Comparison of predation pressure in temperate and subtropical seagrass habitats based on chronographic tethering

Propeller scarring within seagrass beds is common in shallow coastal waters. Scarring has the potential to fragment seagrass beds, resulting in habitat loss, decreased productivity, and the possibility for further erosion and degradation. We conducted a study in Thalassia testudinum beds in Puerto Rico to determine whether seagrass macrofauna are affected by this disturbance. Four sampling zones (propeller scar, seagrass-scar interface, homogeneous seagrass located 5 m from the scar, and homogeneous seagrass located 10 m from the scar) were compared among 10 replicate seagrass beds. Scarring modified faunal assemblages at the scale of the propeller scar; there was significantly lower total macrofaunal abundance and fewer species in scars. When individual taxa were considered, shrimp and mollusc abundances were lower in scars compared to the other sampling zones. Resident fish abundance was not significantly different among zones. Dominant shrimp species in scars differed from seagrass zones. Crabs and molluscs responded negatively to scarring as indicated by significantly lower densities of these 2 taxa up to 5 m from scars. The extent to which these results 'scale up' remains unknown and future studies should focus on larger, more intensely scarred areas.

Section: Discussionmentioning

confidence: 96%

Effects of propeller scarring on macrofaunal use of the seagrass Thalassia testudinum

Uhrin¹,

Holmquist²

2003

“…Vegetation might affect crab communities through a series of physical, chemical and biological changes in the benthic systems (Nomann & Pennings 1998, Peterson et al 2001. Our study identified sediment grain size, water content and vegetation canopy structure (e.g.…”

Section: Environmental Factors Influencing the Crab Distributionmentioning

confidence: 96%

Effects of invasive cordgrass on crab distributions and diets in a Chinese salt marsh

Qin¹,

Chu²,

Wang³

et al. 2010

The effects of invasive cordgrass Spartina alterniflora on burrowing crab communities in the salt marshes of the Yangtze River Estuary, China, were studied. Crab abundance, distribution and diets were compared in native Phragmites australis and invasive S. alterniflora stands. Spartinainvaded stands had 42% higher crab density than did native P. australis stands, largely because 2 dominant grapsoid crabs, Helice tientsinensis and Chiromantes dehaani, thrived in S. alterniflora stands. Sediment grain size, water content and vegetation stem height were the main factors correlated with crab distributions. Crab diet analyses revealed that crab stomach fullness was similar in stands of different plant species, indicating that in Spartina-invaded stands crabs can find compatible food quantity as in native plant stands. Both H. tientsinensis and C. dehaani from S. alterniflora stands had significantly higher δ 13 C values than those from P. australis stands, suggesting that the crabs consumed S. alterniflora in the invasive marshes. This non-selective feeding may be driving the success of H. tientsinensis and C. dehaani in invasive Spartina stands.

“…Rather, predation events are focused at particular points in space and time, and are intimately linked with connectivity (Sheaves 2005). Small-scale predation hot spots often occur at interfaces such as between unvegetated substrates and seagrass (Peterson et al 2001), and just outside the refuges provided by macrophyte and woody debris (Sass et al 2006). Thus connections between habitats are often areas of high predation potential, so that the process of moving to utilise temporally available feeding or refuge habitats can represent a significant risk (Sheaves 2005).…”

Section: Connectivity and Predator-prey Dynamicsmentioning

confidence: 99%

Consequences of ecological connectivity: the coastal ecosystem mosaic

Sheaves¹

2009

316

216

Connectivity links habitats in space and time. It is a key process that facilitates many life-history functions of myriad species in a variety of contexts over a wide range of scales. Perhaps its most obvious application is to the multifaceted linkages among the diverse habitat units comprising ecosystem complexes like the coastal ecosystem mosaic (CEM) -the tightly interlinked coastal, estuarine, wetland and freshwater habitats at the interface of land and sea. The ability to utilise this diversity of connected habitats is integral to the life histories of a broad spectrum of organisms, with connectivity between habitats being crucial to important functions like nursery utilisation. Although connectivity is an obvious feature of the CEM, investigation of its implications has largely been restricted to the migration of organisms. However, connectivity has much broader conceptual relevance. It is a pervasive and multifaceted process affecting and enabling the lives of organisms over the full range of conceptual scales, with ecosystem components connected by a diversity of factors, including physical and biological translocation of nutrients, ontogenetic, life history, spawning and feeding migrations, food-web dynamics, predator-prey interactions, and many more. All of these play crucial roles in structuring biological populations, communities and assemblages, and in driving the biological processes that support them. Moreover, connectivity is a prominent and necessary component of ecological concepts, ranging from estuarine dependence and metapopulation dynamics to foraging arena theory. Considering connectivity as a multifaceted process leads to specific hypotheses about the functioning of the CEM and similar ecosystem complexes. KEY WORDS: Connectivity · Coastal ecosystems · Estuarine · Wetland · Ecosystem interactionsResale or republication not permitted without written consent of the publisher