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Reproduction and Development, 22:1-3 (1992) 193-202 193 Balaban, Philadelphia/Rehovot 0168-8170/92/$05.00 © 1992 Balaban

Testing generalizations about latitudinal variation in reproduction and recruitment patterns with sicyoniid and caridean

RAYMOND T. BAUER Center for Research, Department of Biology, University of Southwestern Louisiana, Lafayette, Louisiana 70504-2451, USA

Summary

Study of latitudinal variation in seasonality of reproduction and recruitment of benthic marine is useful in generating and testing hypotheses about causal factors acting on reproduction such as temperature and larval food supply that might be altered by changes in world climate. Analysis of latitudinal variation in reproductive patterns might be made with comparisons (a) among species with a common phylogenetic history from different latitudes and habitats and (b) among phylogenetically different taxa from the same location. Hypotheses on variation of reproductive seasonality with latitude are tested here with results of a study on nine species of caridean and two species of sicyoniid shrimp sampled from a tropical meadow in Puerto Rico. Breeding condition was determined by the presence or absence of incubated embryos (carideans) and the state of ovarian development in both carideans and sicyoniids. Recruitment was estimated from the percentage of individuals of monthly population samples in the juvenile size classes. Comparison of reproductive patterns among tropical, subtropical, and cool temperate Sicyonia spp. supports the paradigm of continuous reproduction in the tropics with increased restriction of breeding season with an increase in latitude. A greater intensity of breeding effort appears to accompany the shorter breeding period associated with an increase in latitude. At the tropical site most females of all caridean species carried embryos during all months of the year. With the onset of sexual maturity, caridean females produced consecutive broods for the rest of their relatively short (< 6 month) life span. In both sicyoniid and caridean species, recruitment occurred throughout the year but was highly variable, i.e., episodic rather than truly continuous or seasonal. Patterns of recruitment were highly concordant among but not between sicyoniid and caridean species, indicating that different sets of environmental factors controlled recruitment in the two groups. It is suggested that simultaneous study of adult reproduction and larval ecology is necessary to understand patterns of reproduction and recruitment. Coordinated effort on a global scale in studying latitudinal variation in reproduction and recruitment is suggested in order to predict the consequences of climate change on commercially and ecologically important marine invertebrate species.

Economic and Applied Aspects of Invertebrate Reproduction. Proceedings of the Sixth International Congress on Invertebrate Reproduction, Trinity College, Dublin, 28 June - 3 July 1992. 194

Introduction to temporal patterns of in which the duration of high productivity is negatively corre­ Making generalizations about biological phenome­ lated with latitude. Thus, reasoning from Thorson's na from empirical studies is a useful and necessary ideas, at low latitudes there is relatively little varia­ tool for summarizing information on those phenome­ tion in primary and secondary productivity (larval na. More importantly, such generalizations or general food supply) throughout the year in coastal areas, and principles serve a heuristic function by acting as a there is little selection for seasonality in reproductive model or paradigm for making and testing hypotheses cycles. At higher latitudes (temperate, boreal), breed­ on causal factors or selective pressures that may be ing seasons and peak larval output should roughly responsible for the patterns observed. Quite often coincide with the seasonal pulses of productivity. The generalizations are oversimplifications that do not situation is more complex in polar regions where hold up as more studies are conducted on the biologi­ temperature variation is again slight. Although prima­ cal phenomenon of interest and contradictory results ry and secondary productivity in the plankton is high­ are encountered. The paradigm is then either discard­ ly seasonal, restricted to intense bursts in the polar ed or modified, but in the process new, often impor­ summer, current information shows that reproduction tant information is discovered, and our understanding of invertebrates with planktotrophic larvae is not of the biological world increases. necessarily highly seasonal and correlated with the Generalizations about