Lotta C. Kluger. Estimation of the Ecological Carrying Capacity of a bay's system subjected to bivalve aquaculture

Transcription

1 Lotta C. Kluger Estimation of the Ecological Carrying Capacity of a bay's system subjected to bivalve aquaculture

2 BACKGROUND Bivalve molluscs: valuable resources Have been harvested for a long time Aquaculture became important alternative Avoid over-exploitation of natural populations Development often bottom-up process Without systematic planning (Filgueira et al. 2013)

3 BACKGROUND Clearance of large amounts of water alteration of flows of matter & energy Depletion removes food for zooplankton & other filter feeders trophic consequences (Dowd 2003) (Grant et al. 2005) Provision of habitat change in biodiversity Lack of control & overstocking: Habitat destruction Assessment for sustainability needed!

4 STUDY AREA Sechura Bay North Peru (5.6 S, 80.9 W) Large & shallow bay Temperatures comp. high Scallop fishery scallop culture Peruvian bay scallop (Argopecten purpuratus)

5 SECHURA: Hot spot for scallop culture

6 Research questions for today Q1: How is intense bottom culture changing energy flows within the bay s system? Q2: What is the bay s biological (long-term) carrying capacity for scallop cultivation?

7 Step 1 Q1: How is intense bottom culture changing energy flows within the bay s system? Title of manuscript: Assessing the system impact of scallop bottom culture through a community analysis and trophic modelling approach Submitted (09/2015) to MEPS

8 Q1 Objectives of work 1. Assessing the impact of scallop bottom culture on the bay s ecosystem Comparison of culture state with pre-culture state Community analyses Trophic modelling PERMANOVA, SIMPER, ABC Ecopath with Ecosim (EwE)

9 Results Q1 Comparison of pre-culture to culture conditions Abundance rank plots: Species diversity & evenness Evenness Species richness

10 Results Q1 Comparison of pre-culture to culture conditions SIMPER Analysis: Which species contribute most to dissimilarity? Caulerpa Scallops Predatory gastropods

11 Based on Taylor et al. (2008) Results Q1 Construction of food-web model Changes in trophic flows & system characteristics

12 Discussion Q1 Comparison of pre-culture to culture conditions System size Disturbance (reduced cycling) Species diversity & evenness (rank-plot) (TM) (TM) (CA) Community composition differs sign. (PERMANOVA) (CA) Scallop & its predators contr. most to dissimilarity (SIMPER) System functioning not changed (TM) TM=Trophic modelling, CA=community analysis

13 Discussion Q1: How is intense bottom culture changing energy flows within the bay s system? Introduction of scallop aquaculture has induced changes (community composition, degree of disturbance) but overall system functioning seems not affected Evaluation of changes crucial Identification of limits required to allow for sustainable use where to go from here?

14 CARRYING CAPACITY Maximum amount of cultivated organisms that a system can support without causing unacceptable impacts on the system. (Inglis et al. 2000; McKindsey et al. 2006)

15 CARRYING CAPACITY BUT: What means unacceptable? Ecol. carrying capacity definitions: Based on food or oxygen availability Bivalve growth characteristics Waste production Holistic approach needed (Inglis et al. 2000, Dame 1996, Gillibrand & Turrel 1997, Grant et al. 2005, Carver & Mallet 1990, Uribe & Blanco 2001, Grant 2006, Weise et al. 2009,

16 Step 2 Q2: What is the bay s biological (long-term) carrying capacity for scallop cultivation? Title of manuscript : Carrying capacity as a tool for ecosystem-based management of a scallop aquaculture system Accepted (09/2015), Ecological Modelling

17 Q2 Objectives of work 1. Address ecological carrying capacity in a more holistic way 2. Explore potential impact of a further increase in culture activities

18 Approach Q2 Construct steady-state EwE model Explore effect of further culture expansion: Force bivalve biomass to increase to 4 different levels Ecosim forcing functions Evaluate system response: - Ecological Network indices - Impact on other funct. group s biomasses

19 Q2 System response System size System cycling

20 Q2 Construct steady-state EwE model Explore effect of further culture expansion: Force bivalve biomass to increase to 4 different levels Ecosim forcing functions Evaluate system response: - Ecological Network indices - Impact on other funct. group s biomasses Threshold for ECC: before any group falls below 10% of its original standing stock

21 Q2 Impact on other groups Threshold for ECC: before any group falls below 10% of its original standing stock Scallop competitors Scallop predators

22 Q2 Discussion System size Disturbance (reduced cycling) Biodiversity (species depletion) Inter-specific trophic connections important for the identification of ECC

23 Summary Q2: What is the bay s biological (long-term) carrying capacity for scallop cultivation? 1. Current magnitude of scallop bottom culture (147 t km -2 ) does not yet exceed ecological carrying capacity 2. Exceeding scallop biomass levels of >458 t km -2 may cause other functional groups biomasses to fall below the 10% threshold potentially threaten ecosystem functioning, emphasizing the necessity for an ecosystem-based approach to ECC.

24 Summary 3. A further expansion may cause scallop predator biomasses to increase, representing in turn a top-down control on other groups of the system 4. Suggested ECC threshold may serve as ecosystem-based threshold to bivalve aquaculture for other systems exposed to bivalve culture.

25 !!! MUCHAS GRACIAS, THANK YOU!!!??? QUESTIONS???