Random walk, zonation and the food searching strategy of Terebralia palustris (Mollusca, Potamididae) in Kenya

Terebralia palustris is a common mud-whelk present at a particularly high density in all Indo-West Pacific mangroves. Young snails feed on nothing but mud while larger specimens are able to feed on fallen leaves too. In Kenya (Mida Creek) under the canopy, competition for mangrove leaves can be very high due to the high density of Sesarmidae crabs. On open exposed muddy platforms, no Sesarmidae occur but the leaf density is very low because the leaves are only randomly present as they are deposited and removed twice a day by the tide. However, the snail density is always very high, raising the question as to whether the snails use a special searching strategy to optimize their resource finding rather than a purely random movement. By analyzing the snails' movements on a uniform area at different levels and comparing them with simulated random paths, we could show that the snails' movements are not purely random. The distribution of different size classes of T. palustris in Mida Creek was known to be quite odd: the same simulation approach suggests that the zonation asymmetry could reasonably be due to the stochastic recruitment of juveniles in space and time and maintained by a substantial long-lasting spatial inertia. © 2008 Elsevier Ltd. All rights reserved.Link_to_subscribed_fulltex

Rhythmic vertical migration of the gastropod Cerithidea decollata in a Kenyan mangrove forest

In Mida Creek, Kenya (3°20′S, 40°5′E), at high water, the snail Cerithidea decollata dwells on the trunks of mangrove trees (Avicennia marina), while during low water it migrates to the ground, foraging at various distances from the trunk, where it aggregates again well before the incoming tide. Snails from the upper shore level are 150-200 m distant from those living at the lower shore level and they cluster at lower heights on trunks. In any case, sufficient height is usually attained to avoid being submersed. An experiment was designed (February and October 2005), exchanging individuals from different shore levels subject to different tide regimes, in order to test whether snails rely on internal information or on external, direct cues, to adapt their behaviour to local conditions. Results show that C. decollata mostly rely on internal information, presumably based on an internal clock. When individuals from upper and lower shore levels were exchanged, their internal clocks continued to govern when to ascend the home trunk and how high to climb for five to six successive tides, after which the behaviour was reset to the new local conditions. © 2007 Springer-Verlag.Link_to_subscribed_fulltex

Effects of urban wastewater on crab and mollusc assemblages in equatorial and subtropical mangroves of East Africa

info:eu-repo/semantics/publishe

Growth stages of the two insect pests infesting on <i>S</i>. <i>alba</i>.

<p>Growth stages of the two insect pests infesting on <i>S</i>. <i>alba</i>.</p

The two woodborer species infesting <i>S</i>. <i>alba</i> in Kenya.

<p>The two woodborer species infesting <i>S</i>. <i>alba</i> in Kenya.</p

Scheme indicating the major and common mangrove zones, with the tidal range and presence of insect infestation of both metarbelid moth and <i>B</i>. <i>rubra</i>, as observed along the Kenyan coast.

<p>Scheme indicating the major and common mangrove zones, with the tidal range and presence of insect infestation of both metarbelid moth and <i>B</i>. <i>rubra</i>, as observed along the Kenyan coast.</p

Scheme diagram of the hosts’ protection mechanisms against infestation by the insect pests.

<p>Scheme diagram of the hosts’ protection mechanisms against infestation by the insect pests.</p

Infestation of the four sampling sites in Gazi.

<p>The figures are percentage totals ± standard deviation of new and old infestation inside the sampling plots. No species other than <i>S</i>. <i>alba</i> were infested in any of the studied plots.</p