latitudinal variation in summer pulse of planktonic productivity (Pearse et annual patterns of reproduction in near-shore, benthic al., 1991; Thorson, 1950). marine invertebrates have been useful in suggesting Although reviews and summaries of the literature the underlying environmental factors that might ac­ on marine invertebrate reproduction certainly do count for the patterns observed. Orton (1920) hypoth­ seem to indicate a tendency for extended reproductive esized that relatively constant temperature conditions seasons at lower latitudes, with more restricted ones in tropical with high water temperatures year- at higher latitudes, there are certainly many excep­ round was the cause of continuous reproduction in tions reported [see reviews for invertebrates in gener­ populations of a variety of tropical marine inverte­ al in Giese and Pearse (1974); for in Sas- brates. Seasonal variation in water temperature, the try (1983)]. Thus, there are tropical taxa in which pattern of which is strongly tied to latitude, has al­ different species may either have seasonal or continu­ ways been considered an important proximate factor ous breeding (Cameron, 1986; Hendler, 1979). Trop­ or environmental stimulus in triggering and maintain­ ical reef often have restricted breeding periods ing gametogenesis and thus defining the breeding (Harrison et al., 1984; Schlesinger and Loya, 1985). season of marine invertebrates as well as other marine Some tropical species have semiannual breeding and terrestrial . Thorson (1950) suggested that seasons in areas subject to major semi-annual envi­ the important selective pressure acting on timing of ronmental perturbations, i.e., monsoons (Giese and reproduction in marine invertebrates with planktotro- Pearse, 1974). phic larvae might be the temporal variation of larval Thus, general or simplistic models about the rela­ food supply, that is, the seasonal pattern of primary tionship between length of breeding pattern and lati­ and secondary productivity. Thus, the temporal avail­ tude may not be applicable to all or most near-shore ability of larval food supply was supposed to be the benthic invertebrates. There probably is no one gen­ "real" reason ("ultimate factor"; Baker, 1938) for the eralization about reproduction or recruitment that can observed seasonality (or lack thereof) in reproduction be made about all or most taxa. The term "near-shore and larval output in benthic invertebrates. Tempera­ benthic invertebrate" refers to a variety of taxonomic ture (and/or other environmental variables) act as groups with very different phylogenetic histories, environmental cues ("proximate factors") on the each taxa with its own reproductive capabilities and physiological systems of these benthic invertebrates. constraints imposed by its particular , physi­ By means of these cues, spawning of or release ology, and ecology. At similar latitudes there may be of planktotrophic larvae is timed to coincide with much variation from one benthic habitat to another in periods of favorable food supplies in the plankton. a variety of abiotic and biotic factors that influence Thorson's (1950) classic paper presented evidence reproductive patterns. for several invertebrate groups that the breeding A corollary to the hypothesis of a latitudinal gradi­ season became more restricted or seasonal with an ent in breeding and larval production of near-shore increase in latitude. As noted above, he attributed this invertebrates is that recruitment patterns should mir- 195 ror (with a suitable lag period) reproductive patterns, (seagrass meadows) in a tropical locale, Puerto Rico, i.e., continuous recruitment in tropical latitudes with West Indies, based on data reported in Bauer (1989) increasing seasonality of recruitment with an increase and Bauer and Rivera Vega (1992). In addition, com­ in latitude in temperate and boreal latitudes (Bauer, parisons will be made among Sicyonia species from 1989), The caveat expressed above about compari­ this tropical locale (Bauer and Rivera Vega, 1992) sons of reproductive patterns among different taxa and Sicyonia spp. from other latitudes using data also applies to recruitment. Different taxa may have taken from other studies (Anderson et al., 1985; planktotrophic larvae that are affected by very differ­ Kennedy et al., 1977). These comparisons are made ent pressures in the plankton (e.g., disparate food possible because the intensity of sampling and the supplies, predators) that may influence larval success methods of estimating reproductive activity were and recruitment in a variety of ways. As larvae arrive similar among the three studies cited. at the juvenile and adult habitat, benthic predators may be