Potential indirect effects of shellfish culture on the reproductive success of benthic predators

Abstract

Summary1. Environmental assessments of coastal aquaculture are concerned mostly with direct impacts on natural assemblages in the vicinity of shellfish or fin-fish farms. As the size and density of farmed sea space increases, there is greater potential for indirect effects on food webs beyond the immediate culture area. 2. We investigated the potential indirect effects of long-line mussel Perna canaliculus farms on the demography of an important benthic predator, the sea star Coscinasterias muricata . Surveys beneath four active farms, an abandoned farm and three unfarmed areas of seabed in Pelorus Sound, New Zealand, described the direct effects of mussel culture on the distribution and abundance of sea stars and other benthic consumers. These data were used to calibrate a model that simulated the fertilization success of sea star populations in farmed and unfarmed areas of the bays. 3. Deposits of living mussels and mussel shells covered up to 55% of the seafloor beneath farm sites, but were absent from soft sediments at unfarmed sites. Mean densities of sea stars were up to 39 times larger at active farm sites than in unfarmed areas and were correlated with the abundance of living mussels on the seafloor. 4. Within individual farms, the distribution of sea stars was highly aggregated at small spatial scales, with most (63%) individuals occurring within 2 m of their nearest neighbour. In unfarmed areas, sea stars were widely dispersed (< 1 80 m − 2 ). 5. Our simulations indicate that, because of the extremely clumped distributions of sea stars, spawning individuals at farm sites would on average have substantially greater fertilization success ( c. 90% of eggs) than those foraging in areas where farms are absent (<< 2% of eggs), and total zygote production could be as much as 1500 times greater than in unfarmed areas. 6. Synthesis and applications . This study demonstrates the potential for significant bottom-up effects of aquaculture on surrounding ecological assemblages. If, as has been suggested, sperm limitation is a major constraint on recruitment of asteroids and other invertebrate predators, supplemental provisioning from increased farm development could result in occasional outbreaks of populations, over a broader area than the farmed location. Without appropriate monitoring such events are likely to be dismissed as rare, natural phenomena rather than a consequence of shellfish culture.

Effects of intensive scallop mariculture on macrobenthic assemblages in Sishili Bay, the northern Yellow Sea of China

“…Moreover, the benthos can also benefit from the suspended culture system. For example, the scallop cultivation structures can provide refuge for overfishing to endemic marine fishes and invertebrates in ways similar to artificial reefs, and may increase the productivity of some motile fishes and epifauna (Inglis & Gust, 2003;Clynick et al, 2008;D'Amours et al, 2008;Han et al, 2011).…”

Review of recent carrying capacity models for bivalve culture and recommendations for research and management

“…The biomass and diversity of such epibiota may be substantial (Tenore and González, 1976;Carbines, 1993;Kilpatrick, 2002) and may contribute considerably to the total productivity of the site. For example, recent work by Inglis and Gust (2003) suggests that mussel farms in New Zealand may also increase not only the abundance, but also the productivity of starfish by increasing the starfish's relative growth rate and chance of successful reproduction.…”

Efficiency of starfish mopping in reducing predation on cultivated benthic mussels ( Mytilus edulis Linnaeus)

“…Starfish within such dense populations act as highly efficient predators, increasing their consumption when they encounter high-density prey patches, with aggregations in Morecambe Bay having been noted to advance up to 200 m a month destroying mussel beds that lay in their path (Dare, 1982;Inglis and Gust, 2003). A rubens is thought to be one of the most destructive species feeding on beds of cultivated mussels, as well as on natural populations, in northern Europe (Dare, 1982;Gallagher et al, 2008).…”

“…Mussels, when relaid on the seabed as part of benthic cultivation operations, thus, provide starfish with an abundance of prey in their natural environment (Barbeau et al, 1998;Miron et al, 2005). Consequently marine farming activities may influence the size and dynamics of aggregating starfish populations (Inglis and Gust, 2003). Observations of dense…”