Observe the effects of herbivores on the abundance of algae and to test whether the presence of algae on the substratum determines further settlement of more algae.

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Abstract

An experiment was carried out on the rocky intertidal shore at Maroubra beach in NSW. The aims were to observe the effects of herbivores on the abundance of algae and to test whether the presence of algae on the substratum determines further settlement of more algae. The experiment was carried out by dividing 20 plots into 5 treatments, incorporating a control, looking at the effects oh herbivore exclusion through anti-fouling paint and algal settlement through scraping of the rocky shore. It was shown that the removal of herbivores significantly altered the abundance of algae but that scraping had no significant effect for algal recruitment. Reasons for this are discussed.

Introduction.

The ‘Sub tidal zone that connects land and sea has been somewhat frivolously studied by ecologists yet comprehensively studied by both zoologists and marine botanists’ (adapted from; Carefoot, T., 1977), the ecological complexity is of great magnitude and there is an acute relationship between the organisms of the intertidal zone.

Intertidal organisms have become specially adapted to survive the rapid and significant changes in temperature, salinity, moisture, pH, dissolved oxygen, and food supply that occur on a daily basis due to the movement of the tides. This distribution pattern of different species along the shore is referred to as vertical, or intertidal, zonation. Typically, physical stresses (abiotic) set upper boundaries and biological stresses (competition, predation etc.(biotic)) set lower boundaries (Little,
et al 1996).

The size and species composition of the intertidal will vary with degree of exposure. Large waves increase the size of the supralittoral ("splash") zone, and allow species to live higher in the intertidal. High levels of wave action also select for certain species and morphologies that can withstand the large forces without being ripped off of the rocks. The following is a brief overview of physical and biological characteristics of different regions in the intertidal zone.

, and amount of

The size of this zone depends on slope, splash, climate, and amount of shade. This zone is only covered by water during the highest high tides and marine organisms found here are adept at surviving in these arid conditions. Dissolved nutrients and oxygen are limited in the supralittoral and it is sparsely populated. The effects of herbivory on algal species is best seen in this region as there is a balance in abundance of both alae species and gastropod species.

The effects of herbivory and its effects depend on a number of internal variables; the season will affect the activity of gastropods and the growth rate of algae. The species of gastropods will have an effect on their preferred species of algae and to the same effect the palatable nature of algal species will affect their rate of consumption. The complexity of the food web at the site will effect the balance of intermediaries (ie; herbivorous snails, and producers; algae). Finally the topography and environmental characteristics of the area will affect abundances and distribution of both gastropods and algae,  

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In this experiment we will study the effect of herbivory in local gastropods on differing algal species, furthermore the effects this has on percentage cover of the algae.

Seasonal proportions of algae to barnacles varied on season

winter more barnacles, summer more algae,

Green most palatable, not much eats encrusting algae,

expected results

Aims

 In our experiment we are testing two main hypotheses:

  1. Herbivores decrease algal abundance, and;
  2. The Strength of this effect is a function of whether there is some algae already in a plot.

Methods

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