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

Abstract

Rhodoliths are free-living forms of non-geniculated 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, although 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 in 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 have 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 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 makes the 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 to >30 m) that are influenced by currents. Both the types, but especially current beds, are also influenced by bioturbation (Marrack, 1999). In order to persist, these algal beds require light, nutrients, and movement from water motion (waves and currents) or bioturbation, which maintain them in an unattached and unburied state (Bosence, 1983a, b; Marrack, 1999).