University Events

Description: Department of Fisheries Oceanography


Describing echinoderm (Echinodermata) populations on Georges Bank and evaluating direct and indirect effects of marine protected areas on these populations


By
Judith Rosellon Druker

Advisor
Kevin Stokesbury



Wednesday, November 16, 2016
9:00 am

SMAST I, Room 204
706 S Rodney French Blvd
New Bedford, MA

Abstract: Marine protected areas (MPAs) may have both direct and indirect effects on marine ecosystems. Direct effects are primarily related to changes in species abundance and body sizes, while indirect effects include modifications to trophic interactions, such as predation. This study examined both effects on echinoderms populations and on the echinoderm-groundfish (prey-predator) complex on Georges Bank. Using video survey techniques, we analyzed distribution and estimated density, biomass, and body size of four groups of echinoderms (brittle stars, sand dollars, sea stars, and sea urchins) from 2005 to 2012. We evaluated the influence of MPAs on this echinoderm assemblage controlling for several environmental factors (depth, temperature, sediment type, and sediment stability). We also used fishery independent trawl survey and stomach content data, to compare relative abundance, diet, and body sizes of three groundfish echinoderm-specialist species (American plaice Hippoglossoides platessoides, haddock Melanogrammus aeglefinus, and ocean pout Macrozoarces americanus) before (1987-1994) and after (2005-2012) implementation of MPAs. We determined areas with significant spatio-temporal correlation between predator and prey species. Finally, we evaluated the influence of time period, depth, sediment type, management area, and proportion of echinoderm prey in diet, on consumption rates by these predator species. Brittle stars were confined to the northern edge of the bank, sand dollars were mainly located in the central and south-western areas, sea stars were highly aggregated on the southern edge, and sea urchin were randomly located through- out the entire region. While MPAs appeared to influence the distribution of sand dollars and sea stars, the distribution of brittle stars and sea urchins seemed to be defined by preferred habitat conditions, regardless of any fishing pressure. With the exception of brittle stars, echinoderm body sizes were always larger in the areas with lowest densities. This suggested that reduction of fishing inside certain MPAs positively affected sand dollar and sea star populations, via enhanced recruitment. While American plaice relative abundance, body size, and consumption rates remained similar between time periods, haddock and ocean pout exhibited increase in relative abundance, changes in distribution, decrease of body sizes, and an increase of consumption rates, after MPAs implementation. We also observed a general increase in the proportion of sand dollars and sea stars in the diet of predators post MPAs implementation. In summary, these results indicated that MPAs have the potential to affect this predator-prey complex via modification of consumption hotspots (e.g. location where feeding is enhanced). As echinoderms are main predator and prey for commercially targeted species, the detailed information (on the scale of kilometers) on abundance, spatial distribution, and size structure of echinoderm populations provided in this study is valuable for the implemen- tation of Ecosystem Based Fisheries Management. Furthermore, we have presented here a series of steps that can be used as a structured methodology to determine indirect effects of MPAs on trophic interactions. This has important implications in MPAs planning and monitoring, since these indirect effects are rarely part of initial evaluations.


for more information, please contact

Christine Fox (cfox@umassd.edu)