The influence of stage-dependent dispersal on the population dynamics of three amphipod species

A legacy of invasive sun corals: Distinct mobile invertebrate assemblages at near-reef coral-dominated rubble

Fast-growing and reproducing sun corals have successfully invaded rocky reefs around the Atlantic Ocean, markedly reducing the diversity of fouling invertebrates and macroalgae, and profoundly changing the composition of reef-associated mobile invertebrates. Here, we address sun-coral rubble depositions and report, for the first time, the effects of sun corals on near-reef soft-bottom invertebrate assemblages. Abundance, richness and diversity were higher at rubble habitats compared to bare sandy grounds, which could be a positive effect of substrate complexity. All those parameters were also higher at rubble patches dominated by sun-coral fragments compared to rubble patches dominated by pebbles or shell fragments, also suggesting possible additive effects of coral-borne chemical attraction (sun-coral specific, as inputs of other coral species were virtually absent). Different epifaunal groups were exclusive of rubble habitats and a subset of those exclusive of sun-coral rubble, explaining the incremental richness across habitats. The relative abundance of the two dominant groups - polychaetes (p) and amphipods (a) - contributed the most to the observed contrasts on community structure, as their proportion (p:a) changed from 10:1 in bare sand to nearly co-dominance in coral rubble. While previous research suggested that spreading sun corals reduce prey supply for fish foraging on reef walls, our results suggest they may increase prey abundance and diversity at the adjacent non-consolidated habitat, possibly reshaping trophic pathways connecting the benthic and the pelagic environment.

Colonization of novel algal habitats by juveniles of a marine tube-dwelling amphipod

Background

Dispersal is an important process affecting population dynamics and connectivity. For marine direct developers, both adults and juveniles may disperse. Although the distribution of juveniles can be initially constrained by their mothers’ choice, they may be able to leave the parental habitat and colonize other habitats. We investigated the effect of habitat quality, patch size and presence of conspecific adults on the colonization of novel habitats by juveniles of the tube-dwelling amphipod Cymadusa filosa associated with the macroalgal host Sargassum filipendula.

Methods

We tested the factors listed above on the colonization of juveniles by manipulating natural and artificial plants in both the field and laboratory.

Results

In the laboratory, juveniles selected high-quality habitats (i.e., natural alga), where both food and shelter are provided, when low-quality resources (i.e., artificial alga) were also available. In contrast, habitat quality and algal patch size did not affect the colonization by juveniles in the field. Finally, the presence of conspecific adults did not affect the colonization of juveniles under laboratory condition but had a weak effect in the field experiment. Our results suggest that C. filosa juveniles can select and colonize novel habitats, and that such process can be partially affected by habitat quality, but not by patch size. Also, the presence of conspecifics may affect the colonization by juveniles. Successful colonization by this specific developmental stage under different scenarios indicates that juveniles may act as a dispersal agent in this species.

Localised Effects of a Mega-Disturbance: Spatiotemporal Responses of Intertidal Sandy Shore Communities to the 2010 Chilean Earthquake

Determining the effects of unpredictable disturbances on dynamic ecological systems is challenged by the paucity of appropriate temporal and spatial coverage of data. On 27 February 2010, an 8.8 Mw mega-earthquake and tsunami struck central Chile and caused coastal land-level changes, massive damage to coastal infrastructure, and widespread mortality of coastal organisms. Wave-exposed sandy beaches showed significant changes of species abundances from before to after the earthquake, but the highly dynamic biotic and abiotic conditions of these habitats make difficult to draw clear-cut conclusions from these patterns. Here, we analysed a beyond-BACI (Before-After Control-Impact) sampling design to test whether the effects of the Maule earthquake on sandy-shore species diversity, abundance, and structure were heterogeneous along the shore. Invertebrate species abundances were quantified before (i.e. February 2010) and after (i.e. March 2010, September 2010, and March 2011) the earthquake at three sandy shores randomly located within the earthquake rupture area and three sites within a “control” area located >400 km southward from epicentre. Immediately after the earthquake took place, the three sites located in the rupture area showed anomalous beach-profile uplifts that did not comply with the erosion (i.e. “negative” uplifts) that regularly occurs during late summer in the region. Species richness, abundance, and community structure significantly varied from before to after the strike, but these patterns of change varied among sites within both areas. Only the site with the strongest and persistent beach-profile uplift within the rupture area showed significant concomitant changes in species richness and community structure; after 13 months, this community showed a similar multivariate structure to the before-disturbance state. This site, in particular, was located in the section of the rupture area that received most of the impact of the after-earthquake tsunami. Therefore, our results suggest that the effects of the Maule mega-earthquake on the ecological communities were spatially heterogeneous and highly localised. We suggest that high mobility and other species’ adaptations to the dynamic environmental conditions of sandy beaches might explain the comparatively high resilience of these assemblages. With this work we hope to motivate further experimental research on the role of individual- and population-level properties in the response of sandy-beach communities to interacting sources of disturbances.

Role of sources and temporal sinks in a marine amphipod

Spatially structured habitats challenge populations to have positive growth rates and species often rely on dispersing propagules to occupy habitats outside their fundamental niche. Most marine species show two main life stages, a dispersing stage and a sedentary stage affecting distribution and abundance patterns. An experimental study on Corophium acherusicum, a colonial tube-building amphipod, showed the strong influence that a source population can have on new habitats. More importantly, this study shows the effect of temporal sinks where newly established populations can show reduced growth rates if the propagule supply from a source is removed. Sink populations had a reduction in abundance and became male-biased as females left colonies. The consequences arising from short-term dispersal and temporal sinks could be due to different selection pressures at the source and sink populations. These consequences can become reflected in long-term dynamics of marine populations if we shift focus to non-random dispersal models incorporating behaviour and stage-dependent dispersal.

