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

Charles.Griffiths@uct.ac.za

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