Reef Check News
An In-Depth Look at Abalone: Part I
By Anna Neumann, North Coast Regional Manager, Reef Check California Program
Within 24 hours of an abalone egg becoming fertilized, it hatches into a free-swimming larva. This larval phase can last from 4 to 15 days (depending on the species) and ends when the larva settles to the bottom and begins its metamorphosis into a juvenile abalone. Newly settled abalone graze on crustose coralline algae (a calcareous red algae) and live on coralline algae until they reach about 6mm (0.24 in) in shell length. Ninety percent of abalone deaths occur in this juvenile phase. This is typical survivorship for marine organisms that produce millions of larvae but once they grow larger, death rates dramatically decrease and individuals typically live up to 30 years. To hide from predators, many juvenile abalone live in cracks or under rocks. As the abalone grow they switch from feeding on coralline algae to kelp and move out from the smaller spaces. Abalone in northern California predominantly eat bull kelp (Nereocystis luetkeana) while abalone in southern California feed on giant kelp (Macrocystis pyrifera) [DFW, 2005]. Growth rates vary among the species. According to the California Department of Fish and Wildlife the largest red abalone was collected by John Pepper in 1993 in Humboldt County and measured 12.3 inches (313.4 mm).
The causes of mortality of abalone can be divided into natural and human induced mortality. Human causes include fishing, pollution, and habitat destruction. Natural causes include old age, predation, disease, and environmental factors. As in many marine animals, likelihood of death by predation decreases with the age and size of the abalone; their main predators include invertebrates, fish and sea otters. Octopuses and rock crabs (Cancer spp.) are their main invertebrate predators, but sheep crab (Loxorhynchus grandis), California spiny lobster (Panulirus interruptus), Nuttall’s hornmouth (Ceratostoma nuttalli) and Kellett’s whelks (Kellettia kelletti) also prey on young abalone. The major fish predators include California sheephead (Semicossyphus pulcher), Cabezon (Scorpaenichthys marmoratus), Kelp greenling (Hexagrammos decagrammus), Kelp bass (Paralabraz clathratus), Moray eel (Gymnothorax mordax), and Bat rays (Myliobatis californica).
Abalone are often considered to be slow moving creatures with limited ranges, however studies done by Ault and DeMartini in 1987 show seasonal migrations of abalone. Abalone move from shallow water in the spring to deeper water in the summer and back to shallow waters in the winter. The movement is considered a response to seasonal changes in food availability. More sunlight in summer months and reduced wave action from storms allows kelp to grow at deeper depths than in the winter, providing them constant food sources. Abalone also tend to move the most at night when they go on feeding excursions and the extent of their movement is based on size and availability of food and shelter [DFW, 2005].
Sea otters are important abalone predators in areas where they overlap. Historical sea otter distributions overlapped with abalone populations along the entire California coast. Human exploitation of sea otters caused local extinctions of the southern sea otter population which allowed the abalone populations to expand until commercial and recreational fishing began depleting their stocks to dangerously low levels. In 2000 the Fish and Wildlife Service listed the sea otter under the federal Endangered Species Act and in 2003 a recovery plan was developed which called for sea otters populations to increase naturally throughout their historic range. If successful, their recovery could play a role in further depletion of abalone populations [DFW, 2005]. Today the abalone-sea otter prey-predator interaction presents an interesting problem because they are both rare and protected in much of their historic ranges.
Another prominent cause of death of abalone has been a disease called Withering Syndrome (WS). Abalone affected by the disease show signs of atrophy of the foot muscle and gonadal tissues, emaciation and lethargy. Eventually the abalone is too weak to cling to the substrate and is dislodged. Once dislodged the abalone can be battered by the waves and eaten by predators or scavengers [DFW, 2005]. WS has caused widespread declines of black abalone populations along the central California coast and in the Channel Islands. Mass die offs were first noticed on the Channel Islands in 1986. The initial mass mortalities followed El Niño events that caused coastal waters to warm in 1982 and 1983. In 1988 the disease struck on the mainland in Diablo Cove following warm water discharge by a local power plant. This led to the hypothesis that WS may be triggered by elevated seawater temperatures [Raimondi, 2002]. Studies done by Raimondi et al. conducted surveys of abalone at seven sites along the California coast and determined that mass die-offs were not exclusively associated with times of elevated sea water temperatures due to El Niño. Nevertheless, rapid declines of black abalone were found at 2 of the 7 sites in conjunction with the strong El Niño events in 1997 and 1998, and declines occurred at faster rates in El Niño years as compared to non-El Niño years. Raimondi et al. concluded that the presence of a pathogen along with elevated sea water temperatures accelerate the development of WS. Red, pink, green and white abalone have also shown signs of WS but only while in captivity, and not in the wild. The agent responsible for the disease is an intracellular bacterium Candidatus Xenohaliotis californiensis [DFW, 2005].
Several different types of shell-boring organisms also pose a threat to abalone. Piddock clams (Penitella conradi) are known to drill into the shell of the abalone. Date mussels (Lithophaga subula) and Cliona celata californiana, a boring sponge, secrete acid into small holes in the shell. Severe infections of boring organisms can inhibit abalone growth and cause the shells to deform. The abalone aquaculture industry has been battling the parasitic sabellid polychaete (Terebrasabella heterouncinata). The polychaete lives on the edge of the abalone shells and infestations can cause a disruption in normal shell growth and result in deformed, brittle shells. [DFW, 2005]
In 2011 a red tide (phytoplankton bloom) event in Sonoma County caused a mass die-off of abalone and other sub-tidal invertebrates. The alga was identified as Gonyaulax spinifera which is known to create a biotoxin called Yessotoxin. This biotoxin was found in low levels in the dead abalone. Estimates of mortality from this event ranged from 12 to 30 percent depending on the location. Data collected by Reef Check documented this decrease in abalone along the Sonoma Coast.
Department of Fish and Wildlife. Abalone Recovery and Management (ARMP), December 9th 2005. http://dfg.ca.gov/marine/armp/index.asp
Department of Fish and Wildlife. Abalone Status Report 2001. https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=34209&inline=true
Fimrite, Peter. Red tide killing abalone off California. SF Gate. September 17, 2011. http://www.sfgate.com/bayarea/article/Red-tide-killing-abalone-off-California-2309794.php
Raimondi, Peter T., et. al. October 25 2002, Continued declines of black abalone along the coast of California: are mass moralities related to El Nino events?. Marine Ecology Progress Series, Vol 242: 143-152