acting differentially on the larvae and post- larvae as they settle and metamorphose during re­ Data Base cruitment into the benthic population of the species. Populations of were sampled monthly for Perhaps the most constructive approach to an analy­ sis of the relationship between seasonality in repro­ one year in seagrass meadows, composed of turtle duction and recruitment with change in latitude would grass (Thalassia testudinum) and manatee grass be to make comparisons that factor out, as much as (Syringodium filiforme), located at Dorado (18°N, possible, variation due to differences in (a) phylo- 66°W), on the north coast of Puerto Rico, West genetic history and (b) habitat. Thus, one might study Indies. Samples were taken with pushnets both during and compare temporal patterns in reproduction and the day and night, but the vast of majority of individu­ recruitment (1) among (relatively) unrelated taxa als for all species were captured at night when the from similar latitudes and habitats, i.e., species that shrimps and other macroinvertebrates are most active. experience similar environmental pressures but which Nearly 75,000 caridean shrimps were collected be­ have separate phylogenetic histories and/or (2) among longing to 18 species (Bauer, 1985a). Nine species (relatively) closely related taxa from different lati­ accounted for 99.9% of this abundance (Table 1), and tudes and/or habitats, i.e., species with a common the reproductive and recruitment patterns of these phylogenetic history exposed to dissimilar environ­ species were analyzed (Bauer, 1989). Approximately mental pressures. Thus, differences in breeding and 7,500 penaeoid shrimps were collected, and 85.9% of recruitment patterns among unrelated taxa from the these individuals belonged to two species, Sicyonia same sampling site might be attributable to - parri and 5. laevigata (Bauer, 1985b) whose breeding specific reproductive and recruitment capabilities and and recruitment patterns were reported in Bauer and constraints. Among closely related species from Rivera Vega (1992). different latitudes or habitats, variations in reproduc­ For the carideans the index of breeding activity tion and recruitment might be ascribed to major envi­ used was the percentage of adult females that were ronmental factors that vary among sampling sites. ovigerous, i.e., incubating fertilized embryos. Stage In this report I use the approach outlined above to of ovarian maturity on a scale of 1 (no development) compare and contrast reproduction and recruitment to 4 (ovary full of large vitellogenic eggs, female near between two relatively unrelated groups of decapod spawning) was also observed and recorded for fe­ crustacean shrimps, sampled at the same location, males (Bauer, 1989). In the sicyoniid (penaeoid) with distinct modes of reproduction. Caridean shrimps in which females do not incubate embryos, shrimps, like all pleoeyemate decapods (, the ovarian maturity (immature versus mature, based , ), incubate their embryos to advanced on visual estimates of relative frequency of postvitel- zoeal larvae. In contrast, penaeoid shrimps (Deea- logenic eggs) was recorded for all females examined poda, ) eggs that are immedi­ (Bauer and Rivera Vega, 1992). ately fertilized and released into the plankton where In each caridean species females were defined as embryonic development takes place, after which they "adult" (potentially capable of reproducing) if they hatch as relatively undeveloped nauplius larvae. I will were as large or larger than the smallest female ob­ make comparisons of reproductive and recruitment served carrying embryos. In Sicyonia spp. adult patterns among and between nine species of carideans females were those as large or larger than the smallest and two penaeoids (Sicyonia) from the same habitat female observed with a mature ovary. 196

Table 1. Comparison in caridean and Sicyonia () out a recognizable seasonal component. Furthermore, shrimp species in monthly values for percentage of adult it was possible to determine if females carrying em­ females with mature ovaries bryos were developing another batch for spawning after the current brood of incubated embryos hatched. Perc sntage of adult females This was done by recording the stage of ovarian with mature ovaries development and stage of embryonic development in females from samples and observing the pattern of Species Med ian Min Max N hatching and spawning in captive females. In all Caridea: species observed the sequence of events in live ovig­ Alpheus normanni 16 0 35 588 erous females was hatching of embryos, a molt within Latreuies fucorum 24 15 56 1147 a day or two of hatching, and subsequent spawning of Leander lenuicornis 