Barnacle reproductive hotspots linked to nearshore ocean conditions

Abstract

Coastal marine ecosystems provide important ecosystem services to human populations worldwide. Understanding the contexts in which a species has markedly higher reproductive output is vital for effective management and conservation of these valuable and highly impacted systems. We documented reproductive hotspots along the Oregon coast for an ecologically significant marine invertebrate, the intertidal barnacle Balanus glandula. Greater larval production in both natural and experimental populations was associated with higher primary productivity in the adjacent nearshore ocean, providing strong evidence for bottom-up forcing. Mean cumulative larval production per 100 cm2 in natural barnacle populations in the region of higher primary productivity was almost 5x that of populations in the less productive region. Mean estimated larval production per individual in experimental populations in the region of higher primary productivity was >2x that of populations in the region of lower productivity, and mean larval production per 100 cm2 was >120x greater in the region of higher productivity. Our results highlight the importance of spatial heterogeneity in reproduction and other ecological processes in the marine environment and provide a mechanistic basis for evaluating the relative contributions of different sites when designing marine reserves and other protected areas. Our findings also advance the understanding of the role of bottom-up influences on population and community dynamics and contribute data for the next generation of models of marine community dynamics.

Fig. 1.

Map of the Oregon coast. (a) The main study sites nested within each cape (n = 3 per cape). (b) Long-term chlorophyll a values (μg/liter) from May to September (1998-2003) at latitudinally matched sites (n = 7 per cape). Arithmetic means + standard errors are shown. Means with dissimilar letters were different (t test by cape: t = -6.917, P < 0.0001, df = 12). Sites north of 44.6° N were classified as Cape Foulweather sites, and those south of 44.6° N were classified as Cape Perpetua sites.

Fig. 2.

Larval production in the experiment per barnacle (a) and per 100 cm² (b). LS means and standard errors based on ln-transformed data are shown (standard errors are too small to be visible in a at this scale). Means with dissimilar letters were different (linear contrasts by cape for a, F = 21.561, P < 0.0001, df = 1, 29; b, F = 7.907, P = 0.048, df = 1, 143). See Methods for full site names. No brooding animals were found at DBN or DBS, so the LS means in b were very small.

Fig. 3.

Cumulative larval production per 100 cm² in the natural populations. Means with dissimilar letters were different (t test by cape: F = -3.409, P = 0.076, df = 2). See Methods for full site names.

Fig. 4.

Monthly mid-intertidal recruitment of B. glandula. Ln-transformed means + standard errors are shown. See Methods for full site names.