marine biology fieldwork -jetty communities

Rocky shore Zonation practical for the Cambridge (CIE 9693) A level Marine science course.  TRACC teach this class once each year from January to April.  The first fieldwork practical of the course was a study of the zonation on the man made wooden jetty on Pom Pom Island, Sabah Malaysia.

The students marked the posts at 50 cm intervals relative to the tidal chart datum (lowest astronomical tide).  The location of the barnacle zone and the snail zone was measured in relation to this fixed chart datum.  The vertical position relative to the tide of all of the visible snails was measured for 7 jetty legs.   Observations were made that the snails were more abundant on the N side legs (shaded by the jetty above) and on the South side legs (not shaded from above) the snails were mostly on the side of the leg away from the sun.

The results showed clear concentration into discrete zones by both barnacles and snails.  The barnacles were concentrated into the zone from 50cm above cd to 90cm above cd with a few on the shady North legs at upto 110cm.
The snails were more abundant on the North legs (average 14 per leg) than on the South Legs (average 5 per leg).  The snails were also found higher up the Shady legs (average position of top snail was 1.7m (N legs) compared with 1.4m (S Legs).  The zonation of the snails is on the kite graph and the snails were most abundant at 1.4m above CD.

It is clear that the snails are actively choosing the shady jetty legs and if they are on the sunny side legs then they find the shadiest spot.  On the shady legs they can also rest between tides higher up the leg presumably because it is cooler.

These results lead to more questions about ecology and behaviour that the A level class will be answering in the near future.

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