Reef Fish Study IELTS Reading with Answers

READING PASSAGE 1
You should spend about 20 minutes on Questions 1-13 which are based on Reading Passage 1 below.

Reef Fish Study

Tom Holmes examines the relationship between size and survival in fish on Australia’s Great Barrier Reef

It is a widely held belief among those who study animals that larger size conveys some form of advantage throughout life. The idea that certain body characteristics may influence a prey’s ability to survive when being attacked by a predator has received considerable attention in the past, and has been applied to a wide range of both animals and habitats. Body size, weight, growth rate, overall condition, sensory development and escape speed have all been linked to survival. Of these, body size has received the most attention from researchers, which has subsequently led to the development of a number of theories on how this characteristic may influence the predator-prey relationship. One of the most popular of these is known as the ‘bigger is better’ hypothesis. This theory predicts that larger body size should increase an individual’s ability to escape from a predator due to the characteristics associated with this, such as overall strength and visual development. Bigger is thought to be better, but is this always the case?

Compared with other habitats and ecosystems, not a great deal is known about predator-prey relationships within tropical reef communities. What we do know is largely limited to predator identity and, to some extent, to what these predators eat. But what drives these interactions and how does body size influence the outcome? How would fish populations respond to the removal of certain predators from a reef fish community? It is precisely these questions that have led our research team to Lizard Island, in the northern sector of the Great Barrier Reef. We want to examine the predator-prey relationship during the ‘early juvenile’ or larval phase of tropical fish, and determine whether a predator’s choice of prey is influenced by factors such as the prey’s size, weight and swimming speed, as these characteristics vary from individual to individual at the beginning of the juvenile stage.

Most coral reef fish have a life cycle consisting of an open ocean larval phase followed by a juvenile to adult phase near the reef. The transition between the two stages is marked by rapid and dramatic changes in the body of the fish, and a sudden move from the open ocean to coral reef habitats. This point is commonly known as ‘settlement’. Not surprisingly, it is also characterised by increased levels of mortality in the first 48 hours following settlement, as individuals are forced to adapt to life not only on the reef but also with a previously unknown set of predators.

However, studying the interactions between predators and prey during this phase is no easy task. On the northern Great Barrier Reef, coral reef fish settlement usually occurs within 2-3 days of a new moon during the warmer summer months. These short windows of opportunity, combined with the difficulties associated with working underwater, transporting fish and adapting them to the laboratory, often make research a daunting task. These obstacles are overcome using a combination of innovative techniques, long working hours and a measure of sheer persistence. We collect the larval fish immediately prior to settlement using purpose-built traps that use artificial light to attract and contain fish of this life stage only. These fish are subsequently transported to an aquarium, along with predatory fish, before being used in a series of aquarium and field-based trials.

According to the ‘bigger is better’ hypothesis, being larger at the time of settlement should result in an increased chance of surviving an attack by a predator during the period immediately following settlement. However, our initial research shows that this is not always true. There may be several reasons for this.

Communities of reef-based predators can differ considerably over quite small distances. Species that are abundant in one location may be particularly rare in a similar habitat just 100 metres away. In the same way that different predators prefer different types of prey, so too do they prefer different sizes of prey. This relationship is driven by physical characteristics of predators, such as mouth size, and behavioural differences between different predator species. As a result, the predator community into which a reef fish settles may very well determine which individuals survive.

So why don’t larger individuals survive more often than smaller fish over this period? The answer may well lie in an alternative hypothesis known as ‘optimal foraging theory’. According to this theory, being either very large or very small in size should assist prey to escape during a predatory encounter. The theory predicts that a predator should prefer those individuals that provide the greatest energy return. This is generally a trade-off between the potential energy intake from eating a fish and the amount of energy required to catch it. Larger prey provide a higher energy return but smaller prey generally require less energy to catch. This usually results in a preference for medium-sized prey.

At the time of settlement, juvenile reef fish vary in the characteristics that can help them survive a predatory attack. However, these characteristics are not strongly associated with body size. For example, larger individuals are not necessarily faster. This means that they may be easier to catch than smaller prey. If this is the case then, according to the optimal foraging theory, predators should prefer larger prey because of their greater energy return. Consequently, larger prey individuals may be targeted by some predators at the time of settlement. Our research hopes to show that larger size may, in fact, be a distinct disadvantage during certain life stages.

