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Marsci 202 PSet 3

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Homework 3

Q1

  • Sea Fans belong to the Phylum Cnidaria and Class Anthozoa because of:
    1. Presence of Cnidocytes: Specialized stinging cells used for prey capture and defense, characteristic of all Cnidarians.
    2. Polyp-Only Life Cycle: As Anthozoans, they exist solely in the polyp form and do not have a medusa stage.
  • Blue Crabs belong to the Phylum Arthropoda and Class Malacostraca because of:
    1. Exoskeleton and Jointed Appendages: Arthropods possess a chitinous exoskeleton and segmented bodies with jointed limbs.
    2. Body Segmentation into Tagmata: Malacostracans have bodies divided into head, thorax, and abdomen, with a carapace covering the thorax.

Q2

Similarities:

  1. External Appendages for Prey Capture. Sea Fans use their polyps and tentacles to trap plankton, while Blue Crabs use their claws to grab and manipulate larger prey like clams.
  2. Feeding Influenced by Water Flow. Their feeding rates are affected by the hydrodynamic conditions.
  3. Heterotrophic/Carnivorous Feeding. Both consume other organisms for nutrition.

Differences:

  1. Feeding Mechanism: Sea Fans are passive suspension feeders using tentacles to capture plankton, while Blue Crabs are active predators/scavengers using claws to capture prey.
  2. Mobility: Sea Fans are sessile organisms attached to substrates, whereas Blue Crabs are mobile and can move to locate food.
  3. Prey Type: Sea Fans feed on microscopic plankton, while Blue Crabs consume larger organisms like clams and other benthic fauna.

Q3 & Q4

Code

 
# Data for Sea Fans and Blue Crabs
sea_fans_data = {
    "Replicate": [1, 2, 3, 4, 5, 6, 7, 8, 
                  1, 2, 3, 4, 5, 6, 7, 8],
    "Treatment": ["Low Flow (2cm/s)"]*8 + ["High Flow (20cm/s)"]*8,
    "# copepods eaten": [21, 32, 27, 34, 45, 52, 29, 30, 
                1020, 987, 675, 1156, 721, 447, 823, 678]
}
 
blue_crabs_data = {
    "Replicate": [1, 2, 3, 4, 5, 6, 7, 8, 
                  1, 2, 3, 4, 5, 6, 7, 8],
    "Treatment": ["Low Flow (2cm/s)"]*8 + ["High Flow (20cm/s)"]*8,
    "# clams eaten": [9, 6, 11, 8, 7, 6, 12, 11, 
                      2, 1, 3, 0, 2, 1, 2, 1]
}
 
sea_fans_df = pd.DataFrame(sea_fans_data)
blue_crabs_df = pd.DataFrame(blue_crabs_data)
 
# Calculate mean and standard deviation
sea_fans_stats = sea_fans_df
    .groupby("Treatment")["# copepods eaten"]
    .agg([np.mean, np.std])
blue_crabs_stats = blue_crabs_df
    .groupby("Treatment")["# clams eaten"]
    .agg([np.mean, np.std])
 
# dataframe manipulate for t-tests between high flow and low flow
sea_fans_low_flow = sea_fans_df[
    sea_fans_df["Treatment"] == "Low Flow (2cm/s)"
    ]["# copepods eaten"]
sea_fans_high_flow = sea_fans_df[
    sea_fans_df["Treatment"] == "High Flow (20cm/s)"
    ]["# copepods eaten"]
 
blue_crabs_low_flow = blue_crabs_df[
    blue_crabs_df["Treatment"] == "Low Flow (2cm/s)"
    ]["# clams eaten"]
blue_crabs_high_flow = blue_crabs_df[
    blue_crabs_df["Treatment"] == "High Flow (20cm/s)"
    ]["# clams eaten"]
 
sea_fans_ttest = stats.ttest_ind(
    sea_fans_low_flow, sea_fans_high_flow
    )
blue_crabs_ttest = stats.ttest_ind(
    blue_crabs_low_flow, blue_crabs_high_flow
    )
 
