Coastal development impacts on nearshore estuarine nekton communities

Transcription

1 Coastal development impacts on nearshore estuarine nekton communities D.M. Bilkovic and M.M. Roggero Virginia Institute of Marine Science Center for Coastal Resources Management Gloucester Point, Virginia September 6, 2007

2 Coastal development leads to disruption of ecosystem services Loss of diversity, functional groups of species, ecosystem resilience and may cause regime shifts

3 Shoreline Modification in Chesapeake Bay Bulkhead No Structure Riprap Revetment In Maryland, 28% of coastal, tidal shoreline is hardened (over 1,840 kilometers)

4 Research Objectives Long term program goals--include estimating how ecosystems respond to specific manageable stressors, if thresholds exist, and how multiple stressors may interact to affect nearshore communities Project goals 1) To estimate levels of development stressors at the land-water interface that elicit fish community responses Amount of Developed Upland Land Use Shoreline Modification (Bulkhead, Riprap, Natural) Developed lands and Shoreline modification combinations 2) To link habitat condition monitoring datasets to support nearshore ecosystem models.

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6 Fish and Habitat Survey Protocols Two replicate seine hauls were conducted during Jul-Aug 2005 Relative abundance, diversity, & fish community indices Shoreline condition categorized on site as bulkhead, riprap or natural (verification of GIS data from shoreline inventory) Qualitative assessment of amount of subtidal habitat Upland land use was estimated from the National Land Cover Dataset at varying buffer widths (200 and 1000m) around the site

7 Fish Collection Results 8626 fish collected, 33 species; range: species per site Average sizes = 10.4 ± 0.8 cm (range cm) Abundant species included: Atlantic menhaden (Brevoortia( tyrannus) Atlantic silverside (Menidia( menidia) White perch (Morone( americana) Bay anchovy (Anchoa( mitchilli) Spot (Leiostomus( xanthurus) Striped bass (Morone( saxatilis)

8 Statistical Analyses 1) Multimetric Index -integrate information into ecologically meaningful measures Comparison among Fish Community Index, shoreline condition, and upland land use measures 2) Multivariate approaches of community analyses inclusion of species specific abundances Explore similarities among sites with MDS plots and ANOSIM

9 Estuarine Fish Community Index Metric References: Jordan and Vaas 2000, Deegan et al 1997, Bilkovic et al Index combines a series of metrics that assess the structural and functional makeup of fish assemblages and can be used as an indicator of ecological integrity. Species Richness/Diversity Measures Species Richness Proportion of benthic-associated spp Number of dominant spp (90% of total abundance) Number of resident spp Fish Abundance Ln abundance Trophic Composition Trophic Index Relative proportions of three broadly defined trophic guilds based on primary prey items: carnivores, planktivores, and benthivores Nursery Function Number of estuarine spawning spp Number of estuarine nursery spp

10 Ecological Thresholds Fish Community Index in the Nearshore Fish Community Index in the Nearshore Developed land use (%) within 200m Developed land use (%) within 1000m Cumulative prob ability of a change point occurring Cumulative probability of a change point occurring Established a threshold of fish community response to gradients of developed lands Significant negative fish community response occurred at 23% developed lands 95% probability a threshold occurred

11 Upland development in relation to fish community integrity Upland development categorized as High ( 23%) or Low (<23%) Fish community index at High development sites significantly lower than Low development sites (One-way ANOVA; p<0.0001) Fish Community Index (SE) Low High Upland Development (23% Threshold)

12 Shoreline modification in relation to fish community integrity Fish Community index lowest for bulkhead sites the most altered shorelines Natural and riprap revetment sites similar (One-way ANOVA; p=0.04) Fish Community Index (SE) Jennings et al. 1999, Trial et al. 2001, Bilkovic et al. 2006, Seitz et al Natural Riprap Bulkhead Shoreline condition

13 Upland land use and shoreline modification in relation to fish community integrity Sites with low development-natural natural shoreline had higher fish community integrity than the sites with high development-bulkhead shoreline (p=0.008, ANOVA and Tukey pairwise comparisons) Fish Community Index (SE) LowDev/NatRip LowDev/Bulkhead HighDev/NatRip HighDev/Bulkhead Upland Development and Shoreline Condition

14 Multivariate approach (MDS) with ANOSIM 2D Stress: 0.16 Dev & Shl HighB HighN LowB LowN Pairwise ANOSIM Results R-statistic (p-value) LowN vs HighN (0.274 (0.047)) LowN vs HighB (0.494 (0.001)) LowN vs LowB (0.755 (0.007)) Sites with Low Development and Natural/Riprap Shoreline had different fish assemblages from all other combinations of condition The maintenance of a natural shoreline in low development areas was linked to diverse communities with tidal marsh species present. This was not the case with high upland development scenarios.

15 Habitat Linkages Percentage of Structural Benthic Habitat (SE) Natural Riprap Bulkhead Shoreline Condition Amount of structural benthic habitat was highest at sites with natural shoreline (30%), as opposed to hardened shoreline (riprap or bulkhead; 6 %) indicating a potential land-water nexus

16 Link habitat condition datasets to support nearshore ecosystem modelsm Acquired a large database of shoreline inventories throughout the Chesapeake Bay Begun to image and classify nearshore subtidal habitat with acoustic survey technology Combine geospatial datasets to support restoration/conservation targeting integrative assessments development of habitat suitability models ecological forecasting of habitat and living marine resources distributions under future environmental conditions (e.g. sea level rise) and management actions Shoreline survey

17 Conclusions Both upland development and the placement of erosion control structures on the shoreline were associated with reduced fish community integrity. Evident ecological thresholds, or breakpoints at which the fish community notably responded to a disturbance, occurred at relatively low levels of development (>23%) indicating that comprehensive shoreline and watershed land use plans are imperative to minimize impacts Fish community integrity was lowest along bulkheaded shorelines, and indistinguishable between natural and riprap revetment sites, which may mimic natural shorelines. The preservation of riparian zones and natural shoreline conditions, may help mitigate the stress from upland watershed development below the threshold---however, additional research is necessary to establish what shoreline type, and/or riparian buffer type & width may be most effective in high development scenarios.

18 Next steps Further research on underlying mechanisms driving shifts in condition are important next steps for supporting coastal management Identification of landscapes that are at the point of crossing a threshold Further research on the most appropriate spatial or temporal scale(s) at which threshold values apply for targeted habitat or biotic communities Develop shallow-water ecosystem models in context with the landscape for use in ecological forecasting and targeting tools Support shoreline management and permitting program efforts to consider cumulative, along with local, impacts during risk assessments and prior to decision-making.