you're reading...


Kelp: It’s whats for dinner (or where you live)

Simonson, E. J., Scheibling, R. E., & Metaxas, A. (2015). Kelp in hot water: II. Effects of warming seawater temperature on kelp quality as a food source and settlement substrate. Mar Ecol Prog Ser, 537, 105-119.  doi: 10.3354/meps11421

Last month, you may have read our post about Erika Simonson et al.’s work on how kelp in Nova Scotia is responding to warming waters. Simonson and her colleagues took kelp samples from the dense groves off the coast and grew them in a laboratory at temperatures representing predicted future water conditions. They found that kelp tissue degrades more rapidly at higher temperatures. The damaged tissue growing in warmer water could presage a wholesale community shift from leafy kelp fronds to mats of turf algae. Besides being less photogenic, turf algae are also less productive than kelp and would not support the diverse, highly productive ecosystems that live around the kelp.

Figure 1 - Two snails on a kelp leaf. The bottom snail is Lacuna vincta (photo: Asbjørn Hansen, Creative Commons License)

Figure 1 – Two snails on a kelp leaf. The bottom snail is Lacuna vincta (photo: Asbjørn Hansen, Creative Commons License)

But Simonson was not content to just consider the direct effect of warmer water on kelp. Indirect effects on the ecosystem, such as changes in the food web, might compound the primary environmental impact to the kelp. Simonson considered two possible community changes that could result from altered kelp tissue: First, whether Lacuna vincta, a native sea snail, finds the damaged kelp more or less appetizing (fig. 1). And, second, if Membranipora membranacea, a kind of invasive moss, found the damaged kelp more suitable for settlement (fig. 2).

Sea snails, like your kid brother, are picky eaters; they prefer to graze on kelp that contains a lot of nitrogen and low levels of a substance called phlorotannins. Phlorotannins are chemicals that kelp produce in their cell wall to protect themselves from UV light and grazers. The kelp grown in warm water might accumulate different levels of nitrogen or pholortannins, which, in turn, might encourage or discourage the snails from eating it.

Elevated levels of phlortannins might also serve to protect kelp from the invasive moss, M. membranacea. While snails eat the kelp, M. membranacea likes to live on it. More phlorotannins could keep the moss from settling on the kelp leaves in the first place. The warm water kelp tissue may also be less appealing simply because the damaged leaves have less surface area.

For these experiments, Simonson and her group had to collect kelp, snails, and moss. The team got samples of the kelp and the snails by SCUBA diving off the coast of Nova Scotia. M. membranacea was collected in its larval stage from plankton net samples taken near-by. Back at the lab, the kelp was grown in two temperature treatments: 11° and 21° C. The cooler water represents the ambient current temperature while the warmer simulates predicted maximum conditions in the next 100 years. The snails and moss were kept in separate tanks of ambient seawater.


Figure 2 – M. membranacea is the white net structure growing on the kelp leaf. This is taken after the moss settles on the plant. It starts life as a drifting plankton until it finds someplace to settle (photo: Eugene van der Pijil via Wikipedia, Creative Commons License)

To test if these organisms prefer warm water kelp to cool water kelp, Simonson conducted weekly “choice, no-choice” experiments. The procedure is designed to see which type of kelp the snails and moss prefer. Kelp tissue was trimmed from plants grown in both the 11° and 21° C water and presented to the animals in different combinations. For the no-choice tests, the snails and moss were given just samples from the 11o or the 21o C kelp. The choice test entailed giving the test subjects tissue from each temperature tank.

The scientists monitored the snails’ growth rate and egg production to see if the they preferred kelp from either treatment. Growth rate was recorded as the change in length of the shell. Egg production was logged as the number of new eggs counted weekly from the specimen. They likewise counted how many M. membranacea larvae settled on the kelp leaves in each experimental set-up. In addition to tracking the feeding/settling behavior, Simonson also measured the chemical properties of the kelp to record changes in its nitrogen and phlorotannin content. The team repeated the whole experiment three times from beginning to end.

Simonson found that the snails and moss had no discernable preference for kelp grown at either temperature. The snails ate everything regardless of how it was grown. The snails seemed to eat more of the kelp pretreated in 21°C water in both the choice and no-choice tests. Simonson suggests this is because snails prefer softer food, like the damaged kelp tissue, regardless of nutritional content. Similarly, M. membranacea settled in equal quantities on kelp grown under both conditions.

The chemical data showed that the water conditions did not have a significant effect on the amount of nitrogen or phlorotannins produced by the kelp. This explains the behavior of both organisms. The snails were not attracted by higher levels of nitrogen in either kind of kelp, nor were they repelled by higher levels of pholortannins. M. membranacea also did not have to worry about different levels of pholortannins and settled wherever it pleased.

The authors found that neither grazing by snails nor settlement by the moss was enhanced on kelp grown at warmer temperatures. Simonson argues, however, that these secondary effects will act additively to increase biomass loss of kelp in a warming ocean. Snails will keep eating kelp, the moss will keep growing on it, and all while the tissue itself degrades in warmer water. This triple threat of tissue damage will cause more kelp to die and get ripped up in storm events. Eventually kelp groves will drastically recede, impacting habitat availability, community productivity, and the export of kelp detritus (i.e. food) to coastal and deepwater environments.


No comments yet.

Post a Comment


  • by oceanbites 2 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 3 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 4 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 5 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 5 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 5 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 6 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 6 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 6 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 7 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 7 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 7 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 7 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 8 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 9 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 9 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 9 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 10 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 11 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 11 months 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