shallow- water hard-substrate communities 

 (Ogburn 1984; Darcy 1985a, b; Hay 1986; Hay 

 et al. 1987, 1988). 



4.4 ORGANIZATION OF SHADED, SUBTIDAL 

 COMMUNITIES 



Organisms growing on shaded hard 

 substrates have long been regarded as a 

 source of trouble since they also grow on 

 the bottom of boats and must be 

 periodically scraped off. As a result 

 this assemblage is often referred to as 

 the fouling community. Low light 

 availability generally limits the growth 

 of macroalgae on these substrates, 

 allowing sessile animals to dominate. 



The starting point of community 

 development on unoccupied substrate is the 

 recruitment of larvae to that substrate. 

 This process is extremely unpredictable; 

 different patterns of initial development 

 are possible from month to month and from 

 year to year (Mook 1976, 1980; Sutherland 

 and Karlson 1977). Instead of preparing 

 the way for subsequent arrivals, most 

 resident adults strongly inhibit the 

 recruitment and growth of other species 

 (Sutherland 1974, 1977, 1978, 1981; 

 Sutherland and Karlson 1977). This 

 pattern of development appears to conform 

 to what Connell and Slayter (1977) have 

 termed the inhibition model of succession. 

 Species vary in their ability to resist 

 subsequent invasion and larvae vary in 

 their ability to invade assemblages of 

 adult organisms. As a result, the 

 direction and rate of community 

 development are dependent on the order of 

 invasion and are difficult to predict. 



The endpoint of community development 

 depends on location and, at times, on the 

 perspective of the observer. Sutherland 

 and Karlson (1977) have argued that near 

 Beaufort, NC, community composition never 

 stops changing and that no climax 

 community is present. As pointed out in 

 previous sections, the winter species 

 assemblage is extremely variable from year 

 to year. However, Sutherland (1981) has 

 also argued that one endpoint is a 

 community dominated by the solitary 

 tunicate Styela pi icata . This species 

 predictably dominates summer assemblages, 



inhibits recruitment by other species when 

 present, and reinvades in spring after 

 sloughing off the previous fall. This is 

 analogous to the mussel communities 

 studied by Paine (1966, 1974) and Menge 

 (1976), where patches of mussels are 

 removed by a variety of disturbances, but 

 eventually reinvade. Thus, whether or not 

 a "climax" is present depends on which 

 period is chosen as a reference point and 

 the length of the observation period. 



Other shallow water fouling 

 communities near Beaufort in North 

 Carolina "terminate" at different 

 endpoints. In their studies, Sutherland 

 and Karlson worked primarily at the dock 

 of the Duke University Marine Laboratory 

 and the nearby pilings of the railroad 

 bridge across the Beaufort channel . 

 Pilings near the Atlantic Beach bridge in 

 Bogue Sound are dominated by the colonial 

 tunicate Apl idi urn constel 1 atum , which 

 apparently can maintain this competitive 

 dominance for long periods of time. Wells 

 et al . (1964) found the fouling community 

 at Cape Hatteras to be dominated by the 

 colonial tunicate Botryllus schlosseri and 

 various species of sponges. 



Near Cape Canaveral in Florida, 

 community development in shallow water 

 ended in assemblages dominated by the 

 tubiculous amphipod Corophium lacustra and 

 several species of Balanus , in spite of 

 differences in initial development (Mook 

 1981). The Florida assemblage was 

 persistent, showing few annual changes in 

 species composition. 



On pilings in deeper waters (>2m) 

 near Beaufort, NC, the fouling community 

 is dominated by long-lived forms such as 

 the hydroid Hvdracti ni a echinata , the 

 sponge Xestospongia hal ichondroides and 

 the anemone Diadumene leucolena (Karlson 

 1978). These species are resistant to 

 grazing by the sea urchin Arbaci a 

 punctul ata , which removes other less 

 resistant forms. Grazer resistant forms 

 tend to recruit at very low intensities, 

 but gradually come to dominate through 

 vegetative growth (or binary fission in 

 anemones). In the presence of A^. 

 punctulata , these grazer resistant 

 endpoints would presumably be observed 

 regardless of differences in initial 

 development. Indeed, Karlson (1978) 



44 



