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.

Coral reefs are critically important marine ecosystems that are threatened worldwide by cumulative impacts of global climate change and local stressors. The Solomon Islands comprise the southwestern boundary of the Coral Triangle, the global center of coral diversity located in the Indo-Pacific, and represent a bright spot of comparatively healthy coral reef ecosystems. However, reports on the status of coral reefs in the Solomon Islands are based on monitoring conducted at 5 stations in 2003–2004 and 2006–2007, with no information on how corals in this region have responded to more recent global bleaching events and other local stressors. In this study, we compare reef condition (substrate composition) and function (taxonomic and morphological diversity of hard corals) among 15 reefs surveyed in the Western Province, Solomon Islands that span a range of local disturbance and conservation histories. Overall, we found high cover of live hard coral (15–64%) and diverse coral assemblages despite an unprecedented 36-month global bleaching event in the three years leading up to our surveys in 2018. However, there was significant variation in coral cover and diversity across the 15 reefs surveyed, suggesting that impacts of global disturbance events are moderated at smaller scales by local anthropogenic factors (fisheries extraction, land-use impacts, marine management) and environmental (hydrodynamics) conditions. Our study provides evidence that relatively healthy reefs persist at some locations in the Solomon Islands and that local stewardship practices have the potential to impact reef condition at subregional scales. As coral reef conservation becomes increasingly urgent in the face of escalating cumulative threats, prioritising sites for management efforts is critical. Based on our findings and the high dependency of Solomon Islanders on coral reef ecosystem services, we advocate that the Western Province, Solomon Islands be considered of high conservation priority.

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Citation: Denley, D., and A. Metaxas. 2016. Quantifying mortality of modular organisms: a comparison of partial and whole-colony mortality in a colonial bryozoan. Ecosphere 7(10):e01483. 10. 1002/ecs2.1483 Abstract. Comprehensive studies on the population dynamics of colonial organisms require estimates of mortality from the level of the individual module (partial mortality) to the entire colony (wholecolony mortality), as well as determining the factors that affect mortality at each level of organization. However, accurate measurements of whole-colony and partial mortality of modular organisms can be difficult to obtain, and few studies involve concurrent measurements of modular and colony mortality. We implemented multiple approaches to measure whole-colony and partial mortality of modular species using the colonial bryozoan Membranipora membranacea as a model organism. M. membranacea is a cosmopolitan species and of particular ecological significance in the northwest Atlantic, where it is the dominant epiphyte on laminarian kelps and the main driver for the defoliation of kelp beds. Rates of whole-colony mortality were measured in the field (1) indirectly through repeated subsampling cohort analyses and (2) directly by tagging colonies in situ. Partial mortality of colonies was measured (1) in the field by quantifying the proportion of degenerated zooids per colony and (2) in the laboratory by monitoring loss of colony surface area during seasonal senescence of colonies over winter. Temporal patterns differed substantially between partial and whole-colony mortality, suggesting that factors affecting mortality of individual modules differ from those affecting whole colonies. Our study indicated that the accuracy of common methods for measuring mortality of modular organisms depends on the species-specific life-history characteristics. However, we suggest that rates and mechanisms of whole-colony and partial mortality can be most accurately quantified by revisiting tagged individuals in situ and recording loss of entire colonies (wholecolony mortality) and loss of living colony area (partial mortality) between successive sampling times. For M. membranacea, measuring whole-colony or partial mortality in isolation would overestimate important demographic rates and underestimate the influence of temperature on mortality, respectively. This study demonstrates the need to include mortality measurements from the level of the individual module to the entire colony when quantifying population dynamics of colonial organisms.