Effects of interactions between algae and grazing gastropods on the structure of a low-shore intertidal algal community

Abstract

At low levels on shores in New South Wales, foliose algae are abundant and often occupy all substrata; microalgal grazing gastropods are rare or absent. At higher levels, foliose algae are sparse or absent and grazing gastropods are abundant. Hypotheses for the causes of the lower vertical limits of distribution of these grazers include the effects of increased predation or the deleterious physiological effects of increased period of submergence at lower levels on the shore. Alternatively, the presence of the algae, because they occupy space and deprive the grazers of substratum for feeding, may prevent the downward movement, or survival of the grazers at low levels. Under the first two of these hypotheses, algae are able to colonize and grow in low-shore areas as an indirect result of factors which remove grazers. Under the third hypothesis, the algae are directly responsible for the lack of grazers.Experimental clearings of the low-shore algae and introductions of the mid-shore limpets Cellana tramoserica and Siphonaria denticulata were used to test these hypotheses. C. tramoserica grazes microalgae and removes them from the substratum, preventing colonization. S. denticulata, in contrust, crops the algae, leaving a visible cover of algae on the substratum, which can grow rapidly. Because of its method of feeding, S. denticulata had no measurable impact on the rates of colonization, nor on the dry weights of algae, compared with those of ungrazed areas. C. tramoserica could keep cleared areas tree from foliose algae, but only when the limpets were mainfained in great density (10 per 900 cm). They were less effective where wave-action was greater.Neither species of limpets could survive when placed onto beds of mature algae, because they had no substratum on which to cling and were swept away by the waves. C. tramoserica did not invade clearings below their lower limit of distribution where they had to move over a bed of foliose algae. Few C. tramoserica moved directly downshore into cleared areas. When placed on bare rock within low-shore beds of algae of different ages, S. denticulata remained amongst the algae and maintained their tissue-weights. Few C. tramoserica remained in areas with well-developed algae, compared with areas having sparse algal growth. Those Cellana which remained amongst well-developed algae lost weight, whereas limpets in areas with less algal growth mammtained their weights. In experimental cages in low-shore beds of algae, where the limpets were inaccessible to potential predators, C. tramoserica lost weight and died. On cleared areas they survived for many weeks, but lost weight and died as algae grew and covered the substratum. In the absence of predation, the micro-algal grazer C. tramoserica could not survive in lowshore areas because algae grew too fast and occupied the substratum, making it inaccessible for the limpets to graze; the algae, once grown beyond small sporelings, are not a suitable food-source for C. tramoserica, and the loss of weight and death of these limpets is a...

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

“…They also decreased survival of Siphonaria denticulata, as shown for other patellid and siphonarian limpets (e.g. Underwood & Jernakoff 1981, Creese & Underwood 1982, Lasiak & White 1993. This may have been due to removal of food or interference when feeding.…”

“…Patelloida latistrigata are more common on concrete than on sandstone walls. S. denticulata graze on fronds of macro-algae and do not remove algal propagules as do patellid or acmaeid limpets, such as P. latistrigata (Underwood & Jernakoff 1981 Tested against: Thus, micro-algal food may persist in the presence of large densities of S. denticulata. Patellid limpets, in contrast, remove nearly all algal spores and many species outcompete siphonarian limpets, although they seldom cause local extinctions because of strong intraspecific competition (Creese & Underwood 1982, Ortega 1985, Lasiak & White 1993.…”

Depth distribution and abundance of benthic organisms and fishes at the subtropical Kermadec Islands

“…In New Zealand and on the south-east coast of Australia, this zone is usually occupied by a dense assemblage of fucalean algae, and gastropod abundances are low (Underwood & Jernakoff 1981;Choat & Schiel 1982). The greatest numbers of herbivorous species occurred at the intertidal-subtidal interface at Raoul Island (cf, Oliver 1915).…”

Nutrient loading and consumers: Agents of change in open-coast macrophyte assemblages

“…The abundance of herbivores and their interactions with macrophytes vary across intertidal landscapes, changing dramatically over environmental gradients (40). For example, local productivity can exceed consumption rates, and even reverse the sign and nature of a plant-herbivore interaction, leaving herbivores overwhelmed by macrophytes and competing with them for space (40,41). Macrophytes must also pass through small life history stages that are vulnerable to consumers.…”