Questions 1-4

Do the following statements agree with the information given in Reading Passage 1?
In boxes 1-4 on your answer sheet, write

TRUE if the statement agrees with the information
FALSE if the statement contradicts the information
NOT GIVEN if there is no information on this

1. Research to date has concentrated on the importance of escape speed in surviving an attack by a predator.

TRUE
FALSE
NOT GIVEN

2. According to the ‘bigger is better’ hypothesis, larger animals have better eyesight.

TRUE
FALSE
NOT GIVEN

3. Early-juvenile reef fish share similar characteristics.

TRUE
FALSE
NOT GIVEN

4. Fully developed reef fish have a slower swimming speed than juveniles.

TRUE
FALSE
NOT GIVEN

Questions 5-7
Complete the summary below.
Choose NO MORE THAN TWO WORDS from the passage for each answer.
Write your answers in boxes 5-7 on your answer sheet.

Life cycle of fish in the Lizard Island study

Phase 1: Larval stage
takes place in the 5. ____________.

Phase 2: Juvenile stage
takes place close to the 6.____________.
the move from one habitat to another is called settlement.
7.____________ rates are high in the early part of this stage.

Phase 3: Adult stage

Questions 8-13
Complete the notes below.
Choose NO MORE THAN TWO WORDS from the passage for each answer.
Write your answers in boxes 8-13 on your answer sheet.

Lizard Island study
Aim:
to study the relationship between predator and prey in juvenile reef fish

Problems:
time – change of habitat takes place in summer and is linked to the 8__________
working conditions
adaptation – difficult to move and settle fish into the 9____________.

Method:

larval fish are drawn into a special trap with the aid of 10____________.
11____________ are also collected
both undergo trials

Possible reasons why ‘bigger’ is not always ‘better’:

the number and type of predatory fish on the reef can vary from place to place
physical features (e.g. 12____________) affect which prey a predator can eat
optimal foraging theory suggests that the most common choice of prey should be 13____________ in size
large juvenile fish may swim slowly and so may be targeted more often

Reef Fish Study IELTS Reading Answers

1. FALSE
The statement suggests that researchers have mainly focused on escape speed. However, the passage indicates that body size has attracted the greatest attention from researchers. Therefore, the answer is FALSE.

2. TRUE
The statement suggests that larger animals may have better eyesight. The passage supports this idea by linking larger body size with characteristics such as visual development. Therefore, the answer is TRUE.

3. FALSE
The statement suggests that individual fish share similar characteristics during the early juvenile stage. However, the passage explains that these characteristics differ from one individual to another at the beginning of this stage. Therefore, the answer is FALSE.

4. FALSE
The statement contradicts the information provided in the passage. Therefore, the answer is FALSE.

5. open ocean
The question asks where the larval stage occurs. According to the passage, fish spend their larval stage in the open ocean. Therefore, the answer is *open ocean*.

6. reef
The question asks where the juvenile stage takes place. The passage explains that fish move towards the reef as they progress through the juvenile stage and towards adulthood. Therefore, the answer is *reef*.

7. mortality
The statement refers to the high death rate during the early stage of development. The passage highlights that mortality increases significantly within the first 48 hours. Therefore, the answer is *mortality*.

8. new moon
The question relates to the timing of habitat change, also known as settlement. The passage states that settlement generally takes place during summer, within two to three days of a new moon. Therefore, the answer is *new moon*.

9. laboratory
The passage explains that transporting fish and helping them adjust to laboratory conditions is a challenging process for researchers. Therefore, the answer is *laboratory*.

10. artificial light
The passage describes how traps use artificial light to attract larval fish. This lighting helps researchers collect the fish for further study. Therefore, the answer is *artificial light*.

11. predatory fish
According to the passage, larval fish are transported together with predatory fish during collection. Therefore, the answer is *predatory fish*.

12. mouth size
The passage explains that a fish’s physical characteristics influence its choice of prey. One important factor determining which prey it can consume is its mouth size. Therefore, the answer is *mouth size*.

13. medium
The passage refers to optimal foraging theory, which explains how animals select prey. According to this theory, fish tend to prefer prey of a medium size. Therefore, the answer is *medium*.

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