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.
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).
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
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.
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
Nerita atramentosa) were significantly larger and one (N.
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).