3. Meiofauna. 
In the past, meiofauna has been distinguished from macrofauna merely on 
the basis of relative size. Macrofauna was defined as those animals retained 
by a 500-micrometer mesh, and meiofauna as those metazoan animals passing 
through a 500-micrometer mesh, but being retained by a 64-micrometer mesh 
(McIntyre, 1964; Muus, 1967; Hulings and Gray, 1971). However, McIntyre 
(1968) and Cox (1976) noted that macrofauna and meiofauna fill different 
ecological niches. Macrofauna are generally burrowers that feed on 
particulate organic matter (detritus and plankton), whereas meiofauna is 
generally interstitial and feeds on dissolved organic matter that has become 
particlized (microdetritus) and epipsammic bacteria (Cox, 1976). 
There are other differences, especially in community structure. Whereas 
sandy beaches usually possess impoverished macrofauna, they display abundant, 
stable, and diverse meiofauna (McIntyre, 1968, 1969; McIntyre and Murison, 
1973; McLachlan, 1977b). The number of species of meiofauna is generally an 
order of magnitude greater than the number of species of macrofauna. The 
numerically dominant meiofaunal groups are usually nematodes and copepod 
crustaceans (McIntyre, 1971; Sikora, Erkenbreacher, and Coull, 1977); the 
macrofauna is usually dominated by mollusks, and either amphipod or decapod 
crustaceans (Dexter, 1969; McIntyre, 1971; Cox, 1976). There are other indi- 
cations that these communities remain ecologically separate. These include 
nonnormal size array and differences in habitat, migratory behavior, and 
reproduction. Sanders (1960) theorized that when a normal community is divided 
into size classes, the largest groups (according to biomass measurements) 
should be those members of the community with the smallest size. Conversely, 
as the size of individual organisms increases, the relative proportion of 
total biomass should decrease. However, in actual situations frequency polygons 
for meiofauna compared to macrofauna always show that the macrofaunal groups 
constitute far more of the biomass than meiofaunal groups (McLachlan, 1977a). 
Thus on the basis of size class distribution, macrofaunal and meiofauna evi- 
dently represent different communities. The meiofauna occupies a different 
spatial niche than the macrofauna. The most diverse group of macrofauna on 
any beach is most likely occupying the surface in the intertidal zone, whereas 
most of the meiofauna will likely be found deeper in the sands above the high 
tide mark. Because of this difference in habitat migratory differences are 
also common. Macrofauna generally migrates directly with the tide; meiofauna 
migrates with fluctuations in the water table, if at all. If the meiofauna 
migrates with the tide, it is done only after a lag of up to 4 hours (Riedl 
and McMahan, 1974). There is generally no seasonal migration of the meiofauna, 
whereas the macrofauna often leaves the beach during winter (Saloman, 1976; 
Matta, 1977; Leber, 1977). Finally there are likely to be differences in 
reproduction. Meiofauna generally reproduces all year long, bears few young, 
broods them, and displays interstitial larval life histories. The macrofauna 
generally only breeds for a short time, has large numbers of eggs, and 
exhibits free-swimming pelagic larval life histories (Riedl and McMahan, 1974). 
Figure A-2 indicates that the meiofaunal community is composed of detritus 
feeders, epistrate browsers and lickers, and meiofaunal predators (Cox, 1976), 
however, the meiofauna appears to be at the top of a food web separate from 
the macrofauna (McIntyre and Murison, 1973; Cox, 1976; McLachlan, 1977a). 
Although meiofaunal community structure is evolutionarily advanced, meiofauna 
70 
