The Role of Rhodolith Beds in the Recruitment of Invertebrate Species from the Southwestern Gulf of California, México

Abstract

Rhodoliths are free-living forms of nongeniculate coralline red algae (Corallinaceae, Rhodophyta) that form extensive beds worldwide over broad latitudinal and depth ranges (Foster, 2001). Synonymous with the maerl beds common in the northeastern Atlantic, rhodolith beds are hard benthic substrates, albeit mobile, made up of branching crustose coralline thalli. Collectively, they create a fragile biogenic matrix over carbonate sediment deposits thought to be the result of long-term accumulation of dead thalli (Bosence, 1983a). A wide morphological variation of individuals exists and appears to be a response to variation in physical factors (Bosence, 1983b; Steller and Foster, 1995). This variation in morphology and incorporation of whole rhodolith and carbonates into the fossil record has led to their use as paleoindicators of environmental conditions (Foster et al., 1997). Unconsolidated rhodolith deposits have long been harvested for human use as soil amendment in European waters (Blunden et al., 1977, 1981). However, recent studies have shown that such beds are highly susceptible to anthropogenic disturbance such as trawling harvesting and reduced water quality (review in Birkett et al., 1998). Slow rhodolith growth (Rivera et al., 2003; Steller, 2003) combined with the negative impacts of burial make recovery after disturbance predictably slow. Foster et al. (1997) found rhodolith beds to be very common in the Gulf of California and suggested that there are two main types of beds: wave beds in shallow water (0–12 m) that are influenced by wave action (Steller and Foster, 1995), and current beds in deeper water (10–>30 m) that are influenced by currents. Both types, especially current beds, are also influenced by bioturbation (Marrack, 1999). To persist, these algal beds require light, nutrients and movement from water motion (waves and currents), or bioturbation, which maintains them in an unattached and unburied state (Bosence, 1983a, b; Marrack, 1999).