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Journal of Experimental Marine Biology and Ecology, 241 1999 15–29
Predation by fish on assemblages of intertidal epibiota: effects of predator size and patch size
S.D. Connell , M.J. Anderson
Centre for Research on Ecological Impacts of Coastal Cities , Marine Ecology Laboratories A11,
University of Sydney , Sydney N.S.W. 2006, Australia
Received 24 August 1998; received in revised form 12 April 1999; accepted 28 April 1999
Abstract
We tested the hypothesis that effects of predation by fish on epibiota are independent of the size of fish and the area foraged. We used cages with different sizes of mesh to exclude fish of different
sizes. Sizes of mesh were chosen following observations that there were small , 200 mm TL and large . 200 mm TL predatory fish at the study site. Predation by fish was intense on oysters
and directly or indirectly reduced the density of the gastropod, Bembicium auratum. The cover of algae was positively affected by predation, possibly because predation on oysters created more
space for algae. Predation by small fish toadfish was intense, but the effects of large fish were negligible. Predation was, however, independent of the sizes of experimental panels i.e. area
foraged over the range examined 5 3 5, 10 3 10, 20 3 20 cm. Our results highlight the importance of doing experiments to test hypotheses derived from known aspects of the biology of
the predators and prey being studied.
1999 Elsevier Science B.V. All rights reserved.
Keywords : Assemblage; Fouling; Patch size; Multivariate; Experiment
1. Introduction
The effect of predators on the structure of ecological assemblages has been studied in many marine habitats reviews: Paine, 1977; Choat, 1982; Hixon, 1997. Fish are major
predators, particularly for epibiota on hard substrata reviews: Choat, 1982; Hixon, 1997. Despite this, considerable variability has been detected in the effect of fish
predation on epibiota cf. Sutherland and Karlson, 1977; Russ, 1980; Choat and Kingett,
Corresponding author. Present address: Department of Environmental Biology, University of Adelaide, South Australia 5005, Australia. Tel.: 1 61-8-8303-6125; fax: 1 61-8-8303-5576.
E-mail address : sean.connelladelaide.edu.au S.D. Connell
0022-0981 99 – see front matter
1999 Elsevier Science B.V. All rights reserved. P I I : S 0 0 2 2 - 0 9 8 1 9 9 0 0 0 6 7 - 2
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.D. Connell, M.J. Anderson J. Exp. Mar. Biol. Ecol. 241 1999 15 –29
1982; Menge et al., 1985. To date, little attempt has been made to explain this variability and most work has focused on variation of predation by fish on substrata of
different topographic complexity e.g. Menge and Sutherland, 1976; Russ, 1980; Menge et al., 1985.
Assemblages of predatory fish are characterised by extreme spatial and temporal variability in composition and abundance Williams and Hatcher, 1983; Choat and
Ayling, 1987; Connell and Kingsford, 1998 and diet Hiatt and Strasburg, 1960; Parrish, 1987; Connell, 1998a. Hence, the intensity of predation and its effects on
composition of benthic assemblages may be strongly related to the types of predators present. Despite this, studies of predation by fish on invertebrates have typically not
attempted to differentiate among different predators but see Ayling, 1981; Choat and Kingett, 1982. Rather, they have been designed only to test the overall effects of fish of
whatever kinds happen to be present. If the composition of predators leads to predictable changes in the structure of benthic assemblages, then such knowledge may provide a
basis for predicting where, when and how predation is likely to be important.
Variation in the intensity of predation may also be explained by the response of predators to the patchiness of their prey. Many predators, including fish, actively search
for their prey, so it can be predicted that predation will not be uniformly distributed among patches of varying size Charnov, 1976. Several types of predators have been
shown to respond differently to different sized patches of prey. In terrestrial habitats, birds prefer to feed from larger flowers e.g. Brody and Mitchell, 1997. In marine
habitats, birds and fish feed more intensely on the siphons of clams where the prey occur in greater densities Whitlatch et al., 1997 and large predatory fish kill more juvenile
fish that occur in larger schools Connell, 1998b. Although it has been recognised that size of patch affects the colonisation and development of epibiotic assemblages see
review by Connell and Keough, 1985, no experiments have tested the hypothesis that the consequences of predation vary among different sized patches of epibiota.
The hypotheses tested here were that assemblages of epibiota i differ when exposed to different sizes of predatory fish and ii are more affected by predation on larger
patches of habitat. These hypotheses were tested on wooden structures used for farming oysters oyster leases in the intertidal zone of an estuary of New South Wales, Australia
where i it is known that the size of patches influences the early stages of development of epibiotic assemblages and ii observations suggest that sessile invertebrates are eaten
by fish Anderson, 1998. Oyster leases represent a major coastal habitat of New South Wales, occupying | 4700 hectares of intertidal habitat in 30 major bays and estuaries.
2. Methods
