Our Conclusions

In these web pages, you have been looking for possible reasons why insects are only rarely found in the largest habitat on earth. There are at least six principle hypothesis. The first hypothesis suggests that insects are limited by salinity. While this may be true for the majority of insects, many flies have efficient osmoregulatory mechanisms that allow then to tolerate salinity in excess of 3x that of the ocean. The second hypothesis suggests that ocean depth limits an insect's ability to complete its development. This is true of many insects and yet, chironomid fly larvae survive at depths below those that even the deepest diving mammals can reach. The third hypothesis suggests that the combination of salinity and depth imposes a further limitation of oxygen content in ocean water. Again, certain fly larvae are able to survive months without oxygen, and numerous aquatic insects survive in polluted waters with similar or lower oxygen concentrations. The fourth hypothesis is that flowering plants which have co-evolved with insects on land are nearly absent from the ocean and thus prevent insects from occuring there. This hypothesis is undermined by the fact that one flowering plant, the seagrass does well in the ocean but is relatively free from insects. The fifth hypothesis considers nutritional limitation. Although marine Halobates do differ in fatty acid composition, other insects should be able to make a similar leap, acquiring the ability to feed on abundant ocean plankton.

Finally, the sixth hypothesis considers the fact that insects were successful because they colonized land. By moving away from the ocean, they adapted to a terrestrial existence while their major competitors the crustaceans stayed in the sea and continued to adapt. As millions of years passed, insects lost their ability to successfully compete in the ocean while crustaceans have had only limited success in invading land. This is our pick, for the most likely explanation for the absence of insects in the oceans. As potential evidence, we note that the only insects that live on the open ocean, live on its surface. As such, they never come in contact with the crustaceans living beneath its surface!

There are other possible explanations and evidence for these alternative hypotheses. Perhaps one of your ideas is a better hypothesis than those we thought of; we'd like to hear from you.

Your adventure is now complete... please email us with questions or comments!

Back to the marine insects home page.

 

Send comments on this web site to Wyatt Hoback at hobackww@unk.edu.
Send comments or questions about marine sea skaters to Lanna Cheng at lcheng@ucsd.edu.


For further information on Marine Insects, check your local library for the book Marine Insects, 1976 edited by Lanna Cheng, North-Holland Publishing Company.

Drawn images in this website are by Doug Golick and are copywritten.
Photographs are mostly by Lanna Cheng and are copywritten.
Data are taken from the Marine Insects book and from various papers and reviews on the insect species living in contact with the ocean.

Lanna Cheng continues to actively research marine insects at the University of California, San Diego.

Leon Higley is a professor at the University of Nebraska-Lincoln where he teaches entomology and researches insect-plant interactions and other stuff.

Doug Golick is a web designer at the University of Nebraska Lincoln.

Wyatt Hoback is an assistant professor of Biology at the University of Nebraska at Kearney where he teaches biology, entomology, limnology, ichthyology, and ecology. He researches insect competition and the effects of introduced species on ecosystems.