An experimental evaluation of the influence of barnacles, crevices and seasonal patterns of grazing on algal diversity and cover in an intertidal barnacle zone

On artificial surfaces (seawalls) in Sydney Harbour (Australia), local biodiversity of grazers differs between sandstone and concrete constructions because limpets Siphonaria denticulata are more abundant on sandstone, while Patelloida latistrigata are more abundant on concrete walls. Competition between siphonarian and patellid limpets is unstudied on artificial structures, although the limpets are common and are known to compete in natural habitats. We tested hypotheses that the substratum (concrete or sandstone), intra-and/or interspecific competition, or a combination of factors, influence recruitment, survival, rates of grazing, or the quantity and types of algal food to explain the observed patterns. Such analyses enable better understanding of the processes influencing diversity. Both species recruited more to concrete than to sandstone plates. S. denticulata recruited more in the presence of conspecifics and slightly less in the presence of P. latistrigata. Results varied between locations and experiments, but each species survived better on concrete, which had more macro-and micro-algal food. Increased densities of P. latistrigata reduced survival of conspecifics and of S. denticulata. S. denticulata had no effect on survival of P. latistrigata, but reduced amounts of macro-algae. P. latistrigata did not affect macro-algae. Initially, there were more micro-algae on concrete and a minor effect of large densities of S. denticulata. After 95 d, differences between habitats decreased and P. latistrigata were more strongly associated with reduced amounts of micro-algae. Neither substratum, density, nor mix of limpets affected rates of grazing. Thus, interspecific interactions were similar to predictions from knowledge of natural habitats, despite the different characteristics of artificial habitats and the reduced intertidal area available for grazing. Recruitment and competition were important in explaining different densities of these limpets on sandstone and concrete walls. Increasing urbanization requires more experimental tests to identify how well current theories of intertidal ecology and of the processes maintaining local biodiversity can apply to artificial shorelines.

Section: Discussionmentioning

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Differential patterns of distribution of limpets on intertidal seawalls: experimental investigation of the roles of recruitment, survival and competition

Iveša¹,

Chapman²,

Underwood³

et al. 2010

“…In contrast, juvenile barnacles in crevices were less likely to be bulldozed by limpets than were those on open surfaces (Dayton 1971) and many juvenile algae survive better in areas of complex topography or cracks and crevices, where grazers cannot eat them (Lubchenco 1980) or where moisture enhances their growth (Jernakoff 1985). Complex topography can also influence the outcome of competition for space among barnacles (Walters & Wethey 1986).…”

Section: Discussionmentioning

confidence: 97%

Landing on one's foot: small-scale topographic features of habitat and the dispersion of juvenile intertidal gastropods

Underwood¹

2004

The associations of densities of very early recruits of mobile intertidal species with features of their habitat have rarely been examined in the field. Here, experimental manipulation of local topography (by provision of cracks, grooves and pits of various sizes) demonstrated species-specific responses by animals naturally recruiting into experimental plots. Densities of small (< 3 mm) juvenile snails (Austrocochlea porcata, Bembicium nanum and Nerita atramentosa) and limpets (Cellana tramoserica and Patelloida latistrigata) varied among experimental topographies in consistent ways. Although local densities were influenced by appropriate topographic features, only N. atramentosa and P. latistrigata showed increased density per area of shore with alteration of topography. For the former species, provision of grooves and large pits also caused enhanced densities on open surfaces. P. latistrigata had decreased densities on open surfaces, but very much enhanced densities in grooves and other features, thus increasing total numbers in an area. Experimental transplantation and subsequent movements of small juveniles demonstrated very similar patterns to those shown after natural recruitment, indicating behavioural responses to local topography. Responses to small-scale topography can explain small-scale variation in numbers of very early recruits of intertidal gastropods.

