Figure 1: Twin fan worm Bispira volutacornis

Mankind is having a major impact on every ecosystem on earth. From the very tops of the tallest peaks to the deepest abysses in our oceans, the world is changing, and how we measure these impacts, is also changing. Bioindicator species are helping us understand how we have affected our world and can even give us an insight into what these ecosystems used to be like, before records began.

A bioindicator is a species which has an observable response to a certain environmental stress. They can be categorized in several different ways including type of stress (temperature, pollution, UV exposure e.t.c) or type of response (behavioural, physiological). They allow us to see, not only the changes occurring in an environment, but how this change is affecting the ecosystem as a whole. The only downside is that first, a bioindicator must be discovered. That is what this project is all about.

Figure 2: Common brittle star (Ophiothrix fragiles), mimetizing in the rocky habitat.

Marine ecosystems usually observe relatively little change in their environments compared to their terrestrial counterparts. Temperature is regulated much more consistently and below a few meters there is very little impact from the weather. This makes the marine world a hotbed of potential bioindicators as, due to the lack of natural change, marine species have not evolved a resistance to stress so are often very sensitive.

Figure 3: Individual of Yellow umbrella slug (Tylodina perversa) .

The presence of a sewage treatment plant on the southern coast of Samos island provides the perfect gradient of “clean” and “contaminated” water. Here at Archipelagos, we are hoping to discover what impact this sewage plant has on the abundance and diversity of the invertebrate species. Marine invertebrates make ideal bioindicators because they are either sessile (don’t move) or they don’t migrate, so noincidence of seasonal abundance should affect the results. At 200m along the coast, transects are being performed in order to calculate a biodiversity index at each point. A team identifies every invertebrate species found within a 50m by 2m area.

The original hypothesis was that the biodiversity of the bays would decrease with decreasing distance from the plant. However, in the early stages of the analysis, it appears that biodiversity is increasing as the transects get closer to the sewage plant.Progress is slow due to the need for flat seas in order to complete transects safely which is rare during the winter months. Currently, over 1,600 individuals have been recorded belonging to over 40 different taxa. Arbacia lixula, Elysia timida and Balanophyllia europaea have currently proven the most abundant.

Figure 4. Snorkelers entering the water off of the rocky coastline.


Benedict Charles Rickards
BSc in Zoology
University of Leeds