Causes of Macrofaunal Outline on a Dissipative Beach

Investigating the causes of macrofaunal outline on a dissipative beach in Abberffraw.

Aim: To investigate macrofaunal abundance and distribution pattern across five different shore levels.

Hypothesis: whether physical and biological factors have direct correlation on community structures of infauna species. Cisneros et al. (2011) and Croker & Hatfield (1980) have tested this hypothesis and reported significance.

Figure lists are illustrating distribution and abundance of 31 species sampled on a vertical gradient across 5 shore heights. Out of these, three polychaetes species; Scolelepis squamata, Scoloplos armiger, Nephtys sp, including twocrustaceans Bathyporeia sp, and Eurydice pulchra were found throughout sampling stations (Fig 2). As shore slope decreases species diversity increases (Fig 1). Station 2 had maximum abundance (4050 ind./ m²) whereas station 4 had the greatest species richness (SR = 18) (Fig 1).

Sandy shores are dynamic environments with biotic (Croker & Hatfield, 1980) and abiotic (Cisneros et al., 2011) conditions changing continuously, influencing species spatial scales along shores. Three major environmental factors, influencing community structures (McLachlan & Brown, 2006); 1. beach type (physical gradient/ sediment texture); 2. tidal regime (wave action/ moisture/ organic enrichment); and 3. swash climate (water filtration) (Defeo, & McLachlan, 2005). Zonation patterns are evident, due to tidal movement (Brazeiro & Defeo 1996), seasonal migration (De Alava & Defeo 1991), and predation contributing to the variations. Ansell et al., (1999), reported that predators migrate following prey species. Cisneros et al. (2011), stated physical drivers influenced macrofaunal community.

Abberffraw shore consists of fine grainy sand particles with small interstitial space facilitating burrowing (McLachlan et al., 1996) and slower water filtration (McLachlan & Brown, 2006) providing suitable living conditions. Dominating middle and lower shores are Polychaetes (Connor et al., 1997) in water-saturated sediments whiles crustaceans are generally distributed at different shore levels (Dahl, 1952). Work, et al., (2008) found that water drainage is critical in determining polychaets presence; Scolelepis squamat, Scoloplos armiger andNephtys sp.can tolerate drained sediments (Connor et al., 1997) explaining the occurrence at higher stations (Fig 2). More studies are needed in determine zonation and causes (Defeo, & McLachlan, 2005).

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