24 0 56 184 the eggs in the mature ovary within a day or two of Processa bermudensis 28 13 55 468 the post-hatching molt. In preserved material there Hippolyte curacaoensis 28 9 46 601 was a statistically significant correlation between Processa riveroi 30 29 70 198 stage of ovarian maturity and stage of embryonic Latreutes parvulus 38 12 80 502 development in all species. Thus, as a brood of previ­ Periclimenes 40 23 60 486 ously spawned embryos was being incubated, the americanus ovary of most females matured so that a new spawn Thor manningi 43 32 84 466 took place soon after hatching of the embryos, female molting, and mating (there is no storage in Penaeoidea: these carideans). Periods between spawns varied from Sicyonia parri 13 0 26 848 1-2 weeks in these species. Reproduction in these Sicyonia laevigata 26 0 42 456 small seagrass carideans can be characterized as both continuous and intense, both at the level of the popu­ min, minimum; max, maximum; N, total number of adult lation and the individual. Cohort analysis of some of females examined. the species indicated that female life span on the seagrass meadows is a matter of months, certainly Recruitment was defined as the entry of individu­ much less than a year (Bauer, 1986; Rivera Vega, als from the plankton into the juvenile and adult 1985; Salva, 1984), probably due to the intense shrimp populations in the seagrass beds. Monthly predation that occurs on small macroinvertebrates in seagrass meadows (Heck and Orth, 1980; Randall, recruitment was estimated by calculating from 1967). monthly size frequency distributions the proportion of the population in the "juvenile" size classes, which were defined as the lower 25% of all possible size The index of breeding intensity or activity differed for the carideans (percent adult females incubating classes observed in that species. The upper size limit embryos) (Bauer, 1989) from that used for the sicyo­ defined in this way for "juveniles" approximately niids (percent adult females with mature ovaries), as coincided with the size of male and female sexual the latter do not incubate embryos (Bauer and Rivera maturity in both the caridean and sicyoniid species Vega, 1992). I have calculated values for percentage (Bauer. 1989; Bauer and Rivera Vega, 1992). of adult females with mature ovaries (stages 3 and 4) for the caridean species for comparison with sicyoniid species in which "mature" (dominated by large post- Comparisons among Caridean and Sicyoniid vitellogenic eggs) ovaries were used as the indicator Species at the Same Tropical Location of reproductive activity (Table 1). The median, mini­ mum, and maximum values for the caridean species Bauer (1989) analyzed reproductive patterns of the are generally higher than those of the two sicyoniid nine caridean species listed in Table 1 based on the species (Table 1). percentage of adult females incubating embryos. A relatively high percentage of adult females in all What might account for the apparently higher level species were ovigerous throughout the year. Statisti­ of reproductive intensity in terms of ovarian develop­ cal tests for possible concordance among species in ment of the carideans relative to the sicyoniids? One highs and lows of this estimate of breeding showed no might first ask if the values are comparable. Is the common pattern. Thus, on the population level re­ period for ovarian development, i.e., period between production was continuous throughout the year with­ spawns, shorter in carideans? The time interval be- 197

tween spawns varied from 1-2 weeks in females of same habitat, with the duration of periods between the nine caridean species. Although the period of an spawns similar or perhaps somewhat longer than that ovarian cycle in the tropical Sicyonia species is un­ for the carideans. However, the survivorship of an known, it is doubtful that it could be shorter than that individual fertilized put immediately into the determined for the carideans. Anderson etal. (1985), plankton by a Sicyonia female is probably less than for instance, reported a mean period of 19 days be­ that for any individual caridean embryo. The sicyo­ tween spawns in . If the duration of niid embryo, starting out at the zygote stage, must ovarian development is longer in the sicyoniids than develop completely in the plankton to hatching as a that given for the carideans, or if ovarian cycles are nauplius , which then must develop through all not continuous as in the caridean species, then the the larval stages to the postlarva which will settle out intensity of reproductive effort, as estimated in of the plankton as a recruit into the benthic population Table 1, would appear lower than that of