Reef Organisms: Fishes Flashcards
What is the fish biomass baseline for the wilderness vs fishes reefs?
Wilderness baseline: ~1900 kg ha-1 (100x100m)
Fished reefs: ~740 kg ha-1 (~40% of wilderness) -> shows the profound effect of fishing
Name 5 major fish taxa (orders). If possible name some examples within them
- Labroidei (damselfishes, wrasses, parrotfish)
- Blennoidei (blennies)
- Gobioidei (gobies, dartfish)
- Percoidei (butterflyfishes, angelfishes)
- Acanthuroidei (surgeonfishes)
Name the types of secondary consumers.
Carnivores
Corallivores (e.g., butterfly and angelfish which feed on coral tissue)
Planktivores (e.g., damselfish, which feed on zooplankton from the water column - note zooplankton not phytoplankton otherwise would be herbivores)
Name the main roles within a food web.
- Producers
- Primary consumers
- Secondary consumers
- Scavengers
- Decomposers and detritus feeders (often bacteria and fungi)
Can mixed forms of feeding in reef fishes exist?
Yes
Name three examples of iconic herbivores.
- Surgeonfish (identifiable by their “scalpel” like tail) e.g., regal and yellow tangs
- Herbivorous Parrotfish (e.g., scaris psittacus, which demonstrate significant sexual dimorphism, with males and females looking very different)
- Damselfish (e.g., Stegastes nigricans (Algal-farming damselfish), which look after their own algal garden, feeding from it and protecting it from others)
What is an example of a fish demonstrating sexual dimorphism?
Parrotfish (bright male, dull female) - scaris psittacus
What is an example of an algal farming fish?
Stegastes nigricans (an Algal farming damselfish) which look after their own algal garden, feeding from it and protecting it from others
Name two examples of corallivores (fish).
- Butterflyfishes (Chaetodontidae) - some also have other feeding methods, so have mixed forms (some exclusively feed on corals).
- Excavating parrotfish -> Feeds on coral tissue and the algae sitting inside this tissue and as endolytic forms in the skeleton -> therefore can inflict substantial damage on the coral skeleton (e.g., porites coral).
Name three iconic examples of fish planktivores.
- Damselfish (e.g., chromis sp. hide in coral for protection, but also provide nutrients and oxygen for this host coral)
- Clownfish (e.g., amphiprion sp. - hide in anemone tentacles and make nutrients bioavailable)
- Anthias (Anthias sp.)
Why are damselfish beneficial for their coral host?
Oxygen provision -> When they sleep, they sit between the branches, moving their fins while they sleep and bringing in fresh water to the coral, benefiting nutrient exchange.
Nutrient bioavailability -> make nutrients from the water column bioavailable for the coral symbionts (these nutrients otherwise would have passed by), thereby benefiting the coral host.
Why are clownfish beneficial to the anemone they live in? What benefits do the fish get?
The clownfish pick plankton out of water and hang out between anemone tentacles for safety. Waste nitrate excreted can be taken up by the anemone, thereby benefiting the host.
Why are clownfish especially suited to living in anemones?
They cover themselves in mucous to prevent stinging from the anemone.
Sex change -> Clownfish are first born as male (all of them!). When a certain size (not age) is reached they change their sex to become a female. The most dominant clownfish in the hierarchy will get the most food, growing the fastest and therefore becoming a female soonest. This female will reproduce with the males, laying the eggs in the anemone before the larvae disperse upon hatching.
Why?
This is good because the strongest fish will reproduce. Clownfish are also slow and clumsy, so they stay in the anemone and don’t have to look for mates by leaving.
If the female dies, the next male in the hierarchy will become female (growing bigger and becoming female) -> this means that the reproductive community remains intact
Name four iconic examples of fish carnivores.
- Groupers (Serranidae) and Moray Eels (Muraenidae) -> hunt together, with different body shapes allowing them to cover both the water column and the cracks and crevices, benefiting each other (symbiosis)
- Red Lionfish (pterois volitans) - poisonous/venomous with a big mouth, consuming whatever can fit. Invasive in the Caribbean – problematic as they don’t have many predators here.
- Great Barracuda
- Blacktip reef shark -> an apex predator but numbers are dwindling due to shark finning (huge biomass declines)
What is an example of an invasive carnivorous fish?
Red Lionfish (pterois volitans) - Invasive in the Caribbean – problematic as they don’t have many predators here.
What is a Phase Shift? What is a common example in a reef system?
Transitions from one stable reef state to another, normally occurring due to disturbances.
Normally reef systems switch between being:
- Coral dominated
- Macroalga-dominated (mostly brown algae related to kelp, very sturdy/rigid)
What prevents phase shifts from occurring?
Ecological feedback loops -> keep these ecosystems in a stable state, allowing these ecosystems to display resistance to state shifts unless perturbations are large enough. This is known as resilience (the capacity to recover from stress).
What is an example of a method to test the role of herbivorous fish in phase shifts between coral and macroalgal dominated reefs? Use time frame used in case study
Monitor benthic cover (coral vs macroalgae) in reef patches with and without herbivore exclusion over three years.
Excluded herbivores with these cages or gave access to them (always had cages to ensure the structure was the same e.g., controls on light, currents etc.) -> i.e., use open cages (partial cages), closed cages and open plots?
What were the results of the case study when looking at the role of herbivorous fish in phase shifts between coral and macroalgal dominated reefs? What does this suggest can be done to increase resilience?
Summary: exclusion of herbivores resulted in a phase shift to macroalgal dominance and prevented reef recovery.
- The algal cover in the closed cages was significantly higher and coral cover much lower.
This suggests that, after a disturbance, resilience can be increased by ensuring herbivore numbers are high enough (reduce fishing).
What was found in the case study to affect the rate of coral recovery other than herbivore presence?
Faster rates of coral recovery were only found in sites where the cover of macroalgae was low and had not increased over time.
Essentially: once a phase shift has occurred, it couldn’t easily be reversed, suggesting that other factors need to be considered such as nutrient influx into the reefs (top-down or bottom-up controls on algae).
What can be a problem of fish herbivores for reef systems?
Even though overall positive effects of herbivores seem to prevail in most cases, having too many excavating herbivores, such as excavating parrot fish, can damage the reefs.
Therefore, more herbivores does not always equal more reef resilience.
What is important to remember when relying on herbivores for reef resilience?
Even though overall positive effects of herbivores seem to prevail in most cases, having too many excavating herbivores, such as excavating parrot fish, can damage the reefs.
Herbivores also don’t share the same functions -> only a few species are capable of consuming the macroalgae causing the phase shifts (E.g., the naso unicornis). This means that some species are more important than others. If the above fish is missing, then phase shifts may not be reversible even if protected.
Are fishing closures a key conservation
tool to promote coral reef resilience
under the pressure of global warming? What does this mean for finding the best protection strategies?
Yes (e.g., promote herbivores, which tend to be associated with coral dominated reefs rather than macro-algal dominated reefs).
However -> they are not always the “silver bullet” (too many excavating herbivores can damage the reef, and some herbivores are less important in reef maintenance than others).
Therefore: the specific ecosystem needs to be studied to find the best strategy to maintain stability or support recovery.
