Reproductive Patterns and Seasonal Occurrence of the Sea Hare Aplysia brasiliana Rang (Gastropoda, Opisthobranchia) At South Padre Island, Texas

4 Pages·1991·1.9 MB·English

by  N E Strenth

Reproductive patterns and seasonal occurrence of the Sea
Hare Aplysia brasiliana Rang (Gastropoda, Opisthobranchia)
at South Padre Island, Texas
Ned E. Strenth1 and James E. Blankenship2
'Department of Biology, Angelo State University, San Angelo, Texas 76909, U.S.A.
2The Marine Biomedical Institute, The University of Texas Medical Branch, Galveston, Texas 77550, U.S.A.
Abstract. MonthlycollectionsofAplysiabrasilianaRangweremadeatSouthPadreIsland,Texasoveran 18monthperiod. Seasonalchangesindistribu-
tionofweight classessupporttheexistenceofamaximumlifecycleofapproximately 1 year. Large numbersofjuveniles in springcollectionsare produced
by the reproductive activities ofoverwintering adults or possibly recruitment oflarvae from other areas. The spring recruitment is followed by the disap-
pearance from the population by large overwintering specimens. Springjuveniles increase in size and weight by late summer. Early fall collections yielded
no specimens. A minor period of secondary recruitment can occur during late fall or early winter. Winter collections, when successful, yielded reduced
numbers oflarge adults.
A numberofinvestigationsconductedonnaturally oc- in the south Laguna Madre at South Padre Island, Texas, at
curring aplysiid populations have centered upon duration of depths of < 1 m, from July, 1977 through December, 1978.
life cycles, seasonal changes in size or weight, reproductive All knownhabitatsofAplysiajyrasiliana wereestablisheddur-
activities, and recruitment into the population by recently ing preliminary field work in 1975 and 1976. While each of
metamorphosed juveniles (Miller, 1960; Carefoot, 1967; thesehabitats was surveyedduring each trip, collectiontech-
Usuki, 1970; Audesirk, 1979; Sarver, 1979; Gev etai, 1984). niquesandsuccess varied withtheseason. Winterandspring
Followingareviewofthesestudies, Carefoot(1987) concluded collections were most productive during early morning low
that, whileconsiderable variationdoesexist in some species, tides. These low tides trapped nocturnally active specimens
most sea hares do, in fact, exhibit an annual life cycle. in shallow grass flats which are common along the western
Thisconclusion isconsistent withcurrent information coastal margin of the island. Recently metamorphosed
forthe sea hareAplysia brasiliana, which is common to the juveniles were collected inthe spring from artificial habitats
GulfofMexico(StrenthandBlankenship, 1978a). ForFlorida ofbrokenconcrete, brickand stone, whichhadbeendeposited
populations of A. brasiliana, both Krakauer (1969) and near the east abutmentofthe old causeway. During summer
Hamilton et al. (1982) concluded that this species exhibits months, swimming specimens were collected with dip nets
alifecycleofapproximately oneyear. Krakauer's (1969) con- at night near the lights of fishing piers located along the
clusions relative to A. brasiliana (as A. willcoxi Heilprin) western side of South Padre Island. Specimens were also
were, however, based upon only a one year series ofcollec- found on rocks ofthe boat slip at the Coast Guard Station
tionsofrelatively small sample sizes. The study by Hamilton andthe channel side ofthe northjetty. Following collection,
et al. (1982) was based upon large sample sizes but unfor- specimens were weighed to the nearest gram.
tunately was limited to the months of March through June.
Krakauer (1969) also characterized the life cycle of A. RESULTS AND DISCUSSION
brasiliana in Floridaashaving "two wavesofsettling" with
a major "spawning period" in late March and early April. DURATION OF LIFE CYCLE
Following several years ofpreliminary field work, this study The results (Fig. 1) ofthis study supporttheexistence
was undertaken in an effort to clarify the life cycle of A. ofa maximum life cycleofapproximately 1 year forAplysia
brasiliana. brasilianaat South Padre Island, Texas. Summercollections,
such as those of 1977, were generally characterized by the
METHODS presence of specimens in the 50 to 300 gm weight range.
