Hypoxia Effects on Demersal and Benthic Fauna

Transcription

1 Hypoxia Effects on Demersal and Benthic Fauna Nancy N. Rabalais 1 R. Eugene Turner 2 1 Louisiana Universities Marine Consortium 2 Louisiana State University Center for Sponsored Coastal Ocean Research, Coastal Ocean Program, NGOMEX Hypoxia Studies

2 Hypoxia = Dissolved O 2 < 2 mg/l (=2 ppm) Shrimp (kg h -1 ) Finfish (kg h -1 ) Bottom D.O. (mg/l) Bottom D.O. (mg/l) (data from Leming and Stuntz, 1984; SW Louis. Coast, June 1982)

3 (mg O 2 l -1 ) Nekton Most present Absent (fish kills) Demersal invertebrates Most present Few mantis & penaeid shrimp Absent Present Stressed (starfish, brittle stars) Dead Bacterial mats Larger infauna Present & burrowed Epibenthic invertebrates Macroinfauna Present & burrowed Stressed (anemones, Moribund gastropods) polychaetes Dead Anoxic sediment, H 2 S in sediment and water Dead (mg O 2 l -1 ) (Rabalais, Harper & Turner, 21)

4 Photos Removed Charismatically Stressed or Dead Organisms (Downing 22)

5 D.O. mg/l Severe Hypoxia 199, C6A Number of Species Other Sipuncula Ophiuroidea Crustacea Gastropoda Bivalvia Nemertea Polychaeta Mean No. of Individuals/m 2 Mediomastus ambiseta Paraprionospio pinnata Ampharete sp. A Magelona sp. H Owenia fusiformis Aspidosiphon sp. Clymenella torquata 4 2 (Rabalais et al., 21) Month 8 9 1

6 D. O. (mg/l) Severe Hypoxia 1991, C6B Month Number of Species Other Sipuncula Ophiuroidea Crustacea Gastropoda Bivalvia Nemertea Polychaeta Mean No. of Individuals/m 2 Mediomastus ambiseta Paraprionospio pinnata Ampharete sp. A Magelona sp. H Aspidosiphon sp. Sigambra tentaculata 2 (Rabalais et al., 21) Month 8 9 1

7 D.O. mg/l Intermittent Hypoxia 199, WD32 8 Number of Species Other Sipuncula Ophiuroidea Crustacea Gastropoda Bivalvia Nemertea Polychaeta Mediomastus ambiseta Mean No. of Individuals/m 2 Paraprionospio pinnata Ampharete sp. A Magelona sp. H Magelona sp. I Tellina versicolor Armandia maculata 1 (Rabalais et al., 21b) Month 8 9 1

8 199 Mean Number of Individuals Depth (cm) April ND May June July August September ND ND (Rabalais et al., 21b) October

9 Results of the nonlinear multidimensional scaling analysis on matrix 'SEASON' with superimposed bottom dissolved oxygen (mg/l) UA4.8 UB4 UA3-1 mg/l O mg/l O mg/l O 2 >3 mg/l O 2.4 UB3 1 = WINTER 3 = SUMMER 2 = SPRING 4 = FALL. -.4 SH4 SH1 SH3 SH2 UA1 UA2 UB2 UB Clustering at hierarchical level of Bray-Curtis Dissimilarity >.5 Clustering at hierarchical level of Bray-Curtis Dissimilarity =.37 (Rabalais et al., 21b)

10 Comparison of benthic communities from hypoxia-affected environments Dauer et al. (1992) Chesapeake Mainstem Tributaries Polyhaline Hypoxic Mesohaline Hypoxic Density (no. m -2 ) 1,978 1,723 3,65 92 Biomass (g AFDW m -2 ) Species (no. sample -1 ) Louisiana Shelf Louisiana Shelf Rabalais et al. (1993) Periodic Hypoxia Seasonally Severe Hypoxia Spring Spring Hypoxic April 199 April 199 Jul-Aug 199 Density (no. m -2 ) 8,637 18, Biomass (g AFDW m -2 ) Biomass (g C m -2 ) Species (no. sample -1 ) Feb-May 1991 Feb-May 1991 Jul-Aug 1991 Density (no. m -2) 2,873 6,486 1,346 Biomass (g AFDW m -2 ) Biomass (g C m -2 ) Species (no. sample -1 ) (Rabalais et al., 21b)

11 Effects of Hypoxic/Anoxic Events on Meiofaunal Communities Mean Density (Ind. 1 cm -2 ) Prior hypoxia During hypoxia Devils Hole 27 mud..6 3 mo Total 1,5 2,68 (Bermuda) a Gulf of Mexico (USA) b 8-13 mud < 2 5 mo Total Nematoda Copepoda Kinorhyncha ~ 8 3,8 ~ 6 3,1 ~ 1 41 ~ ~ 5 1,1 ~ 5 1,1 ~ 2 ~ 1 11 Gullmar Fjord (Sweden) c 1 mud.3 2 mo Nematoda 8,9 1,2 After hypoxia 1,3 1,7 During hypoxia Gulf of Mexico (USA) d 18 mud. > 3 mo Nematoda Copepoda a Coull [1969] b Murrell and Fleeger [1989] c Hendelberg and Jensen [1993] d Wetzel et al. [21] (Modified from Wetzel et al. 21)

12 Benthic Foraminiferans Percentage Quinqueloculina Year (AD) AE index Buliminella E3 G27 C % frequency Hypoxia Index SWDI Foraminiferans Glauconite 2 1. Ostracods % of coarse grains Reducing Envt. Benthic Diversity (Sen Gupta et al. 1996, Rabalais et al. 1996, 22)

13 Characteristics of Louisiana Shelf Benthos Subjected to Seasonally Severe Hypoxia Reduced species richness Severely reduced abundances (but never azoic) Low biomass Limited taxa (none with direct development) Characteristic resistant infauna (e.g., a few polychaetes and sipunculans) Limited recovery following abatement of oxygen stress (Rabalais et al., 21b)

14 Distance (km) postlarval recruitment spawning emigration Litopenaeus setiferus White Shrimp Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Distance (km) postlarval recruitment spawning emigration Farfantepenaeus aztecus Brown Shrimp 1 spawning (source: N. Rabalais, LUMCON) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1 Depth (m) Depth (m)

15 (Downing et al., 1999) River discharge Salinity in nursery area Preferable nursery habitat for brown shrimp More hypoxia Suitable habitat for brown shrimp offshore River discharge Salinity in nursery area Preferable nursery habitat for brown shrimp Less hypoxia Suitable habitat for brown shrimp offshore and the ultimate predator Source: N. N. Rabalais, LUMCON

16 2 o Production in Benthos Implications for Fisheries Temporally & spatially enhanced Enhanced predation Marginally As stress increases High post-hypoxia recruitment High turnover rates & ultimately higher production Higher yield Prolonged, severe faunal depression, large areas Predators excluded Stressed fauna intact Suitable habitat absent Low post-hypoxia recruitment Turnover rates similar, biomass less, overall production lower Lower yield (potential dichotomy, N. N. Rabalais)

17 (Modified from Caddy, 1993) Oligotrophic Mesotrophic Eutrophic (Dystrophic?) SE North Sea N Gulf of Mexico?? Adriatic Sea Great Lakes Kattegat Baltic Sea Seto Inland Sea Yellow Sea NW Black Sea Chesapeake Bay? Production and Fishery Yield Other zooplankton Zooplanktivorous fish feeders (e.g., jellyfish) Demersal fish Seasonal Permanent bottom hypoxia Benthos Oligo- Meso- Eu- Dys-trophic Nutrient Loading