Download Marine alien and invasive species in South Africa

Marine alien and invasive species in South Africa
Prof. Charles Griffiths
Centre for Invasion Biology, Zoology Department, University of Cape Town
[email protected]
Balanus glandula ( white zone) and Mytilus galloprovincialis ( black zone) in Table Bay
No species
:
Terrestrial Marine FW
Total
Mammal
13
-
-
13
Bird
7
-
1
8
Reptile
1
-
-
1
Fish
-
-
17
17
Ascidian
-
9
-
9
Insect
394
3
3
400
Myriopod
9
-
-
9
Arachnid
40
-
1
41
Crustacean
8
23
5
36
Annelid
39
9
-
48
Mollusc
32
12
8
52
Cnidarian
-
13
1
14
other
7
11
4
Total
550
80
40
670
Overall Alien
and Invasive
Animals in SA
Marine aliens:
- The vectors of introduction
Dry ballast
Ship boring
Ship fouling
Ballast water
Aquaculture
Changing importance of vectors over time:
Aquaculture
Ship fouling
Ballast water
Ship boring
Dry ballast
1700
1800
1900
2000
Recognition dates and arrival dates:
(Mead et al. 2011a & b)
(a)
(b)
Earliest DOC:
pushed back
100 years
Date of recognition as alien (left) dark = confirmed, light = cryptogenic
-First paper listing aliens only 1992, rate of recognition since 2000 very rapid (>6
species per year since 2000 !)
Backdating to earliest museum records (right panel) shows steady introduction rate
since 1840, with recent acceleration, due to combination of local taxonomic work,
higher introduction rate and recent directed searching (circled)
Difficulties of identification of aliens:
- Why have we been so slow to recognize these introductions?
• Most likely sites of introduction (harbours, aquaculture facilities
etc.) seldom surveyed.
• Aliens misidentified as local species.
• Aliens mistakenly considered to be “cosmopolitan” when in fact
have been widely introduced.
• Introduced species re-described as new ‘indigenous’ species.
• Lack of taxonomic expertise in introduced taxa.
Current composition of introduced marine biota
(87 confirmed, 40 cryptogenic)
Alien species
Protoctista
Dinoflagellata
Porifera
Cnidaria
Polychaeta
Cirripedia
Copepoda
Isopoda
Amphipoda
Decapoda
Pycnogonida
Insecta
Gastropoda
Bivalvia
Brachiopoda
Bryozoa
Echinodermata
Ascidiacea
Pisces
Rhodophyta
Chlorophyta
Angiospermae
5
10
Number of species
Cryptogenic species
15
20
Distribution of introductions around coast –
-mostly protected sites invaded
- few species are widespread or abundant on open coast
14
Saldanha
CapeTown
Alexander
Bay
South Africa
Durban
27
38
Richards Bay
12
Knysna
23
24
14
26
East London
Port Elizabeth
Where do the introductions come from?
- All over, but most from Europe/N Atlantic
North
Atlantic
North
Pacific
Europe
Japan
Caribbean
Indo-Pacific
Chile
Australia
Tristan da Cuhna
Example of complexity of impacts:
Mediterranean mussel, Mytilus galloprovincialis
Region of origin: Europe
Date of introduction: 1979
SA distribution: entire west coast, spreading along the south
coast to East London
2004 W
Namibia
1993
1986 L
1982
SB
1979 CT
1989
South
Africa
K
1995
D
EL
PE
 2004
1990
Farm introduction
1979
Biomass
Impact 1.
Up-shore movement of centre of gravity of mussel beds
High
Mid
Low
Mytilus
galloprovincialis
1988
Biomass
Aulacomya ater
High
Mid
Low
Marcus Island (Hockey & Van Erkom Shurink 1992)
Impact 2. Large increase in intertidal mussel biomass
(especially on W. Coast)
Species
W Coast
S Coast
KZN
Total wet t (%)
Mytilus galloprovincialis
47 457
2 863
0
50 335 (44.2)
Aulacomya ater
10 609
535
0
11 144 (9.8)
6 542
697
0
7 239 (6.4)
-
31 787
13 400
45 187 (39.6)
Choromytilus meridionalis
Perna perna
(Modified from Van Erkom Schurink & Griffiths 1990)
Table Bay
1979
Table Bay
2004
Impact 3. Elevated biodiversity and faunal density in
invaded areas ( esp. midshore zone)
Species richness
Infaunal density.m2
Before
After
Before
After
1. (highest) Not invaded
3
2
4 000
5 000
2. Peak Mytilus zone
6
17
4 500
9 000
3. Mytilus invaded
1
13
< 1 000
6 000
4. Mytilus invaded
10
20
100 000*
17 000
5. Indigenous mussels
displaced by Mytilus
24
8
90 000*
6 000
Intertidal zone (high to low)
* Massive settlement of small gastropod
Marcus Island (Robinson et al. 2007)
Impact 4. Competition for primary rock space
Two possible outcomes:
1. Co-exist with smaller Scutellastra granularis, as can live on mussel
shells
B=25
G=16
Frequency
0 % M. galloprovincialis
B=36
G=23
Frequency
Size class
50 % M. galloprovincialis
B=33
G=21
Frequency
Size class
100 % M. galloprovincialis
Size class
(Griffiths et al .1992)
alternative outcome:
2. Displace larger Scutellastra argenvillei, as these cannot
attain sexual maturity living on mussel shells
(Steffani & Branch 2003)
% Contribution to diet
Impact 5. Increased food resources for Oystercatchers
Mussels
Other
Limpets
Oystercatcher density
1979
1979
1988
1990
(Hockey & Van Erkom Shurink 1992 and Hockey unpublished)
Impact 6. Commercial culture & recreational harvesting
3000 tpa Mytilus cultured in
Saldanha Bay, large intertidal stocks
available for subsistence use
Note: West coast rocky intertidal now totally alien
dominated by 3 major species!
Upper shore
covered by Balanus
glandula
Midshore by
Mytilus galloprovincialis
Lowshore by
Semimytilus algosus
Acknowledgements:
Thanks to NRF-DST Centre of Excellence for Invasion Biology for financial support