Lecture 10: Indexes of Biotic Integrity

Indexes of Biotic Integrity

A method of evaluating the biological condition or 'health' of aquatic ecosystems based on the organisms living there

Richness

The number of different species present in an area

Abundance

The number of individual organisms in a population within an area

Evenness

The proportion of individuals among the different species, how evenly distributed they are

Diversity

The relationship between richness, abundance, and evenness

Indicator species

Species whose presence, absence, or abundance indicates specific environmental conditions

Bioindicator definition

Organisms whose population size or physiological state reflects environmental quality and cumulative disturbance

Biomonitor definition

The use of living organisms to evaluate environmental 'health' over time

Threshold criteria

Abiotic factor limits (e.g., pH, DO, nutrients) that define environmental quality standards.

Biotic integrity definition

The degree to which an ecosystem's biological community remains similar to undisturbed conditions

High biotic integrity

Environment is pristine or minimally altered; strong ecosystem function and resilience

Low biotic integrity

Environment is heavily altered or stressed; reduced biodiversity and ecosystem stability

Ecosystem integrity factors

Determined by production/respiration ratio (P/R) and stability or resilience

Clean Water Act connection

The IBI concept is derived from the 1972 Clean Water Act for assessing biological condition of waters.

Baseline biological integrity

The natural, pre-human state of ecosystem structure and function used for comparison

Purpose of the IBI

To evaluate ecosystem condition by comparing biological community metrics like richness, indicators, hybrids, and invasives

IBI measures what

The integrated net impact of stressors on community structure and ecological function

Indicator species absence suggests

pollution or stress in the system

Limitation of IBI

Does not identify the exact cause of impairment, only indicates that one exists.

Chemical tests vs. IBI

Chemical tests provide a short term snapshot; IBIs reflect cumulative biological responses

Regional specificity of IBIs

IBIs must be tailored to local species and environmental conditions; require trained professionals

Multiple IBI agreement

When multiple IBIs show similar results, the assessment is more conclusive

First IBI developed

James Karr (1981), using fish, algae, macroinvertebrates, pupal exuvia, and vascular plants

Taxonomic expertise issue

Declining professional ability to identify species accurately limits IBI use

Impervious surface threshold

Ecosystems often show significant impairment when watershed impervious surfaces exceed 15%

Algae IBIs purpose

Use algae as biological indicators of water quality, including diatoms and soft algae

Diatom IBI (GDI)

Uses Generic Diatom Index; diatoms are resilient to chemicals, and their frustules don't decompose, making them good long term indicator

Soft algae IBI

More difficult because soft algae require broad taxonomic expertise, preserve poorly, and are highly region specific

Macroinvertebrate IBIs (EPT)

Based on Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies).

When not to use EPT IBI

In areas where EPT species are naturally low in richness

Why is EPT IBI useful

Aquatic insects live full life cycles in water and integrate cumulative effects of pollutants

Fish IBIs (Karr metrics)

Ten metrics evaluating fish community diversity, tolerance, and condition (e.g. total number of fish species)

Invasive species

Non native species introduced to a new region that cause ecological, economic, or health damage

Typical steps of invasion

Introduction → establishment → outcompetes natives → disrupts native species relationships

Why do invasive species thrive?

No natural predators or competitors that control their population. May outcompete many native species due to this.

Asian Carp facts

Introduced 1970s to clean aquaculture ponds; now widespread; considered edible by humans

Sea Lamprey facts

Introduced 1830s; preyed on large fish, leading to invasive alewife dominance and lake trout decline

Zebra Mussel facts

Introduced 1988 (Lake St. Clair); prolific filter feeder; clogs machinery; removes algae competitors → increases HABs

Rusty Crayfish facts

Introduced 1960s; aggressive; outcompetes native crayfish

Eurasian Milfoil facts

Introduced 1940s; unpalatable to herbivores; massive biomass clogs machinery

Starry Stonewort facts

Introduced 1978; unpalatable; poor habitat; forms dense biomass mats

Bangia facts

Introduced 1960s (marine → freshwater); competitively excludes native Cladophora; monitoring stopped after 2002