the cari­ of the seagrass meadows. The caridean embryo, on deans. the other hand, is cared for by the female throughout However, reproductive effort per spawn in terms of its embryonic development and hatches as an numbers of fertilized eggs produced is probably advanced zoeal larva that will spend much less time greater in the sicyoniids than in the carideans. The subject to the vagaries and dangers of the planktonic incubatory caridean females produce larger eggs and environment before settlement into the seagrass mead­ fewer embryos than do the free-spawning sicyoniids. ows. Thus, given the trade-offs among number of Egg size at spawning was 240-440/t in the nine cari­ embryos produced per spawn, number of spawns per dean species (Bauer, 1991) compared with approxi­ reproductive lifetime, presence or absence of parental mately 200ft in the two Sicyonia spp. The median care, and duration of time spent by larvae in the number of embryos per brood (spawn) in the nine plankton, it is probable that the sicyoniids and cari­ caridean species varied from 56-600 and was less deans from the tropical seagrass habitat have similar than 100 in five species (Bauer, 1991). The number of reproductive effort. eggs spawned by the Sicyonia spp. has not been mea­ The evidence thus indicates that, once sexual sured, but in the much larger S. ingentis the mean maturity is reached, females of both groups go number of eggs per spawn was 86,000 (Anderson et through continuous cycles of ovarian maturity and al., 1985). Even scaled down for the differences in spawning until they die, probably through predation, size of adult sicyoniid females (Table 2), it is likely after a life span of a few to several months (less than that the number of eggs spawned in the tropical Sic­ one year) after arriving at the seagrass meadows. yonia is at least an order of magnitude larger than that Settlement can occur during anytime of the year (see for the comparably sized carideans. "Recruitment Patterns..." below). Thus, an individu­ al female cannot "track" any particular season that might be more favorable to breeding, and there can be Table 2. Relationship between size (carapace length) and no selection for seasonality in breeding patterns. longevity of females in Sicyonia species from three different latitudes (biogeographical areas)' Additionally, it may be that there is little or no pre­ dictable variation in mortality in the larval (plankton­ ic) environment so that there would be no selection Species Size range of Longevity adult female (months) for breeding during any particular time of the year. (mm CL) Although the caridean and sicyoniid shrimps have very different phylogenetic histories and reproductive S. parri 3-9 6-8 physiologies, the common selective pressures of the S. laevigata tropical environment in which they co-occur, perhaps (tropical) together with their short life spans, appear to have S. brevirostris 17-35 20-22 produced a similar pattern of continuous, non-season­ (subtropical) S. ingentis 24-45 >22? al reproduction. (cool temperature) Latitudinal Comparisons in Reproductive Patterns of Sicyoniid Shrimps

Sicyonia spp. may thus be putting out many more In this section I compare temporal patterns in fertilized eggs per spawn than carideans from the reproduction among Sicyonia spp. from different 198 latitudes. The intensity of sampling and methods for A S. ingentis (cool temperate) estimating breeding activity (percentage of females with mature ovaries) are comparable among the tropi­ • S. brcviroslris (subtropical) cal species Sicyonia parri and S. laevigata from - Y S. parri (tropical) grass meadows in Puerto Rico (18°N; Bauer and too r Rivera Vega, 1992), S. brevirostris from the Atlantic o coast of Florida, USA (28°N; Kennedy et al., 1977), OS and S. ingentis from the west coast of California, US A (34 ° N; Anderson et al., 1985). The east coast of g Florida is bathed by the warm, north-flowing Gulf s Stream while the sampling site in California is influ­ a enced by the cool, south-flowing California current. Thus, comparisons are being made among species < from environments that are essentially tropical, sub­ s tropical, and temperate. w zH Populations of the tropical species Sicyonia parri w u Jen Feb M»r Apr Mey Jtin Jul Aui Sep Oct Nov Dec and S. laevigata exhibited continuous reproduction al without any obvious seasonal peak (Bauer and Rivera MONTH Vega, 1992). When compared with the subtropical S. Fig. 1. Temporalpatternofovarianmaturity in threeSi'cyo- brevirostris and the temperate zone S. ingentis, a nia spp. from different latitudes. Data for S. parri are from pattern of increasing seasonality with at higher lati­ Bauer and Rivera Vega (1982), for