International Journal of Marine Science 2015, Vol.5, No.13, 1-11
2
may contribute substantially to species reacting to
local heterogeneity of habitats (Gu¨nther, 1992). High
rates of post-settlement movement are considered
important in providing a mechanism for rapid
dispersal and recolonization of surfaces by
invertebrates (Cummings et al., 1995). Some benthic
invertebrates are highly mobile as adults, and many
benthic species undertake regular nocturnal excursions
into the water column (Ohlhorst, 1982), and
defaunated sites often may be colonized within a few
hours, days or weeks (Virnstein and Curran, 1986). In
addition, transport of bedload and suspended load may
move juvenile and adult benthic stages of soft bottom
macrofauna, particularly bivalves and gastropods
(Cummings et al., 1995). It is now widely understood
that above-sediment movement by post-settlement
macrofauna is an important process structuring
soft-sediment systems and can have significant
influence on patterns of macrofaunal distribution and
abundance (Gu¨nther, 1992). Therefore, knowledge of
the ability of macrofauna to colonize new habitats is
generally important in determining the factors that
may be responsible for the rate and degree of
colonization of substrates. Experiments investigating
colonization may provide useful information about
rates of movement into unoccupied habitat (Bell and
Devlin, 1983) and can be used to measure distances
over which fauna can disperse.
Several studies have demonstrated that, rates of
macroinvertebrates colonization of new substrates
differ among taxa, and are affected by the
characteristics of the substrate (Smock, 1996).
Organic matter in form of detrital material of plant
origin, are known to be important source of food for
benthic invertebrates, therefore can influence their
choice and subsequent colonization of surfaces.
Studies have demonstrated a relationship between
allocthotonus organic matter input and invertebrate
community metrics such as abundance and diversity
(Commito et al., 1995). Experimental removal of
organic matter inputs has been shown to reduce
invertebrate abundance and biomass (Stewart, 1992;
Underwood and Chapman, 1992) and alter stream
food webs (Hall et al., 1994). Invertebrates improve
their fitness by seeking out BOM patches in
detritus-limited systems (Rowe and Richardson,
2001) and prefer organic matter with higher
Nitrogen content (Hall, 1994).
Organic matter incorporated into sand via retention in
debris dams, pools, and backwater areas, or mixed
into sand during flood-induced bed movement
function as a long-term food resource (Pain and Levin,
1981; Warwick, 1993). Invertebrates associated with
organic matter patches may also serve as an important
food source for fish populations and because organic
matter is an important energy source for aquatic food
webs (Hall et al. 2000), it may influence overall
productivity in aquatic systems.
Studies on the olonization of benthic invertebrates on
detrital plant materials are few. In this study,
formulated substrate of different compositions were
used to mimic varying scenarios that may arise as a
result of the deposition of plant debris from riparian
vegetation or farming operations (a common feature in
most water bodies in Nigeria) into estuarine systems.
This experimental study was designed to test the
hypotheses that substrate composition exerts a major
influence on the type and abundance of benthic
communities.
1 Material and Methods
1.1 Description of Study area
The experiment was performed in the estuarine Lagos
Lagoon system in south-west Nigeria. The lagoon is
part of the barrier-lagoon complex of the Nigerian
coastal zone. It lies between longitude 3º54" and 4 º
13"E and latitude 6 º25" and 6 º35" N, more than 50
km in length, between 3 and 13 m in width, and
separated from the Atlantic Ocean by a long sand spit
of 2 to 5 km wide (Webb, 1958). The lagoon is
characterised by fresh and brackish water conditions
occasioned by the heavy input of rainfall run-offs and
river discharges during the rainy season, and the
influences of tidal incursion and increased surface
water evaporation during the dry seasons. It has an
area of about 208 km
2
(FAO, 1969). It is generally
between 0.5 – 2 m deep in most parts with a
maximum of about 5 m in the main lagoon and 25 m
in some dredged parts of the Lagos Harbour. The tidal
range is about 0.3 – 1.3 m. The interconnecting creeks
are also very shallow and are sites of active siltation.
The lagoon sediments range between mud, sandy mud,
muddy sand and sand (Ajao and Fagade, 1991). The
lagoon also has a defined salinity gradient, linked with
the tidal pattern (Webb, 1958).
