a living microbialite from Great Salt Lake, Utah. Photo credit: K. Barrett.

Microbialite formation and long-term survival requires adequate levels of calcium carbonate, as this compound forms the “backbone” of the biological communities that interact with them. In seawater, calcium carbonate goes between solid and dissolved phases; how much of it stays in the solid form depends on a number of factors, including salinity, nutrient concentration, and temperature of the water. Thus changes to any of these parameters in local water conditions can significantly impact microbialite formation and the communities that thrive on them.

The study

A layered form of microbialites called stromatolites occurring along the coast of South Africa at Cape Morgan live at the interface of constant groundwater seepage and tidal or storm-induced seawater flooding and experience constantly fluctuating water conditions. The researchers went on a quest to identify the role of salinity, temperature, and nutrients in structuring stromatolites in this unique and variable setting.

Conceptual diagram of the three pools sampled at each study site. Modified from Alvesgaspar via WikiCommons.

The study site

This study took place at three sites (see the map, below) along a gradient of low to high human influence. At each site, the researchers identified three zones from which to sample:

1) upper pools that receive continuous inflow from groundwater seepage;

2) middle pools that receive upland and ocean inputs, and;

3) lower, seaward pools receiving ocean water.

Map showing locations of the three study sites located along Port Elizabeth, South Africa. Photo credit: Google Maps, modified by K. Barrett.

What data did they collect?

The researchers continuously monitored temperature and salinity at each zone within the three sites over the course of one year. They also measured dissolved inorganic nitrogen (DIN; such as ammonium), and dissolved inorganic phosphorus (DIP; phosphates), pH, and dissolved oxygen.

They analyzed the data to look for differences in patterns of salinity, temperature, and nutrients among the three sites and among the three zones within each site.


The role of nutrients

The researchers observed a clear trend of increasing DIN and DIP concentrations at sites with higher levels of human influence. Freshwater provided the main source of DIN, and upper pools had higher DIN concentrations than lower pools. While freshwater provided nitrogen, an important nutrient for building proteins, seawater provided phosphorus to the lower and middle pools. DIP is important for stromatolites because the availability of phosphorus often limits algal growth. They also found that DIN decreased from the upper pools to lower pools, likely due to these nutrients being used by photosynthesizing algae and cyanobacteria.

Salinity is key

Stromatolites within the main pools, where the greatest influence of tides occurred, experienced the greatest fluctuations in salinity, with conditions ranging from freshwater, brackish, to marine. Imagine being a barnacle living through such a wide range of salinity; for you and me, that would be analogous to experiencing all four seasons in 24 hours! Different algal and bacterial species have their own tolerances to salinities, which means that the swings in salinity within the middle pools can “turn the tables” as to which species dominates in the stromatolites. This fluctuating salinity also benefits the stromatolites by keeping away hungry invertebrates that could chow down on the nutritious algae growing on the stromatolites. The degree to which salinity fluctuates, rather than just the absolute salinity, is important in sustaining the stromatolite community.


The Big Picture

As more development occurs along the coastline, increased pollution could threaten the persistence of these rare ecosystems. Especially in stromatolite pools closer to human influences, higher nutrient runoff could alter the balance in the microbialite-forming communities. Understanding the conditions in which stromatolites form and thrive furthers our understanding of their role in coastal ecosystems and how it might change in the future. This in turn can help inform conservation efforts to keep these systems protected in the long-term.





No comments yet.

Post a Comment


  • by oceanbites 3 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 4 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 5 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 7 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 9 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 9 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 10 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 10 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 11 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 11 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 12 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 12 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 1 year ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com