These animals increased in size and weight during the late
Collections were made onacontinuousmonthly basis fall and winter. By March of the following spring (Fig. 1),
American Malacological Bulletin, Vol. 9(1) (1991):85-88
85
86 AMER. MALAC. BULL. 9(1) (1991)
Jul. 1977 Jan, 1978 Jul, 1978
N = 69 N = 58 N = 22
nUn^ n n 1 m n ' 0_
E3
Aug. 1977 Feb. 1978 Aug, 1978
N = 131 N = 30 N = 91
n -, n rn
8,
rjj Sep. 1977 Mar. 1978 Sep. 1978
T33 N = O N = 58 N = 0
n 1 n
s ONct=. O1977 NApr,= 199778 ONct=. 01978
o fl n m g
B
Nov, 1977 MM May. 1978 Nov. 1978
N = 142 N = 122 N = 26
n nf1n _ n n
fi
Dec. 1977 Jun. 1978 Dec. 1978
N = 70 N = 106 N = 15
100 200 300 400 5O0 600 700 100 200 3O0 400 500 6O0 700 100 200 300 4O0 5O0 6O0
IndividualSpecimenWeightsin50gmIntervals
Fig. 1. NumbersofspecimensofAplysiabrasiliana ineach 50gm weightclassofmonthlycollectionsat SouthPadreIsland, Texas fromJuby, 1977through
December, 1978.
the population was characterized by specimens in the 250 - was followedby amid-summercrash inthepopulation. While
600 gm range. The marked appearance oflarge numbers of the June, July and August collections were characterized by
recently recruitedjuveniles in the April, 1978 collection, as specimens under 50 gm, there were no specimens in the 1
well as moderate numbers of large specimens in the 450 - - 10 gm range which had characterized the April collection.
700 gm size, clearly revealed the overlap of generations. The small specimens present in the June, July and August
These very large specimens were absent from the popula- collections of 1978 were therefore considered to be spring
tion by the following month. Similar life cycle lengths have recruits which were unable to increase in size due to com-
been reported by Carefoot (1967) forA. punctata Cuvier, by petition, rather than recent recruits to the population. Col-
Audesirk(1979) forA. califomica Cooper, andby Usuki (1970) lections made during the summer of 1977 (Fig. 1) as well as
for A. kurodai (Baba) and A. juliana Quoy and Gaimard. those of 1976, appear to support this conclusion. These col-
lections werecharacterizedby specimens in the50 - 300gm
RECRUITMENT range, as well as the absence ofsmaller specimens in the 1
The resultsofthis study (Fig. 1) confirmthepresence - 50gm range. Thesummercollectionsof 1977aretherefore
ofa majorperiodofrecruitmentofrecently metamorphosed considered typical for this species.
juveniles during the spring ofthe year. The April, 1978 col- The presenceofone 12 gmspecimenaswellas several
lection clearly revealed the marked appearance of large others weighing less than 50gm in the November, 1977 col-
numbers of specimens in the 1 - 50 gm weight class. The lection (Fig. 1) supports the existence ofa minor period of
presence ofspecimens weighing less than 50 gm in the col- secondary recruitmentduringthe late fall orearly winer. The
lections ofJune, July and August of 1978 initially suggested lifecycleofAplysiabrasiliana atSouthPadreIslandappears
a continuous 5 month period ofrecruitment. This does not, tobecharacterizedbythepresenceofamajorperiodofspring
however, appear to be the case. Based upon field observa- recruitment followed by a very minor period of secondary
tions made during 1975, 1976 and 1977, the spring recruit- recruitment during late fall or early winter. Usuki (1970)
ment of 1978 appeared unusually large. Hundreds ofswim- reported similar findings forA. kurodai inthe SeaofJapan.
ming specimens were observed in May. Small to medium Aplysiabrasiliana appearstoexhibit a relatively high
sized specimenswereveryabundantonthe rocksofthejetty reproductive potentialduring muchofits lifecycle. Uponcap-
and Coast Guard Station. ture, specimens wereobservedtoengagereadily incopulatory
A marked decline in numbers of specimens was evi- andegglayingactivitiesthroughout mostoftheyear. Despite
dent by early summer and, despite an extensive collecting this fact, recruitment is clearly not a continual process. Re-
effort, the July collection resulted in only 22 specimens. It cent life history studies (e.g. Sarver, 1979; Gev etai, 1984)
appears that the unusually large spring recruitment of 1978 have established the relationship ofthe seasonal abundance
STRENTH AND BLANKENSHIP: APLYSIA REPRODUCTION PATTERNS 87
ofselect algal species with thetimingofmetamorphosis and standing population of A. brasiliana which is character-
subsequent recruitment ofjuveniles into naturally occurring ized by slight to moderate increases in size of individual
populations ofvarious aplysiid species (see Carefoot, 1987, specimens rather than a population undergoing decline and
for review). replacement.
