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Marine alien and invasive species in South Africa
Prof. Charles Griffiths
Centre for Invasion Biology, Zoology Department, University of Cape Town
Balanus glandula ( white zone) and Mytilus galloprovincialis ( black zone) in Table Bay
Overall Alien and Invasive
Animals in SA
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
Marine aliens: - The vectors of introduction
Dry ballast
Ship boring
Ship fouling
Ballast water
Aquaculture
Changing importance of vectors over time:
1700 1800 1900 2000
Ship fouling
Ship boring
Dry ballast
Ballast water
Aquaculture
Recognition dates and arrival dates:
(Mead et al. 2011a & b)
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)
(a) (b)
Earliest DOC:
pushed back
100 years
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)
Number of species
Alien species
20
Protoctista Dinoflagellata Porifera
Polychaeta Cnidaria
Cirripedia
Isopoda Amphipoda Decapoda Pycnogonida Insecta Gastropoda Bivalvia Brachiopoda Bryozoa Echinodermata Ascidiacea Pisces Rhodophyta Chlorophyta Angiospermae
Copepoda
15 10 5
Cryptogenic species
Distribution of introductions around coast – -mostly protected sites invaded - few species are widespread or abundant on open coast
South Africa
Saldanha
CapeTown Knysna Port Elizabeth
East London
Durban
Richards Bay
23 38
26
27
24
14
12
Alexander Bay
14
Where do the introductions come from? - All over, but most from Europe/N Atlantic
North Pacific
North Atlantic
Europe
Caribbean
Chile
Tristan da Cuhna Australia
Indo-Pacific
Japan
Region of origin: Europe
Date of introduction: 1979
SA distribution: entire west coast, spreading along the south coast to East London
South Africa
1979
1982
1986 1993
1989
1990 Farm introduction
2004 1995
2004 Namibia
SB CT K PE
EL
L
W
D
Example of complexity of impacts:
Mediterranean mussel, Mytilus galloprovincialis
Impact 1.
Up-shore movement of centre of gravity of mussel beds
1979
Marcus Island (Hockey & Van Erkom Shurink 1992)
High Mid Low
Bio
mas
s
1988
High Mid Low
Bio
mas
s
Mytilus galloprovincialis
Aulacomya ater
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)
Choromytilus meridionalis 6 542 697 0 7 239 (6.4)
Perna perna - 31 787 13 400 45 187 (39.6)
(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)
Intertidal zone (high to low) 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
Marcus Island (Robinson et al. 2007)
* Massive settlement of small gastropod
Impact 4. Competition for primary rock space
Two possible outcomes:
1. Co-exist with smaller Scutellastra granularis, as can live on mussel shells
Size class
Fre
qu
ency
Size class
Fre
qu
ency
Size class
Fre
qu
ency
0 % M. galloprovincialis
50 % M. galloprovincialis
100 % M. galloprovincialis
B=25
G=16
B=36
G=23
B=33
G=21
(Griffiths et al .1992)
alternative outcome:
2. Displace larger Scutellastra argenvillei, as these cannot attain sexual maturity living on mussel shells
(Steffani & Branch 2003)
Impact 5. Increased food resources for Oystercatchers
(Hockey & Van Erkom Shurink 1992 and Hockey unpublished)
1979 1988
% C
on
trib
uti
on
to
die
t
1979 1990
Oys
terc
atch
er
de
nsi
ty
Other
Limpets
Mussels
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