ogo? oh no! effects of invasive algae genelle watkins ... · observed nearshore ‘aholehole...

Ogo? Oh no! Effects of Invasive Algae

Removal in Maunalua Bay

Jared Char, Casey Ching, Rylen Nakama, Paul Riley,

Genelle Watkins

Macroinvertebrate Assemblages

What are the effects of removing invasive algae from

Maunalua Bay on the nearshore ecosystem?

Fish StocksFishermen

Perspectives

Native Hawaiian

Seagrasses

Seagrasses and Limu in MB● Historically, Maunalua Bay supported large

patches of native seagrass (Halophila hawaiiana)

○ Highly susceptible to burial, smothering by sediments

○ Requires high levels of sunlight to flourish

● Invasive Alien Algae (IAA)○ Capture runoff/sediment from streams○ Increased sediment load results in anoxic

zones, decrease in species richness○ By 2003, 100% coverage in areas bordering

seagrass meadows

Seagrass Restoration!● H. hawaiiana currently listed as vulnerable by IUCN● Naturally propagates through vegetative growth, produces seeds infrequently

○ Impractical to wait for H. hawaiiana to self-spread

○ Spread thru transplanting!

● Murphy (2013) tested various methods of transplanting○ Most successful attempts were transplanting cores

○ Plug transplants more effective, cheaper than outplanting lab-grown individuals

○ Still resulted in 50% failure rate

● Cause of transplant failure?○ Poor site selection-substrate too soft, too much wave activity, turbidity too high

○ “Transplantation should be avoided unless the site historically supported seagrass and an

anthropogenic disturbance that is no longer present resulted in its loss” (Murphy 2013)

Marine Invertebrate Communities in Maunalua Bay

● A significant component of marine biodiversity

○ Tako, White Crab, ‘Opae

● Ecological Importance of Invertebrates

○ Control sedimentation, water quality

○ Direct targets of recreational fishermen

○ Provide a prey base for predatory fishes

● Fish abundances strongly correlated with

the availability of prey

● We can expect responses in the regional and

temporal abundances of certain species

Surveys of Invertebrate Assemblages

● Invertebrate Communities found in Mudweed

○ Overall Similar to Invertebrate

Communities in Native Limu

● Mudweed provides habitat for a diverse

assemblage of polychaete worms

● The widespread removal of mudweed

represents “a massive disturbance”

● Ecosystem Restoration?

○ Tentatively YES

○ Existence of Uncertainties, future studies

Fish Populations● Residents and visitors utilize Maunalua Bay

for fishing recreationally

● Fish biomass in Maunalua Bay is lower than

in other comparable locations

● While invasive algae is harmful, it can

provide shelter for juvenile fishes

● Removal of invasive algae leaves bare sand

and fish become vulnerable

● Friedlander & Parrish (1998) found that

“mean hole volume” (shelter for fish) was

related to more or bigger fish

Observation of Fish Assemblage● Measured presence of species,

counts, and length estimates within 10mX10m plots characterized by Malama Maunalua

● 24 plots were each monitored for 2-3 minutes for fish between 6 AM and 12 PM

● Four 30m transects conducted at night between 8 and 11 PM

Observations of Fish Assemblage

● Very few fish inside and outside the huki

plots

● Most plots were empty when observed

● No statistical difference in biomass

between locations

● Fishes in plots ○ O’opu ohune (Gobies)○ Ala’ihi (Squirrelfish)

○ O’ama/Weke (Yellowfin Goatfish)○ Omilu (Bluefin Trevally)○ Kokala (Porcupinefish)○ ‘Ulae (Lizardfish)○ Nehu (Anchovy)○ Upupalu (Cardinalfish)○ Hinalea (Wrasse)

● Observed nearshore○ ‘Aholehole (Flagtail)○ Mullet○ Kaku (Barracuda)

Average biomass (g/m^2) Fish Counted

DayHuki 1.12 7

No Huki 0.02 2All Sites 0.57 9Night

Invasive Algae 1.18 6

Sandy Bottom 0.10 2All Sites 0.64 8

Survey methods and questions

● Where are you from?● How long have you been fishing?● How long have you fished in Maunalua Bay?● What are you fishing for?● Where are you catching the most fish?*● What are you planning on doing with the fish you catch? ● Have you observed changes in your fish catch since you began using this

resource? ○ If so, how has your catch changed?

● Are there any questions about Maunalua Bay that you would like answered?

*map should go here*5 locations typically fished; onshore and willing fishers

MB Fishers demographic● 14/18 Respondents from the Hawaii Kai

area

● Experience Within MB

○ < 5 years: 11 respondents

○ 10-25 years: 2 respondents

○ 26-50 years: 3 respondents

○ 50+ years: 2 respondents

● 18/18 Recognized pono fishing practices

What are they fishing for? (Target fish species) 1. ʻOʻio → 18/182. Papio → 17/183. Ulua → 4/184. Weke → 4/185. Moi → 3/186. Kaku → 2/187. Taʻape and Toau →

1/18 (For the purpose of removing invasives)

1

2

3

4

67

5

What are they catching? ● 2 Participants caught fish on the day they were surveyed

○ 1 barracuda

○ 1 tagged ʻoʻio

○ Non-participant: Observed catching undersize palani

● 2 Participants regularly catch SOMETHING (including undersize, illegals, etc.)

● 5 participants acknowledge the additional influence of seasonal changes and

moon phases

Q: What is negatively affecting the fish populations?● 16 participants responded…

● (10) Illegal fishing practices eg. lay nets

● (4) Water recreation activities in MB

● (2) Algae removal

● (1) Development eg. dredging

Future Research & Recommendations

● Need better understanding of seagrass biology!

● Need to remove anthropogenic effects that caused seagrasses to fail

● We require a greater understanding of marine invertebrate ecology in Maunalua Bay

● Investigation into natural disappearances of Mudweed

● More extensive characterization of fish larvae community

“Please do not silence the local fishing community, as fishing is, to many, a way we

feel intimately connected to this place.”

Questions?