Mature veliger larvae of Aplysia brasiliana readily A suitable explanation to account for the location of
metamorphose inthepresenceofthe redalga Callithamnion specimens during September and October does not appear
and, to a lesser degree, Polysiphonia (Strenth and Blanken- forthcoming from observations made duringthe courseofthis
ship, 1978b). While Callithamnion can be found throughout study. While discounting reproductive migration in general,
most ofthe year (Sorensen, 1979), it reaches its maximum Carefoot (1987:204) states that the theory of feeding migra-
abundanceat South Padre Islandduring March (Penn, 1974). tions isoften "attractive inthat itaccounts for seasonal gaps
This seasonal abundance ofCallithamnionjust precedes the in abundance." Neitherthe theory ofreproductive migration
majorperiodofrecruitmentofjuvenileA. brasiliana intothe northatoffeeding migrationappeartoprovideafeasibleex-
population in April. While many additional environmental planation (see below) to account for the disappearance of
factors should be considered, it appears possible that this Aplysiabrasilianaat South PadreIslandduringtheearly fall
seasonal peakofCallithamnion couldbea majorcontributing of the year.
factor in the timing ofthe spring recruitment ofjuvenile A. Aplysia brasiliana is a known burrower (Aspey and
brasiliana at South Padre Island, Texas. Blankenship, 1976). Individual specimens could be under-
going continual orprolonged intermittent periods ofburrow-
ing inthe soft substratumofthe south Laguna Madre during
SEASONAL OCCURRENCE September and October. It should be emphasized that this
The disappearance of specimens from otherwise hypothesis is conjectural and not supported by field work.
normally occupied habitats during the months ofSeptember It shouldbenoted, however, thatdecreased foragingactivities
and October (Fig. 1) appears to be a normal aspect of the by burrowed A. brasiliana during September and October
life cycle of Aplysia brasiliana at South Padre Island. could possibly facilitate a rebound in the standing crop of
Krakauer(1969) alsofailedtocollect specimensofthis species Callithamnion, which in turncould account forthe secondary
in Florida during this same time period. Studies on other period of recruitment during late fall or early winter.
aplysiids have reported similar decreases in numbers of
specimens during the fall of the year. Audesirk (1979:413) MIGRATION
reported a "nearly total disappearance of animals" for A. In his review of migration theory as it relates to life
californica during October, November and December. Gev cycles of aplysiids, Carefoot (1987:203) states that "This
et al. (1984:69) reported that "The Aplysia season ends in theory ofmigrationhas fallen intodisfavourfromlackofsup-
September" for A. depilans Gmelin and A. fasciata Poiret portingevidence". While individual specimens wereobserved
alongthe Mediterranean coast ofIsrael. Both Audesirk(1979) to exhibit localized movements in association with foraging
andGev etal. (1984) relatedthis noticeabledropin numbers behavior, thecurrent study provides nosupport forthe migra-
ofspecimens duringthe fall ofthe year to the decline ofone tion theory as it relates toAplysia brasiliana at South Padre
year class, which in turn is replaced by the succeeding Island, Texas. Thiscouldbedue inpart tothe somewhat con-
generation. fined nature of the south Laguna Madre as well as the
Resultsobtainedduringthecourseofthis studydonot presence in the lagoon of both adult food {Laurencia and
support the above premise as it relates toAplysia brasiliana Gracilaria) as well as metamorphosing substrata(Callitham-
at South Padre Island. While some minor recruitment nion and Polysiphonia) for developing larvae. Juveniles and
could occur during November or December following the adultswerecollectedfromtheexact samehabitats duringdif-
absence ofcollectable fall specimens, there is no majorshift ferent times of the year.
in modal weight class during the fall such as that observed While specimens ofAplysia brasiliana are found oc-
for the month of April, 1978 (Fig. 1). In addition, average casionally beached onthe GulfofMexico side ofthe island,
weights of specimens increased from August to November the nature ofthe offshore substrate does not appear to favor
during both years. The average weightduring 1977 increased theattachmentofsuitablebenthic marinealgae. Consequently,
from 139 gm (N = 131) in August to 220 gm (N = 142) in the immediate offshore environment of South Padre Island
November. During 1978, the average weight increased from appears to offer little ifany favorable habitat for completion
67 gm (N = 91) inAugustto206gm(N = 26) inNovember. of all or part of the life cycle ofA. brasiliana. While not
The demonstrated presence ofcontinual weight increase in surveyed in this study, deeper off-shore reefs are known
specimens fromAugustto November, as well asthe absence habitats (Tunnell and Chaney, 1970) for A. brasiliana and
of large numbers of recently recruited juveniles in the could provide for variations in life cycles not observed dur-
early winter collections, serve to support the existence ofa ing the course of this study.
