Musseis in seagrass meadows: their influence on macroinvertebrate abundance and secondary production in the northern Gulf of Mexico

Abstract

ABSTRACT. From 1989 to 1990, we studied a previously undescribed mussel Modiolus americanus (Leach) habitat (with densities as high as 2000 ind. m-2) within the seagrass meadows of St. Joseph Bay, Florida, USA. Using suction sampling, we compared macroinvertebrate abundance, biomass, and annual production estimates in mussel habitat with 3 other habitats: monotypic stands of Thalassia testudinum (Banks ex Konig), Halodule wrightii Aschers and unvegetated sand flats. Previous studies have positively correlated macrofaunal densities and species number with measures of vegetation abundance or architecture. This relationship was not found to be strong in our study. Macroinvertebrate abundance, biomass, and annual production were usually equivalent or higher in mussel than in the other 3 habitats despite aboveground seagrass biomass usually being intermediate between pure stands of T testudinum and H. wrightii, and leaf surface area lowest. Of particular interest was annual macroinvertebrate production whlch ranged from 228.77 to 428.59 g ash-free dry mass (AFDW) m-2 in mussel habitat, followed in descending order by pure stands of T. testudinum (144.90 to 245.44 g AFDW m-'), H. wrightii (83.98 to 180.44 g AFDW m-2), and sand flats (19.83 to 42.47 g AFDW m-').These production estimates illustrate the positive effect that mussels can have in elevating already high levels of macroinvertebrate production in seagrass meadows.

An experimental test of the mechanism by which suspension feeding bivalves elevate seagrass productivity

“…Mimics were sufficiently negatively buoyant to remain in place within the sediment for the duration of the experiment. The mussel densities used in this experiment approximate the range of abundances most often observed in the bay (Valentine & Heck 1993).…”

“…Only the shallowest portions of the seagrass habitat are exposed during low tides, and wave energy is minimal. Associated with these T. testudinum beds is the semi-infaunal tulip mussel, Modiolus americanus, which is found in densities as high as 2000 individuals m -2 (Valentine & Heck 1993). Determining potential mechanisms of Thalassiamussel interactions.…”

“…Mimics were sufficiently negatively buoyant to remain in place within the sediment for the duration of the experiment. The mussel densities used in this experiment approximate the range of abundances most often observed in the bay (Valentine & Heck 1993).Nutrient enrichment had 3 levels (nutrient loading achieved by 0, 500 and 1500 mussels m -2 ). The nutrient addition treatment was accomplished by adding levels of nutrient approximating the biodeposition rates of Modiolus americanus.…”

Variability of the carbonate chemistry in a shallow, seagrass-dominated ecosystem: implications for ocean acidification experiments

“…As many of the marine organisms in Saint Joseph Bay have been observed associated with the seagrass beds (e.g. Valentine and Heck 1993;Heck et al 2000Heck et al , 2003, we chose to collect benthic water samples. Water samples for carbonate chemistry were collected monthly throughout 2012 and daily during the week of 28 July-4 August 2012.…”

“…Approximately 15 miles (,24 km) long and 6 miles (,9.7 km) wide, the average water depth in the bay is 6.4 m, with the deepest area (9-18 m) located in the north-west region of the bay. The bay contains ,30 km 2 of dense, stable populations of continuous and discontinuous seagrass beds (FERI 2006;FDEP 2012) primarily comprising Thalassia testudium with scattered patches of well sorted, siliceous sand (Valentine and Heck 1993;Beddingfield and McClintock 2000). Several invertebrate and vertebrate species have been observed to occur in high densities associated with the seagrass beds within the bay including amphipods, mussels, crabs, scallops, gastropods, sea urchins, sand dollars, sea turtles and a variety of juvenile fish (Valentine and Heck 1993;Heck et al 2000;Heck et al 2003).…”