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Dinoflagellate Blooms and Sardine in the Southern Benguela

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Dinoflagellate Blooms and Sardine in the Southern Benguela Climate change impacts on a dominant species: dinoflagellate blooms and sardine in the southern Benguela C.D. van der Lingen, L. Hutchings, T. Lamont, and G.C. Pitcher Some predicted effects of climate change on marine ecosystems Increasing sea temperature (UNEP 2008) Increasing sea level (IGPCC 2007) Increasing extreme weather events Decreasing dissolved oxygen Decreasing pH Changes in salinity Changes in circulation patterns Changing species distributions Increasing harmful algal blooms (HABs) Harmful Algal Blooms Favourable conditions of light, nutrient availability (eutrophication) and warm stratified waters can trigger algal blooms, typically (but not always) dominated by dinoflagellates (red tides) Pose threats to human health (toxic seafood, respiratory and skin irritation from red-tide aerosols) Fish kills (directly via toxicity and indirectly via anoxia following bloom decay) and marine mammal strandings; negative impacts on aquaculture Apparent increase in frequency, severity and geographic distribution of HABs worldwide has prompted international cooperation on HABs HABs in the southern Benguela HABs common in the southern Benguela, predominantly non-toxic Dinophycae Most dinoflagellate blooms west of Cape Agulhas, typically during Jan-May; spatial Reported dinoflagellate- difference in species composition dominated red tides (1989-1997) Toxic species cause mass mortalities of fish, shellfish, marine mammals and seabirds Paralytic (PSP) and Diarrhetic Shellfish Poisoning (DSP) common Species composition Harmful effects of high biomass, non-toxic (1989-1997) blooms include marine organism mortality arising from hypoxia or anoxia, and mechanical or physical damage Pitcher and Calder (2000) What does this have to do with sardine? The Cape Town sardine run of late- Koeberg 2011 (i) Blouberg Sardine very close inshore and/or washed up from several localities around Cape Town during early to mid- Hout Bay November 2011; “trapped close to beach by seals”, Noordhoek Muizenberg Kommetjie Fish Hoek “feebly swimming and dying” and “thin and weak”; and Misty Cliffs “seabed littered with dead pilchards”. Fish preyed upon Scarborough by seals, seabirds and humans Thought by some to be due to “cold shock”; by others linked to bloom of Gonyaulax polygramma extending from St Helena Bay to Walker Bay Noordhoek www.peoplespost.co.za 2011 Pelagic Spawner Biomass survey – fish (i) DAFF acoustic survey conducted every spring to estimate abundance Courtesy J. Coetzee and map distribution of sardine, anchovy and redeye round herring Fish biological data (length, weight, age, reproductive state, condition etc) collected Sardine Anchovy Also abiotic data Redeye and phyto-, zoo- and ichthyo- plankton samples 2011 Pelagic Spawner Biomass survey – fish (ii) 180 Length-weight relationships determined for each 160 (g) 140 Sardine species and used to calculate condition factor: 120 100 2.9745 WEIGHT y = 0.0115x 80 r² = 0.8717 CF = observed weight/expected weight 60 n = 1 484 40 WET BODY 20 0 Spatial distribution of mean CF plotted 5 10 15 20 25 CAUDAL LENGTH (cm) 180 160 (g) 140 Anchovy 120 2.8475 100 y = 0.0135x WEIGHT WEIGHT 80 r² = 0.9651 60 n = 2 000 40 WET WET BODY 20 0 5 10 15 20 25 CAUDAL LENGTH (cm) 180 160 (g) 140 Redeye 120 100 y = 0.0084x3.0911 WEIGHT WEIGHT 80 r² = 0.9844 60 n = 2 713 40 WET WET BODY 20 0 5 10 15 20 25 CAUDAL LENGTH (cm) 2011 Pelagic Spawner Biomass survey – fish (iii) 1.4 Sardine CF showed marked spatial pattern, with low 1.3 1.2 CF inshore off the south coast (particularly low off 1.1 Mossel Bay) and high CF offshore 1 0.9 AVERAGE CF AVERAGE 0.8 Above Average CF 1.4 0.7 Below Average CF 0.6 1.3 0 100 200 300 400 DEPTH (m) 1.2 1.3 Above-average CF 1.2 Below-average CF 1.1 1.1 1 1 0.9 AVERAGE CF 0.9 AVERAGE CF AVERAGE Above Average CF0.8 0.8 Below Average CF0.7 0 50 100 150 200 0.7 DEPTH (m) CT sardine run CF1.3 0.6 1.2 0 50 100 150 Photo:200 Y. Geja 250 3001.1 350 DEPTH (m) 1 No such pattern observed for anchovy or redeye CF AVERAGE 0.9 Above-average CF 0.8 Below-average CF 0.7 What caused the low sardine CF inshore 0 100 200 300 400 500 (and of fish from CT sardine run)? DEPTH (m) 2011 Pelagic Spawner Biomass survey – environment (i) Normal SST pattern but anomalous SSS pattern with high salinity (>35.5 g.kg-1) water over WAB and CAB High salinity water extended down 50- 70m Hypoxic (<1.5 ml.l-1) conditions at the bottom inshore CAB Anomalous oceanographic conditions 2011 Pelagic Spawner Biomass survey – environment (ii) Satellite data showed high 15 October2011 2 November 2011 chlorophyll a levels inshore off the west and south coast from mid-October to mid-November 20 October 2011 7 November 2011 Peak concentrations