Benthic fauna of the inner part of Benthic fauna of the inner part of Ariake Bay: long-term changes in Ariake Bay: long-term changes in several ecological parametersseveral ecological parameters

Presented by :

Fiddy Semba Prasetiya

Vrije University of Brussels

Presented to fullfill assignment of Marine Biodiversity Partim BenthosPresented to fullfill assignment of Marine Biodiversity Partim Benthos, Vrije University of Brussels, November 20, Vrije University of Brussels, November 20thth 2008 2008

General IntroductionGeneral Introduction

• Role of benthic ecosystems in marine ecosystems

Nutrients

Phytoplankton

ZooplanktonFish

Detritus

Sediment

Resuspended sediment

Benthic Organisms

Bacteria

Purification process

Sediment

Organic loads

Toxic substances

Organic loads Toxic substances

Water column

Environmental change in Environmental change in Ariake BayAriake Bay

Reclamation dike in Isahaya Bay

• Decrease in particle size of sediment• Increase in transparency• Decrease in tidal amplitude

Disturbance on benthic ecosystem:• The increase in red tides and hypoxia • Decreasing of bivalves catch

Atrina spp. Scapharca spp

Ruditapes philippinarum

Source: www.naris.go ; www.hk-fish.net

Objective of ResearchObjective of Research

• To investigate the subtidal benthic fauna of the inner part of Ariake Bay,

• Compared statistically the changes in the benthic fauna between the present data and the 1989 data in Koga (1991) which indicates the condition before the ecosystem degradation

Study siteStudy site• This research is located in the inner north part of the bay• The inner part of Ariake Bay mainly consists of vast tidal

flats and shallow subtidal area of generally less than 15 m in depth, and is roughly divided into two parts according to bottom type:

- The muddy western part off Rokkaku River and Shiota River estuaries with 6 to 7Mdφ

- The sandy eastern part off Chikugo river 34Mdφ• This research is located in the same stations as Kasagi

et al. (2007); 45 subtidal stations with 28 mud and 17 sand bottoms

Study Site

Source : www.unepatlas.com

Location of the study site and the sampling stations

Note:- Dashed lines

indicate contour depth (m)

- Dotted points are mud bottoms, and

- The squares are sand bottoms

Sampling and processingSampling and processing

• Sediment sample was taken by using a Smith-McIntyre grab sampler (22.5 x 22.5 cm), and gently sieved the sediment with a 1 mm opening mesh

• The residual samples on the mesh were fixed with 10% formalin solution stained with Rose Bengal, and brought to the laboratory.

• The animals were sorted out, identified to the lowest feasible taxon, and counted

• The bulk wet weight was weighed for each species by pooling individuals using an electric balance nearest to 0.001 g

Estimation of species richness

This estimate is based on the observed frequency of rare species in the community and obtained from:

Where:

s = observed total number of species

n = total stations

k = number of unique species

Fj= number of stations containing unique species

Results and discussionResults and discussion

Benthic fauna in muddy and sandy bottom:Benthic fauna in muddy and sandy bottom:- 51 Polychaeta species 51 Polychaeta species - 25 crustaceans25 crustaceans- 23 molluscs23 molluscs- A few brittle stars and a sea cucumberA few brittle stars and a sea cucumber- 2 stations in the muddy area had no organism 2 stations in the muddy area had no organism The mean number of species per station was significantly The mean number of species per station was significantly

higher in the sandy bottom than in the muddy bottom higher in the sandy bottom than in the muddy bottom (mean(mean±SE; mud = 5.5±0.8, sand = 15.2±2.3)±SE; mud = 5.5±0.8, sand = 15.2±2.3)

The mean abundances of each taxon in 1989 and 2006

Total macrobenthos, polychaetes,ophiuroidea and others in 2006 were significantly fewer than those in 1989

The decrease in bivalves was nearly significant, and that in crustaceans did not differ between the two years

The relative abundances of each taxon in 1989 and 2006

No interactions between taxa, bottom type and years

Compositional patterns of taxa were similar irrespective of bottom types and years

The relative biomass of each taxon in 1989 and 2006

There was no significant difference in the biomass of any taxa between the two bottoms, except that Ophiuroidea tended to be lower in mud than sand

The relative biomass of each taxon did not differ between the bottom types

In the sandy bottom, total biomass in 2006 was 96.851.0 gww/m2, about 45% of which was bivalves on average

The Distribution of dominant bivalve species

The Distribution of dominant bivalve species

The Distribution of dominant bivalve species

The Distribution of dominant bivalve species

The Distribution of dominant bivalve species

The Distribution of dominant bivalve species

Suspected causes for decrease in Suspected causes for decrease in the macrobenthosthe macrobenthos

• The occurrence of bottom hypoxia in summer • The change in sediment grain size • Benthic succession from large long-lived to small short

lived species assemblages with long- term organic pollution on the bottom

Dominating species of Theora fragilis, Raeta pulchellus, Paraprinospio and

capitellidae pollychaetes

Benthic indicators of organically Benthic indicators of organically polluted areapolluted area

• Source: www.microseashell.com

Theora fragilis Raeta pulchellus Capitellidae polychaetes

ConclusionsConclusions

The benthic ecosystem of the inner part of The benthic ecosystem of the inner part of Ariake Bay has clearly deterioratedAriake Bay has clearly deteriorated

There is a changes in benthic ecosystems from There is a changes in benthic ecosystems from the decline in abundance, biomass and the the decline in abundance, biomass and the distribution of dominant species between 1989 distribution of dominant species between 1989 and 2006and 2006

Recovery of benthic ecosystems in the inner part Recovery of benthic ecosystems in the inner part would be unlikely unless those stressors are would be unlikely unless those stressors are removedremoved

Benthos research in relation with marine Benthos research in relation with marine ecosystem managementecosystem management

Monitoring habitats and ecosystems is desirable to detect the changes happening within the reserve and provide conservation managers with information to base management decisions on

Monitoring is recommended for every years

Terima KasihThank you

Dank uMerci

GraciasArigato gozaimas

Distribution of capitellid and spionid Distribution of capitellid and spionid polychaetes in 2006polychaetes in 2006

Distribution of gammaridea in 1989 and 2006Distribution of gammaridea in 1989 and 2006

YearYear Occurring frequency of Occurring frequency of mud (%)mud (%)

Occurring frequency of sand Occurring frequency of sand bottoms (%)bottoms (%)

19891989 81.881.8 33.333.3

20062006 50.050.0 76.576.5