Settlement of barnacle larvae is governed by Euclidean and not fractal surface characteristics

Abstract

Summary 1.Extensive research has been carried out on the biological, physical and chemical characteristics of surfaces that promote, or prevent, marine fouling. The texture of the substratum is probably the most important factor affecting settlement of the Acorn Barnacle Semibalanus balanoides in the field. The aim of this study was to examine the relationship between fractal and Euclidean descriptions of substratum surface complexity and settlement of the Acorn Barnacle. 2. Replicate settlement panels with smooth, fine, medium and coarse surfaces were manufactured using a precise and accurate technique. Two-dimensional profiles were measured using a laser profilometer, and two surface complexity indices, potential settling sites (PSS) and the Minkowski fractal dimension (MFD) were calculated. PSS is a Euclidean measure of the surface complexity taking into account the body size and settlement behaviour of the barnacle larvae, whereas MFD is a fractal dimension related to the complexity of the surface at a variety of scales. 3. In a field experiment, settlement density of S. balanoides was positively related to both PSS and MFD. To break the correlation between PSS and MFD, surfaces were modified by sandblasting with either 64-125-µm or 250-500-µm grains. This decreased MFD but did not affect PSS. 4. A further field experiment found that this erosion using small-scale sand particles had no effect on settlement of the barnacle. It was concluded that S. balanoides larvae were responding to characteristics of the surface related to PSS and not MFD. 5. Although a correlation was found between species abundance and the fractal complexity of its habitat, further experimentation showed that there was no causality in this relationship. Many surveys, with no experimentation, of aquatic and terrestrial communities have shown relationships between organisms and their habitat and assumed causality; however, care must be taken in interpretation of such studies. Jacobi & Langevin 1996;Wieczorek & Todd 1998). The most common fouling marine invertebrates are barnacles, which are ecologically and economically important and consequently they have been extensively studied (see, for example, Stubbings 1975;Crisp 1984;Southward 1987). The thoracian barnacles are characterized by the Acorn Barnacle Semibalanus balanoides L. The adult barnacle is sessile and dispersion and colonization of new sites is achieved by a planktonic larva. The process of moving from the final stage planktonic larva (cyprid) to the settled adult barnacle requires careful selection of the settlement site if metamorphosis is to be successful and fitness of the adult is to be maximized (e.g. Young 1987;Hoffman 1988;Raimondi 1988, Raimondi 1990Walters & Wethey 1991;Pineda 1994). Many barnacle species have been shown to be highly selective in their choice of the settlement site, even in a high energy littoral zone, and parameters such as colour (Kon-ya & Miki 1994) Much work has been carried out on the effect of surface roughness on the settlement of barnacles. ...

Interactions between substratum rugosity, colonization density and periwinkle grazing efficiency

“…These sedentary polychaetes were 5 times less abundant in the Koehler (1999) study. On the other hand, similar preferences of B. improvisus for low initial rugosity surfaces were reported by Hills et al (1999) and Andersson et al (1999). On the 3 coarsest substrata Balanus improvisus preferentially grew in the crevices between beads -exclusively so on 0.5 and 1 mm rugosities.…”

Fractal measures of habitat structure: maximum densities of juvenile cod occur at intermediate eelgrass complexity

“…The density of freshwater invertebrate species increased with fractal dimension of stream bottoms (Taniguchi & Tokeshi 2004) but no relationship between resident fauna and fractal dimension of habitat was found in a study on spider diversity in shrub patches (Whitehouse et al 2002), or a study of barnacle larvae settlement to benthic substrates (Hills et al 1999). Gastropod density increased with fractal dimension on rocky intertidal shores, but not in mangrove habitat (Beck 1998).…”

Habitat complexity: approaches and future directions

“…In addition, this type of complexity plays an important role in early stages of succession of other types of intertidal habitat, e.g., by increasing the recruitment of sessile fauna (Hills et al, 1999).…”