S. brevirostris from tudes emerges (Fig. 1). Anderson et al. (1985) made Kennedyetal. (1977) (average of data for 1973-1974), and the observation that reproductive effort was less for S. ingentis from Anderson et al. (1985). intense but annual breeding period was longer in S. brevirostris than in S. ingentis. The inclusion of a Thus, there has been selection for seasonality in tropical species, S. parri, completes the picture and breeding patterns in these species. The small tropical reveals greater intensity of reproduction (percentage sicyoniids live less than one year and may settle and of females with mature ovaries) within a shorter time grow to sexual maturity at any time during the year span with an increase in latitude. Thus, populations of (see below). Females cannot afford to delay reproduc­ S. parri show a relatively low percentage of ripe tion for any particular period of the year. The result females throughout the year. Breeding also occurs of the interaction of short life span, settlement at any throughout the year in S. brevirostris, but there is a time of the year, and a physically benign environment strong seasonal peak from December through March favorable to year round gametogenesis and spawning (Fig. 1). Breeding and spawning are highly seasonal have resulted in continuous reproduction at the level in S. ingentis, in which the percentage of females with of the population and (probably) at the level of the ripe ovaries is quite high in the summer and early fall individual female in the tropical Sicyonia spp. while breeding apparently ceases during the rest of the year (Fig. 1). It is instructive to interpret these reproductive pat­ Recruitment Patterns of Tropical Caridean terns in terms of some life history characteristics of and Sicyoniid Species these species. Table 2 gives a summary of the rela­ Temporal patterns of recruitment estimated by the tionship between size of the adult female and longevi­ percentage of the population in juvenile size classes ty. The estimates of longevity come from cohort were described for the nine caridean species (Bauer, analyses from Rivera Vega (1985) for the tropical 1989) and the two Sicyonia spp. (Bauer and Rivera species and from Kennedy et al. (1977) while that for Vega, 1992) at the tropical seagrass meadow location. S. ingentis is an approximation based on female size Observations during sampling had indicated that compared with that of S. brevirostris. Females of the although small juvenile shrimps were taken in all larger Sicyonia spp, live at least two years, so that months, intense recruitment had occurred only during individual females have the opportunity to breed certain months of the year, i.e, there were months in during a period of the year which might be most which large influxes of juveniles of several species favorable for larval development and settlement. were observed. These observations were confirmed 199 by statistical analysis of possible concordance among is hypothesized that the seasonality is due to increased the seagrass species in the estimates of recruitment. seasonality of larval food supply in the plankton as For the nine caridean species, tests of concordance in suggested by Thorson (1950). The breeding patterns the highs and lows of recruitment were highly signifi­ of these sicyoniids are qualitatively concordant with cant. The months of high recruitment of carideans did annual patterns of phyto- and (larval not group into any apparent seasonal pattern; recruit­ food) abundances reported in studies carried out at or ment in these species is best described as "episodic" near areas where the adults were sampled [the south (Bauer, 1989). Recruitment values for Sicyonia spe­ coast of Puerto Rico (Yoshioka et al., 1985); east cies were analyzed later (Bauer and Rivera Vega, coast of Florida (Tester and Steidihger, 1979; Walker 1992). Estimates of recruitment were highly correlat­ et al., 1979); southern California coastal waters ed between the two Sicyonia species, and again the (Chelton et al., 1982)J. In addition, the life history pattern is best described as episodic. However, when constraint of female life span must be taken into composite values for caridean and sicyoniid recruit­ account. The Sicyonia spp. studied outside of the ment estimates were compared, there was no correla­ tropics live much longer than the tropical species, tion. The environmental factors controlling caridean long enough for selection for larval output at the most and sicyoniid recruitment appear to have been quite favorable period of the year to have been possible. different. Comparisons were not made in the body of this paper between the tropical caridean species (Bauer, 1989) and carideans