### Show the stats & p-val
sea_fans_stats, blue_crabs_stats, 
sea_fans_ttest.pvalue, blue_crabs_ttest.pvalue

Output

                       mean         std
 Treatment                              
 High Flow (20cm/s)  813.375  230.081313
 Low Flow (2cm/s)     33.750   10.053429,
                     mean      std
 Treatment                        
 High Flow (20cm/s)  1.50  0.92582
 Low Flow (2cm/s)    8.75  2.37547,
 1.595498936667517e-07,
 1.2862551269462247e-06

Code

# Plotting the bar graph
fig, ax = plt.subplots(1, 2, figsize=(12, 6))
 
# Sea Fans Plot
ax[0].bar(
    sea_fans_stats.index, 
    sea_fans_stats["mean"], 
    yerr=sea_fans_stats["std"], 
    capsize=5)
ax[0].set_xlabel("Flow Treatment")
ax[0].set_ylabel("Mean Copepods Eaten")
ax[0].text(
    0.5, 
    max(sea_fans_stats["mean"]), 
    f"P-value = {sea_fans_ttest.pvalue:.4f}",
    ha='center')
ax[0].set_title("Sea Fans")
 
# Blue Crabs Plot
ax[1].bar(
    blue_crabs_stats.index, 
    blue_crabs_stats["mean"],
    yerr=blue_crabs_stats["std"],
    capsize=5)
ax[1].set_xlabel("Flow Treatment")
ax[1].set_ylabel("Mean Clams Eaten")
ax[1].text(
    0.5, 
    max(blue_crabs_stats["mean"]), 
    f"P-value = {blue_crabs_ttest.pvalue:.4f}", 
    ha='center')
ax[1].set_title("Blue Crabs")
 
plt.tight_layout()
plt.show()

Output

Figure: The effect of flow rate (2 cm/s and 20 cm/s) on the feeding rates of sea fans and blue crabs. Bars represent the mean number of prey (copepods or clams) consumed under low and high flow conditions. Error bars indicate standard deviation. Significant differences were observed between flow treatments for both species, with sea fans showing a higher feeding rate under high flow conditions and blue crabs showing a lower feeding rate. P-values for t-tests are presented within each.

Q5

Effects of Water Flow on Feeding Rates of Sea Fans and Blue Crabs

Abstract

This study investigates the impact of water flow on the feeding rates of Sea Fans (Phylum Cnidaria, Class Anthozoa) and Blue Crabs (Phylum Arthropoda, Class Malacostraca). Feeding rates were measured under low (2 cm/s) and high (20 cm/s) flow conditions. Results indicate that high flow significantly increased feeding rates in Sea Fans while decreasing feeding rates in Blue Crabs. These findings highlight species-specific responses to water flow and underscore the importance of hydrodynamic conditions in marine ecosystems.

Research Questions

  1. How does water flow rate affect the feeding rates of Sea Fans?
  2. How does water flow rate affect the feeding rates of Blue Crabs?
  3. Are the effects of water flow on feeding rates similar or different between these two species?

Results

Figure: The effect of flow rate (2 cm/s and 20 cm/s) on the feeding rates of sea fans and blue crabs. Bars represent the mean number of prey (copepods or clams) consumed under low and high flow conditions. Error bars indicate standard deviation. Significant differences were observed between flow treatments for both species, with sea fans showing a higher feeding rate under high flow conditions and blue crabs showing a lower feeding rate. P-values for t-tests are presented within each.

In Sea Fans, the mean number of copepods consumed under low flow was , whereas under high flow, it increased to . A t-test confirmed that this difference is statistically significant (). Conversely, Blue Crabs showed a decrease in feeding rates from clams under low flow to clams under high flow, with the difference also being statistically significant (). These results suggest that high water flow enhances feeding in Sea Fans but inhibits feeding in Blue Crabs.

Discussion

The study demonstrates a stark contrast in how water flow affects the feeding strategies of Sea Fans and Blue Crabs. Sea Fans exhibited significantly higher feeding rates under high flow conditions. This can be attributed to their passive suspension feeding mechanism, where increased water flow delivers more planktonic prey to their extended polyps. The structural morphology of Sea Fans, with their fan-like branches, is adapted to capture food particles efficiently in flowing water. In contrast, Blue Crabs showed reduced feeding rates under high flow. As active predators and scavengers, Blue Crabs rely on their ability to detect and capture prey, which can be hindered by strong currents. High flow conditions may disrupt their sensory cues or make it energetically unfavorable to pursue prey.

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