you're reading...


Benthic biology on a thermally boring deep-sea ridge

Sautya, S., Ingole, B., Jones, D., Ray, D., & Kameshraju, K. (2017). First quantitative exploration of benthic megafaunal assemblages on the mid-oceanic ridge system of the Carlsberg Ridge, Indian Ocean. Journal of the Marine Biological Association of the United Kingdom, 97(2), 409-417. doi:10.1017/S0025315416000515

The deep ocean hosts an abundance of life. Benthic fauna, those that live on the oceans’ bottoms, make up a large portion of marine life. Basic habitats of benthic communities include sediment (soft bottom) and rock (outcrops, ridges). For instance, the Mid-Ocean Ridge (MOR- the mountain chain that seams the ocean floor) hosts biologically diverse communities of benthic organisms and fishes.   Chemosynthetic (organisms that gain energy from chemical reactions) communities, in areas of high temperature fluid venting on MORs, have gained ample attention.   Heterotrophic (animals that get energy by consuming organic matter) communities dwelling areas that are not thermally significant however, have been the focus of very few studies.

Recognizing a lack of faunal attention in some areas of the MOR, a group of scientists in India and the United Kingdom investigated the density distribution of a benthic community with respect to depth and substratum type in two sections of the Carlsberg Ridge in the Indian Ocean.

Study Site:

The Carlsberg ridge is at the Somalia-India and Arabian plate divergence zone below 1600m to 4000 meters of water. The ridge is slowly spreading at a half spreading rate of 11-16 mm/year.  In cross-section the ridge is a V-shaped valley with a wide floor, steep walls, and transform faults. Site surveys of the area are common but there is little focus on the benthic fauna (bottom community) is areas that are not associated with active vent systems. No previous studies in the area have quantified the bottom community (how man individuals are in a given area) and then related the distribution to substratum and depth.

Materials and Methods:

Community assessment was done using video and photographs collected by ROV Sonne in 2007. The images photographed 2 locations on the ridge (Figure 1 in the original article shows transects on Carlsberg Ridge).   Both focus areas include off axial highs (mounds), valley walls, and a floor. Images were taken from 1-5 meters about the seafloor. Individuals were included in the quantification analysis if they were greater than 1cm in size when measured from a distance of 2.5 meters above.   Table 2 in the original article summarizes the numerous transects by name, location, area size, temperature, transect length, number of individuals identified, and the number of taxa represented.   Fauna identification was only to the taxon level because of limitations of details captured in the photographs; species identification was not reliable.

The substratum on the outcrop was divided into 8 types based on geomorphology and composition. For instance, the type of basalt present, the degree of sediment cover, and the percentage of cobble are all factors impacting substratum categorization. Areas used for the density analyses were calculated from the length of the transects and the width of the transects. Transect width was determined from laser scalars and ROV altitude.

How the assemblage varied with bottom type and depth was statistically analyzed by identifying how multiple variables (factors) were alike and different between transects.

What they found:

The two focus areas were split into three sections based on geomorphology: off axial highs (shallow), the valley walls, and the rift floor (deep). The off axial highs had a combination of gradually sloped sections with basalt blocks, sediment covered bases of basalt walls, talus on broken pillow fragments at the base of scarps and small mounds, and some thick pillow mounds with light sediment cover.   The walls primarily were cracked pillows with light sediment cover on the ledges. The deep valley floor had the highest variability of substratum, hosting all 8 of the bottom types defined by the researchers.   Substratum types in the focus areas are described in Figure 2 and Table 2 of the original article.   The main two groups of substratum identified were basalt with cobble and sediment, found in shallow areas, and sediment, which was found in deeper regions.

With regards to fauna, the number of individuals and the assemblage densities varied with depth.   In the shallow off-axis areas 272 individuals were noted, representing 19 taxa. The density range was 61-171 individuals per 1000 square meters (average 116 +/- 55). In the mid-depth areas 1632 individuals were observed, representing 69 taxa. The density range was 6-54 individuals per 1000 square meters (average 24 +/- 15). In the deepest areas 186 individuals were counted, representing 22 taxa. The density range was 8-35 individuals per 1000 square meters (average 21 +/- 5). The greatest densities were in the shallow regions and the lowest was in the deepest section surveyed.

Figure 1: Echinoderm at 3000 meters (not from Carlsberg Ridge)

The types of faunal groups present at each depth segment also varied. The five main groups identified were Porifera, Cnidaria, Echinodermata (Figure 1), Anthropoda, and Chordata. Typical on off-axial highs were Cnidarians, Poriferans, and Echinoderms. The middle depth group (valley walls) hosted primarily Echinoderms and the deeper regions were dominated by Porifera (Table 3 summaries the abundance range in the three depth segments).


The decrease in assemblage density with depth is typical of deep ocean assemblages. The change is attributed to the availability of food being less in deeper areas.  The variability is also associated with the availability of substrate types, some organisms prefer hard versus soft bottoms to attach to, and the presence of strong currents (which usually carry food and also flush the organisms).

Mapping organisms on sections of the seafloor for which there is already available image and video documentation is a great way to learn about who is living on the Earth. Understanding their distributions relative to the environment can help aid in deciphering the relationship between biological community and geochemical environments.   And of course, the information about animals present from investigations like this one can be added to the global Census of Marine Life (CoML) to try and create a more complete picture of Earth’s biosphere.




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 6 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 8 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 9 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 11 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