//
you're reading...

Book Review

The Rumble in the Coral Jungle? How reef degradation is impacting damselfish competition

 

 

Article: Boström-Einarsson, L., et al. (2014). “Habitat degradation modifies the strength of interspecific competition in coral dwelling damselfishes.” Ecology 95(11): 3056-3067.

http://dx.doi.org/10.1890/13-1345.1

Background:

Competition is a fundamental component of ecology. Whether among individuals of the same species (intraspecific competition) or between individuals of different species (interspecific competition), competition helps shape and structure communities. Competition occurs over resources, and depending on what kind of organism you are, resources vary. In marine environments, species compete for food, nutrients, space, and light, among others. Competition is also highly density dependent, meaning that the number of individuals present has an impact on the intensity of competition.

Coral reefs support highly diverse communities. Covering less than 1% of the world’s oceans, they house about 25% of all marine species. Reefs provide complex habitat, refuge, and food; but supporting so many species in such a small area also means that there is a lot of competition for resources (Fig 1). Previous research has shown that competition for space within reefs can influence the structure of fish communities. For example, competitively dominant fish species can actually increase the death rate of less dominant species by restricting access to preferred space, leaving the weaker fish open to predation.

Space is a valuable resource in coral reefs.

Fig 1: Space is a valuable resource in coral reefs.

Coral reefs are fragile habitats. We often hear about bleaching events, coral disease, or dynamite fishing wreaking havoc on reefs and their inhabitants. Additionally, the future doesn’t look great for reefs as warming and more acidic oceans are going to impact the health of these ecosystems. So how does degradation of reefs affect competition? A few theories have been proposed:

  1. Greater limitation of resources will ramp up competition
  2. Competitive hierarchies could switch, meaning the more submissive species would start to outcompete the dominant species – this would happen if the submissive species weren’t as negatively effected by the changing habitat
  3. Degradation could create new competitive rivals if resources started overlapping

These theories have yet to be experimentally tested…until now. A group of researchers out of Australia decided to test how competition between two damselfish species was impacted by degradation of their reef habitat.

The Study:

Researchers from James Cook University set up a field manipulation to study the competition between two common damselfish species: Chrysiptera parasema (Fig 2) and Dascyllus melanurus (Fig 3). These two species occupy the same ecological niche and rely on live coral for habitat as juveniles. Previous studies have shown D. melandrus to be competitively dominant over C. parasema. Knowing that competition among these fish is density dependent, researchers included a density component in this study.

Fig 2: Chrysiptera parasema juvenile (ichythologist.tumblr.com)

Fig 2: Chrysiptera parasema juvenile (ichthyologist.tumblr.com)

Fig 3: Dascyllus melanurus juveniles (dixsonlab.com)

Fig 3: Dascyllus melanurus juveniles (dixsonlab.com)

 

 

 

 

 

 

 

 

Experimental plots were established in field sites of the coast of Papua New Guinea. Researchers used one species of coral, Acropora longicyathus (Fig 4), at two levels of health, either 100% healthy or 10% healthy. Plots were established on sandy bottoms away from other reefs. They were created by transplanting the appropriate amount of live and recently dead coral to their plots, plots were 0.5m X 0.5m. Once the coral plots were established, researchers anesthetized, collected, and tagged (for monitoring) individual juvenile fish of both species and transplanted them onto one of their plots. Numbers of individuals of both species varied between plots in order to test the density dependence factor as well as gather information on both inter and intraspecific competition. Stocks of fish ranged from 10-40 fish per plot. Over the course of 60 days, researchers observed plots for mortality, movement between plots, and behavior and interactions of fish within a plot.

Fig 4: Acropora longicyathus (coral.aims.gov.au)

Fig 4: Acropora longicyathus (coral.aims.gov.au)

Overall, researchers found that competition between species was stronger on healthy reefs resulting in an increase in C. parasema mortality with increasing competitor abundance, thus it was density dependent (Fig 5). The interspecific competition yielded higher mortality in C. parasema than the intraspecific competition. However, on degraded reefs, impacts from both inter and intraspecific competition were completely altered. Mortality rates were similar on all these reefs despite competitor abundance; meaning in degraded reefs, competition and mortality was density independent. Behaviorally, degraded reefs resulted in increased “agnostic interactions” (or interactions defined as a nip or chase by one fish to another) with increased abundance (Fig 6). Making it seem as though the fish in degraded habitats were more “on edge”, and were more interactive.

This figure shows the proportional mortality of C. parasema (a and b) and D. melanurus (c and d). This figure also separates out healthy from degraded habitats (left column and right column respectively). Black dots represent data from interspecific competition and open dots represent data from intraspecific competition.

Fig 5: This figure shows the proportional mortality of C. parasema (a and b) and D. melanurus (c and d). This figure also separates out healthy from degraded habitats (left column and right column respectively). Black dots represent data from interspecific competition and open dots represent data from intraspecific competition.

Fig 6: This figure shows the agnostic interactions for both species. C. parasema (a and b) and D. melanurus (c and d). Again columns represent healthy and degraded habitat.

Fig 6: This figure shows the agnostic interactions for both species. C. parasema (a and b) and D. melanurus (c and d). Again columns represent healthy and degraded habitat.

 

 

 

 

 

 

 

 

 

 

 

The Significance:

In a typical, healthy reef, competition between fish is density dependent and the competitively dominant species will ultimately win out. This competition is a structuring ecological force that has allowed species to adapt to roles and niches. But ecosystems like coral reefs are vulnerable to degradation. This research is the first to look at how habitat degradation impacts competition, showing that when a habitat is degraded, all of the density dependence and competition is thrown out the window. These established relationships between species crumble under these conditions. It is important to note that although the competition and density dependence factor are a wash, mortality in these fish increases with degraded habitat, it’s just not linked to the same factors. With reefs threatened from a number of sources in the future, we may soon be seeing a new set of rules (or lack thereof) come into play. Competition is a key process in regulating populations and communities, and it appears that this process is lost in a degraded system.

This review ties nicely in with another recent oceanbites post that focuses on behavioral changes in damselfish in degraded reefs. By interweaving these two studies we can start to paint a broader picture of how reef destruction and degradation is impacting individuals, communities, and interactions.

Discussion

No comments yet.

Post a Comment

Instagram

  • 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