Selective settlement by larvae of Membranipora membranacea and Electra pilosa (Ectoprocta) along kelp blades in Nova Scotia, Canada

Abstract

Many larval sessile marine invertebrates exhibit settlement preferences, and larval behavioral responses to cues at settlement can ultimately influence the distribution of adults and an individual's lifetime fitness. Two epifaunal bryozoans, the invasive Membranipora membranacea and the native Electra pilosa, commonly co-occur on kelp species in the subtidal habitats of Nova Scotia, Canada. Outbreaks of M. membranacea have been linked to mass defoliation of the kelp canopy; however, E. pilosa has not been associated with any significant effect on its host substrate. To examine whether larvae of M. membranacea and E. pilosa exhibit settlement preference for a particular location along the blades of the kelps Saccharina latissima and Laminaria digitata, abundances of newly settled colonies were quantified at different locations along the kelp blade. Algae were sampled at 2 sites on the southwestern shore of Nova Scotia (The Lodge and Feltzen South) from September 2009 to October 2010, over one complete cycle of the annual life cycle of M. membranacea, and thus over a wide range of bryozoan percent cover. Settlers of both bryozoans were significantly more abundant towards the younger, more proximal regions of blades of both kelps across all sampling periods. These patterns did not vary seasonally with increasing colony density. Both M. membranacea and E. pilosa larvae showed preferential settlement, suggesting that they can detect small-scale differences in habitat quality at the scale of a single kelp blade.

Wasted effort: recruitment and persistence of kelp on algal turf

“…Warm temperatures also increase settlement and growth of the invasive bryozoan Membranipora membranacea, which encrusts, weakens, and causes fragmentation of kelp blades (Saunders & Metaxas 2009, Scheibling & Gagnon 2009). Furthermore, M. membranacea has a settlement affinity to new tissue adjacent to the basal meristem (Brumbaugh et al 1994, Denley et al 2014, which may increase the likelihood of erosion of the meristem as the colony grows towards the stipe (Ryland & Stebbing 1971). The combined effects of increasing temperatures late in the summer and encrustation by M. membranacea, coupled with increased wave activity in the autumn, likely caused the considerable loss of blade tissue of the large rockattached kelps, such that only bare stipes remained.…”

Growth response of calcifying marine epibionts to biogenic pH fluctuations and global ocean acidification scenarios

“…Even though bryozoans do not seem to benefit from algae in terms of growth, other factors have been suggested that support preferred settlement on algae. Those include low competition for space (Manríquez and Cancino 1996), minimized risk of predation and thus, increased longevity of colony survival (Nikulina and Schäfer 2006; Denley et al 2014), lower risk of smothering by sediment (Denley et al 2014), supply of organic matter (food) by macroalgae (Manríquez and Cancino 1996), and higher food availability as the algae sways through the water column (Okamura 1988; Pratt 2008).…”

Quantifying mortality of modular organisms: a comparison of partial and whole‐colony mortality in a colonial bryozoan

“…Smaller colonies of M. membranacea were able to avoid whole‐colony mortality, presumably as a result of selective settlement toward younger more basal regions on blades of host kelps (Denley et al. ). Selective settlement allows M. membranacea recruits the maximum amount of time to grow before becoming at risk of mortality due to breakage or erosion of the kelp substrate.…”

“…Consequently, its population dynamics have been well studied, both in Nova Scotia and circumglobally (see Saunders and Metaxas , , , Denley et al. ). Unlike most corals (e.g., Pisapia and Pratchett ), the sheet‐like growth of M. membranacea makes it possible to visually measure partial mortality as a reduction in two‐dimensional colony surface area, allowing the full extent of partial mortality to be quantified from a single photograph.…”