between Cape 27 October 2011 15 November 2011 Agulhas and Plettenberg Bay in early-November 2011 Pelagic Spawner Biomass survey – environment (iii) Small (<100µm) dinoflagellates (including mixotrophic Gonyaulax polygramma and several colourless, heterotrophic genera e.g. Protoperidinium and Gyrodinium) completely dominated net (>10µm) phytoplankton community inshore between Cape Columbine and Plettenberg Bay 100 80 Diatoms 60 Dinoflagellates % 40 20 0 6.1 10.1 13.1 17.1 20.1 23.1 25.1 28.1 33.1 35.1 38.1 41.1 46.1 49.1 53.1 58.1 Percentage composition of net (>10µm) phytoplankton at inshore CTD stations 2011 Pelagic Spawner Biomass survey – environment (iv) Dinoflagellates moderately abundant (>25 000 cells.L-1) between Cape Columbine and Plettenberg Bay; Gonyaulax polygramma abundant (>200 000 cells.L-1) off Cape Peninsula and Mossel Bay (area of lowest sardine CF) 350000 G. polygramma blooms 300000 observed off SA coast 250000 previously (first -1 200000 150000 reported in False Bay in L Cells 100000 1962); responsible for 50000 0 fish and invertebrate 6.1 10.1 13.1 17.1 20.1 23.1 25.1 28.1 33.1 35.1 38.1 41.1 46.1 49.1 53.1 58.1 kills from anoxia following decay Abundance of all dinoflagellates and of G. polygramma at inshore CTD stations 2011 Pelagic Spawner Biomass survey – synthesis 1. Marked spatial pattern in sardine CF: fish inshore in poor condition (cf CT 2011 sardine run) and those offshore in good condition 2. No spatial pattern in CF of either anchovy or redeye 3. Anomalous oceanographic conditions (high salinity water and hypoxic bottom waters off CAB) observed off the south coast 4. High chlorophyll a levels in surface waters inshore the south coast before and during survey; dinoflagellates (particularly G. ploygramma) dominated inshore phytoplankton community - also anomalous (cf CT 2011 sardine run) 5. Why did these anomalous conditions negatively impact sardine but not anchovy or redeye? =/ = Why only sardine? (i) Anchovy Differences in branchial basket morphology (used to retain plankton prey) - sardine have many more gill rakers giving a smaller gill raker gap (i.e. finer filtering mesh) than either anchovy or redeye 0.8 Sardine 0.7 King and MacLeod (1976) 0.6 Anchovy (mm) 0.5 Redeye GAP GAP 0.4 0.3 GILL GILL RAKER 0.2 0.1 0 0 5 10 15 20 25 CAUDAL LENGTH (cm) Effects on dietary composition with sardine feeding on smaller prey (different denticle structure further Sardine aids retention of small particles) Why only sardine? (ii) Sardine Both sardine and anchovy directly observed (in laboratory experiments) to filter-feed (not yet for redeye) Sardine can retain very small particles (down to 17µm) whereas anchovy can only retain particles > 200µm T. weissflogii S. costatum van der Lingen (1994) Anchovy Why only sardine? (iii) ? Sardine (but not anchovy nor redeye) able to retain on their gill rakers the small dinoflagellates that bloomed off the west and south coast in spring 2011 We hypothesize that sardine “irritated” in some way by dinoflagellates (via retention when feeding and possibly also when respiring) and so avoided blooms Sardines inshore of blooms were coastally trapped, where they lost condition because of a cessation of feeding and probable respiratory stress due to crowding in small water volumes, and likely experienced high predation (cf Cape Town 2011 sardine run) Un-developed gonads of poor condition fish suggested prolonged starvation (either no gonad development or gonad resorption following atresia) Implications for spawning success and subsequent recruitment strength – likely to reduce productivity of the southern Benguela sardine population The bigger picture – wind forcing Daily averaged QuikSCAT wind data for Jan-Dec 2011 from 4 coastal locations (Cape Columbine, Cape Point, Mossel Bay and Cape St Francis) used to calculate Ekman transport 2 2 20 ) 1 - ) ) upwelling upwelling s upwelling 1 1 - - 15 3 s (a) 1.5 1.5 (b) s (c) 3 3 10 1 1 5 0.5 0.5 0 -5 CC 0 0 Climatological mean -10 -0.5 -0.5 Cape Columbine downwelling Cape Columbine downwelling Ekman transport transport (m Ekman -15 Ekman transport (m Cape Columbine downwelling -1 -1 -20 (1984-2010) and Ekman transport anomaly (m Jul-2011 Jul-2011 Oct-2011 Jan-2011 Sep-2011 Jan-2011 Sep-2011 Oct-2011 Feb-2011 Dec-2011 Jun-2011 Dec-2011 Feb-2011 Jun-2011 Nov-2011 Apr-2011 Nov-2011 Apr-2011 Aug-2011 Oct-2011 Aug-2011 Sep-2011 Dec-2011 Mar-2011 Mar-2011 May-2011 Nov-2011 May-2011 2 2 20 ) monthly Ekman 1 - ) ) upwelling upwelling s upwelling 1 1 - - 15 3 s 1.5 (d) 1.5 (e) s (f) 3 3 10 1 1 transport (left); 5 0.5 0.5 0 -5 CP 0 0 monthly anomalies -10 -0.5 -0.5 Cape Point downwelling Cape Point downwelling downwelling Ekman transport (m -15 Ekman transport transport (m Ekman Cape Point -1 -1 -20 (centre); and daily Ekman transport anomaly (m Jul-2011 Jul-2011 Oct-2011 Jan-2011 Sep-2011 Jan-2011 Sep-2011 Oct-2011
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