PADI Divemaster Certification Practice Exam

How do alien species negatively impact aquatic environments?

1. They slow down current flow

2. They have no natural predators

3. They are usually smaller than native species

4. They only impact freshwater ecosystems

The correct answer is: They have no natural predators

The correct choice highlights that alien species often thrive in new environments because they lack natural predators. In their native habitats, these species have a balance maintained by predators that keep their populations in check. When introduced into a new aquatic environment, alien species may proliferate uncontrollably, leading to ecological imbalances. This unchecked growth can result in the alien species outcompeting native organisms for resources such as food and habitat, ultimately leading to declines in native populations. The absence of natural predators means there is nothing to regulate their numbers, allowing them to dominate ecosystems that were previously stable and could support diverse communities of native species. In contrast to this understanding, the other options do not accurately reflect the mechanisms by which alien species can negatively impact aquatic environments. For example, the assumption that alien species slow down current flow does not address the ecological consequences of their presence. Similarly, whether they are smaller or not does not inherently affect their ability to compete with or displace native species. Lastly, while some alien species can have effects in freshwater ecosystems, the assertion that they only impact freshwater environments is too restrictive, as many alien species also affect marine ecosystems significantly.