from other latitudes, as among Discussion and Conclusions Sicyonia spp., because comparable specific data were The classical paradigm of continuous reproduction not available in the literature. However, Kikuchi (1962) reported that females of seagrass caridean in the tropics and seasonal reproduction at higher C latitudes, increasingly restricted in time with an in­ species from Tomioka Bay, Japan, (32 N) wereovig- crease in latitude, receives support from results of the erous seasonally, either during the spring and summer studies on caridean and sicyoniid shrimps addressed (most species) or during the winter (Heptacarpus in this report. Although caridean shrimps and Sic­ spp.). Allen (1966), studying caridean shrimp popula­ yonia (penaeoid) shrimps are both decapod crusta­ tions off the northeast coast of England, a boreal ceans, they have distinct phylogenetic histories (Bur- locale (55°), found that most species were carrying kenroad, 1962). Their reproductive capacities and embryos in the winter, although some species were constraints, as well as their larval life histories, are ovigerous in the summer months. Reproduction was quite different, as discussed above. Yet in the same thus quite seasonal, and Allen reported that hatching tropical environment, near-shore seagrass meadows, of larvae and their entry into the plankton occurred in reproduction in species of both groups was similar synchrony with either the spring (winter breeders) or (i.e., continuous), both on the level of the population fall (summer breeders) plankton blooms in that area. and the individual (certainly so in carideans, probably Considerable literature exists on breeding patterns in so in sicyoniids). Common environmental factors boreal pandalids (see Butler, 1980; Williams, 1984). (selective pressures) such as a relatively stable, physi­ Ovigerous and hatching periods are certainly highly cally benign habitat favorable to reproduction, a seasonal in these high-latitude carideans. Extensive (assumed) relatively stable temporal pattern of larval research on Pandalus borealis (Haynes and Wigley, food (plankton productivity), as well as specific life 1969; Horsted and Smidt. 1956; Rasmussen, 1953) history constraints (life span much less than one year) demonstrates an increase in adult life span and incu­ have selected for continuous reproduction in these bation period of embryos, as well as hatching of tropical species. embryos later in spring and summer, with an increase in latitude. These studies show the utility of compar­ Specific comparisons in reproduction could be ing populations of \hc same widely distributed species made among Sicyonia spp., i.e., species with a com­ among latitudes when looking for causal factors of mon phylogenetic history from tropical, subtropical, seasonality of reproduction. and cool temperate environments. The comparisons showed that with an increase in latitude, reproductive Although the comparisons among tropical, temper­ periods become more restricted in time. Within those ate, and boreal groups of caridean species are not as increasingly seasonal periods of breeding, reproduc­ firm as those reported above for Sicyonia spp., the tive effort appears to be greater at higher latitudes. It conclusion of increased seasonality of breeding sea- 200 son with increase in latitude is strongly suggested. shrimps, crabs, lobsters, , , and Thorson's (1950) hypothesis that the selective pres­ ? Will it be beneficial at a particular site, sure resulting in seasonality in reproduction (for stimulating reproduction and favorably influencing species with planktotrophic larvae) is seasonality in recruitment and population sizes of commercially and plankton production is supported by these studies. ecologically important species? Or will temperature Although all tropical shrimp species studied in rise (and its complex effects on and with other vari­ Bauer (1989) and Bauer and Rivera (1992) were ables, such as planktonic productivity) cause popula­ putting larvae or fertilized eggs into the plankton tion declines and/or unfavorable shifts in distribution? throughout the year, recruitment back from the plank­ The consequence of doing nothing until the effects of ton cannot be truly described as continuous. Recruit­ global sea warming (or changes in other climatic ment was not seasonal but rather highly variable variables) are upon us will be that any transforma­ throughout the year (i.e., episodic). Pulses of recruit­ tions in coastal and habitats will not have ment were concordant among caridean species and been anticipated, making it impossible to adjust for among the two Sicyonia species, but episodes of cari­ them. The economic and social impacts of such