L6 - Rocky Shore Ecosystems

Question 1

Introduction

Extensively studied

• Diversity (strong environmental gradients)
• Accessibility
• Ease of manipulations

Development of ecological theory

• Role of keystone predators in community dynamics
• Effects of disturbance (patch dynamics, succession)
• Clearing encrusters and observing what returns

Answer 1

Aim

Lecture 1

Environmental conditions

Ecosystem components & energy flow

Organism adaptations

Lecture 2

Demonstrate how biological interactions influence species distribution & abundance

Use of manipulative experiments to test ecological theory

Question 2

Distribution of biota

structure and order to distribution

low tide dominated by algae/neptunes necklace

algae

oyster

black lichons? in terrerstrial zone

Answer 2

Northern Hemisphere

Same Biological Niche and structure

Question 3

Why does this structure occur?

Water movement results in gradual transition between the marine and terrestrial environments

Organisms can withstand different degrees of stress

Universal because emersion & immersion is the overriding factor controlling species composition and distribution

Position along gradient determines exposure to air and how much stress from physical environment

Answer 3

Tide Generating Forces

Question 4

Tide Generating Forces

Concept of critical tide levels

Question 5

Division of Shore

Supralittoral

influenced by salt spray

salt tolerant lichens

Supralittoral fringe

wave splash, covered at mean high water spring

black lichens (Verrucaria sp.), periwinkle snails (Littorina sp)

Answer 5

Division of Shore

Midlittoral

regular immersion & emersion (mean high water - mean low water)

subdivided

barnacles

oysters &/or mussels

polychaete tube worms (Pomotoceros)

algae Corallina & Hormosira

Infra- or Sublittoral

rarely uncovered

dominated by kelps (Ecklonia radiata)

Question 6

Vertical Extent of Zones: Wave Exposure

Answer 6

Vertical Extent of Zones: Wave Exposure

A & B

Larger diversity of biota due to sheltered conditions/more suitable habitat

C

Wind/Wave activity high

less diversity but higher population

Question 7

Vertical Extent of Zones: Substrate

Restrcited to cracks and crevecis because…

Micro habitats.. influence organism distribution at low tide?

Answer 7

Division of Shore

• No two shores are exactly the same with respect to wave exposure, topography etc, hence organism distribution patterns differ from shore to shore
• • However the order with which the species occur is the same although the width of the divisions and degree of overlap may vary. Some species may disappear altogether

Question 8

Eco system primary producers

Macroalgae

Carbon fixers

Low in N

(hard to digest and hard to eat)

Most Rocky shore grazers do not eat Macroalgae

Important habitat formers (early succesors)

Answer 8

Ecosystem Structure Primary Producers

Provide habitat

Relatively low importance as a food source via direct grazing

Question 9

Ecosystem Structure Consumers

Encrusting suspension-feeders

Includes bivalves, crustaceans and polychaetes

Occupy space but as they don’t move they’re dependant on wave motion to bring in food such as phytoplankton…?

Answer 9

Ecosystem Structure Consumers

Encrusting suspension-feeders: Barnacles

Filter-feeders

Main food source is phytoplankton

Occupy space (compete with algae)

Question 10

Ecosystem Structure Consumers

Mobile grazers

Gastropods & echinoderms

Includes limpets, chitons, topshells

Adaptive radula

Open spaces and clear rock to feed on bacteria…?

No macroalgae

Answer 10

Require open spaces

Important structuring force

Remove algal spores & larvae

Compete with encrusting species

Incredibly important

Aquaculture

When grazing community removed blooms of *early succesors

Question 11

Ecosystem Structure Consumers

Mobile predators

Echinoderms & gastropods

Feed on encrusting species

Create space

Important structuring force

Radula adapted to drill piece

enzymes spill into hole made in prey

digests prey alive

Less predation further up shore but higher desecation

(extreme dryness)

Answer 11

Adaptations

Up to 75% water loss at low tide

adaptive shells reflect/absord solar radiation

Adaptations

Mechanical stress

Limitation in size

Shape

Attachment

Salinity stress

Osmoconformers

See adaptations to water loss

Question 12

Summary

• What are the main physical forces structuring intertidal communities?
• Describe the major distribution pattern of intertidal organisms
• Who are the key components of the intertidal community and what is their trophic status?
• Adaptations for survival in the intertidal region