Marine invertebrates are multicellular animals that lack a vertebral column and live in the marine environment. Common marine invertebrates include sponges, cnidarians (such as jellyfish), marine worms, mollusks (snails, slugs), arthropods (crabs, shrimp, lobsters), and echinoderms (sea stars, sea urchins).
Invasive marine invertebrates occur around the world, but are often found in harbors, yacht basins, and bays.ref As with other invasive species, hull-fouling and ballast water are likely to be the most common pathways for the spread of invasive invertebrates, along with intentional and accidental release of aquaculture species. ref
Intentional introduction of invertebrates has occurred, for example, in Hawaii where commercially important shellfish were released (e.g., mangrove crab (Scylla serrata) from Samoa, oysters (Crassostrea spp.) from San Francisco, and littleneck clams (Tapes japonicum) from Japan. ref The impacts of these species on Hawaiian ecosystems are still not well known. ref Other examples of marine invertebrate invasives in Hawaii include the snowflake coral (Carijoa riisei), the Caribbean barnacle (Chthamalus proteus), the keyhole sponge (Mycale grandis), and the Philippine mantis shrimp (Gonodactylus falcatus).
The Caribbean barnacle (Chthamalus proteus) was released in the early 1970s in Hawaii and is now the most abundant organism in the upper intertidal areas of many harbors and bays in the Hawaiian Islands and extends to Midway and Guam. This barnacle has almost completely displaced another barnacle (Balanus amphitrite) where these species co-occur.
Philippine Mantis Shrimp
The Philippine mantis shrimp, released in Hawaii in the early 1950s, has been shown to outcompete the native stomatopod, Pseudosquilla ciliata, and has almost completely replaced it in shallow reefs of O‘ahu.
A native marine sponge from the Indo-Pacific (Chalinula nematifera) is an invasive species that overgrows live corals in the tropical Eastern Pacific. This sponge is thought to have been introduced through fouling on ship hulls that came from the Indo-Pacific to Mexico. Scientists are currently working to develop long-term monitoring to determine if this species represents a threat to Mexican coral reef systems. ref
Ecological impacts of marine invasive invertebrates include displacement of native species, changes to community structure and food webs, and alteration of fundamental processes, such as nutrient cycling and sedimentation.
Socioeconomic impacts of marine invasive invertebrates include damages to economies by adversely affecting fisheries and fouling of ships’ hulls and clogging intake pipes. ref Direct impacts to human health include increased frequency of toxic red tides which threaten public health and marine fisheries. Red tides are attributed partly to dinoflagellates and their cysts in ships’ ballast tanks. Additionally, a bacterium that can cause the dangerous cholera disease, Vibrio cholerae, has been spread in ballast tanks of ships by attaching to a variety of marine organisms (e.g., copepods ref). Other socioeconomic impacts include the high costs associated with combating invasive species, including control and eradication.