Activities of people on rocky intertidal areas are diverse and have different levels of impact on the biota. Tide pooling; collecting for food, aquaria or research; educational field trips; seaside strolling; photographing and fishing are probably the most common activities on rocky shores. Heavy human use of the intertidal zone can be very destructive through trampling, overturning rocks (and failing to return them), and the intensive collection of certain species.

 

The effects of collecting by humans on Southern Hemisphere rocky intertidal shores have been examined in a number of studies, particularly in Chile, South Africa and to some extent Australia (e.g., Castilla and Durán 1985; Kingsford et al. 1991; Underwood 1993b, a; Addessi 1994; Siegfried 1994; Davis 1995; Griffiths and Branch 1997; Castilla 1999). In Chile, comparison of human-excluded ‘no-take’ areas with human-impacted sites showed an increase in the abundance of keyhole limpets (Fissurella spp.) coupled with a dramatic decline in the abundance of mid-intertidal macroalgae that resulted in extensive food-web modifications (Moreno et al. 1984; Moreno 1986; Oliva and Castilla 1986; cited in Castilla 1999). This led Castilla (1999) to argue that humans, as top predators in these systems, should be considered a keystone species and incorporated in ecological studies and models just like any other species (See Section 5.4.4). Davis (1995) discussed human-exclusion experiments in Chile and their effects on community structure and diversity of marine invertebrates, and how these findings were applied as management strategies. For example, densities of the “Piure” (Pyura chilensis), a commercially exploited tunicate, were more than three orders of magnitude higher within protected reserves than outside them, and only around 6% of individuals in the harvested populations grew large enough to reach sexual maturity (Davis 1995). This was indicative of over-exploitation. In South Africa, comparisons between paired human-exploited and non-exploited rocky shores demonstrated that selective predation by humans of the mussel Perna perna and the limpets Cellana capensis and Patella spp. increased species richness. Overall it led to a significantly greater cover of unexploited sessile species such as macroalgae because the remaining limpet population could no longer control algal growth at the sporeling stage (Hockey 1994). A review of the effects of exploitation of coastal invertebrates and seaweeds in South Africa (Griffiths and Branch 1997) found that direct impacts, such as radical changes in population densities and size distributions of many target species, have generally been well documented, although effects on community dynamics are far less well appreciated. In San Diego, California, the long-term effects of human disturbance on a rocky intertidal community included reduced density of all species in heavily visited sites, increased numbers of some small gastropods, disappearance of five species of echinoderms and decline in the density of predators such as octopuses (Addessi 1994).

 

Targeted organisms on Australian temperate rocky shores include molluscs (e.g., mussels, limpets, abalone, octopuses), echinoderms (sea urchins), and ascidians (cunjevoi). Human harvesting of intertidal and subtidal species of invertebrates and algae on the rocky coast of NSW is widespread and can be destructive. The patterns and consequences of harvesting in NSW were summarised by Underwood (1993b). Direct effects included the loss of the individuals actually taken and the potential loss of breeding populations. Indirect effects included the loss of food for other species, which depend on the harvested species, and the loss of habitat for non-exploited species caused by removal of harvested species with which they interact (Underwood 1993b).

 

The activities of humans on rocky reefs along the coast of NSW were also surveyed by Kingsford et al. (1991), who found that intertidal invertebrates (ascidians, crabs and gastropods) were primarily taken by fishermen for bait, whilst some echinoids and gastropods were used as food. In particular, large numbers of the ascidian Pyura stolonifera (cunjevoi) were taken for use as bait (see also Fairweather 1991). The collection of this species, in addition to the effect on the local population from the removal of large reproductively active individuals, may have an ecological impact, although there is currently poor understanding of such effects. For instance, the removal of cunjevoi may result in loss of habitat for other species as P. stolonifera are an important substratum for the growth of algae in areas grazed by chitons. They also serve as habitat for a wide range of other organisms and as prey for certain species, including the sooty oystercatcher, a bird listed as vulnerable (A. Davis pers. comm.) and several species of large triton whelks (Cabestana spengleri and Charonia lampas (Ranellidae)) (WFP pers. observ.). The impacts of collection for bait on the population dynamics of cunjevoi were examined by Fairweather (1991), whose results suggested that declines in Pyura beds at some of the sites examined (in NSW) were linked to severe and chronic harvesting by fishermen.

 

Keough et al. (1993) examined the effect of human collecting for food and bait on mollusc populations in northern Port Phillip Bay, Victoria. Three of four collected species (Cellana tramoserica, Austrocochlea constricta, and Nerita atramentosa) were significantly larger and one (N. atrementosa) was markedly more abundant at protected than heavily visited sites. The only species that showed no significant difference (Turbo undulatus) has a distribution extending into the subtidal zone and may have its intertidal populations replenished from deeper water (Keough et al. 1993).



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Department of Environment and Heritage