Life history affects how species experience succession in pen shell metacommunities

In nature, very few species are common and broadly distributed. Most species are rare and occupy few sites; this pattern is ubiquitous across habitats and taxa. In spatially structured communities (metacommunities), regional distribution and local abundance may change as the relative effects of within-habitat processes (e.g., species interactions) and among-habitat processes (e.g., dispersal) may vary through succession. A field experiment with the marine benthic inhabitants of pen shells (Atrina rigida) tested how common and rare species respond to succession and metacommunity size. I followed community development through time and partitioned species into sessile and motile based on their natural history. Rare species drive diversity patterns and are influenced by metacommunity size: there are strong abundance-distribution differences between common and rare species in large metacommunities, but motile species show lower rates of change than sessile species. In small metacommunities both common and rare species have similar changes through time; the dichotomous distinction of common and rare species is not present. Edge effects in metacommunities affect species' changes in distribution and abundance. In large metacommunities diversity is higher in edge habitats relative to small metacommunities during early succession. However, edge effects benefit motile species over time in small metacommunities showing a rapid increase in diversity. Individual mobility is sensitive to regional community size and allows individuals to sort among different communities. In contrast, sessile species do not show this edge effect. Metacommunity theory is a useful framework for understanding spatially structured communities, but the natural history of coexisting species cannot be ignored.

Spatial variation in population structure and its relation to movement and the potential for dispersal in a model intertidal invertebrate

Dispersal, the movement of an individual away from its natal or breeding ground, has been studied extensively in birds and mammals to understand the costs and benefits of movement behavior. Whether or not invertebrates disperse in response to such attributes as habitat quality or density of conspecifics remains uncertain, due in part to the difficulties in marking and recapturing invertebrates. In the upper Bay of Fundy, Canada, the intertidal amphipod Corophium volutator swims at night around the new or full moon. Furthermore, this species is regionally widespread across a large spatial scale with site-to-site variation in population structure. Such variation provides a backdrop against which biological determinants of dispersal can be investigated. We conducted a large-scale study at nine mudflats, and used swimmer density, sampled using stationary plankton nets, as a proxy for dispersing individuals. We also sampled mud residents using sediment cores over 3 sampling rounds (20-28 June, 10-17 July, 2-11 August 2010). Density of swimmers was most variable at the largest spatial scales, indicating important population-level variation. The smallest juveniles and large juveniles or small adults (particularly females) were consistently overrepresented as swimmers. Small juveniles swam at most times and locations, whereas swimming of young females decreased with increasing mud presence of young males, and swimming of large juveniles decreased with increasing mud presence of adults. Swimming in most stages increased with density of mud residents; however, proportionally less swimming occurred as total mud resident density increased. We suggest small juveniles move in search of C. volutator aggregations which possibly act as a proxy for better habitat. We also suggest large juveniles and small adults move if potential mates are limiting. Future studies can use sampling designs over large spatial scales with varying population structure to help understand the behavioral ecology of movement, and dispersal in invertebrate taxa.

Changes in habitat heterogeneity alter marine sessile benthic communities

Habitat heterogeneity is considered an important mechanism influencing diversity patterns in spatially structured habitats. However, spatial heterogeneity is not static and it can change along temporal scales. These changes, whether gradual or rapid, have the potential of forcing species extinctions or facilitating the introduction of nonnative species. Here, we present modeling results that show how changes in spatial heterogeneity over several generations can produce strong changes in benthic species composition residing in eastern Long Island Sound, USA. For many benthic species, hard substrate is a limiting resource which can vary in availability among different coastal areas. We modeled gradual changes from a heterogeneous landscape (mimicking patches of natural hard and soft substrate) to a homogenous one (analogous to a fully developed coast with hard, manmade substrate) and followed the abundance and distribution patterns of species possessing four different life histories. We also modeled changes from homogeneous to heterogeneous landscapes. We found that as regions become more homogeneous, species extinctions become more frequent and poor dispersers dominate locally. In contrast, as habitats become more heterogeneous, species distributing across localities leads to regional species coexistence and fewer extinctions. These results suggest that focusing on changing habitat heterogeneity can be a useful management strategy to prevent poor dispersing species, such as invasive ascidians, from driving communities to monocultures.

Habitat destruction and metacommunity size in pen shell communities

1. In spatially structured communities, habitat destruction can have two effects: first, a main effect that occurs because of the loss of habitat area within a larger region, and a secondary effect due to changes in the spatial arrangement of local communities. Changes to the spatial arrangement can, in turn, affect the migration and extinction rates within local communities. 2. Our study involved the experimental destruction of entire local communities within larger regions in natural marine microcosms. Large and small arrays of dead pen shells were created in a shallow bay in north Florida, and the colonization by both encrusting and motile species on this empty substrate were followed through time. After most species had become established, half of the large arrays were perturbed to create small arrays by removal of half the shells, simulating habitat destruction. 3. After 48 days of further community development, comparisons of the large arrays, reduced arrays and original small arrays suggested that the mechanisms by which habitat destruction affects diversity could depend upon the size of the region affected and the natural history of the species being studied. 4. Habitat destruction reduced the diversity of motile species to a level lower than that found in the undisturbed small arrays, suggesting that the species that assembled in the original large metacommunities negatively influenced the species that occurred ultimately in the converted small arrays. 5. With sessile species, habitat destruction created richness levels that were intermediate to those of small and large arrays. The initial predestruction richness appears to have had a positive effect; because sessile species cannot disperse as adults, they may not respond to significant shifts in metacommunity size later in succession. Initial metacommunity size may be important for allowing individuals to select appropriate habitats before they settle.