“…In m a n n e systems, the lmportance of nutrients and grazers in regulating phytoplankton abundance and community structure is well documented (see Harrison et a1 1983, Hecky & Kilham 1988, Retd et a1 1990, Gervals 1991, Morales et a1 1991, Wassman 1991 for reviews) However, the relative Importance of these 2 factors still remains unclear, mainly because of the difficulty in conductmy experimental manipulations in the ocean Recently, Kivl et a1 (1993) man~pulated the nutrient reglme and abundance of grazers In factorial experiments in enclosures in the Baltic Sea and found that the relative importance of bottom-up and topdown regulat~on of the phytoplankton assemblages varied with season Community organ~zation of rocky intert~dal shores has been studied extensively, and the importance of top-down regulating factors is well established ( e g Paine 1966, Dayton 1971, 1984, Connell 1972, Menge 1976Lubchenco & Menge 1978, Petra~tls 1983, Sousa 1984, Underwood & Denley 1984Jernakoff 1985 Filter-feeders such as mussels and barnacles are often the dornlnant space occupiers on these shores One of thelr food sources 1s phytoplankton the abundance and specles compos~tlon of w h~c h can be greatly affected by nutrient concentration However the effect of nutrient availability in the regulat~on of rocky lntertldal communities remains largely unknown Menge (1992) suggested that t h~s g a p In our knowledge IS partly the result of the d~fficulty in experimentally manipulating the concentratlons of nutrients In these systems On shores with colon~es of seabirds, guano can be a source of increased nutrients (Gannlng & Wulff 1969, Bosman & Hockey 1986) and a few descriptive s t u d~e s have suggested that the supply of guano may affect the abundance and community composit~on of macroalgae (Bosman & Hockey 19861988Wootton 1991 In an unreplicated experiment, Bosman et a1 (1986) observed an increase in chlorophyll a of benthic microalgae when they increased the supply of guano to the high intertidal zone of a rocky shore In South Africa…”

Section: Introductionmentioning

confidence: 99%

Top-down and bottom-up regulation of phytoplankton assemblages in tidepools

Meta×as¹,

Scheibling²

1996

ABSTRACT-We examined the relative importance of bottom-up (nutrient availability) and top-down (grazing) factors in regulating phytoplankton assemblages in tidepools on a rocky shore near Halifax, Nova Scotia, Canada. We manipulated the concentration of nutrients and density of micrograzers in pools in the h~g h intertidal and splash zones in 3 repeated, 1 to 2 wk experiments in November 1992 and June and August 1993 For each expenment, we set up 4 orthogonal treatments in enclosures in each of 3 or 4 pools: (1) micrograzers removed and nutrients enriched, (2) micrograzers removed and nutrients at natural levels, (3) micrograzers at natural densities and nutrients enriched, and (4) both micrograzers and nutrients at natural levels. For each treatment, we measured the change in abundance over 1 wk intervals of 5 taxonomic groups of phytoplankton: centric diatoms, pennate diatoms, cryptomonads, prasinophytes, and chlorophytes. We examlned the effects of nutrient concentration, grazer denslty, and pool on the phytoplankton assenthlage uslng multivariate analysis of variance. There were significant effects of grazer density in June and August, and of nutrient concentration in August, which varied among phytoplankton groups and tidepools. In 1 pool in June, reduction in grazer density had a negative effect on pennate diatoms, cryptomonads and chlorophytes in the first week of the experiment, but a posihve effect on pennate diatoms In the second week. In another pool in the second week, grazer reduction had a positive effect on prasinoph.ytes but a negative effect on chlorophytes. In 1 pool in August, nutrient enrichment had a posltlve effect on pras~nophytes in the first week of the experiment, and grazer reduction had a negative effect on cryptomonads and chlorophytes in the second week. In another pool in the first week, nutrient enrichment had a negative effect on chlorophytes. Based on the frequency of significant effects, we concluded that grazing is more important than the nutrient regime in regulating phytoplankton assemblages in tidepools. The large variability among tidepools in the response of phytoplankton to our manipulations supports our previous suggestion that regulation of these assemblages occurs at the scale of the individual pool rather than the intertidal zone.