The effects of Caulerpa taxifolia on invertebrate abundance in Agua Hedionda Lagoon California Karoly Tippets Abstract Sea beds composed of eel grass Zostera marina Caulerpa taxifolia and both vegetation types were sampled at a lagoon in San Diego County at the first known invasion site of the Caribbean algae C taxifolia in the United States The handcollected samples captured organisms from the surrouding water column top sediment layer and vegetative matter The abundance of Isopoda Amphipoda and Spirorbidae populations were quantified Weight adjusted samples were analyzed by means of the non parametric Mann Whitney U test The most significant decrease p 0 05 in abundance of all three taxa was between the eel grass and Caulerpa samples The effects of C taxifolia invasions and the ramifications on the benthic ecology of nearshore lagoons could be devastating to the basal levels of the food chain Introduction The challenges of dealing with invasive species have become of global concern with the relative ease of transcontinental movement Ricciardi et al 2000 Marine invasive organisms are more prevalent than their terrestrial counterparts due in part to the unwitting transmission on the hulls and in the ballast water of ships The accidental introduction of C taxifolia an algae native to the Caribbean Sea into the Mediterranean Sea in 1984 occurred when a small piece of algal material exited out of a flow through aquarium in Monaco Meinesz and Hesse 1991 This exotic alga now covers hundreds of hectares of the Mediterranean seafloor with patches reported up to hundreds of kilometers from original release point Joussen et al 1998 The spread of C taxifolia is due to an initial lack of eradication efforts and the amazing adaptability of this species to new environmental conditions including colder water temperatures Chrisholm et al 2000 Other characteristics of the algae that hinder containment efforts are the use of fragmentation as a method of dispersal Ceccherelli and Cinelli 1999 Smith and Walters 1999 and the lack of suitable biocontrol organisms Lemee et al 1996 Coquillard et al 2000 Zuljevic et al 2001 Thibaut et al 2001 The absence of biocontrol organisms is due to the production of caulerpenyne by C taxifolia Caulerpenyne is a naturally occurring neurotoxin that severely retards grazers Pedrotti et al 1996 Bitou et al 1999 Ricci et al 1999 Pedrotti and Lemee 1999 Studies correlating the detrimental effects of C taxifolia on invertebrates have focused on physiological impacts caused by the neurotoxin caulerpenyne Mozzachiodi et al 2001 The majority of research focusing on the non caulerpenyne affects of C taxifolia on fauna has been conducted on fish These studies have described qualitative and quantitative changes in fish communities Relini et al 1998 Relini et al 2000 and specific physiological changes in some fish Uchimura et al 1999 C taxifolia is also known to cause a reduction in density and abundance of native sea grasses in the Mediterranean Sea De Villele and Verlaque 1995 Ceccherelli and Cinelli 1997 Ceccherelli and Cinelli 1998 C taxifolia was first discovered in the United States in June 2000 in Agua Hedionda Lagoon California and to date there have been no published studies conducted on the new infestation Agua Hedionda is an ideal study site not only because it allows observations of a preliminary infestation of C taxifolia but also the lagoon has a preestablished baseline for native populations MEC 1995 which may be useful in identifying any opportunistic species Study of this organism will be important on an ecological level if eradication efforts in the previously infested Huntington Harbor CA and Agua Hedionda Lagoon are not successful A decline in certain keystone species including amphipods may result in an eventual decline in all species dependent upon these organisms for food with ramifications extending up the food chain The objective of this study is to determine the effects of C taxifolia upon the abundance of marine invertebrates by comparing population differences in infested areas with C taxifolia with those colonized only by native sea grasses Methods Description of study subjects Three taxa were chosen for analysis Amphipoda Isopoda and Spirobidae Amphipods and isopods were chosen because they are two of the most dominate invertebrate phyla represented in Agua Hedionda Lagoon according to a 1995 technical report MEC 1995 and form a necessary trophic level near the bottom of the food chain Borga et al 2001 The calcareous tube forming worms Spirobids were chosen to represent the effects of C taxifolia on organisms that use eel grass as a primary substrate upon which they live Infaunal and epifaunal organisms are reasonable choices as bioindicators owing to their close association with the flora in addition to their relative immobility Lafont et al 2001 Nerbonne and Vondracek 2001 Data Collection To assess changes in invertebrate abundance caused by the invasion of C taxifolia three cover types were chosen from within Agua Hedionda Lagoon CA The three types of cover are 100 C taxifolia a roughly 50 50 mix of C taxifolia and eel grass and 100 eel grass All sample sites are located in the lagoon on the eastern side of Interstate 5 Sampled sites were within a 150m2 area of the lagoon and all samples were roughly equidistant from each other The small alcove in which the sampling took place ranges from shallows 2 m to depths of 8 m During the month of August 2000 24 one gallon samples were removed from the alcove The samples were collected via use of a SCUBA device to diminish production of currents that could fragment and consequently spread the C taxifolia One gallon plastic jars were used to collect the samples at an average depth of 4 meters below the surface of the water The jars were dug into the sediment deep enough to obtain most of the rhizome mass anchoring the C taxifolia in the Caulerpa and mix samples The samples contained all of the vegetative material from each bunch of eel grass or C taxifolia Samples were immediately transported to shore drained of water and filled with formalin Proper storage of samples should be in 70 isopropyl alcohol Due to financial and time constraints samples were stored in formalin for approximately one year As each of the 24 jars was sorted the formalin was filtered through a mm screen The jar was filled with tap water and left to soak for one hour The jar was again filtered through a mm screen to prevent loss of
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