Evolutionary ecology

Maria finishes her Master thesis

Spawning area for bearded goby on outer shelf off central Namibia in anoxic waters reported recently by Maria L. Seivåg in her Master thesis

Gonads from typical stage 3 male Sufflogobius bibarbatus. Top picture:...
Gonads from typical stage 3 male Sufflogobius bibarbatus. Top picture: sneaker male with large testes and small seminal vesicles (SV). Bottom picture: territorial male with large seminal vesicles. The seminal vesicles contain a sticky material used for building nests and for attaching eggs females lay in the nests.
Maria Larsen Seivåg

Maria Larsen Seivåg has been studying Variation in reproductive strategies in African bearded goby Sufflogobius bibarbatus for her master project at the University of Bergen. The happy ending of Maria’s work was achieved on the 20th September when she obtained her Master degree in Marine Biology. Her findings confirmed the presence of two alternative reproductive tactics, territorials and sneakers, and hinted on the existence of a third unknown tactic. The territorial males have tiny testes, but large seminal vesicles (SV; see lower part of the figure below), whereas the sneakers have small seminal vesicles and large testes (see upper part of the figure below). Maria has developed a macroscopic maturity stage key that accounts for both the testes and the seminal vesicles. Using histology, she found that this key reflected macroscopically determined maturity in a satisfactory manner.

Maria also report that low bottom oxygen stood out as the most important factor in limiting size, condition and spawning activity in male bearded gobies, and the demersally nest-bound territorials appeared the most affected by the lack of such.

Across the shelf area off central Namibia between 20.5° and 24.5°S, the fish collections and environmental data that Maria scrutinized suggested a spawning area in the hypoxic outer area (0.37–0.40 ml l-1 dissolved bottom oxygen) while the anoxic middle area (0.10–0.17 ml l-1 dissolved bottom oxygen) appeared to be too low in oxygen for spawning to take place. From the results of this study, the bearded goby seems to work a delicate balance between oxygen levels that are low enough to deter predators yet high enough to feed and spawn in.