Benthic Communities: Case Studies in Fiji and

Canada

Dr Edward Anderson Division of Marine StudiesThe University of the South Pacific

anderson_ed@usp.ac.fj(679) 323-2948

Benthic Communities and Marine Pollution

• Benthic habitat classification based on sonic mapping of the seafloor does not complete an investigation of pollution.

• Coupled with this should be mapping of communities. • Benthos, and particularly infauna, in sieve sizes

macofauna (>200μm) and meiofauna (>64 μm) are most useful, because they must remain in the local area

• The apparatus for this is simple: a sediment grab, a way to separate the animals form the sediment, and a microscope.

• The problem is that benthic animals which are useful for determining pollution status are small, and their identification is difficult.

Useful for Pollution Studies – But Some Difficult to Identify

• Macrofauna • Annelid Worms – Mostly Polychaetes and

Oligochaetes

• Crustacea – Amphipods, Isopods, Crabs, Tanaids,

• Molluscs – Bivalves, Gastropods

• Echinoderns – Starfish, Ophiuroids, Urchins

• Many others

• Meiofauna• Crustacea - Harpacticoid Copepods

• Nematodes

• Many others

Environmental Effect of Salmon Aquaculture in Net Pens

• The case study from Canada is an investigation of benthic recovery from pollution under net-pen culture of salmon.

• The pens are fed with pelletized fish meal.• Waste meal and fish feces go to the bottom.• In a small area of the ocean (typically 100m x 500m) the

equivalent waste from a city of 250,000 is deposited.

Methods

• Identification

• Currents

• Sediment particle size

• H2S

• Visual

The study sites• Eight recently

fallowed sites sites were selected

• Site were chosen for suitable soft bottom, and a nearby reference site.

• Sites were visited in each year from 1991 to 1994.

• Primary sampling device: a Ponar grab.

• Sampling was from an outboard motor boat equipped with a hydraulic winch.

Small, But Effective

Example Study Sites

▲ Sansum Narrows : high current, 19m, course sand

Tranquil Inlet: low current, 27m silt/sand ►

Community Structure

• We sampled 25 sites in triplicate for 2-4 years.

• 348 taxa were identified, most to species.

• The raw data: 19 pages of species identifications and counts.

• You don’t want to read this!

Alternatives

• Some form of summary is necessary. Some options:

• Univariate• Diversity

• Multivariate• Cluster analysis

• Factor analysis

• I will deal mostly with deversity

Best Measure of Diversity

S

iii PPH

1

)log('

• H’ takes into account both the number of species, and the distribution of species in that number

where i is the i th species in order of abundance

S is the total number of species

Pi is the proportion of individuals in the sample belonging to species i

(the probability that an individual selected at random will be

found to belong to species i (in other words, Pi is just ni /N)

nj is the abundance of species i

N is the total number (abundance) of individuals in the sample

Main Result

• A diversity analysis showed that recovery time varied from 0 months at a high current site to 50 months at a low current site.

• Measurements of community diversity were confirmed by sediment particle size, H2S and current measurements.

High currentSandShallow

Low currentSiltDeeper

Confirmations

• Measurements of community diversity were confirmed by sediment H2S, particle size and current measurements.

• The effects were confined within a few hundred meters of the net pens.

• The effects are reversible.

• High H2S accompanies pollution from oxygen consuming wastes, which are the major sources of marine pollution worldwide.

TRE and TRER, 1991 and 1993

Case Study in Suva

• The case study from Suva, Fiji is student work

• There were 460 students over the 14 years that either I or Dr Vikila Vuki ran the course.

This is half of the class of 2006 in MS312, Marine Pollution

Measurements

• We measured pollution at Walu Bay, Draunibota Bay (Lami, near Suva) and at Kinoya sewage outfall.

• This study was repeated in most years from 2001 to 2010, with similar results.

• Pollution in Suva, and in particular Walu Bay, is not getting better.

Walu Bay• Why Walu Bay?

• Near to USP

• Large area of soft bottom

• Similar depth

• Lots of pollution• Local food

processing

• Upstream industries

• Probable sewage (not from container ships)

H2S Hach Kit Test

• Preparation• 15 ml of sediment sample.

• Add seawater

• Drop in an Alka Seltzer tabled. This will release CO2, and sparge out the H2S.

• Reaction• In the vial cap, there is a

filter paper impregnated with Lead Acetate – colorless and soluble

• Lead acetate is converted to lead sulfide by H2S, dark colour, insoluble

Hach Kit (continued)

• The filters are read by reference to a colour chart.• The method is semi-

quantitative.

• Fast

• No special equipment

• There are other methods – but they require special equipment or access to a laboratory or both.

Community Analysis CategoryTaxon D1 D2 C1 C2 B1 B2 A1 A2

1Polychaetes and other worms

Pol 8 14 3 0 1 0 0 0

2Bivalves (clams)

Biv 3 1 0 1 0 0 0 0

3 Other molluscs Omo 4 4 0 1 0 0 0 0

4 Crustacea Cru 3 3 2 1 0 0 0 0

5 Forams 10 200 2 16 20 6 137 100

6 Fish 1

7 Other

N 1-4 18 22 5 3 1 0 0 0

S 1-4 4 4 2 3 1 0 0 0

H' 0.592 0.439 0.292 0.477 0.000 - - -

H2S 0.1 0.1 0.1 0.5 0.3 3 5 3

Results

• Benthos was completely absent at Station A, in the inner reaches of Walu Bay, H2S was high, bottom current very low.

• In the overlying water oxygen was near normal at the surface and also at 1m above bottom at all stations.

• At the entrance to Walu Bay, Station C, diversity and H2S content were near normal.

• At Station D, 450m offshore, they were normal.

Comparisons

• The study in Canada involved about one year of effort, spread over three years.• The range covered was large.

• The analysis was very detailed.

• Several taxon experts were necessary.

• A manual for the identification of marine invertebrates is essential.

Comparisons (continued)

• The student effort was confined to two field sessions and four laboratory sessions• None of the students had any experience

in identifying marine invertebrates to the species level, for the taxa interest.

• We used a large mesh size (500μm versus 200μm for practical reasons.

• There is no manual.

• The method is robust.

End. Questions?