88 AMER. MALAC. BULL. 9(1) (1991)
CONCLUSIONS Carefoot, T. H. 1987. Aplysia: Its biology and ecology. AnnualReviewof
Oceanography andMarine Biology 25:167-284.
The results ofthis study are consistent with and sup- Gev, S.,Y. AchituvandA. J. Susswein. 1984. Seasonaldeterminantsofthe
port the conclusions ofboth Krakauer (1969) and Hamilton life cycle in two species ofAplysia found in shallow waters along
et al. (1982) that the maximum length of the life cycle of BthieolMoegdyitaenrdraEnceoalnogCyoa7s4t:6o7f-I8s3r.ael.JournalofExperimentalMarine
Aplysia brasiliana is approximately one year. This species Hamilton,P. V.,B.J. RussellandH.W. Ambrose. 1982.Somecharacteristics
exhibits a major period of recruitment during the spring of a spring incursion of Aplysia brasiliana into shallow water.
followed by a marked loss oflarge overwintering specimens Malacological Review 15:15-19.
from the population. A minor period of secondary recruit- Krakauer, J. M. 1969. The ecology ofAplysia willcoxi Heilprin at Cedar
ment can occur during late fall or early winter. The reason Key, Florida. Master's Thesis, University ofFlorida, Gainesville,
Florida, U.S.A. 87 pp.
forthe absence ofcollectable specimens duringthe early fall Miller, M. C. 1960. A note on the life history ofAplysiapunctata Cuvier
currently remains obscure. in Manx waters. ProceedingsoftheMalacologicalSocietyofLon-
don 34:165-167.
ACKNOWLEDGMENTS Penn, G. J. 1974. Seasonal periodicity of dominant, benthic, marine
macroalgaeofthenorthjettyofBrazosSantiagoPass,Texas,asrelated
toenvironmental factors. Master'sThesis, Pan American Univers-
MalacolTohgeicapJreUsennitoantimoenetoifngthaetrWeosouldtss HoofltehiwsasstmuadydeduprosisnigbltehebyAameFraciuclatny Sarver,iDt.y,J.Ed1i9n79b.urRge,crTueixtamse,ntU.aSn.dAj.uv4e5niplpe.survivalintheseahareAplysia
DevelopmentGranttooneofus(N.E.S.)fromAngeloStateUniversity. Field juliana(Gastropoda: Opisthobranchia).MarineBiology54:353-361.
studiesweresupportedbyaNational ScienceFoundationgrant(BBS871068) Sorensen, L. 1979. A GuidetoTheSeaweedsofSouthPadreIsland, Texas.
to one ofus (J.E.B.). Appreciation is extended to the faculty and staffof Gorsuch Scarisbrick Publishers. Dubuque, Iowa, U.S.A. 123 pp.
TthheisPasntuAdmyewroiucladnnUontivhearvseitbyeeMnarpiosnseibLlaebowriatthooruyttatheSiorustuhppPoardtr.eAIsvlaenrdy,sTpeexcaisa.l Strenth,mNo.nE.TeaxnadsJa.nEd. FBlloarnikdeansshpiepc.ie1s97o8fa.ApOlnystihae(vaGlaisdtrnoapmoedao,ftOhpeisctohmo--
thanks goes to Barbara Strenth for preparation ofthe figure. branchia). Bulletin ofMarine Science 28(2):249-254.
Strenth, N. E. and J. E. Blankenship. 1978b. Laboratory culture, meta-
LITERATURE CITED morphosis and development of Aplysia brasiliana Rang 1828
(Gastropoda: Opisthobranchia). Veliger 21(1):99-103.
Aspey, W. P. and J. E. Blankenship. 1976. Aplysia behavioral biology:II. Tunnell,anJ.dWO.nea-nhdalAf.FHa.thCohmanReeye.f,19N7o0r.tAhwcehsetcekrlnisGtuolfftohfeMmeoxlilcuos.ksCoonftSreivbeun-
Induced burrowing in swimming A. brasiliana by burrowed con-
tions in Marine Science 15:193-203.
specifics. Behavioral Biology 17:301-312.
Audesirk, T. E. 1979. A field studyofgrowth and reproduction inAplysia Usuki, I. 1970. Siudie*- on the life history ofAplysiidaeand theirallies in
the Sado district of the Japan Sea. Science Reports ofNiigata
californica. Biological Bulletin 157(3):407-421. D
University, Series (Biology) 7:91-105.
Carefoot,T. H. 1967. StudiesonasublittoralpopulationofAplysiapunctata.
JournaloftheMarineBiologicalAssociationofthe UnitedKingdom Date of manuscript acceptance: 21 December 1990
47:335-350.