Spatially heterogeneous, synchronous settlement of Chthamalus spp. larvae in northern Baja California

Abstract

We evaluated the spatial variability in barnacle settlement at scales of 10s to 100s of meters (among-sites: 300 m; within-site: 30 m) along 1 km of coastline in the Bay of Todos Santos, northern Baja California, Mexico. Settlement of the intertidal barnacles Chthamalus spp. was monitored daily from April 1 to May 10, 2002, and thereafter every other day to September 18, 2002. Concurrently, temperature of the water column was measured every 15 min, and hourly wind speed and direction data were acquired from a nearby site. We identified 12 settlement pulses during our study, with all but 2 pulses showing significant differences in mean settlement at either or both spatial scales. Despite a high variability in numbers, settlement pulses were synchronous between sites. The occurrence of settlement pulses was significantly correlated with a rapid increase in the stratification of nearshore waters, but not correlated with sudden fluctuations in the direction of winds perpendicular to the shore. Sudden changes in the stratification of nearshore waters have been associated with the occurrence of internal tidal bores. Our results suggest that internal motions, more specifically internal tidal bores, could be an important mechanism for the onshore transport of larvae in the Bay of Todos Santos. KEY WORDS: Synchronous settlement · Spatial variability · Intertidal barnacle · Chthamalus · Baja CaliforniaResale or republication not permitted without written consent of the publisher

Onshore transport of plankton by internal tides and upwelling-relaxation events

“…Settlement, however, clearly peaked following minimum temperatures during the spring tide as temperatures were beginning to rise. Thus, internal tides take a form that is conducive to the shoreward transport of cyprids soon after spring tides, as has been observed elsewhere along the west coast of North America (Shanks 1983, 1986, 2009, Pineda 1991, Ladah et al 2005). …”

“…A number of studies have presented data purported to demonstrate that cyprids are transported onshore by upwelling-relaxation events, reviewed by Shanks (2009), but these studies followed recruitment at weekly or longer intervals and suffer from aliasing as well as an unknown amount of mortality between settlement and the recruitment measurement (Shanks 2009). Many studies that have measured cyprid settlement daily have, however, found significant correlations between settlement and the fortnightly tidal cycle (Shanks 1986, 2009, Pineda 1991, Pineda & Caswell 1997, Ladah et al 2005, Tapia & Navarrete 2010, suggesting that transport was due to the internal tides. These studies found weak or no evidence to support delivery of cyprids by upwelling-relaxation events, although Hawkins & Hartnoll (1982) ob served higher settlement during onshore winds.…”

Larval recruitment in a region of strong, persistent upwelling and recruitment limitation

“…Large, tidally generated internal waves and bores can transport larvae onshore along the 80 Pacific coast of the USA (Pineda 1994, Shanks 2002, Ladah et al 2005. Internal waves can deliver larvae to shore in warm, saline surface waters during any phase of the tidal amplitude cycle (Table 1; Rosenfeld 1990, Shanks 2002.…”

Acoplamento Plâncton-Bentos: O Papel Do Suprimento Larval Na Estrutura Das Comunidades Bentônicas De Costões Rochosos

“…O deslocamento da termoclina para regiões menos profundas da coluna d'água induziria os movimentos internos das massas d'água e o transporte das larvas. Assim, a variabilidade espacial do assentamento larval registrado ao longo da costa poderia estar relacionado à variabilidade na intensidade da estratifi cação da coluna d'água, onde locais com maior estratifi cação apresentariam maior assentamento (Pineda & Lopez 2002, Ladah et al 2005. A alternância entre água fria e quente promove a formação de frentes de água quente que se movimentam em direção à costa (Pineda 1994).…”