dean and sicyoniid recruitment did not occur at the changes could be considerable and therefore must be same time. This clearly indicates that different sets of predicted, if possible. factors were acting on larvae or postlarvae to account The most direct way to investigate what effect clima­ for this pattern. However, this tells us nothing about tic change, especially global sea warming, might have which environmental variables produced these differ­ on reproduction and recruitment in coastal faunas is ential patterns in recruitment. As with most such to study latitudinal variation in these processes in studies on reproduction of adults and settlement of species that are as closely related as possible. As juveniles back from the plankton into the benthic discussed in the introduction, such an approach will environment, the larvae and the larval (planktonic) be most productive if the effects of environmental environments were not sampled simultaneously with factors that vary with latitude are studied in species those of the adults. Usually, this level of sampling with a common phylogenetic history. This is a "re­ effort is beyond the scope of individual investigators ductionist" approach in the sense that one would or small groups of collaborators. But only a study of begin with low level taxonomic units, make para­ reproduction and recruitment in the benthic (juvenile digms about reproduction that apply to those taxa, and adult) habitat, concurrent with a study on larval and then expand comparisons to more and more mortality in the plankton, together with measurement distantly related taxa until the generalization breaks of environmental variables likely to influence these down. The specific paradigm would then be restricted processes, will yield an understanding of the relation­ a particular group of taxa. Larger scale generaliza­ ship between breeding and subsequent settlement in tions about variations in reproduction and recruitment marine benthic invertebrates. among taxa and among biogeographical areas could Climatic change, whether from natural or anthro­ then be made on a firm basis. A complementary pogenic causes, will have an effect on patterns of approach would be to look at the effect of common reproduction and recruitment of marine invertebrates. variables at the same locale on a "phylogenetic vari­ Certainly there is much evidence that global warming ety" of species. Predictions about the effects of possi­ and cooling has occurred in the past and that species ble climatic change such as global sea warming on have been affected by it in various ways, including marine would then be based on a solid shifts in distribution and, perhaps of greater concern, scientific basis. . Various climatic models predict global My recommendation is that a large-scale global warming due to an increase in "greenhouse" gases in effort be conducted by marine scientists to determine the atmosphere that would be as large as any natural what the current patterns of reproduction and recruit­ fluctuation the earth has experienced, and more im­ ment are in different taxa from different locales, portantly, that might occur at a rate several times studies which should include both the benthic and faster than that which has ever occurred in the past (larval) planktonic habitats of species. Coordination (Peters, 1991; U.S. Congressional Hearings on Glob­ of effort, concordance in methodology, and exchange al Warming, 1989). What will be the consequences of of information among participants would be crucial to predicted rises in sea temperature on coastal inver­ such an effort. Cooperation and collaboration among tebrates important in fisheries and aquaculture such as national governments, academic institutions, and 201

international agencies will be important in order to Bauer, R.T., Analysis of embryo production in a caridean supply the personnel, funding, and material support shrimp inhabiting tropical seagrass meadows. In; needed for such a major but essential undertaking. Crustacean Egg Production, A. Wennerand A. Kuris, eds.,BalkemaPress, Rotterdam, 1991, pp. 181-192. Bauer, R.T. and Rivera Vega, L., Pattern of reproduction and recruitment in two sicyoniid shrimp species Acknowledgements (: Penaeoidea) from a tropical seagrass habi­ Numerous students in the Department of Biology, tat, J. Exp. Mar. Biol. Ecol., in press. University of Puerto Rico, Rio Piedras, provided Burkenroad,M.D.. The evolution of the Eucarida (Crusta­ invaluable assistance in the field and in the laboratory cea, Eumalacostraca) in relation to the record, Tulane Stud. Geology, 2 (1963) 3-16. during the work on tropical seagrass shrimps. 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