River Bio Detectives

Trophic Crime: Robs native zooplankton & insect larvae of primary food; blankets rocky trout beds with rotting shell heaps.

Eurasian Watermilfoil

Myriophyllum spicatum

Origin: Spread on recreational boat propellers.

Super-Power: Can regenerate an entire colony from a tiny 1-inch fragmented stem.

Trophic Crime: Forms thick surface mats that block sunlight to native eelgrass and crashes dissolved oxygen during nocturnal decay.

Key Rule: Invasives lack natural predators and multiply exponentially! Slide 4 of 7

Chain Reaction: Anatomy of a Trophic Cascade

Systems Modeling

When an invasive consumer enters the bottom tier, shockwaves ripple through every trophic level:

Step 1: Producers

Phytoplankton

Asian clams consume 80% of micro-algae, crashing base food supply.

Step 2: Primary Cons.

Mayflies & Scuds

Sensitive insects starve; cannot compete with millions of clams.

Step 3: Secondary Cons.

Brook Trout

Fish lose primary prey; gravel spawning beds get smothered by clam shells.

Step 4: Apex Predators

Osprey & Eagles

Raptors abandon nesting grounds due to severe shortage of mid-sized fish.

Lesson: You don't need a poison spill to cause an ecosystem extinction cascade. Slide 5 of 7

Your Detective Mission: Analyze 3 River Stations

Worksheet Guide

Station A: White Mountain Run

Upstream Pristine Baseline

Forested canopy, high riffles, high DO (>8.5 mg/L). Heavy presence of Mayflies & Stoneflies. Clams: 0.

FBI Score: 2.1 (Excellent)

Station B: Concord Confluence

Suburban Marina Zone

Recreational boat launches. Milfoil cover 65%. Clam density 1,200/m². Trout numbers down 70%.

FBI Score: 5.8 (Fair / Stressed)

Station C: Merrimack Tidewater

Lower River Estuary

Brackish waters, slower flow. High salinity naturally restricts freshwater clams, but turbidity remains elevated.

FBI Score: 6.2 (Fair)

Work with your partner to calculate FBI scores and graph Station B population shifts! Slide 6 of 7

Final Deliverable: Community Conservation Pitch

Take Action

Select one evidence-backed proposal to present to the Merrimack Watershed Council:

Strategy 1: Clean-Drain-Dry Boat Stations

Mandatory high-heat power wash stations at all public marinas to kill milfoil fragments and clam larvae.

Strategy 2: Benthic Smother Barriers

Deploy biodegradable burlap mats over infested riverbeds to block light from milfoil and restore gravel for trout beds.

Strategy 3: Riparian Reforestation Corridors

Plant native willow and red maple buffers to cool river water temperatures and reduce runoff sediment fueling algae.

Ready to save the Merrimack? Open your field worksheet and begin Phase 1! Slide 7 of 7

Merrimack River Bio-Detective • Student Modeling Lab Page 1 of 2

Part 2 & 3 • Systems Modeling & Simulation

Food Web Disruption Modeling

Trophic Ripple Analysis

Diagram 1: Energy Transfer & Competition Flow Arrows indicate energy direction (\(A \rightarrow B\) means B eats A)

River Osprey (Apex Predator)

Feeds on mature trout & perch

▲ (Energy Flow)

Native Brook Trout (Secondary Consumer)

Feeds on Mayflies & Daphnia; Spawns on gravel beds

▲ ▲

Water Fleas (Daphnia) Native Zooplankton

Mayfly Nymphs Sensitive Bioindicator

Asian Clams (INVASIVE) Competes with Daphnia & Mayflies

▲ ▲ ▲ (Robbing Energy)

River Phytoplankton (Micro-Algae) Base Food: Heavily consumed by Asian Clams

Eurasian Watermilfoil (INVASIVE) Blocks light from native eelgrass nursery zones

Part 2: Cascade Impact Predictions

Predict the impact on each population after Asian Clams & Milfoil spread across the river reach:

Part 3: Ecological Reasoning & Evidence

1. Trace the chain reaction: Asian clams do not eat Brook Trout. Explain step-by-step how the clam explosion caused trout to decline by over 70%:

2. Eurasian watermilfoil dies and decomposes rapidly each October. How does this seasonal decay affect dissolved oxygen and overwintering fish eggs?

Merrimack River Bio-Detective • Student Modeling Lab Page 2 of 2

Family Biotic Index (FBI) Analysis \(\text{Score} = \frac{\sum (n \times t)}{\text{Total Organisms}}\)

Station A's calculated FBI score is 2.85 (Excellent water quality). Use the data above to answer the following:

1. Why did the count of sensitive Mayflies and Caddisflies plunge at Station B while Midge larvae exploded? Support with specific water chemistry data (DO and Temperature):

2. How does the presence of 185 Asian clams at Station B relate to the collapse of native filter feeders and insect grazers?

Merrimack River Bio-Detective • Student Field Data Log Page 1 of 2

Part 3 & 4 • Longitudinal Trends & Policy Pitch

Conservation Action Plan

Action Directive

Part 3: Station B 10-Year Population History (Marina Reach)

Part 4: Merrimack Watershed Council Policy Proposal

The Conservation Commission is funding one immediate remediation initiative for Station B. Select ONE strategy and synthesize field data to defend your proposal:

[ ] Option A: Decon Wash Install pressurized thermal boat-wash station at Station B marina to stop hitchhiking larvae.

[ ] Option B: Benthic Mats Lay biodegradable jute mats across 200m of spawning gravel to suffocate milfoil roots and clams.

[ ] Option C: Riparian Canopy Plant dense native alder and willow trees along 1km of riverbank to cool water and block runoff.

1. Selected Strategy Title & Specific Ecological Threat Addressed:

2. Data Justification (Cite at least TWO data points from Part 1, 2, or 3 supporting why this action is essential):

3. Predicted 3-Year Ecological Outcome (How will DO levels, mayflies, and trout numbers respond if this plan succeeds?):

4. Community Engagement Plan (How can local middle school students and anglers assist in implementing or monitoring this solution?):

Merrimack River Bio-Detective • Student Field Data Log Page 2 of 2